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t(4;11) MLL-AF4 acute leukemia is one of the most aggressive malignancies in the infant and pediatric population, yet we have little information on the molecular mechanisms responsible for disease progression. This impairs the development of therapeutic regimens that can address the aggressive phenotype and lineage plasticity of MLL-AF4–driven leukemogenesis. This study highlights novel mechanisms of disease development by focusing on 2 microRNAs (miRNAs) upregulated in leukemic blasts from primary patient samples: miR-130b and miR-128a. We show that miR-130b and miR-128a are downstream targets of MLL-AF4 and can individually drive the transition from a pre-leukemic stage to an acute leukemia in an entirely murine Mll-AF4 in vivo model. They are also required to maintain the disease phenotype. Interestingly, miR-130b overexpression led to a mixed/B-cell precursor (BCP)/myeloid leukemia, propagated by the lymphoid-primed multipotent progenitor (LMPP) population, whereas miR-128a overexpression resulted in a pro-B acute lymphoblastic leukemia (ALL), maintained by a highly expanded Il7r+c-Kit+ blast population. Molecular and phenotypic changes induced by these two miRNAs fully recapitulate the human disease, including central nervous system infiltration and activation of an MLL-AF4 expression signature. Furthermore, we identified 2 downstream targets of these miRNAs, NR2F6 and SGMS1, which in extensive validation studies are confirmed as novel tumor suppressors of MLL-AF4+ leukemia. Our integrative approach thus provides a platform for the identification of essential co-drivers of MLL-rearranged leukemias, in which the preleukemia to leukemia transition and lineage plasticity can be dissected and new therapeutic approaches can be tested.

Results of two parallel phase II trials of transplantation of unrelated umbilical cord blood or bone marrow from HLA-haploidentical relatives provided equipoise for direct comparison of these donor sources. Between June 2012 and June 2018, 368 patients aged 18-70 years with chemotherapy-sensitive lymphoma or acute leukemia in remission were randomly assigned to undergo cord blood (n=186) or haploidentical (n=182) transplant. Reduced intensity conditioning comprised total body irradiation with cyclophosphamide and fludarabine for both donor types. Graft-versus-host disease prophylaxis for cord blood transplantation was cyclosporine and mycophenolate mofetil and for haploidentical transplantation, post-transplant cyclophosphamide, tacrolimus and mycophenolate mofetil. The primary endpoint was 2-year progression-free survival. Treatment groups had similar age, sex, self-reported ethnic origin, performance status, disease and disease status at randomization. Two-year progression-free survival was 35% (95% CI, 28-42%) compared to 41% (95% CI, 34-48%) after cord blood and haploidentical transplants, respectively (p=0.41). Pre-specified analysis of secondary endpoints recorded higher 2-year non-relapse mortality after cord blood, 18% (95% CI, 13-24%) compared to haploidentical transplantation, 11% (95% CI, 6-16%), p=0.04. This led to lower 2-year overall survival after cord blood compared to haploidentical transplantation, 46% (95% CI, 38-53) and 57% (95% CI 49-64%), respectively (p=0.04). The trial did not demonstrate a statistically significant difference in the primary endpoint, 2-year progression-free survival, between the donor sources. While both donor sources extend access to reduced intensity transplantation, analyses of secondary endpoints, including overall survival, favor haploidentical bone marrow donors. (Funded by the National Heart, Lung, and Blood Institute-National Cancer Institute; ClinicalTrials.gov number, NCT01597778).

Acute lymphoid leukemia (ALL) is a subtype of acute leukemia which portends a high risk of central nervous system (CNS) infiltration, which decreases overall survival (OS). Conventional cytology (CC) has been the standard for CNS disease assessment, although flow cytometry (FC) has gained space across several centers. In this study, we intend to: i) access the impact of CNS involvement (defined by CC or FC) on OS, event-free survival (EFS) and relapse of ALL patients treated in a public health center; ii) find variables associated with CNS infiltration. Methods This retrospective study encompassed 105 cases of newly diagnosed ALL at Instituto do Cancer de Sao Paulo. Data were collected from Leukemia clinic database, approved by Local Ethics Committee. Variables related to cerebrospinal fluid (CSF) were collected from the first lumbar puncture (LP). Traumatic LP was defined as more than 10 red blood cells/μL. CNS status was assessed through the COG's classification and divided into positive/negative. Intensive intrathecal chemotherapy was given in CNS2 or 3 cases, while cranial irradiation was scheduled for CNS3 patients. Results A total of 105 cases were diagnosed from 2014 to 2020. Median age at diagnosis was 37 years (range, 15-79) with a male majority (58%). Most cases had a B-cell phenotype (76%), followed by T (19%) and ambiguous (5%). Philadelphia chromosome was found in 39%. Eighty-nine percent received corticosteroid at the time of LP with a median time of 7 days. Traumatic LP was reported in 50%. CSF was positive for disease in 15% (16/104) and 26% (19/72),by CC and FC, respectively. Among those with a positive CC, 56% (9/16) had a traumatic LP,but they were not statistically correlated (p = 0.8). Prior chemotherapy was associated to higher traumatic LP rates (56 vs 31%, p = 0.019). CNS1, CNS2 and CNS3 were found in 84%, 14% and 2% of cases, respectively. At the time of PL,44% of patients presented blasts in peripheral blood. By comparing CC and FC, we found one case with CCpos/FCneg whereas 9/19 with FCpos did not have CCpos. Sensitivity and specificity of CC for CNS disease were 53% and 98%. Higher white-blood cell (WBC) counts were found in subjects with positive CC or FC (Mann-Whitney test, p = 0.007 for CC). Also, the blast percentage was relevant for CNS positivity (p = 0.027). Genetic subgroup, age, CD34 expression and phenotype were not correlated with CNS invasion. Most patients received adapted versions of BFM (n = 43), GRAAPH (n = 24) and GRAALL-Elderly (n = 18) regimens. Median OS for the whole cohort was 16.4 months, with a 3y OS of 42.5% (95% CI 33.5-54). For BFM subset, OS and EFS were 53.5% and 37.3%. We did not find correlation between CNS disease with OS or EFS in univariate analysis. Three-year relapse rate was 38.5% (95% CI 29-49) whereas non-relapse mortality (NRM) was 33%. In multivariate analysis, a positive CC increased relapse rate (HR = 2.3 [95% CI 1.1-4.9, p 0.029]), aswell as initial WBC. Among relapses, only one was isolated in CNS and 13 had also concomitant bone marrow involvement. Conclusion Several studies have demonstrated correlation between CNS infiltration and shorter OS in ALL, even though it relies on how these patients are managed and how CNS is assessed upfront. Our data showed that those with a positive CSF cytology had a higher risk of relapse, whereas FC was not able to discriminate this risk. Survival rates are increasing over the last years by the adoption of a stratified risk strategy. CSF contamination did not increase CNS involvement or relapse rates.

Although allogeneic hematopoietic cell transplantation (allo-HCT) is currently the standard curative treatment of acute leukemia, relapse remains unacceptably high. Measurable (minimal) residual disease (MRD) after allo-HCT may be used as a predictor of impending relapse and should be part of routine follow-up for transplanted patients. Patients with MRD may respond to therapies aiming to unleash or enhance the graft-versus-leukemia effect. However, evidence-based recommendations on how to best implement MRD testing and MRD-directed therapy after allo-HCT are lacking. Here, I describe our institutional approach to MRD monitoring for preemptive MRD-triggered intervention, using patient scenarios to illustrate the discussion.

Background: Allogeneic HCT continues to be the optimal consolidation strategy for many patients with AML. Cytogenetic and molecular abnormalities are known to influence post-transplant outcomes. We tested the prognostic ability of a modified (mELN) classification system based on available CIBMTR genetic data, to predict post-transplant outcomes. Methods: Adult patients with a diagnosis of AML in first complete remission (CR1) with available pre-transplant cytogenetic and molecular mutational data, receiving a first allogeneic HCT from 2013-2017, were included. Patients were stratified according to mELN genetic classification in three distinct groups: favorable (Fav), intermediate (IM) and adverse (Adv). Clinical outcomes following HCT were compared among groups after adjusting for significant patient, disease, and transplant-related variables. The primary endpoint was disease free survival (DFS). Secondary endpoints were overall survival (OS), non-relapse mortality (NRM), cumulative incidence of relapse, acute GVHD, and chronic GVHD. Cox proportional hazard models were used to compare endpoints among mELN risk groups, age groups and genetic subsets within the adverse-risk group. Results: Demographic characteristics are summarized in Table 1. 2289 patients (Fav, n=181; IM n=1185; and Adv n=923) met the inclusion criteria. Median follow-up for survivors was 35 months. Importantly, 41% of transplant recipients (n=936) were >60 years, 76% (n=1743) had de novo AML and 48% (n=1111) received a myeloablative conditioning regimen. Univariate analysis (UVA) demonstrated significant differences in 2-year OS (Fav: 67.7%, IM: 64.9% and Adv: 53.9%; p Initial multivariate analysis (MVA) of mELN risk groups indicated that there was no significant difference in clinical outcomes between the Fav and IM risk groups. Thus, these groups were combined for subsequent analyses. Adv risk (vs. Fav/IM) led to significantly worse OS (HR 1.39 [1.24-1.57] p= This mELN classification effectively stratified both younger (60 y/o) patients for OS (Adv vs. Fav/IM HR for 60: 1.44 [1.21-1.72] p60: 1.41 [1.19-1.66] p60: 1.42 [1.15-1.76] p=0.001). NRM was higher for older patients (>60 y/o) in both the Fav/IM (HR 1.40 [1.10-1.78] p=0.007) and Adv-risk cohorts (HR 1.59 [1.18-2.13] p=0.002). Genetic subset comparisons within the adverse-risk group showed that patients carrying monosomy 5, del(5q) or monosomy 7 had inferior 2-year OS (42.6%, p Conclusion: Stratification using mELN criteria resulted in clear prognostic separation of OS, DFS and relapse in this large cohort of AML patients undergoing allogeneic HCT. While Fav and IM groups had similar OS, DFS and relapse rates; patients in the Adv risk group had the highest risk of relapse and inferior DFS/OS. However, the majority of patients in all cohorts had favorable outcomes for HCT in CR1. Our findings confirm the value of a combined genetic prognostic model in the AML HCT setting and justify the use of this stratification system in future HCT trials. Correlation of genetic subtypes with other important transplant variables, such as conditioning intensity and pre-transplant MRD status deserves further evaluation. There remains a subset of Adv-risk patients for which post-transplant outcomes continue to be poor, even when transplanted in CR1. Novel peri-transplant pre-emptive/therapeutic strategies are urgently needed for this high-risk cohort. Disclosures de Lima: Celgene: Research Funding; Pfizer: Other: Personal fees, advisory board, Research Funding; BMS: Other: Personal Fees, advisory board; Incyte: Other: Personal Fees, advisory board; Kadmon: Other: Personal Fees, Advisory board. Komanduri:Kiadis: Consultancy; Takeda: Consultancy; Celgene: Consultancy; Atara: Consultancy, Membership on an entity's Board of Directors or advisory committees; Adaptimmune: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Kite/Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees. Kebriaei:Ziopharm: Other: Research Support; Jazz: Consultancy; Kite: Other: Served on advisory board; Amgen: Other: Research Support; Novartis: Other: Served on advisory board; Pfizer: Other: Served on advisory board. Bhatt:National Marrow Donor Program: Research Funding; Rigel Pharmaceuticals: Other; Jazz: Research Funding; Agios: Other: Personal Fees; Incyte: Other: Personal Fees, Research Funding; Takeda: Other: Personal Fees; Partner Therapeutics: Other: Personal Fees; Pfizer: Other, Research Funding; CSL Behring: Other; Tolero Pharmaceuticals: Research Funding; Oncoceutics: Other: Drug support for a trial; Partnership for health analytic research, LLC: Other: Personal Fees; Omeros: Other: Personal Fees; Abbvie: Other: Personal Fees, Research Funding. Saad:Orcabio: Other: research support; Kadmon: Other: research support; Amgen: Other: research support; Incyte Pharmaceuticals: Other: Personal Fees; Magenta Therapeutics: Other: Personal Fees. Copelan:Amgen: Membership on an entity's Board of Directors or advisory committees. Defilipp:Incyte: Research Funding; Regimmune: Research Funding; Syndax Pharmaceuticals: Consultancy. Nishihori:Karyopharm: Other: Research support to institution; Novartis: Other: Research support to institution. Weisdorf:Incyte: Research Funding; FATE Therapeutics: Consultancy.

Background HLA-haploidentical (haplo) blood or marrow transplantation (BMT) with post-transplantation cyclophosphamide (PTCy) is widely used, but few factors that inform donor selection have been identified. Based on prior observations for HLA-B leader (EW Petersdorf et al. Lancet Haematol 2020), HLA-DRB1 (YL Kasamon et al. BBMT 2010), and HLA-DPB1 (SR Solomon et al. BBMT 2018), we hypothesized that mismatching at individual HLA loci may influence BMT outcomes, but single and additive HLA gene effects have not been evaluated systematically in the context of haploBMT with PTCy. Methods The Center for International Blood and Marrow Transplant Research (CIBMTR) identified 1,434 patients who underwent T-cell-replete haploBMT with PTCy for acute leukemia or myelodysplastic syndrome (MDS) between 2008-2017. Multivariable models assessed transplant outcomes associated with 3 HLA-factors: (1) B-leader dimorphism (MM, MT, TT) matching; (2) HLA-DRB1 mismatching in the graft-versus-host (GVH) direction; and (3) nonpermissive HLA-DPB1 mismatching in the GVH direction using the T-cell epitope-3 model, which classifies HLA-DPB1 mismatches into permissive or non-permissive. All final models contained the HLA factors and adjusted for other significant clinical covariates at p Results Diagnoses were 58% AML, 23% ALL, 19% MDS. 22% of AML patients were in advanced disease stage (relevant analyses were stratified for disease stage for both acute leukemia and MDS). Median recipient age was 54 (range 1-78) years. Median follow up among survivors was 12 (range 2-119) months. Marrow was the graft source in 43% of recipients. Myeloablative conditioning was used in 45% of recipients. Fifty percent of recipients had hematopoietic cell transplantation-comorbidity index (HCT-CI) scores of ≥3. HLA-DP typing was missing in 52% of cases and thus all models had a "missing" category for HLA-DP. Mismatching in the GVH direction at HLA-A, HLA-C, or HLA-DQ was not associated with study outcomes [overall survival (OS), disease-free survival (DFS), relapse, nonrelapse mortality (NRM), or grade II-IV acute, grade III-IV acute, or chronic graft-versus-host disease (gr2-4a or cGVHD)]. When compared to leader-matched patients, HLA-B leader-mismatching was associated with worse OS and DFS (hazard ratio [HR] 1.25 [95% CI, 1.09 to 1.44]; P=.002, and HR 1.18 [95% CI, 1.03 to 1.34]; P=.01, respectively), and higher risk of NRM (HR 1.38 [95% CI, 1.10 to 1.74]; P=.005), but was not associated gr2-4a or cGVHD, or relapse. In contrast, when compared to matching at HLA-DRB1, the presence of any GVH direction mismatch at HLA-DRB1 was associated with improved DFS (HR 0.80 [95% CI, 0.68 to 0.94]; P=.007) and lower risk of relapse (HR 0.69 [95% CI, 0.56 to 0.86]; P=.0008), but with no effect on OS, gr2-4a or cGVHD, or NRM. Similarly, any nonpermissive GVH mismatching at HLA-DPB1 was also associated with improved DFS (HR 0.72 [95% CI, 0.55-0.94], p=.015) and OS (HR 0.59 [95% CI, 0.43-0.82], p=.002), with a tendency towards lower relapse (HR 0.75 [95% CI, 0.54-1.05], p=.09), but with no effect on gr2-4a or cGVHD, or NRM. When combining the effects of leader matching at HLA-B and mismatching at HLA-DRB1 there was an additive improvement in both DFS and OS (Figure 1 A and B) with significantly lower NRM (p=0.03) and relapse (p=0.008) when compared to other groups. Within this unselected large cohort, favorable haplo donors based on B-leader matching and HLA-DRB1 mismatching were used for 48.5% of recipients and had improved DFS (HR 0.68 [95% CI, 0.52 to 0.88], p=.004) when compared to B-leader mismatched and HLA-DRB1 matched pairs, suggesting that with intentional selection of donors based on these factors, even more could receive a favorable combination. Conclusion HLA-B leader mismatching is a risk factor for NRM and worse OS and DFS, whereas either HLA-DRB1 or nonpermissive HLA-DPB1 mismatch is associated with reduced relapse and improved DFS, after haploBMT with PTCy. PTCy dissociates the graft-versus-leukemia effect of HLA-DRB1 and nonpermissive HLA-DPB1 mismatching from GVHD. The best outcomes after haploBMT with PTCy are seen when a donor is HLA-B leader matched and HLA-DRB1 mismatched. When there is more than one potential haplo donor for an acute leukemia or MDS patient, selection based on HLA considerations may improve DFS and OS. Figure Disclosures Shaw: Orca Bio: Consultancy. Lee:Takeda: Research Funding; AstraZeneca: Research Funding; Novartis: Research Funding; Incyte: Consultancy, Research Funding; Syndax: Research Funding; Pfizer: Consultancy, Research Funding; Amgen: Research Funding; Kadmon: Research Funding.

Post transplant cyclophosphamide (PTCy) graft-versus-host disease (GVHD) prophylaxis has allowed haploidentical (Haplo) transplantation to be performed with results similar to that after matched unrelated donor (MUD) transplantation with traditional prophylaxis. The relative value of transplantation with MUD versus Haplo donors when both groups receive PTCy/calcineurin inhibitor/mycophenolate containing GVHD prophylaxis is not known. We compared outcomes after 2036 Haplo and 284 MUD transplantations with PTCy GVHD prophylaxis for acute leukemia or myelodysplastic syndrome in adults between 2011 and 2018. Cox regression models were built to compare outcomes between donor types. Recipients of myeloablative and reduced intensity regimens were analyzed separately. Among recipients of reduced intensity regimens, 2-year graft failure (3% versus 11%), acute grade II-IV GVHD (HR 0.70, p=0.022), acute grade III-IV GVHD (HR 0.41, p=0.016) and non-relapse mortality (HR 0.43, p=0.0008) were lower after MUD compared to Haplo transplantation. Consequently, disease-free (HR 0.74, p=0.008; 55% versus 41%) and overall survival (HR 0.65, p=0.001; 67% versus 54%) were higher after MUD compared to Haplo transplants. Among recipients of myeloablative regimens, day-100 platelet recovery (95% versus 88%) was higher and grade III-IV acute (HR 0.39, p=0.07) and chronic GVHD (HR 0.66, p=0.05) were lower after MUD compared to Haplo transplantation. There were no differences in graft failure, relapse, non-relapse mortality, disease-free and overall survival between donor types with myeloablative conditioning regimens. These data extend and confirm the importance of donor-recipient HLA matching for allogeneic transplantation. A MUD is the preferred donor, especially for transplantations with reduced intensity conditioning regimens.

Mixed-phenotype acute leukemia is a rare subtype of leukemia in which both myeloid and lymphoid markers are co-expressed on the same malignant cells. The pathogenesis is largely unknown, and the treatment is challenging. We previously reported the specific association of the recurrent t(8;12)(q13;p13) chromosomal translocation that creates the ETV6-NCOA2 fusion with T/myeloid leukemias. Here we report that ETV6-NCOA2 initiates T/myeloid leukemia in preclinical models; ectopic expression of ETV6-NCOA2 in mouse bone marrow hematopoietic progenitors induced T/myeloid lymphoma accompanied by spontaneous Notch1-activating mutations. Similarly, cotransduction of human cord blood CD34+ progenitors with ETV6-NCOA2 and a nontransforming NOTCH1 mutant induced T/myeloid leukemia in immunodeficient mice; the immunophenotype and gene expression pattern were similar to those of patient-derived ETV6-NCOA2 leukemias. Mechanistically, we show that ETV6-NCOA2 forms a transcriptional complex with ETV6 and the histone acetyltransferase p300, leading to derepression of ETV6 target genes. The expression of ETV6-NCOA2 in human and mouse nonthymic hematopoietic progenitor cells induces transcriptional dysregulation, which activates a lymphoid program while failing to repress the expression of myeloid genes such as CSF1 and MEF2C. The ETV6-NCOA2 induced arrest at an early immature T-cell developmental stage. The additional acquisition of activating NOTCH1 mutations transforms the early immature ETV6-NCOA2 cells into T/myeloid leukemias. Here, we describe the first preclinical model to depict the initiation of T/myeloid leukemia by a specific somatic genetic aberration.

Introduction The COVID-19 pandemic has affected the entire world. Health systems have been affected in such a way that patients with diseases other than COVID-19 have suffered serious consequences. In Latin America, the disease has emerged in a fragile system with more disparities, making our patients more vulnerable. Acute leukemia patients have a high risk of severe COVID-19 disease. Various expert recommendations have emerged with the aim of minimizing the risk of COVID-19 without affecting leukemia-related outcomes. However, multiple logistical issues tangentially associated with the pandemic have also appeared, potentially limiting the quality of management of these patients. The objective of this study was to register treatment modifications associated with the COVID-19 pandemic and its short-term consequences in Latin American countries. Methods We included patients older than 14 years, from 14 centers of 4 Latin American countries (Mexico, Peru, Guatemala and Panama), with the diagnosis of acute leukemia, who were on active treatment since the first case of COVID-19 was documented in each country. We documented their baseline characteristics and followed the patients prospectively until July 15, were data-cutoff for this pre-planned analysis was performed. The primary outcome was the incidence of COVID-19 disease and its complications. Secondary outcomes included treatment and consult modifications, and cause of death during the study period. Logistic regression was performed to determine factors associated with COVID-19 and all-cause mortality. Results We recorded the information of 635 patients: 58.1% Ph-negative ALL, 25.7% AML, 9% APL and 7.2% Ph+ALL. The median age was 35 years (14-90 years); 58.8% were consideredf high-risk patients. The majority were on CR (68.3%) receiving consolidation or maintenance therapy, while 14.5% were newly diagnosed and 17.2% with relapsed/refractory disease. The majority (91.8%) were treated in centers that were also receiving COVID-19 patients, 40.2% in centers were patients could not be electively hospitalized for leukemia treatment because of the COVID-19 pandemic. The COVID-pandemic led to treatment-modifications in 40.8% of the cases. Reasons for modifications were associated with logistical issues (22.4%), medical decisions (15.1%) or patient choice (3.3%). The most frequent modification was chemotherapy delay (17.3%) followed by regimen modification (13.4%) and dose-reductions (10.1%). (Figure 1) 83 patients (13.1%) developed COVID-19 disease, the majority mild-moderate disease (54.2%), 27.7% severe disease and 18.1% critically ill; 27.7% required mechanical ventilation and 37.7% died from COVID-19 disease, representing 4.9% of the entire cohort. We identify as risk factors for COVID-19 disease the presence of active leukemia (newly diagnosed or relapsed) (OR 3.46 [95% CI: 2.16-5.5], p On the other hand, 16.7% of patients died during period analyzed due to leukemia (57.5%), COVID-19 (29.2%) or treatment related-mortality (13.2%). Independent factors associated with mortality were AML vs. ALL (OR 1.89 [95% CI: 1.12-3.18], p=0.016), relapsed-refractory disease (OR 8.34 [95% CI: 4.83-14.41], p Discussion/Conclusions The COVID-19 pandemic led to significant modifications in the standard of care treatment of patients with acute leukemia. The incidence of COVID-19 disease in acute leukemia patients was considerable and more than a third of the patients with acute leukemia and COVID-19 disease died. Despite a short-follow up, 16.7% of the patients died and leukemia-related deaths were the most frequent. In low- and middle-income countries with fragile health systems, the collateral damage for patients with acute leukemia may be just as important as the direct consequences of COVID-19. Disclosures Alvarado: Roche: Speakers Bureau; Novartis: Speakers Bureau; Amgen: Speakers Bureau; Celgene: Speakers Bureau; Alexion: Speakers Bureau. De la Peña-Celaya:Amgen: Speakers Bureau; Janssen: Speakers Bureau; Novartis: Speakers Bureau. Perez:Roche: Speakers Bureau; Celgene: Speakers Bureau; Novartis: Speakers Bureau. Gomez-Almaguer:Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene/BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AstraZeneca: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

TO THE EDITOR: Marital status is known to affect timely diagnosis, definitive treatment, and survival in solid cancers.[1][1] In contrast, inpatient management of hematological malignancies including acute leukemia has been suggested to reduce importance of adherence and home support when compared

TO THE EDITOR: Mixed phenotype acute leukemia (MPAL) represents a heterogeneous group of leukemias accounting for 2% to 5% of all newly diagnosed acute leukemias.[1][1][⇓][2][⇓][3][⇓][4]-[5][5] Although most cases of acute leukemia display the differentiation pattern of a single lineage

Pinometostat (EPZ-5676) is a first-in-class small-molecule inhibitor of the histone methyltransferase disrupter of telomeric silencing 1-like (DOT1L). In this phase 1 study, pinometostat was evaluated for safety and efficacy in adult patients with advanced acute leukemias, particularly those involving mixed lineage leukemia (MLL) gene rearrangements (MLL-r) resulting from 11q23 translocations. Fifty-one patients were enrolled into 6 dose-escalation cohorts (n = 26) and 2 expansion cohorts (n = 25) at pinometostat doses of 54 and 90 mg/m(2) per day by continuous intravenous infusion in 28-day cycles. Because a maximum tolerated dose was not established in the dose-escalation phase, the expansion doses were selected based on safety and clinical response data combined with pharmacodynamic evidence of reduction in H3K79 methylation during dose escalation. Across all dose levels, plasma pinometostat concentrations increased in an approximately dose-proportional fashion, reaching an apparent steady-state by 4-8 hours after infusion, and rapidly decreased following treatment cessation. The most common adverse events, of any cause, were fatigue (39%), nausea (39%), constipation (35%), and febrile neutropenia (35%). Overall, 2 patients, both with t(11;19), experienced complete remission at 54 mg/m(2) per day by continuous intravenous infusion, demonstrating proof of concept for delivering clinically meaningful responses through targeting DOT1L using the single agent pinometostat in MLL-r leukemia patients. Administration of pinometostat was generally safe, with the maximum tolerated dose not being reached, although efficacy as a single agent was modest. This study demonstrates the therapeutic potential for targeting DOT1L in MLL-r leukemia and lays the groundwork for future combination approaches in this patient population. This clinical trial is registered at www.clinicaltrials.gov as NCT01684150.

Introduction: In Ontario, Canada, acute leukemia (AL) care is delivered to patients at three levels of specialized service provider sites: 1) Transplant and AL Service Sites, providing all services, including stem cell transplant, chimeric antigen receptor T-cell therapy, and high intensity chemotherapy (e.g., induction); 2) AL Service Sites, providing a subset of services, including high intensity chemotherapy; and 3) AL Shared-Care Partner Centres providing consolidation and less intense chemotherapy, supportive care and follow-up. Sites and healthcare are government funded, through a single-payer system. In 2017, Cancer Care Ontario (now a part of Ontario Health), the government agency managing the delivery of cancer services, released the Acute Leukemia Provincial Plan to provide a vision for the delivery of timely access to high-quality, coordinated services for patients with AL in Ontario. Working with the 14 Regional Cancer Programs in the province, a 10-year plan for expansion to meet the expected demand was developed. Subsequently, provincial stakeholders, including clinical and administrative leaders from across the Province identified a need to develop guidance to ensure all provider sites (existing, new and in development) have the same infrastructure, expertise, quality management, and policies and procedures necessary to deliver high quality care for this specialized, high-need patient population. Methods: The AL Specifications Working Group (WG) was formed to lead the development of organizational guidance. A systematic literature review and jurisdictional scan using key search terms identified existing standards and recommendations. Recommendations were extracted from relevant texts and reviewed. Through informal consensus, the WG endorsed recommendations "as is", adapted recommendations to meet the needs of Ontario, or rejected recommendations deemed not relevant. Where recommendations were lacking, but thought to be needed, new recommendations were written. Results: The literature search identified 2,651 potential texts, of which 17 texts were deemed relevant (Figure 1) and 642 recommendations were extracted. After three rounds of review by the WG members, the Cancer Care Ontario team, and targeted external stakeholders, 229 recommendations were approved (Figure 2). Recommendations were written for each level of service provider using the terminology shall (must be complied with), should (recommended or advised) and may (permissive). Recommendations were grouped into 9 sections: 1) 15 General recommendations related to infrastructure, patient volumes and service provider availability, 2) 25 Clinical Unit recommendations related to inpatient and outpatient structure and services, 3) 99 Personnel recommendations related to roles, responsibilities and training of the multidisciplinary clinical team, 4) 43 Quality Management program and plan recommendations, 5) 22 Policies and Procedures recommendations, 6) 9 Patient Care recommendations, 7) 2 Clinical Research recommendations, 8) 9 Data Management recommendations, and 9) 5 Laboratory Services recommendations related to testing access and turnaround times. In June 2021, the recommendations were shared with impacted stakeholder groups, including health care providers and hospital administration through the release of the Organizational Requirements for Acute Leukemia Service Providers in Ontario: Recommendations Report 2021 (https://www.cancercareontario.ca/en/guidelines-advice/types-of-cancer/69431). The full list of recommendations is available in the Report. Conclusions: The development of these recommendations will serve as a framework for improvement and expansion at existing and new service sites, with the aim of ensuring AL service providers throughout Ontario have the same necessary organizational and operational requirements in place. A gap assessment will inform next steps for focused efforts to provide high quality care which will meet the needs of patients into the future. Figure 1 Figure 1. Disclosures Buckstein: Takeda: Research Funding; TAIHO: Research Funding; Otsuka: Research Funding; Celgene: Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees. Sabloff: BMS: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; TaiHo: Membership on an entity's Board of Directors or advisory committees; Jaxx: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; ROCHE: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees. Yee: Onconova: Research Funding; Astex: Membership on an entity's Board of Directors or advisory committees, Research Funding; Forma Therapeutics: Research Funding; Geron: Research Funding; F. Hoffmann La Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Tolero: Research Funding; Janssen: Research Funding; MedImmune: Research Funding; Jazz: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees; TaiHo: Membership on an entity's Board of Directors or advisory committees; Shattuck Labs: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Paladin: Membership on an entity's Board of Directors or advisory committees; Otsuka: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb/Celgene: Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria; Genentech: Research Funding.

Background: More and more cases of leukemia with heart injury have been reported, mostly due to tumor cell infiltration, endothelial injury and high viscosity of leukemia cells in circulating blood. To evaluate whether the newly diagnosed acute leukemia patients have suffered heart-related injuries, and determine the possible related factors, we carried out this study. Methods: From January 2015 to August 2019, we retrospectively selected 408 patients from the Department of Hematology and Cardiology, Zhongnan Hospital of Wuhan University. There were 200 newly diagnosed acute leukemia patients (including 15 acute hyperleukocytic leukemia patients), 105 patients without cancer and no known heart disease, and 103 cases of confirmed coronary heart disease. We collected the basic information of patients, echocardiographic data and myocardial enzyme results. We also followed up all newly diagnosed acute leukemia patients for prognostic analysis. All data were logarithmically transformed to make the data normally distributed. Normally distributed samples were compared using independent sample t-tests, Mann-Whitney U rank sum test was used for non-normally distributed samples and qualitative data was using chi-square test. The log-rank test was used to perform univariate analysis through Kaplan-Meier curves, and meaningful values were screened for multivariate COX regression analysis. The statistical analysis was performed with the SPSS software. Results: Compared with the control group, patients with newly diagnosed acute leukemia had already experienced some heart-related injuries. The average values of myocardial enzyme indexes such as CKMB,LDH,hs-cTnI,BNP and echocardiography indexes such as LV,EDV,ESV,SV,EF were all significantly different. But the degree of heart damage was lower than that of the coronary heart disease group. Compared with hyperleukocytic leukemia, non-hyperleukocytic leukemia had suffered more serious heart damage, especially myocardial enzyme indexes such as HBDH and LDH were significantly increased. Analyze the relationship between age, gender, cardiovascular risk factors (hypertension, diabetes and smoking history), myocardial enzyme indexes, echocardiography indexes and survival, to screen for risk factors related to the prognosis of the disease. Variables with statistically significant effect measurement values include age (p Classification based on the clinical diagnosis of echocardiography in newly diagnosed acute leukemia patients, significant differences in myocardial enzymes and related indicators of echocardiography were included for ROC plots. The 3 indicators with the highest results for the area under the curve (AUC) from ROC plots were LV, EDV and HBDH, AUC were 0.721,0.619 and 0.615, respectively. This result revealed that the best predictor of leukemia myocardial damage was LV. It showed the predict ability of LV (AUC = 0.721, 95%CI = 0.643-0.799, P Conclusions： According to our research, we have confirmed that the cardiac function of newly diagnosed acute leukemia patients is significantly different from that of patients without leukemia, and these differences will have an impact on the prognosis of patients. Among them, the best predictor of leukemia heart damage is LV, and EF is an independent risk factor for the prognosis of leukemia patients. In addition, newly diagnosed acute leukemia patients are more likely to have an increase in left ventricular diameter and a significant decrease in ejection fraction. Further research is needed to explore the specific mechanism in the future. Disclosures No relevant conflicts of interest to declare.

Hyperleukocytosis, most commonly defined as a white blood cell (WBC) count greater than 100,000/μL, is an emergency in acute leukemia, possibly resulting in life-threatening microvascular obstruction, or leukostasis, leading to neurologic (CNS hemorrhage, thrombosis) or pulmonary (respiratory distress, hypoxia) complications. The underlying mechanisms remain poorly understood and are canonically attributed to blood hyperviscosity secondary to high WBC count and abnormal biophysical properties of leukemia cells themselves (leukemia immunophenotype, increased cell size, adhesion, and stiffness). Leukapheresis is a commonly-used therapy for rapid cytoreduction in symptomatic patients, but the procedure carries risk and existing guidelines are supported by scant evidence. Interestingly, despite hematocrit(Hct)/hemoglobin(Hgb) levels being major drivers of blood viscosity due to the high prevalence of circulating red cells (RBCs), how Hct/Hgb mediates hyperviscosity in acute leukemia is unknown. This is clinically important as Hct/Hgb often decrease as leukemic cell counts rise, and acute leukemia patients with anemia are often transfused. While sickle cell disease guidelines advise using a target post transfusion Hct of 30% to minimize iatrogenic hyperviscosity and its morbid complications, no guidelines have been established for acute leukemia. As such, can RBC transfusion actually increase leukostasis risk in acute leukemia? To explore this question requires new biophysical tools as the complexity of blood viscosity increases substantially at the microvascular level as the physical properties of the cells themselves become the major determinants of resistance to blood flow. To that end, we developed "microvasculature-on-a-chip" devices that recapitulate microvascular biophysical and hemodynamic conditions to investigate how the differing presentations of acute leukemia and transfusion support affect the effective blood viscosity at the microvascular level to cause "in vitro leukostasis." A multiple-vessel "multiplex" microfluidic device that operates at the appropriate size scale and mimics the microvascular geometry was designed to enable assessing accurate biophysical measurements of blood hyperviscosity. The devices were microfabricated using standard polydimethylsiloxane-based photolithography (Figure 1). Acute B-cell lymphoblastic (B-ALL, 697), acute T-cell lymphoblastic (T-ALL, Jurkat) and acute myelocytic (AML, HL60) leukemia cell lines were maintained via standard cell culture conditions. Patient samples were obtained through our institution's IRB. RBCs from healthy donors were isolated and mixed with leukemia cells to achieve target Hct/Hgb and WBC levels. Various physiologic leukemia "mixtures" were then perfused under physiologic microcirculatory flow conditions through the microvascular device and microchannels occlusion was tracked via videomicroscopy (Figure 2). Using a standard least squares multivariable linear regression with first and second order effects, microchannel size, Hct/Hgb, WBC count and leukemia cell type all showed statically significant effect on in vitro leukostasis, or microchannel occlusion over time, (all p values < 0.03) (Figure 3). Overall, severe anemia appears to be protective against in vitro leukostasis and there appears to be Hct/Hgb thresholds above which in vitro leukostasis becomes more prevalent, though this is different for B-ALL versus T-ALL. This is in contrast to AML, where severe anemia does not appear to offer protection against in vitro leukostasis as occlusion was appreciated at all Hct/Hgb levels. These data suggest when determining risk for leukostasis, WBC count and leukemia immunophenotype should not be the sole determinants. Here we show Hct/Hgb levels affect microvascular blood viscosity and risk for microvascular occlusion. These results may impact decisions regarding RBC transfusions and possibly initiation of leukapheresis in asymptomatic patients. Having a model to assess risk associated with RBC transfusions and informing clinicians when a patient might become at risk for leukostasis can have a significant impact on their clinical outcome, morbidity and mortality. Ongoing studies incorporating patient lymphoid and myeloid leukemia cells are needed to support this cell line data. Figure 1 Figure 1. Disclosures Kemp: Parthenon Therapeutics: Membership on an entity's Board of Directors or advisory committees. Lam: Sanguina, Inc.: Current holder of individual stocks in a privately-held company.

Background: Post-transplant cyclophosphamide (PTCy) has been shown to significantly reduce transplant related mortality (TRM) post hematopoietic stem cell transplantation (HSCT) and is being increasingly used for acute myelogenous leukemia (AML) patients (pts) undergoing HSCT including from unrelated donors (UD). These publications mainly include pts transplanted in first complete remission (CR1). We recently reported outcome in 1879 AML pts transplanted in second CR (CR2) with conventional graft-versus-host disease (GVHD) prophylaxis (Leukemia 2020). Results may differ in transplantation with PTCy as GVHD prophylaxis, eliminating proliferating alloreactive T cells, and upregulating T regulatory cells while suppressing host natural killer (NK) cells immediately after transplantation, changing the biology and characteristics of the transplantation. Methods: The study aim was to assess outcome of adult AML pts, aged ≥18 years in CR2 undergoing HSCT from a 9-10/10 UD with PTCy, in 2010-2019.Statistics included multivariate analysis (MVA) adjusting for potential confounding factors was performed using a Cox's proportional-hazards regression model for main outcomes. Results: In total, 127 pts were included. Median follow-up was 19.2 (95% CI, 14.7-28) months (mos). Median age was 45.5 (range, 18.2-71.3) years. 54.3% were male. Cytogenetic risk (MRC classification) was favorable, intermediate, and adverse in 15.7%, 55.9%, and 5.5% of pts, respectively (missing data-22.8percentage) Median year of transplantation was 2017. Time from diagnosis to transplantation was 20.4 (range, 4.1-182.4) months. All pts were at CR2 at time of transplantation. Donors were 10/10 and 9/10 UD in 60.6% and 39.4% of pts, respectively. 77.8% and 47.2% of the pts and donors, respectively, were cytomegalovirus (CMV) seropositive. Conditioning was myeloablative in 50.4% and reduced intensity in 49.6%. The most frequent (61.4%) conditioning consisted of busulfan and fludarabine. All pts received PTCy as anti GVHD prophylaxis in combination with immunosuppression, which was cyclosporine A /mycophenolate mofetil (MMF) in 21.3% and MMF/tacrolimus in 23.6%. 33.9% of the pts received In vivo T-cell depletion. Grafts were peripheral blood in 93.7% and bone marrow in 6.3% of transplants. Karnofsky performance score (KPS) was > 90 in 71.2% and the hematopoietic cell transplantation-specific comorbidity index (HCT-CI) was zero in 61.5% of the pts. Engraftment was achieved by 97.6% with day (d) 60 absolute neutrophil count (ANC) > 0.5 x 10 9/L in 96.8%, and d 180 incidence of acute (a) GVHD II-IV and III-IV was 26.2% and 9.2%, respectively. The 2-year total and extensive chronic (c) GVHD was 34.3% and 13.8 %, respectively. The 2-year non-relapse mortality (NRM) was 17.2%. The 2-year relapse incidence (RI) was 21.1%. RI was the main cause of death in 41% of pts who died, followed by infections (23.1%) and GVHD (20.5%). The 2-year leukemia-free survival (LFS), overall survival (OS) and GVHD-free, relapse-free survival (GRFS) was 61.7%, 65.2% and 49.3%, respectively (Figure). In MVA time from diagnosis to transplant was significant prognostic factor for RI, LFS, OS and GRFS hazard ratio (HR) =0.19 (95% CI 0.07-0.48, p Conclusions: Outcome of AML pts undergoing HSCT from a 9-10/10 MUD in CR with PTCy as GVHD prophylaxis, are similar to previous reports using conventional GVHD prophylaxis with 26% of pts developing aGVHD ,34% cGVHD and NRM of 17%. These results are also similar to those we previously observed in pts undergoing HSCT from UD with PTCy while in CR1. Figure 1 Figure 1. Disclosures Labopin: Jazz Pharmaceuticals: Honoraria. Kulagin: X4 Pharmaceuticals, Alexion, Apellis, Biocad: Research Funding; Novartis, Generium, Sanofi, Roche, Johnson & Johnson, Pfizer: Speakers Bureau. Blaise: Jazz Pharmaceuticals: Honoraria. Yakoub-Agha: Jazz Pharmaceuticals: Honoraria. Ciceri: IRCCS Ospedale San Raffaele: Current Employment. Mohty: Sanofi: Honoraria, Research Funding; Pfizer: Honoraria; Novartis: Honoraria; Takeda: Honoraria; Jazz: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Gilead: Honoraria; Celgene: Honoraria, Research Funding; Bristol Myers Squibb: Honoraria; Astellas: Honoraria; Amgen: Honoraria; Adaptive Biotechnologies: Honoraria.

Introduction Anemia is a common complication of hematological chemotherapy for acute leukemia and following hematopoietic stem cell transplantation (HSCT). Exposure to allogeneic blood transfusions has been associated with unfavorable outcome in several studies in a non-surgical settings. Retrospective studies in hematological intensive unit have suggested that single red blood cell (RBC) unit transfusion policy may reduce the number of RBC used in comparison with a classical double RBC unit transfusion policy, without clinical impact. The aim of the study was to demonstrate that single RBC transfusion was non inferior to the standard double RBC transfusion arm in terms of severe complication or mortality for inpatient with hematological malignancies. Key secondary endpoint, was the comparison of the numbers of RBC units transfused in each arm. Method In a phase 3 multicenter randomized trial, 245 adults' patients with acute leukemia requiring intensive chemotherapy or patients receiving autologous or allogeneic HSCT were randomly assigned (1:1) to receive either single RBC unit (1 RBC arm, n=125) per transfusion or double RBC (2 RBC arm, n=120) per transfusion when hemoglobin level was below 8g/dL. The primary composite endpoint was the percentage of patients who developed a grade ≥3 complications defined as stroke, transient ischemic attack, acute coronary syndrome, heart failure, elevated troponin level, intensive care unit transfer, death, new pulmonary infiltrates, and/or transfusion-related infections during hospital stays. The secondary endpoint was the number of red cell units transfused per patient per hospital stay. The primary endpoint was compared between groups by non-inferiority analysis for the proportion risk difference using Farrington-Manning method with a non-inferiority margin of 0.1, in ITT dataset. Results Hematological disease were as followed: AML (59%), ALL (13.1%), Lymphoma (16.4%), others (11.5%). The median age was 55 years. Baseline characteristics were well balanced between the 2 arms (Figure 1A). A total of 981 and 592 transfusions have been necessary in the 1 RBC arm and 2 RBC arm, respectively. The median of RBC unit per transfusion was 1(1-1) and 2(2-2) in the 1 RBC and 2 RBC arm, respectively. The mean pre transfusion hemoglobin level was 7.49 +/- 0.83 g/dL in the 1 RBC arm and 7.46 +/- 0.67 g/dL in the 2 RBC arm (p=0.275). Hemoglobin level at discharge was 9.35 +/-1.14 g/dL in the 1 RBC arm and 9.58 +/-1.13 g/dL in the 2 RBC arm (p=0.118). The median (IQR) of red-cell units transfused per patient was 7 (4-12) in the single arm and 8 (4-12) in the double arm (p=0.65). The median number of platelet transfusion event was 7 (3.5-11.5) in the 1 RBC arm and 7 (3-13) in the 2 RBC arm (p=0.69). The median (IQR) number of red cell unit transfused per cycle and per day was 7 (3-9) and 0.28 (0.17-0.37) in the 1RBC arm and 6 (4-10) and 0.27 (0.20-0.38) in the 2 RBC arm (p=0.61 and p=0.47). The predefined non-inferiority criteria was achieved with 28 patients developing a serious complication in the 1 CGR arm (22.4%) and 28 patients in the 2 RBC arm (23.3%) (Risk difference 0.009; 95% Confidence interval [-0.0791- 0.0978] (Figure 1B). Conclusion: Single RBC transfusion policy is non inferior to double RBC transfusion policy in hematological intensive care unit for patient receiving a bone marrow transplant or intensive chemotherapy. Single RBC unit transfusion can be used safely in daily clinical practice. The single RBC transfusion policy does not reduce the number of RBC transfusion. Figure 1 Figure 1. Disclosures Jardin: Genexpath: Patents & Royalties: The author is a potential inventor on a patent application for the LymphoSign, which has been licensed for by Genexpath Patents & Royalties. .

Background: Patients with hematologic malignancies relapsing after allogeneic blood or marrow transplantation (BMT) have limited response to conventional salvage therapies with an expected 1-year overall survival (OS) of Methods: Lymphocytes obtained from the BMT donor were manufactured to target TAAs; WT1, PRAME and survivin, which are over-expressed and immunogenic in most hematologic malignancies. Patients received TAA-T infusions at doses of 0.5-4x10 7/m 2. Patients were evaluated for acute infusion-related toxicity, cytokine release syndrome (CRS), neurotoxicity, GVHD and monitored for clinical response post-infusion. T-cell receptor sequencing was conducted on the TAA-T product and the recipients' peripheral blood prior to and post-infusion to monitor persistence and expansion of the product. Results: Twenty-three BMT recipients with relapsed/refractory (n=11) and/or high-risk (n=12) acute myeloid leukemia (n=20) and acute lymphoblastic leukemia (n=3) were infused post-transplant. No patient developed CRS or neurotoxicity, and only one patient developed grade III GVHD. Of the patients who relapsed post-BMT and received bridging therapy, the majority (n=9/11) achieved complete hematologic remission before receiving TAA-T. Relapsed patients exhibited a 1-year OS of 36% and 1-year leukemia-free survival of 27.3% post-TAA-T (Figure 1A and B). The poorest prognosis patients (relapsed less than 6 months after transplant) exhibited a 1-year OS of 42.8% post-relapse (n=7) (Figure 1C). Median survival was not reached for high-risk patients who received pre-emptive TAA-T post-transplant (n=12) with eight of the nine (88.9%) evaluable patients at 1-year post-infusion remaining alive (Figure 1B). Of those, five (62.5%) were alive and in continued remission at the time of submission. Evaluation of unique T-cell receptor clonotypes (present in the product but not the recipient prior to infusion) demonstrated expansion and persistence in patients up to 1-year post-infusion (Figure 1D). Conclusions: Although as a Phase-I study, concomitant anti-leukemic therapy was allowed, TAA-T cell therapy was shown to be safe and well-tolerated with sustained remissions observed in high-risk and relapsed patients. Moreover, adoptively transferred TAA-T expanded in vivo as detected by T-cell receptor V-beta (TCRVb) sequencing persisted up to at least 1-year post-infusion (Figure 1D). (ClinicalTrials.gov numbers, NCT002203902) Figure 1 Figure 1. Disclosures Cruz: Mana Therapeutics: Consultancy, Current holder of individual stocks in a privately-held company, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Catamaran Bio: Consultancy, Patents & Royalties, Research Funding. Hanley: Mana Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Cellevolve: Consultancy; Maxcyte: Membership on an entity's Board of Directors or advisory committees. Bollard: SOBI: Honoraria, Membership on an entity's Board of Directors or advisory committees; Cabaletta Bio: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Catamaran Bio: Membership on an entity's Board of Directors or advisory committees; Cellectis: Honoraria, Membership on an entity's Board of Directors or advisory committees; ROCHE: Consultancy, Honoraria; Repertoire Immune Medicines: Current equity holder in publicly-traded company; Neximmune: Current equity holder in publicly-traded company; Mana Therapeutics: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties.

Chronic neutrophilic leukemia (CNL) is a rare myeloproliferative neoplasm (MPN) characterized by peripheral blood leukocytosis consisting primarily of segmented neutrophils and band forms, hypercellular bone marrow with granulocytosis, hepatosplenomegaly, and the presence of activating colony-stimulating factor 3 receptor (CSF3R) mutations. Blast transformation occurs frequently in patients with acquired CNL, with a median overall survival of 21 months from diagnosis. Typically, CSF3R mutations in CNL are thought to be somatic; however, we and others have reported rare cases of germline activating CSF3R mutations producing a familial CNL. Here we report the clinical course of a patient with CNL along with definitive evidence of inherited germline transmission of the CSF3R T618I mutation. Spanning four generations, with affected family members of ages 1.6 - 51 years, this is the largest reported pedigree of a family with familial CNL (Figure 1A). The proband is a 49-year-old female referred to our center with a history of lifelong leukocytosis and leukocyte count of 115.1 x 10 9/L with 75% granulocytes and 11% bands, platelet count of 341 x 10 9/L, and hemoglobin of 12.5 g/dL with hematocrit of 38%. The family history was also remarkable for leukocytosis. Prior therapies for the proband included imatinib, splenectomy, and hydroxyurea. Additional testing by our center revealed a T618I CSFR3 mutation, and the absence of mutations in ASXL1 and SETBP1 or a BCR-ABL translocation. Treatment with ruxolitinib resulted in improvement of her leukocyte count to 43.0 x 10 9/L with 73% granulocytes, and reduction in her alkaline phosphatase from 732 IU/L to 296 IU/L. There has been no evidence of gain of any known deleterious somatic mutations that frequently co-occur with somatic T618I CSF3R mutations in CNL in the patient to date. Germline analysis of genomic DNA extracted from cultured mesenchymal stromal cells from the proband and Sanger sequencing demonstrated a heterozygous T618I mutation. Mutational analysis of the proband's family members confirmed a heterozygous CSF3R T618I mutation in all living affected family members, while all unaffected family members tested were homozygous wild type. There has been no evidence of leukemic transformation in any affected family members to date. Mutational analysis was not feasible on the proband's deceased mother and brother with a putative CNL diagnosis due to lack of DNA samples; however, there was no evidence of transformation to acute leukemia in either of the two deceased family members. Because CSF3R can produce anti-apoptotic signaling, we hypothesized that autoactivating T618I mutations could prolong neutrophil survival. Polymorphonuclear cells (PMNs) isolated from the proband and from normal donors were cultured in vitro and apoptosis assessed at 24-hour intervals. Neutrophils expressing the CSF3R T618I had prolonged survival with a >40% decrease in apoptosis after 48 hours in culture (Figure 1B). RNA-seq followed by pathway analysis demonstrated significant decreases in activation of canonical apoptotic pathways in PMNs, including both the extrinsic and mitochondrial dependent pathways. Immunoblotting for candidate anti- and pro-apoptotic proteins revealed increased expression of the anti-apoptotic BCL2 family member MCL1 in T618I-expressing PMNs. Notably, inhibition of MCL1 using S63845 reversed the anti-apoptotic effect induced by ligand-activation of the CSF3R receptor in PMNs (P < 0.001, Figure 1C). In conclusion, we demonstrate hereditary CNL within a large family tree with no observed transformation to acute leukemia in any affected individuals up to age 51, suggesting a potentially more indolent course. Nonetheless, our observations highlight the need for germline testing of patients with CNL to better understand the natural history of CNL. Moreover, our data provide further insight into the pathobiology of CNL and potential novel targets for therapy. Figure 1 Figure 1. Disclosures Voorhees: Bristol-Myers Squibb Company.: Other: Data Safety & Monitoring; AbbVie Inc, Bristol-Myers Squibb Company; Consulting Agreement: GlaxoSmithKline, Novartis, Oncopeptides: Other: Advisory Committee.

Background: Outcomes of adults with relapsed/refractory T-cell acute lymphoblastic leukemia or lymphoma (T-ALL or T-LBL respectively) and acute myeloid leukemia (AML) have remained poor despite the availability of newer agents. CD38 is a 45 kDa transmembrane glycoprotein expressed by lymphoid and myeloid cells with several important functions including a role in immune escape from tumor cells [Chillemi A et al. Front Immunol 2017, Furano A et al. J Immunol 1990]. Several studies have demonstrated that CD38 is expressed in tumor cells of patients with T-ALL and AML and potentially targetable using CD38 blocking agents [Naik J et al. Haematologica 2019, Bride KL et al. Blood 2018, Tembhare et al. J Immunother Cancer 2020, Farber M et al. ASH 2018]. XmAb18968 is structurally distinct CD3-CD38 bi-specific T-cell engager with a full fragment crystallizable (Fc) domain modified to minimize Fcγ receptor binding and non-selective activation of T cells and other immune effector cells. XmAb18968 has optimized relative affinities for both CD3 and CD38 which results in reduced cytokine release without compromising target cell killing. We hypothesize targeting CD38 in relapsed/refractory- T-cell ALL/LBL and AML is safe and feasible using XmAb18968, a novel CD3-CD38 bispecific antibody. Study design and methods: This is an investigator-sponsored multi-institutional phase I study evaluating the safety and tolerability of XmAb18968. Patients aged 18 years or above with T-ALL, T-LBL or AML (including undifferentiated leukemia and bi phenotypic leukemia), in relapsed/refractory status (at least one line of prior therapy) including measurable residual disease relapse, CD38 expression ≥ 20%, and adequate organ function will be eligible. Major exclusion criteria are hematopoietic cell transplantation (HCT) within 6 months of enrollment, active acute GVHD, veno-occlusive disease, and acute promyelocytic leukemia. The study is planned to be conducted at 6 sites in United States. The primary endpoint is to determine the recommended phase 2 dose (RP2D) and toxicity profile of XmAb18968. The secondary endpoints include determination of response rates, duration of response, survival and pharmacokinetics. Exploratory endpoints include correlation of responses with genomic profile, assessment of serum cytokine response, identifying the changes in phenotypic expression of activated T-cells and leukemic cells, correlation of the phenotypic expression with changes in the transcriptome at the single-cell level, proteomics evaluation of cytokine secretion at the single-cell level and correlation of response with N-glycan profiling, quantitative site-occupancy and direct glycopeptide analysis. The study will follow 3+3 design for dose escalation and de-escalation in case of dose limiting toxicity (DLT). Dose escalation will proceed in two separate groups: Group A for subjects with T-ALL and T-LBL and Group B for subjects with AML. Patients will be entered sequentially to each dose level, starting with the first dose level. The DLT observation period for dose-escalation will be 28-days. RP2D will be defined as the highest dose level at which none of the first 3 treated subjects, or no more than 1 of the first 6 treated subjects experience a DLT. A minimum of 24 and a maximum of 60 patients will be needed for the dose escalation phase. Disclosures Guru Murthy: Curio Sciences: Honoraria; Techspert: Consultancy; Qessential: Honoraria; CancerExpertNow: Honoraria; DAVA Oncology: Honoraria; TG Therapeutics: Other: Advisory board meeting; Cardinal health: Honoraria; Guidepoint: Consultancy. Johnson: Miltenyi Biotec: Research Funding. Abedin: AltruBio: Research Funding; Amgen: Honoraria; Agios: Honoraria; Helsinn: Research Funding; Pfizer: Research Funding; Astellas Pharma Inc.: Research Funding; Actinium: Research Funding. Stock: Pfizer: Consultancy, Honoraria, Research Funding; amgen: Honoraria; agios: Honoraria; jazz: Honoraria; kura: Honoraria; kite: Honoraria; morphosys: Honoraria; servier: Honoraria; syndax: Consultancy, Honoraria; Pluristeem: Consultancy, Honoraria. Shah: Precision Biosciences: Consultancy; Kite, a Gilead Company: Consultancy, Honoraria, Other: Expenses, Research Funding; Pharmacyclics/Janssen: Honoraria, Other: Expenses; Acrotech/Spectrum: Honoraria; BeiGene: Consultancy, Honoraria; Amgen: Consultancy; Pfizer: Consultancy, Other: Expenses; Novartis: Consultancy, Other: Expenses; Bristol-Myers Squibb/Celgene: Consultancy, Other: Expenses; Adaptive Biotechnologies: Consultancy; Servier Genetics: Other; Jazz Pharmaceuticals: Research Funding; Incyte: Research Funding. Leonard: Amgen: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees. Pratz: Agios: Consultancy; BMS: Consultancy, Honoraria; Novartis: Consultancy; Astellas: Consultancy, Honoraria, Research Funding; Cellgene: Consultancy, Honoraria; Millenium: Research Funding; University of Pennsylvania: Current Employment; Abbvie: Consultancy, Honoraria, Research Funding. Luger: Syros: Honoraria; Agios: Honoraria; Daiichi Sankyo: Honoraria; Jazz Pharmaceuticals: Honoraria; Brystol Myers Squibb: Honoraria; Acceleron: Honoraria; Astellas: Honoraria; Pfizer: Honoraria; Onconova: Research Funding; Celgene: Research Funding; Biosight: Research Funding; Hoffman LaRoche: Research Funding; Kura: Research Funding. Badar: Pfizer Hematology-Oncology: Membership on an entity's Board of Directors or advisory committees. Atallah: Novartis: Consultancy, Honoraria, Research Funding; Amgen: Consultancy; Abbvie: Consultancy, Speakers Bureau; Takeda: Consultancy, Research Funding; BMS: Honoraria, Speakers Bureau; Pfizer: Consultancy, Research Funding.

Introduction: Health disparities for underrepresented U.S. minority populations with hematologic cancers contribute to differential treatment and higher death rates. The Hispanic population (including people of Mexican, South/Central American, Cuban, Puerto Rican, or other Spanish-speaking cultures, regardless of race) collectively constitutes the largest minority group in the United States. Hispanic patients have been reported to have an increased incidence of B-cell acute lymphoblastic lymphoma (B-ALL) and acute promyelocytic leukemia (APL). While APL is associated with favorable outcomes compared to other acute leukemias, registry data suggest poorer outcomes in Hispanic patients with both acute lymphocytic leukemia (ALL) and acute myeloid leukemia (AML). The Hispanic paradox is an epidemiological paradox that refers to the finding that Hispanic patients have paradoxically comparable, or better, health outcomes compared to their U.S. non-Hispanic White counterparts despite barriers to care such as lower socioeconomic status. This paradox has also been reported in hematologic malignancies. Definitive data regarding differences in outcome between Hispanic and non-Hispanic patients with acute leukemias (AL) are lacking. We sought to compare outcomes of Hispanic patients and non- Hispanic patients with acute leukemia with access to care, and examine whether the Hispanic paradox reported in hematologic malignancies is attributable to enrichment of patients with highly curable disease such as APL. Methods: Using data from a Vizient Clinical Data Base, a healthcare claims database, we identified patients with leukemia using ICD 10 codes for acute leukemia. Adult patients with AL, ages 18-89 who were treated between January 2020 and June 2021 were evaluated. Data from 121 academic centers was included. We focused on academic centers to limit the impact of access to care . Demographic information was obtained from the registry, to which ethnicity was self-reported. Patients were stratified by age, and we compared complication rates, number of complications, number of deaths, percent deaths and mortality index between Hispanic and non-Hispanic patients. The key metric used to compare outcomes of Hispanic patients with non-Hispanic patients was the severity adjusted mortality index, which is the ratio of observed mortality over expected mortality for patients with the same diagnosis in this registry. Chi-squared test is used for to determine the statistical significance of differences in mortality (by age group) in Hispanics v. non-Hispanic patients. Initial analysis included all patients with acute leukemias, and the data was subsequently reanalyzed excluding patients with APL, as APL is known to portend a favorable prognosis. Results: A total of 29,967 patients were with acute leukemia were evaluated; of these patients, 2903 identified as Hispanic and 27,064 were non- Hispanic. As seen in table 1, patients of Hispanic origin generally had lower treatment related complication rates in all age groups compared to their age matched non-Hispanic counterparts. Except for the 51-64 and 80-84 age groups the mortality index was lower in Hispanic patients compared to non-Hispanic peers. Differences in mortality between Hispanic and non-Hispanic patients in all age groups were not statistically significant. Trends to a lower mortality index in Hispanic patients are highlighted in green in table 1. When patients with APL were excluded from the analysis, the trend lower mortality in Hispanic patients in most age groups persisted. Again, the mortality index was comparatively higher in hispanic patients in the 51-64 and 80-84 age groups, but differences in mortality between Hispanic and non- Hispanic patients were not statistically significant. Exclusion of APL patients did not have a significant impact on the complication rate or mortality supporting that the Hispanic paradox is independent of higher rates of very favorable risk myeloid malignacies in this population. Conclusions: Hispanic patients with access to academic cancer centers have the potential for non-inferior outcomes compared to non-Hispanic patients. Equivalent outcomes as assessed by mortality index were not attributable solely to the higher incidence of very favorable risk disease such as APL in the Hispanic population. Figure 1 Figure 1. Disclosures Watts: Takeda: Consultancy, Research Funding; Genentech: Consultancy; Rafael Pharma: Consultancy; Celgene/BMS: Consultancy. Bradley: Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Sekeres: Takeda/Millenium: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees.

Background Post-transplant cyclophosphamide (PTCy) is a powerful strategy to prevent occurrence of graft-versus-host disease (GvHD) following allogeneic hematopoietic stem cell transplantation (HSCT). Initially developed in the setting of haploidentical HSCT, PTCy has been increasingly used for fully HLA-matched transplants with favorable results. The purpose of this retrospective multi-center study is to evaluate PTCy-based GvHD prevention for patients with acute leukemia receiving a traditionally prohibitive highly mismatched HSCT and to describe their outcome. Methods This is a registry-based study employing the data set of the Acute Leukemia Working Party (ALWP) of the European Society of Blood and Marrow Transplantation (EBMT). We retrospectively assessed the outcome of adult patients with acute myeloid or lymphoblastic leukemia (AML/ALL), transplanted between 2010 and 2020 with grafts from HLA-mismatched donors with more than 5/10 mismatches using PTCy-based GvHD prophylaxis. Results The study cohort consisted of 59 patients, with a median time of follow up of 20 (95% CI, 14-39) months. The median age was 47 (range, 18-69) years. Forty-four patients had a diagnosis of AML, 14 of ALL and one case of mixed phenotype acute leukemia. At time of transplant, 39 (66%) were in first or second complete remission, 4 (7%) were in later remission and 16 (27%) had active, relapsed or refractory, disease. Conditioning regimens were myeloablative for 54% of cases and peripheral blood was the preferred source of stem cells (64%). All donors were related. Most patients (85%) received a 4/10 HLA-matched transplant, the most commonly mismatched loci were C and DQB1, often with a double mismatch involving the same locus. Two cases of fully mismatched donors were also recorded. PTCy was always associated with other immunosuppressive treatments, especially with the standard combination of calcineurin inhibitors and mycophenolate mofetil. In only 8 cases in vivo T-cell depletion was realized with anti-thymocyte globulin. A large proportion of patients (86%) attained engraftment with a median time of 19 (range, 11-37) days. Only 8 patients did not reach engraftment and all of them died of infection or disease relapse in the first one-hundred days (range, 6-99) after HSCT. Thirty-three patients (58%) did not present any sign of acute GvHD (aGvHD). Cumulative incidence of grade II-IV and grade III-IV aGvHD at day 180 were 30.3% and 14.3%, respectively. At 2 years, the cumulative incidence of chronic GvHD (cGvHD) was 21%, and 7% for extensive cGvHD. Twenty-four patients died during the study period, mostly because of leukemia progression (n=13, 54%), infectious complications (n=6, 25%) and interstitial pneumonia (n=2, 8%). Other causes of death were hemorrhage, GvHD, and another non HSCT-related that accounted for one case (4%) each. At 2 years, the overall survival (OS), leukemia-free survival (LFS), and a GVHD and relapse free survival (GRFS) were 56%, 54% and 47% respectively. Rates of relapse incidence and non-relapse mortality were 28% and 19%, respectively. Conclusion According to this preliminary data overview, transplantation in a highly mismatched framework is possible, without unfavorable OS, LFS and GVHD rates. Despite the important limitation of the retrospective non-controlled nature of this analysis, these findings suggest that PTCy-based strategies could help overcome the barrier of HLA-matching and configure a new setting of transplantation, encouraging more in-depth investigations. Figure 1 Figure 1. Disclosures Labopin: Jazz Pharmaceuticals: Honoraria. Angelucci: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene BSM: Honoraria, Other: DMC; Blue Bird Bio: Honoraria, Membership on an entity's Board of Directors or advisory committees; Menarini-Stemline: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: steering commitee, Speakers Bureau; Vertex Pharmaceuticals: Honoraria, Other: DMC; Crispr therapeutics: Honoraria, Other: DMC; Glaxo: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees. Yakoub-Agha: Jazz Pharmaceuticals: Honoraria. Mohty: Takeda: Honoraria; Jazz: Honoraria, Research Funding; Gilead: Honoraria; Adaptive Biotechnologies: Honoraria; Sanofi: Honoraria, Research Funding; Pfizer: Honoraria; Novartis: Honoraria; Janssen: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Bristol Myers Squibb: Honoraria; Amgen: Honoraria; Astellas: Honoraria.

Background: Achieving a first complete remission (CR1) is the primary goal in the treatment of AML and is an important prognostic factor for transplantation outcome in general and even more so for autologous transplantation (AutoSCT). However, there are no data for AutoSCT indicating whether the number of chemotherapy courses (1 vs 2) needed to achieve CR1 is of prognostic significance for transplantation outcome. Methods: Using the EBMT/ALWP registry, we compared transplantation outcomes of adult patients (pts) aged ≥18 years with de novo AML that underwent a peripheral blood AutoSCT in 2000-2019 in CR1 achieved following one vs two chemotherapy courses. The primary outcome was the Leukemia Free Survival (LFS). Multivariate analysis (MVA) adjusting for differences between the groups and knowns factors were performed using Cox's proportional- hazards regression model for outcomes. Results: 1825 pts were included: 1532 (84%) with one and 293 (16%) with two induction chemotherapies courses. Time from diagnosis to AutoSCT was 4.7 (3.9-5.8) vs 5.7 (4.7-7.1) months, respectively (p 90 was higher in pts receiving 1 vs 2 inductions, 71% and 58% of pts, respectively (p Day 30 neutrophil engraftment incidence was 96% and 96.5%. Five -year non-relapse mortality (NRM) was 6.2% vs 6.0% for pts achieving CR1 with 2 vs 1 chemotherapy courses, respectively, and did not differ significantly (HR=1.31 (95% CI: 0.81-2.10), p=0.27). Five -year relapse incidence (RI) was higher :67.2% vs 52.3%, (HR=1.46 (95% CI: 1.25-1.72), p Conclusions: The five -year RI was higher and transplantation outcomes significantly inferior in pts with AML undergoing AutoSCT but who received two lines of chemotherapy to achieve CR1. Such pts may benefit from additional novel therapies in the conditioning or post-AutoSCT or be considered for allogeneic transplantation in an attempt to reduce their high RI and improve outcomes. Figure 1 Figure 1. Disclosures Labopin: Jazz Pharmaceuticals: Honoraria. Blaise: Jazz Pharmaceuticals: Honoraria. Huynh: Jazz Pharmaceuticals: Honoraria. Mohty: Takeda: Honoraria; Jazz: Honoraria, Research Funding; Astellas: Honoraria; Janssen: Honoraria, Research Funding; Bristol Myers Squibb: Honoraria; Novartis: Honoraria; Celgene: Honoraria, Research Funding; Amgen: Honoraria; Gilead: Honoraria; Pfizer: Honoraria; Adaptive Biotechnologies: Honoraria; Sanofi: Honoraria, Research Funding. Pigneux: Amgen: Consultancy; Sunesis: Consultancy, Research Funding; BMS Celgene: Consultancy, Research Funding; Roche: Consultancy, Research Funding; Novartis: Consultancy, Research Funding.