Search

Chimeric antigen receptor (CAR) T-cell therapy can induce durable remissions of relapsed/refractory B-acute lymphoblastic leukemia (ALL). However, case reports suggested differential outcomes mediated by leukemia cytogenetics. We identified children and young adults with relapsed/refractory CD19+ ALL/lymphoblastic lymphoma treated on 5 CD19-directed CAR T-cell (CTL019 or humanized CART19) clinical trials or with commercial tisagenlecleucel from April 2012 to April 2019. Patients were hierarchically categorized according to leukemia cytogenetics: High-risk lesions were defined as KMT2A (MLL) rearrangements, Philadelphia chromosome (Ph+), Ph-like, hypodiploidy, or TCF3/HLF; favorable as hyperdiploidy or ETV6/RUNX1; and intermediate as iAMP21, IKZF1 deletion, or TCF3/PBX1. Of 231 patients aged 1 to 29, 74 (32%) were categorized as high risk, 28 (12%) as intermediate, 43 (19%) as favorable, and 86 (37%) as uninformative. Overall complete remission rate was 94%, with no difference between strata. There was no difference in relapse-free survival (RFS; P = .8112), with 2-year RFS for the high-risk group of 63% (95% confidence interval [CI], 52-77). There was similarly no difference seen in overall survival (OS) (P = .5488), with 2-year OS for the high-risk group of 70% (95% CI, 60-82). For patients with KMT2A-rearranged infant ALL (n = 13), 2-year RFS was 67% (95% CI, 45-99), and OS was 62% (95% CI, 40-95), with multivariable analysis demonstrating no increased risk of relapse (hazard ratio, 0.70; 95% CI, 0.21-2.90; P = .7040) but a higher proportion of relapses associated with myeloid lineage switch and a 3.6-fold increased risk of all-cause death (95% CI, 1.04-12.75; P = .0434). CTL019/huCART19/tisagenlecleucel are effective at achieving durable remissions across cytogenetic categories. Relapsed/refractory patients with high-risk cytogenetics, including KMT2A-rearranged infant ALL, demonstrated high RFS and OS probabilities at 2 years.

Children living in poverty experience excessive relapse and death from newly diagnosed acute lymphoblastic leukemia (ALL). The influence of household poverty and neighborhood social determinants on outcomes from chimeric antigen receptor (CAR) T-cell therapy for relapsed/refractory (r/r) leukemia is poorly described. We identified patients with r/r CD19+ ALL/lymphoblastic lymphoma treated on CD19-directed CAR T-cell clinical trials or with commercial tisagenlecleucel from 2012 to 2020. Socioeconomic status (SES) was proxied at the household level, with poverty exposure defined as Medicaid-only insurance. Low-neighborhood opportunity was defined by the Childhood Opportunity Index. Among 206 patients aged 1 to 29, 35.9% were exposed to household poverty, and 24.9% had low-neighborhood opportunity. Patients unexposed to household poverty or low-opportunity neighborhoods were more likely to receive CAR T-cell therapy with a high disease burden (>25%), a disease characteristic associated with inferior outcomes, as compared with less advantaged patients (38% vs 30%; 37% vs 26%). Complete remission (CR) rate was 93%, with no significant differences by household poverty (P = .334) or neighborhood opportunity (P = .504). In multivariate analysis, patients from low-opportunity neighborhoods experienced an increased hazard of relapse as compared with others (P = .006; adjusted hazard ratio [HR], 2.3; 95% confidence interval [CI], 1.3-4.1). There was no difference in hazard of death (P = .545; adjusted HR, 1.2; 95% CI, 0.6-2.4). Among children who successfully receive CAR T-cell therapy, CR and overall survival are equitable regardless of proxied SES and neighborhood opportunity. Children from more advantaged households and neighborhoods receive CAR T-cell therapy with a higher disease burden. Investigation of multicenter outcomes and access disparities outside of clinical trial settings is warranted.

Background T-ALL/LBL represent a class of devastating hematologic cancers with high rates of relapse and mortality in both children and adults. Despite intensive multi-agent chemotherapy regimens, fewer than 50% of adults and 85% of children with T-ALL survive beyond five years. For those who relapse after initial therapy, salvage regimens induce remissions in only ~20-30% of cases, and survival is dismal. T-ALL/LBL is a genetically diverse group, but with universal overexpression of CD7, making this a suitable target for immunotherapy. Despite the success of CAR-T cells in B-cell malignancies, CAR-T cell development in T-cell malignancies has proven challenging due to fratricide and high risk of contamination of the genetically modified CAR-T product with the patient's malignant T cells. WU-CART-007 is a CD7-directed, genetically modified, allogeneic, 'off the shelf', fratricide-resistant chimeric antigen receptor (CAR) T-cell product for the treatment of CD7+ve hematologic malignancies. Methods This multicenter, open-label, dose-escalation, Phase 1/2 study (NCT#04984356) of WU-CART-007 in patients ≥ 12 years old, with relapsed or refractory T-ALL/LBL is designed to characterize the safety, tolerability, dose-limiting toxicities (DLTs), and maximum tolerated dose (MTD)/maximum administered dose (MAD; if no MTD defined) (Phase 1), and to investigate the preliminary anti-tumor activity, as measured by objective response rate (ORR) and duration of response (DOR) (Phase 2). Phase 1 is comprised of a dose escalation segment and will proceed according to a standard 3+3 design testing up to 4 dose levels from 1 to 9 x 10 8 cells. Adolescent patients, ages 12-17, will be eligible for enrollment in Phase 1 Dose Escalation beginning at Dose level 3 and 4, and during Phase 2 Cohort Expansion. Upon reaching the MTD and/or RP2D, the Phase 2 portion comprised of the cohort expansion segment will be launched. A Simon's optimal two-stage design will be implemented to enroll patients (an interim analysis for futility in the first stage and the final analysis in the second stage) for Phase 2 dose expansion cohort to confirm safety and explore preliminary efficacy. All patients will receive a single infusion of WU-CART-007 cells on day 1 following a lymphodepleting conditioning therapy consisting of fludarabine and cyclophosphamide on days -5 to -3. Patients will be hospitalized for a minimum of 7 days following WU-CART-007 administration. Response will be assessed on Cycle 1 Day 28 (± 1 days), and at Months 3, 6, 12, and 24, by bone marrow aspirate and biopsy and PET/CT if indicated. Response will be defined as per modified NCCN Guidelines Version 2.2020. Disclosures Ghobadi: Atara: Consultancy; Amgen: Consultancy, Research Funding; Wugen: Consultancy; Celgene: Consultancy; Kite, a Gilead Company: Consultancy, Honoraria, Research Funding. Locke: Janssen: Consultancy, Other: Scientific Advisory Role; Kite, a Gilead Company: Consultancy, Other: Scientific Advisory Role, Research Funding; Iovance Biotherapeutics: Consultancy, Other: Scientific Advisory Role; Legend Biotech: Consultancy, Other; Novartis: Consultancy, Other, Research Funding; Takeda: Consultancy, Other; Wugen: Consultancy, Other; Cowen: Consultancy; Umoja: Consultancy, Other; Bluebird Bio: Consultancy, Other: Scientific Advisory Role; Calibr: Consultancy, Other: Scientific Advisory Role; BMS/Celgene: Consultancy, Other: Scientific Advisory Role; GammaDelta Therapeutics: Consultancy, Other: Scientific Advisory Role; Cellular Biomedicine Group: Consultancy, Other: Scientific Advisory Role; Amgen: Consultancy, Other: Scientific Advisory Role; Allogene Therapeutics: Consultancy, Other: Scientific Advisory Role, Research Funding; EcoR1: Consultancy; Emerging Therapy Solutions: Consultancy; Gerson Lehrman Group: Consultancy; Moffitt Cancer Center: Patents & Royalties: field of cellular immunotherapy. Maude: Wugen: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy, Research Funding. Davidson-Moncada: Wugen: Current Employment. Cooper: Wugen: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company, Patents & Royalties; NeoImmune Tech: Patents & Royalties; RiverVest: Consultancy.

Introduction: The most common severe toxicity associated with chimeric antigen receptor T-cells targeting CD19 (CART19) is cytokine release syndrome (CRS; PMID: 29972754). Our group and others have published seminal observations on the biology of CRS through cytokine profiling, measuring a small number of analytes (PMID: 27076371, 33434058). Multiple biomarkers including interferon gamma (IFNG), IL-6, and IL-10 have been associated with the development of severe CRS in previous studies (PMID: 33434058). To date, the only biomarker predictive of the development of CRS prior to infusion has been disease burden. To obtain a more robust understanding of CRS biology, we performed comprehensive secretome profiling to measure more than 1400 serum analytes on serial serum samples collected from patients treated with the 41BB-containing CTL019 on two clinical trials. Methods: Serum from patients enrolled on two clinical trials of the CART19 product CTL019 (NCT01626495 & NCT02906371) were obtained serially from pre-infusion to one month post infusion. Patients were categorised as having "minimal" (no CRS, Grade 1, or Grade 2) or "severe" (Grade 3 or 4) CRS. The serum secretome was profiled using the Olink Explore 1536 Analysis platform (Olink, Upsala, Sweden). 1484 proteins were measured from serum via proximity extension assay (PEA) high-multiplex immunoassay. Differential expression analysis, correlation analyses and receiver operating characteristic (ROC) calculations were performed using R (version 4.0.4) in RStudio. Significance was based on a fold change of greater than 2 or less than -2 and a false discovery rate of less than 0.05 calculated using a Benjamini-Hochberg correction. Results: 26 patients (10 NCT01626495 & 16 NCT02906371) were included comprising 128 unique datapoints from baseline to 35 days post-infusion. Thirteen patients had minimal and 13 had severe CRS. Differentially expressed proteins between minimal and severe CRS at the peak timepoint are shown in (A; green represents IFNG responsive proteins). Not surprisingly, proteins involved in IL-6 and IFNG signalling were increased, including biomarkers of hemophagocytic lymphohistiocytosis (HLH) such as VSIG4, CXCL9, CXCL10, CD163. The IL-18 signalling axis was dysregulated at peak CRS in severe patients with markedly elevated IL18 and IL18BP, despite prior reports suggesting IL-18 up-regulation is unique to the late CRS seen with CART22 (PMID: 32925169). Soluble markers of checkpoint inhibition, including soluble PDL1 (CD274) and LAG3 were also highly elevated. Finally, biomarkers of endothelial damage, such as PLAT, TMSB10 and CALCA were significantly elevated in patients with severe CRS. Pathway analysis revealed significant dysregulation in targetable cytokine, chemokine, and signalling pathways (B). A volcano plot of differentially expressed proteins at pre-infusion (C) identified a single protein, MILR1, as a candidate biomarker that was highly differentially expressed in patients who would subsequently develop severe CRS. MILR1 expression decreased over time (D). An ROC of MILR1 as a predictor for development of severe CRS (E) demonstrated pre-infusion elevated MILR1 could accurately predict development of severe CRS (sensitivity 88%, specificity 97%, AUC=0.977). We identified correlates of MILR1 at pre-infusion and found that MILR1 correlated most highly with soluble FLT3 (R=0.86, p Conclusions: With comprehensive secretome profiling we made multiple novel insights into the biology of CRS after CART19 and identified several potentially targetable proteins and pathways that could mitigate severe CRS. Similar secretome profiling in patients who developed neurotoxicity will also be shown. We identified two novel pre-infusion biomarkers that demonstrate significant capacity to predict the development of severe CRS following CART19 infusion. The inverse relationship apparent between FLT3 and FLT3LG that persists over time is an important finding that implies a potential biological role for FLT3/FLT3 ligand in the development of severe CRS. Mechanistic studies exploring the role of MILR1 and FLT3 in the initiation of CRS are ongoing. Figure 1 Figure 1. Disclosures Lambert: Novartis, shionogi, argenx, Rigel, octapharma: Consultancy; Rigel, Novartis, Sysmex, octapharma: Research Funding. Bassiri: Kriya Therapeutics: Consultancy, Current holder of individual stocks in a privately-held company; Guidepoint Global: Consultancy. Levine: Vycellix: Membership on an entity's Board of Directors or advisory committees; Tmunity Therapeutics: Other: Co-Founder and equity holder; Ori Biotech: Membership on an entity's Board of Directors or advisory committees; Immusoft: Membership on an entity's Board of Directors or advisory committees; Immuneel: Membership on an entity's Board of Directors or advisory committees; Avectas: Membership on an entity's Board of Directors or advisory committees; Akron: Membership on an entity's Board of Directors or advisory committees; In8bio: Membership on an entity's Board of Directors or advisory committees. Maude: Wugen: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy, Research Funding. June: Tmunity, DeCART, BluesphereBio, Carisma, Cellares, Celldex, Cabaletta, Poseida, Verismo, Ziopharm: Current equity holder in publicly-traded company; Novartis: Patents & Royalties; AC Immune, DeCART, BluesphereBio, Carisma, Cellares, Celldex, Cabaletta, Poseida, Verismo, Ziopharm: Consultancy. Barrett: Tmunity Therapeutics: Current Employment. Grupp: Novartis, Kite, Vertex, and Servier: Research Funding; Novartis, Roche, GSK, Humanigen, CBMG, Eureka, and Janssen/JnJ: Consultancy; Novartis, Adaptimmune, TCR2, Cellectis, Juno, Vertex, Allogene and Cabaletta: Other: Study steering committees or scientific advisory boards; Jazz Pharmaceuticals: Consultancy, Other: Steering committee, Research Funding. Teachey: Janssen: Consultancy; NeoImmune Tech: Research Funding; Sobi: Consultancy; BEAM Therapeutics: Consultancy, Research Funding.

Background: Anti-CD19 Chimeric Antigen Receptor (CAR) T cell therapy has emerged as a mainstay in the treatment of patients with relapsed/refractory (r/r) B-cell acute lymphoblastic leukemia (ALL). While trials have shown encouraging survival rates, up to 50% of patients receiving CART eventually relapse. Identification of risk factors for subsequent relapse is crucial, as this could allow tailored surveillance and treatment approaches for high-risk patients, potentially leading to improved morbidity and mortality. Complete remission with incomplete hematologic recovery (CRi) has been associated with decreased remission duration and overall survival in acute leukemias. As count suppression following CAR T cell therapy is frequently seen, this study evaluated CRi as a prognostic marker for worse relapse-free (RFS) and overall survival (OS) after CAR T cell therapy in comparison to complete remission with hematologic recovery (CR). Methods: Patients with r/r ALL who achieved a complete morphologic remission after receiving anti-CD19 CAR T cell treatment with the 4-1BB-containing products CTL019 or humanized CART19 in the context of a clinical trial (NCT01626495, NCT02374333, NCT02228096, NCT02435849, NCT02906371) or commercial product (tisagenlecleucel) at Children's Hospital of Philadelphia from 4/2012-4/2019 were identified. Patients who received prior CAR therapy, and those with Trisomy 21 were excluded. Demographic, disease and treatment characteristics, and outcome data were abstracted from the medical record or clinical trial datasets. CR was defined as achieving a morphologic remission with both an absolute neutrophil count (ANC) ≥1,000/µL and a transfusion-independent platelet count ≥100,000/µL at any time between 27-33 days after CAR T cell infusion, whereas those achieving a morphologic remission without complete hematologic recovery were defined as CRi. RFS and OS were described for each cohort. Exposure-outcome association was assessed via the log-rank test and multivariable Cox proportional hazard regression. Results: Of the 206 patients included in the analysis, 104 (51%) achieved CR, 102 (49%) CRi. Forty patients (39%) met criteria for CRi with both ANC 25% bone marrow blasts (43% vs 19%) at infusion, whereas more CR patients were MRD-negative (50% vs 30%) at infusion (p=0.002). CRi patients were also more likely to have Grade 3/4 CRS (38% vs 6.7%). Median length of follow-up for patients with CR was 39 months (range 7-89), which was not statistically significantly different than for those patients with CRi (41 months, 11-98, p=0.875). There was no difference in RFS when stratified by hematologic recovery (Figure 1, p=0.2165), with RFS at 36 months for CR of 57% (47-69) and CRi of 46% (36-59). OS was significantly lower (Figure 2, p=0.0081) for those with CRi, with 36-month OS for CR of 81% (74-89), and for CRi of 63% (54-73). In multivariable analysis adjusting for sex, prior blinatumomab, relapse number, disease burden at infusion, and maximum CRS grade, CR was not associated with either RFS (HR 0.76 [95%CI 0.50-1.17] p=0.2182) or OS (HR 0.74 [95%CI 0.43-1.29] p=0.2908), in comparison to CRi, Table 2. Discussion: Complete remission with incomplete hematologic recovery, manifesting as neutropenia and/or thrombocytopenia, at the first disease assessment following CAR T cell infusion should not be regarded as a harbinger of relapse and demonstrates that patients with CRi have similar probability of durable remission without further therapy. Anticipatory guidance should be provided to patients, and their families, that CRi is more frequently seen in patients who experience high grade CRS, who have high disease burden at infusion, and who are treated in first relapse. Figure 1 Figure 1. Disclosures Callahan: Novartis: Speakers Bureau. Rheingold: Optinose: Other: Spouse's current employment; Pfizer: Research Funding. Grupp: Novartis, Roche, GSK, Humanigen, CBMG, Eureka, and Janssen/JnJ: Consultancy; Novartis, Adaptimmune, TCR2, Cellectis, Juno, Vertex, Allogene and Cabaletta: Other: Study steering committees or scientific advisory boards; Novartis, Kite, Vertex, and Servier: Research Funding; Jazz Pharmaceuticals: Consultancy, Other: Steering committee, Research Funding. Maude: Wugen: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy, Research Funding.

Background: CAR-modified T cells targeting CD19 have produced remarkable responses in relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL); however, relapse continues to be a substantial challenge. CD19+ relapses, which account for 33-78% of relapses, are associated with loss of CAR T-cell surveillance due to short persistence. Thus, strategies to improve functional persistence to prevent and treat CD19+ relapsed disease are crucial. Here, we report our experience administering reinfusions of murine or humanized 4-1BB CD19 CAR T cells in an effort to prolong persistence in patients with demonstrated short persistence to mitigate relapse risk, treat CD19+ relapsed disease, and produce responses after nonresponse to initial CAR infusion. Methods: This analysis included patients aged Results: Among 229 CAR-naïve and 33 CAR-exposed patients treated with CD19 CAR between 2012-2020, 81 received ≥1 reinfusion (investigational CTL019, n=44; commercial tisagenlecleucel, n=11; huCART19, n=13 CAR-naïve and n=13 CAR-exposed). In addition, 18 patients received PD-1 blockade after their first (n=11) or subsequent (n=7) reinfusions. Indications for first reinfusion were peripheral BCR (CAR-naïve, n=32; CAR-exposed, n=6), hematogones (CAR-naïve, n=21; CAR-exposed, n=4), CD19+ MRD/relapse (CAR-naïve, n=10, CAR-exposed, n=0), and nonresponse to initial infusion (CAR-naïve, n=5, CAR-exposed, n=3). CRS grade ≥2 (Penn scale) occurred in 19 patients (grade 2, n=13; grade 3, n=4; grade 4, n=2). Grade 3-4 events only occurred in patients with active disease at time of reinfusion. Twenty-two patients had an inpatient admission within 30 days of first reinfusion, of which 7 required intensive care unit admission Among the 63 patients reinfused for relapse prevention, 33 (52%) had a CR at day 28. With a median duration of follow-up of 38 mos, 13 experienced a subsequent relapse (7 CD19+, 4 CD19-, 2 CD19-subset negative), 4 received alternative therapy or allogeneic hematopoietic stem cell transplantation (HSCT) in remission, and 16 remain in remission without further therapy at a median of 39 mos after first reinfusion. The median duration of B-cell aplasia was 8 mos (IQR 2-35) after reinfusion. Of the 30 with no response (NR), 10 had a subsequent CD19+ relapse, 15 received alternative therapy or HSCT, and 5 remain in remission without further therapy at a median of 43 mos after reinfusion. CIR and OS were not statistically significantly different between patients with CR or NR (CIR, p=0.26; OS, p=0.25) (Figure A-B). However, at 24 mos after reinfusion, CIR was 29% (95% CI, 11-44%) for CR compared to 61% (95% CI, 24-80%) for NR; OS was 90% (95% CI, 80-100%) for both groups. Of the 10 patients reinfused for relapse, 5 (50%) had a CR; 2 subsequently experienced a CD19+ relapse, 2 received an HSCT in remission, and 1 remains in remission without further therapy at 18 mos after reinfusion. Of the 8 patients reinfused for nonresponse to initial infusion, 7 were evaluable; none had a CR, and all died at a median of 2.5 mos after reinfusion. Conclusions: Reinfusion of CTL019/tisagenlecleucel or huCART19 is safe, may prolong B-cell aplasia in patients with short CAR persistence and reduce relapse risk, and can induce remissions in patients with CD19+ relapsed disease. Thus, reinfusion may provide an alternative to HSCT for short persistence. However, reinfusion is not effective for patients with nonresponse to initial CAR infusion. Figure 1 Figure 1. Disclosures Callahan: Novartis: Speakers Bureau. Rheingold: Optinose: Other: Spouse's current employment; Pfizer: Research Funding. June: Tmunity, DeCART, BluesphereBio, Carisma, Cellares, Celldex, Cabaletta, Poseida, Verismo, Ziopharm: Current equity holder in publicly-traded company; Novartis: Patents & Royalties; AC Immune, DeCART, BluesphereBio, Carisma, Cellares, Celldex, Cabaletta, Poseida, Verismo, Ziopharm: Consultancy. Grupp: Novartis, Roche, GSK, Humanigen, CBMG, Eureka, and Janssen/JnJ: Consultancy; Novartis, Adaptimmune, TCR2, Cellectis, Juno, Vertex, Allogene and Cabaletta: Other: Study steering committees or scientific advisory boards; Novartis, Kite, Vertex, and Servier: Research Funding; Jazz Pharmaceuticals: Consultancy, Other: Steering committee, Research Funding. Maude: Novartis Pharmaceuticals Corporation: Consultancy, Research Funding; Wugen: Consultancy.

Adoptive transfer of T cells genetically modified to express chimeric antigen receptors (CARs) targeting the CD19 B cell-associated protein have demonstrated potent activity against relapsed/refractory B-lineage acute lymphoblastic leukemia (B-ALL). Not all patients respond, and CD19-negative relapses have been observed. Overexpression of the thymic stromal lymphopoietin receptor (TSLPR; encoded by CRLF2) occurs in a subset of adults and children with B-ALL and confers a high risk of relapse. Recent data suggest the TSLPR signaling axis is functionally important, suggesting that TSLPR would be an ideal immunotherapeutic target. We constructed short and long CARs targeting TSLPR and tested efficacy against CRLF2-overexpressing B-ALL. Both CARs demonstrated activity in vitro, but only short TSLPR CAR T cells mediated leukemia regression. In vivo activity of the short CAR was also associated with long-term persistence of CAR-expressing T cells. Short TSLPR CAR treatment of mice engrafted with a TSLPR-expressing ALL cell line induced leukemia cytotoxicity with efficacy comparable with that of CD19 CAR T cells. Short TSLPR CAR T cells also eradicated leukemia in 4 xenograft models of human CRLF2-overexpressing ALL. Finally, TSLPR has limited surface expression on normal tissues. TSLPR-targeted CAR T cells thus represent a potent oncoprotein-targeted immunotherapy for high-risk ALL.

Early T-cell precursor (ETP) acute lymphoblastic leukemia (ALL) is a recently described subtype of T-ALL characterized by a unique immunophenotype and genomic profile, as well as a high rate of induction failure. Frequent mutations in cytokine receptor and Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathways led us to hypothesize that ETP-ALL is dependent on JAK/STAT signaling. Here we demonstrate aberrant activation of the JAK/STAT pathway in ETP-ALL blasts relative to non-ETP T-ALL. Moreover, ETP-ALL showed hyperactivation of STAT5 in response to interleukin-7, an effect that was abrogated by the JAK1/2 inhibitor ruxolitinib. In vivo, ruxolitinib displayed activity in 6 of 6 patient-derived murine xenograft models of ETP-ALL, with profound single-agent efficacy in 5 models. Ruxolitinib treatment decreased peripheral blast counts relative to pretreatment levels and compared with control (P < .01) in 5 of 6 ETP-ALL xenografts, with marked reduction in mean splenic blast counts (P < .01) in 6 of 6 samples. Surprisingly, both JAK/STAT pathway activation and ruxolitinib efficacy were independent of the presence of JAK/STAT pathway mutations, raising the possibility that the therapeutic potential of ruxolitinib in ETP-ALL extends beyond those cases with JAK mutations. These findings establish the preclinical in vivo efficacy of ruxolitinib in ETP-ALL, a biologically distinct subtype for which novel therapies are needed.

As a consequence of acquired or intrinsic disease resistance, the prognosis for patients with relapsed or refractory T-cell acute lymphoblastic leukemia (T-ALL) is dismal. Novel, less toxic drugs are clearly needed. One of the most promising emerging therapeutic strategies for cancer treatment is targeted immunotherapy. Immune therapies have improved outcomes for patients with other hematologic malignancies including B-cell ALL; however no immune therapy has been successfully developed for T-ALL. We hypothesize targeting CD38 will be effective against T-ALL. We demonstrate that blasts from patients with T-ALL have robust surface CD38 surface expression and that this expression remains stable after exposure to multiagent chemotherapy. CD38 is expressed at very low levels on normal lymphoid and myeloid cells and on a few tissues of nonhematopoietic origin, suggesting that CD38 may be an ideal target. Daratumumab is a human immunoglobulin G1κ monoclonal antibody that binds CD38, and has been demonstrated to be safe and effective in patients with refractory multiple myeloma. We tested daratumumab in a large panel of T-ALL patient-derived xenografts (PDX) and found striking efficacy in 14 of 15 different PDX. These data suggest that daratumumab is a promising novel therapy for pediatric T-ALL patients.

Tisagenlecleucel (CTL019) is an investigational immunotherapy that involves reprogramming a patient's own T cells with a transgene encoding a chimeric antigen receptor to identify and eliminate CD19-expressing cells. We previously reported that CTL019 achieved impressive clinical efficacy in patients with relapsed/refractory B-cell acute lymphoblastic leukemia (ALL) and chronic lymphocytic leukemia (CLL), including the expansion and persistence of CTL019 cells, which correlates with response to therapy. Here, we performed formal cellular kinetic analyses of CTL019 in a larger cohort of 103 patients treated with CTL019 in 2 different diseases (ALL and CLL). CTL019 was measured in peripheral blood and bone marrow, using quantitative polymerase chain reaction and flow cytometry. CTL019 levels in peripheral blood typically peaked at 10 to 14 days postinfusion and then declined slowly over time. Patients with complete response (CR)/CR with incomplete count recovery had higher levels of CTL019 in peripheral blood, with greater maximal concentration and area under the curve values compared with nonresponding patients (P < .0001 for each). CTL019 transgene levels were measurable up to 780 days in peripheral blood. CTL019 trafficking and persistence were observed in bone marrow and cerebrospinal fluid. CTL019 expansion correlated with severity of cytokine release syndrome (CRS) and preinfusion tumor burden in pediatric ALL. The results described here are the first detailed formal presentation of cellular kinetics across 2 diseases and highlight the importance of the application of in vivo cellular kinetic analyses to characterize clinical efficacy and CRS severity associated with CTL019 therapy.

Background: CTL019 is a therapy derived from autologous T cells expressing a CD19-specific chimeric antigen receptor (CAR) that was approved by the FDA in August 2017 (tisagenlecleucel). Complete and durable remissions have been seen in the setting of pediatric and young adult patients with relapsed and refractory B cell acute lymphoblastic leukemia (ALL) (Maude NEJM 2018). Initial case reports suggested that there may be differential outcomes mediated by cytogenetic characteristics of the leukemia at CAR T cell infusion. Here, we report results from a single institution experience of 112 patients. Methods: Patients with relapsed/refractory ALL were identified as having received CTL019 either in the context of a clinical trial (NCT02906371) or commercial product (tisagenlecleucel) at Children's Hospital of Philadelphia from October 2016 to April 2019. Patients who received prior CAR T therapy were excluded. Demographic, cytogenetic, and outcome data were manually abstracted from the medical record or clinical trial datasets. High risk lesions were defined as MLL(KMT2A) rearrangements, Philadelphia-chromosome (Ph+), Ph-like, hypodiploidy, and TCF3/HLF fusion. Favorable cytogenetics were defined as the presence of hyperdiploidy or ETV6/RUNX1fusion and intermediate were defined as iAMP21, IKZF1deletion, or TCF3/PBX1. Patients were classified according to their highest risk cytogenetic characteristic and stratified by cytogenetic risk category present at CAR T cell infusion. Relapse-free survival (RFS) and overall survival (OS) was described for cohorts with more than 10 patients. Results: One hundred and twelve patients were included in the analysis, with a median age of 11 years (range 1-29) at infusion, of which 32% had had a previous allogeneic hematopoietic stem cell transplant (alloHSCT). Disease burden at the time of CTL019 infusion was heterogenous, with 61% having detectable disease in the bone marrow and 21% having more than 25% blasts by flow cytometry. Thirty-six patients (32%) had leukemias with high-risk genetic lesions at infusion, including 12 with MLL rearrangements and 18 with Ph+ or Ph-like lesions (Table 2). Thirty-one patients (28%) had hyperdiploidy or ETV6/RUNX1; 3 additional were in conjunction with high-risk cytogenetics (t(17;19) and 2 with Ph+), and 3 in the setting of intermediate-risk cytogenetics (iAmp21, TCF3/PBX1, IKZF1deletion). Figure 1 demonstrates RFS for those patients in remission at day 28 following infusion, stratified by cytogenetic risk category. Complete remission (CR) rate in the high-risk cytogenetics group was 94%. RFS at 12 months was 69% (0.50-0.82), 69% (0.40-0.86), and 67% (0.48-0.80) for non-informative, favorable, and high-risk cytogenetic groups, respectively. Figure 2 shows OS of patients infused with CTL019, again stratified by cytogenetic categories of interest, with a maximum follow-up time of 30 months. OS at 12 months was 84% (0.68-0.93) and 76% (0.56-0.88) for the non-informative and high-risk cytogenetic groups, respectively. There were no deaths in that time period for the favorable risk category. There was no statistically significant difference in RFS or OS for patients with high-risk cytogenetics. The intermediate-risk cytogenetics group (n Conclusion: Durable remissions can be achieved with CTL019 across several high-risk cytogenetic subtypes of B-ALL. Stratifying outcomes by cytogenetic risk category in this unadjusted analysis does not show a statistically significant difference in either RFS nor OS. Further investigation is needed to parse out the contribution of individual cytogenetic lesions as well as the effects of other relapse and survival risk factors at play. Figure Disclosures Rheingold: Novartis: Consultancy; Pfizer: Research Funding. Callahan:Novartis: Consultancy. Hunger:Bristol Myers Squibb: Consultancy; Amgen: Consultancy, Equity Ownership; Jazz: Honoraria; Novartis: Consultancy. Grupp:Novartis: Consultancy, Research Funding; Roche: Consultancy; GSK: Consultancy; Cure Genetics: Consultancy; Humanigen: Consultancy; CBMG: Consultancy; Novartis: Research Funding; Kite: Research Funding; Servier: Research Funding; Jazz: Other: study steering committees or scientific advisory boards; Adaptimmune: Other: study steering committees or scientific advisory boards. Maude:Kite: Consultancy; Novartis: Consultancy.

CD19-specific chimeric antigen receptor (CAR) T cell therapies have been highly effective against B cell malignancies. We previously demonstrated that differential responses to anti-CD19 CAR T cell therapy in chronic lymphocytic leukemia (CLL) are associated with early memory T cell signature in apheresed, pre-manufacturing T-cells (CAR T-cell precursors). We tested the hypothesis that the composition of CAR-T precursor cells determines clinical efficacy in adult and pediatric Acute Lymphoblastic Leukemia (ALL), Non-Hodgkin's Lymphoma (NHL), Multiple Myeloma (MM), and CLL. Apheresed T cells were engineered to express 4-1BB plus CD3-zeta-signaling CARs targeting CD19, or B cell maturation antigen (BCMA). The same 9-day manufacturing process was used for all trials. CAR T cell kinetics were monitored using a CAR gene-specific quantitative PCR assay and standard clinical response assessments were performed. Apheresed T cells from 36 CLL, 30 adult ALL, 58 pediatric ALL, 33 NHL, and 25 MM patients were immunophenotyped by flow cytometry. The CLL cohort was used to discover phenotypically distinct subpopulations associated with the two main response groups; these associations were validated in the remaining patient cohorts. Eight CD8+ T cell populations or clusters were identified using the shared-nearest-neighbor clustering method (PMID: 31178118) in the CLL cohort. T cell subsets exhibiting naive (cluster 6) or early memory (cluster 4) features were significantly enriched in responding patients, whereas an effector memory CD8 subpopulation (cluster 2) marked the non-responding patients. Mapping these clusters onto apheresed CD8+ T cells from the other four diseases showed that cluster 4 predicted response to CAR T cell therapy in NHL and myeloma but not in adult and pediatric ALL. We also examined the expression of activation-regulated molecules including HLA-DR, Ki67, and exhaustion-related molecules PD1, CTLA4, TIM3, and LAG3. A CD27+ CD8+ population expressing low level CTLA4 but none of the activation or negative regulatory molecules was significantly enriched in responding CLL patients; this cluster validated in NHL and myeloma. A similar analysis on apheresed CD4+ T cells identified an early memory population (cluster 6) enriched in CLL responders, which expresses CCR7 and CD27 but not CD45RO, CD127, CD28, or other late memory/effector molecules. However, this population did not validate in any of the other diseases. Though not statistically significant, the CD4+ clusters with the largest effect size for enrichment in responders from NHL and myeloma trials exhibited early memory T cell features and lack of HLA-DR expression, suggesting that quiescent early memory state in CD4 may also be associated with clinical responses. A separate analysis of checkpoint inhibitory receptors and activation markers in memory CD4 T cell subsets confirmed the early memory, non-activated state of this population in CLL and was validated in myeloma but none of the other diseases. In vivo activation was a shared theme in CD4+ T cells for non-responding patients as well, though these CLL-defined CD4+ apheresed T cells clusters did not significantly validate in other diseases. In summary, our data confirm and extend our predictive biomarker profile in CLL to mature B cell and plasma cell malignancies by showing that a non-cycling, non-activated early memory CD8+ T cell population in pre-manufacturing cells was validated as a biomarker in myeloma, and NHL. We also showed that responder-associated apheresed CD4+ T cells with early memory features identified in CLL after CD19 CAR T infusions are validated in myeloma after BCMA CAR T. Thus, differentiation state and in vivo activation, and potentially exhaustion, separate response groups. Our findings inform next-generation CAR T-cell manufacturing using the populations identified herein as a starting population. Disclosures Pruteanu: Novartis: Employment. Cohen:Poseida Therapeutics, Inc.: Research Funding. Garfall:Surface Oncology: Consultancy; Novartis: Research Funding; Janssen: Research Funding; Amgen: Research Funding; Tmunity: Research Funding. Milone:Novartis: Patents & Royalties: patents related to tisagenlecleucel (CTL019) and CART-BCMA; Novartis: Research Funding. Gill:Novartis: Research Funding; Tmunity: Research Funding; Carisma: Equity Ownership, Research Funding; Sensei: Consultancy; Aro: Consultancy; Fate: Consultancy. Frey:Novartis: Research Funding. Ruella:Nanostring: Consultancy, Speakers Bureau; Novartis: Patents & Royalties: CART for cancer; AbClon: Membership on an entity's Board of Directors or advisory committees. Lacey:Novartis: Patents & Royalties: Patents related to CAR T cell biomarkers; Tmunity: Research Funding; Novartis: Research Funding. Svoboda:Merck: Research Funding; BMS: Consultancy, Research Funding; Incyte: Research Funding; Pharmacyclics: Consultancy, Research Funding; Celgene: Research Funding; Kite: Consultancy; Seattle Genetics: Consultancy, Research Funding; Kyowa: Consultancy; AstraZeneca: Consultancy. Chong:Tessa: Consultancy; Novartis: Consultancy; Merck: Research Funding. Fraietta:LEK Consulting: Consultancy; Cabaletta: Research Funding; Tmunity: Research Funding. Davis:Cabaletta: Research Funding; Tmunity: Research Funding. Nasta:Rafael: Research Funding; Aileron: Research Funding; Takeda/Millennium: Research Funding; Incyte: Research Funding; Roche/Genentech: Research Funding; Merck: Consultancy; Atara: Research Funding; Debiopharm: Research Funding. Levine:CRC Oncology: Consultancy; Vycellix: Membership on an entity's Board of Directors or advisory committees; Tmunity Therapeutics: Equity Ownership; Novartis: Consultancy, Patents & Royalties, Research Funding; Cure Genetics: Consultancy; Avectas: Membership on an entity's Board of Directors or advisory committees; Brammer Bio: Membership on an entity's Board of Directors or advisory committees; Incysus: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy. Maude:Kite: Consultancy; Novartis: Consultancy. Schuster:Nordic Nanovector: Honoraria; Pfizer: Honoraria; AstraZeneca: Honoraria; Pharmacyclics: Honoraria, Research Funding; Genentech: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Loxo Oncology: Honoraria; Merck: Honoraria, Research Funding; Acerta: Honoraria, Research Funding; Novartis: Honoraria, Patents & Royalties: Combination Therapies of CAR and PD-1 Inhibitors with royalties paid to Novartis, Research Funding; AbbVie: Honoraria, Research Funding; Gilead: Honoraria, Research Funding. Stadtmauer:Celgene: Consultancy; Tmunity: Research Funding; Novartis: Consultancy, Research Funding; Takeda: Consultancy; Janssen: Consultancy; Amgen: Consultancy; Abbvie: Research Funding. Grupp:Novartis: Consultancy, Research Funding; Roche: Consultancy; GSK: Consultancy; Cure Genetics: Consultancy; Humanigen: Consultancy; CBMG: Consultancy; Novartis: Research Funding; Kite: Research Funding; Servier: Research Funding; Jazz: Other: study steering committees or scientific advisory boards; Adaptimmune: Other: study steering committees or scientific advisory boards. Porter:Incyte: Membership on an entity's Board of Directors or advisory committees; American Board of Internal Medicine: Membership on an entity's Board of Directors or advisory committees; Kite: Membership on an entity's Board of Directors or advisory committees; Glenmark Pharm: Membership on an entity's Board of Directors or advisory committees; Immunovative: Membership on an entity's Board of Directors or advisory committees; Genentech: Employment; Wiley and Sons: Honoraria; Novartis: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding. June:Novartis: Research Funding; Tmunity: Other: scientific founder, for which he has founders stock but no income, Patents & Royalties. Melenhorst:Novartis: Research Funding, Speakers Bureau; Parker Institute for Cancer Immunotherapy: Research Funding; Stand Up to Cancer: Research Funding; Incyte: Research Funding; IASO Biotherapeutics, Co: Consultancy; Simcere of America, Inc: Consultancy; Shanghai Unicar Therapy, Co: Consultancy; Colorado Clinical and Translational Sciences Institute: Membership on an entity's Board of Directors or advisory committees; Genentech: Speakers Bureau; National Institutes of Health: Research Funding.

We recently conducted a clinical trial of CD22-directed chimeric antigen receptor (CAR) T cells in children and adults with relapsed or refractory B-cell acute lymphoblastic leukemia (ALL). While we did observe some transient responses, overall outcomes were inferior to another recent trial of CD22 CAR T cells in ALL performed at the NCI (Fry, T.J. et al. Nat Med, 2018). Intriguingly, these trials used a CAR that employed the same antigen-binding and intracellular signaling domains, and differed only in the length of linker connecting the variable regions of the single chain variable fragment (scFv). Based on these clinical observations, we sought to identify how the scFv linker impacts CAR biology and regulates CAR-driven T cell activity. The University of Pennsylvania's CD22 CAR contained a long 20 amino acid scFv linker ("CAR22-L") while the NCI's CAR had a 5 amino acid linker ("CAR22-S"). We began by investigating the impact of linker length on CAR biochemistry. Both CAR22-L and CAR22-S had similar antigen-binding affinities (KD of 1.67nM and 6.05nM, respectively). Chromatography revealed that CAR22-L remained monomeric in solution while CAR22-S formed homodimers. To explore how dimerization influenced surface-membrane biology, we developed GFP-tagged versions of each CAR and performed confocal microscopy on CAR+ T cells. CAR22-L exhibited homogenous surface membrane expression, while CAR22-S appeared to self-aggregate and cluster (Fig. 1a). We investigated the impact of this clustering on receptor signaling and found that CAR22-S demonstrated high levels of signaling molecule activation (i.e. Akt, p70-S6 and STAT3) in the absence of antigen engagement. This is consistent with previous reports establishing that CAR clustering can lead to tonic signaling (Long, A.H. et al. Nat Med, 2015). Importantly, this tonic signaling did not lead to autonomous T cell proliferation. We proceeded to evaluate how clustering and tonic signaling impacted CAR function upon antigen engagement. Microscopic evaluation of CAR T cells combined with CD22+ Nalm6 cells revealed greater actin and microtubule organizing complex polarization (P = 0.02 and 0.01, respectively) in CAR22-S cells, consistent with superior immune synapse formation. This was accompanied by increased phosphorylation of PI3K, MAPK and calcium signaling proteins (Fig. 1b) after CAR engagement. RNA sequencing revealed significantly greater activation of immune response gene programs in CAR22-S cells as compared to CAR22-L after overnight exposure to Nalm6. We next investigated the impact that this enhanced receptor-driven activity had on CAR T cell anti-tumor function. CAR T cells were combined with Nalm6 in vitro and residual Nalm6 was serially quantified, revealing that CAR22-S mediated greater tumor control than CAR22-L, particularly at later time periods (P < 0.001). This was associated with greater secretion of IFNg, IL-2 and TNFa (all P < 0.001). Finally, we compared anti-tumor efficacy in xenograft models of systemic Nalm6. NOD/SCID/cg-/- mice were engrafted with Nalm6 and received 1x106 CAR T cells 7 days later. CAR22-S demonstrated greater in vivo expansion (P < 0.0001) and enhanced control of systemic disease (Fig. 1c,P = 0.017), resulting in prolongation of animal survival (Fig. 1d,P = 0.013). Based on these observations, we have designed a novel, affinity-enhanced CD22 CAR and confirmed that shorter linker length improves anti-tumor activity of this CAR. T cells expressing this CAR are currently undergoing evaluation in a phase I clinical trial (ClinicalTrials.org Identifiers NCT03620058 and NCT02650414). Thus far, 4 children and 2 adults have been infused with manageable toxicity. Early outcomes are promising, with 67% achieving complete remission at day 28, compared to 50% in our original CART22 trials. In summary, by investigating the potential mechanisms for an apparent discrepancy in outcomes between two different clinical trials, we demonstrate that reducing the length of the scFv linker results in significant changes to CAR biochemistry that directly lead to antigen-independent receptor activity. In contrast to previously published data demonstrating that tonic signaling of CD28-costimulated CARs is detrimental to T cell function (Long, A.H. et al. Nat Med, 2015), we found that tonic signaling of 4-1BB-costimulated CARs may be beneficial, possibly by priming T cells for rapid response to antigen. Disclosures Singh: University of Pennsylvania: Patents & Royalties. Frey:Novartis: Research Funding. Engels:Novartis: Employment. Zhao:Novartis: Employment. Peng:Novartis: Employment. Granda:Novartis: Employment. Ramones:Novartis: Employment. Lacey:Novartis: Research Funding; Novartis: Patents & Royalties: Patents related to CAR T cell biomarkers; Tmunity: Research Funding. Young:novartis: Research Funding. Brogdon:Novartis: Employment. Grupp:Roche: Consultancy; GSK: Consultancy; Novartis: Consultancy, Research Funding; Humanigen: Consultancy; CBMG: Consultancy; Novartis: Research Funding; Kite: Research Funding; Servier: Research Funding; Jazz: Other: study steering committees or scientific advisory boards; Adaptimmune: Other: study steering committees or scientific advisory boards; Cure Genetics: Consultancy. June:Novartis: Research Funding; Tmunity: Other: scientific founder, for which he has founders stock but no income, Patents & Royalties. Maude:Novartis: Consultancy; Kite: Consultancy. Gill:Novartis: Research Funding; Tmunity Therapeutics: Research Funding; Carisma Therapeutics: Research Funding; Amphivena: Consultancy; Aro: Consultancy; Intellia: Consultancy; Sensei Bio: Consultancy; Carisma Therapeutics: Equity Ownership. Ruella:AbClon: Membership on an entity's Board of Directors or advisory committees; Nanostring: Consultancy, Speakers Bureau; Novartis: Patents & Royalties: CART for cancer.

Background: CD19-targeted chimeric antigen receptor T cell therapy (CART19) has demonstrated remarkable clinical efficacy in treating relapsed/refractory B cell ALL, but associated toxicities may require treatment in inpatient or intensive care units (ICU). We sought to: (1) describe inpatient and ICU resource utilization within 30 days of CART19 infusion; and (2) evaluate trends in resource utilization from 2012-2019. Methods: We identified patients treated with CART19 on a clinical trial (NCT01626495, NCT02906371, and NCT02374333) or with the commercial product, tisagenlecleucel, at Children's Hospital of Philadelphia. Patients who received a prior cell therapy product were excluded. Demographic, pharmacy, and inpatient data were extracted from the electronic medical record from day of infusion (day 0) to day +30, censored at disease progression or death, using a semi-automated EPIC data query tool (ExtractEHR). The Virtual Pediatric Systems (VPS) database was queried for clinical data, resource utilization data, and Pediatric Risk of Mortality (PRISM) 3 and Pediatric Index of Mortality (PIM) 2 severity of illness scores. Log-binomial regression and linear regression were used to estimate the association of patient characteristics with the need for inpatient/ICU admission and inpatient/ICU length of stay (LOS), respectively. Similar models were used to estimate trends in outcomes from 2012-2019. Results: A total of 213 patients were included in the analyses. Median patient age was 12.4 years (range 1.4-29.1) at infusion; 60% were male, 66% were Caucasian, and 80% were non-Hispanic. Prior to CART19, 42% had an allogeneic hematopoietic cell transplant (alloHCT). At time of infusion, 19% had high disease burden, defined as bone marrow blasts ≥40% by flow cytometry. From 2012-2019, the proportion of patients with prior alloHCT or high disease burden decreased (Table 1). CART19 was infused in the outpatient setting in 93% of patients. In the 30 days after infusion, 70% had at least one inpatient admission, starting at a median of day +2 (IQR +1 to +6). Among the 149 patients admitted, median cumulative inpatient LOS was 7 days (IQR 4-13). Cumulative LOS increased with increasing grade of cytokine release syndrome (CRS). Median LOS was 0, 5, and 15 days for patients with no, mild, and severe CRS, respectively. From 2012-2019, there were linear trends toward decreases in proportion of patients admitted (p ICU admission was required for 23% (95% CI, 17-29) of the cohort, starting at a median of day +5 (IQR +4 to +6.5). ICU admission was more frequent for patients with high disease burden than those with low disease burden [68% (95% CI, 52-81) vs. 11% (95% CI, 7-17), p Other than high disease burden, baseline patient characteristics were not significantly associated with inpatient/ICU admission or inpatient/ICU LOS. Conclusion: In a cohort of 213 pediatric patients with ALL who received CART19, over 90% were safely infused in the outpatient setting. Though the majority of patients required at least one inpatient admission, the proportion of patients admitted to the hospital or ICU and cumulative inpatient LOS in the 30 days post-infusion decreased over the past 7 years. Mortality was 1%. Additional analyses will investigate the impact of changes in supportive care practices on resource utilization outcomes. Disclosures Grupp: GSK: Consultancy; Cure Genetics: Consultancy; Humanigen: Consultancy; CBMG: Consultancy; Novartis: Research Funding; Kite: Research Funding; Novartis: Consultancy, Research Funding; Roche: Consultancy; Servier: Research Funding; Jazz: Other: study steering committees or scientific advisory boards; Adaptimmune: Other: study steering committees or scientific advisory boards. Maude:Novartis: Consultancy; Kite: Consultancy.

The mechanisms underlying the maintenance of long-lasting humoral immunity are not well understood. Studies in mice indicate that plasma cells (PCs) can survive up to a lifetime, even in the absence of regeneration by B cells, implying the presence of long-lived PCs as a mechanism for long-lasting immunity. Evidence from humans treated with anti-CD20, which depletes circulating B cells, also suggests B-cell-independent long-term survival of some PCs. On the other hand, antibody responses may be sustained solely by short-lived PCs with repopulation from clonally related memory B cells. To explore PC longevity and humoral immunity in humans, we investigated the fate of PCs and their antibodies in adult and pediatric patients who received chimeric antigen receptor-based adoptive T-cell immunotherapy targeting CD19 to treat B-cell lineage malignancies (CTL019). Treatment with CTL019 is frequently associated with B-cell aplasia that can persist for years. Serum antibody titers to vaccine-related antigens were measured, and quantitative assessment of B cells and PCs in blood and bone marrow was performed at various time points before and after CTL019 therapy. While total serum immunoglobulin concentrations decline following CTL019-induced B-cell aplasia, several vaccine/pathogen-specific serum immunoglobulin G and A (IgG and IgA) titers remain relatively stable for at least 6 and 12 months posttreatment, respectively. Analysis of bone marrow biopsies after CTL019 revealed 8 patients with persistence of antibody-secreting PCs at least 25 months post-CTL019 infusion despite absence of CD19(+)CD20(+) B cells. These results provide strong evidence for the existence of memory B-cell-independent, long-lived PCs in humans that contribute to long-lasting humoral immunity.

Abstract CAR T cell therapy in relapsed B-ALL can result in complete response (CR) rates of 80-90%, but relapse-free survival declines to 60% within the first 12-months due to both CD19-positive and negative relapses. CD19-positive relapses that occur during this time are largely due to early CAR T cell loss. We hypothesize that inhibiting the PD-1:PD-L1 (programmed cell death 1) checkpoint axis may decrease T cell exhaustion, thereby improving CAR T cell function and persistence. We report our single institution experience of the use of PD-1 inhibitors in patients with relapsed or refractory B lymphoblastic malignancies treated with CD19-directed CAR T cell therapy. Methods: Patients treated with CD19-directed CAR T cell therapy (murine CTL019 or humanized CTL119) at the Children's Hospital of Philadelphia who demonstrated repeated early CAR T cell loss or partial/no response to CAR T cell therapy received a PD-1 inhibitor starting no sooner than 14 days after CAR T cell infusion and after resolution of cytokine release syndrome (CRS) symptoms, with the possibility of repeated doses up to every 3 weeks. Results: Fourteen patients, ages 4-17 years, with heavily pretreated, relapsed B-ALL (n=13) or B lymphoblastic lymphoma (n=1), were treated with CD19-directed CAR T cell therapy (CTL019, n=4; or CTL119, n=10) in combination with pembrolizumab (n=13) or nivolumab (n=1). Three of 6 patients treated with CD19 CAR T cells in combination with a PD-1 inhibitor for early B cell recovery re-established B cell aplasia (a reflection of CAR T cell function) for 5-15 months, 2 of whom have persistent B cell aplasia with ongoing pembrolizumab therapy. Four patients started pembrolizumab for bulky extramedullary disease unresponsive to or relapsed after CAR T cells, with 2 partial and 2 complete responses seen. In one patient, significant CAR T cell proliferation was measured within days of starting pembrolizumab and in temporal correlation to radiographic disease response. In 4 patients who failed to achieve disease remission with initial CAR T cell infusion, no CRs were achieved with the addition of pembrolizumab, although partial responses were seen, and one patient progressed with CD19-dim/negative disease. CRS symptoms and fever typical of CAR T cell proliferative responses were observed in 3/14 patients within 2 days of starting pembrolizumab. Other early and delayed adverse effects associated with PD-1 inhibition were tolerable or reversible upon discontinuation, and including 1 case each of acute pancreatitis, hypothyroidism, arthralgias, urticaria, as well as 4 patients with grade 3-4 cytopenias. No grade 5 toxicities or graft-versus-host disease flares occurred. Two patients discontinued pembrolizumab for delayed adverse effects after multiple doses; both patients relapsed/progressed with CD19+ disease a few weeks after discontinuation. Discussion: T cell exhaustion or activation induced CAR T death (AICD) has been suspected to contribute to poor persistence of CAR T cells. We hypothesized that the PD-1 checkpoint pathway may be involved in CAR T cell exhaustion in some cases, which may be overcome by checkpoint inhibition. Here, promising responses were specifically seen in those with early B-cell recovery and bulky extramedullary disease. In contrast, PD-1 inhibition had partial, but no durable, effect in the four B-ALL patients with poor initial marrow response to CAR T cell therapy alone, suggesting a different mechanism such as AICD may be responsible for poor initial responses. No unexpected or fatal toxicities were seen. This cohort shows initial evidence that checkpoint inhibitors can be used effectively and safely with CAR T cell therapy in children with relapsed B-ALL, and that this strategy may augment CAR T cell effect and persistence. Disclosures Teachey: Amgen: Consultancy; La Roche: Consultancy. Callahan:Novartis Pharmaceuticals Corporation: Consultancy. Porter:Genentech: Other: Spouse employment; Novartis: Other: Advisory board, Patents & Royalties, Research Funding; Kite Pharma: Other: Advisory board. Lacey:Novartis Pharmaceuticals Corporation: Patents & Royalties; Tmunity: Research Funding; Parker Foundation: Research Funding; Novartis Pharmaceuticals Corporation: Research Funding. June:Tmunity Therapeutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Tmunity Therapeutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Novartis Pharmaceutical Corporation: Patents & Royalties, Research Funding; Immune Design: Membership on an entity's Board of Directors or advisory committees; Immune Design: Membership on an entity's Board of Directors or advisory committees; Novartis Pharmaceutical Corporation: Patents & Royalties, Research Funding; Celldex: Consultancy, Membership on an entity's Board of Directors or advisory committees. Grupp:Novartis Pharmaceuticals Corporation: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy; Adaptimmune: Consultancy; University of Pennsylvania: Patents & Royalties. Maude:Novartis Pharmaceuticals Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Introduction: CTL019 is an anti-CD19 genetically modified autologous T-cell immunotherapy developed at the University of Pennsylvania (Penn) that was recently approved for treatment of relapsed/refractory pediatric and young adult B-cell acute lymphoblastic leukemia (ALL) and adult relapsed/refractory diffuse large B-cell lymphoma (DLBCL) as tisagenlecleucel (Novartis). For ALL, the FDA-approved dose is 0.2 to 5.0 x 106 CAR-positive viable T cells per kg of body weight for patients ≤ 50 kg or 0.1 to 2.5 x 108 CAR-positive viable T cells for pts > 50 kg; for DLBCL, the FDA-approved dose is 0.6 to 6.0 x 108 CAR-positive viable T cells. For CTL019 manufactured at Penn, the dose is determined by flow cytometric staining of CAR-positive T cells, which are cryopreserved in product bags along with replicate aliquots of the final formulation in vials, simultaneously cryopreserved for release testing. The CTL019 product release criteria include a post thaw viability assessment using a vial of replicate aliquot of the final formulation for Trypan blue exclusion or dual fluorescence automated cell counting (Luna-FL, Logos Biosystems). There are no published data examining the relationship between CTL019 viability release testing and clinical outcomes. Methods: We analyzed CTL019 post thaw viability release testing in patients treated on one prospective single institution clinical trial of CD19-expressing non-Hodgkin lymphomas (NHL) (NCT02030834) and two single-institution prospective pediatric ALL clinical trials (NCT01626495 and NCT02906371). Patients were assessed for response to therapy and CAR T-cell expansion. Receiver operating characteristic (ROC) curves were constructed for prediction of complete responses based on sensitivity and specificity of CAR T-cell product post thaw viability release test results. Results: 39 pts with relapsed/refractory NHL (24 diffuse large B-cell lymphoma and 15 follicular lymphoma) were enrolled and received the protocol-specified dose of CTL019. Best response rate was 56% (22/39) complete responses (CR). 123 pts with relapsed/refractory pediatric ALL were enrolled and received the protocol-specified dose of CTL019. Best response rate was 96% (118/123) CR/complete remission with incomplete blood count recovery (CRi). For patients with NHL infused with CTL019, product % viability had a median of 89.8% viability (range: 73.7%-97.7%); product % viability quintiles were as follows: 20%-tile=81.7%, 40%-tile=88.3%, 60%-tile=91.1%, 80%-tile=94.8%). ROC area for NHL patients was 0.47 (95%CI: 0.28-0.65). For patients with ALL infused with CTL019, product % viability had a median of 89.3% viability (range: 56.0%-98.4%); product % viability quintiles were as follows: 20%-tile=82.3%, 40%-tile=87.5%, 60%-tile=90.9%, 80%-tile=94.4%). ROC area for ALL patients was 0.52 (95%CI: 0.32-0.71). For patients with NHL, progression-free survival (PFS) was not significantly influenced by product viability release test results by Cox proportional hazards (HR: 1.0, 95%CI: 0.94-1.09, p=0.7). For patients with NHL, peak CAR T-cell expansion was not significantly correlated with product viability release test results (r2=0.12, p=0.5). Data collection for Cox analysis to investigate the effect of release test viability on PFS and correlation of release test viability with peak CTL019 expansion in ALL is ongoing and will be presented. Conclusions: Our data suggest that, within the ranges obtained in these trials, there is no clear dose-response relationship between CTL019 product viability release test results and clinical response rates in pediatric and young adult ALL or DLBCL. Figure Figure. Disclosures Chong: Novartis: Consultancy. Levine:Cure Genetics: Consultancy; Brammer Bio: Consultancy; CRC Oncology: Consultancy; Incysus: Consultancy; Novartis: Consultancy, Patents & Royalties, Research Funding; Tmunity Therapeutics: Equity Ownership, Research Funding. Grupp:Novartis Pharmaceuticals Corporation: Consultancy, Research Funding; Adaptimmune: Consultancy; University of Pennsylvania: Patents & Royalties; Jazz Pharmaceuticals: Consultancy. Davis:Novartis Institutes for Biomedical Research, Inc.: Patents & Royalties. Siegel:Novartis: Research Funding. Maude:Novartis Pharmaceuticals Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees. Frey:Novartis: Consultancy; Servier Consultancy: Consultancy. Porter:Genentech: Other: Spouse employment; Novartis: Other: Advisory board, Patents & Royalties, Research Funding; Kite Pharma: Other: Advisory board. June:Immune Design: Membership on an entity's Board of Directors or advisory committees; Tmunity Therapeutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Celldex: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis Pharmaceutical Corporation: Patents & Royalties, Research Funding; Immune Design: Membership on an entity's Board of Directors or advisory committees; Tmunity Therapeutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Novartis Pharmaceutical Corporation: Patents & Royalties, Research Funding. Schuster:Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Dava Oncology: Consultancy, Honoraria; Merck: Consultancy, Honoraria, Research Funding; Novartis Pharmaceuticals Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Nordic Nanovector: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech: Honoraria, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees.

Background Quantitative polymerase chain reaction (qPCR) is an analytical method that has been used to investigate the in vivo kinetics of chimeric receptor antigen (CAR) transgene following the infusion of tisagenlecleucel. B cell aplasia, likely an "on-target toxicity" of tisagenlecleucel, has been considered a measure of functional persistence. (Maude SL et al. Blood 2015;125(26):4017-4023) Although the CAR transgene can be detected in peripheral blood of tisagenlecleucel treated patients, it is unclear whether CAR transgene detection by qPCR could be reliably used to inform treatment decision in an individual patient. Methods Transgene levels in blood measured by qPCR from pivotal phase II studies in relapsed/refractory (r/r) pediatric and young adult acute lymphoblastic leukemia (B-ALL) patients (pts) (ELIANA [NCT02435849, N=75]; ENSIGN [NCT02228096, N=29]) and adult diffuse large B cell lymphoma (DLBCL) pts (JULIET [NCT02445248, N=93]) were used to investigate the relationship between transgene persistence and clinical response. Results To determine whether CAR qPCR measurements are associated with or predictive of response, CAR transgene levels and timing of peak levels were examined. In both ALL and DLBCL pts, there were detectable CAR transgene levels by qPCR in both responders and non-responders. The geometric mean maximal expansion (geo mean Cmax) was similar between responding and non-responding adult DLBCL pts, while 1.7 fold differences were observed in pediatric ALL pts (geo mean Cmax in copies/µg: responders, 32700, n=79; non-responders, 19500, n=10; Table 1). For both DLBCL and ALL pts, high inter-individual variability in transgene levels was noted. Similarly, higher CAR-T cell expansion from flow cytometry data pooled from responding pediatric ALL and chronic lymphocytic leukemia (CLL) pts were observed relative to non-responding pts (Mueller KT et al. Blood 2017;130(21):2317-2325), while the levels in DLBCL pts were comparatively lower in blood, likely due to partitioning of functional CAR-T cells to the target sites including lymph nodes. The median time to maximal transgene level ranged from 9-10 days in DLBCL responders and non-responders and pediatric ALL responders, while non-responding pediatric ALL pts showed delayed expansion with median Tmax of 20 days. The median time corresponding to last quantifiable transgene level (Tlast), an indicator of persistence, was higher in responding pts compared to non-responding pts, indicating a trend for longer persistence in both DLBCL and ALL pts with continued response (Table 1). Similarly, the half-life estimated from the terminal slope of the cellular kinetic profile, an additional indicator of persistence, was higher in responding pts relative to non-responding pts for both DLBCL and ALL (Table 1). Despite this general trend, in some cases, transgene levels were not detectable at later time points in pts with continued response. The swimmer plot for representative responder ALL (Figure 1a) and DLBCL pts (Figure 1b) with responses and transgene levels demonstrate that although the majority of responding pts show persistent transgene levels, some pts maintained a favorable clinical response despite a decline in transgene levels to below the level of quantification of 50 copies/µg. Conclusion In both ALL and DLBCL, CAR transgene is initially detected at high levels with high variability in both responders and non-responders. While the majority of responding pts tend to have persistent transgene levels, some pts maintain favorable clinical responses despite a lack of quantifiable transgene. These results indicate that qPCR testing for CAR transgene in blood of tisagenlecleucel treated pts should not be used for making treatment decisions for individual pts. In addition, the qPCR measurements in peripheral blood do not reflect on the trafficking of CAR positive cells to sites outside peripheral blood. The assessment by flow cytometry remains an important assay to distinguish high expression in responding vs non-responding pts in ALL and CLL, and further evaluation of target tissue is needed in DLBCL to understand the utility of CAR expression as a means to distinguish responder and non-responders. Also, further data are needed to improve our understanding of how CAR transgene levels relate to disease burden and duration of response and whether this information is clinically useful. Disclosures Awasthi: Exelixis: Equity Ownership; Celgene: Equity Ownership; Novartis Institutes for Biomedical Research: Employment. Mueller:Novartis Institutes for Biomedical Research: Employment; Novartis Pharmaceuticals Corporation: Equity Ownership, Other: Patent pending. Tam:Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BeiGene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Research Funding. Rives:Amgen: Consultancy, Other: advisory board ; Novartis Pharmaceuticals Corporation: Consultancy, Other: Symposia, advisory boards ; Jazz Pharma: Consultancy, Other: Symposia, advisory boards ; Shire: Consultancy, Other: Symposia, advisory boards . McGuirk:Bellicum Pharmaceuticals: Research Funding; Fresenius Biotech: Research Funding; Novartis Pharmaceuticals Corporation: Honoraria, Other: speaker, Research Funding; Astellas Pharma: Research Funding; Gamida Cell: Research Funding; Kite Pharma: Honoraria, Other: travel accommodations, expenses, speaker ; Pluristem Ltd: Research Funding. Pulsipher:Adaptive Biotech: Consultancy, Research Funding; Amgen: Honoraria; CSL Behring: Consultancy; Novartis: Consultancy, Honoraria, Speakers Bureau. Jaeger:Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Mundipharma: Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Consultancy, Honoraria; Takeda-Millenium: Membership on an entity's Board of Directors or advisory committees; Takeda-Millenium: Membership on an entity's Board of Directors or advisory committees; AOP Orphan: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Membership on an entity's Board of Directors or advisory committees; Bioverativ: Membership on an entity's Board of Directors or advisory committees; Infinity: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees; MSD: Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Baruchel:Novartis: Membership on an entity's Board of Directors or advisory committees; Shire: Research Funding; Jazz Pharmaceuticals: Consultancy, Honoraria, Other: Travel, accommodations or expenses; Amgen: Consultancy; Roche: Consultancy; Servier: Consultancy; Celgene: Consultancy. Myers:Novartis Pharmaceuticals Corporation: Consultancy, Honoraria, Research Funding, Speakers Bureau. Balke-Want:Novartis Pharmaceuticals Corporation: Honoraria. Schuster:Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Novartis Pharmaceuticals Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Merck: Consultancy, Honoraria, Research Funding; Dava Oncology: Consultancy, Honoraria; Nordic Nanovector: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech: Honoraria, Research Funding. Stefanski:Novartis Pharmaceuticals Corporation: Consultancy, Honoraria, Speakers Bureau. Bishop:Novartis Pharmaceuticals Corporation: Speakers Bureau; Juneau Therapeutics: Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Seattle Genetics: Consultancy, Membership on an entity's Board of Directors or advisory committees; United Healthcare: Employment. Waldron:Novartis Pharmaceuticals Corporation: Employment, Equity Ownership. Anak:Novartis Pharma AG: Employment. Chakraborty:Novartis Institutes for Biomedical Research: Employment. Bleickardt:Novartis Pharmaceuticals Corporation: Employment. Wong:Novartis Pharmaceuticals Corporation: Employment, Equity Ownership. Bubuteishvili Pacaud:Novartis Pharmaceuticals Corporation: Employment, Equity Ownership. Waller:Kalytera: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celldex: Research Funding; Pharmacyclics: Other: Travel Expenses, EHA, Research Funding; Cambium Medical Technologies: Consultancy, Equity Ownership. Maude:Novartis Pharmaceuticals Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Background: Chimeric antigen receptor T-cells (CAR-T) have emerged as a promising treatment for children with relapsed/refractory acute lymphoblastic leukemia (ALL). While CAR-T outcomes have been published, little data exist on how to manage these patients for the weeks to months between T-cell collection and CAR-T infusion. Unlike stem cell transplant (SCT), where higher burden of disease is associated with poor outcomes and is often a contraindication, successful outcomes for children with high disease burden pre-CAR-T have been demonstrated. Thus, traditional high-intensity chemotherapy for relapsed ALL that aims to minimize disease burden but carries significant morbidity may not be the best option for pre-CAR-T populations. We thus compared our population-based experience in using high vs. low-intensity chemotherapy regimens to bridge patients in terms of toxicity, inpatient days, and success in reaching CAR-T infusion. Methods: The Hospital for Sick Children (Sickkids) is the provincial referral centre for cellular therapy for children in Ontario, Canada. All Ontario children referred to Sickkids between 2014-2018 for first T-cell collection with intent to proceed to CAR-T therapy were included and followed until CAR-T infusion, decision to pursue alternative therapy, or death. Bridging regimen details were collected and classified as low vs. high intensity based on whether such therapy was likely associated with >7 days of neutropenia. Disease and outcome variables were compared between high vs. low intensity regimens using Chi squared, Fisher's exact, or Wilcoxon tests. Results: The cohort included 32 patients with a median age of 9.7 years at the time of first T-cell collection [interquartile range (IQR) 6.0-12.3]. The median number of previous relapses was 2 (IQR 1-2), 14 (44.0%) had undergone prior SCT, and 4 (12.5%) had Down syndrome. The vast majority of patients (28, 87.5%) were successfully bridged to receive CAR-T therapy with a median time to infusion of 81 days (IQR 60-105). Two patients experienced manufacturing failure and pursued SCT instead, 1 died of toxicity, and 1 was still awaiting infusion at the end of the study period. Low-intensity bridging regimens were used following collection for 19 (59.4%) patients, most often based on low-dose intravenous methotrexate, 3-drug induction (vincristine/steroids/asparaginase), or maintenance therapy. The most common high-intensity regimens included cyclophosphamide/etoposide, high dose cytarabine, or 4-drug induction (vincristine/steroids/asparaginase/anthracycline). Patients receiving high-intensity therapy did not seem to have more aggressive disease prior to starting bridging treatment (as indicated by peripheral blasts, number of previous relapses, prior SCT) that would have justified choosing high-intensity treatments. Patients receiving initial high-intensity regimens were however more likely to have been collected in first half of the study period (Table 1). Patients receiving initial high-intensity regimens also developed more microbiologically documented infections and experienced a greater number of inpatient days (Table 1). Excluding patients experiencing manufacturing failure or still awaiting CAR-T at the end of the study period, the likelihood of receiving CAR-T also did not vary [high-intensity regimen - 11/12 (91.7%) vs. low-intensity regimen - 17/17 (100%); p=0.41]. Conclusions: We demonstrate in our population-based cohort of heavily pre-treated and high-risk patients that initial low-intensity chemotherapy had a very high likelihood of successfully bridging children to CAR-T infusion. Low-intensity bridging regimens were associated with lower rates of toxicity and higher quality of life as indicated by fewer inpatient days. Low-intensity regimens should be considered the first line option in this population. Disclosures Grupp: Jazz Pharmaceuticals: Consultancy; Adaptimmune: Consultancy; University of Pennsylvania: Patents & Royalties; Novartis Pharmaceuticals Corporation: Consultancy, Research Funding. Maude:Novartis Pharmaceuticals Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees.

BACKGROUND Tisagenlecleucel is an FDA approved chimeric antigen receptor (CAR)-T cell therapy that reprograms T cells to eliminate CD19+ B cells. ELIANA (NCT02435849) is a phase 2 pivotal study of tisagenlecleucel in pediatric/young adult patients (pts) with CD19+ r/r B-cell acute lymphoblastic leukemia (ALL), the first global trial of a CAR-T cell therapy. The primary objective was met, with an overall remission rate (ORR) of 81% (complete remission [CR] + CR with incomplete blood count recovery [CRi]). Here we present an update of ELIANA, with additional pts and additional 11 mo follow-up from the previous report (Maude et al. N Engl J Med 2018). METHODS Eligible pts were aged ≥3 y at screening and ≤21 y at diagnosis and had ≥5% leukemic blasts in bone marrow. Tisagenlecleucel was centrally manufactured at 2 sites (Morris Plains, NJ, USA and Leipzig, Germany) by lentiviral transduction of autologous T cells with a vector encoding for a second generation 4-1BB anti-CD19 CAR and expanded ex vivo. Tisagenlecleucel was provided to pts at 25 study centers in 11 countries on 4 continents using cryopreserved apheresed mononuclear cells, central production facilities, and a global supply chain. The primary endpoint, ORR within 3 mo and maintained for ≥28 d among infused pts, was assessed by an independent review committee. Secondary endpoints included duration of remission (DOR), overall survival (OS), safety, and cellular kinetics. RESULTS As of April 13, 2018, 113 pts were screened and 97 enrolled. There were 8 manufacturing failures (8%) and 10 pts (10%) were not infused due to death or adverse events (AEs). Following lymphodepleting chemotherapy in most pts (76/79; fludarabine/cyclophosphamide [n=75]), 79 pts were infused with a single dose of tisagenlecleucel (median dose, 3.0×106 [range, 0.2-5.4×106] CAR-positive viable T cells/kg), and all had ≥3 mo of follow-up or discontinued earlier (median time from infusion to data cutoff, 24 mo [range, 4.5-35 mo]). Median age was 11 y (range, 3-24 y); 61% of pts had prior hematopoietic stem cell transplant (SCT). Among the 65 pts with CR/CRi, 64 (98%) were MRD- within 3 mo. Median DOR by K-M analysis was not reached (Figure): responses were ongoing in 29 pts (max DOR, 29 mo and ongoing); 19 pts relapsed before receiving additional anticancer therapy (13 died subsequently); 8 pts underwent SCT while in remission, 8 received additional anticancer therapy (non-SCT) and 1 discontinued while in remission. The probability of relapse-free survival at 18 mo was 66% (95% CI, 52%-77%). Median OS was not reached; OS probability at 18 mo was 70% (95% CI, 58%-79%). Cytokine release syndrome (CRS) occurred in 77% of pts (grade [G] 3/4; 48%; graded using the Penn scale); 39% of pts received tocilizumab for treatment of CRS with or without other anti-cytokine therapies; 48% of pts required ICU-level care for CRS, with a median ICU stay of 7 d. All cases of CRS were reversible. Most common G 3/4 nonhematologic AEs (>15%) other than CRS were neutropenia with a body temperature >38.3°C (62% within 8 wk of infusion), hypoxia (20%), and hypotension (20%). 13% of pts experienced G 3 neurological events, with no G 4 events or cerebral edema. Based on laboratory results, 43% and 54% of pts had G 3/4 thrombocytopenia and neutropenia not resolved by d 28; the majority of events resolved to G ≤2 by 3 mo. 25 post-infusion deaths were reported: 2 within 30 d (1 disease progression, 1 cerebral hemorrhage); 23 after 30 d of infusion (range, 53-859 d; 18 disease progression, 1 each due to encephalitis, systemic mycosis, VOD [hepatobiliary disorders related to allogeneic-SCT], bacterial lung infection, and an unknown reason after study withdrawal). Tisagenlecleucel expansion in vivo correlated with CRS severity, and persistence of tisagenlecleucel along with B-cell aplasia in peripheral blood was observed for ≥2.5 y in some responding pts. Analysis of B-cell recovery and correlation with relapse will be presented. CONCLUSIONS With longer follow-up, the ELIANA study continues to confirm the efficacy of a single infusion of tisagenlecleucel in pediatric and young adults with ALL without additional therapy. AEs were effectively and reproducibly managed globally by appropriately trained personnel at study sites. The achievement of high overall response rates and deep remissions, in combination with the median duration of response and overall survival not being reached, further corroborate previously reported results. Figure. Figure. Disclosures Grupp: Novartis Pharmaceuticals Corporation: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy; Adaptimmune: Consultancy; University of Pennsylvania: Patents & Royalties. Maude:Novartis Pharmaceuticals Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees. Rives:Shire: Consultancy, Other: Symposia, advisory boards ; Jazz Pharma: Consultancy, Other: Symposia, advisory boards ; Novartis Pharmaceuticals Corporation: Consultancy, Other: Symposia, advisory boards ; Amgen: Consultancy, Other: advisory board . Baruchel:Celgene: Consultancy; Amgen: Consultancy; Roche: Consultancy; Jazz Pharmaceuticals: Consultancy, Honoraria, Other: Travel, accommodations or expenses; Novartis: Membership on an entity's Board of Directors or advisory committees; Shire: Research Funding; Servier: Consultancy. Bittencourt:Novartis Pharmaceuticals Corporation: Consultancy; Jazz Pharmaceuticals: Consultancy, Honoraria. Bader:Riemser: Research Funding; Cellgene: Consultancy; Medac: Patents & Royalties, Research Funding; Neovii: Research Funding; Novartis: Consultancy, Speakers Bureau. Laetsch:Bayer: Consultancy; Pfizer: Equity Ownership; Eli Lilly: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy; Loxo Oncology: Consultancy. Stefanski:Novartis Pharmaceuticals Corporation: Consultancy, Honoraria, Speakers Bureau. Myers:Novartis Pharmaceuticals Corporation: Consultancy, Honoraria, Research Funding, Speakers Bureau. Qayed:Novartis: Consultancy. Pulsipher:CSL Behring: Consultancy; Amgen: Honoraria; Adaptive Biotech: Consultancy, Research Funding; Novartis: Consultancy, Honoraria, Speakers Bureau. Martin:Novartis Pharmaceuticals Corporation: Research Funding; Jazz Pharmaceuticals: Research Funding. Nemecek:Novartis Pharmaceuticals Corporation: Other: advisory boards. Boissel:Servier: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis Pharmaceuticals Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees. Leung:Novartis Pharmaceuticals Corporation: Employment. Eldjerou:Novartis Pharmaceuticals Corporation: Employment. Yi:Novartis Pharmaceuticals Corporation: Employment. Mueller:Novartis Institutes for Biomedical Research: Employment; Novartis Pharmaceuticals Corporation: Equity Ownership, Other: Patent pending. Bleickardt:Novartis Pharmaceuticals Corporation: Employment.

Introduction. Anti-CD19 chimeric antigen receptor T cells (CART19 or CTL019) have shown impressive clinical activity in B-cell acute lymphoblastic leukemia (B-ALL) and are poised to receive FDA approval. However, some patients relapse after losing CD19 expression. Since CD22 remains highly expressed in relapsed/refractory (r/r) B-ALL even in these patients, anti-CD22 CART (CART22) have been developed. The National Cancer Institute (NCI) reported 4/9 complete remission (CR) in patients receiving CART22, with 100% CR at the highest T cell dose (NCT02315612)(S hah NN, ASH 2016 #650). Patients and Methods. We generated a second-generation CAR22 differing from that used by the NCI only by the use of a longer linker [4x(GGGGS); LL vs. 1x(GGGGS); SL] between the light and heavy chains of the scFv (Fig. 1 A). This construct was tested in two pilot clinical trials in adults (NCT02588456)and children with r/r-ALL (NCT02650414). CART22 cells were generated using lentiviral transduction as in our previous studies. The protocol-specified CART22 dose was 2x106-1x107 cells/kg for pediatric patients For the preclinical studies, we generated CART22LL and CART22SL and tested them in vivo using xenograft models. NOD-SCID gamma chain deficient (NSG) mice were engrafted with either a luciferase+ standard B-ALL cell line (NALM6) or primary B-ALL cells obtained from a patient relapsing after CART19 (CHP110R). We also used 2-photon imaging to study the in vivo behavior and immune synapse formation and flow cytometry to asses T cell activation. Results. CART22 cells were successfully manufactured for 10/12 patients. In the adult cohort 3/3 patients developed CRS (gr.1-3) and no neurotoxicity was observed; in the pediatric cohort out of 5 evaluable patients (1 discontinued for lineage switch to AML on pre-infusion marrow), 3/5 developed cytokine-release syndrome (CRS) (all grade 2) and 1 patient had encephalopathy (gr.1). CART22 cells expanded in the PB with median peak of 1977 (18-40314) copies/ug DNA at day 11-18. Interestingly, in an adult patient who had previously received CART19 a second CART19 re-expansion was observed following CART22 expansion (Fig 1 B). At day 28, in the adult cohort the patient who was infused in morphologic CR remained in CR, while the other 2 had no response (NR); in the pediatric cohort 2/5 patients were in CR, 1 in partial remission (PR) that then converted to CR with incomplete recovery at 2 months, and 2 NR. No CD22-negative leukemia progression was observed. Since our results with a long linker appeared inferior compared to the previously reported CART22 trial (short linker), we performed a direct comparison of the 2 different CAR22 constructs. In xenograft models, CART22SL significantly outperformed CART22LL (Fi 1 C) with improved overall survival. Moreover, CART22SL showed higher in vivo proliferation at day 17 (Fig 1 D). Mechanistically, intravital 2-photon imaging showed that CART22SL established more protracted T cell:leukemia interactions than did CART22LL, suggesting the establishment of productive synapses (Fig 1 E). Moreover, in vivo at 24 hrs higher T cell activation (CD69, PD-1) was observed in CART22SL from the BM of NALM-6-bearing mice. Conclusions. Here we report the results of two pilot clinical trials evaluating the safety and feasibility of CART22 therapy for r/r B-ALL. Although feasible and with manageable toxicity CART22LL led to modest clinical responses. Preclinical evaluation allowed us to conclude that shortening the linker by 15 amino acids significantly increases the anti-leukemia activity of CART22, possibly by leading to more effective interactions between T cells and their targets. Finally, with the caveats of cross-trial comparison, our data suggest that xenograft models can predict the clinical efficacy of CART products and validate the use of in vivo models for lead candidate selection Disclosures Ruella: Novartis: Patents & Royalties, Research Funding. Maude: Novartis Pharmaceuticals: Consultancy, Other: Medical Advisory Boards. Engels: Novartis: Employment. Frey: Novartis: Research Funding. Lacey: Novartis: Research Funding; Genentech: Honoraria. Melenhorst: Novartis: Research Funding. Brogdon: Novartis: Employment. Young: Novartis: Research Funding. Porter: Incyte: Honoraria; Novartis: Honoraria, Patents & Royalties, Research Funding; Immunovative Therapies: Other: Member DSMB; Genentech/Roche: Employment, Other: Family member employment, stock ownship - family member; Servier: Honoraria, Other: Travel reimbursement. June: WIRB/Copernicus Group: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celldex: Honoraria, Membership on an entity's Board of Directors or advisory committees; Immune Design: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Novartis: Patents & Royalties, Research Funding; Tmunity Therapeutics: Equity Ownership, Research Funding. Grupp: Jazz Pharmaceuticals: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy, Other: grant; University of Pennsylvania: Patents & Royalties; Adaptimmune: Consultancy. Gill: Novartis: Patents & Royalties, Research Funding.

A single-center trial of CD19 directed, lentiviral transduced chimeric antigen receptor (CAR) T cells (CTL019) for relapsed and refractory (r/r) B-ALL pediatric patients showed rates of CR >90% with prolonged CAR T cell persistence/CR without further therapy in the majority of patients infused (Maude NEJM 2014). We report here the feasibility, safety and efficacy of the first multicenter global pivotal registration CAR T cell trial. Features of this trial include: i) the first trial in which industry-manufactured cells were provided to all patients; ii) enrollment across 25 centers in the US, EU, Canada, Australia, and Japan; iii) successful transfer and manufacturing of cells in a global supply chain; and iv) successful implementation of cytokine release syndrome (CRS) management across a global trial. All patients had CD19 positive B-ALL with morphologic marrow tumor involvement at registration (>5% blasts), and were either primary refractory; chemo-refractory after first relapse, relapsed after second line therapy; or ineligible for allogeneic SCT. CTL019 was manufactured from patient PBMC under GMP conditions in the US, at a centralized "sponsor-owned" manufacturing facility, and supplied to all sites. The primary endpoint of overall remission rate (CR+CRi) within 3 months and secondary endpoints (EFS, DOR, OS and safety) were assessed by an independent review committee. Based on preliminary data as of March 2016, 57 patients were enrolled. There were 3 manufacturing failures (5%), 5 patients were not infused due to death or adverse events (9%), and 15 patients were pending infusion at the data cut off. Following fludarabine/cyclophosphamide lymphodepleting chemotherapy in the majority of the patients, 34 patients (median age 11 [3-23], 50% with prior HSCT) were infused with a single dose of CTL019 at a median dose of 2.9 x106 transduced CTL019 cells/kg (0.2 to 4). Among 29 patients reaching D28 prior to the data cutoff, 83% (24/29) achieved CR or CRi by local investigator assessment, all of which were MRD-negative. Two early deaths occurred prior to initial disease assessment, one due to disease progression and one due to intracranial hemorrhage. Two patients did not respond. One patient was in CR by BM at D28, but CSF was not assessed, therefore this patient was classified as "incomplete" assessment. Safety was managed by a protocol-specified CRS algorithm with no cases of refractory CRS. Using the Penn CRS grading scale, 82% of patients experienced CRS, with 7 grade 3 (21%) and 8 grade 4 (24%) events. 44% patients with CRS required anti-cytokine therapy; all received tocilizumab with or without other anti-cytokine therapy, with complete resolution of CRS. Besides CRS, the most common grade 3 and 4 non-hematologic AEs were febrile neutropenia (29%), increased bilirubin (21%), increased AST (21%), and hypotension (21%). 21% of patients experienced grade 3 or 4 neuropsychiatric events including confusion, delirium, encephalopathy, agitation and seizure; no cerebral edema was reported. CTL019 in vivo cellular kinetics by qPCR demonstrated transgene persistence in blood in responding patients at and beyond 6 months. Overall exposure (AUC 0-28d) and maximal expansion (Cmax) of CTL019 DNA measured by qPCR was higher in responding compared with non-responding patients. In summary, this pivotal global study in pediatric and young adult patients with r/r B-ALL receiving CTL019, confirms a high level of efficacy and a similar safety profile to that shown in the prior single center experience. Safety was effectively and reproducibly managed by appropriately trained investigators. The study has completed accrual. At the meeting, updated data from a planned formal interim analysis including safety, efficacy (primary and selected secondary endpoints), cellular kinetics, and impact of anti-cytokine therapy will be presented for more than 50 patients infused at 25 global sites. Disclosures Grupp: Jazz Pharmaceuticals: Consultancy; Novartis: Consultancy, Research Funding; Pfizer: Consultancy. Laetsch:Novartis: Consultancy; Loxo Oncology: Consultancy. Bittencourt:Seattle Genetics: Consultancy; Jazz Pharmaceuticals: Consultancy, Other: Educational Grant. Maude:Novartis: Consultancy. Myers:Novartis Pharmaceuticals: Consultancy. Rives:Novartis: Consultancy; Jazz Pharma: Consultancy. Nemecek:Medac, GmbH: Research Funding; Novartis: Consultancy; National Marrow Donor Program: Membership on an entity's Board of Directors or advisory committees. Schlis:Novartis: Honoraria. Martin:Jazz Pharmaceuticals: Other: One time discussion panel; Novartis: Other: Support of clinical trials. Bader:Medac: Consultancy, Research Funding; Riemser: Research Funding; Neovii Biotech: Research Funding; Servier: Consultancy, Honoraria; Novartis: Consultancy, Honoraria. Peters:Novartis: Consultancy; Jazz: Speakers Bureau; Amgen: Consultancy; Pfizer: Consultancy; Medac: Consultancy. Biondi:Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Cellgene: Other: Advisory Board; BMS: Membership on an entity's Board of Directors or advisory committees. Baruchel:Servier: Consultancy; Novartis: Consultancy; Celgene: Consultancy; Jazz: Consultancy; Baxalta: Research Funding. June:University of Pennsylvania: Patents & Royalties; Johnson & Johnson: Research Funding; Celldex: Consultancy, Equity Ownership; Pfizer: Honoraria; Immune Design: Consultancy, Equity Ownership; Novartis: Honoraria, Patents & Royalties: Immunology, Research Funding; Tmunity: Equity Ownership, Other: Founder, stockholder . Sen:Novartis: Employment. Zhang:Novartis: Employment. Thudium:Novartis: Employment. Wood:Novartis Pharmaceuticals: Employment, Other: Stock. Taran:Novartis: Employment. Pulsipher:Chimerix: Consultancy; Jazz Pharmaceutical: Consultancy; Novartis: Consultancy, Other: Study Steering Committee; Medac: Other: Housing support for conference.

T cells bearing a second-generation anti-CD19 chimeric antigen receptor (CAR) induce complete remission in >90% of patients with acute lymphoblastic leukemia (ALL) at our institution. However, disease may recur and we recently identified two molecular mechanisms of relapse (PMID: 26516065). We here present a novel mechanism of antigen-negative relapse in a pediatric ALL patient. A 21 year-old male patient was in third relapse at the time of enrollment onto our CTL019 trial (ClinicalTrials.Gov #NCT01626495). The patient achieved an MRD-negative complete remission 1 month after CTL019 infusion but relapsed nine months later. Quantitative PCR analysis of the transgene and flow cytometry for CAR19 protein analysis showed the expected expansion of the CART cells followed by log-normal decay following disease eradication. At relapse, however, the transgene copy numbers had increased without a concomitant rise in CAR19 protein-expressing T cells. The CAR protein was found to be expressed by the now CD19-negative CD45dimCD10+CD3negCD22+ leukemia. Molecular analysis via next-generation immunoglobulin heavy chain sequencing (NGIS) of the apheresis product, used for CTL019 manufacturing, and relapse marrow at 9 months demonstrated clonal identity of the relapsed clone, which carried two rearranged IgH alleles. Sequencing of the CD19, CD21, CD81, and CD225 loci did not reveal any mutations. The analysis of lentiviral vector integration sites (LVIS) of the infusion product and post-infusion specimens showed the following: a) the infusion product carried over 15,000 unique integration sites; b) only 7 LVIS were shared between this sample and month 9 and 20 relapse specimens, none of which were near proto-oncogenes; c) the relapsed leukemia carried two LVIS, one on chromosome 10, >50 kb distal from neuropilin (NRP1) and the second in an intron of proprionyl coenzyme A carboxylase-A (PCCA). Flow cytometric and qRT-PCR analysis of leukemic cells in the apheresis and relapse showed that NRP1 levels were indistinguishable, suggesting that the lentiviral vector did not act as an enhancer for NRP1. Furthermore, qRT-PCR demonstrated that the lentiviral integration did not affect the gene expression levels of PCCA. Investigation into the origins of the leukemic CAR transduction event showed that the patient did not exhibit replication-competent lentivirus. However, NGIS analysis of infusion product revealed the leukemic clonotypes this sample, indicating that the gene transfer occurred during the manufacturing of the CTL019 cells. A retrospective analysis of 115 aphereses from ALL patients showed that the index patient had an unusually high disease burden in the apheresis product with 63% of all cells expressing CD19; at harvest, however, the CTL019 product consisted of 99.21% T cells, highlighting the purging effect of the CD19-specific T cells during manufacturing. NGIS analysis of infusion products of 17 additional ALL patients also identified the leukemic clonotype(s) in 6 more products. Only one additional patient demonstrated CAR19 protein expression on the leukemic cells, and this clone was not dominant at relapse (0.075% of all leukemic cells expressed the CAR). Our investigation into the biology of CAR19-expressing ALL cells showed the following: 1) the in vitro analysis of BBζ-signaling CAR19 showed no evidence of cytokine secretion; 2) the infusion of the baseline leukemia and CAR19-expressing leukemic cells from the same patient in mice did not demonstrate differential pharmacodynamics, even after restimulation with human CD19-expressing murine B cells in vivo; 3) the CD19 protein was detectable using flow cytometry and confocal microscopy, but only with an antibody recognizing an intracellular epitope; 4) importantly, the relapsed clone was indeed resistant to killing by CART19 cells in a xenograft model yet retained sensitivity to anti-CD22 CAR T cells. In conclusion, our data therefore show that a single leukemic cell accidentally transduced with CAR19 survived the 10-day manufacturing process and, upon reinfusion into the patient, was the sole clone at relapse 9 months later. This leukemic clone evaded CTL019 detection via downregulation of the target antigen in a cell-autonomous fashion. Disclosures Lacey: Novartis: Research Funding. Xu:Novartis: Research Funding. Ruella:novartis: Patents & Royalties: Novartis, Research Funding. Barrett:Novartis: Research Funding. Kulikovskaya:Novartis: Research Funding. Ambrose:Novartis: Research Funding. Patel:Novartis: Research Funding. Reich:Novartis: Research Funding. Scholler:Novartis: Patents & Royalties: Royalties, Research Funding. Nazimuddin:Novartis: Research Funding. Fraietta:Novartis: Patents & Royalties: Novartis, Research Funding. Maude:Novartis: Consultancy. Gill:Novartis: Patents & Royalties, Research Funding. Levine:Novartis: Patents & Royalties, Research Funding; GE Healthcare Bio-Sciences: Consultancy. Orlando:Novartis: Employment. Grupp:Jazz Pharmaceuticals: Consultancy; Pfizer: Consultancy; Novartis: Consultancy, Research Funding. June:Tmunity: Equity Ownership, Other: Founder, stockholder ; Pfizer: Honoraria; Immune Design: Consultancy, Equity Ownership; Celldex: Consultancy, Equity Ownership; University of Pennsylvania: Patents & Royalties; Johnson & Johnson: Research Funding; Novartis: Honoraria, Patents & Royalties: Immunology, Research Funding. Melenhorst:Novartis: Patents & Royalties: Novartis, Research Funding.

Background: Acute lymphoblastic leukemia (ALL) is the most common pediatric malignancy and is most often of B-cell lineage (Roberts, et al. NEJM 2014). One subtype of B-cell ALL, Philadelphia chromosome-like ALL (Ph-like ALL), is BCR-ABL negative with a gene expression signature similar to that of BCR-ABL positive ALL and is prognostic for poor clinical outcomes (Roberts, et al. NEJM 2014). Ph-like ALL is often associated with rearrangements involving the cytokine receptor-like factor 2 (CRLF2) component of the thymic stromal lymphopoietin receptor (TSLPR) leading to its overexpression (Shochat, et al., JEM 2011). TSLPR is a heterodimer of CRLF2 and IL-7Rα that signals to promote the proliferation and differentiation of B-cell progenitors and acts to promote B-cell transformation in the context of Ph-like ALL (Maude, et al. Blood 2012). Glucocorticoid (GC) therapy plays a central role in the treatment of childhood ALL and resistance to GCs confers a poor prognosis (Piovan, et al. Cancer Cell, 2013). This study examined the role of TSLPR signaling in mediating primary GC resistance and the effects of downstream signal transduction inhibitors to confer GC sensitivity. Methods: Viably cryopreserved splenocytes were obtained from 19 patient-derived xenografts of Ph-like ALL banked in the Children's Oncology Group or Children's Hospital of Philadelphia leukemia biorepositories. Assays were also performed using the Mutz 5 Ph-like ALL cell line. Flow cytometry was used to assess the protein expression of TSLPR and GC receptor (GR). Levels of pERK and pAKT were measured by phosphoflow cytometry at baseline and following TSLP stimulation. Cells were cultured in the presence of 1µM dexamethasone (dex), a GC, with or without 1µM trametinib, a MEK1/2 inhibitor, or 1µM MK2206, a pan-AKT inhibitor, in the presence of TSLP and viability was assessed by Hoechst staining and flow cytometry at 48 hours. Results: Of the 19 Ph-like ALL samples in this study, 11 were CRLF2-rearranged (CRLF2R) and 8 were non-rearranged (CRLF2NR). CRLF2 rearrangements involved P2RY8 or IGH and 9 of 11 samples had concomitant activating mutations in JAK1 or JAK2. CRLF2NRsamples expressed a variety of other translocations involving genes such as JAK2, PDGFR, and ABL1. CRLF2R cells were shown to have significantly greater TSLPR protein expression relative to CRLF2NR cells (p = 0.03). In the presence of TSLP, CRLF2 rearrangement status predicted responsiveness to dex, with CRLF2Rsamples demonstrating significant resistance to dex relative to CRLF2NRsamples (p = 0.004). There was no significant reduction in cell viability following dex treatment in CRLF2R samples (p = 0.5), while dex effectively attenuated cell viability in CRLF2NRsamples (p = 0.008). Importantly, there was no difference in GR expression between these two groups (p = 0.6). CRLF2R samples demonstrated hyperresponsiveness to TSLP stimulation, with a significant induction of pERK and pAKT that exceeded the response of CRLF2NRsamples (p = 0.007 and p = 0.0005, respectively) despite no differences in basal phosphoprotein levels between the two sample groups. Inhibition of MAPK signaling with trametinib or of AKT signaling with MK2206 significantly sensitized CRLF2Rcells to dex in the presence of TSLP when used in combination relative to dex alone (p = 0.0003 and p < 0.0001, respectively) and resulted in a significant reduction in cell viability relative to untreated cells (p < 0.0001 and p < 0.0001, respectively). The Mutz 5 cell line, which expresses both a CRLF2 rearrangement and a JAK2 activating mutation, was used to assess the effect of simultaneous pathway inhibition. Mutz 5 cells were treated with dex alone or dex in combination with trametinib and/or MK2206. While dex alone had no significant effect on cell viability, the addition of trametinib or MK2206 resulted in a 43% and 36% reduction in cell viability, respectively. Furthermore, combined treatment with dex, trametinib, and MK2206 resulted in a 72% reduction in cell viability, demonstrating the efficacy of simultaneous MAPK and PI3K pathway inhibition to confer dex sensitivity. Conclusion: MAPK and PI3K pathway signaling play a role in mediating primary GC resistance in CRLF2R Ph-like ALL, making these pathways potential therapeutic targets for enhancing the efficacy of GC therapy in this patient group. Disclosures Maude: Novartis: Consultancy. Teachey:Novartis: Research Funding.

Chimeric antigen receptor (CAR)-modified T cells with CD19 specificity (CTL019) are a highly effective novel immune therapy for relapsed/refractory ALL. Cytokine release syndrome (CRS) is the most significant and in some cases a life-threatening toxicity. These patients are often neutropenic and immunosuppressed and at high risk for sepsis. In addition, there have been cases where concurrent infectious complications potentially fueled underlying CRS leading to hypotension and hypoxia refractory to anti-cytokine directed therapies (Frey et al. abstract 2296, ASH 2014). Discriminating between sepsis and CRS can be a significant clinical challenge in the critical time-window required to initiate effective therapy, especially given that the treatments for CRS, including anti-cytokine therapies and corticosteroids, may worsen severe infections. We recently published an extensive study of 43 cytokines and soluble cytokine receptors, and clinical biomarkers in a cohort of 63 CTL019-treated ALL patients. Peak levels of 24 cytokines in the first month after infusion were highly associated with severe CRS, and CRS predictive models were described (Teachey et al. Cancer Discovery, June 1, 2016 6; 664). The object of these current studies was to compare biomarker profiles in CRS and sepsis, and attempt to identify a profile that would discriminate between the two clinical syndromes, particularly at the time of ICU admission. We evaluated 50 cytokines, soluble receptors, and other serum biomarkers in 66 adult and pediatric patients treated with CTL019 and who developed CRS (ALL-CRS cohort), 15 patients not treated with CTL019 but who developed sepsis leading to ICU admission (sepsis cohort), and 10 normal healthy children (control cohort). Of the 66 patients treated with CTL019 and who developed CRS, 30 (45%) required ICU admission. The biomarkers tested included the ones described in our published work plus a panel of seven additional biomarkers (Angiopoietin 2, [ANG2] sCD163, Pentraxin 3 [PTX3], sCD14, PAI-1, P-selectin, ICAM-1) that have previously been reported in the literature to be associated with sepsis. After adjusting for multiple comparisons, the following biomarkers were significantly elevated in sepsis compared to normal subjects: ANG2, GCSF, IFNα, IL1RA, IL4, IL6, MIG, MIP1α, PTX3, TNFα, sCD163, sCD30, sIL-1RI, sIL-1RII, sIL-2Rα, sIL-4R, sRAGE, sTNFRI, sTNFRII, sVEGFR1, sVEGFR2, sVEGFR3, and VEGF, whereas IL13 and RANTES were significantly lower in sepsis. In subjects with ALL and CRS, within 72 hours of ICU admission following CTL019 therapy (N=29), 23 biomarkers were significantly different compared to sepsis after adjusting for multiple comparisons; 16 were elevated in CRS: GM-CSF, HGF, IFN-γ, IFN-α, IL-10, IL-15, IL-5, IL-6, IL-8, IP-10, MCP1, MIG, MIP-1β, sIL-2Rα, sTNFRI, and sTNFRII; whereas 7 were elevated in sepsis subjects: CD163, IL-1β, sCD30, sIL-4R, sRAGE, sVEGFR-1, and sVEGFR-2. Figure 1 shows representative box-plots for sCD163 (elevated in sepsis) and IP-10 (elevated in CRS). Detailed biomarker profiling and an algorithm for discriminating between sepsis and CRS in patients treated with CTL019 will be presented. These comprehensive profiling data provide novel insights into CRS biology and importantly, will help us discriminate between CRS and sepsis in patients who become critically ill after receiving CAR T cell therapy. These data have direct translational therapeutic relevance. Disclosures Lacey: Novartis: Research Funding. Shaw:Novartis: Research Funding; Vitality Institute: Research Funding. Teachey:Novartis: Research Funding. Weiss:NIGMS K23GM110496: Research Funding; ThermoFisher Scientific: Honoraria; Up-To-Date: Patents & Royalties: Up-To-Date. Chen:Novartis: Research Funding. Frey:Novartis: Research Funding; Amgen: Consultancy. Porter:Genentech: Employment; Novartis: Patents & Royalties, Research Funding. Maude:Novartis: Consultancy. Grupp:Novartis: Consultancy, Research Funding; Pfizer: Consultancy. Pequignot:Novartis: Research Funding. June:Novartis: Honoraria, Patents & Royalties: Immunology, Research Funding; Johnson & Johnson: Research Funding; Celldex: Consultancy, Equity Ownership; Pfizer: Honoraria; Immune Design: Consultancy, Equity Ownership; Tmunity: Equity Ownership, Other: Founder, stockholder ; University of Pennsylvania: Patents & Royalties. Melenhorst:Novartis: Research Funding.

Introduction CTL019 is a novel, investigational, chimeric antigen receptor (CAR) immunotherapy whereby autologous T cells are genetically modified with a chimeric antigen receptor to target CD19 on the surface of malignant as well as healthy B cells. The cellular kinetics of CTL019 have been evaluated in several trials for patients with relapsed/refractory CD19+ leukemias, including pediatric acute lymphoblastic leukemia (pALL), adult ALL (aALL), and chronic lymphocytic leukemia (CLL) (Maude 2014, Porter 2015). Methods The cellular kinetic profile of CTL019 was determined in peripheral blood (PB) and bone marrow (BM) through serial measurements using flow cytometry and quantitative real-time polymerase-chain-reaction (qPCR) assay in 3 studies comprised of (i) 55 pALL patients (NCT01626495), (ii) 28 adult CLL patients from a dose selection study (NCT01747486), and (iii) 14 CLL and 6 adult ALL patients (NCT01029366). The flow cytometry assay used a CAR19-specific anti-idiotype antibody to enumerate CTL019 T cells as a % of CD3+ T cell (Porter 2015). Cellular kinetic parameters included: maximal extent of expansion as measured by peak copies of CTL019 DNA and peak % by flow cytometry (Cmax), area under the curve at day 28 (AUC0-28d) describing expansion and persistence in the first month, and time to reach Cmax (Tmax). Parameters were derived by non-compartmental methods. Where estimable, persistence was described by the half-life (T1/2) based on the slope of the terminal phase. Results Following infusion, CTL019, expansion and persistence was evident in the patients who responded to CTL019 as measured by both PK assays across all 3 studies. Table 1 summarizes (arithmetic mean (SD)) the CTL019 kinetic parameters. With complete remission (CR/CRi), CTL019 cells undergo rapid in vivo expansion beyond the original CTL019 dose with maximal expansion at a mean of 11 days in pALL and aALL and approximately 14-18 days in adult CLL as determined by qPCR and flow cytometry (Table 1). In CR/CRi patients the transgene level-profiles in PB reveal a kinetic profile with an initial rapid expansion followed by a slower decay function with some fluctuations of transgene over time resulting in higher AUC0-28d and Cmax, while non-responder (NR) patients tend to have a lower expansion and faster decay (shorter T1/2)of CAR positive T-cells resulting in lower AUC0-28d and Cmax by, leaving the mechanism to be further explored. In pALL, significantly higher AUC0-28d and Cmax were observed in CR/CRi patients compared to NR patients by flow cytometry; however, a wide range of mean AUC0-28d and Cmax was observed in NR patients (n=3) resulting from significant expansion in one NR patient as determined by qPCR. In CLL, the exposure metrics AUC0-28d and Cmax were approximately 12 times higher in CR/CRi patients compared with PRi/NR/PD in NCT01747486; a similar trend was observed in NCT01029366. Similar findings were captured by the flow cytometry based measurements as summarized in Table 1. In pALL and CLL, CR/CRi patients tend to maintain higher levels of CTL019 transgene over longer periods of time (>6 months) compared to NR patients as demonstrated by the longer T1/2 value. Cellular kinetic parameters were not summarized by response category for aALL due to the small sample size (n=5 CR/CRi; n=1 NR). CTL019 transgene levels ranged from below the limit of quantification (BLQ) to 178,000 copies/ug in aALL patients with CR/CRi and BLQ to 21,900 copies/ug in the NR. CTL019 positive cells were also shown to traffic to BM at 1 month in responders (CR/CRi), irrespective of the disease. Conclusions Overall, significantly higher levels of in vivo proliferation and persistence were observed in patients who successfully responded to CTL019 (i.e. CR/CRi/PR) compared to NRs in both CLL and (adult and pediatric) ALL patients, as captured by both analytical measures, indicating that the kinetics of CTL019 T cells and that proliferation and persistence of CTL019 reasonably predicts response to therapy. These are the first three studies to demonstrate that cellular kinetics may predict responses to CAR based cellular therapy. These results imply that measures to increase proliferation and persistence of CAR T cells may enhance responses in resistant patients. Figure. CTL019 concentration-time profiles for %CD3+/CTL019+ measured by flow cytometry and cellular kinetic parameters for qPCR and flow cytometry for p-ALL and adult CLL Figure. CTL019 concentration-time profiles for %CD3+/CTL019+ measured by flow cytometry and cellular kinetic parameters for qPCR and flow cytometry for p-ALL and adult CLL Disclosures Mueller: Novartis Pharmaceuticals: Employment. Chakraborty:Novartis Pharmaceuticals: Employment, Equity Ownership. Wood:Novartis Pharmaceuticals: Employment, Other: Stock. Awasthi:Novartis Pharmaceuticals: Employment. Quintas-Cardama:Novartis Pharmaceuticals: Employment, Equity Ownership. Han:Novartis Pharmaceuticals: Employment, Equity Ownership. Maude:Novartis: Consultancy. Grupp:Jazz Pharmaceuticals: Consultancy; Pfizer: Consultancy; Novartis: Consultancy, Research Funding. Porter:Novartis: Patents & Royalties, Research Funding; Genentech: Employment. Frey:Novartis: Research Funding; Amgen: Consultancy. Marcucci:Novartis: Research Funding. Levine:GE Healthcare Bio-Sciences: Consultancy; Novartis: Patents & Royalties, Research Funding. Melenhorst:Novartis: Research Funding. June:Celldex: Consultancy, Equity Ownership; Immune Design: Consultancy, Equity Ownership; Pfizer: Honoraria; Novartis: Honoraria, Patents & Royalties: Immunology, Research Funding; University of Pennsylvania: Patents & Royalties; Tmunity: Equity Ownership, Other: Founder, stockholder ; Johnson & Johnson: Research Funding. Lacey:Novartis: Research Funding.

Background: CTL019 is an investigational therapy derived from autologous T-cells expressing a CD19-specific chimeric antigen receptor (CAR). A single center, phase I/IIa trial of CTL019 showed complete and durable remissions in pediatric/young adult patients (pts) with relapsed/refractory (R/R) B-cell acute lymphoblastic leukemia (B-ALL) (Maude et al NEJM 2014); these results have yet to be reproduced in a multicenter setting. Here, we report results from a 6-month interim analysis of the first multicenter phase II trial of an engineered cell therapy in leukemia. Methods: 9 US sites participated in this single-arm phase II study in pediatric/young adult pts with R/R B-ALL. Leukapheresis products were shipped for centralized manufacturing according to the University of Pennsylvania (Penn) process in an academic-industry collaboration. T cells were transduced with a lentiviral vector encoding a CAR composed of anti-CD19 scFv, CD3ζ and 4-1BB domains. Following lymphodepletion with fludarabine and cyclophosphamide, a single dose of CTL019 cells was administered (target dose 2.0-5.0×106 cells/kg for ≤50 kg and 1.0-2.5×108 cells for >50 kg). The primary endpoint was overall remission rate (ORR = CR + CRi [CRi, complete remission with incomplete blood count recovery] maintained at 2 evaluations ≥28 days apart) as determined by an Independent Review Committee. Secondary objectives included minimal residual disease (MRD), relapse-free survival (RFS), overall survival (OS) and safety. All analyses were performed on infused patient set. Results: 29/35 pts enrolled (82.9%) were infused with CTL019; 6 withdrew prior to infusion (2 manufacturing failures [1 lack of growth, 1 contamination]; 4 deaths [median, 48 days from enrollment; 2 progressive disease, 1 multi-organ failure, 1 pneumonia]). Mean bone marrow involvement at enrollment was 68.2% (SD, 27.3%; Table 1). 2 pts did not receive lymphodepleting chemotherapy due to leukopenia. Collection, manufacturing and infusion were feasible in a multicenter setting with a median time from enrollment to infusion of 37 days. Target cell dose was met in 24/33 (72.7%) manufactured products. ORR in all infused pts was 69.0% (20/29 pts; 98.95% CI 43.6, 88.1). Of the 5 pts who received CTL019 below the target dose, 2 achieved CR/CRi. Of note, deep remission with no evidence of MRD ( Conclusions: In this first multicenter trial of CAR-modified T cell therapy, CTL019 therapy was feasible and efficacious, showing a high ORR with durable remissions in pediatric/young adult pts with R/R B-ALL. Despite the high rate of toxicity with CTL019 in the R/R setting, the rate of grade 3 or 4 CRS was comparable to the single center study, and standardized management of CRS was successful in a multicenter trial with no deaths attributable to CRS. In this highly refractory population, a vast majority of eligible pts can be successfully infused in a timely fashion and outcomes appear reproducible in a multicenter setting despite a more heterogeneous population than the single center study. The trial is continuing under Novartis manufacturing. Disclosures Maude: Novartis: Consultancy. Pulsipher:Medac: Other: Travel support for a study group; Chimerix: Consultancy, Other: Advisory Board ; Jazz Pharmaceutical: Consultancy, Other: Advisory Board; Novartis: Consultancy, Other: Advisory Board, Steering Committee for Phase II Study. Grupp:Pfizer: Consultancy; Novartis: Consultancy, Research Funding. Davies:Novartis: Honoraria. Verneris:Bimogen: Other: Advisory Board. Schlis:Novartis: Honoraria. Driscoll:Novartis: Consultancy. June:Immune Design: Consultancy, Equity Ownership; Pfizer: Honoraria; Celldex: Consultancy, Equity Ownership; Novartis: Honoraria, Patents & Royalties, Research Funding; Johnson & Johnson: Honoraria; Novartis: Honoraria, Patents & Royalties, Research Funding; Tmunity Therapeutics: Equity Ownership. Levine:GE Healthcare Bio-Sciences: Consultancy; Novartis: Patents & Royalties, Research Funding. Wood:Novartis Pharmaceuticals: Employment, Other: Stock. Yi:Novartis: Employment.

Background: Early T-cell precursor acute lymphoblastic leukemia (ETP-ALL) is an uncommon childhood leukemia that has been associated with very poor clinical outcomes in some studies. ETP-ALL cells arrest at a more immature differentiation stage than other T-lymphoblasts, and are hypothesized to retain multi-lineage differentiation potential, which may contribute to chemoresistance with standard lymphoid-directed therapy. Based on the recent clinical success of chimeric antigen receptor (CAR)-modified T-cells in children with B-ALL, we sought to identify potential surface protein targets on ETP lymphoblasts using differential gene expression analysis combined with a bioinformatic algorithm to predict surface expression. Methods: Cell-surface targets on ETP-ALL were predicted by identifying overexpressed transcripts based on gene expression and a bioinformatic algorithm to predict surface expression. Using several gene expression platforms and reference databases, (Oncogenomics website-Pediatric Oncology Branch, NCI, Gene Expression Omnibus, Gene Ontology, Human Protein References Database) ETP-ALL samples were compared to peripheral blood mononuclear cell (PBMC) controls on an individual transcript basis. A list of the top 25 transcripts was generated based on cell surface proteins, and the resultant list ordered by the degree of difference from PBMC controls. We next used human leukemia cells from six established ETP-ALL patient-derived xenograft (PDX) models using flow cytometry to evaluate for cell surface expression of proteins encoded by the overexpressed transcripts. Additionally, since CD7 and CD33 expression on ETP-ALL patient samples is universal with minimal normal tissue distribution, we developed two new second-generation anti-CD7 or anti-CD33 CAR constructs using a 41-BB/CD3ζ backbone. Results: Multiple gene transcripts encoding cell surface proteins potentially amenable to CAR T-cell targeting were overexpressed in ETP-ALL cells in comparison to PBMC controls. Many of these proteins are involved in cell signaling, cell adhesion, and metastasis, and thus potentially important for leukemic cell survival. TSPAN7 (also known as TALLA-1) was the strongest differentially expressed transcript. Despite identification of several transcripts, we did not detect increased surface expression of multiple antigens that were identified as top 25 transcripts, including TALLA-1, MCAM, EPHB6, or TSLPR. Interestingly, TALLA-1 was expressed on the more mature T-cell ALL lines, JURKAT and HPB-AU, suggesting that the surface expression of TALLA protein may be developmentally regulated. Although a new target could not be identified, given the universal expression of CD7 and CD33 on ETP-ALL, we proceeded with development of CARs targeting these antigens. CD33 CAR T-cells had excellent in vitro activity in human AML cell line MOLM-14 with minimal anti-leukemia activity in six tested ETP-ALL PDX models, perhaps due to their lower CD33 expression. We next tested T-cells transduced with a bicistronic CD7-redirected CAR with a truncated EGFR (EGFRt) to facilitate measurement of transduction efficiency and to provide a CAR deletion method. Despite high EGFRt surface expression in transduced T-cells, these CD7 CAR T-cells did not demonstrate in vitro activity against ETP-ALL or mature T-ALL samples despite high CD7 surface expression on all leukemia cell lines. We postulated that abnormal CAR distribution within the T-cell itself could be a potential factor in the observed lack of CD7 CAR T-cell activity. Using fluorescent-labeling to assess CAR surface membrane distribution, we detected high intracellular expression of the CD7 CAR, and noted that it did not traffic to the cell surface. Conclusions: We applied multimodal techniques to evaluate for cell surface expression on ETP-ALL that could serve as a target for immunotherapy. Although novel targets could not be identified, we were able to design an active anti-CD33 CAR. Further studies are in progress to evaluate what degree of antigen expression is needed to be amenable to targeted therapy. Additionally, ongoing studies are assessing whether optimization of CAR design can enhance cell surface trafficking and thereby potentially improve the anti-leukemia efficacy of CD7 CAR T-cells. Disclosures Orentas: Lentigen Technology, Inc.: Employment. Maude:Novartis: Consultancy. Teachey:Novartis: Research Funding.

Background Targeted immunotherapy with CTL019, CD19-specific chimeric antigen receptor (CAR)-modified T cells, can produce potent and sustained responses in children with relapsed/refractory acute lymphoblastic leukemia (ALL). However, a subset of patients has limited persistence, which can increase the risk of relapse. Most CAR single chain variable fragment (scFv) domains, including that of CTL019, are of murine origin; therefore, anti-mouse reactivity is one potential cause of immune-mediated rejection that may be overcome by fully human or humanized CAR designs. We developed a humanized anti-CD19 scFv domain and now report on treatment with humanized CD19-directed CAR T cells (CTL119). Design A pilot/phase 1 study of CAR-modified T cells containing a humanized anti-CD19 scFv domain (CTL119) enrolled children and young adults with relapsed/refractory B-ALL with or without prior exposure to a CAR T cell product. Patients previously treated with CD19-specific CAR-modified T cells were eligible if they met 1 of 3 criteria: 1) CD19+ relapse 2) no response to prior CAR T cell therapy or 3) early B cell recovery indicating poor persistence of CAR T cells. Patient-derived T cells were transduced ex vivo with a lentiviral vector encoding a CAR composed of CD3z, 4-1BB, and humanized anti-CD19 scFv domains and activated/expanded with anti-CD3/CD28 beads. The humanized scFv domain was developed by grafting the complementary determining regions of both the heavy and light chains onto human germline acceptor frameworks. Patients received lymphodepletion with cyclophosphamide and fludarabine 1 week prior to infusion with CTL119. Results Thirty children and young adults aged 29 mo-24 yr were infused with CTL119. Eighteen patients had received prior allogeneic stem cell transplant (SCT). Eleven patients who previously received murine-derived CD19-specific CAR-modified T cells (CTL019, n=7; other, n=4) were retreated for B cell recovery (n=5), CD19+ relapse (n=5), or no response to prior CAR T cells (n=1). CNS disease or other extramedullary disease was the indication for enrollment in 6 and 3 patients, respectively. At assessment 1 month after infusion, 26/30 patients (87%) achieved a complete response (CR), defined as morphologic remission with B cell aplasia. Of 11 patients previously treated with murine CD19-specific CAR-modified T cells, 7 (64%) achieved a CR at 1 month, 4 demonstrated no response. Multiparameter flow cytometry for minimal residual disease (MRD) was negative at a detection level of 0.01% in 5/7 responding patients. Two responding patients with positive MRD progressed to CD19+ relapse at 1.6 and 3 mo. In patients with no prior exposure to a CD19 CAR T cell product, MRD-negative CR was achieved in 19/19 patients (100%). One patient relapsed with CD19+ extramedullary disease at 2.8 mo. With a median follow-up of 4.2 mo (range, 1.0-14.1 mo) for all responding patients in both cohorts, 23/26 remain in remission with 1 proceeding to SCT in remission. B cell aplasia, a functional marker of CD19-targeted CAR T cell persistence, continued for 3 months or more in 11/18 patients with adequate follow-up: 1/6 retreatment, 10/12 CAR-naïve. Cytokine release syndrome (CRS) was observed in 28/30 patients and mild in most patients (grade 1, n=6; grade 2, n=18). Three patients experienced grade 3 CRS requiring supplemental oxygen or low-dose vasopressor support and 1 experienced grade 4 CRS requiring high-dose vasopressor and ventilatory support. Severe CRS was successfully managed with the IL6R antagonist tocilizumab in 3 patients. Neurologic toxicity included encephalopathy (n=5) and seizure (n=4) and was fully reversible. Conclusion In the first study of humanized anti-CD19 CAR T cells, CTL119 induced remissions in children and young adults with relapsed/refractory B-ALL, including 64% of patients previously treated with murine CD19-directed CAR T cells and 100% of CAR-naïve patients. Further investigation into CAR T cell persistence and anti-CAR responses will be vital to improve durable remission rates in this highly refractory population. Disclosures Maude: Novartis: Consultancy. Barrett:Novartis: Research Funding. Teachey:Novartis: Research Funding. Shaw:Novartis: Research Funding; Vitality Institute: Research Funding. Brogdon:Novartis: Employment. Scholler:Novartis: Patents & Royalties: Royalties, Research Funding. Marcucci:Novartis: Research Funding. Levine:GE Healthcare Bio-Sciences: Consultancy; Novartis: Patents & Royalties, Research Funding. Frey:Amgen: Consultancy; Novartis: Research Funding. Porter:Novartis: Patents & Royalties, Research Funding; Genentech: Employment. Lacey:Novartis: Research Funding. Melenhorst:Novartis: Research Funding. June:Novartis: Honoraria, Patents & Royalties, Research Funding; Celldex: Consultancy, Equity Ownership; Pfizer: Honoraria; Immune Design: Consultancy, Equity Ownership; Johnson & Johnson: Honoraria; Novartis: Honoraria, Patents & Royalties, Research Funding; Tmunity Therapeutics: Equity Ownership. Grupp:Pfizer: Consultancy; Jazz Pharmaceuticals: Consultancy; Novartis: Consultancy, Research Funding.

Blinatumomab is a CD19/CD3-bispecific T-cell receptor-engaging (BiTE) antibody with efficacy in refractory B-precursor acute lymphoblastic leukemia. Some patients treated with blinatumomab and other T cell-activating therapies develop cytokine release syndrome (CRS). We hypothesized that patients with more severe toxicity may experience abnormal macrophage activation triggered by the release of cytokines by T-cell receptor–activated cytotoxic T cells engaged by BiTE antibodies and leading to hemophagocytic lymphohistiocytosis (HLH). We prospectively monitored a patient during blinatumomab treatment and observed that he developed HLH. He became ill 36 hours into the infusion with fever, respiratory failure, and circulatory collapse. He developed hyperferritinemia, cytopenias, hypofibrinogenemia, and a cytokine profile diagnostic for HLH. The HLH continued to progress after discontinuation of blinatumomab; however, he had rapid improvement after IL-6 receptor-directed therapy with tocilizumab. Patients treated with T cell-activating therapies, including blinatumomab, should be monitored for HLH, and cytokine-directed therapy may be considered in cases of life-threatening CRS. This trial was registered at www.clinicaltrials.gov as #NCT00103285.

CRLF2 rearrangements, JAK1/2 point mutations, and JAK2 fusion genes have been identified in Philadelphia chromosome (Ph)–like acute lymphoblastic leukemia (ALL), a recently described subtype of pediatric high-risk B-precursor ALL (B-ALL) which exhibits a gene expression profile similar to Ph-positive ALL and has a poor prognosis. Hyperactive JAK/STAT and PI3K/mammalian target of rapamycin (mTOR) signaling is common in this high-risk subset. We, therefore, investigated the efficacy of the JAK inhibitor ruxolitinib and the mTOR inhibitor rapamycin in xenograft models of 8 pediatric B-ALL cases with and without CRLF2 and JAK genomic lesions. Ruxolitinib treatment yielded significantly lower peripheral blast counts compared with vehicle (P < .05) in 6 of 8 human leukemia xenografts and lower splenic blast counts (P < .05) in 8 of 8 samples. Enhanced responses to ruxolitinib were observed in samples harboring JAK-activating lesions and higher levels of STAT5 phosphorylation. Rapamycin controlled leukemia burden in all 8 B-ALL samples. Survival analysis of 2 representative B-ALL xenografts demonstrated prolonged survival with rapamycin treatment compared with vehicle (P < .01). These data demonstrate preclinical in vivo efficacy of ruxolitinib and rapamycin in this high-risk B-ALL subtype, for which novel treatments are urgently needed, and highlight the therapeutic potential of targeted kinase inhibition in Ph-like ALL.

Background Targeted immunotherapy with T cells expressing a chimeric antigen receptor (CAR) can produce dramatic anti-tumor responses. We previously demonstrated complete remissions (CRs), prolonged persistence, and sustained responses in children and adults with relapsed/refractory (r/r) acute lymphoblastic leukemia (ALL) treated with CD19-specific CAR-modified T cells (CTL019). However, a subset (~25%) of patients has limited persistence of CTL019, which can increase the risk of relapse. We hypothesized that repeat infusion may prolong persistence in some patients but would be ineffective in patients with immune-mediated rejection. As most CAR single chain variable fragment (scFv) domains, including that of CTL019, are of murine origin, anti-mouse reactivity is one potential cause of immunogenicity that may be overcome by fully human or humanized CAR design. We now report on retreatment with murine or humanized CD19-directed CAR T cells. Aims We sought to 1) prolong persistence by reinfusion of murine CTL019 in children with r/r CD19+ ALL and evidence of poor persistence and 2) determine the safety and efficacy of CD19-directed CAR T cells with a humanized scFv domain in children with B cell recovery or CD19+ relapse after prior CAR T cell therapy. Method T cells collected from patients were transduced with a lentiviral vector encoding a CAR composed of murine or humanized anti-CD19 scFv, CD3z, and 4-1BB domains, activated/expanded ex vivo with anti-CD3/anti-CD28 beads, cryopreserved, and then infused. The humanized scFv was developed by grafting the complementary determining regions of both the heavy and light chains onto human germline acceptor frameworks. Results Of 50 patients in CR at 1 month after CTL019 infusion (50/53 CR), 14 patients received a repeat infusion of murine CTL019 at 3 and/or 6 months after initial infusion and 11 are evaluable for response. Indications were B cell recovery (n=4), CD19+ minimal residual disease (MRD, n=2), or undetectable CTL019 in peripheral blood by flow cytometry (≤0.1% CTL019+ of CD3+, n=5). Minimal toxicities were observed and included fever and fatigue. CTL019 reinfusion induced B cell aplasia for a second time in 1 of 4 children treated for B cell recovery. Two of these patients later relapsed, 1 with CD19+ and 1 with CD19- disease. Of 2 patients with CD19+ MRD, 1 had no response and subsequently experienced a CD19+ relapse and the second became MRD-negative but had B cell recovery. All 5 children reinfused for poor CTL019 persistence demonstrated continued B cell aplasia 3-15 months after repeat infusion with detectable CTL019 in peripheral blood by flow cytometry (0.2-2.8% CTL019+ of CD3+) in 4 patients. Of this group, 4 patients remain in remission 12-21 months after initial infusion, and 1 experienced a CD19- relapse. To overcome the potential for anti-murine immune-mediated rejection, patients previously treated with CAR-modified T cells were eligible for a phase 1 study of humanized CD19-directed CAR T cells (CTL119). Five children were infused for B cell recovery (n=3) or CD19+ relapse (n=2). Cytokine release syndrome (CRS), seen in 2 patients, was limited to fever, headache, and nausea and did not require vasopressor or respiratory support. Three patients showed no response and progressed (n=1) or relapsed with CD19+ (n=1) or CD19- (n=1) ALL. Responses were demonstrated in 2 patients: 1) MRD-negative CR in a patient treated for CD19+ relapse and 2) reduction in MRD and return of B cell aplasia in a patient treated for CD19+ MRD and B cell recovery, with subsequent progression to CD19+ relapse. Both responding patients were previously resistant to murine CTL019 reinfusion, suggesting a possible immune-mediated rejection mechanism. Ongoing studies are investigating anti-CAR responses. Conclusion Repeat infusion of murine CTL019 may prolong B cell aplasia in patients with early evidence of poor persistence and in a fraction of patients with B cell recovery. In the first demonstration of humanized anti-CD19 CAR efficacy, retreatment with CTL119 expressing a humanized scFv induced remission of ALL refractory to prior CD19-directed murine CAR T cell therapy, suggesting that immune-mediated rejection may be an important mechanism of resistance in the subset of patients with rapid CAR cell loss and loss of B cell aplasia. Further investigation into anti-CAR responses will be vital to improve durable remission rates in this highly refractory population. Disclosures Maude: Novartis: Consultancy, Research Funding. Off Label Use: CTL019 and CTL119 for relapsed/refractory ALL. Rheingold:Endo: Other: Husband's employer, has equity interest; Novartis: Consultancy. Aplenc:Sigma Tau: Consultancy. Teachey:Novartis: Research Funding. Shaw:Novartis: Research Funding. Brogdon:Novartis: Employment. Loew:Novartis: Employment. Zheng:Novartis: Patents & Royalties. Levine:Novartis: Patents & Royalties, Research Funding. Porter:Novartis: Patents & Royalties, Research Funding. Lacey:Novartis: Research Funding. Melenhorst:Novartis: Research Funding. June:Novartis: Research Funding; University of Pennsylvania: Patents & Royalties: financial interests due to intellectual property and patents in the field of cell and gene therapy. Conflicts of interest are managed in accordance with University of Pennsylvania policy and oversight. Grupp:Novartis: Consultancy, Research Funding.

Background. Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is associated with genomic alterations that activate JAK/STAT and PI3K/Akt/mTOR signal transduction and with poor clinical outcomes. Therapeutic disruption of PI3K pathway signaling in Ph-like ALL has been minimally investigated to date, however. We hypothesized that PI3K isoform-selective or dual PI3K pathway protein inhibition would robustly inhibit Ph-like ALL proliferation in vivoand abrogate aberrant signaling. Methods. NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice were engrafted with primary CRLF2/JAK-mutant or ABL/PDGFR-mutant Ph-like ALL specimens (Table 1) and treated with inhibitors of PI3K? (BYL719), PI3K? (idelalisib), PI3K/mTOR (gedatolisib), TORC1/TORC2 (AZD2014) or with vehicle. Treated patient-derived xenograft (PDX) models were assessed for pharmacodynamic inhibition of signal transduction phosphoproteins at 72 hours by phosphoflow cytometry and for residual ALL in murine spleens after 3-4 weeks of inhibitor or vehicle treatment by quantitative flow cytometry. Subsequent studies tested the efficacy of gedatolisib with the JAK1/2 inhibitor ruxolitinib (CRLF2/JAK-mutant models) or gedatolisib with the SRC/ABL inhibitor dasatinib (ABL/PDGFR-mutant models). Table 1. Genomic characteristics of Ph-like ALL specimens utilized for PDX studies. USI Disease status CRLF2/JAK alterations ABL/PDGFR alterations PALTWS D IGH@-CRLF2* PAMDKS D IGH@-CRLF2, JAK2R683G PAMDRM D IGH@-CRLF2,JAK2GPinsR683 ALL121 R IGH@-CRLF2, JAK2R683G ALL4364 R P2RY8-CRLF2, JAK2R683G PAKMVD D JAK1 S646F PAKYEP D BCR-JAK2 PAKKCA D EBF1-PDGFRB PAKVKK D NUP214-ABL1 PANSFD D ETV6-ABL1 USI = unique specimen identifier. D = de novo, R = relapse. * non-Ph-like by prediction analysis of microarrays. Results. All tested PDX models demonstrated inhibition of leukemia proliferation and abrogation of activated signaling with PI3K pathway inhibition. Gedatolisib treatment resulted in near-eradication of leukemia in CRLF2/JAK-mutant models (n=7) with mean 92.2% (range 86.0-99.4%) leukemia reduction vs vehicle treatment (p Conclusions. PI3K pathway inhibition is a biochemically relevant therapeutic approach for Ph-like ALL. Dual PI3K/mTOR inhibition with gedatolisib monotherapy potently inhibited leukemia proliferation and demonstrated additive or synergistic activity in combination with JAK or SRC/ABL inhibition in JAK-mutant or ABL/PDGFR-mutant Ph-like ALL, respectively. These data provide compelling rationale for testing combinations of signal transduction inhibitors without or with cytotoxic chemotherapy in children and adults with Ph-like ALL. Disclosures Off Label Use:preclinical testing of signal transaction inhibitors in Ph-like ALL models. Teachey:Novartis:Research Funding. Maude:Novartis:Consultancy, Research Funding. Perl:Actinium Pharmaceuticals:Consultancy; Asana Biosciences:Consultancy; Arog Pharmaceuticals:Consultancy; Ambit/Daichi Sankyo:Consultancy; Astellas US Pharma Inc.:Consultancy. Hunger:Sigma Tau:Consultancy; Jazz Pharmaceuticals:Consultancy; Spectrum Pharmaceuticals:Consultancy; Merck:Equity Ownership. Grupp:Novartis:Consultancy, Research Funding.

[Graphic][1] CAR T cells with anti-CD19 specificity have demonstrated considerable promise against highly refractory hematologic malignancies. Dramatic responses with complete remission rates as high as 90% have been reported in patients (pts) with relapsed/refractory ALL treated with CTL019 (Maude et al., NEJM 2014). Marked in vivo CAR T cell proliferation (100 to 100,000x) leads to improved efficacy but can be associated with adverse events, including cytokine release syndrome (CRS). To better understand manifestations of CRS, we studied clinical, laboratory, and biomarker data of 39 children and 12 adults with relapsed/refractory ALL treated with anti-CD19 CAR T cells. T cells were lentivirally transduced with a CAR composed of anti-CD19 single chain variable fragment/4-1BB/CD3 (Porter, NEJM 2011). 43 cytokines, chemokines, and soluble receptors (collectively termed cytokines hereafter) were serially measured, using Luminex bead array. Other biomarkers were tested in a CLIA/CAP certified lab. 48 of 51 pts developed grade 1-5 CRS (CRS1-5) (see Table). Most pts developed mild (grade 1-2) to moderate (grade 3) CRS (34/51). 14 pts developed severe (grade 4-5) CRS (12 grade 4, 2 adults with grade 5). 21 pts were treated with the IL-6 inhibitor tocilizumab, and most had rapid marked clinical improvement in CRS evidenced by quick resolution of fever and weaning of vasoactive medications. We found peak levels of 24 cytokines, including IFNg, IL6, IL8, sIL2Ra, sgp130, sIL6R, MCP1, MIP1a, and GM-CSF during the first month after CTL019 infusion were highly associated with CRS4-5 compared to CRS0-3, significant by the Holm-Bonferroni adjusted p-value. Analyzing cytokines from the first 3 days after infusion, sent before patients developed severe CRS, only 2 cytokines, sgp130 and IFNg, were strongly associated with later development of severe CRS (p10,000ng/ml), splenomegaly, and hypofibrinogenemia. Of the tested cytokines, 18 have been previously studied in children with HLH. We found a near identical pattern of cytokines differentially elevated in HLH also elevated in pts with CRS4-5 compared with CRS0-3. IL6, sIL6R, and sgp130 were markedly elevated in pts with CRS4-5; this IL6 cytokine pattern, along with the pronounced response to tocilizumab, establishes that IL6 trans-signaling is clinically relevant. These data represent the largest and most comprehensive profiling of the clinical and laboratory manifestations of CAR T cell related CRS and provide novel insights into CRS biology. They represent the first data that can accurately predict which pts treated with CAR T cells have a high probability of becoming critically ill. These data have direct therapeutic relevance and may guide future cytokine directed therapy. The first 4 authors contributed equally. | Gr1 | Supportive care only | | ---- | ------------------------------------------------------------------------------------------------------ | | Gr2 | IV therapies +/- hospitalization. | | Gr3 | Hypotension requiring IV fluids or low-dose vasoactives or hypoxemia requiring oxygen, CPAP, or BIPAP. | | Gr4 | Hypotension requiring high-dose vasoactives or hypoxemia requiring mechanical ventilation. | | Gr 5 | Death | Table 1. CRS grading Disclosures Teachey: Novartis: Research Funding. Off Label Use: tocilizumab. Lacey: Novartis: Research Funding. Shaw: Novartis: Research Funding. Melenhorst: Novartis: Research Funding. Frey: Novartis: Research Funding. Maude: Novartis: Consultancy, Research Funding. Aplenc: Sigma Tau: Consultancy. Chen: Novartis: Research Funding. Gonzalez: Novartis: Research Funding. Pequignot: Novartis: Research Funding. Rheingold: Endo: Other: Husband's employer, has equity interest; Novartis: Consultancy. June: Novartis: Research Funding; University of Pennsylvania: Patents & Royalties: financial interests due to intellectual property and patents in the field of cell and gene therapy. Conflicts of interest are managed in accordance with University of Pennsylvania policy and oversight. Porter: Novartis: Patents & Royalties, Research Funding; Genentech: Other: Spouse Employment. Grupp: Novartis: Research Funding. [1]: /embed/inline-graphic-2.gif

BACKGROUND CARs combine a targeting antibody (scFv) domain with intracellular signaling domains. We have previously reported on CTL019 cells expressing an anti-CD19 CAR, which have resulted in up to 100,000x in vivo proliferation, durable anti-tumor activity, and prolonged persistence in pts with B cell tumors, including sustained CRs in adults and children with ALL (Grupp et al., NEJM 2013, Maude et al., NEJM 2014). We now report on outcomes and longer follow up of the first 53 pts with relapsed/refractory (r/r) ALL treated on our pilot trial in pediatric ALL. METHODS T cells were lentivirally transduced with a CAR composed of anti-CD19 scFv/4-1BB/CD3ζ, activated/expanded ex-vivo with anti-CD3/anti-CD28 beads, and then infused into children with r/r CD19+ ALL. 48/53 pts received lymphodepleting chemotherapy the week prior to CTL019 infusion. The targeted T cell dose range was 107 to 108 cells/kg with a transduction efficiency of 3.6-45%. T cells for manufacturing were collected from the pt regardless of prior SCT status, and not their allo donors. RESULTS We treated 53 children and young adults with CD19+ ALL, median age 11y, (4-24y). To assess disease burden after lymphodepleting chemotherapy, pts had BM aspirations performed 1D prior to 1st CTL019 infusion: 41/53 pts had detectable ALL while 12 were MRD(-). A median of 4.3x106 CTL019 cells/kg (1-17.4x106/kg) were infused over 1-2D (1 pt got cells over 3D). There were no infusional toxicities >gr2, although pts who developed fevers within 24h of infusion did not receive a planned 2nd infusion of CTL019 cells. 50 pts (94%) achieved a CR, including a patient with CD19+ T ALL, 3 did not respond. MRD measured by clinical flow cytometry was All but 5 (90%) of pts developed grade 1-4 cytokine release syndrome (CRS) at peak T cell expansion. Detailed cytokine analysis showed marked increases of IL6 and IFNγ (both up to 1000x), and IL2R. Treatment for CRS was required for hemodynamic or respiratory instability in 28% of patients and was reversed in all cases with the IL6-receptor antagonist tocilizumab, together with short courses of corticosteroids in 9 pts. Although T cells collected from the 35 pts who had relapsed after allo SCT were median 100% donor origin, no GVHD has been seen. Grade 4 CRS was associated with high disease burden prior to infusion and with elevations in IL-6, ferritin (suggesting macrophage activation syndrome) and C reactive protein after infusion. Persistence of CTL019 cells can be detected by flow cytometry and/or QPCR, and results in the pharmacodynamic marker of CTL019 function, B cell aplasia, which continued for 3-39 months after infusion in pts with ongoing responses. B cell aplasia has been treated with IVIg without significant infectious complications. CONCLUSIONS: CTL019 cells can undergo robust in vivo expansion and can persist for 3 years or longer in children and young adults with r/r ALL, allowing for the possibility of long-term disease control without subsequent therapy such as SCT. This approach also has promise as salvage therapy for patients who relapse after allo SCT with a low risk of GVHD. CTL019 therapy is associated with a significant CRS that responds rapidly to IL-6-targeted anti-cytokine treatment. CTL019 cells can induce potent and durable responses for patients with r/r ALL; however, recurrence with cells that have lost CD19 is an important mechanism of CTL019 resistance. Rapid loss of CTL019 cells (prior to 3 months) is associated with a high risk of CD19+ relapse. CTL019 therapy has received Breakthrough Therapy designation from the FDA in pediatric and adult ALL, and phase 2 multicenter registration trials are well underway. Disclosures Grupp: Novartis: Consultancy, Research Funding. Maude:Novartis: Consultancy, Research Funding. Shaw:Novartis: Research Funding. Aplenc:Sigma Tau: Consultancy. Lacey:Novartis: Research Funding. Levine:Novartis: Patents & Royalties, Research Funding. Melenhorst:Novartis: Research Funding. Rheingold:Novartis: Consultancy; Endo: Other: Husband's employer, has equity interest. Teachey:Novartis: Research Funding. Wood:Novartis Pharmaceuticals Corporation: Employment. Porter:Novartis: Other: IP interest, Research Funding; Genentech: Other: Spouse employment. June:University of Pennsylvania: Patents & Royalties: financial interests due to intellectual property and patents in the field of cell and gene therapy. Conflicts of interest are managed in accordance with University of Pennsylvania policy and oversight; Novartis: Research Funding.

CTLO19 cells are CAR-modified T cells which recognize CD19 and produce high durable remission rates for pts with relapsed or refractory acute lymphoblastic leukemia (ALL). Cytokine Release Syndrome (CRS) has emerged as the major treatment related effect from CTL019, with symptoms that include high fevers and malaise but can progress to capillary leak, hypoxia and hypotension. CRS occurs hours to days after CTL019 infusion and correlates with rapid in vivo CTL019 expansion and marked elevation of serum IL6. In most cases, CRS is self-limited or rapidly reversed with anti-cytokine directed therapies. Here we report 3 cases of refractory CRS in adult pts with ALL. Our experience offers insight into clinical and investigational parameters describing this syndrome; highlights the variance of CRS across disease types and illustrates complexities of CRS management during concurrent infectious illness. As of 7/1/14, 97 pts (30 pediatric ALL, 12 adult ALL, 41 CLL, 14 NHL) have been treated with CTLO19. To capture clinical manifestations of CRS across protocols, we developed a novel CRS grading scale which will be described. Severe CRS (Gr 3-5) occurred in 27 (64%) of ALL pts and only 16 (29%) of CLL/NHL pts (p=0.001). 12 adults with ALL received CTL019; 8/9 evaluable pts achieved CR (MRD negative) at 1 month and 1 pt with extramedullary disease had marked reduction of PET avid disease which is maintained at 1 yr. Severe CRS occurred in 11 of 12 adult ALL pts. CRS was self-limited in 2 pts, rapidly reversed with anti-IL6 directed therapy in 6 pts and was refractory to therapy, contributing to death in 3 pts who were not evaluable for disease response. No baseline attributes differentiate these 3 pts from the 9 adult ALL pts with manageable Gr1-4 CRS. We have shown however that ALL disease burden correlates with CRS severity (in press) and all 3 pts had significant disease burden at baseline. All received lymphodepleting chemotherapy with cyclophosphamide 300 mg/m2 q12h x 6 followed by infusion of CTLO19 cells. These 3 pts each received 6.50E+06, 6.70E+06 and 8.45E+06 CTLO19 cells/kg compared to median CTL019 dose of 3.62E+06 in the 9 adult ALL pts with manageable CRS. Pt 21413-03 developed CRS 12 hrs after infusion and tested positive for influenza B on D3. Despite broad spectrum antimicrobials (including oseltamivir) and anticytokine directed therapy with tocilizumab (4mg/kg x 2) and steroids, he died with refractory hypotension on D5. Pt 21413-06 had extensive disease after 2 prior allogeneic SCTs and developed CRS within 12 hrs of infusion. In addition to broad spectrum antibiotics, she received tocilizumab 8mg/kg (D 3, 6 and 12); intermittent high dose steroids (D 4-15) and etanercept (D14). She died D15 with hypotension, hypoxic respiratory failure and concurrent MDR pseudomonas sepsis and pneumonia. Pt 21413-11 developed CRS within 24 hrs of infusion. He received tocilizumab 8mg/kg (D3&4); siltuximab (D5&15) and intermittent high dose steroids (D 4-15). After an initial response, he developed recurrent fever, pulmonary infiltrates and blood cultures positive for stenotrophomonas. He died D15 with refractory hypoxia and hypotension. All 3 pts’ clinical CRS correlated with marked in vivo CTL019 expansion and progressive serum cytokine elevations (data to be shown). CONCLUSIONS: CRS is the major toxicity of CTL019 therapy and its clinical course varies depending on disease type (more frequent and severe in ALL) and disease burden (in ALL). The 3 refractory CRS cases described here (of 97 total pts treated) have all occurred in adult ALL pts with significant disease burden who received relatively high doses of CTL019 cells. In addition, all 3 had significant infectious complications which potentially fueled underlying CRS and/or were made more virulent due to impairment of immunity with administration of anti-cytokine directed therapies. Future protocol modifications will be made goal of limiting severity of CRS while maintaining high durable remission rates. Further exploration is planned to better correlate timing and choice of anticytokine directed therapy in relation to clinical and investigation parameters of CRS. Disclosures Frey: Novartis: Research Funding. Off Label Use: USe of CART19 cells to treat CLL. Levine:Novartis: Patents & Royalties, Research Funding. Lacey:Novartis: Research Funding. Grupp:Novartis: Consultancy, Research Funding. Schuster:Novartis: Research Funding. Hwang:NVS: Research Funding. Leung:Novartis: Employment. Shen:Novartis: Employment. Ericson:Novartis: Employment. Melenhorst:Novartis: Research Funding. June:Novartis: Patents & Royalties, Research Funding. Porter:Novartis: Patents & Royalties, Research Funding.

BACKGROUND CARs combine a single chain variable fragment (scFv) of an antibody with intracellular signaling domains. We have previously reported on CTL019 cells expressing an anti-CD19 CAR. Infusion of these cells results in 100 to 100,000x in vivo proliferation, durable anti-tumor activity, and prolonged persistence in pts with B cell tumors, including sustained CRs in adults and children with ALL (Grupp et al., NEJM 2013, Maude et al., NEJM 2014). We now report on outcomes and longer follow up of the first 30 pts with relapsed, refractory ALL treated on our pilot trial in pediatric ALL. METHODS T cells were lentivirally transduced with a CAR composed of anti-CD19 scFv/4-1BB/CD3ζ, activated/expanded ex-vivo with anti-CD3/anti-CD28 beads, and then infused into children with relapsed or refractory CD19+ ALL. 26/30 pts received lymphodepleting chemotherapy the week prior to CTL019 infusion. The targeted T cell dose range was 107 to 108 cells/kg with a transduction efficiency of 11-45%. T cells for manufacturing were collected from the pt regardless of prior SCT status, not allo donors. RESULTS 30 children median age 10y (5-22y) with CD19+ ALL were treated. 25/30 pts had detectable disease on the day before CTL019 cell infusion, while 5 were MRD(-). A median of 3.6x106 CTL019 cells/kg (1.1-18x106/kg) were infused over 1-3 days. There were no infusional toxicities >grade 2, although 9 pts developed fevers within 24 hrs of infusion and did not receive a planned 2nd infusion of CTL019 cells. 27 pts (90%) achieved a CR, including a patient with T cell ALL aberrantly expressing CD19+. 3 did not respond. MRD measured by clinical flow cytometry was negative in 23 responding pts and positive at 0.1% (negative at 3 mo), 0.09%, 0.22%, and 1.1% in 4 pts. With median follow up 8 mo (1-26 mo), 16 pts have ongoing CR, with only 3 patients in the cohort receiving subsequent treatment such as donor lymphocyte infusion or SCT, 6-month EFS measured from infusion is 63% (95% CI, 47-84%), and OS is 78% (95% CI, 63-95%). CTL019 cells were detected in the CSF of 17/19 pts and 2 pts with CNS2a disease experienced a CR in CSF. 10 pts with a CR at 1 mo have subsequently relapsed, half with CD19(-) blasts. 2/5 pts who relapsed with CD19(-) disease had previously been refractory to CD19-directed blinatumomab and subsequently went into CR with CTL019. Figure 1 Figure 1. All responding pts developed grade 1-4 cytokine release syndrome (CRS) at peak T cell expansion. Detailed cytokine analysis showed marked increases of IL6 and IFNγ (both up to 1000x), and IL2R. Treatment for CRS was required for hemodynamic or respiratory instability in 37% of patients and was rapidly reversed in all cases with the IL6-receptor antagonist tocilizumab, together with corticosteroids in 5 pts. Although T cells collected from the 21 pts who had relapsed after allo SCT were median 100% donor origin, no GVHD has been seen. Grade 4 CRS was strongly associated with high disease burden prior to infusion and with elevations in IL-6, ferritin (suggesting macrophage activation syndrome) and C reactive protein after infusion. Persistence of CTL019 cells detected by flow cytometry and/or QPCR, and accompanied by B cell aplasia, continued for 1-26 months after infusion in pts with ongoing responses. QPCR showed very high levels of CTL019 proliferation, with all patients achieving peak levels >5000 copies/ug gDNA and 26 patients with peak levels >15,000 copies/ug gDNA. B cell aplasia has been treated with IVIg without significant infectious complications. Probability of 6-mo CTL019 persistence by flow was68% (95% CI, 50-92%) andrelapse-free B cell aplasia was 73% (95% CI, 57-94%). CONCLUSIONS: CTL019 cells can undergo robust in-vivo expansion and can persist for 2 years or longer in pts with relapsed ALL, allowing for the possibility of long-term disease response without subsequent therapy such as SCT. This approach also has promise as a salvage therapy for patients who relapse after allo-SCT with a low risk of GVHD. CTL019 therapy is associated with a significant CRS that responds rapidly to IL-6-targeted anti-cytokine treatment. CTL019 cells can induce potent and durable responses for patients with relapsed/refractory ALL; however, recurrence with cells that have lost CD19 is an important mechanism of CLT019 resistance. CTL019 therapy has received Breakthrough Therapy designation from the FDA in both pediatric and adult ALL, and phase II multicenter trials have been initiated. Disclosures Grupp: Novartis: Consultancy, Research Funding. Barrett:Novartis: Research Funding. Chew:Novartis: Research Funding. Lacey:Novartis: Research Funding. Levine:Novartis: Patents & Royalties, Research Funding. Melenhorst:Novartis: Research Funding. Rheingold:Novartis: Consultancy. Shen:Novartis: Employment. Wood:Novartis Pharma: Employment. Porter:Novartis: managed according to U Penn Policy Patents & Royalties, Research Funding. June:Novartis: Research Funding, Royalty income Patents & Royalties.

CTL019 are autologous T cells genetically modified to express a chimeric antigen receptor (CAR) consisting of an external anti-CD19 domain with the CD3z and 4-1BB signaling domains, and mediate potent anti-tumor effects in patients (pts) with advanced, R/R CLL, ALL and NHL. CRS is the most serious toxicity of CTL019 therapy; symptoms can include fevers, nausea, myalgias, capillary leak, hypoxia, and hypotension. Standard CRS grading criteria are not applicable to CAR T cell therapies. To better capture clinical manifestations of CRS and guide intervention after CTL019, we devised a novel CRS grading scale. that was applied to 40 pts treated with CTL019 for R/R CLL; 14 pts on an initial pilot and 26 pts on an ongoing dose-optimization trial (reported separately). Our new CRS grading system is shown below. Pts were 80% male, a median age of 65 (range 51-78) and received a median of 4 prior therapies (range 1-10). 41% had known mutation at p53. 83% of 24 pts tested had unmutated IgVH. Response rate to CTL019 (CR+PR) was 42%. CRS was the major toxicity and occurred in 57% (23/40) of pts. CRS was gr 1 in 10%, gr 2 in 17%, gr 3 in 15% and gr 4 in 15%. Development of CRS correlated with response; 13/23 (57%) pts with CRS responded versus 4/17 (24%) pts without CRS responded (p=0.05). CRS was associated with elevations in IL-6, IFN-g, and other cytokines; details for 33 pts will be presented. Peak fold-increase over baseline for IL-6 was a median of 10.6x (range 0.28–649) and for IFN- g a median of 32.9x (1–7243x). For pts with CRS, this increase in IL-6 was a median of 23.5x compared to 1.86x in pts without CRS (p=0.001); and in IFN- g was a median of 97.2xin pts with CRS compared to 24.2x without (p=0.018). Increasing CRS severity was associated with peak fold change in IL-6 (p< 0.0001) and IFN- g (p=0.015). Notably, unlike cytokine changes associated with sepsis, TNF-a did not markedly increase during CRS. CRS occurred with a consistent and often dramatic increase in ferritin, C reactive protein (CRP), and hemophagocytosis, suggesting concurrent macrophage activation syndrome (MAS). Increasing CRS severity was associated with an increasing trend for peak ferritin (log scale, p

Background CARs combine a single chain variable fragment (scFv) of an antibody with intracellular signaling domains into a single chimeric protein. We previously reported on CTL019 cells expressing a CAR with intracellular activation plus costimulatory domains. Infusion of these cells results in 100 to 100,000x in vivo proliferation, durable anti-tumor activity, and prolonged persistence in pts with B cell tumors, including 1 sustained CR in a patient with ALL (Grupp, et al. NEJM 2013). We now report on outcomes and longer follow up from our pilot studies treating 20 pts (16 children and 4 adults) with relapsed, refractory ALL. Methods T cells were lentivirally transduced with a CAR composed of anti-CD19 scFv/4-1BB/CD3ζ, activated/expanded ex-vivo with anti-CD3/anti-CD28 beads, and then infused into pts with relapsed or refractory CD19+ ALL. 17/20 pts received lymphodepleting chemotherapy the week prior to CTL019 infusion. The targeted T cell dose range was 107 to 108 cells/kg with a transduction efficiency (TE) of 11-45%. On the adult protocol, the target dose was 5 x 109 total cells split over 3 days with a TE of 6-31%. 11 pts had relapsed ALL after a prior allogeneic SCT. T cells were collected from the pt, regardless of prior SCT status, and not from allo donors. All pts s/p allo SCT had to be 6 mos s/p SCT with no GVHD or GVHD treatment. Results 16 children median age 9.5 y (5-22y) and 4 adults median age 50y (26-60y) with CD19+ ALL were treated. One child had T cell ALL aberrantly expressing CD19. 14/16 pediatric pts had active disease or +MRD after chemotherapy on the day prior to CTL019 cell infusion, while 2 were MRD(-). 3 of 4 adults had active disease prior to lymphodepleting chemotherapy, while 1 was in morphologic CR. Lymphodepleting chemotherapy varied with most receiving a Cytoxan-containing regimen the week prior to CTL019. A median of 3.7x106 CTL019 cells/kg (0.7-18x106/kg) were infused over 1-3 days. There were no infusional toxicities >grade 2, although 5 pts developed fevers within 24 hrs of infusion and did not receive planned subsequent infusions of CTL019 cells. 14 patients (82%) achieved a CR, including the patient with CD19+ T ALL, 3 did not respond, and 3 are pending evaluation. 11/17 evaluable pts have ongoing BM CR with median follow up 2.6 mo (1.2-15 mo). Three patients with a CR at 1 month have subsequently relapsed, 1 with CD19(-) disease. Median follow-up as of August 1, 2013 was 2.6 mo (1-15 mo) for all pts. All responding pts developed some degree of delayed cytokine release syndrome (CRS), concurrent with peak T cell expansion, manifested by fever, with variable degrees of myalgias, nausea, anorexia. Some experienced transient hypotension and hypoxia. Detailed cytokine analysis showed marked increases from baseline values of IL6 and IFNγ (both up to 1000x), and IL2R, with mild or no significant elevation in systemic levels of TNFα or IL2. Treatment for CRS was required for hemodynamic or respiratory instability in 7/20 patients and was rapidly reversed in all cases with the IL6-receptor antagonist tocilizumab (7 pts), together with corticosteroids in 4 pts. Although T cells collected from the 11 pts who had relapsed after allo SCT were generally 100% of donor origin, no GVHD has been seen. Persistence of CTL019 cells detected by flow cytometry and/or QPCR in pts with ongoing responses continued for 1-15 months after infusion, resulting in complete B cell aplasia during the period of CTL019 persistence. Pts have been treated with IVIg without any unusual infectious complications. One child who entered a CR subsequently developed MDS with a new trisomy 8 in ALL remission and has gone to SCT, and 1 child developed a single leukemia cutis lesion at 6 mo, still BM MRD(-). Conclusions CTL019 cells are T cells genetically engineered to express an anti-CD19 scFv coupled to CD3ζ signaling and 4-1BB costimulatory domains. These cells can undergo robust in-vivo expansion and can persist for 15 mo or longer in pts with relapsed ALL. CTL019 therapy is associated with a significant CRS that responds rapidly to IL-6-targeted anti-cytokine treatment. This approach has promise as a salvage therapy for patients who relapse after allo-SCT, and collection of tolerized cells from the recipient appears to have a low risk of GVHD. CTL019 cells can induce potent and durable responses for patients with relapsed/refractory ALL. Multicenter trials are being developed to test this therapy for ALL in the phase 2 setting. Disclosures: Grupp: Novartis: Research Funding. Chew:Novartis: Patents & Royalties. Levine:Novartis: cell and gene therapy IP, cell and gene therapy IP Patents & Royalties. Litchman:Novartis Phamaceuticals: Employment, Equity Ownership. Rheingold:Novartis: Research Funding. Shen:Novartis Pharmaceuticals: Employment, Equity Ownership. Wood:Novartis Pharmaceuticals: Employment, Equity Ownership. June:Novartis: Patents & Royalties, Research Funding.

Abstract 249 CRLF2 genomic rearrangements that lead to overexpression have been identified in a subset of children with clinically high-risk B-precursor ALL and are highly associated with activating JAK2 mutations (Harvey et al., Blood 2010; Mullighan et al., PNAS 2009 and Nat Genet 2009). These children frequently respond poorly to current intensive cytotoxic chemotherapy regimens and suffer high rates of relapse and mortality. New therapies for these patients are urgently needed. These leukemias exhibit gene expression profiles similar to those of BCR-ABL1 positive ALL, suggesting aberrant kinase activation. We previously demonstrated aberrant JAK/STAT and PI3K/mTOR signaling in CRLF2-overexpressing ALL cell lines and primary human samples in vitro, and thus hypothesize that inhibition of these hyperactive signaling networks has therapeutic relevance. To further characterize this high-risk subset of ALL, we have established multiple xenograft models of CRLF2-rearranged and JAK2-mutated ALL, providing a robust platform for preclinical testing of signal transduction inhibitors. In this model, primary human ALL samples are intravenously injected into NOD/SCID/γc null (NSG) mice, and engraftment is determined by flow cytometry of peripheral blood for human CD19+/CD45+ blasts. Eighteen of 21 primary cryopreserved specimens provided by the Children's Oncology Group engrafted successfully. In order to biochemically characterize the xenografts, we measured phosphorylation of relevant signal transduction proteins by phosphoflow cytometry. Spleens of mice xenografted with CRLF2-rearranged ALL had uniformly increased surface staining of human CRLF2, a component of the heterodimeric receptor complex for the cytokine, thymic stromal lymphopoeitin (TSLP). In vitro stimulation of the CRLF2-overexpressing ALL xenograft spleens with TSLP induced phosphorylation of STAT5, Akt, S6, and 4EBP1, but not of ERK 1/2. In additon, in vitro JAK inhibition with INCB018424 abrogated TSLP-induced JAK/STAT and PI3K/mTOR signaling. The mTOR inhibitor sirolimus, mTORC1/2 inhibitor PP242, and PI3K/mTOR inhibitor PI-103 potently inhibited phosphorylation of S6 and 4EBP1 in these xenograft specimens. These data suggest that the JAK/STAT and PI3K/mTOR pathways may interact in these CRLF2-overexpressing leukemias. These data led us to hypothesize that inhibition of the PI3K/mTOR or JAK/STAT pathways may represent potential therapeutic targets; therefore, we utilized these very high-risk ALL xenograft models to study novel, targeted therapies. Once xenografts had engrafted with sufficient disease burden to detect >5% peripheral CD19+/CD45+ blasts, mice were randomized to receive the mTOR inhibitor sirolimus, the JAK inhibitor INCB018424, or vehicle for three to four weeks. Disease burden was assessed weekly by flow cytometric determination of CD19+/CD45+ blast count in peripheral blood, and at sacrifice, by spleen CD19+/CD45+ blast count. To assess potential differential efficacy based on CRLF2 overexpression (CRLF2+) and/or JAK2 activating mutations (JAK2mut), we treated mice with each subtype of ALL. Sirolimus induced a significant decrease in peripheral blast count in 7 of 7 primary ALL xenografts tested (2 JAK2mut/CRLF2+ samples, 1 JAK2mut/CRLF2- sample, 2 JAK2wt/CRLF2+ samples, and 2 JAK2wt/CRLF2- samples) and a significant decrease in spleen blast count in 6 of 7 samples tested. The most profound reduction of disease burden was seen in the JAK2mut/CRLF2+ leukemias. In addition, the JAK inhibitor INCB018424 decreased peripheral blast count and spleen blast count in a JAK2mut/CRLF2+ xenograft. We next determined if sirolimus conferred a survival advantage in xenografts of 2 ALL specimens, a robust responder and an intermediate responder to sirolimus by blast count. Sirolimus treatment significantly prolonged survival of both xenografts (63 days vs. 23 days, p=0.0015; 91 days vs. 58 days, p=0.0027). Additional human ALL xenograft studies of INCB018424 and other kinase inhibitors are ongoing. The preclinical in vivo efficacy of sirolimus and INCB018424 suggests that novel, targeted therapies have therapeutic potential in CRLF2-overexpressing ALL. Based in part on these data, both INCB018424 and temsirolimus (a parenteral ester of sirolimus) are currently being investigated in multi-center early phase clinical trials for children with relapsed or refractory leukemias. Disclosures: No relevant conflicts of interest to declare.