Development of an actinium-225 radioimmunoconjugate for targeted alpha therapy against SARS-CoV-2

Targeted alpha therapy offers unique opportunities for the treatment of tumours and infections. Here, we report the development of a new radioimmunoconjugate construct that targets SARS-CoV-2 infected cells, which act as viral reservoirs and promote virus replication and infection spread. The chosen antibody selectively binds to the ACE2-receptor binding domain of the spike protein, and prevents the protein binding to the receptor. Furthermore, the antibody has been radiolabelled with 225Ac, and the therapeutic performance of the resulting radioimmunoconjugate has been demonstrated in vitro against cells mimicking SARS-CoV-2 infection.

Efficacy of Oral Decitabine/Cedazuridine (ASTX727) in the CMML Subgroup from the Ascertain Phase 3 Study

text: Background/Introduction: Chronic Myelomonocytic Leukemia (CMML) is an uncommon MDS/MPN overlap syndrome that has historically been included under the umbrella of myelodysplastic syndromes (MDS) for clinical trial and treatment. As a result, DNA methyltransferase inhibitors (DNMTi) such as decitabine or azacitidine have been the established standard of care for the treatment of CMML. The oral bioavailability of these agents has been limited due to rapid degradation by cytidine deaminase (CDA) in the gut and liver so treatment has required intravenous infusion or subcutaneous injections daily for 5-7 days every month (m) adding significant burden to older cancer patients due to daily time commitment and travel to treatment centers. In the context of pandemic SARS-CoV-2, parenteral therapy also increases contact with medical settings with increased infection risk. Oral decitabine 35 mg/cedazuridine 100 mg (ASTX727) is an oral fixed dose combination of decitabine and the CDA inhibitor cedazuridine that produced equivalent exposure (99%;90% CI 93% to 106%) to IV decitabine 20 mg/m 2 in a randomized cross-over study (Garcia-Manero et al, ASH 2019), and Median overall survival (mOS) for the entire study population in the ASCERTAIN study was approximately 32 months (Savona, 2021). Here, we present outcome data for this study for the enrolled subpopulation of patients with CMML. Methods: We used a randomized cross over design in which patients were randomized in the first 2 cycles 1:1 to either Sequence A: (decitabine 35 mg/ cedazuridine 100 mg in Cycle 1 followed by IV decitabine at 20 mg/m 2 in Cycle 2), or Sequence B: (IV decitabine in Cycle 1 followed by oral decitabine/cedazuridine in Cycle 2). We conducted an intra-patient comparison of decitabine PK (primary PK endpoint: decitabine AUC equivalence over 5 days of dosing). Cycles were repeated every 28 days (unless delays were needed). All patients received oral decitabine/cedazuridine in Cycles 3 and above until disease progression or unacceptable toxicity. Patients were eligible per the FDA-approved label of IV decitabine (MDS patients by FAB classification including CMML, or MDS IPSS Intermediate-1, 2 or high-risk patients). Clinical endpoints were best response according to International Working Group (IWG) 2006 response criteria, transfusion independence for at least 8 or 16 consecutive weeks, overall survival, and safety. Adverse events (AEs) were graded by Common Terminology Criteria for Adverse Events (CTCAE) v 4.03. Results: Of the 133 patients enrolled and treated in ASCERTAIN, 16 (12%) had a diagnosis of CMML with demographics and as follows: median age 71.5 years, 69% Male/31% Female, median weight 87kg (range 65-124), 25% ECOG 0, 75% ECOG 1. Population disease characteristics were: 19% poor or intermediate risk cytogenetics, with median baseline hemoglobin 90 g/L, neutrophils 1.27 X 10 9/L, platelets 84 x 10 9/L, bone marrow blasts 5%, with 38% RBC transfusion dependent. Patients received a median of 7 cycles of therapy (range 3-24). Treatment-emergent adverse events of CTCAE Grade 3 or higher in > 10% of patients, independent of relationship to ASTX727, were cytopenias (neutropenia [69%], thrombocytopenia [63%], anemia [56%], leukopenia [19%]), febrile neutropenia (31%), fatigue (13%). Two patients (12.5%) had Complete Responses (CR), 8 (50%) had marrow CR ([mCR], including 3 (19%) with hematologic improvement (HI);Overall Response rate (ORR) [CR + PR+ mCR + HI] was 75%. Of six patients with baseline RBC transfusion dependence 3 (50%) became transfusion independent. Leukemia-free survival was 28.2 months and after a median follow up of more than 33 months, median overall survival had not been reached. Two patients (13%) went on to Hematopoietic Stem Cell Transplant (HCT). Conclusions: In the overall study, oral decitabine/cedazuridine delivered equivalent PK exposure to 5 days of IV decitabine 20mg/m 2 with a resultant clinical activity safety and efficacy profile in CMML patients consistent with the published literature (e.g Zeidan, et a 2017) and the Phase 2 experience. The use of oral decitabine/cedazuridine is a reasonable approach in CMML patients. References: Garcia-Manero, et al ASH 2019 Savona, et al, Int. MDS Symposium, 2021 Zeidan, et al, Cancer 2017: 3754-3762. [Formula presented] Disclosures: Savona: Geron: Consultancy, Membership on an entity's Board of Directors or advisory committees;CTI: Consultancy, Membership on an entity's Board of Directors or advisory committees;Karyopharm: Consultancy, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees;BMS-Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees;NOVARTIS: Consultancy, Membership on an entity's Board of Directors or advisory committees;Ryvu: Consultancy, Membership on an entity's Board of Directors or advisory committees;Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees;Taiho: Consultancy, Membership on an entity's Board of Directors or advisory committees;TG Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding;Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding;ALX Oncology: Research Funding;Astex: Research Funding;Incyte: Research Funding. McCloskey: Pfizer: Consultancy;Takeda: Consultancy, Speakers Bureau;Incyte: Speakers Bureau;Novartis: Consultancy;COTA: Other: Equity Ownership;BMS: Honoraria, Speakers Bureau;Amgen: Speakers Bureau;Jazz: Consultancy, Speakers Bureau. Griffiths: Boston Biomedical: Consultancy;Celgene/Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding;Abbvie: Consultancy, Honoraria;Taiho Oncology: Consultancy, Honoraria;Genentech: Research Funding;Astex Pharmaceuticals: Honoraria, Research Funding;Takeda Oncology: Consultancy, Honoraria;Novartis: Honoraria;Apellis Pharmaceuticals: Research Funding;Alexion Pharmaceuticals: Consultancy, Research Funding. Yee: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding;Forma Therapeutics: Research Funding;Geron: Research Funding;Shattuck Labs: 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;F. Hoffmann La Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding;AbbVie: Honoraria;Janssen: Research Funding;Onconova: Research Funding;Genentech: Research Funding;Otsuka: Membership on an entity's Board of Directors or advisory committees;MedImmune: Research Funding;Jazz: Research Funding;Astex: Membership on an entity's Board of Directors or advisory committees, Research Funding;Tolero: 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;Pfizer: Membership on an entity's Board of Directors or advisory committees;Paladin: Membership on an entity's Board of Directors or advisory committees. Zeidan: BeyondSpring: Consultancy;Janssen: Consultancy;Boehringer Ingelheim: Consultancy, Research Funding;BioCryst: Other: Clinical Trial Committees;AstraZeneca: Consultancy;Pfizer: Other: Travel support, Research Funding;Kura: Consultancy, Other: Clinical Trial Committees;Incyte: Consultancy, Research Funding;Ionis: Consultancy;Daiichi Sankyo: Consultancy;Epizyme: Consultancy;Novartis: Consultancy, Other: Clinical Trial Committees, Travel support, Research Funding;Loxo Oncology: Consultancy, Other: Clinical Trial Committees;Genentech: Consultancy;Geron: Other: Clinical Trial Committees;Cardiff Oncology: Consultancy, Other: Travel support, Research Funding;BMS: Consultancy, Other: Clinical Trial Committees, Research Funding;Gilead: Consultancy, Other: Clinical Trial Committees;Aprea: Consultancy, Research Funding;Astellas: Consultancy;Astex: Research Funding;Jazz: Consultancy;Jasper: Consu tancy;Amgen: Consultancy, Research Funding;Agios: Consultancy;ADC Therapeutics: Research Funding;Acceleron: Consultancy, Research Funding;AbbVie: Consultancy, Other: Clinical Trial Committees, Research Funding. Al-Kali: Novartis: Research Funding;Astex: Other: Research support to institution. Patel: Agios: Membership on an entity's Board of Directors or advisory committees;Celgene-BMS: Membership on an entity's Board of Directors or advisory committees;PVI: Honoraria. Sabloff: Takeda: Membership on an entity's Board of Directors or advisory committees;BMS: Membership on an entity's Board of Directors or advisory committees;Astellas: Membership on an entity's Board of Directors or advisory committees;Novartis: 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;Abbvie: Membership on an entity's Board of Directors or advisory committees;Pfizer: Membership on an entity's Board of Directors or advisory committees;ROCHE: Membership on an entity's Board of Directors or advisory committees;Celgene: Membership on an entity's Board of Directors or advisory committees. Dao: Astex Pharmaceuticals, Inc.: Current Employment. Fazal: Janssen Oncology: Consultancy, Honoraria, Speakers Bureau;Taiho Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau;Gilead Sciences: Consultancy, Honoraria, Speakers Bureau;Novartis: Consultancy, Honoraria, Speakers Bureau;Agios: Consultancy, Honoraria, Speakers Bureau;Sanofi Genzyme: Consultancy, Honoraria, Speakers Bureau;Takeda: Consultancy, Honoraria, Speakers Bureau;Glaxo Smith Kline: Consultancy, Honoraria, Speakers Bureau;AMGEN: Consultancy, Honoraria, Speakers Bureau;Incyte: Consultancy, Honoraria, Speakers Bureau;Jazz Pharmaceuticals:Consultancy, Honoraria, Speakers Bureau;Bristol Myers Squibb: Consultancy, Honoraria, Speakers Bureau;Stemline Therapeutics: Consultancy, Honoraria, Speakers Bureau;Karyopharm Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau. Odenike: Celgene, Incyte, AstraZeneca, Astex, NS Pharma, AbbVie, Gilead, Janssen, Oncotherapy, Agios, CTI/Baxalta, Aprea: Research Funding;AbbVie, Celgene, Impact Biomedicines, Novartis, Taiho Oncology, Takeda: Consultancy. Kantarjian: Ipsen Pharmaceuticals: Honoraria;Astra Zeneca: Honoraria;Astellas Health: Honoraria;Aptitude Health: Honoraria;Pfizer: Honoraria, Research Funding;Novartis: Honoraria, Research Funding;Jazz: Research Funding;Immunogen: Research Funding;Daiichi-Sankyo: Research Funding;BMS: Research Funding;Ascentage: Research Funding;Amgen: Honoraria, Research Funding;AbbVie: Honoraria, Research Funding;KAHR Medical Ltd: Honoraria;NOVA Research: Honoraria;Precision Biosciences: Honoraria;Taiho Pharmaceutical Canada: Honoraria. DeZern: Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees;Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees;Taiho: Consultancy, Membership on an entity's Board of Directors or advisory committees;Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees. Roboz: Janssen: Research Funding;AbbVie: Consultancy;Actinium: Consultancy;Agios: Consultancy;Amgen: Consultancy;Astex: Consultancy;Astellas: Consultancy;AstraZeneca: Consultancy;Bayer: Consultancy;Blueprint Medicines: Consultancy;Bristol Myers Squibb: Consultancy;Celgene: Consultancy;Daiichi Sankyo: Consultancy;Glaxo SmithKline: Consultancy;Helsinn: Consultancy;Janssen: Consultancy;Jasper Therapeutics: Consultancy;Jazz: Consultancy;MEI Pharma - IDMC Chair: Consultancy;Mesoblast: Consultancy;Novartis: Consultancy;Otsuka: Consultancy;Pfizer: Consultancy;Roche/Genentech: Consultancy. Busque: Novartis: Consultancy. Leber: Novartis: 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, peakers Bureau;BMS: Honoraria, 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;AMGEN: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau;TaiHo: Honoraria, Membership on an entity's Board of Directors or advisory committees;Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau;Otsuka: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau;Astellas: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau;Jazz: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Hao: Astex Pharmaceuticals, Inc.: Current Employment. Keer: Astex Pharmaceuticals, Inc.: Current Employment. Azab: Astex Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees.

Oral Decitabine/Cedazuridine in Patients with Lower Risk Myelodysplastic Syndrome: A Longer-Term Follow-up of from the Ascertain Study

[Formula presented] Background/Introduction: Lower-risk (IPSS low risk and Int-1) myelodysplastic syndromes (MDS) are typically treated supportively to address cytopenias. DNA methyltransferase inhibitors (DNMTi) such as azacitidine and decitabine (DEC) are FDA-approved for higher risk MDS patients (pts), and while the DEC USPI includes IPSS Int-1 pts, it is not widely used in this population. Approved intravenous (IV) or subcutaneous (SC) regimens require 5-7 days of treatment every month burdening older cancer pts due to daily travel and treatment time and may increase potential risk from pandemic SARS-CoV-2 infection. Because DNMTis are rapidly degraded by cytidine deaminase (CDA) in the gut and liver, oral availability has only been recently possible. A randomized study with CC-486, an oral formulation of azacitidine, in the Int-1 population showed a median overall survival (mOS) of approximately 17 months for both placebo and treated patients (Garcia-Manero, 2021). Oral DEC 35 mg/cedazuridine 100 mg (ASTX727) or DEC-C, is an oral fixed dose combination (FDC) of DEC and the CDA inhibitor cedazuridine (CED) resulting in equivalent exposure (99%;90% CI 93% to 106%) to standard IV DEC 20 mg/m 2 for 5 days in an intra-patient randomized cross-over study (Garcia-Manero et al, ASH 2019). Here, we present data on patients with lower risk MDS from that study. Methods: We used a randomized cross over design with pts randomized 1:1 in the first 2 cycles to either Sequence A: (DEC 35 mg/ CED 100 mg in Cycle 1 and IV DEC at 20 mg/m 2 in Cycle 2), or Sequence B (IV DEC in Cycle 1 and oral DEC/CED in Cycle 2). Cycles were repeated every 28 days unless delays were needed, and all patients received oral DEC-C in Cycles 3+ until disease progression or unacceptable toxicity. We conducted an intra-patient comparison of DEC PK (DEC AUC equivalence over 5 days of dosing). Pts were eligible as per the FDA-approved label of IV DEC (MDS pts by FAB classification including CMML, or MDS IPSS Intermediate-1, 2 or high-risk pts). Clinical endpoints were best response as assessed by an independent expert panel according to IWG 2006 response criteria, transfusion independence (TI), overall survival (OS), and safety. Results: Of the 133 pts treated in ASCERTAIN, 69 had a diagnosis of lower-risk MDS (93% Int-1, 7% LR). Median age was 70.0 years (range 45-87), 65% were male, median weight was 84 kg (range 50-127), median baseline hematologic parameters were: hemoglobin 89 g/L (range 69.8-146.5), WBCs 1.50 X 10 9/L (range 0.11-7.1), platelets (plt) 86 x 10 9/L (range 5-703), bone marrow blasts 4% (range 0-18), cytogenetics: 7 (10.1%) poor-risk, 21 (30.4%) intermediate risk, 37 (53.6%) better-risk, 4 (5.7%) missing or not evaluable. 27(39%) of the pts were RBC transfusion dependent (TD) and 6 (9%) plt TD. 17 (25%) had received prior MDS treatment, 3% prior DNMTi. Pts received a median of 9 cycles of therapy (range 1-28). Treatment-emergent adverse events of CTCAE Gr 3 or higher in >10% of pts, independent of relationship to ASTX727, included cytopenias (neutropenia [59%], thrombocytopenia [58%], anemia [48%], leukopenia [26%]), febrile neutropenia (32%), and pneumonia (19%). Sixteen pts (23%) achieved Complete Response (CR), 18 (26%) had marrow CR (mCR), including 9 (13%) with hematologic improvement (HI). Overall Response rate (ORR;CR + PR+ mCR + HI) was 57%. Of those RBC or plt TD at baseline, 13 (48%) became RBC TI and 4 (67%) became plt TI. With approximately 32 months of median follow up, neither median leukemia-free survival (mLFS) nor mOS had been reached (Figure 1). Twelve pts (17%) went on to allogeneic stem cell transplant. Conclusions: Oral decitabine/cedazuridine given as a FDC in MDS pts produced equivalent PK exposure to 20 mg/m 2 IV DEC;in lower risk MDS pts with treatment indicated, the agent was generally well-tolerated with prolonged treatment and could result in mLFS and mOS which exceeds 32 months. This FDC and other dosing regimens of oral DEC-C should be further studied in this patient population. References: Garcia-Mane o, et al, ASH 2019 Savona, et al, Int. MDS Symp. 2021 Garcia-Manero, et al, Phase III, Randomized, Placebo-Controlled Trial of CC-486 (Oral Azacitidine) in Patients with Lower-Risk Myelodysplastic Syndromes. J.Clin.Onc. 2021 39:13, 1426-1436 [Formula presented] Disclosures: McCloskey: Pfizer: Consultancy;Jazz: Consultancy, Speakers Bureau;COTA: Other: Equity Ownership;Incyte: Speakers Bureau;Takeda: Consultancy, Speakers Bureau;Novartis: Consultancy;BMS: Honoraria, Speakers Bureau;Amgen: Speakers Bureau. Griffiths: Alexion Pharmaceuticals: Consultancy, Research Funding;Abbvie: Consultancy, Honoraria;Taiho Oncology: Consultancy, Honoraria;Genentech: Research Funding;Novartis: Honoraria;Takeda Oncology: Consultancy, Honoraria;Astex Pharmaceuticals: Honoraria, Research Funding;Celgene/Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding;Apellis Pharmaceuticals: Research Funding;Boston Biomedical: Consultancy. Yee: Paladin: Membership on an entity's Board of Directors or advisory committees;TaiHo: Membership on an entity's Board of Directors or advisory committees;Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding;Genentech: Research Funding;Geron: Research Funding;Janssen: Research Funding;Jazz: Research Funding;MedImmune: Research Funding;Onconova: Research Funding;Tolero: Research Funding;AbbVie: Honoraria;Bristol-Myers Squibb/Celgene: Membership on an entity's Board of Directors or advisory committees;Otsuka: 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;Takeda: Membership on an entity's Board of Directors or advisory committees;F. Hoffmann La Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding;Forma Therapeutics: Research Funding;Astex: Membership on an entity's Board of Directors or advisory committees, Research Funding. Zeidan: Novartis: Consultancy, Other: Clinical Trial Committees, Travel support, Research Funding;Genentech: Consultancy;Ionis: Consultancy;Astellas: Consultancy;Epizyme: Consultancy;AbbVie: Consultancy, Other: Clinical Trial Committees, Research Funding;Jasper: Consultancy;Cardiff Oncology: Consultancy, Other: Travel support, Research Funding;BeyondSpring: Consultancy;Loxo Oncology: Consultancy, Other: Clinical Trial Committees;Janssen: Consultancy;Acceleron: Consultancy, Research Funding;AstraZeneca: Consultancy;Kura: Consultancy, Other: Clinical Trial Committees;Gilead: Consultancy, Other: Clinical Trial Committees;Agios: Consultancy;Daiichi Sankyo: Consultancy;Boehringer Ingelheim: Consultancy, Research Funding;Geron: Other: Clinical Trial Committees;BMS: Consultancy, Other: Clinical Trial Committees, Research Funding;BioCryst: Other: Clinical Trial Committees;Pfizer: Other: Travel support, Research Funding;Aprea: Consultancy, Research Funding;ADC Therapeutics: Research Funding;Jazz: Consultancy;Incyte: Consultancy, Research Funding;Amgen: Consultancy, Research Funding;Astex: Research Funding. Al-Kali: Astex: Other: Research support to institution;Novartis: Research Funding. Patel: Celgene-BMS: Membership on an entity's Board of Directors or advisory committees;PVI: Honoraria;Agios: Membership on an entity's Board of Directors or advisory committees. Sabloff: Pfizer: Membership on an entity's Board of Directors or advisory committees;Novartis: Membership on an entity's Board of Directors or advisory committees;Astellas: 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;TaiHo: Membership on an entity's Board of Directors or advisory committees;Jaxx: Membership on an entity's Board of Directors or advisory committees;Celgene: Membership on an entity's Board of Directors or advisory ommittees;BMS: Membership on an entity's Board of Directors or advisory committees;Abbvie: Membership on an entity's Board of Directors or advisory committees. Dao: Astex Pharmaceuticals, Inc.: Current Employment. Fazal: Taiho Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau;Stemline Therapeutics: Consultancy, Honoraria, Speakers Bureau;Sanofi Genzyme: Consultancy, Honoraria, Speakers Bureau;Novartis: Consultancy, Honoraria, Speakers Bureau;Karyopharm Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau;Jazz Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau;Janssen Oncology: Consultancy, Honoraria, Speakers Bureau;Incyte: Consultancy, Honoraria, Speakers Bureau;Glaxo Smith Kline: Consultancy, Honoraria, Speakers Bureau;Gilead Sciences: Consultancy, Honoraria, Speakers Bureau;Bristol Myers Squibb: Consultancy, Honoraria, Speakers Bureau;AMGEN: Consultancy, Honoraria, Speakers Bureau;Agios: Consultancy, Honoraria, Speakers Bureau;Takeda: Consultancy, Honoraria, Speakers Bureau. Odenike: AbbVie, Celgene, Impact Biomedicines, Novartis, Taiho Oncology, Takeda: Consultancy;Celgene, Incyte, AstraZeneca, Astex, NS Pharma, AbbVie, Gilead, Janssen, Oncotherapy, Agios, CTI/Baxalta, Aprea: Research Funding. Kantarjian: AbbVie: Honoraria, Research Funding;Novartis: Honoraria, Research Funding;Ascentage: Research Funding;Pfizer: Honoraria, Research Funding;BMS: Research Funding;Daiichi-Sankyo: Research Funding;Amgen: Honoraria, Research Funding;Ipsen Pharmaceuticals: Honoraria;Jazz: Research Funding;Astellas Health: Honoraria;Immunogen: Research Funding;Astra Zeneca: Honoraria;Aptitude Health: Honoraria;KAHR Medical Ltd: Honoraria;NOVA Research: Honoraria;Precision Biosciences: Honoraria;Taiho Pharmaceutical Canada: Honoraria. DeZern: Takeda: Consultancy, Membership on an entity's Board of Directors or advisorycommittees;Taiho: Consultancy, Membership on an entity's Board of Directors or advisory committees;Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees;Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees. Roboz: Novartis: Consultancy;Mesoblast: Consultancy;Jasper Therapeutics: Consultancy;Jazz: Consultancy;MEI Pharma - IDMC Chair: Consultancy;Daiichi Sankyo: Consultancy;Otsuka: Consultancy;Bristol Myers Squibb: Consultancy;Blueprint Medicines: Consultancy;Bayer: Consultancy;AstraZeneca: Consultancy;Astellas: Consultancy;Astex: Consultancy;Amgen: Consultancy;Agios: Consultancy;Actinium: Consultancy;AbbVie: Consultancy;Janssen: Research Funding;Celgene: Consultancy;Glaxo SmithKline: Consultancy;Helsinn: Consultancy;Janssen: Consultancy;Pfizer: Consultancy;Roche/Genentech: Consultancy. Busque: Novartis: Consultancy. Leber: Astellas: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau;Otsuka: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau;Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau;TaiHo: Honoraria, Membership on an entity's Board of Directors or advisory committees;AMGEN: 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;BMS: Honoraria, 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;Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau;Jazz: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Hao: Astex Pharmaceuticals, Inc.: Current Employment. Keer: Astex Pharmaceuticals, Inc.: Current Employment. Azab: Astex Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees. Savona: Geron: Consultancy, Membership on an entity's Board of Directors or advisory committees;Karyopharm: Cons ltancy, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees;CTI: Consultancy, Membership on an entity's Board of Directors or advisory committees;BMS-Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees;NOVARTIS: Consultancy, Membership on an entity's Board of Directors or advisory committees;Ryvu: Consultancy, Membership on an entity's Board of Directors or advisory committees;Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees;Taiho: Consultancy, Membership on an entity's Board of Directors or advisory committees;TG Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding;Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding;ALX Oncology: Research Funding;Astex: Research Funding;Incyte: Research Funding.

Randomized, Phase III Study of Early Intervention with Venetoclax and Obinutuzumab Versus Delayed Therapy with Venetoclax and Obinutuzumab in Newly Diagnosed Asymptomatic High-Risk Patients with Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma (CLL/SLL): Evolve CLL/SLL Study (SWOG S1925;NCT#04269902)

Background: Currently, asymptomatic patients with CLL/SLL are observed without treatment until development of symptoms or cytopenias. Historically, early intervention studies in patients with CLL/SLL with non-specific chemoimmunotherapy agents have not resulted in an overall survival (OS) benefit and have resulted in toxicity. The introduction of targeted therapies, such as venetoclax (an oral BCL2 inhibitor;V) and obinutuzumab (an intravenous anti-CD20 monoclonal antibody;O), have provided tolerable/efficacious options for patients with CLL. In the CLL14 study, symptomatic patients with CLL receiving frontline therapy with VO had longer progression-free survival (PFS) and deeper remissions [more undetectable minimal residual disease (uMRD)] compared with those receiving chlorambucil and O (Fischer 2019). The CLL-International Prognostic Index (CLL-IPI;Table 1) is a validated prognostic model to predict which patients are at highest risk of a shorter time to first therapy and shorter OS. A score of ≥4 is considered high-risk on this scale. We aim to use VO as early intervention in asymptomatic, high-risk CLL patients, assessed by CLL-IPI, to potentially improve OS and thus alter the natural history of the disease. Methods: On 12/14/20, we activated the S1925 study (NCT#04269902 ) for adult patients with CLL or SLL, who were diagnosed within 12 months of enrollment. Eligible patients have a CLL-IPI score ≥4 (Table 1) or complex cytogenetics (≥3 cytogenetic abnormalities) and do not meet any criteria for initiation of treatment by the International Working Group for CLL (IWCLL;Hallek 2018) guidelines. Enrolled patients are randomized in a 2:1 manner to early versus delayed (at the time IWCLL indication for treatment is met) therapy with VO (Figure 1). VO is administered as previously described (Fischer 2019). The primary endpoint is OS. We hypothesize that early intervention with VO will improve the rate of 6-year OS from 60% to 80%. This design requires 222 eligible patients for 88% power (2-sided a=0.05) for the primary comparison. To allow for 10% ineligibility, we will enroll 247 patients. Estimated accrual time is 4 years. Secondary endpoints include: rates of response, PFS, and relapse-free survival;safety;time to second CLL-directed therapy;and quality of life (assessed by FACT-Leukemia). As COVID19 is an infection with particularly high morbidity and mortality in patients with CLL, incidence of this infection and complications including death will be recorded and compared between patients followed on the early versus delayed intervention arms. The primary translational objective is to evaluate the prognostic association between OS and peripheral blood MRD status at 15 months after treatment initiation by flow cytometry. Secondary translational objectives include describing the association of other clinical outcomes, baseline prognostic factors, and IWCLL-defined response with MRD status at multiple timepoints. Current Status: At the time of submission, 7 patients have been registered and randomized per protocol. Accrual is ongoing. [Formula presented] Disclosures: Stephens: Adaptive: Membership on an entity's Board of Directors or advisory committees;TG Therapeutics: Membership on an entity's Board of Directors or advisory committees;Epizyme: Membership on an entity's Board of Directors or advisory committees;Beigene: Membership on an entity's Board of Directors or advisory committees;Innate Pharma: Membership on an entity's Board of Directors or advisory committees;AstraZeneca: Consultancy;CSL Behring: Consultancy;Celgene: Consultancy;Novartis: Research Funding;Abbvie: Consultancy;JUNO: Research Funding;Arqule: Research Funding;Mingsight: Research Funding;Karyopharm: Membership on an entity's Board of Directors or advisory committees, Research Funding. Moseley: BioSight Ltd: Consultancy. Hill: AbbVie: Consultancy, Honoraria, Research Funding;Gentenech: Consultancy, Honoraria, Research Funding;Beigene: Consultancy, Honoraria, Research Funding;Pfizer: Consultancy, Honoraria;Kite, Gilead Company: Consultancy, Honoraria, Other: Travel Support, Research Funding;Karyopharm: Consultancy, Honoraria, Research Funding;AstraZenica: Consultancy, Honoraria;Celgene (BMS): Consultancy, Honoraria, Research Funding;Novartis: Consultancy, Honoraria, Research Funding;Epizyme: Consultancy, Honoraria;Incyte/Morphysis: Consultancy, Honoraria, Research Funding. Pagel: Pharmacyclics/AbbVie: Consultancy;Actinium Pharmaceuticals: Consultancy;Incyte/MorphoSys: Consultancy;BeiGene: Consultancy;Epizyme: Consultancy;Kite, a Gilead Company: Consultancy;AstraZeneca: Consultancy;Gilead: Consultancy;MEI Pharma: Consultancy. Shadman: Mustang Bio, Celgene, Bristol Myers Squibb, Pharmacyclics, Gilead, Genentech, Abbvie, TG Therapeutics, Beigene, AstraZeneca, Sunesis, Atara Biotherapeutics, GenMab: Research Funding;Abbvie, Genentech, AstraZeneca, Sound Biologics, Pharmacyclics, Beigene, Bristol Myers Squibb, Morphosys, TG Therapeutics, Innate Pharma, Kite Pharma, Adaptive Biotechnologies, Epizyme, Eli Lilly, Adaptimmune, Mustang Bio and Atara Biotherapeutics: Consultancy. Danilov: Genentech: Consultancy, Honoraria, Research Funding;Takeda Oncology: Research Funding;TG Therapeutics: Consultancy, Research Funding;Abbvie: Consultancy, Honoraria;Beigene: Consultancy, Honoraria;Pharmacyclics: Consultancy, Honoraria;Gilead Sciences: Research Funding;Bristol-Meyers-Squibb: Honoraria, Research Funding;Rigel Pharm: Honoraria;Bayer Oncology: Consultancy, Honoraria, Research Funding;SecuraBio: Research Funding;Astra Zeneca: Consultancy, Honoraria, Research Funding. Mato: Pharmacyclics LLC, an AbbVie Company: Consultancy, Research Funding;DTRM BioPharma: Consultancy, Research Funding;Acerta/AstraZeneca: Consultancy, Research Funding;Sunesis: Consultancy, Research Funding;BeiGene: Consultancy, Research Funding;Johnson and Johnson: Consultancy, Research Funding;Genentech: Consultancy, Research Funding;AbbVie: Consultancy, Research Funding;Nurix: Research Funding;Genmab: Research Funding;LOXO: Consultancy, Research Funding;Janssen: Consultancy, Research Funding;AstraZeneca: Consultancy;Adaptive Biotechnologies: Consultancy, Research Funding;MSKCC: Current Employment;TG Therapeutics: Consultancy, Other: DSMB, Research Funding. Brander: Juno Therapeutics/Celgene/Bristol Myers Squibb: Research Funding;Pfizer: Consultancy, Other: Biosimilars outcomes research panel;TG Therapeutics: Consultancy, Research Funding;Novartis: Research Funding;ArQule/Merck: Consultancy;Verastem: Consultancy;BeiGene: Research Funding;ArQule: Research Funding;NCCN: Other: panel member;AstraZeneca: Research Funding;Pharmacyclics LLC, an AbbVie Company: Consultancy, Research Funding;LOXO: Research Funding;Ascentage: Research Funding;Genentech: Consultancy, Research Funding;DTRM: Research Funding;MEI Pharma: Research Funding;AbbVie: Consultancy, Other: informCLL registry steering committee, Research Funding. Coutre: Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding;Pharmacyclics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding;AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding;AstraZeneca: Consultancy, Membership on an entity's Board of Directors or advisory committees;Beigene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Data Safety Monitoring Committee, Research Funding;Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees;Acerta: Other: Data Safety Monitoring Committee, Research Funding. O'Brien: Kite, Regeneron, Acerta, Caribou, Gilead, Pharmacyclics, TG Therapeutics, Pfizer, Sunesis: Research Funding;Amgen, Astellas, Celgene, GlaxoSmithKline, Janssen Oncology, Aptose Biosciences Inc., Vaniam Group LLC, AbbVie, Alexion, Verastem, Juno Therapeutics, Vida Ventures, Autolus, Johnson and Johnson, Merck, Bristol Myers Squibb, NOVA Research Company, El Lill: Consultancy. Erba: AbbVie Inc;Agios Pharmaceuticals Inc;Bristol Myers Squibb;Celgene, a Bristol Myers Squibb company;Incyte Corporation;Jazz Pharmaceuticals Inc;Novartis: Speakers Bureau;AbbVie Inc: Other: Independent review committee;AbbVie Inc;Agios Pharmaceuticals Inc;ALX Oncology;Amgen Inc;Daiichi Sankyo Inc;FORMA Therapeutics;Forty Seven Inc;Gilead Sciences Inc;GlycoMimetics Inc;ImmunoGen Inc;Jazz Pharmaceuticals Inc;MacroGenics Inc;Novartis;PTC Therapeutics: Research Funding;AbbVie Inc;Agios Pharmaceuticals Inc;Astellas;Bristol Myers Squibb;Celgene, a Bristol Myers Squibb company;Daiichi Sankyo Inc;Genentech, a member of the Roche Group;GlycoMimetics Inc;Incyte Corporation;Jazz Pharmaceuticals Inc;Kura Oncology;Nov: Other: Advisory Committee. OffLabel Disclosure: The trial studies early intervention with venetoclax and obinutuzumab in patients with CLL/SLL who are asymptomatic and observation would be standardly recommended.

Clinical Predictors of Outcome in Adult Patients with Acute Leukemias and Myelodysplastic Syndrome and COVID-19 Infection: Report from the American Society of Hematology Research Collaborative (ASH RC) Data Hub

Background: Predictors of severe infection and outcomes with COVID-19 in patients (pts) with acute myeloid leukemia (AML), acute lymphocytic leukemia (ALL) and myelodysplastic syndromes (MDS) are lacking. Pts with active disease may experience worse outcomes due to overall prognosis and cytopenias. Here we identify risk factors for severe COVID-19 infection and mortality in pts with AML, MDS, and ALL using the ASH RC COVID-19 Registry for Hematology. Methods: The ASH RC COVID-19 Registry for Hematology includes features and outcomes of a laboratory-confirmed or presumptive diagnosis of SARS-CoV-2 infection in adult pts with ongoing or a history of blood disorders. The Registry opened for data collection on April 1, 2020 and is a global effort housed on a secure data platform hosted by Prometheus Research, an IQVIA company. Data are made publicly available and regularly updated on the ASH RC website. Pt characteristics, outcomes, and predictors were analyzed and stratified by disease status (active initial diagnosis and relapsed/refractory vs. remission) and type of hematologic malignancy. Variables included age, comorbidities, type of hematologic malignancy (AML, MDS, ALL), neutrophil and lymphocyte count at time of COVID-19 diagnosis, and active treatment at the time of COVID-19 diagnosis. COVID-19 severity was defined as mild (no hospitalization required), moderate (hospitalization required), or severe (ICU admission required). Categorical pt characteristics for each response group and associations between response groups and characteristics (i.e., alive vs. dead, severity vs. non-severity) were summarized by frequency with differences between response groups evaluated by Fisher's exact test and odds ratios with 95% confidence intervals (CIs) estimated by logistic regression. Multivariable analyses identified independent predictors of outcomes. Results: Analyses were conducted on data from 257 pts with AML (n=135), MDS (n=40), and ALL (n=82);46% were in remission and 44% had active disease (10% unknown). Overall mortality from COVID-19 infection was 21%. Pts with active disease were significantly more likely to present with moderate and severe COVID-19 compared to those in remission (remission vs. active disease, severe 33% (n=20) vs. 67%(n=40), moderate 45% (n=35) vs.55% (n=42), and mild: 67% (n=56) vs. 33% (n=28), p value <0.001) (Figure 1). This was significant when categorized as severe vs. non severe as well (p=0.002). COVID-19 severity was also associated with AML diagnosis, major comorbidities, and neutropenia and lymphopenia at the time of COVID-19 diagnosis. Univariate analyses of increased mortality after COVID-19 diagnosis were significantly associated with advanced age, male sex, pre-diagnosis survival < 6 months, active disease status, neutropenia, lymphopenia and forgoing ICU care. Multivariable analyses in all pts (Figure 1), revealed that increased COVID-19 related mortality was significantly associated with neutropenia at diagnosis (OR 3.15, 95% C.I. 1.31-8.08, p=0.01), estimated pre-COVID-19 prognosis of < 6 months (OR 8.58, 95% C.I. 3.24-24.46, p<0.001) and forgoing ICU care (OR 6.66, 95% C.I. 2.56-18.23, p<0.001). Among hospitalized pts, increased COVID-19 mortality was associated with estimated pre-COVID-19 prognosis of < 6 months (OR 6.77, 95% C.I. 2.34-22.24, p<0.001) and forgoing ICU care (OR 3.98, 95% C.I. 1.45-11.66, p=0.007). Pts who were older, male, smokers, with active disease, or estimated to have pre-COVID-19 survival of < 6 months were more likely to forgo ICU care. Forgoing ICU care (n=37,16%) was associated with a higher COVID-19 mortality in all pts (n=234, OR 15.6, 95% C.I. 6.4-40.9, p<0.001), hospitalized pts (n=143, OR 9.2, 95% C.I., 3.5-26.5, p<0.001) and in pts where ICU admission was indicated and declined (n=61 OR 5.6, 95% C.I. 1.1-56.4, p=0.03)). Neither active disease status nor ongoing cancer treatment were associated with increased mortality among hospitalized patients. Conclusions: These data suggest that patients with active disease experience significantly higher COVID-19 severity but not increased mortality from COVID-19. Patients who had neutropenia and a pre-COVID-19 prognosis of < 6 months had higher mortality from COVID-19 infection and may be more likely to forgo ICU care. If desired by patients, aggressive support for hospitalized patients with COVID-19 is appropriate regardless of remission status. [Formula presented] Disclosures: Desai: Agios: Consultancy;Janssen R&D: Research Funding;Kura Oncology: Consultancy;Bristol Myers Squibb: Consultancy;Astex: Research Funding;Takeda: Consultancy. Goldberg: AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding;Aprea: Research Funding;Prelude Therapeutics: Research Funding;Pfizer: Research Funding;Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees;DAVA Oncology: Honoraria;Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees;Arog: Research Funding;Celularity: Research Funding;Aptose: Consultancy, Research Funding. Anderson: Sanofi-Aventis: Membership on an entity's Board of Directors or advisory committees;Celgene: Membership on an entity's Board of Directors or advisory committees;Gilead: Membership on an entity's Board of Directors or advisory committees;Janssen: Membership on an entity's Board of Directors or advisory committees;Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees;Pfizer: Membership on an entity's Board of Directors or advisory committees;Millenium-Takeda: Membership on an entity's Board of Directors or advisory committees;Scientific Founder of Oncopep and C4 Therapeutics: Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company;AstraZeneca: Membership on an entity's Board of Directors or advisory committees;Mana Therapeutics: Membership on an entity's Board of Directors or advisory committees. Neuberg: Pharmacyclics: Research Funding;Madrigal Pharmaceuticals: Other: Stock ownership. Radhakrishnan: Emcure Pharmaceuticals: Other: payment to institute;Bristol Myers Squibb: Other: payment to institute;Astrazeneca: Consultancy, Honoraria;Cipla Pharmaceuticals: Honoraria, Other: payment to institute;Pfizer: Consultancy, Honoraria;Johnson and Johnson: Honoraria;Novartis: Honoraria;Aurigene: Speakers Bureau;Roche: Honoraria, Other: payment to institute;Intas Pharmaceutical: Other: payment to institute;Dr Reddy's Laboratories: Honoraria, Membership on an entity's Board of Directors or advisory committees;Janssen India: Honoraria;NATCO Pharmaceuticals: Research Funding. Roboz: Novartis: Consultancy;Mesoblast: Consultancy;Amgen: Consultancy;Actinium: Consultancy;AbbVie: Consultancy;Janssen: Consultancy;Blueprint Medicines: Consultancy;Astex: Consultancy;Janssen: Research Funding;Daiichi Sankyo: Consultancy;Jazz: Consultancy;Agios: Consultancy;Glaxo SmithKline: Consultancy;Celgene: Consultancy;Otsuka: Consultancy;Astellas: Consultancy;Helsinn: Consultancy;MEI Pharma - IDMC Chair: Consultancy;Jasper Therapeutics: Consultancy;Bristol Myers Squibb: Consultancy;AstraZeneca: Consultancy;Bayer: Consultancy;Pfizer: Consultancy;Roche/Genentech: Consultancy. Sehn: Novartis: Consultancy;Genmab: Consultancy;Debiopharm: Consultancy. Sekeres: Takeda/Millenium: Membership on an entity's Board of Directors or advisory committees;Novartis: Membership on an entity's Board of Directors or advisory committees;BMS: Membership on an entity's Board of Directors or advisory committees. Tallman: Syros: Membership on an entity's Board of Directors or advisory committees;Kura: Membership on an entity's Board of Directors or advisory committees;NYU Grand Rounds: Honoraria;Innate Pharma: Membership on an entity's Board of Directors or advisory committees;Novartis: Membership on an entity's Board of Directors or advisory committees;Biosight: Membership on an entity's Board of Directors or advisory committees;Roche: Membership on an entity's Board of Directors or advisory committees;Jazz Pharma: Membership on an entity's Board of Directors or advisory committees;Oncolyze: Membership on an entity's Board of Directors or advisory committees;KAHR: Membership on an entity's Board of Directors or advisory committees;Orsenix: Membership on an entity's Board of Directors or advisory committees;Daiichi-Sankyo: Membership on an entity's Board of Directors or advisory committees;Abbvie: Membership on an entity's Board of Directors or advisory committees;Amgen: Research Funding;Rafael Pharmaceuticals: Research Funding;Glycomimetics: Research Funding;Biosight: Research Funding;Orsenix: Research Funding;Abbvie: Research Funding;Mayo Clinic: Honoraria;UC DAVIS: Honoraria;Northwell Grand Rounds: Honoraria;NYU Grand Rounds: Honoraria;Danbury Hospital Tumor Board: Honoraria;Acute Leukemia Forum: Honoraria;Miami Leukemia Symposium: Honoraria;New Orleans Cancer Symposium: Honoraria;ASH: Honoraria;NCCN: Honoraria. Wood: Pfizer: Research Funding;Teladoc: Consultancy;Koneksa Health: Consultancy, Current equity holder in publicly-traded company.

Clinical Characteristics and Outcomes of Patients with Newly Diagnosed De Novo Acute Myeloid Leukemia (AML) during the COVID-19 Pandemic

Introduction The COVID-19 pandemic disrupted non-urgent and preventive medical care. During the early peak of the pandemic, an estimated 41% of US adults delayed or avoided medical care (Czeisler et al, CDC, 2020). While there were documented declines in the number of emergency department visits for myocardial infarction, stroke and hyperglycemia, similar data is not available related to acute myeloid leukemia (AML) (Lange et al, CDC, 2020). A delay in the diagnosis of AML could lead to presentation when patients are less able to withstand chemotherapy or have a higher disease burden which could compromise overall survival (OS). In this retrospective analysis, we aim to elucidate if there was a difference in clinical, cytogenetic, or molecular presentations and if there was an effect on early mortality as determined by overall survival at 1 and 6 months. Methods We compared the clinical, cytogenetic, and baseline molecular genetics of consecutive adult patients diagnosed with de novo AML at Dana-Farber Cancer Institute/Brigham and Women's (DFCI/BWH) Hospital from March 23, 2020, the date of the Massachusetts COVID State of Emergency, to August 23, 2020 to a historical cohort of similar patients between presenting between March 23, 2017 and August 23, 2020. Data was obtained from the Hematological Malignancy Data Repository and via review of the medical record. Patients were excluded from this cohort if they were diagnosed with acute promyelocytic leukemia, had known antecedent myeloid malignancy, or if they did not have DFCI/BWH 96-gene next-generation sequencing panel (RHP) performed at the time of diagnosis. Baseline clinical, laboratory, cytogenetic, and molecular characteristics and outcomes were compared between the pre-pandemic and pandemic cohorts using chi-squared, Fisher's exact, and Wilcoxon rank sum analyses (where appropriate) at a significance of p<0.05. Results Thirty-eight AML patients presented during the COVID-19 pandemic (PAN) and 308 in the pre-pandemic (PREPAN) period. There was no statistically significant difference in the monthly rate of new patients presenting in PREPAN and PAN cohorts (8 vs. 6 new patients/month, p=0.73). The median age at presentation (64 PREPAN vs. 65 PAN, p=0.77), sex, and therapeutic approach (intensive, non-intensive, supportive care, other) were not statistically different between cohorts. Presenting white blood cell count, platelet count, and fibrinogen were not different between cohorts, while hematocrit was significantly lower in the PAN cohort (23.8% vs. 26.0%, p=0.001). There was a trend for a higher median blast percentage (28.5% vs. 13%, p=0.09) in the PAN cohort. There were no differences between the cohorts in the median number of cytogenetic abnormalities, nor in the incidence of complex karyotype, (25.3% vs. 23.7%) across PREPAN and PAN respectively. There were also no significant differences in the European LeukemiaNet (ELN) risk classification scores across the PREPAN and PAN time periods, with 57.8% vs. 52.6% of total patients presenting with adverse risk disease respectively. When specific mutations of TP53, NPM1, and FLT3 were evaluated, only FLT3 demonstrated a statistical difference with a higher proportion in the pandemic group (p=0.04). OS at 1-month (97.4% and 93.2%, p=0.15) and 6-months (71.1% and 75.0%, p-0.87) were not statistically different in the PREPAN and PAN cohorts, respectively. Conclusion These data represent a novel analysis of the presenting clinical, cytogenetic and molecular characteristics of de novo AML during the COVID-19 pandemic. In contrast to other diseases, we did not see fewer de novo AML presentations during the peak of the COVID pandemic. While the reasons are unknown and require validation in large cohorts, the symptoms of leukemia including symptomatic anemia (low hematocrit) and higher WBC and blast count possibly driven by FLT3 mutations may drive patients to seek emergent clinical evaluation despite COVID pandemic barriers. The lack of difference in cytogenetic or other prognostic entities may demonstrate a lack of ymptom correlation causing patients to present for care. The higher incidence of FLT3 mutations and lower hematocrit could reflect more symptomatic presentation of AML during the COVID pandemic. Since these differences may be a surrogate for a higher disease burden, it will be important to compare outcomes at longer time points. [Formula presented] Disclosures: DeAngelo: Pfizer: Consultancy;Novartis: Consultancy, Research Funding;Jazz: Consultancy;Incyte: Consultancy;Forty-Seven: Consultancy;Autolus: Consultancy;Amgen: Consultancy;Agios: Consultancy;Takeda: Consultancy;Glycomimetrics: Research Funding;Blueprint: Research Funding;Abbvie: Research Funding;Servier: Consultancy. Stone: Bristol Meyers Squibb: Consultancy;Astellas: Membership on an entity's Board of Directors or advisory committees;BerGen Bio: Membership on an entity's Board of Directors or advisory committees;Boston Pharmaceuticals: Consultancy;Innate: Consultancy;Foghorn Therapeutics: Consultancy;Gemoab: Membership on an entity's Board of Directors or advisory committees;Glaxo Smith Kline: Consultancy;Celgene: Consultancy;Elevate Bio: Membership on an entity's Board of Directors or advisory committees;OncoNova: Consultancy;Syntrix/ACI: Membership on an entity's Board of Directors or advisory committees;Syndax: Membership on an entity's Board of Directors or advisory committees;Janssen: Consultancy;Agios: Consultancy, Research Funding;Amgen: Membership on an entity's Board of Directors or advisory committees;Aprea: Consultancy;Arog: Consultancy, Research Funding;Jazz: Consultancy;Macrogenics: Consultancy;Novartis: Consultancy, Research Funding;Actinium: Membership on an entity's Board of Directors or advisory committees;Abbvie: Consultancy;Syros: Membership on an entity's Board of Directors or advisory committees;Takeda: Consultancy. Garcia: AstraZeneca: Research Funding;Prelude: Research Funding;Pfizer: Research Funding;Genentech: Research Funding;Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees;Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees;AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Winer: Abbvie: Consultancy;Takeda: Consultancy;Novartis: Consultancy.

Safety and Efficacy of Cusatuzumab in Combination with Venetoclax and Azacitidine (CVA) in Patients with Previously Untreated Acute Myeloid Leukemia (AML) Who Are Not Eligible for Intensive Chemotherapy;An Open-Label, Multicenter, Phase 1b Study

Background: Acute myeloid leukemia (AML) is driven by aberrant leukemic stem cells (LSCs) that initiate and sustain malignancy. To circumvent resistance to therapy, combination therapies with additive mechanisms of action are needed. CD70, a tumor necrosis factor receptor ligand, and its receptor CD27 are expressed on LSCs and AML blasts, but not on hematopoietic stem cells. Cusatuzumab, a high-affinity humanized monoclonal anti-CD70 antibody, kills CD70-expressing cells by Fc domain-mediated effector functions and is a potent inhibitor of CD70-CD27 signaling. Here we report initial results of a study of cusatuzumab in combination with the current standard of care therapy, venetoclax plus azacitidine (CVA), in patients with untreated AML (de novo or secondary) ineligible for intensive chemotherapy due to age ≥75 years or medical comorbidities. Methods: The primary objective of this open label, multicenter, phase 1b study was to assess safety and tolerability of CVA. Key secondary objectives included response rate per ELN 2017 criteria and time to response. Patients received cusatuzumab 10 or 20 mg/kg IV on Day 3 and Day 17, a 3-day ramp-up of venetoclax (100, 200, and 400 mg PO) followed by 400 mg daily dosing, and azacitidine 75 mg/m 2 SC or IV on Days 1-7 of each 28-day cycle. Results: Based on data through Jul 9, 2021, 44 patients enrolled with median age 75 years (range 32-89), 36.4% had secondary AML, 40.9% had an ECOG performance status of 2, and ELN risk was favorable, intermediate and adverse in 18.2%, 20.5% and 61.4%, respectively. All patients received 20 mg/kg cusatuzumab except for 3 patients who received a starting dose of 10 mg/kg with the option to escalate to 20 mg/kg. Of these 3 patients, 1 escalated to 20 mg/kg. At a median follow-up of 29.1 weeks, the median number of treatment cycles was 4.0 (range 1.0-11.0). Grade 3 or above TEAEs were reported in 97.7% of patients;the most common (reported in ≥10%) were neutropenia (68.2%), thrombocytopenia (65.9%), febrile neutropenia (36.4%), anemia (34.1%), leukopenia (29.5%), sepsis (27.3%), and lymphopenia (15.9%). Treatment-emergent serious adverse events (SAEs) were reported in 75% of patients;the most common (reported in at least ≥5%) were febrile neutropenia (27.3%), sepsis (22.7%), COVID-19 (6.8%), and thrombocytopenia (6.8%). Treatment-emergent SAEs of grade ≥3 were reported in 72.7% of the patients. Infusion-related reactions (IRRs) were reported for 11.4% of patients with 2.3% at grade ≥3. Six (13.6%) patients discontinued treatment due to AEs, and 5 (11.4%) TEAEs resulted in death. The mortality rate within 30 days from start of treatment was 4.5%. Table 1 summarizes best response to study treatment. In the intent-to-treat analysis set (n=44) complete remission (CR) rate was 45.5%, while CR + CR with partial hematologic recovery (CRh) + CR with incomplete hematologic recovery (CRi) was 77.3%;MLFS was observed in 11.4% of patients. Of 34 responders (defined as CR, CRi or CRh), 47% were MRD negative by flow cytometry at or after achievement of response. Median time to first response for patients who achieved CR, CRh or CRi was 4.21 (3.0-25.0) weeks. Best response rates in the post-hoc response evaluable analysis set (n=42) that excluded two patients who died before the first disease evaluation were: CR in 47.6%, CR + CRh + CRi in 81.0% and MLFS in 11.9% of patients (Table 1). The majority (97.1%) of responders experienced at least one cycle delay in administration of CVA post response. Conclusions: Cusatuzumab administered in combination with venetoclax and azacitidine to elderly patients with untreated AML was generally well tolerated and demonstrated a safety profile consistent with that previously reported with venetoclax-azacitidine, with the addition of generally manageable IRRs. Response rates support an additive effect of cusatuzumab to the standard of care with potential for improved clinical outcomes. However, further clinical trials are needed for validation of these initial results. HK and GB contributed equally to this publ cation. [Formula presented] Disclosures: Roboz: AstraZeneca: Consultancy;Janssen: Research Funding;Bristol Myers Squibb: Consultancy;Jasper Therapeutics: Consultancy;Agios: Consultancy;Novartis: Consultancy;Amgen: Consultancy;Blueprint Medicines: Consultancy;Janssen: Consultancy;Helsinn: Consultancy;Daiichi Sankyo: Consultancy;Glaxo SmithKline: Consultancy;Celgene: Consultancy;Jazz: Consultancy;MEI Pharma - IDMC Chair: Consultancy;Mesoblast: Consultancy;Actinium: Consultancy;AbbVie: Consultancy;Astex: Consultancy;Bayer: Consultancy;Astellas: Consultancy;Roche/Genentech: Consultancy;Pfizer: Consultancy;Otsuka: Consultancy. Aribi: Seagen: Consultancy. Brandwein: Astellas: Honoraria;Jazz: Honoraria;Amgen: Honoraria;Taiho: Honoraria;BMS/Celgene: Honoraria;Pfizer: Honoraria;Abbvie: Honoraria;University of Alberta: Current Employment. Döhner: Astellas: Consultancy, Honoraria, Research Funding;AstraZeneca: Consultancy, Honoraria;Berlin-Chemie: Consultancy, Honoraria;Amgen: Consultancy, Honoraria, Research Funding;Abbvie: Consultancy, Honoraria, Research Funding;Agios: Consultancy, Honoraria, Research Funding;Celgene: Consultancy, Honoraria, Research Funding;GEMoaB: Consultancy, Honoraria;Helsinn: Consultancy, Honoraria;Janssen: Consultancy, Honoraria;Jazz: Consultancy, Honoraria, Research Funding;Novartis: Consultancy, Honoraria, Research Funding;Oxford Biomedicals: Consultancy, Honoraria;Pfizer: Research Funding;Roche: Consultancy, Honoraria;Gilead: Consultancy, Honoraria;Bristol Myers Squibb: Consultancy, Honoraria, Research Funding;Astex: Consultancy, Honoraria;Ulm University Hospital: Current Employment. Fiedler: Jazz Pharmaceuticals: Consultancy, Other: support for meeting attendance;Abbvie: Consultancy, Honoraria;Morphosys: Consultancy;Celgene: Consultancy;Pfizer: Consultancy, Research Funding;Novartis: Consultancy;ARIAD/Incyte: Consultancy;Amgen: Consultancy, Other: support for meeting attendance, Patents & Royalties, Research Funding;Servier: Consultancy, Other: support for meeting attendance;Daiichi Sankyo: Consultancy, Other: support for meeting attendance;Stemline: Consultancy. Gandini: argenx: Current Employment, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months. Geddes: University of Calgary: Current Employment;Taiho: Consultancy, Membership on an entity's Board of Directors or advisory committees;Jazz: Consultancy, Membership on an entity's Board of Directors or advisory committees;Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees;Novartis: Consultancy;BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau;Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees;Amgen: Consultancy;Paladin: Consultancy;Janssen: Research Funding;Geron: Research Funding;Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding. Hou: University of Pittsburgh Medical Center Hillman Cancer Centers: Current Employment;AbbVie: Honoraria;AstraZeneca: Honoraria;Karyopharm: Honoraria;Chinese American Hematology Oncology Network: Membership on an entity's Board of Directors or advisory committees. Howes: Janssen R&D, part of Johnson & Johnson: Current Employment;Johnson & Johnson: Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Hultberg: argenx: Current Employment, Patents & Royalties. Huselton: University of Rochester: Current Employment. Jacobs: Argenx BV: Current Employment, Current equity holder in publicly-traded company;University of Antwerp: Ended employment in the past 24 months. Kane: Janssen R&D, part of Johnson & Johnson: Current Employment, Current equity holder in publicly-traded company. Lech-Marańda: Takeda: Membership on an entity's Board of Directors or advisory committees;AbbVie: Membership on an entity's Board of Directors r advisory committees;Novartis: Membership on an entity's Board of Directors or advisory committees;Roche: Membership on an entity's Board of Directors or advisory committees;Janssen-Cilag: Membership on an entity's Board of Directors or advisory committees;Amgen: Membership on an entity's Board of Directors or advisory committees;Sanofi: Membership on an entity's Board of Directors or advisory committees;Gilead: Membership on an entity's Board of Directors or advisory committees, Research Funding. Louwers: argenx: Current Employment, Patents & Royalties: Patents (no royalties). Nottage: Janssen R&D, part of Johnson & Johnson: Current Employment;Johnson & Johnson: Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Platzbecker: Novartis: Honoraria;AbbVie: Honoraria;Janssen: Honoraria;Celgene/BMS: Honoraria;Geron: Honoraria;Takeda: Honoraria. Rampal: Pharmaessentia: Consultancy;BMS/Celgene: Consultancy;Abbvie: Consultancy;Sierra Oncology: Consultancy;Incyte: Consultancy, Research Funding;Blueprint: Consultancy;Disc Medicine: Consultancy;Jazz Pharmaceuticals: Consultancy;Constellation: Research Funding;Kartos: Consultancy;Stemline: Consultancy, Research Funding;CTI: Consultancy;Novartis: Consultancy;Memorial Sloan Kettering: Current Employment. Salman: Janssen: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Shah: Janssen R&D, part of Johnson & Johnson: Current Employment. Stuart: Clinical Drug Development Consultants LLC: Current Employment;Argenx: Consultancy;Cleave Therapeutics: Consultancy;Triphase Accelerator Corp: Consultancy;IgM Biosciences: Consultancy;Revolution Medicines: Consultancy;Jiya Corp:Consultancy;Geron Corp: Current holder of individual stocks in a privately-held company. Subklewe: Janssen: Consultancy;Pfizer: Consultancy, Speakers Bureau;Takeda: Speakers Bureau;Klinikum der Universität München: Current Employment;MorphoSys: Research Funding;Novartis: Consultancy, Research Funding, Speakers Bureau;Roche: Research Funding;Seattle Genetics: Consultancy, Research Funding;Miltenyi: Research Funding;Gilead: Consultancy, Research Funding, Speakers Bureau;Amgen: Consultancy, Research Funding, Speakers Bureau;BMS/Celgene: Consultancy, Research Funding, Speakers Bureau. Sumbul: argenx: Current Employment. Wang: Takeda: Consultancy, Honoraria, Other: Advisory board;Jazz Pharmaceuticals: Consultancy, Honoraria, Other: Advisory Board;Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees;Stemline Therapeutics: Consultancy, Honoraria, Other: Advisory board, Speakers Bureau;AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees;Kite Pharmaceuticals: Consultancy, Honoraria, Other: Advisory Board;GlaxoSmithKline: Consultancy, Honoraria, Other: Advisory Board;Genentech: Membership on an entity's Board of Directors or advisory committees;BMS/Celgene: Membership on an entity's Board of Directors or advisory committees;DAVA Oncology: Consultancy, Speakers Bureau;Kura Oncology: Consultancy, Honoraria, Other: Advisory board, steering committee, Speakers Bureau;Novartis: Consultancy, Honoraria, Other: Advisory Board;Mana Therapeutics: Consultancy, Honoraria;Pfizer: Consultancy, Honoraria, Other: Advisory Board, Speakers Bureau;Rafael Pharmaceuticals: Other: Data safety monitoring committee;Gilead: Consultancy, Honoraria, Other: Advisory board;Daiichi Sankyo: Consultancy, Honoraria, Other: Advisory board;PTC Therapeutics: Consultancy, Honoraria, Other: Advisory board;Genentech: Consultancy;MacroGenics: Consultancy. Wierzbowska: Jazz: Research Funding;Pfizer: Honoraria;Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees;Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees;Astellas: Honoraria, Membership on an entity's Board of Directors or advisory comm ttees;Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees;BMS: Honoraria. Yao: Statagize LLC: Current Employment;Puma Biotechnology, Inc.: Ended employment in the past 24 months;Argenx: Consultancy. Yee: Astex: Membership on an entity's Board of Directors or advisory committees, Research Funding;Janssen: Research Funding;TaiHo: Membership on an entity's Board of Directors or advisory committees;Otsuka: Membership on an entity's Board of Directors or advisory committees;Onconova: Research Funding;Pfizer: Membership on an entity's Board of Directors or advisory committees;Tolero: Research Funding;Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding;Paladin: Membership on an entity's Board of Directors or advisory committees;MedImmune: Research Funding;AbbVie: Honoraria;Bristol-Myers Squibb/Celgene: Membership on an entity's Board of Directors or advisory committees;Shattuck Labs: Membership on an entity's Board of Directors or advisory committees;Forma Therapeutics: Research Funding;Takeda: Membership on an entity's Board of Directors or advisory committees;Geron: Research Funding;Genentech: Research Funding;F. Hoffmann La Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding;Jazz: Research Funding. Kantarjian: Immunogen: Research Funding;Astra Zeneca: Honoraria;KAHR Medical Ltd: Honoraria;Astellas Health: Honoraria;Pfizer: Honoraria, Research Funding;NOVA Research: Honoraria;Ascentage: Research Funding;Precision Biosciences: Honoraria;Novartis: Honoraria, Research Funding;Aptitude Health: Honoraria;Ipsen Pharmaceuticals: Honoraria;Jazz: Research Funding;Daiichi-Sankyo: Research Funding;BMS: Research Funding;Amgen: Honoraria, Research Funding;AbbVie: Honoraria, Research Funding;Taiho Pharmaceutical Canada: Honoraria. Borthakur: Protagonist: Consultancy;Ryvu: Research Funding;Astex: Research Funding;GSK: Consultancy;Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees;Takeda: Membership on an entity's Board of Directors or advisory committees;University of Texas MD Anderson Cancer Center: Current Employment;ArgenX: Membership on an entity's Board of Directors or advisory committees.

ATG and Post-Transplant Cyclophosphamide Predisposes to Inferior Outcome When Using Cryopreserved Stem Cell Grafts

Background During 2020, the novel COVID-19 pandemic lead to cryopreservation of allogeneic hematopoietic stem cell (HSCT) grafts based on NMDP and EBMT recommendations, to secure grafts before start of conditioning chemotherapy. We examined the impact of this change in practice on patient outcomes. Methods We retrospectively analyzed the outcomes of 483 patients who received HSCT between Aug 2017 and Aug 2020, at Princess Margaret Cancer Centre, Canada, comparing the outcomes between those who received cryopreserved (CRYO, n=135) or fresh peripheral blood stem cell grafts (FRESH, n=348). Median follow-up: 12.3 months. Probability of overall survival (OS) was calculated using the Kaplan-Meier product-limit method and heterogeneity of time-to-event distribution functions were compared by the log-rank test. Cumulative incidences of aGvHD and cGvHD, relapse, and non-relapse mortality (NRM) were estimated using the cumulative incidence method considering competing risk, and groups were compared using Gray's test. Death was considered as a competing event for relapse, aGvHD and cGvHD, and relapse was considered a competing event for NRM, aGvHD and cGvHD. Results Median age was 58y;54.5% were males. Acute myeloid leukemia was commonest HSCT indication (n=248, 49.1%). Donors: MUD 10/10 n=233;MUD 9/10 (MMUD) n=48, matched related donor (MRD) n=112, Haploidentical n=88. Transplant conditioning: 79 (23%) and 23 (17%) patients received myeloablative conditioning (MAC) in the FRESH and the CRYO groups, respectively (p ns). In the FRESH group, 253 (73%) patients and 114 (84%) patients in the CRYO group received ATG followed by posttransplant cyclophosphamide (PTCy) and Cylosporine GvHD prophylaxis. OS at the 2y timepoint, FRESH group (n=348), was 67.0% (61.1-72.3%), compared to 48.7% (38.1-58.4%) for patients in the CRYO group (n=135), p=0.002, Figure 1a. This was mainly due to MRD cohort outcomes: 2y OS in MRD FRESH group (n=65), was 85.2% (73.3-92.0%), compared to 45.1% (29.9-59.1%) in MRD CRYO group (n=47), p<0.001, Figure 2a. Multivariate analysis (MVA) for OS, significant factors were increasing patient age, DRI high/v.-high, HCT-CI ≥ 3, Donors: Haplo and MMUD, cryopreservation, Table 1. NRM at 1y for FRESH (n=348) 17% (13.2-21.2) vs CRYO (n=135) 22.1 % (14.8-30.4), p ns. However, in the MRD cohort, NRM at 1y for FRESH group (n=65), was 1.5% (0.1-7.4%), compared to 15.4% (6.6-27.4%) for CRYO group (n=47), p=0.003, Figure 2b. On MVA, NRM adverse significant factors were patient age, DRI high/v.-high, Donors: Haplo and MMUD, Table 1. Cumulative incidence (CI) of relapse at 2y for FRESH 22.4% (17.5-27.7) vs CRYO 27.0 % (18.8-35.9) p=0.07. The CI of moderate-severe cGvHD at 1y for FRESH group (n=315) was 21.5% and 10.8% in the CRYO group, p=0.027, Figure 1c. Patients with FRESH 10/10 MUDs (n=180), had CI of moderate-severe cGvHD at 1y of 20.6%, compared to CRYO 10/10 MUDs (n=35), 6.0% p ns for MUDs;FRESH MRD (n=64) CI was 30.1%;and CRYO MRD (n=43) 10.3%, p=0.008 for MRD, Figure 1d. On MVA, significant adverse factors for chronic GvHD were increasing donor age, male recipient/female donor, whilst graft CRYO was protective, Table 1. GvHD-and Relapse free Survival (GRFS) at 2y for FRESH 54.0% (47.9-59.6) vs CRYO 43.4% (33.4-53.0) p<0.05, Figure 1b. However, in the MRD cohort, GRFS at 2y in FRESH group (n=65), was 74.2% (61.3-83.4%), compared to 40.7% (26.3-54.6%) for CRYO group (n=47), p=0.001;other donor types no difference, Figure 1c. On MVA, significant factors correlated with worse GRFS were: DRI high and very-high, cryopreservation, Donors: Haplo and MMUD, Table 1. Compared to FRESH group, CRYO group experienced reduced cGvHD, delay in neutrophil engraftment, higher graft failure and increased CMV reactivation, with no difference in relapse incidence or acute GvHD. Conclusion Cryopreservation was associated with inferior outcomes post-HSCT particularly in the MRD cohort, possibly due to combination ATG and post-transplant cyclophosphamide impacting differential tolerance to cryopreservation on components of the stem ce l graft;further studies are warranted to elucidate mechanisms for this observation. [Formula presented] Disclosures: Law: Novartis: Consultancy;Actinium Pharmaceuticals: Research Funding. Lipton: Bristol Myers Squibb, Ariad, Pfizer, Novartis: Consultancy, Research Funding. Kim: Bristol-Meier Squibb: Research Funding;Paladin: Honoraria, Research Funding;Pfizer: Honoraria, Research Funding;Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Mattsson: MattssonAB medical: Current Employment, Current holder of individual stocks in a privately-held company.

Incidence and Predictors of Sars-Cov-2 Antibody Responses Following COVID-19 Vaccination in Allogeneic Stem Cell Transplant Recipients

Background Pharmacologic immunosuppression and incomplete immune reconstitution after allogeneic stem cell transplant (alloSCT) may impair a patient's ability to mount an immune response to vaccines, including currently available COVID-19 vaccines. Since immunocompromised patients are susceptible to severe COVID-19 and likely to respond poorly to vaccination, we sought to characterize SARS-CoV-2 antibody responses after vaccination in alloSCT patients to determine predictors of serologic response, which may inform timing of vaccine administration. Methods This retrospective analysis included adult patients who underwent alloSCT at the University of Pennsylvania between 1/1/2019 and 1/1/2021. Chart review identified patients who had received COVID-19 vaccines and had post-vaccination antibody titers drawn by July 2021 as part of routine care (n=63). Antibodies to SARS-CoV-2 spike protein receptor binding domain were detected using an assay developed at the Hospital of the University of Pennsylvania. Variables analyzed include interval between transplant date and initial vaccination, active GVHD, concurrent immunosuppressive therapy, absolute CD4 count greater than or equal to 200 cells/mm3 peri-vaccination, and total IgG greater than or equal to 400 mg/dL peri-vaccination. Immunosuppressive therapy was defined as tacrolimus, rituximab, ruxolitinib, prednisone 10 mg daily or greater, or extracorporeal photopheresis. Predictors of positive antibody response were assessed using a multivariate, binary logistic regression. Results Median transplant to vaccine interval was 458 days (range 125 to 813) for the 63 vaccinated patients with serologies available. GVHD was present in 23/63 (37%), and 19/63 (30%) were receiving immunosuppressive therapies at the time of vaccination. CD4 count greater than 200 cells/mm3 was observed in 49 patients (78%), and total IgG greater than 400 mg/dL was observed in 51 patients (81%). In total, 50/63 patients (79%) were positive for SARS-CoV-2 IgG antibodies. Positive serologies were observed in 41/49 (84%) with CD4 counts greater than 200 cells/mm3, compared to 9/14 (64%) with CD4 less than 200 cells/mm3. Our model found that peri-vaccination CD4 count greater than 200 cells/mm3 was a significant predictor of positive SARS-CoV-2 IgG serologies in this population (OR 2.14, 97.5% CI = 0.7 to 3.8, p= 0.005). Transplant to vaccine interval, total IgG levels, GVHD status, and immunosuppressive therapies were not significant predictors of serologic response. As of July 2021 no patients had developed COVID-19 after vaccination, regardless of serologic response. Conclusions This retrospective observational study demonstrates that the majority of alloSCT patients vaccinated against COVID-19 within 2 years of transplant, including those with active GVHD and on immunosuppressive therapies, can mount serologic responses. CD4 count greater than 200 cells/mm3 is a significant predictor of positive serologic response, though even among patients with CD4 counts under 200 cells/mm3 over 60% developed SARS-CoV-2 IgG antibodies. Disclosures: Perry: Incyte: Consultancy, Speakers Bureau;Abbvie,: Speakers Bureau;Kadmon: Consultancy. Pratz: University of Pennsylvania: Current Employment;Abbvie: Consultancy, Honoraria, Research Funding;Astellas: Consultancy, Honoraria, Research Funding;Cellgene: Consultancy, Honoraria;Novartis: Consultancy;BMS: Consultancy, Honoraria;Agios: Consultancy;Millenium: 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. Perl: Astellas: Consultancy, Research Funding;Loxo: Consultancy;AbbVie: Consultancy, Research Funding;Syndax: Consultancy;BMS/Celgene: Consultancy;Roche: Consultancy;Fujifilm: Research Funding;Daiichi Sankyo: Consultancy, Research Funding;Forma: Consult ncy;Arog: Research Funding;Genentech: Consultancy;Actinium: Consultancy;Onconova: Consultancy;Sumitomo Dainippon: Consultancy. Porter: ASH: Membership on an entity's Board of Directors or advisory committees;Incyte: Membership on an entity's Board of Directors or advisory committees;DeCart: Membership on an entity's Board of Directors or advisory committees;Genentech: Current equity holder in publicly-traded company, Ended employment in the past 24 months;American Society for Transplantation and Cellular Therapy: Honoraria;Kite/Gilead: Membership on an entity's Board of Directors or advisory committees;Janssen: Membership on an entity's Board of Directors or advisory committees;National Marrow Donor Program: Membership on an entity's Board of Directors or advisory committees;Novartis: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding;Tmunity: Patents & Royalties;Wiley and Sons Publishing: Honoraria. Hexner: Blueprint medicines: Membership on an entity's Board of Directors or advisory committees, Research Funding;PharmaEssentia: Membership on an entity's Board of Directors or advisory committees;Tmunity Therapeutics: Research Funding. Frey: Sana Biotechnology: Consultancy;Kite Pharma: Consultancy;Syndax Pharmaceuticals: Consultancy;Novartis: Research Funding.