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T cells expressing CD19-specific chimeric antigen receptors (CD19-CARs) have potent antileukemia activity in pediatric and adult patients with relapsed and/or refractory B-cell acute lymphoblastic leukemia (B-ALL). However, not all patients achieve a complete response (CR), and a significant percentage relapse after CD19-CAR T-cell therapy due to T-cell intrinsic and/or extrinsic mechanisms. Thus, there is a need to evaluate new CD19-CAR T-cell products in patients to improve efficacy. We developed a phase 1/2 clinical study to evaluate an institutional autologous CD19-CAR T-cell product in pediatric patients with relapsed/refractory B-ALL. Here we report the outcome of the phase 1 study participants (n = 12). Treatment was well tolerated, with a low incidence of both cytokine release syndrome (any grade, n = 6) and neurotoxicity (any grade, n = 3). Nine out of 12 patients (75%) achieved a minimal residual disease-negative CR in the bone marrow (BM). High disease burden (≥40% morphologic blasts) before CAR T-cell infusion correlated with increased side effects and lower response rate, but not with CD19-CAR T-cell expansion. After infusion, CD8+ CAR T cells had a proliferative advantage over CD4+ CAR T cells and at peak expansion, had an effector memory phenotype with evidence of antigen-driven differentiation. Patients that proceeded to allogeneic hematopoietic cell transplantation (AlloHCT) had sustained, durable responses. In summary, the initial evaluation of our institutional CD19-CAR T-cell product demonstrates safety and efficacy while highlighting the impact of pre-infusion disease burden on outcomes. This trial was registered at www.clinicaltrials.gov as #NCT03573700.

Subsequent malignancies are well-documented complications in long-term follow-up of cancer patients. Recently, genetically modified immune effector (IE) cells have shown benefit in hematologic malignancies and are being evaluated in clinical trials for solid tumors. Although the short-term complications of IE cells are well described, there is limited literature summarizing long-term follow-up, including subsequent malignancies. We retrospectively reviewed data from 340 patients treated across 27 investigator-initiated pediatric and adult clinical trials at our center. All patients received IE cells genetically modified with γ-retroviral vectors to treat relapsed and/or refractory hematologic or solid malignancies. In a cumulative 1027 years of long-term follow-up, 13 patients (3.8%) developed another cancer with a total of 16 events (4 hematologic malignancies and 12 solid tumors). The 5-year cumulative incidence of a first subsequent malignancy in the recipients of genetically modified IE cells was 3.6% (95% confidence interval, 1.8% to 6.4%). For 11 of the 16 subsequent tumors, biopsies were available, and no sample was transgene positive by polymerase chain reaction. Replication-competent retrovirus testing of peripheral blood mononuclear cells was negative in the 13 patients with subsequent malignancies tested. Rates of subsequent malignancy were low and comparable to standard chemotherapy. These results suggest that the administration of IE cells genetically modified with γ retroviral vectors does not increase the risk for subsequent malignancy.

Supplementary Figures 11-18

Supplementary Data from Common Trajectories of Highly Effective CD19-Specific CAR T Cells Identified by Endogenous T-cell Receptor Lineages

Chimeric antigen receptor (CAR) T-cell therapy has had limited success in early-phase clinical studies for solid tumors. Lack of efficacy is most likely multifactorial, including a limited array of targetable antigens. We reasoned that targeting the cancer-specific extra domain B (EDB) splice variant of fibronectin might overcome this limitation because it is abundantly secreted by cancer cells and adheres to their cell surface. In vitro, EDB-CAR T cells recognized and killed EDB-positive tumor cells. In vivo, 1 × 106 EDB-CAR T cells had potent antitumor activity in both subcutaneous and systemic tumor xenograft models, resulting in a significant survival advantage in comparison with control mice. EDB-CAR T cells also targeted the tumor vasculature, as judged by IHC and imaging, and their antivascular activity was dependent on the secretion of EDB by tumor cells. Thus, targeting tumor-specific splice variants such as EDB with CAR T cells is feasible and has the potential to improve the efficacy of CAR T-cell therapy.

Supplementary Figures 1-10

Supplementary Data from A Costimulatory CAR Improves TCR-based Cancer Immunotherapy

T-cell receptors (TCR) recognize intracellular and extracellular cancer antigens, allowing T cells to target many tumor antigens. To sustain proliferation and persistence, T cells require not only signaling through the TCR (signal 1), but also costimulatory (signal 2) and cytokine (signal 3) signaling. Because most cancer cells lack costimulatory molecules, TCR engagement at the tumor site results in incomplete T-cell activation and transient antitumor effects. To overcome this lack of signal 2, we genetically modified tumor-specific T cells with a costimulatory chimeric antigen receptor (CoCAR). Like classical CARs, CoCARs combine the antigen-binding domain of an antibody with costimulatory endodomains to trigger T-cell proliferation, but CoCARs lack the cytotoxic CD3ζ chain to avoid toxicity to normal tissues. We first tested a CD19-targeting CoCAR in combination with an HLA-A*02:01-restricted, survivin-specific transgenic TCR (sTCR) in serial cocultures with leukemia cells coexpressing the cognate peptide–HLA complex (signal 1) and CD19 (signal 2). The CoCAR enabled sTCR+ T cells to kill tumors over a median of four additional tumor challenges. CoCAR activity depended on CD19 but was maintained in tumors with heterogeneous CD19 expression. In a murine tumor model, sTCR+CoCAR+ T cells improved tumor control and prolonged survival compared with sTCR+ T cells. We further evaluated the CoCAR in Epstein–Barr virus–specific T cells (EBVST). CoCAR-expressing EBVSTs expanded more rapidly than nontransduced EBVSTs and delayed tumor progression in an EBV+ murine lymphoma model. Overall, we demonstrated that the CoCAR can increase the activity of T cells expressing both native and transgenic TCRs and enhance antitumor responses.

Supplementary Figures 1 to 17

Supplementary Figure 3: C7R signaling does not change phenotypic composition of GD2-CAR T-cells during culture.

The inability of chimeric antigen receptor (CAR) T cells to sustain their effector function after repeated exposure to tumor cells is a major obstacle to their success in patients with solid tumors. To overcome this limitation, we designed a novel chimeric cytokine receptor to create an autocrine loop that links activation-dependent GM-CSF production by CAR T cells to IL18 receptor signaling (GM18). Expression of GM18 in CAR T cells enhanced their effector function in an antigen- and activation-dependent manner. In repeat stimulation assays, which mimic chronic antigen exposure, CAR.GM18 T cells had a significantly greater ability to expand and produce cytokines in comparison with their unmodified counterparts targeting EPHA2 or HER2. In vivo, CAR.GM18 T cells induced tumor regression at cell doses at which standard CAR T cells were ineffective in two solid tumor xenograft models. Thus, our study highlights the potential of hijacking cytokines that are physiologically secreted by T cells to bolster their antitumor activity.Significance:We designed a chimeric cytokine receptor (GM18) that links CAR T-cell activation to MYD88 signaling. GM18 endows CAR T cells with sustained effector function in the setting of chronic antigen exposure, resulting in potent antitumor activity in preclinical solid tumor models.This article is highlighted in the In This Issue feature, p. 1601

Supplemental Figure 1: Activation of iCO molecules in T cells enhances NF-κB signaling;Supplemental Figure 2: Activation of iCO molecules enhances cytokine production in T cells;Supplemental Figure 3: CID dose-dependent IL2 production of HER2ζ.iCO T cells can be controlled by CID;Supplemental Figure 4: iCO activation enhances pro-inflammatory cytokine secretion of HER2ζ.iCO T cells;Supplemental Figure 5: Signal 1 is critical for HER2ζ.iCO T-cell effector function;Supplemental Figure 6: HER2ζ.iCO and HER2.CD28ζ T-cell lines have similar T-cell subset composition;Supplemental Figure 7: HER2ζ.iCO T cells have reduced PD-1 surface expression;Supplemental Figure 8: Recurrent tumors from HER2ζ.iCO T-cell + CID and HER2.CD28 ζ T-cell treated mice express HER2;Supplemental Figure 9: HER2ζ.iCO and HER2.CD28ζ T-cell lines have similar T-cell subset composition in vivo;Supplemental Figure 10: Anatomic location of tumors in treated mice;Supplemental Figure 11: Chemokine secretion of A549 cells, and chemokine receptor expression of T cells;Supplemental Figure 12: PD-L1 expression in tumor cell lines;Supplemental Figure 13: Generation of T-cells expressing HER2.CD28ζ.iCO;Supplemental Figure 14: iCO activation enhances expansion and pro-inflammatory cytokine secretion of HER2ζ.iCO and HER2.CD28ζ.iCO T-cells;Supplemental Figure 15: iCO activation enhances cytolytic activity of HER2ζ.iCO and HER2.CD28ζ.iCO T-cells; Supplemental Figure 16: Second CID injection eliminates recurrent tumors in 2/3 mice

S1: T-cell immunophenotyping by flow cytometry. S2: Determination of TSCM presence in PBMC and NT T-cells by flow cytometry. S3: CD19-ENGT-cells and CD19-ENGT-cells expressing CD80 and/or 41BBL kill Nalm 6 cells efficiently. S4: Experimental set up of Serial Killing Assay. S5: CD19- ENG.41BBL/CD80 T-cells have improved ability to sequentially kill CD19 target cells. S6: CD19-ENG T-cells expressing CD80 or 41BBL and CD80 have improved ability to sequentially kill CD19 target cells. S7: Nalm 6 express PD-L1 after exposure to IFNgamma. S8: CD19 ENG.41BBL/CD80 T-cells expand in vivo and persist long-term at low levels.

Tumor signal comparison.

Supplementary Figure 6: Efficient retroviral transduction of T-cells with Î"34, C7R, GD2-CAR, and GD2-CAR.C7R constructs.

Supplementary Figure 5: C7R does not significantly increase intracranial EphA2-CAR T-cell expansion against U373 tumors

One obstacle for human solid tumor immunotherapy research is the lack of clinically relevant animal models. In this study, we sought to establish a chimeric antigen receptor (CAR) T-cell treatment model for naturally occurring canine sarcomas as a model for human CAR T-cell therapy.Canine CARs specific for B7-H3 were constructed using a single-chain variable fragment derived from the human B7-H3–specific antibody MGA271, which we confirmed to be cross-reactive with canine B7-H3. After refining activation, transduction, and expansion methods, we confirmed target killing in a tumor spheroid three-dimensional assay. We designed a B7-H3 canine CAR T-cell and achieved consistently high levels of transduction efficacy, expansion, and in vitro tumor killing. Safety of the CAR T cells were confirmed in two purposely bred healthy canine subjects following lymphodepletion by cyclophosphamide and fludarabine. Immune response, clinical parameters, and manifestation were closely monitored after treatments and were shown to resemble that of humans. No severe adverse events were observed.In summary, we demonstrated that similar to human cancers, B7-H3 can serve as a target for canine solid tumors. We successfully generated highly functional canine B7-H3–specific CAR T-cell products using a production protocol that closely models human CAR T-cell production procedure. The treatment regimen that we designed was confirmed to be safe in vivo. Our research provides a promising direction to establish in vitro and in vivo models for immunotherapy for canine and human solid tumor treatment.

T cells expressing CD19-specific chimeric antigen receptors (CARs) with endodomains that encode a signaling domain derived from CD3ζ and CD28 or 41BB have potent antitumor activity in early-phase clinical studies for B-cell malignancies. Besides CD19-specific CARs, other approaches are actively being pursued to redirect T cells to CD19, including recombinant bispecific T-cell engager (BiTE) proteins or T cells genetically modified to express BiTEs [engager (ENG) T cells]. As BiTEs provide no costimulation, we investigated here if provision of costimulation through CD28 and 41BB enhances the effector function of CD19-ENG T cells. CD19-ENG T cells expressing CD80 and 41BBL on their cell surface (CD19-ENG.41BBL/CD80 T cells) were generated by retroviral transduction. CD19-ENG.41BBL/CD80 T cells retained their antigen specificity and had superior effector function compared with both unmodified T cells and CD19-ENG T cells expressing either CD80, 41BBL, or no costimulatory molecule, as judged by cytokine (IFNγ and IL2) production, T-cell proliferation, and their ability to sequentially kill target cells. In vivo, CD19-ENG.41BBL/CD80 T cells had superior antileukemia activity in the BV173 xenograft model, resulting in a survival advantage in comparison to CD19-ENG T cells. Thus, provision of costimulation is critical for the effector function of ENG T cells. Cancer Immunol Res; 5(10); 860–70. ©2017 AACR.

Supplementary Figure 1: IL13Rα2-CAR and/or IL15 expression does not change T-cell phenotype. Supplementary Figure 2: Cell surface expression of IL13Rα2. Supplementary Figure 3: IL15 improves cell viability in the absence of exogenous cytokines. Supplementary Figure 4: Transgene expression is upregulated upon T cell activation. Supplemental Figure 5: IL13Rα2-CAR.IL15 T cells display activation-dependent IL15 production and greater proliferative capacity. Supplementary Figure 6: CID induces cell death in T cells genetically modified with retroviral vector encoding iC9.dNFGR.IL15. Supplemental Figure 7: Addition of exogenous IL15 increases CAR T-cell expansion in vitro. Supplementary Figure 8: IL13Rα2 or HER2 antigen loss variants are not killed by IL13Rα2- or HER2-CAR T cells.

Supplementary Figure from B7-H3 Specific CAR T Cells for the Naturally Occurring, Spontaneous Canine Sarcoma Model

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults and is virtually incurable with conventional therapies. Immunotherapy with T cells expressing GBM-specific chimeric antigen receptors (CAR) is an attractive approach to improve outcomes. Although CAR T cells targeting GBM antigens, such as IL13 receptor subunit α2 (IL13Rα2), HER2, and EGFR variant III (EGFRvIII), have had antitumor activity in preclinical models, early-phase clinical testing has demonstrated limited antiglioma activity. Transgenic expression of IL15 is an appealing strategy to enhance CAR T-cell effector function. We tested this approach in our IL13Rα2-positive glioma model in which limited IL13Rα2-CAR T-cell persistence results in recurrence of antigen-positive gliomas. T cells were genetically modified with retroviral vectors encoding IL13Rα2-CARs or IL15 (IL13Rα2-CAR.IL15 T cells). IL13Rα2-CAR.IL15 T cells recognized glioma cells in an antigen-dependent fashion, had greater proliferative capacity, and produced more cytokines after repeated stimulations in comparison with IL13Rα2-CAR T cells. No autonomous IL13Rα2-CAR.IL15 T-cell proliferation was observed; however, IL15 expression increased IL13Rα2-CAR T-cell viability in the absence of exogenous cytokines or antigen. In vivo, IL13Rα2-CAR.IL15 T cells persisted longer and had greater antiglioma activity than IL13Rα2-CAR T cells, resulting in a survival advantage. Gliomas recurring after 40 days after T-cell injection had downregulated IL13Rα2 expression, indicating that antigen loss variants occur in the setting of improved T-cell persistence. Thus, CAR T cells for GBM should not only be genetically modified to improve their proliferation and persistence, but also to target multiple antigens.Summary: Glioblastoma responds imperfectly to immunotherapy. Transgenic expression of IL15 in T cells expressing CARs improved their proliferative capacity, persistence, and cytokine production. The emergence of antigen loss variants highlights the need to target multiple tumor antigens. Cancer Immunol Res; 5(7); 571–81. ©2017 AACR.

Supplementary Figure 1: CD34-IL7R* (C7R) is stably expressed in T-cells and enhances constitutive STAT5 activation relative to IL7R*.

Supplementary Figure 4: C7R prolongs survival of GD2-CAR T-cells but does not support autonomous cell expansion.

Supplemental Table 1: Differential gene expression in GD2-CAR.C7R T-cells compared to GD2-CAR T-cells.

Supplementary Figure 2: Efficient retroviral transduction of C7R and Î"34 in both CD4 and CD8 selected T-cells.

Supplemental Materials and Methods

Supplemental Figure Legends

Anti-PD-L1 antibody and PD-L1 mini-body enhance HER2.CAR T-cell proliferation in vitro.

PD-L1 mini-body is expressed at tumor site 10 days post-injection of HER2.CAR T-cells, but minimally impacts CD4+ T-cell phenotype long-term.

Chimeric antigen receptor–modified T cells (CAR T cells) produce proinflammatory cytokines that increase expression of T-cell checkpoint signals such as PD-L1, which may inhibit their functionality against solid tumors. In this study, we evaluated in human tumor xenograft models the proinflammatory properties of an oncolytic adenovirus (Onc.Ad) with a helper-dependent Ad (HDAd) that expresses a PD-L1 blocking mini-antibody (mini-body; HDPDL1) as a strategy to enhance CAR T-cell killing. Coadministration of these agents (CAd-VECPDL1) exhibited oncolytic effects with production of PD-L1 mini-body locally at the tumor site. On their own, HDPDL1 exhibited no antitumor effect and CAd-VECPDL1 alone reduced tumors only to volumes comparable to Onc.Ad treatment. However, combining CAd-VECPDL1 with HER2.CAR T cells enhanced antitumor activity compared with treatment with either HER2.CAR T cells alone or HER2.CAR T cells plus Onc.Ad. The benefits of locally produced PD-L1 mini-body by CAd-VECPDL1 could not be replicated by infusion of anti-PD-L1 IgG plus HER2.CAR T cells and coadministration of Onc.Ad in an HER2+ prostate cancer xenograft model. Overall, our data document the superiority of local production of PD-L1 mini-body by CAd-VECPDL1 combined with administration of tumor-directed CAR T cells to control the growth of solid tumors. Cancer Res; 77(8); 2040–51. ©2017 AACR.

Supplementary Data from HER2-Specific T Cells Target Primary Glioblastoma Stem Cells and Induce Regression of Autologous Experimental Tumors

LD50 of Onc.Ad, HDAd or CAd-VEC in each cell line.

PD-L1 mini-body induces dose-dependent IFNb secretion and T-cell proliferation similar to anti-PD-L1 IgG in MLR.

Systemic treatment of PD-L1 IgG reduces the amount of human T-cells in mice at 24 hrs post-injection.

Co-infection of Onc.Ad with HDPD-L1 increased PD-L1 mini-body in vitro, but PD-L1 mini-body was undetectable in the serum of mice.

Cancer cells express HER2 and PD-L1 expression is induced in the presence of recombinant IFN�, and HER2.CAR T-cells express PD-1 in the presence of target cells.

One obstacle for human solid tumor immunotherapy research is the lack of clinically relevant animal models. In this study, we sought to establish a chimeric antigen receptor (CAR) T-cell treatment model for naturally occurring canine sarcomas as a model for human CAR T-cell therapy. Canine CARs specific for B7-H3 were constructed using a single-chain variable fragment derived from the human B7-H3–specific antibody MGA271, which we confirmed to be cross-reactive with canine B7-H3. After refining activation, transduction, and expansion methods, we confirmed target killing in a tumor spheroid three-dimensional assay. We designed a B7-H3 canine CAR T-cell and achieved consistently high levels of transduction efficacy, expansion, and in vitro tumor killing. Safety of the CAR T cells were confirmed in two purposely bred healthy canine subjects following lymphodepletion by cyclophosphamide and fludarabine. Immune response, clinical parameters, and manifestation were closely monitored after treatments and were shown to resemble that of humans. No severe adverse events were observed. In summary, we demonstrated that similar to human cancers, B7-H3 can serve as a target for canine solid tumors. We successfully generated highly functional canine B7-H3–specific CAR T-cell products using a production protocol that closely models human CAR T-cell production procedure. The treatment regimen that we designed was confirmed to be safe in vivo. Our research provides a promising direction to establish in vitro and in vivo models for immunotherapy for canine and human solid tumor treatment.

The seventh multi-stakeholder Paediatric Strategy Forum focused on chimeric antigen receptor (CAR) T-cells for children and adolescents with cancer. The development of CAR T-cells for patients with haematological malignancies, especially B-cell precursor acute lymphoblastic leukaemia (BCP-ALL), has been spectacular. However, currently, there are scientific, clinical and logistical challenges for use of CAR T-cells in BCP-ALL and other paediatric malignancies, particularly in acute myeloid leukaemia (AML), lymphomas and solid tumours. The aims of the Forum were to summarise the current landscape of CAR T-cell therapy development in paediatrics, too identify current challenges and future directions, with consideration of other immune effector modalities and ascertain the best strategies to accelerate their development and availability to children. Although the effect is of limited duration in about half of the patients, anti-CD19 CAR T-cells produce high response rates in relapsed/refractory BCP-ALL and this has highlighted previously unknown mechanisms of relapse. CAR T-cell treatment as first- or second-line therapy could also potentially benefit patients whose disease has high-risk features associated with relapse and failure of conventional therapies. Identifying patients with very early and early relapse in whom CAR T-cell therapy may replace haematopoietic stem cell transplantation and be definitive therapy versus those in whom it provides a more effective bridge to haematopoietic stem cell transplantation is a very high priority. Development of approaches to improve persistence, either by improving T cell fitness or using more humanised/fully humanised products and co-targeting of multiple antigens to prevent antigen escape, could potentially further optimise therapy. Many differences exist between paediatric B-cell non-Hodgkin lymphomas (B-NHL) and BCP-ALL. In view of the very small patient numbers with relapsed lymphoma, careful prioritisation is needed to evaluate CAR T-cells in children with Burkitt lymphoma, primary mediastinal B cell lymphoma and other NHL subtypes. Combination trials of alternative targets to CD19 (CD20 or CD22) should also be explored as a priority to improve efficacy in this population. Development of CD30 CAR T-cell immunotherapy strategies in patients with relapsed/refractory Hodgkin lymphoma will likely be most efficiently accomplished by joint paediatric and adult trials. CAR T-cell approaches are early in development for AML and T-ALL, given the unique challenges of successful immunotherapy actualisation in these diseases. At this time, CD33 and CD123 appear to be the most universal targets in AML and CD7 in T-ALL. The results of ongoing or planned first-in-human studies are required to facilitate further understanding. There are promising early results in solid tumours, particularly with GD2 targeting cell therapies in neuroblastoma and central nervous system gliomas that represent significant unmet clinical needs. Further understanding of biology is critical to success. The comparative benefits of autologous versus allogeneic CAR T-cells, T-cells engineered with T cell receptors T-cells engineered with T cell receptor fusion constructs, CAR Natural Killer (NK)-cell products, bispecific T-cell engager antibodies and antibody-drug conjugates require evaluation in paediatric malignancies. Early and proactive academia and multi-company engagement are mandatory to advance cellular immunotherapies in paediatric oncology. Regulatory advice should be sought very early in the design and preparation of clinical trials of innovative medicines, for which regulatory approval may ultimately be sought. Aligning strategic, scientific, regulatory, health technology and funding requirements from the inception of a clinical trial is especially important as these are very expensive therapies. The model for drug development for cell therapy in paediatric oncology could also involve a ‘later stage handoff’ to industry after early development in academic hands. Finally, and very importantly, strategies must evolve to ensure appropriate ease of access for children who need and could potentially benefit from these therapies.

Purpose To determine the maximum tolerated dose (MTD) of autologous chimeric antigen receptor T cells (HER2-CART) after lymphodepletion and to describe the cellular kinetics, safety, feasibility of repeat treatment cycles, and antitumor activity of HER2-CART in patients with advanced sarcoma. Patients and Methods On this phase I study, 13 patients with progressive, metastatic HER2+ sarcoma were treated in 14 enrollments; one patient who achieved complete remission was re-enrolled because of disease recurrence. Lymphodepletion consisted of fludarabine (Flu) 25 mg/m2/dose x 5 days with or without cyclophosphamide (Cy) 30 mg/kg/dose x 2 days. The dose cohorts evaluated include 1x108 total T-cells/m2 after Flu (cohort A); 1x108 total T-cells/m2 after Flu/Cy (cohort B) and 1x108 CAR-positive T-cells/m2 after Flu/Cy (cohort C). The evaluation of safety was the primary endpoint. Secondary outcomes included assessment of cellular kinetics and antitumor activity. Results All study participants received at least one infusion of HER2-CART after lymphodepletion and were included in the analysis (median age 14 years; range 4-55 years). Seven received multiple HER2-CART infusions. CART expansion was observed after all but two of 21 total infusions given after lymphodepletion. Nine of 12 (75%) patients in cohorts A and B developed grade 1-2 CRS. Two patients in cohort C experienced dose limiting toxicity (DLT) with grade 3-4 CRS. All patients recovered from treatment-related adverse events during study follow-up. Median OS was 8.2 months (95% CI, 4.4-17 months). Antitumor activity was observed at the MTD (cohort B), with 1-year OS and PFS of 62.5% (95% CI, 22.9%-86.1%) and 33.3% (95% CI, 7.8-62.3%), respectively. Three patients remain alive, with one in long-term remission at the sixth year of follow-up. While infused CART products did not exhibit a distinct immunophenotype by sarcoma histology, we observed different trends in expression of immune checkpoints when compared by disease and by treatment response. Conclusion and Relevance: Autologous HER2-CART can be infused safely after lymphodepletion in patients with progressive sarcoma, and the preliminary evidence of antitumor activity observed supports testing their efficacy in a phase II trial. Trial Registration: ClinicalTrials.gov identifier: NCT00902044

Background aims Vesicular stomatitis virus G (VSV-G)-pseudotyped lentiviral vectors (LVs) are widely used to reliably generate genetically modified, clinical-grade T-cell products. However, the results of genetically modifying natural killer (NK) cells with VSV-G LVs have been variable. The authors explored whether inhibition of the IKK-related protein kinases TBK1 and IKKe, key signaling molecules of the endosomal TLR4 pathway, which is activated by VSV-G, would enable the reliable transduction of NK cells by VSV-G LVs. Methods The authors activated NK cells from peripheral blood mononuclear cells using standard procedures and transduced them with VSV-G LVs encoding a marker gene (yellow fluorescent protein [YFP]) or functional genes (chimeric antigen receptors [CARs], co-stimulatory molecules) in the presence of three TBK1/IKKe inhibitors (MRT67307, BX-795, amlexanox). NK cell transduction was evaluated by flow cytometry and/or western blot and the functionality of expressed CARs was evaluated in vitro. Results Blocking TBK1/IKKe during transduction of NK cells enabled their efficient transduction by VSV-G LVs as judged by YFPexpression of 40–50%, with half maximal effective concentrations of 1.1 µM (MRT67307), 5 µM (BX-795) and 24.8 µM (amlexanox). Focusing on MRT67307, the authors successfully generated NK cells expressing CD19-CARs or HER2-CARs with an inducible co-stimulatory molecule. CAR NK cells exhibited increased cytolytic activity and ability to produce cytokines in comparison to untreated controls, confirming CAR functionality. Conclusions The authors demonstrate that inhibition of TBK1/IKKe enables the reliable generation of genetically modified NK cells using VSV-G LVs. The authors’ protocol can be readily adapted to generate clinical-grade NK cells and thus has the potential to facilitate the clinical evaluation of genetically modified NK cell-based therapeutics in the future.

Not available.

Hematological toxicity (hematotoxicity) leading to peripheral cytopenias is a common long-term adverse effect following the use of CD19-chimeric antigen receptor (CD19-CAR) T-cell therapies. However, management remains unclear for patients whose cytopenias persist beyond 1 month after CAR T-cell infusion. We present the case of a 21-year old who received CD19-CAR T-cell therapy for relapse following a haploidentical transplant. He developed hematotoxicity and consequently multiple life-threatening infections. We administered a CD34

Introductory ParagraphChimeric antigen receptor (CAR) technologies have been clinically implemented for the treatment of hematological malignancies; however, solid tumors remain resilient to CAR therapeutics1-3. Natural Killer (NK) cells may provide an optimal class of immune cells for CAR-based approaches due to their inherent anti-tumor functionality. We sought to tune CAR synapses in NK cells by adding an intracellular scaffolding protein binding site to the CAR. We employed a PDZ binding motif (PDZbm) that specifically binds Scribble4resulting in additional scaffolding crosslinking to enhance synapse formation and cell polarization5,6. Combined effects of this novel CAR design resulted in increased effector cell functionalityin vitroandin vivo. Synapse-tuned CAR-NK cells exhibited amplified synaptic strength, number and abundance of secreted cytokines, enhanced killing of tumor cells, and prolonged survival with tumor clearance in two solid tumor models. Thus, synapse tuning has the potential to improve the efficacy of CAR-based cell therapeutics.

Hematological toxicity (hematotoxicity) is the most common long-term adverse effect following the use of CD19-chimeric antigen receptor (CD19-CAR) T-cell therapies. However, its management remains unclear. We present the case of a 21-year-old who received CD19-CAR T-cell therapy for relapse following a haploidentical transplant. He developed hematotoxicity and consequently multiple life-threatening infections. We administered a CD34+ hematopoietic stem cell boost (HSCB) from his transplant donor that led to hematopoietic recovery and resolution of his infections without any effect on the activity of CD19-CAR T cells. CD34+ HSCB can be a safe and effective option to treat hematotoxicity following CD19-CAR T-cell therapy.

Current chimeric antigen receptor-modified (CAR) T-cell products are evaluated in bulk, without assessing functional heterogeneity. We therefore generated a comprehensive single-cell gene expression and T-cell receptor (TCR) sequencing data set using pre- and postinfusion CD19-CAR T cells from blood and bone marrow samples of pediatric patients with B-cell acute lymphoblastic leukemia. We identified cytotoxic postinfusion cells with identical TCRs to a subset of preinfusion CAR T cells. These effector precursor cells exhibited a unique transcriptional profile compared with other preinfusion cells, corresponding to an unexpected surface phenotype (TIGIT+, CD62Llo, CD27−). Upon stimulation, these cells showed functional superiority and decreased expression of the exhaustion-associated transcription factor TOX. Collectively, these results demonstrate diverse effector potentials within preinfusion CAR T-cell products, which can be exploited for therapeutic applications. Furthermore, we provide an integrative experimental and analytic framework for elucidating the mechanisms underlying effector development in CAR T-cell products. Significance: Utilizing clonal trajectories to define transcriptional potential, we find a unique signature of CAR T-cell effector precursors present in preinfusion cell products. Functional assessment of cells with this signature indicated early effector potential and resistance to exhaustion, consistent with postinfusion cellular patterns observed in patients. This article is highlighted in the In This Issue feature, p. 2007