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Background: The two FDA approved mRNA-based SARS-CoV2 vaccines have shown >90% efficacy at preventing COVID and eliciting protective immunity in nearly all healthy individuals. However, the extent of vaccine induced antibody and T cell immunity in immunocompromised patients is not well known. Our study objective is to determine if patients with hematologic malignancies treated with B-cell targeting chimeric antigen receptor (CAR) T cell therapies can mount antibody and T cell immune responses to SARS-CoV2 vaccines. A prospective single-center study to evaluate the SARS-CoV2 immune responses in immunocompromised individuals (COVAX Study) was initiated at University of Pennsylvania following the IRB guidelines. The study enrolled 8 healthy adults,12 patients are in remission after treatment (average of 40.6 months) with CART cells targeting either CD19 or CD19+CD22 and received both doses of SARS-CoV2 vaccine. Methods and Results: Serology to SARS-CoV2 spike-receptor binding domain (RBD) IgG, RBD-IgA, RBD-IgM and spike-specific T cell responses were measured prior to vaccination and serially up to 28 days after booster vaccination. RBD-IgG and RBD-IgA were detected in 8/8 and 7/8 healthy subjects compared to 5/12 and 2/12 CART patients, respectively (Figure A). In the CART cohort, several patients who demonstrated an induction of RBD-IgG (57.2/uL +/- 20.2) compared to those who were RBD-IgG-negative (9/uL +/- 10.1, ANOVA with multiple comparisons test p=0.017) have higher level of circulating B cells. No association was found with time since CART infusion, age, disease type, or vaccine manufacturer. All 8 healthy subjects demonstrated induction of SARS-Cov2 spike-specific CD4 + T cell immunity compared to 7 out of 11 CART patients (Figure B). RBD-IgG responses were not correlated with CD4 + T cell activation (Pearson correlation, R=0.21, p=0.53). Indeed, 3 CART patients demonstrated robust CD4 + T cell activation despite absence of antibody induction. Overall, 8/12 CART patients demonstrated induction of either or both humoral and T cell immune responses. Conclusions: We show that immune responses to SARS-CoV2 mRNA vaccines are induced in majority of patients who have been treated with CART therapies targeting B-cell lineage antigens. Induction of vaccine-specific antibody was strongly associated with the level of circulating B cells. However, in CART cohort patients despite severe humoral immune deficiency, strong CD4 + T cell responses were observed suggestive of a sufficient protective immunity. Figure 1 Disclosures Frey: Novartis: Research Funding; Sana Biotechnology: Consultancy; Kite Pharma: Consultancy; Syndax Pharmaceuticals: Consultancy. Garfall: Amgen: Honoraria; CRISPR Therapeutics: Research Funding; GlaxoSmithKline: Honoraria; Janssen: Honoraria, Research Funding; Novartis: Research Funding; Tmunity: Research Funding. Porter: American Society for Transplantation and Cellular Therapy: Honoraria; Genentech: Current equity holder in publicly-traded company, Ended employment in the past 24 months; ASH: Membership on an entity's Board of Directors or advisory committees; DeCart: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Kite/Gilead: 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. June: AC Immune, DeCART, BluesphereBio, Carisma, Cellares, Celldex, Cabaletta, Poseida, Verismo, Ziopharm: Consultancy; Tmunity, DeCART, BluesphereBio, Carisma, Cellares, Celldex, Cabaletta, Poseida, Verismo, Ziopharm: Current equity holder in publicly-traded company; Novartis: Patents & Royalties.

Background :COVID-19 adversely affects individuals with cancer. Several studies have found that seroconversion rates among patients with hematologic malignancies are suboptimal when compared to patients without cancer. Among patients with hematologic malignancies, seroconversion rates also appear to be influenced by recent treatment and the type of treatment they have received. Patients with non-Hodgkin lymphoma (NHL) and multiple myeloma (MM) are immunocompromised due to impaired humoral and cellular immunity in addition to prescribed immunosuppressive therapy. Chimeric antigen receptor T-cell (CAR T) therapy is now widely used for NHL and MM, but little is known about seroconversion rates after COVID-19 vaccination among these populations. Current national guidelines recommend COVID-19 vaccination to be offered to CAR T recipients as early as three months thereafter. We retrospectively evaluated SARS-CoV-2 spike-binding IgG antibody levels following COVID-19 vaccination among NHL and MM CAR T therapy recipients. Methods:This retrospective study was conducted at three Mayo Clinic sites on NHL and MM patients that received CAR T infusions from Sept 2016 to June 2021. Baseline characteristics were ascertained from medical records. All NHL and MM patients who had received CAR T at any point and were alive at the time that the COVID-19 vaccine first became available were eligible for inclusion for antibody response evaluation. For antibody response to vaccination, antibody spike values > 0.80 U/mL were considered positive. Results: Out of 104 CAR T infusions, 73 patients are alive at the time of this submission. We have had 7 patients with known COVID-19 pre-CAR T and all 7 are currently alive (5 have antibody titers and 2 have not been tested yet). Nineteen patients developed known COVID infection post-CAR T (13 alive and 6 deceased). The mortality of COVID post-CAR T in our sample was 31.5%. Furthermore, of the 13 patients that survived COVID-19, they received CAR T an average of 416 days prior to COVID-19 infection (median = 337, range = 54 - 1406); the 6 patients who died from COVID-19 had received CAR T an average of 250 days prior to COVID-19 infection (median = 164, range = 7 - 846). All 6 deceased patients did not receive COVID-19 vaccination pre-CAR T. Out of 17 CAR T patients tested for antibody spike titers post COVID-19 vaccination, 76.4% were able to mount an antibody response. More patients with MM had a higher titer response to the vaccine (>250 U/mL) compared to the NHL counterparts (0.80-249 U/mL). All patients that received the vaccine, regardless of antibody response, were alive at the time of this submission. Conclusions:The majority of CAR T recipients with NHL and MM are able to mount an antibody response following COVID-19 vaccination in our relatively small sample. The frequency of seroconversion among CAR T recipients seems to be similar to patients with hematologic malignancy who had received a hematopoietic cell transplant reported elsewhere. These findings are limited by our small sample size and may be influenced by the timing of vaccination relative to CAR T. Furthermore, almost half of our patients received IVIG post CAR T which could potentially cause false positive antibody results as pooled immunoglobulin preparations may contain COVID-19 antibodies from vaccinated healthy donors. To better understand the characteristics of the immunologic response against SARS-CoV-2 in patients post-CAR T, larger multicenter studies exploring both humoral and cellular immunity will be needed. JEWN, MI and JM are co-first authors and PV, HM and AR are co-senior authors. Figure 1 Figure 1. Disclosures Munoz: Physicians' Education Resource: Honoraria; Seattle Genetics: Honoraria; Bayer: Research Funding; Gilead/Kite Pharma: Research Funding; Celgene: Research Funding; Merck: Research Funding; Portola: Research Funding; Incyte: Research Funding; Genentech: Research Funding; Pharmacyclics: Research Funding; Seattle Genetics: Research Funding; Janssen: Research Funding; Millennium: Research Funding; Gilead/Kite Pharma, Kyowa, Bayer, Pharmacyclics/Janssen, Seattle Genetics, Acrotech/Aurobindo, Beigene, Verastem, AstraZeneca, Celgene/BMS, Genentech/Roche.: Speakers Bureau; Pharmacyclics/Abbvie, Bayer, Gilead/Kite Pharma, Pfizer, Janssen, Juno/Celgene, BMS, Kyowa, Alexion, Beigene, Fosunkite, Innovent, Seattle Genetics, Debiopharm, Karyopharm, Genmab, ADC Therapeutics, Epizyme, Beigene, Servier: Consultancy; Targeted Oncology: Honoraria; OncView: Honoraria; Kyowa: Honoraria. Bergsagel: Oncopeptides: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Patents & Royalties: human CRBN mouse; Pfizer: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Genetech: Consultancy, Honoraria; GSK: Consultancy, Honoraria. Wang: Incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding; LOXO Oncology: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Research Funding; InnoCare: Research Funding; Novartis: Research Funding; MorphoSys: Research Funding; Eli Lilly: Membership on an entity's Board of Directors or advisory committees; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees. Fonseca: Juno: Consultancy; Kite: Consultancy; Aduro: Consultancy; OncoTracker: Consultancy, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy; AbbVie: Consultancy; Patent: Prognosticaton of myeloma via FISH: Patents & Royalties; Caris Life Sciences: Membership on an entity's Board of Directors or advisory committees; Scientific Advisory Board: Adaptive Biotechnologies: Membership on an entity's Board of Directors or advisory committees; BMS: Consultancy; Amgen: Consultancy; Sanofi: Consultancy; Merck: Consultancy; Mayo Clinic in Arizona: Current Employment; Celgene: Consultancy; Takeda: Consultancy; Bayer: Consultancy; Janssen: Consultancy; Novartis: Consultancy; Pharmacyclics: Consultancy. Palmer: Sierra Oncology: Consultancy, Research Funding; CTI BioPharma: Consultancy, Research Funding; Protagonist: Consultancy, Research Funding; Incyte: Research Funding; PharmaEssentia: Research Funding. Dingli: Novartis: Research Funding; GSK: Consultancy; Apellis: Consultancy; Alexion: Consultancy; Sanofi: Consultancy; Janssen: Consultancy. Kapoor: Sanofi: Research Funding; AbbVie: Research Funding; Takeda: Research Funding; Karyopharm: Consultancy; Cellectar: Consultancy; BeiGene: Consultancy; Pharmacyclics: Consultancy; Sanofi: Consultancy; Amgen: Research Funding; Ichnos Sciences: Research Funding; Regeneron Pharmaceuticals: Research Funding; Glaxo SmithKline: Research Funding; Karyopharm: Research Funding. Kumar: Roche-Genentech: Consultancy, Research Funding; Oncopeptides: Consultancy; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Consultancy, Research Funding; Beigene: Consultancy; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding; Adaptive: Membership on an entity's Board of Directors or advisory committees, Research Funding; Astra-Zeneca: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Tenebio: Research Funding; Merck: Research Funding; Carsgen: Research Funding; KITE: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: 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; Amgen: Consultancy, Research Funding; Bluebird Bio: Consultancy; Antengene: Consultancy, Honoraria; Sanofi: Research Funding. Paludo: Karyopharm: Research Funding. Bennani: Kymera: Other: Advisory Board; Vividion: Other: Advisory Board; Kyowa Kirin: Other: Advisory Board; Daichii Sankyo Inc: Other: Advisory Board; Purdue Pharma: Other: Advisory Board; Verastem: Other: Advisory Board. Ansell: Bristol Myers Squibb, ADC Therapeutics, Seattle Genetics, Regeneron, Affimed, AI Therapeutics, Pfizer, Trillium and Takeda: Research Funding. Lin: Kite, a Gilead Company: Consultancy, Research Funding; Merck: Research Funding; Gamida Cell: Consultancy; Takeda: Research Funding; Juno: Consultancy; Bluebird Bio: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Novartis: Consultancy; Janssen: Consultancy, Research Funding; Sorrento: Consultancy; Legend: Consultancy; Vineti: Consultancy. Murthy: CRISPR Therapeutics: Research Funding.

Introduction: Patients with hematologic malignancies are at an increased risk of morbidity and mortality from COVID-19 disease (Vijenthira, Blood 2020). This is likely a result of combination of immunodeficiency conferred by the disease and the therapeutics. The immunogenicity of the COVID-19 vaccines in patients with exposure to CD19 directed Chimeric Antigen Receptor (CAR)-T cell therapy is not established. CD19 CAR-T cell therapies cause B-cell aplasia, which in turn can affect humoral immune response against novel antigens. Herein, we present results from our prospectively conducted clinical study to evaluate immune responses against mRNA based COVID-19 vaccines in patients with lymphoma who have received CD19 directed CAR-T cell therapy. Methods: All patients and healthy controls were enrolled in a prospective clinical study evaluating immune responses against commercial COVID-19 RNA vaccines in patients with hematologic malignancies. Plasma samples were generated from heparinized peripheral blood of 4 heathy controls (HCs) receiving the same vaccines and 19 B cell lymphoma patients treated with CD19 CAR- T cells. Samples from ~4 weeks post second dose of the vaccine (d56) were available for 14 CAR-T patients, for 5 CAR-T patients samples were available from ~4 weeks after the first dose (d28). Plasma samples were analyzed in an enzyme-linked immunosorbent assay (ELISA) using different full-length recombinant SARS-CoV-2 proteins and control proteins. Neutralizing activity was measured using the cPass Neutralization Antibody Detection Kit (GenScript Biotech). Results: Results from 4 healthy controls and 19 patients (12 males and 7 females) with lymphoma are reported. Median age for the lymphoma patients is 65 years. Eleven patients had large B cell lymphoma, 5 had follicular lymphoma and 3 had mantle cell lymphoma as primary diagnoses. Seventeen patients had advance stage disease (III/IV stage) and had received a median of 3 prior lines of therapy. All patients received CD19 directed CAR-T cell therapy. Ten patients received Moderna vaccine and 9 received Pfizer vaccine. Median time between CAR-T infusion and first COVID-19 vaccine was 258 days. While the peripheral blood plasma from 3/4 HCs already showed substantial SARS-CoV-2 neutralizing activity at ~4 weeks after the first dose of COVID-19 mRNA vaccine, none of the 5 CD19 CAR-T patients analyzed evidenced any antibody-mediated neutralizing activity in their blood at the same point in time (Figure 1A). Around 4 weeks after receiving the second dose of the vaccine, all 4 HCs tested evidenced complete or almost complete neutralizing activity (Figure 1B). In marked contrast, only 1 out of 14 CAR-T patients analyzed evidenced any relevant antibody-mediated SARS-CoV-2 neutralizing activity in their blood (Figure 1B). Interestingly, when we asked whether a globally insufficient antibody-mediated immunity was the underlying cause of the lack of a response to the COVID-19 vaccine in our CAR-T patients, we found that that was clearly not the case since anti-Flu, -TT, and -EBV responses were equivalent to the ones observed in HCs (Figure 2A). However, while at ~4 weeks post second dose of the vaccine the HCs showed marked antibody titers against all the viral spike proteins including their "delta" variants (Figure 2B), that was not the case for our CAR-T patients. The vast majority of our CAR-T patients did not evidence IgG antibody responses against any of the SARS-CoV-2 proteins analyzed such as S1, S1 delta, RBD, RBD delta, or S2 (Figure 2B). Conclusion: In this prospectively conducted clinical study, 18 of 19 patients with lymphoma who have received CD19 CAR-T therapy had poor immunogenicity against mRNA based COVID-19 vaccines as measured by neutralization assays and antibody titers. The antibody titers against B.1.617.2 (delta variant, S1 and RBD protein) were also demonstrably poor. The antibody response to common pathogens (flu, EBV, TT) were preserved, suggesting impaired immune response against novel antigens. Long-term follow-up of this study is ongoing. APR and DJ contributed equally Figure 1 Figure 1. Disclosures Dahiya: Kite, a Gilead Company: Consultancy; Atara Biotherapeutics: Consultancy; BMS: Consultancy; Jazz Pharmaceuticals: Research Funding; Miltenyi Biotech: Research Funding. Hardy: American Gene Technologies, International: Membership on an entity's Board of Directors or advisory committees; InCyte: Membership on an entity's Board of Directors or advisory committees; Kite/Gilead: Membership on an entity's Board of Directors or advisory committees.

Introduction: Data regarding the efficacy of anti-severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) messenger RNA vaccines in immunocompromised hosts are scarce and no data yet appear to be available for patients with hematological malignancies who also received chimeric antigen receptor-T (CAR-T) cells therapy. Methods: The efficacy and safety of one and/or two injections of the BNT162b2 (Pfizer-BioNTech) vaccine was evaluated retrospectively in 23 CAR-T recipients in our Hematology Department, compared to a cohort of 25 healthy caregivers, vaccinated concomitantly between January 28 and May 31, 2021. None of these individuals had a previous clinical history of COVID-19. Results: Overall, the patients (14 males and 9 females) had a median age of 62 years old (range: 21-79) and had received CAR-T for high-grade lymphoma (n= 20) or acute lymphoblastic leukemia (n= 3). Eight and 3 had been respectively previously autografted or allografted and two were allografted after CAR-T. All patients were pretreated for lymphodepletion by fludarabine + cyclophosphamide before CAR-T infusion. The CAR-T provided were axicabtagene ciloleucel (Yescarta, Kite/Gilead, n=16, tisagenlecleucel (Kymriah, Novartis Pharma, n=5 and brexucabtagene autoleucel (KTE-X19, Tecartus, Kite/Gilead, n=1). One additional patient received allogeneic UCART19 (Servier). The median delay between CAR-T administration and the first vaccine (V1) was 401 days (d; range: 113-819). All patients but 2 were in complete remission at V1 and 3 were still on therapy (revlimid n=1, tafasitamab n=1, chemotherapy n=1). After V1, antibody response to the SARS-CoV-2 spike protein receptor-binding domain was tested by the Roche Elecsys® assay at a median time of 29 d (range: 16-32) in 19 patients and 23 d (range:18-32) in controls. At that time, only 4/23 patients (21%) but all controls (100%) had a positive anti-spike antibody response (p250) than in patients (5.9 U/mL range 4.1-41.6, p=0.06). The highest IgG titer (>250) was obtained in 2 controls. The median delay between V1 and the second vaccine (V2) was 28 d (range: 14-46) for patients and 23 d (range: 18-32) for controls. Among the 20 patients tested after V2, 17 had also been tested after V1 while 3 were tested only after V2. All controls were tested after V2. The second serology assay was performed at a median interval from V2 of 52 d (range: 21-99) for patients and 58 d (range: 32-71) for controls. This serology assay was positive in 6 patients (30%), while all controls (100%, p250) after V2. The two patients in relapse and treated by chemotherapy or tafasitamab did not develop antibodies after V2 conversely to the patient under maintenance by revlimid. The delay between CAR-T infusion and vaccine did not influence the antibody response nor did the rate of lymphopenia as almost all patients remained under a lymphocyte threshold of 1x10 9/L. Finally, with a median follow up from V1 of 77 d (range: 49-127) in patients and 81 d (range: 62-95) in controls, no COVID-19 infection has been documented in any of these participants. Conclusion: This study shows that the administration of two doses of BNT162b2 anti-SARS-CoV-2 messenger RNA vaccine provides a low rate of seroconversion (30%) in recipients of CAR-T therapy. This is likely related to the profound B-cell depletion induced by this treatment precisely targeting CD19+ cells. Investigation of the development of specific T-cell responses in these individuals could provide more information about the efficacy of vaccination in this context. Disclosures Moreau: Celgene BMS: Honoraria; Sanofi: Honoraria; Janssen: Honoraria; Abbvie: Honoraria; Amgen: Honoraria; Oncopeptides: Honoraria.

Background The ongoing Coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is having an enormous impact on society worldwide and is especially posing a threat to health in vulnerable patients, such as patients with immune deficiencies. It is expected that patients who received Chimeric Antigen Receptor T-cell (CAR T-cell) therapy for hematologic malignancies are at risk for poor outcomes after COVID-19 due to their severely immunocompromised state caused by prior cumulative immunochemotherapy, on-target/off-tumor B-cell depletion, hypogammaglobulinemia and ongoing cytopenias. Current data are limited to small case series and case reports. This study describes the clinical characteristics and outcomes of CAR T-cell therapy recipients after developing COVID-19 in the largest cohort to date. Methods In response to the COVID-19 pandemic, the European Society for Blood and Marrow Transplantation (EBMT) developed a special COVID-19 report form to capture data from all patients with COVID-19 after treatment with CAR T-cell therapy for hematologic malignancies. Only PCR positive SARS-CoV-2 diagnosed patients before June 1 st, 2021 were included. The aim of this study was to describe the clinical course after COVID-19 diagnosis and evaluate overall survival. Overall survival probabilities were calculated using the Kaplan Meier method. Factors associated with mortality after COVID-19 diagnosis were examined using a Cox proportional hazard model. Results A total of 57 patients from 11 countries were reported to the EBMT. One patient with incomplete data at diagnosis and without any follow up information had to be excluded from the analysis. The median age of these 56 patients was 57.7 years (min-max 5.2 - 72.8) including 55 adults and one child. Of these patients, 32 were male. CAR T-cell therapy was given to 46 patients with B-cell-non-Hodgkin lymphoma, 7 patients with B-cell acute lymphoblastic leukemia, and 3 patients with multiple myeloma. The median time from CAR T-cell infusion to COVID-19 diagnosis was 7.4 months (min-max 0.03 - 25.3). At the time of COVID-19 diagnosis, 62.5% of patients were in complete remission, 12.5% of patients had a partial response and 25% of patients had relapsed/refractory disease. Forty-five patients (80%) were admitted to hospital (median 26,5 days, min-max 3-171) due to COVID-19. Of the admitted patients, 24 (53%) needed oxygen support. Twenty-two (49%) patients were admitted to the intensive care unit (median 14 days, min - max 2-65) and 16 (73%) of these patients received invasive ventilation. At the time of analysis, 25 of the 56 patients had died (44.6%), most (23/25) due to COVID-19, resulting in a COVID-19 attributable mortality rate of 41%. The Kaplan-Meier estimate of overall survival is shown in Figure 1. The median follow-up from COVID-19 diagnosis was 20.9 weeks. In 1 of the 32 alive patients there was no resolution of COVID-19 at the time of analysis. In multivariate analysis, older age (hazard ratio (HR) 1.50, 95% CI 1.11-2.03, p=0.009) and comorbidities (HR 2.56, 95% CI 1.05-6.23, p=0.001) had a negative impact on overall survival. Better performance status at time of admission (HR 0.72, 95% CI 0.59-0.88, p=0.038) had a positive impact on overall survival. Sex, time from CAR T-cell therapy to COVID-19 diagnosis, disease remission status and the occurrence of neurotoxicity or cytokine release syndrome after CAR T-cell infusion did not have a significant effect on overall survival in the multivariate analysis. Conclusion Patients with COVID-19 after B-cell-targeted CAR T-cell therapy have a very poor outcome. As it remains uncertain whether currently applied vaccination strategies against SARS-CoV-2 are effective after CAR T-cell therapy, vaccination of health-care personnel and family members in combination with protective measures against viral exposure are likely to play the most important role in protecting this vulnerable group of patients. Better treatment strategies are urgently needed. Figure 1 Figure 1. Disclosures Ljungman: OctaPharma: Other: DSMB; Enanta: Other: DSMB; Janssen: Other: Investigator; Takeda: Consultancy, Other: Endpoint committee, speaker; AiCuris: Consultancy; Merck: Other: Investigator, speaker. De La Camara: IQONE: Consultancy; Roche: Consultancy. Ortiz-Maldonado: Kite, Novartis, BMS, Janssen: Honoraria. Barba: Novartis: Honoraria; Gilead: Honoraria; BMS: Honoraria; Amgen: Honoraria; Pfizer: Honoraria. Kwon: Novartis, Celgene, Gilead, Pfizer: Consultancy, Honoraria. Sesques: Novartis: Honoraria; Chugai: Honoraria; Kite, a Gilead Company: Honoraria. Bachy: Kite, a Gilead Company: Honoraria; Novartis: Honoraria; Daiishi: Research Funding; Roche: Consultancy; Takeda: Consultancy; Incyte: Consultancy. Di Blasi: Kite, a Gilead Company: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Janssen: Consultancy, Honoraria. Thieblemont: Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Bristol Myers Squibb/Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses , Research Funding; Gilead Sciences: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Kyte: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Cellectis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Hospira: Research Funding; Bayer: Honoraria; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses . Mutsaers: BMS: Consultancy; AstraZeneca: Research Funding. Nicholson: Kite, a Gilead Company: Other: Conference fees, Speakers Bureau; Novartis: Consultancy, Other: Conference fees; BMS/Celgene: Consultancy; Pfizer: Consultancy. Martínez-López: Janssen, BMS, Novartis, Incyte, Roche, GSK, Pfizer: Consultancy; Roche, Novartis, Incyte, Astellas, BMS: Research Funding. Ribera: NOVARTIS: Consultancy, Speakers Bureau; TAKEDA: Consultancy, Research Funding, Speakers Bureau; ARIAD: Consultancy, Research Funding, Speakers Bureau; SHIRE: Consultancy, Speakers Bureau; AMGEN: Consultancy, Research Funding, Speakers Bureau; Pfizer: Consultancy, Research Funding, Speakers Bureau. Sanderson: Kite, a Gilead Company: Honoraria; Novartis: Honoraria. Bloor: Kite, a Gilead Company: Honoraria; Novartis: Honoraria. Ciceri: IRCCS Ospedale San Raffaele: Current Employment. Ayuk: Novartis: Honoraria; Janssen: Honoraria; Takeda: Honoraria; Mallinckrodt/Therakos: Honoraria, Research Funding; Gilead: Honoraria; Miltenyi Biomedicine: Honoraria; Celgene/BMS: Honoraria. Kröger: Novartis: Research Funding; Riemser: Honoraria, Research Funding; Sanofi: Honoraria; Neovii: Honoraria, Research Funding; Jazz: Honoraria, Research Funding; Gilead/Kite: Honoraria; Celgene: Honoraria, Research Funding; AOP Pharma: Honoraria. Kersten: Celgene: Research Funding; Miltenyi Biotec: Consultancy, Honoraria, Other: Travel support; Roche: Consultancy, Honoraria, Other: Travel support, Research Funding; BMS/Celgene: Consultancy, Honoraria; Takeda: Research Funding; Novartis: Consultancy, Honoraria, Other: Travel support; Kite, a Gilead Company: Consultancy, Honoraria, Other: Travel support, Research Funding. Mielke: DNA Prime SA: Speakers Bureau; Immunicum: Other: Data safety monitoring board; Novartis: Speakers Bureau; Miltenyi: Other: Data safety monitoring board; Gilead/KITE: Other: Travel support, Expert panel ; Celgene/BMS: Speakers Bureau.

Background. COVID19 associated moderate to severe acute respiratory distress syndrome (ARDS) is associated with high rates of morbidity and mortality. Immune dysfunction and hyper-inflammatory responses result in a vicious cycle of tissue inflammation and end organ damage. Based on the suggestion of early efficacy of adoptive therapy with allogeneic T regulatory cells in COVID19 ARDS (Gladstone et al., Ann Int Med 2020), Cellenkos ® initiated a randomized, placebo controlled, multi-center trial of multiple doses of CK0802 (allogeneic, off-the-shelf, cryopreserved, cord blood derived T regulatory cells) for treatment of moderate-to-severe COVID19-related ARDS patients. Study design. Multi-center, randomized, blinded, placebo controlled trial of CK0802 at two different doses (100 million cells and 300 million cells ) were compared to placebo. Each patient was randomized to receive the assigned product on days 0, 3 and 7 (Figure 1), without HLA matching. Enrollment was staggered for the first 6 active treatment patients with 7 days between each patient while monitoring for any safety signals. Subsequent patients were enrolled on a continuous basis. DSMB monitoring occurred after every cohort of 15 patients (5 controls; 5 of each active treatment). Results are presented as median (with range) unless otherwise indicated. Primary Outcomes . The two co-primary outcomes were: Dose Limiting Toxicity (DLT) = Regimen related grade 3, 4, or 5 toxicity within 48 hours of first infusionS28 = [Alive and not intubated 28 days after the date of first infusion] = 28-day treatment success Secondary Outcomes . Secondary outcomes, recorded from first day of infusion up to 28 days later, included: i) time to extubation, ii) ventilator-free days; iii) organ failure-free days; iii) ICU free days; iv) PaO 2/FiO 2 between days 0 and 11; and v) 28-day all-cause mortality Covariates. Patient covariates recorded at enrollment included: i) age, ii) gender iii) on vasopressors; iii) on hemodialysis; iv) duration of intubation prior to enrollment. Study Conduct. The multicenter study (n=5 centers) was activated in October 2020 and enrollment completed in March 2021. Results. Forty-five patients were enrolled (60% male, median age 60 [range 21-85], 46.7% Caucasian race). At baseline 13% were on hemodialysis; 62% on vasopressors; SOFA score=8 (6-13); PaO 2=85 mmHg (45-133); FiO 2=60% (40-100); PEEP=10 cmH 2O (5-18) with a median duration of intubation of 48 hrs (0-120) prior to enrollment. Patient were intubated a median of 72 [0-144] hours prior to infusion. Sixty percent of patients were alive and extubated at day 28. Median time to extubation from first infusion was 10.5 [2-46] days and median ventilator free days at day 28 was 12 [0-26]days. No treatment related SAEs were reported. Time to extubation from first infusion was 10.5 days (2-46) and at day 28 the ventilator free days were 12 (0-26). The estimated day 28 overall survival was 78.6% with the following breakdown according to the co-variates: i) age>60 yrs =77.5% vs. age Discussion This is the first clinical trial to examine safety and early efficacy of multiple doses of allogenic, off-the-shelf, cryopreserved, T regulatory cells for the treatment of COVID-19-related ARDS. Full data analysis of treatment groups (placebo; CK0802-100 million; CK0802-300 million) is ongoing and will be presented at the conference. Additional data to be presented will include: 3- and 6- month QOL, mental health, and cognitive index analyses, and paired Biomarker analysis. Figure 1 Figure 1. Disclosures Hari: Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding, Speakers Bureau; GSK: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding, Speakers Bureau; Celgene-BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding, Speakers Bureau; Millenium: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding, Speakers Bureau; Adaptive Biotech: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding, Speakers Bureau; Karyopharm: Consultancy; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Sadeghi: Cellenkos Inc.: Current Employment. Parmar: Cellenkos Inc.: Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding. Mukherjee: Vor Biopharma: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties: coinventor on issued and pending patent applications licensed to Vor Biopharma. S.M. has equity ownership and is on the Scientific Advisory Board of Vor Biopharma., Research Funding.

Background: Adoptive cell immunotherapies for opportunistic virus in immunocompromised patients using haploidentical memory T cells have shown to be safe and effective. Since severe cases of COVID-19 present a dysregulated immune system with T cell lymphopenia and a hyper-inflammatory state we have proposed that a similar strategy could be proven to be efficient for COVID-19 patients. This is a study protocol of an open-label, multicenter, double-arm, randomized, dose-finding phase I/II clinical trial to evaluate the feasibility, safety, tolerability, and efficacy of the administration of a single dose of allogenic SARS-CoV-2 specific memory CD45RA - T cells and Natural Killer (NK) cells in COVID-19 patients with lymphopenia and pneumonia. The aim of the study is to find efficient treatments for patients with moderate/severe COVID-19. Identification of Specific memory T cells and NK cells: i)Memory T Cells: we first determined the existence of SARS-CoV-2 specific T cells within the CD45RA - T memory cells of the blood of convalescent donors. Memory T cells can respond quickly to the infection and provide long-term immune protection to reduce the severity of the COVID-19 symptoms without inducing classically T cell alloreactivity. Also, CD45RA - memory T cells confer protection for other pathogens the donors encountered in their life. ii)NK cells: we determined the phenotype of NK cells after COVID-19 and the main characteristic of SARS-CoV-2 specific NK population in the blood of convalescent donors, as it has been shown for cytomegalovirus infections. Also, NK cells confer protection for other pathogens the donors encountered in their life. Pilot Phase I- Safety, feasibility, and dose escalation: Between September and November 2020 a phase 1, dose-escalation, single-center clinical trial was conducted to evaluate the safety and feasibility of the infusion of CD45RA - memory T cells containing SARS-CoV-2 specific T cells as adoptive cell therapy against moderate/severe cases of COVID-19. Nine participants with pneumonia and/or lymphopenia and with at least one human leukocyte antigen (HLA) match with the donor were infused. The first three subjects received the lowest dose (1x10 5 cells/kg), the next three received the intermediate dose (5x10 5 cells/kg) and the last three received the highest dose (1x10 6 cells/kg) of CD45RA - memory T cells. Clinicaltrials.gov registration: NCT04578210. Findings: All participants' clinical status measured by National Early Warning Score (NEWS) and 7-category point ordinal scales showed improvement six days after infusion. No serious adverse events were reported. Inflammatory parameters were stabilized post-infusion and the participants showed lymphocyte recovery two weeks after the procedure. Donor microchimerism was observed at least for three weeks after infusion in all patients. Interpretation: This study provides preliminary evidence supporting the idea that treatment of COVID-19 patients with moderate/severe symptoms using convalescent SARS-CoV-2 specific CD45RA - memory T cells is feasible and safe. We did not find dose-liming toxicity. The Recommended Phase 2 dose was 1x10 6 CD45RA - T cells. Phase II- Efficacy: Between January 2021 and July 2021 patients have been enrolled based on the matched with the HLA genotype of the convalescent donors and following the protocol inclusion/exclusion criteria. The primary outcome is the incidence of patient recovery at day 14, defined as normalization of fever and oxygen saturation or lymphopenia recovery. Secondary outcomes are the time to normal level of lymphocytes, the proportion of patients showing clinical improvement at day 7, time to first negative SARS-CoV-2 PCR, the incidence of treatment-related adverse events, duration of hospitalization, time to discharge, time to improvement by one category a 7-point ordinal scale or NEWS score, the proportion of patients requiring intensive care unit, and all-cause mortality. In addition, lymphocyte recovery by multiparametric flow cytometry and donor chimerism by real-time PCR in the experimental arm was monitored weekly during the first month. This study provides preliminary evidence supporting the idea that treatment of COVID-19 patients with moderate/severe symptoms using convalescent CD45RA - memory T cells is safe and feasible. The phase II clinical trial is ongoing to demonstrate efficacy. Figure 1 Figure 1. Disclosures Soria: Celgene: Other: Fees; Gilead: Other: Fees; AbbVie: Other: Fees.