Abstract: Allogeneic hematopoietic cell transplantation (HCT) is a curative therapy for hematological malignancies for which graft-versus-host disease (GVHD) remains a major complication. The use of donor T-regulatory cells (Tregs) to prevent GVHD appears promising, including in our previous evaluation of an engineered graft product (T-reg graft) consisting of the timed, sequential infusion of CD34+ hematopoietic stem cells and high-purity Tregs followed by conventional T cells. However, whether immunosuppressive prophylaxis can be removed from this protocol remains unclear. We report the results of the first stage of an open-label single-center phase 2 study (NCT01660607) investigating T-reg graft in myeloablative HCT of HLA-matched and 9/10-matched recipients. Twenty-four patients were randomized to receive T-reg graft alone (n = 12) or T-reg graft plus single-agent GVHD prophylaxis (n = 12) to determine whether T-reg graft alone was noninferior in preventing acute GVHD. All patients developed full-donor myeloid chimerism. Patients with T-reg graft alone vs with prophylaxis had incidences of grade 3 to 4 acute GVHD of 58% vs 8% (P = .005) and grade 3 to 4 of 17% vs 0% (P = .149), respectively. The incidence of moderate-to-severe chronic GVHD was 28% in the T-reg graft alone arm vs 0% with prophylaxis (P = .056). Among patients with T-reg graft and prophylaxis, CD4+ T-cell–to–Treg ratios were reduced after transplantation, gene expression profiles showed reduced CD4+ proliferation, and the achievement of full-donor T-cell chimerism was delayed. This study indicates that T-reg graft with single-agent tacrolimus is preferred over T-reg graft alone for the prevention of acute GVHD. This trial was registered at www.clinicaltrials.gov as #NCT01660607.

Abstract: BACKGROUND: CD22 is expressed on the majority of B-cell malignancies. Autologous CAR T-cells targeting CD22 (CAR22) have yielded objective response rates (ORR) of 70-90% in pediatric patients with relapsed/refractory (R/R) B-cell acute lymphoblastic leukemia (ALL), including those who had previously failed CD19-directed CAR T-cell (CAR19) therapy. Based on these encouraging results, we evaluated CAR22 in adult patients with R/R ALL and for the first time in patients with R/R large B-cell lymphoma (LBCL), including those who had failed prior autologous CAR19 therapy. METHODS: This single-institution phase I dose escalation clinical trial (NCT04088890) is evaluating a CAR construct incorporating the m971 CD22 single chain variable fragments and 41BB/CD3z endodomains integrated within autologous T-cells via lentiviral transduction. After lymphodepletion with fludarabine and cyclophosphamide, patients were infused with fresh or cryopreserved CAR T-cells after a 7- to 11-day closed manufacturing process utilizing the CliniMACS Prodigy device (Miltenyi). The current cohort includes patients treated at dose level 1 (DL1), which was 1x106 CAR+ cells/kg. Primary objectives assessed the ability to successfully manufacture CAR22 and safety. Overall response rate (ORR) at 28 days post-infusion (D28) was a secondary objective. RESULTS: Three patients with LBCL have been enrolled with a median age of 53 years (range, 51-57) and a median of 6 (range, 5-8) prior lines of therapy. All three patients received prior CAR19 and had refractory disease to second-line or later therapy (n=3); had not undergone autologous hematopoietic stem cell transplantation (HSCT) (n=3); had MYC and BCL2 gene rearrangements (double-hit lymphoma; n=2); had high tumor burden (SPD & gt;50 cm2; n=2); had a history of primary refractory disease (n=1); or had never achieved CR to any therapy (n=1). Six patients with ALL have been enrolled with a median age of 43.5 years (range, 23-62) and a median of 6 (range, 4-8) prior lines of therapy. All six patients received prior allogeneic HSCT and had Ph-positive disease (n=3); had central nervous system (CNS) involvement (n=3); had extramedullary disease (n=2); had high disease burden (BM blasts & gt;5%; n=2); had received prior CD19-directed therapy (n=5); or had received prior CD22-directed therapy (n=3). Successful manufacturing of cells at DL1 was achieved in all patients. All patients (LBCL n=3, ALL n=6) reached day 28 and are included in the safety and response analysis presented here; updated results will be presented at the meeting. Eight patients (88.9%) experienced cytokine release syndrome (CRS); all were Grade 1-2. There were no cases of immune effector cell-associated neurotoxicity syndrome (ICANS). No differences in toxicities were seen across the patient age spectrum and no Grade 5 toxicities occurred following CAR22 infusion. In LBCL, all patients achieved a response at D28 (ORR=100%; CR, n=1, PR, n=2). Both patients with a D28 PR improved to CR by day 90 and 180. All patients remain in CR, with a median follow-up of 8.4 months (range, 6-9.3). In ALL, all patients achieved a CR at D28 (ORR=100%; MRD-, n=5, MRD+, n=1). After a median follow up of 5.1 months (range, 1-8.2), three patients relapsed at 2.5, 4, and 5.5 months after infusion; one patient died while undergoing subsequent therapy 7.3 months post-infusion. CD22 expression by flow cytometry was downregulated or absent in two patients after relapse. Peak CAR expansion as detected by peripheral blood flow cytometry reached a median level of 90.1 (LBCL; range, 85.4-350) and 43.4 (ALL; range, 0.9-399.6) CAR+ cells/µL between D14 and D21. In two LBCL patients with progression following CAR19, CAR22 levels were 11.7 and 55.9 fold higher than prior CAR19 levels at peak expansion. CONCLUSIONS: Infusion of CD22-targeting CAR T-cells in R/R LBCL and ALL is safe and well tolerated. Manufacturing of CAR22 was uniformly successful. To date, 3 of 3 heavily treated adult patients with LBCL whose disease relapsed after prior CAR19 have each achieved CR durable to at least 6 months. All adult ALL patients have achieved CR following CAR22, with some early relapses observed. Accrual is ongoing. Disclosures Negrin: Amgen: Consultancy; Biosource: Current equity holder in private company; UpToDate: Honoraria; KUUR Therapeutics: Consultancy; Magenta Therapeutics: Consultancy, Current equity holder in publicly-traded company; BioEclipse Therapeutics: Current equity holder in private company. Rezvani:Pharmacyclics: Research Funding. Shiraz:ORCA BioSystems: Research Funding; Kite, a Gilead Company: Research Funding. Sidana:Janssen: Consultancy. Mackall:BMS: Consultancy; Allogene: Current equity holder in publicly-traded company; Apricity Health: Consultancy, Current equity holder in private company; Nektar Therapeutics: Consultancy; NeoImmune Tech: Consultancy; Lyell Immunopharma: Consultancy, Current equity holder in private company. Miklos:Kite-Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Research Funding; Adaptive Biotech: Consultancy, Other: Travel support, Research Funding; Allogene Therapeutics Inc.: Research Funding; Juno-Celgene-Bristol-Myers Squibb: Consultancy, Other: Travel support, Research Funding; Novartis: Consultancy, Other: Travel support, Research Funding; Pharmacyclics: Consultancy, Other: Travel support, Patents & Royalties, Research Funding; Janssen: Consultancy, Other: Travel support; Miltenyi Biotec: Research Funding. Muffly:Amgen: Consultancy; Adaptive: Research Funding; Servier: Research Funding. OffLabel Disclosure: CD22-directed CAR T-cell Therapy for the treatment of adults with relapsed/refractory LBCL and B-ALL

Abstract: Nonmyeloablative total lymphoid irradiation and antithymocyte globulin (TLI-ATG) conditioning is protective against graft-versus-host disease (GVHD), while retaining graft-versus-tumor activity across various hematologic malignancies. We report our comprehensive experience using TLI-ATG conditioning in 612 patients with hematologic malignancies who underwent allogeneic transplantation at Stanford University from 2001 to 2016. All patients received granulocyte colony-stimulating factor–mobilized peripheral blood grafts and cyclosporine and mycophenolate mofetil for GVHD prophylaxis. The median age was 60 years (range, 21-78), with a median follow-up of 6.0 years (range, 1.0-16.4). Common diagnoses included acute myeloid leukemia (AML; n = 193), myelodysplastic syndrome (MDS; n = 94), chronic lymphocytic leukemia (CLL; n = 80), non-Hodgkin lymphoma (NHL; n = 175), and Hodgkin lymphoma (HL; n = 35). Thirty-four percent of patients had a comorbidity index ≥3, 30% had a high to very high disease risk index, and 56% received unrelated donor grafts, including 15% with HLA-mismatched donors. Ninety-eight percent underwent transplant in the outpatient setting, and 57% were never hospitalized from days 0 through 100. The 1-year rates of nonrelapse mortality (NRM), grade II-IV acute GVHD, and extensive chronic GVHD were 9%, 14%, and 22%, respectively. The 4-year estimates for overall and progression-free survival were 42% and 32% for AML, 30% and 21% for MDS, 67% and 43% for CLL, 68% and 45% for NHL, and 78% and 49% for HL. Mixed chimerism correlated with the risk of relapse. TLI-ATG conditioning was well tolerated, with low rates of GVHD and NRM. Durable remissions were observed across hematologic malignancies, with particularly favorable outcomes for heavily pretreated lymphomas. Several efforts are underway to augment donor chimerism and reduce relapse rates while maintaining the favorable safety and tolerability profile of this regimen.

Abstract: BACKGROUND GVHD and non-relapse mortality (NRM) remain frequent complications of HLA-matched HSCT despite the use of standard immunosuppression like tacrolimus and methotrexate. Alternative GVHD prophylaxis (PPX) strategies like T-cell depletion and post-transplant cyclophosphamide negatively impact relapse, infection, and organ toxicity, and no strategy has yet demonstrated a clear benefit for GVHD-free survival. Orca-T is an investigational cellular product comprising stem and immune cells that leverages highly purified donor regulatory T cells to control alloreactive immune responses. Unlike point-of-care graft engineering approaches, Orca-T is produced in a central GMP laboratory and has been successfully distributed to multiple centers across in the U.S. Early clinical trials using Orca-T showed a good safety profile, promising GVHD control, and potentially improved immune reconstitution. Here, we present trial results from both a single-institution Phase 1/2 trial that has completed enrollment and an ongoing multicenter Phase 1b trial. METHODS As of 28 July 2021, 113 patients aged 18-72 have received Orca-T for AML, ALL, MDS, lymphoma, or myelofibrosis. We present here data from 80 patients that have ≥90 days follow-up. 28 and 52 patients, respectively, received Orca-T followed by single-agent GVHD prophylaxis on a single-center Phase 2 study (NCT01660607) and a multicenter Phase Ib (NCT04013685). Orca-T products were derived from HLA-matched related (n=46) or unrelated (n=34) donors. Patients received a variety of myeloablative conditioning regimens (e.g., non-TBI, n=66; TBI-based, n=14) followed by single-agent PPX with either tacrolimus (n=73) or sirolimus (n=7). Median follow-up for these patients is 541 days (single-center) and 248 days (multicenter). We identified a contemporaneous SOC cohort, and we reported on their clinical outcomes at Stanford (n=95) with both matched related (n=52) and unrelated (n=43) transplant recipients who received unmanipulated PBSC products (median f/u 546) and methotrexate plus tacrolimus prophylaxis. RESULTS The Orca-T investigational cell therapy was manufactured reliably, delivered in less than 72 hours for all patients, and every patient enrolled received Orca-T. The Treg drug product was characterized by high Treg purity of 93.8% +/- 3.1% and a dose of 2.6 +/- 0.4 x 106 per kg (equivalent between trials). An Orca-T product was produced and infused for all patients, and there were no logistics failures or infusion reactions. All patients engrafted and Orca-T patients showed earlier neutrophil (median of 12 days vs. 14 days, p & lt;0.0001 by Mann-Whitney U) and platelet engraftment (14 vs 17 days, p & lt;0.0001) compared to SOC. On the single-center, Phase 2 clinical trial study at Stanford there is evidence of improved 1-year GVHD and relapse-free survival (GRFS) which was 77% (CI 51-88%) for Orca-T patients vs 34% (CI 25-44%) with SOC (Figure 1A). We observed improved rates of & gt;grade 2 acute GVHD at Day +180 (aGVHD, 14% versus 33%), moderate-to-severe chronic GVHD at 1 year (4% versus 42%) and NRM at 1 year (0% versus 13%). Relapse-free (RFS) and overall survival (OS) trended upwards for Orca-T. Severe infectious complications were rare. Key clinical results from both Orca-T trials are summarized in Table 1; 23 of 80 patients had ≥1 year follow-up. Consistent with findings from the single-institution study, on the multicenter study, rates of moderate-to-severe cGVHD and non-relapse mortality were low at 1-year post-transplant at 3% and 4%, respectively. For all patients who received Orca-T across both studies, we observed GRFS of 72% (Figure 1B), RFS of 78%, and OS of 91% at 1 year. These survival rates compare favorably to the contemporaneous SOC control (33%, 71% and 78%, respectively). Immune reconstitution in Orca-T patients with single agent tacrolimus appears similar to SOC except for observable differences in the IL-2 pathway. CONCLUSIONS Manufacture of high precision Orca-T investigational cell therapy drug products was scaled in a central GMP with reliable distribution to centers. Patients that received Orca-T and single-agent PPX showed significantly reduced aGVHD, cGVHD and NRM. Orca-T shows promise to improve GRFS and other transplant outcomes. Orca-T has been granted Regenerative Medicine Advanced Therapy status by the FDA, and a phase 3 prospectively, randomized study is planned. Figure 1 Figure 1. Disclosures Gandhi: Gamida Cell: Consultancy, Membership on an entity's Board of Directors or advisory committees; CareDx Inc: Honoraria. Muffly: Pfizer, Amgen, Jazz, Medexus, Pfizer: Consultancy; Astellas, Jasper, Adaptive, Baxalta: Research Funding; Adaptive: Honoraria, Other: fees for non-CME/CE services: , Research Funding. Shiraz: Kite Pharma-Gilead: Research Funding. Mehta: Kadmon: Research Funding; Incyte: Research Funding; CSLBehring: Research Funding; Syndax: Research Funding. McGuirk: Allovir: Consultancy, Honoraria, Research Funding; Novartis: Research Funding; Magenta Therapeutics: Consultancy, Honoraria, Research Funding; Gamida Cell: Research Funding; Kite/ Gilead: Consultancy, Honoraria, Other: travel accommodations, expense, Kite a Gilead company, Research Funding, Speakers Bureau; Juno Therapeutics: Consultancy, Honoraria, Research Funding; EcoR1 Capital: Consultancy; Bellicum Pharmaceuticals: Research Funding; Pluristem Therapeutics: Research Funding; Fresenius Biotech: Research Funding; Astelllas Pharma: Research Funding; Novartis: Research Funding. Waller: Verastem Oncology: Consultancy, Research Funding; Cambium Oncology: Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Arai: Magenta Therapeutics: Research Funding. Rezvani: US Department of Justice: Consultancy; Nohla Therapeutics: Other: One-time scientific advisory board; Pharmacyclics-Abbvie: Research Funding; Kaleido: Other: One-time scientific advisory board. Weng: Kite Pharma: Research Funding. Miklos: Adaptive Biotechnologies, Novartis, Juno/Celgene-BMS, Kite, a Gilead Company, Pharmacyclics-AbbVie, Janssen, Pharmacyclics, AlloGene, Precision Bioscience, Miltenyi Biotech, Adicet, Takeda: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics, Amgen, Kite, a Gilead Company, Novartis, Roche, Genentech, Becton Dickinson, Isoplexis, Miltenyi, Juno-Celgene-Bristol Myers Squibb, Allogene, Precision Biosciences, Adicet, Adaptive Biotechnologies: Research Funding; Kite, a Gilead Company, Amgen, Atara, Wugen, Celgene, Novartis, Juno-Celgene-Bristol Myers Squibb, Allogene, Precision Bioscience, Adicet, Pharmacyclics, Janssen, Takeda, Adaptive Biotechnologies and Miltenyi Biotechnologies: Consultancy; Pharmacyclics: Patents & Royalties. Frank: Kite-Gilead: Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Research Funding; Allogene Therapeutics: Research Funding. Fernhoff: Orca Bio: Current Employment. Putnam: Orca Bio: Current Employment. McClellan: Orca Bio: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Shaw: Orca bio: Consultancy; mallinkrodt: Other: payments. Abedi: Seattle Genetics: Speakers Bureau; BMS/Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Speakers Bureau. Meyer: Triursus Therapeutics: Current holder of stock options in a privately-held company; GigaImmune: Current holder of stock options in a privately-held company; Orca Biosystems: Research Funding; Indee, Jura: Consultancy.

Abstract: BACKGROUND GVHD remains a frequent and serious complication of HSCT despite the decades-long use of standard immunosuppression, such as tacrolimus and methotrexate, as prophylaxis against GVHD. Preclinical models have shown that the timed infusion of donor-derived high-purity CD4+CD25+FOXP3+ regulatory T cells (Treg) preceding adoptive transfer of conventional T cells (Tcon) prevents GVHD and maintains anti-cancer immunity without the need of pharmacologic agents. Early clinical trials using purified Treg-engineered graft showed safety and feasibility, but more extensive clinical studies are needed to test scalability and efficacy. Orca-T is an industry-manufactured, precision-engineered CD34-selected, Treg-engineered graft made in a central GMP laboratory and distributed to multiple centers in the U.S. We present our early patient experience with Orca-T in an ongoing single center phase 2 trial and a multicenter Phase Ib trial and report a pre-planned evaluation of patients randomized to receive Orca-T plus single-agent GVHD prophylaxis (PPX) or Orca-T and no PPX. METHODS 51 patients with high risk or active hematologic malignancies undergoing myeloablative conditioning were enrolled on two trials: a single-center Phase I/II (n=40, NCT01660607) and a multicenter Phase Ib (n=11; NCT04013685) study. Patients received CD34-selected cells infused with highly purified Treg (target dose: 3.0 x 106 cells/kg) followed 2 days later by the infusion of Tcon (3.0 x 106 cells/kg). Initial GMP manufacturing was demonstrated at Stanford (n=9 grafts; 2016 - 2019) and then transferred to Orca Bio in 2019 for scaled production. We evaluated the 34 patients beyond dose escalation since July 2016 who received Orca-T grafts from either matched related (n=25) or unrelated (n=9) donors and single agent GVHD PPX with either tacrolimus (n=28) or sirolimus (n=6). For comparative analysis, we identified a contemporaneous SOC cohort at Stanford (n=138) with both matched related (n=79) and unrelated (n=59) transplant recipients who received unmanipulated PBSC products (median f/u 546 days) and methotrexate plus tacrolimus. In April 2019, enrollment on a phase 2, stage 1 pre-planned subgroup of 24 patients were randomized to test whether all GVHD PPX could be removed: Orca-T plus either single-agent PPX (Arm 1, n=12) or no PPX (Arm2, n=12). RESULTS The Orca-T drug products were manufactured reliably with high Treg purity (93.8% +/- 3.1%) and a dose of 2.6 +/- 0.4 x 106 per kg (equivalent between arms and trials). Central lab turn-around times were 25.3 +/- 3.0 hours and all vein-to-vein times were less than 72 hrs (Table 1). For trial participants, there were no manufacturing failures, engraftment failures or treatment related mortality. Orca-T patients vs. SOC showed earlier neutrophil (median of 11 days vs. 14 days, p & lt;0.0001 by Mann-Whitney U) and platelet engraftment (11 vs 17 days, p & lt;0.0001) and a shorter hospital stay (15 vs 19 days, p=0.0002). Patients across 4 clinical sites received Orca-T plus single agent GVHD PPX (n=34; median f/u 261 days) had an acute GVHD grade 2-4 incidence of 0% as compared to 33% in the SoC cohort (n=138, p=0.0018 by Log-rank Mantel-Cox test, Fig. 1). The rate of moderate to severe chronic GVHD for Orca-T patients was 4% vs. 44% in the SoC cohort (p=0.016). In a preliminary subset of evaluable Orca- T patients, GVHD & relapse free survival (GRFS) at one year was higher for Orca-T patients vs SoC (69% versus 33%, p=0.006) while relapse and overall survival did not appear to differ. We observed no differences in infectious complications. In patients randomized to PPX vs. no PPX, the incidence of aGVHD grade 2-4 was 0% in Arm 1 and 58% in Arm 2 (p & lt;0.0001, Log-rank Mantel-Cox test), with 17% of these events being Grade 3-4. All GVHD in Arm 2 responded to steroids with no GVHD-related deaths. CONCLUSIONS Manufacture of high precision Orca-T Treg-engineered donor products were successfully scaled in a central GMP with reliable distribution to centers. Patients who received Orca-T and single agent PPX had no grade 2 or greater acute GVHD acute and very little chronic GVHD when compared to SOC. Patients randomized to Orca-T and no PPX showed an increased incidence of acute GVHD vs. those with Orca-T and single agent PPX. Engineered Treg grafts show promise to improve GFRS and other transplant outcomes. Orca-T has been granted RMAT status by the FDA and evaluation continues in an ongoing multicenter clinical trial. Disclosures Meyer: Orca Bio: Research Funding. Moroz:Orca Bio: Research Funding. Miklos:Novartis: Consultancy, Other: Travel support, Research Funding; Pharmacyclics: Consultancy, Other: Travel support, Patents & Royalties, Research Funding; Janssen: Consultancy, Other: Travel support; Miltenyi Biotec: Research Funding; Kite-Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Research Funding; Adaptive Biotech: Consultancy, Other: Travel support, Research Funding; Juno-Celgene-Bristol-Myers Squibb: Consultancy, Other: Travel support, Research Funding; Allogene Therapeutics Inc.: Research Funding. Shiraz:Kite, a Gilead Company: Research Funding; ORCA BioSystems: Research Funding. Muffly:Servier: Research Funding; Adaptive: Research Funding; Amgen: Consultancy. Rezvani:Pharmacyclics: Research Funding. Shizuru:Jasper Therapeutics, Inc: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees. Fernhoff:Orca Bio: Current Employment, Current equity holder in private company. Putnam:Orca Bio: Current Employment, Current equity holder in private company. McClellan:Orca Bio: Current Employment, Current equity holder in private company. Shaw:Orca Bio: Consultancy. McGuirk:Kite Pharmaceuticals: Consultancy, Honoraria, Research Funding, Speakers Bureau; Fresenius Biotech: Research Funding; Bellicum Pharmaceutical: Research Funding; Gamida Cell: Research Funding; Juno Therapeutics: Consultancy, Honoraria, Research Funding; Astellas: Research Funding; Allo Vir: Consultancy, Honoraria, Research Funding; Novartis: Research Funding; Pluristem Ltd: Research Funding. Abedi:BMS, Gilead Sciences: Research Funding; AbbVie, BMS, Gilead Sciences, Seattle Genetics, Takeda: Speakers Bureau. Negrin:Magenta Therapeutics: Consultancy, Current equity holder in publicly-traded company; KUUR Therapeutics: Consultancy; Biosource: Current equity holder in private company; UpToDate: Honoraria; Amgen: Consultancy; BioEclipse Therapeutics: Current equity holder in private company.

Abstract: Background: The prognostic and predictive utility of measurable residual disease (MRD) assessments using bone marrow (BM) aspirates is well-established in the management of acute lymphoblastic leukemia (ALL). However, frequent BM MRD monitoring post-therapy is limited by the invasive, expensive, and at times impractical nature of numerous BM examinations. Limited retrospective reports have suggested that MRD analysis by next-generation sequencing (NGS) using peripheral blood (PB) may provide a viable alternative to MRD monitoring of the BM. We conducted a prospective, multi-institutional observational study of NGS-based MRD of the PB among adult ALL patients undergoing cellular therapies (hematopoietic cell transplantation [HCT] and chimeric antigen receptor T cells [CART] ) in order to determine the correlation between PB and BM MRD and to explore the clinical utility of monitoring MRD in the PB. Methods: Patients & gt;= 18 years-old with ALL were recruited from Stanford University and Kaiser Permanente, Northern California. The MRD analyses were conducted using Adaptive Biotechnologies ClonoSEQ NGS based platform that tracks tumor specific VDJ rearrangement in B and T cell malignancies. Assessment of MRD was obtained from the PB and BM prior to HCT/CART. Among HCT patients, PB MRD was obtained at one month, and then every 2-3 months for the first year following HCT; a paired BM MRD sample was obtained at the 3 month time-point with optional additional BM examinations. Among CART patients, paired PB and BM MRD were obtained at one month, and then every 2-3 months for the first year following CART. The correlation between log10 values of PB and BM MRD samples was evaluated using the Pearson correlation coefficient. Clinical relapse was defined as morphologic leukemia blasts in the marrow or extramedullary site, or administration of a new therapy for rising MRD. Results: Sixty-nine patients scheduled to undergo cellular therapies were enrolled; 3 (4%) did not undergo planned therapy and were excluded and 4 (6%) lacked a detectable clonal leukemia sequence and were thus off study, resulting in a study population of 62 (42 BMT, 17 CART, 3 BMT and CART). The median age was 42 years (IQR 30-53), 36 (58%) were male, 54 (87%) had B-ALL,16 (26%) were BCR-ABL+, and 28 (46%) had extramedullary (EM) involvement. Across all patients, PB MRD was highly correlated with BM MRD (r=0.87; p & lt;0.0001; Figure 1A). Of the 129 paired samples,15 (12%) had discordance with MRD identified in either the PB and not BM (N=7; 5%) or in the BM and not PB (N=8; 6%). Similarly, PB and BM MRD were highly correlated in the HCT (r=0.86; p & lt;0.0001) and CART cohorts (r=0.86; p & lt;0.001; Figure 1B), and among patients with EM involvement (r=0.83; p & lt;0.0001) and marrow only disease (r=0.93; p & lt;0.0001; Figure 1C). With median follow-up of 293 days (IQR: 180-512), 6 (13%) HCT and 13 (65%) CART patients experienced clinical relapse (Figure 2A). Among the 6 patients who relapsed following HCT, 80% had detectable MRD in the PB prior to HCT (1 was missing pre-HCT PB sample). Following HCT, all 6 patients developed detectable MRD, with median time from first MRD positivity to clinical relapse of 71 days (IQR 28-90). Among the 13 patients who relapsed following CART, 85% had detectable MRD in the PB a median of 60 days (50-139) prior to clinical relapse. Finally, serial monitoring of the PB following HCT averted clinical relapse through immunosuppression withdrawal in two patients with rising MRD post-HCT (Figure 2B), thereby directly impacting patient outcomes. Conclusion: This prospective observational study demonstrates a strong correlation between PB and BM NGS MRD results in ALL. These results show that non-invasive monitoring of PB-based MRD in ALL patients undergoing curative intent cellular therapies represents a viable alternative to serial BM examinations, providing clinically actionable information and the opportunity to intervene on impending clinical relapse. Disclosures Muffly: Adaptive: Research Funding; Amgen: Consultancy; Servier: Research Funding. Meyer:Orca Bio: Research Funding. Negrin:Amgen: Consultancy; Magenta Therapeutics: Consultancy, Current equity holder in publicly-traded company; BioEclipse Therapeutics: Current equity holder in private company; Biosource: Current equity holder in private company; UpToDate: Honoraria; KUUR Therapeutics: Consultancy. Rezvani:Pharmacyclics: Research Funding. Sidana:Janssen: Consultancy. Shiraz:ORCA BioSystems: Research Funding; Kite, a Gilead Company: Research Funding. Shizuru:Jasper Therapeutics, Inc: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees. Liedtke:Adaptive: Membership on an entity's Board of Directors or advisory committees; Caelum: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria. Miklos:Kite-Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Research Funding; Adaptive Biotech: Consultancy, Other: Travel support, Research Funding; Allogene Therapeutics Inc.: Research Funding; Novartis: Consultancy, Other: Travel support, Research Funding; Pharmacyclics: Consultancy, Other: Travel support, Patents & Royalties, Research Funding; Juno-Celgene-Bristol-Myers Squibb: Consultancy, Other: Travel support, Research Funding; Janssen: Consultancy, Other: Travel support; Miltenyi Biotec: Research Funding.

Abstract: Introduction: Disease relapse after allogeneic hematopoietic cell transplantation (HCT) is the main cause for an unsuccessful transplant outcome. The prognosis is generally poor and there is no consensus regarding optimal therapy to restore disease control. We retrospectively analyzed 121 patients with hemato-lymphoid malignancies who had disease relapse after a first HCT (HCT1) and received a subsequent allograft (HCT2) or a donor lymphocyte infusion (DLI). The goal of the analyses was to better understand which clinical features was associated with improved outcomes, and to help define the risk-benefit of these two interventions. Methods: Between September 1, 2009 and December 31, 2019, 550 consecutive patients had disease relapse after HCT1 of which 28 (5%) received HCT2 and 93 (17%) received DLI. Results: The HCT1 baseline characteristics were comparable for both groups (Table1). The median time interval from HCT1 to disease relapse was 8 months (range 1-87). Patients who had disease relapse within 6 months of HCT1 had withdrawal of immune suppression (IS) medication whereas most patients with disease relapse beyond 6 months already had had IS drugs discontinued. DLI was the treatment choice for CML, CLL and plasma cell neoplasms, or for a low level of disease relapse/progression. In the HCT2 cohort, the median age was 56 (range 31-70) and 17 (61%) patients were returned to CR with chemotherapy prior to HCT2. Three patients (11%) received a myeloablative regimen and 23 (82%) received a reduced intensity regimen (RIC). The graft source was mobilized peripheral blood in 26 patients (92%) and 20 (71%) had a different donor at HCT2. Karnofsky performance status was & gt;90% in 11 (39%) patients at HCT2. In the DLI cohort, the median age was 60 (range 22-77) and 48 (52%) were returned to CR prior to the first DLI. Patients received a median of one DLI (range 1-4). The median CD3+ T cell dose was 1.0 X107CD3+/kg (range 0.5-30). Karnofsky performance status was & gt;90% in 56 (67%) patients at time of DLI. Both interventions were well tolerated and the 1-year non-relapse mortality (NRM) was 21% (n=6) for HCT2 and 12% (n=11) for DLI. Acute graft-versus-host disease (aGVHD), grades 2-4, occurred in 39% and 24% of the patients who received HCT2 and DLI. The 3-year cumulative incidence of extensive chronic GVHD was 25% for HCT2 and 23% for DLI. The median follow-up for living patients was 37 months. The median event-free survival (EFS) was 18 months for HCT2 and 5 months for DLI (Fig.1A). The estimated 3-year overall survival (OS) was 60% [95% confidence interval (CI): 39-78] for HCT2 and 30% [95% CI: 21-42] for DLI (Fig.1B). The main causes of death were disease progression (n = 4) and GVHD (n = 4) for the HCT2 cohort. The same was true for the DLI cohort, although death from progressive disease was more common (n = 43 patients) compared to death from GVHD (n = 16 patients). Within the limitations of the small number of patients only one factor in univariate analysis was associated with an improved OS for both HCT2 and DLI and this was attainment of complete donor CD3+ T cell chimerism ( & gt;95% donor type) after either intervention. The 3-year OS for patients who attained full donor chimerism was 68% and 66% for HCT2 and DLI, respectively, compared to 33% and 24% for these groups if full donor chimerism was not achieved. The KPS at the time of DLI was significantly associated with improved OS: the median OS was 2, 8 and 19 months when KPS was & lt;70%, 70-80% and 90-100% respectively (p=0.0026). The impact of remission duration after HCT1 associated with OS for DLI but not HCT2. Relapse within 6 months after HCT1 portended a poor prognosis for the DLI group with a median OS of 6-months compared to 19-months if relapse occurred beyond 6-months of HCT1. Conclusion: HCT2 and DLI can both offer long-term disease control for disease relapse after HCT1 albeit only a minority of patients receive these interventions. In our analysis, HCT2 and DLI were well tolerated and the risks of NRM and GVHD appear similar to HCT1. Long-term OS for HCT2 is achieved for about half of the patients when using a RIC and when the patient is returned to CR prior to the intervention. For DLI, a higher performance status and a longer remission after HCT1 were both associated with improved long-term survival. Conditions that enable attainment of full donor chimerism are important to maximize graft-versus-tumor effect for both HCT2 and DLI. Disclosures Muffly: Servier: Research Funding; Amgen: Consultancy; Adaptive: Research Funding. Rezvani:Pharmacyclics: Research Funding. Sidana:Janssen: Consultancy. Shiraz:Kite, a Gilead Company: Research Funding; ORCA BioSystems: Research Funding. Meyer:Orca Bio: Research Funding. Shizuru:Jasper Therapeutics, Inc: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees. Miklos:Juno-Celgene-Bristol-Myers Squibb: Consultancy, Other: Travel support, Research Funding; Pharmacyclics: Consultancy, Other: Travel support, Patents & Royalties, Research Funding; Novartis: Consultancy, Other: Travel support, Research Funding; Kite-Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Research Funding; Janssen: Consultancy, Other: Travel support; Miltenyi Biotec: Research Funding; Adaptive Biotech: Consultancy, Other: Travel support, Research Funding; Allogene Therapeutics Inc.: Research Funding. Negrin:Biosource: Current equity holder in private company; UpToDate: Honoraria; KUUR Therapeutics: Consultancy; BioEclipse Therapeutics: Current equity holder in private company; Magenta Therapeutics: Consultancy, Current equity holder in publicly-traded company; Amgen: Consultancy.

Abstract: Background Treatment with chimeric antigen receptor (CAR) T cell therapies have shown dramatic, often durable responses for relapsed/refractory B-cell malignancies. However, it can be associated with significant side effects such as cytokine release syndrome (CRS), immune effector-cell associated neurotoxicity syndrome (ICANS) and life-threatening consumptive coagulopathies. The underlying pathobiology of such hemostatic defects and their distinct clinical sequelae remains obscure. This retrospective study aims at quantifying CAR T therapy associated bleeding and thrombotic complications and their association with CRS, ICANS, and laboratory derangements. Methods 130 adult patients with DLBCL or B-ALL treated between 2017-2020 with CD19 CAR-T therapy axicabtagene ciloleucel (N=90) or a bispecific CD 19/22 CAR construct utilizing 4-1BB costimulatory domains (N=40) were analyzed to determine dynamics of coagulation parameters and platelet counts as well as incidences of bleeding or thrombosis in the first three months after CAR T infusion. Events were included if graded ≥ 2 or if intervention was required. Platelet counts and coagulation parameters were collected prior to lymphodepletion (pre-LD), day 0, 3, 7, 14, 21, 28, 60 and 90. Results 12 (9.2%) and 8 (6.2%) patients developed bleeding and thrombotic complications in the first three months after CAR-T infusion, respectively. Events are characterized in Figure 1. All bleeding events occurred between days 0-30 (median 17.5, range 8-30), while thrombotic events occurred between days 2-91 (median day 29, range, 2-91). Two (1.5%) patients experienced both bleeding and thrombosis. Bleeding events coincided with the onset of thrombocytopenia and hypofibrinogenemia, and patients who bled had lower platelet (median 22.5 vs. 47 K/uL; p=0.03) and fibrinogen (median 151 vs. 351 ug/mL; p=0.007) nadirs in the first 30 days compared to those without bleeding. Temporally, the lowest median platelet nadir occurred at day 7 in patients with bleeding events vs. day 21 in patients without bleeding, while timing of fibrinogen nadirs were at day 21 in both. Patients with bleeding episodes were more likely to be older (median age: 70 vs. 60 yrs, p=0.03), have thrombocytopenia prior to lymphodepletion therapy (median 117.5 vs. 174.5 K/uL, p=0.01), and have elevated LDH (lymphoma subgroup; p=0.07). Other lab derangements in the first 30 days seen more frequently in patients with bleeding included prolonged thrombin time (TT) (21% vs. 6%; p=0.02), PT (16% vs. 5%; p=0.06), and elevated d-dimer (16% vs. 3%; p=0.01) indicative of a consumptive process. Thrombotic events were not significantly associated with elevated or peak d-dimer values (median 4.97 vs. 2.37 ug/mL, p=0.20). Interestingly, occurrence or severity of CRS was not associated with bleeding or thrombotic events, nor was it associated with marked derangements in coagulation abnormalities. However, higher grade ICANS (grade & gt; 3) was associated with bleeding (42% vs. 15%; p=0.038), thrombosis (50% vs. 16%; p=0.03), and evidence of endothelial activation including PT prolongation (78% vs. 35%; p & lt;0.001), hypofibrinogenemia (57% vs. 20%; p=0.001), and trend towards elevated d-dimer (70% vs. 46%; p=0.06). 13 (10%) patients received anticoagulation for prophylaxis or therapeutic indications that predated CAR T infusion. Four started anticoagulation secondarily for thrombotic events after CAR-T infusion, and one received tissue plasminogen activator (tPA) for an acute stroke. In this group, no patients developed bleeding complications from anticoagulation. Conclusion Both bleeding (9.2%), and thrombotic (6.2%) events are observed after CAR T cell therapy, with bleeding limited to the first month in our cohort. Notably, ICANS was uniquely associated with PT prolongation, hypofibrinogenemia, and increased fibrin degradation, in addition to both bleeding and thrombosis. These results suggest that a systemic coagulopathy coincides with high grade ICANS and whether these neurologic events truly represent sequelae of widespread vascular dysfunction warrants further investigation. Anticoagulation was safe in the patients whom it was indicated. Risk factors for bleeding and thrombotic complications should be studied prospectively to develop risk-assessment models and clinical guidelines for management of bleeding and thrombosis (including prophylaxis) during CAR T therapy. Disclosures Muffly: Adaptive: Research Funding; Servier: Research Funding; Amgen: Consultancy. Negrin:BioEclipse Therapeutics: Current equity holder in private company; Magenta Therapeutics: Consultancy, Current equity holder in publicly-traded company; KUUR Therapeutics: Consultancy; Biosource: Current equity holder in private company; Amgen: Consultancy; UpToDate: Honoraria. Shizuru:Jasper Therapeutics, Inc: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees. Meyer:Orca Bio: Research Funding. Shiraz:Kite, a Gilead Company: Research Funding; ORCA BioSystems: Research Funding. Rezvani:Pharmacyclics: Research Funding. Mackall:Apricity Health: Consultancy, Current equity holder in private company; NeoImmune Tech: Consultancy; Nektar Therapeutics: Consultancy; Allogene: Current equity holder in publicly-traded company; BMS: Consultancy; Lyell Immunopharma: Consultancy, Current equity holder in private company. Miklos:Adaptive Biotech: Consultancy, Other: Travel support, Research Funding; Kite-Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Research Funding; Juno-Celgene-Bristol-Myers Squibb: Consultancy, Other: Travel support, Research Funding; Allogene Therapeutics Inc.: Research Funding; Novartis: Consultancy, Other: Travel support, Research Funding; Pharmacyclics: Consultancy, Other: Travel support, Patents & Royalties, Research Funding; Janssen: Consultancy, Other: Travel support; Miltenyi Biotec: Research Funding. Sidana:Janssen: Consultancy.

Abstract: Introduction: Given similar overall survival (OS) seen in patients receiving delayed vs. early autologous stem cell transplant (ASCT) in multiple myeloma (MM), some patients are electing to proceed with transplant at relapse instead of with upfront therapy. However, there is limited data in the era of novel therapies on expected disease control and outcomes in MM when ASCT is done for relapsed disease. The objective of this single-center retrospective study was to evaluate the outcomes of ASCT in patients with relapsed MM. Methods: Between January 1, 2010, and November 31, 2019, 168 consecutive patients with relapsed MM received ASCT at our center and constitute the study cohort. Progression free survival (PFS) was estimated from start of therapy at relapse until progression or death. PFS-PRIOR represents PFS of the immediate prior line of therapy before current relapse for which ASCT was pursued. OS was estimated from start of therapy at relapse and also from diagnosis until death. Results: Of the 168 patients, the majority underwent transplant in first relapse (69%, n=116) and the majority had not received a prior transplant (80%, n=135). Baseline and treatment characteristics of the cohort are shown in Table 1. High-risk cytogenetics were seen in 27% and ISS stage III disease in 15%. Median PFS-PRIOR was 20 months (range 2-228). The induction regimen used before ASCT included a doublet in 32%, a triplet in 56%, a quadruplet in 1.5% and a chemotherapy-based regimen in 9% of patients. Stem cell collection was done after relapse in 72% of the cohort. Conditioning regimen included melphalan 200 mg/m2 in 90% patients, including melphalan 200 mg/m2+BCNU in 55%. Median time to neutrophil and platelet engraftment was 11 and 16 days, respectively. Response after ASCT was very good partial response or better in 82% (n=124) of patients. Maintenance therapy was given in 35% (n=56) of patients after ASCT, with 73% patients receiving IMiD maintenance and a median duration of maintenance of 7 months (range 1-41). Survival: Median follow-up of this cohort was 61 months. Median PFS from start of treatment was 28 months. Median OS from start of treatment was 69 months and from diagnosis was 118 months. Two patients (1%) died within the first 3 months of complications related to transplant. As expected, patients who received ASCT at first relapse had a longer PFS of 33 months compared to 22 months when the transplant was done at second or later relapse, p=0.003 (Fig. 1A). OS from treatment start in patients undergoing transplant at first relapse was 82 months and those undergoing ASCT at second or later relapse was 45 months, p=0.004 (Fig. 1B). However, there was no difference in OS from diagnosis in these two groups (118 vs 134 months, p=0.97). Subgroup analysis was done in patients undergoing transplant at first relapse. Patients who had a PFS-PRIOR of ≥36 months had OS of 91 months compared to 62 months for those who experienced a shorter PFS-PRIOR, p=0.03. PFS in the subgroup of patients without prior ASCT undergoing transplant in first relapse (N=96) was 30 months. Multivariate Cox proportional hazards analysis was done for PFS and OS incorporating the following covariates: high risk cytogenetics, Karnofsky performance status (KPS), relapse number, PFS-PRIOR ≥36 months, response at ASCT, and use of maintenance. ASCT in first relapse was associated with better PFS with a hazard ratio (HR) of 0.63 (95% CI 0.42-0.94, p=0.03) and OS (HR 0.59, 95% CI 0.35-0.99, p=0.04). Achieving a PFS-PRIOR of ≥36 months was associated with improved PFS (HR 0.62, 95% CI 0.39-0.99, p=0.04) and OS (HR 0.41, 95% CI 0.21-0.82, p=0.01). Better KPS was also associated with longer PFS (HR 0.61, 95% CI 0.41-0.91, p=0.01) and OS (HR 0.52, 95% CI 0.31-0.86, p=0.01). Progressive disease at transplant was, as expected, associated with worse PFS (HR 3.28, 95% CI 1.89-5.70, p & lt;0.001) and OS (HR 2.70, 95% CI 1.39-5.22, p=0.003). Conclusions: This study provides comprehensive data on expected outcomes and prognostic factors amongst patients with MM undergoing ASCT at relapse, with median PFS and OS being 28 and 69 months in a cohort where only a third of patients received maintenance therapy. Disease response at transplant, PFS-PRIOR and KPS were prognostic for survival. These data can serve as a guide when counseling patients undergoing ASCT for relapsed MM and also serve as benchmark in designing clinical trials of transplant and comparative novel therapies for relapsed MM. Disclosures Muffly: Amgen: Consultancy; Adaptive: Research Funding; Servier: Research Funding. Shiraz:Kite, a Gilead Company: Research Funding; ORCA BioSystems: Research Funding. Liedtke:Adaptive: Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Caelum: Membership on an entity's Board of Directors or advisory committees. Rezvani:Pharmacyclics: Research Funding. Meyer:Orca Bio: Research Funding. Shizuru:Jasper Therapeutics, Inc: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees. Negrin:Biosource: Current equity holder in private company; Magenta Therapeutics: Consultancy, Current equity holder in publicly-traded company; BioEclipse Therapeutics: Current equity holder in private company; UpToDate: Honoraria; KUUR Therapeutics: Consultancy; Amgen: Consultancy. Miklos:Pharmacyclics: Consultancy, Other: Travel support, Patents & Royalties, Research Funding; Novartis: Consultancy, Other: Travel support, Research Funding; Allogene Therapeutics Inc.: Research Funding; Juno-Celgene-Bristol-Myers Squibb: Consultancy, Other: Travel support, Research Funding; Kite-Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Research Funding; Janssen: Consultancy, Other: Travel support; Miltenyi Biotec: Research Funding; Adaptive Biotech: Consultancy, Other: Travel support, Research Funding. Sidana:Janssen: Consultancy.

Abstract: BACKGROUND: Patients with relapsed/refractory (R/R) large B-cell lymphoma (LBCL) after failure of CD19-directed CAR T-cell therapy (CAR19) have a dire prognosis, with an overall response rate (ORR) of 29% to conventional salvage therapies, and a median overall survival (OS) of 6 months. CD22 is expressed on the majority of B-cell malignancies. Autologous CAR T-cells targeting CD22 (CAR22) have yielded an ORR of 70-90% in pediatric patients with R/R B-cell acute lymphoblastic leukemia (B-ALL), including those who had previously failed CAR19 therapy. Based on these encouraging results, we evaluated CAR22 in adult patients with R/R LBCL, focusing on those with CAR19-refractory disease. METHODS: This ongoing single-institution phase I dose escalation clinical trial (NCT04088890) is evaluating a CAR construct incorporating the m971 CD22 single chain variable fragments and 41BB/CD3z endodomains integrated within autologous T-cells via lentiviral transduction. After lymphodepletion (LD) with fludarabine and cyclophosphamide, patients are infused with cryopreserved CAR T-cells after a 7- to 11-day closed manufacturing process utilizing the CliniMACS Prodigy device (Miltenyi). Primary objectives assess the ability to successfully manufacture CAR22 and safety. Secondary objectives include efficacy and durability of responses. RESULTS: Twenty-one patients with LBCL [n=12 at dose level 1 (DL1), 1x10 6 CAR+ cells/kg; n=9 at dose level 2 (DL2), 3x10 6 CAR+ cells/kg] have been enrolled with a median age of 64 years (range, 36-79) and a median of 4 (range, 3-8) prior lines of therapy. All patients had at least one high risk feature, including failure of prior CAR19 therapy (n=20); refractory disease to second-line or later therapy (n=17); elevated lactate dehydrogenase (LDH) pre-LD (n=17); high tumor burden (n=9); a history of primary refractory disease (n=7); failure of prior autologous hematopoietic stem cell transplantation (HSCT) (n=6); never achieving CR to any therapy (n=5); or LBCL with MYC gene rearrangements (n=5). Successful manufacturing of cells was achieved in all patients. All patients reached day 28 post-infusion and are included in the safety and efficacy analysis presented here; updated results will be presented at the meeting. Every patient experienced cytokine release syndrome (CRS); 20/21 (95%) were Grade 1-2, 1/21 (5%) were Grade 3. Four patients (19%) experienced immune effector cell-associated neurotoxicity syndrome (ICANS); all cases were Grade 1-2 and resolved within 2 days. Five patients (24%) experienced a hyperinflammatory macrophage activation syndrome (MAS), manifested in all cases by pancytopenia and consumptive coagulopathy (DIC) requiring transfusion and/or growth factor support. One patient who received DL2 had a Grade 5 infectious event in the setting of ongoing MAS and pancytopenia. Relative to DL1, higher prevalence of Grade ≥3 cytopenias beyond D28 (89% vs. 50%) and MAS (33% vs. 17%) were observed at DL2; thus, DL1 was selected as the maximally tolerated dose (MTD). ORR at D28 was 86% (CR, n=11; PR, n=7), and was similar between DL1 and DL2 (92% vs. 78%; p=ns). 3/7 (43%) initial PR improved to CR at a median of 3 months post-infusion. All 14 patients (67% of cohort) who achieved CR remain in remission, with a mean follow-up of 7.3 months (range, 1.2-21.3); median progression free survival (PFS) and OS have not yet been reached. Five patients died from disease progression, and one patient died from septic shock in CR. CD22 expression by flow was downregulated or absent in 1/3 (33%) patients evaluated after relapse. Peak CAR-T expansion as detected by peripheral blood flow cytometry occurred at a median of 14 days, with a trend towards earlier and higher peak levels in DL2 patients. Significantly higher mean CAR-T levels occurred at peak expansion in patients who developed MAS (1070±915 vs. 196±209 CAR+ cells/μL; p=0.001). CONCLUSIONS: Infusion of CAR22 in R/R LBCL is safe and well tolerated at DL1. Manufacturing of CAR22 was uniformly successful. With a mean follow-up of 7.3 months, the ORR and CR rates are 18/21 (86%) and 14/21 (67%), respectively. These data demonstrate CAR22 to be an effective salvage therapy for CAR19-refractory or CD19-negative LBCL. Figure 1 Figure 1. Disclosures Frank: Allogene Therapeutics: Research Funding; Adaptive Biotechnologies: Research Funding; Kite-Gilead: Membership on an entity's Board of Directors or advisory committees. Oak: Kite Pharma-Gilead: Research Funding. Arai: Magenta Therapeutics: Research Funding. Rezvani: Kaleido: Other: One-time scientific advisory board; Nohla Therapeutics: Other: One-time scientific advisory board; Pharmacyclics-Abbvie: Research Funding; US Department of Justice: Consultancy. Shiraz: Kite Pharma-Gilead: Research Funding. Sidana: Janssen: Consultancy, Research Funding; Allogene: Research Funding; Magenta Therapeutics: Consultancy, Research Funding; BMS: Consultancy. Weng: Kite Pharma: Research Funding. Davis: Novartis Pharmaceuticals: Honoraria; Jazz Pharmaceuticals: Research Funding. Feldman: Samsara Biocapital: Consultancy; Obsidian: Consultancy; Lonza PerMed: Consultancy; Gradalis: Consultancy. Mackall: Lyell: Consultancy, Current equity holder in publicly-traded company, Other: Founder; Syncopation Life Sciences: Consultancy, Current holder of individual stocks in a privately-held company, Other: Founder; Apricity: Consultancy, Current equity holder in publicly-traded company; Neoimmune Tech: Consultancy; Nektar: Consultancy, Research Funding. Miklos: Kite, a Gilead Company, Amgen, Atara, Wugen, Celgene, Novartis, Juno-Celgene-Bristol Myers Squibb, Allogene, Precision Bioscience, Adicet, Pharmacyclics, Janssen, Takeda, Adaptive Biotechnologies and Miltenyi Biotechnologies: Consultancy; Pharmacyclics: Patents & Royalties; Pharmacyclics, Amgen, Kite, a Gilead Company, Novartis, Roche, Genentech, Becton Dickinson, Isoplexis, Miltenyi, Juno-Celgene-Bristol Myers Squibb, Allogene, Precision Biosciences, Adicet, Adaptive Biotechnologies: Research Funding; Adaptive Biotechnologies, Novartis, Juno/Celgene-BMS, Kite, a Gilead Company, Pharmacyclics-AbbVie, Janssen, Pharmacyclics, AlloGene, Precision Bioscience, Miltenyi Biotech, Adicet, Takeda: Membership on an entity's Board of Directors or advisory committees. Muffly: Astellas, Jasper, Adaptive, Baxalta: Research Funding; Adaptive: Honoraria, Other: fees for non-CME/CE services: , Research Funding; Pfizer, Amgen, Jazz, Medexus, Pfizer: Consultancy. OffLabel Disclosure: CD22-directed CAR-T therapy for the treatment of adults with relapsed/refractory large B-cell lymphoma