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Chronic graft-versus-host disease (cGVHD) of the lung, or bronchiolitis obliterans syndrome (BOS), is a high-risk disease manifestation associated with poor outcomes. Currently available treatments have demonstrated limited clinical efficacy in this setting. Belumosudil is a novel oral selective rho-associated coiled-coil–containing protein kinase-2 inhibitor that was recently approved by the US Food and Drug Administration in the treatment of cGVHD. We identified 59 subjects with BOS who were enrolled and treated in 2 prospective clinical trials of belumosudil. Patients with BOS had a percentage predicted forced expiratory volume in 1 second (FEV1) of ≤79% at enrollment and clinician attribution of lung disease owing to cGVHD. The National Institutes of Health (NIH) cGVHD lung scores at enrollment were 1 (n = 30, 59%), 2 (n = 23, 39%), or 3 (n = 6, 10%). According to NIH response criteria, the best overall response rate (ORR) for lung cGVHD was 32% (partial response: 17%; complete response: 15%). Response rates were inversely proportional to baseline NIH GVHD lung score at enrollment (lung score 1: ORR 50%; lung score 2: ORR 17%, lung score 3: ORR 0%) (P = .006). In multivariable analysis, male sex, lower baseline NIH cGVHD lung score, and partial response to previous line of cGVHD therapy before enrollment were associated with higher rates of lung-specific response. No significant correlation was identified between pulmonary function evaluations and measures of patient symptoms (NIH lung symptom score or Lee Symptom Scale score for lung). In conclusion, belumosudil treatment was associated with lung-specific clinical responses for subjects with BOS, which were more commonly observed in less advanced disease. Optimization of treatment response evaluations remains a challenge in patients with BOS.

The standard primary treatment for acute graft-versus-host disease (GVHD) requires prolonged, high-dose systemic corticosteroids (SCSs) that delay reconstitution of the immune system. We used validated clinical and biomarker staging criteria to identify a group of patients with low-risk (LR) GVHD that is very likely to respond to SCS. We hypothesized that itacitinib, a selective JAK1 inhibitor, would effectively treat LR GVHD without SCS. We treated 70 patients with LR GVHD in a multicenter, phase 2 trial (NCT03846479) with 28 days of itacitinib 200 mg/d (responders could receive a second 28-day cycle), and we compared their outcomes to those of 140 contemporaneous, matched control patients treated with SCSs. More patients responded to itacitinib within 7 days (81% vs 66%, P = .02), and response rates at day 28 were very high for both groups (89% vs 86%, P = .67), with few symptomatic flares (11% vs 12%, P = .88). Fewer itacitinib-treated patients developed a serious infection within 90 days (27% vs 42%, P = .04) due to fewer viral and fungal infections. Grade ≥3 cytopenias were similar between groups except for less severe leukopenia with itacitinib (16% vs 31%, P = .02). No other grade ≥3 adverse events occurred in >10% of itacitinib-treated patients. There were no significant differences between groups at 1 year for nonrelapse mortality (4% vs 11%, P = .21), relapse (18% vs 21%, P = .64), chronic GVHD (28% vs 33%, P = .33), or survival (88% vs 80%, P = .11). Itacitinib monotherapy seems to be a safe and effective alternative to SCS treatment for LR GVHD and deserves further investigation.

Little is known about whether risk classification at diagnosis predicts post-hematopoietic cell transplantation (HCT) outcomes in patients with acute myeloid leukemia (AML). We evaluated 8709 patients with AML from the CIBMTR database, and after selection and manual curation of the cytogenetics data, 3779 patients in first complete remission were included in the final analysis: 2384 with intermediate-risk, 969 with adverse-risk, and 426 with KMT2A-rearranged disease. An adjusted multivariable analysis detected an increased risk of relapse for patients with KMT2A-rearranged or adverse-risk AML as compared to those with intermediate-risk disease (hazards ratio [HR], 1.27; P = .01; HR, 1.71; P < .001, respectively). Leukemia-free survival was similar for patients with KMT2A rearrangement or adverse risk (HR, 1.26; P = .002, and HR, 1.47; P < .001), as was overall survival (HR, 1.32; P < .001, and HR, 1.45; P < .001). No differences in outcome were detected when patients were stratified by KMT2A fusion partner. This study is the largest conducted to date on post-HCT outcomes in AML, with manually curated cytogenetics used for risk stratification. Our work demonstrates that risk classification at diagnosis remains predictive of post-HCT outcomes in AML. It also highlights the critical need to develop novel treatment strategies for patients with KMT2A-rearranged and adverse-risk disease.

Chronic graft-versus-host disease (cGVHD) is the leading cause of late morbidity and mortality after allogeneic hematopoietic cell transplantation. To better understand patients at highest risk for nonrelapse mortality (NRM), we analyzed patient-, transplant-, and cGVHD-related variables, risk factors, and causes of nonrelapse deaths in an updated cohort of 937 patients enrolled on 2 prospective, longitudinal observational studies through the Chronic GVHD Consortium. The median follow-up of survivors was 4 years (range, 0.1 months to 12.5 years). Relapse accounted for 25% of the 333 deaths. The cumulative incidence of NRM was 22% at 5 years, and it increased over time at a projected 40% (95% confidence interval, 30%-50%) at 12 years. Centers reported that cGVHD (37.8%) was the most common cause of NRM and was associated with organ failure, infection, or additional causes not otherwise specified. The next most frequent causes without mention of cGVHD were infection (17%) and respiratory failure (10%). In multivariable analysis, an increased risk for NRM was significantly associated with the use of reduced intensity conditioning, higher total bilirubin, National Institutes of Health (NIH) skin score of 2 to 3, NIH lung score of 1 to 3, worse modified Human Activity Profile adjusted activity score, and decreased distance on walk test. To summarize, cGVHD NRM does not plateau but increases over time and is most commonly attributed to GVHD or infection, presumably associated with immunocompromised status. Severe skin and lung cGVHD remain challenging manifestations associated with increased NRM, for which novel therapeutic options that do not predispose patients to infections are needed.

There is a lack of large comparative study on the outcomes of reduced intensity conditioning (RIC) in acute myeloid leukemia (AML) transplantation using fludarabine/busulfan (FB) and fludarabine/melphalan (FM) regimens. Adult AML patients from Center for International Blood and Marrow Transplant Research who received first RIC allo-transplant between 2001 and 2015 were studied. Patients were excluded if they received cord blood or identical twin transplant, total body irradiation in conditioning, or graft-versus-host disease (GVHD) prophylaxis with in vitro T-cell depletion. Primary outcome was overall survival (OS), secondary end points were leukemia-free survival (LFS), nonrelapse mortality (NRM), relapse, and GVHD. Multivariate survival model was used with adjustment for patient, leukemia, and transplant-related factors. A total of 622 patients received FM and 791 received FB RIC. Compared with FB, the FM group had fewer transplant in complete remission (CR), fewer matched sibling donors, and less usage of anti-thymocyte globulin or alemtuzumab. More patients in the FM group received marrow grafts and had transplantation before 2005. OS was significantly lower within the first 3 months posttransplant in the FM group (hazard ratio [HR] = 1.82, P < .001), but was marginally superior beyond 3 months (HR = 0.87, P = .05). LFS was better with FM compared with FB (HR = 0.89, P = .05). NRM was significantly increased in the FM group during the first 3 months of posttransplant (HR = 3.85, P < .001). Long-term relapse was lower with FM (HR = 0.65, P < .001). Analysis restricted to patients with CR showed comparable results. In conclusion, compared with FB, the FM RIC showed a marginally superior long-term OS and LFS and a lower relapse rate. A lower OS early posttransplant within 3 months was largely the result of a higher early NRM.

There is marked paucity of data regarding late effects in adolescents and young adults (AYAs) who undergo myeloablative conditioning (MAC) allogeneic hematopoietic cell transplantation (HCT) for acute myeloid leukemia (AML). We evaluated late effects and survival in 826 1-year disease-free survivors of MAC HCT for AYA AML, with an additional focus on comparing late effects based upon MAC type (total body irradiation [TBI] vs high-dose chemotherapy only). The estimated 10-year cumulative incidence of subsequent neoplasms was 4% (95% confidence interval [CI], 2%-6%); 10-year cumulative incidence of nonmalignant late effects included gonadal dysfunction (10%; 95% CI, 8%-13%), cataracts (10%; 95% CI, 7%-13%), avascular necrosis (8%; 95% CI, 5%-10%), diabetes mellitus (5%; 95% CI, 3%-7%), and hypothyroidism (3%; 95% CI, 2%-5%). Receipt of TBI was independently associated with a higher risk of cataracts only (hazard ratio [HR], 4.98; P < .0001) whereas chronic graft-versus-host disease (cGVHD) was associated with an increased risk of cataracts (HR, 3.22; P = .0006), avascular necrosis (HR, 2.49; P = .006), and diabetes mellitus (HR, 3.36; P = .03). Estimated 10-year overall survival and leukemia-free survival were 73% and 70%, respectively, and did not differ on the basis of conditioning type. In conclusion, late effects among survivors of MAC HCT for AYA AML are frequent and are more closely linked to cGVHD than type of conditioning.

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

At Massachusetts General Hospital, we pioneered simultaneous hematopoietic cell (HCT)/kidney transplantation from HLA-identical related donors for the treatment of hematological malignancies with end-stage renal failure. We have now extended this to HLA-haploidentical donors in a pilot trial. Six recipients, 5 of whom were conditioned with fludarabine, cyclophosphamide, and total-body irradiation, underwent combined HCT/kidney transplantation from haploidentical donors; graft-versus-host disease (GVHD) prophylaxis included post-HCT cyclophosphamide, tacrolimus, and mycophenolate mofetil. One patient died as a result of complications of fludarabine neurological toxicity. No neurological toxicity was observed in subsequent patients who received lower fludarabine doses and more intense postfludarabine dialysis. There were no cases of grade 2 to 4 acute GVHD and 1 case of moderate chronic GVHD by 12 months. One patient experienced relapse of multiple myeloma at 30 months after HCT and died 4 years posttransplantation. Overall, 4 of 6 patients remain alive, without disease relapse and with long-term renal rejection–free survival. This trial was registered at www.clinicaltrials.gov as #NCT01758042.

T-cell/histiocyte-rich large B-cell lymphoma (TCRLBCL) is an aggressive variant of diffuse large B-cell lymphoma (DLBCL) characterized by rare malignant B cells within a robust but ineffective immune cell infiltrate. The mechanistic basis of immune escape in TCRLBCL is poorly defined and not targeted therapeutically. We performed a genetic and quantitative spatial analysis of the PD-1/PD-L1 pathway in a multi-institutional cohort of TCRLBCLs and found that malignant B cells harbored PD-L1/PD-L2 copy gain or amplification in 64% of cases, which was associated with increased PD-L1 expression (P = .0111). By directed and unsupervised spatial analyses of multiparametric cell phenotypic data within the tumor microenvironment, we found that TCRLBCL is characterized by tumor-immune "neighborhoods" in which malignant B cells are surrounded by exceptionally high numbers of PD-L1-expressing TAMs and PD-1+ T cells. Furthermore, unbiased clustering of spatially resolved immune signatures distinguished TCRLBCL from related subtypes of B-cell lymphoma, including classic Hodgkin lymphoma (cHL) and DLBCL-NOS. Finally, we observed clinical responses to PD-1 blockade in 3 of 5 patients with relapsed/refractory TCRLBCL who were enrolled in clinical trials for refractory hematologic malignancies (NCT03316573; NCT01953692), including 2 complete responses and 1 partial response. Taken together, these data implicate PD-1 signaling as an immune escape pathway in TCRLBCL and also support the potential utility of spatially resolved immune signatures to aid the diagnostic classification and immunotherapeutic prioritization of diverse tumor types.

Steroid-refractory (SR) acute graft-versus-host disease (GVHD) remains a major cause of nonrelapse mortality (NRM) after allogeneic hematopoietic cell transplantation (HCT), but its occurrence is not accurately predicted by pre-HCT clinical risk factors. The Mount Sinai Acute GVHD International Consortium (MAGIC) algorithm probability (MAP) identifies patients who are at high risk for developing SR GVHD as early as 7 days after HCT based on the extent of intestinal crypt damage as measured by the concentrations of 2 serum biomarkers, suppressor of tumorigenesis 2 and regenerating islet-derived 3α. We conducted a multicenter proof-of-concept “preemptive” treatment trial of α-1-antitrypsin (AAT), a serine protease inhibitor with demonstrated activity against GVHD, in patients at high risk for developing SR GVHD. Patients were eligible if they possessed a high-risk MAP on day 7 after HCT or, if initially low risk, became high risk on repeat testing at day 14. Thirty high-risk patients were treated with twice-weekly infusions of AAT for a total of 16 doses, and their outcomes were compared with 90 high-risk near-contemporaneous MAGIC control patients. AAT treatment was well tolerated with few toxicities, but it did not lower the incidence of SR GVHD compared with controls (20% vs 14%, P = .56). We conclude that real-time biomarker-based risk assignment is feasible early after allogeneic HCT but that this dose and schedule of AAT did not change the incidence of SR acute GVHD. This trial was registered at www.clinicaltrials.gov as #NCT03459040.

The application of allogeneic hematopoietic cell transplantation (allo-HCT) in non-Hodgkin lymphoma (NHL) patients ≥65 years in the United States is limited by lack of Medicare coverage for this indication. Using the Center for International Blood and Marrow Transplant Research (CIBMTR) database, we report allo-HCT outcomes of NHL patients aged ≥65 years (older cohort; n = 446) compared with a cohort of younger NHL patients aged 55-64 years (n = 1183). We identified 1629 NHL patients undergoing a first reduced-intensity conditioning (RIC) or nonmyeloablative conditioning allo-HCT from 2008 to 2015 in the United States. Cord blood or haploidentical transplants were excluded. The median age was 68 years (range 65-77) for the older cohort vs 60 years (range 55-64) in the younger cohort. The 4-year adjusted probabilities of nonrelapse mortality (NRM), relapse/progression (R/P), progression-free survival (PFS), and overall survival (OS) of the younger and older groups were 24% vs 30% (P = .03), 41% vs 42% (P = .82), 37% vs 31% (P = .03), and 51% vs 46% (P = .07), respectively. Using multivariate analysis, compared with the younger group, the older cohort was associated with increased NRM, but there was no difference between the 2 cohorts in terms of R/P, PFS, or OS. The most common cause of death was disease relapse in both groups. In NHL patients eligible for allo-HCT, there was no difference in OS between the 2 cohorts. Age alone should not determine allo-HCT eligibility in NHL, and Medicare should expand allo-HCT coverage to older adults.

Background: Axatilimab (Axa) is an IgG4 humanized monoclonal antibody with high affinity binding to CSF-1R. Axa blocks CSF1 and IL-34 binding and activation of CSF-1R signaling, a key pathway involved in the expansion and infiltration of donor-derived macrophages that mediate chronic graft-versus-host disease (cGVHD). We previously reported preliminary phase (Ph) 1 data demonstrating clinical activity and safety of Axa in patients with active cGVHD (Arora, ASH 2020). Here, we provide updated results, including Ph 2 clinical data, for doses chosen to move forward in a global, randomized pivotal study, AGAVE-201 (SNDX-6352-504). Methods: SNDX-6352-0503 is a Ph 1/2 study evaluating safety, tolerability, and efficacy of Axa in pts ≥6 years of age with active cGVHD despite ≥2 prior lines of systemic therapy. Ph 1 evaluated Axa at doses of 0.15mg/kg (n=1), 0.5mg/kg (n=1), 1mg/kg (n=3), and 3mg/kg (n=6) Q2W and 3mg/kg Q4W (n=6). The Ph 2 dose expansion evaluated Axa at 1mg/kg Q2W (n=23) with a primary objective of overall response rate (CR+PR) at 6 months. The data cutoff was 28 Jun 2021. Results: Forty pts (17 Ph 1 and 23 Ph 2) were enrolled and received at least 1 dose of axatilimab. Median age was 59 y (range, 16-73). Pts had received a median of 4 prior lines of treatment (range, 1-11), including ibrutinib (n=25), ruxolitinib (n=21), and belumosudil (n=8). Pts had a median of 4 involved organ systems at baseline (range, 1-9). At the time of the data cut, 22 pts (Ph 1, n=6; Ph 2, n=16) were continuing study treatment. Reasons for discontinuation included progression (n=5, 13%), physician decision (n=5, 13%), adverse events (AEs) (n=4, 10%; grade [Gr]) 3 periorbital edema, Gr 3 hypersensitivity reaction, Gr 4 CPK increased, Gr 5 fall (n=1 each), other (n=2, 5%), and withdrawal of consent (n=2, 5%). Thirty-eight pts were evaluable for response across Ph 1 & Ph 2. Overall response rate was 66% (n=25/38) and similar in pts previously treated with ibrutinib (n=16/24; 67%), ruxolitinib (n=13/20; 65%), and belumosudil (n=4/7; 57%). Response rates were similar for moderate severity cGVHD (60% [6/10]) vs severe cGVHD (70% [19/27]). A 7-point improvement in the normalized Lee Symptom score was seen in 54% (n=19/35) of pts (Fig 1). Focusing on the 32 pts treated at 2 of the doses selected to move forward (1mg/kg Q2W [n=26] and 3 mg/kg Q4W [n=6]), AEs related to Axa occurred in 66% (n=21/32) of pts with 13% (n=4/32) of pts experiencing grade ≥3 related-AEs. At the 1mg/kg Q2W dose, 62% (n=16/26) of pts experienced a related-AE with 8% (n=2/26) of pts experiencing grade ≥3 related-AEs (hypersensitivity, septic arthritis; both grade 3). Related-AEs, regardless of grade, in the 32 pts demonstrate a trend toward dose dependency (1mg/kg Q2W vs 3 mg/kg Q4W) with a higher proportion having elevations in AST (23% vs 50%), CPK (12% vs 67%), ALT (12% vs 33%), lipase (12% vs 50%), and incidence of periorbital edema (8% vs 50%) in the 3mg/kg Q4W cohort (Table 1). Transient elevated circulating enzyme levels have not been associated with hepatotoxicity or any other end-organ damage and are likely due to CSF-1R blockade on Kupffer cells, which are liver macrophages that mediate clearance of these enzymes. Importantly, the risk of infection was low, and no cases of viral reactivation were reported (cytomegalovirus, Epstein-Barr, and/or herpes simplex virus). Of the 32 pts treated at 1mg/1kg Q2W or 3mg/kg Q4W, 30 pts were considered evaluable for response (2 pts had not undergone a postbaseline assessment at the time of the data cut). A best overall response rate (CR+PR) of 70% (75% [18/24] 1mg/kg Q2W; 50% [3/6] 3mg/kg Q4W) as defined by the 2014 NIH cGVHD Consensus Criteria was observed. Responses were noted in difficult-to-treat organ manifestations, with 31% (n=4/13) experiencing a response in lung, 19% (n=5/27) in skin, and 57% (n=13/23) in joints and fascia. Median time to first response was 0.95 months (Fig 2). Conclusions: Axa is a novel agent targeting a pathway different than other cGVHD treatments. Data from this Ph 1/2 study demonstrate the safety and clinical activity of Axa in heavily pre-treated pts with active cGVHD, particularly those with fibrotic manifestations. A randomized pivotal study (AGAVE-201) has started enrolling a similar pt population, evaluating doses of 1 mg/kg Q2W and 3mg/kg Q4W, along with a lower dose of 0.3mg/kg Q2W. Figure 1 Figure 1. Disclosures Lee: Syndax: Research Funding; Takeda: Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Research Funding; National Marrow Donor Program: Membership on an entity's Board of Directors or advisory committees; Kadmon: Research Funding; AstraZeneca: Research Funding; Incyte: Research Funding; Janssen: Other; Amgen: Research Funding. Arora: Syndax: Research Funding; Pharmacyclics: Research Funding; Kadmom: Research Funding. Defilipp: Incyte Corp.: Research Funding; Regimmune Corp.: Research Funding; Omeros, Corp.: Consultancy; Syndax Pharmaceuticals, Inc: Consultancy. Abu Zaid: Syndax: Consultancy, Research Funding; Pieris: Current equity holder in publicly-traded company; Pharamcyclic: Research Funding; Incyte: Research Funding. Di Stasi: Syndax Pharmaceutical: Honoraria, Membership on an entity's Board of Directors or advisory committees; University of Alabama at Birmingham: Current Employment. Radojcic: Syndax Pharmaceuticals: Research Funding; Regeneron Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Allakos: Membership on an entity's Board of Directors or advisory committees. Meyers: Nuvalent: Consultancy, Membership on an entity's Board of Directors or advisory committees; Syndax Pharmaceuticals, Inc: Current Employment, Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company, Patents & Royalties. Qamoos: Syndax Pharmaceuticals: Current Employment. Ordentlich: Novartis: Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months; Patrys Lmtd: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Syndax Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Twenty-eight Seven Therapeutics: Consultancy; Cymabay Therapeutics: Current equity holder in publicly-traded company; Pfizer: Current equity holder in publicly-traded company; Viking Therapeutics: Current equity holder in publicly-traded company. Quaranto: Syndax Pharmaceuticals, LLC: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Schmitt: Syndax Pharmaceuticals, LLC: Current Employment, Current holder of stock options in a privately-held company; Fractyl Laboratories Inc. (Now Fractyl Health): Ended employment in the past 24 months. Gu: Syndax: Current Employment, Current equity holder in publicly-traded company; AstraZeneca: Ended employment in the past 24 months. Pusic: Syndax: Other: Advisory Board. Kitko: Horizon: Membership on an entity's Board of Directors or advisory committees; Co-investigator on two NIH grants as part of the cGVHD consortium: Research Funding; PER: Other: PER - CME educational talks about GVHD; Vanderbilt University Medical Center: Current Employment.

Background: Patients with Myelodysplastic Syndromes (MDS) and relapsed or refractory Acute Myeloid Leukemia (R/R AML) have poor survival, and the only potentially curative therapy is allogeneic hematopoietic cell transplantation (HCT). Even with HCT, many patients will relapse, and new therapeutic approaches are needed. Post-HCT relapse may relate to failure to eradicate leukemic progenitors or stem cells (LSCs), or to limited graft vs. leukemia effect from the donor T- and NK-cells. TIM-3 (T-cell immunoglobulin domain and mucin domain-3) has a widespread and complex role in immune system regulation, and is preferentially and aberrantly expressed on LSCs. MBG453 (sabatolimab) is a high-affinity humanized anti-TIM-3 IgG4 antibody being studied in combination with azaciditine or decitabine for higher risk MDS or AML. HCT outcomes of patients receiving TIM-3 inhibition is not well described. Aims: Characterize the outcomes of patients treated on the phase 1b study of sabatolimab+HMA who subsequently underwent allogeneic HCT. Methods: Patients with IPSS-R high or very high-risk (HR) MDS, relapsed/refractory (R/R) AML, or de novo AML not candidates for standard chemotherapy, who were HMA naïve, were enrolled in this multi-center, open label phase Ib dose-escalation study (NCT03066648). Escalating doses of sabatolimab were administered i.v. every 2 weeks (Q2W; days 8, 22) or every four weeks (Q4W; day 8) in combination with decitabine (20 mg/m 2; i.v. days 1-5) or azacitidine (75 mg/m 2; i.v. days 1-7). We retrospectively identified patients who underwent HCT after sabatolimab+HMA. We reviewed the medical records for incident acute GVHD (aGVHD) by MAGIC criteria, and chronic GVHD (cGVHD) requiring systemic immunosuppression. The date of immunosuppression was designated the date of cGVHD onset. Results: Data was available for 28 patients who received sabatolimab+HMA and subsequently underwent HCT. The median age was 67 (range 23-77); 18 were male while 10 were female. 19 patients had MDS, 3 patients had CMML, and 6 patients had AML (5 R/R AML). At enrollment, patients had high risk disease based on mutation profile, karyotype, and/or IPSS-R (Table 1). Molecular profiling identified several very high risk molecular features, including 7 patients with mutated TP53 (7/28), 6 with RAS mutations, 4 with mutated ASXL1, and 3 with mutated RUNX1 (Fig 1A). The HMA backbone included azacitidine (n=16) or decitabine (n=12). One patient also received the anti-PD1 antibody spartalizumab. Patients received a median of 4 cycles of treatment (range 1-14). The median time from the last dose of sabatolimab until transplant was 41 days (range 10-152 days). Median follow-up was 21.2 months. Conditioning was reported as myeloablative in 4 patients and reduced intensity in 20 patients. GVHD prophylaxis included post-transplant cyclophosphamide based approaches (n=6), tacrolimus and methotrexate (n=9), and CsA, MMF, and ATG (n=1). Donor source including matched unrelated donor (n=17), matched related donor (n=6), and alternative donors (haplo n=2; 7/8 MMUD n=2). Acute GVHD was seen in 16 patients; maximum grade 3-4 aGVHD occurred in 4 patients - 2 patients with stage 4 GI disease, 1 with stage 3 GI disease, and 1 patient with stage 4 skin GVHD. One patient died on hospice after G4 aGVHD. Chronic GVHD requiring systemic immunosuppression was seen in 8 patients, none of which have died or relapsed. The patient receiving spartalizumab had grade 2 skin GVHD and no cGVHD to date. Median OS after HCT was not reached; at 2 years, RFS was estimated at 64%, while OS was 69% (Fig 1B). Univariate analysis did not find associations between OS and disease (AML vs CMML vs MDS, Fig 1C. p=0.84), ASXL1 p=0.22, RUNX1 p=0.28, or splicing mutations p=0.97. Interestingly, patients with mutations in NRAS or KRAS - a group with poor outcomes with transplant - did not have worse outcomes than RAS WT patients (p=0.66), and had a 2y OS estimated at 80%. TP53 mutations were associated with worse outcomes than TP53 wt disease (Fig 1D. p Summary/Conclusion: Transplant outcomes for patients treated with the anti-TIM3 antibody sabatolimab in combination with HMA for high risk MDS and AML are generally favorable; toxicities related to GVHD were in line with historical rates in this limited cohort. Patients with RAS mutated disease did not have the poor outcomes previously described in this subgroup, while patients with TP53 mutated disease remain high risk. Figure 1 Figure 1. Disclosures Brunner: Janssen: Research Funding; BMS/Celgene: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Acceleron: Consultancy; Agios: Consultancy; Keros Therapeutics: Consultancy; GSK: Research Funding; Aprea: Research Funding; AstraZeneca: Research Funding; Novartis: Consultancy, Research Funding. Traer: ImmunoGen: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees; Schrodinger: Research Funding; Incyte: Research Funding; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Servier/Agios: Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees. Vey: Amgen: Honoraria; BMS: Honoraria; BIOKINESIS: Consultancy, Research Funding; NOVARTIS: Consultancy, Honoraria, Research Funding; SERVIER: Consultancy; JAZZ PHARMACEUTICALS: Honoraria; JANSSEN: Consultancy. Narayan: Genentech: Other: Spouse employment & equity interest; Takeda: Other: Spouse employment & equity interest; Sanofi Genzyme: Other: Spouse employment & equity interest; Novartis: Research Funding. Knapper: Novartis: Consultancy, Research Funding, Speakers Bureau; Astellas: Consultancy, Speakers Bureau; Jazz Pharmaceuticals: Consultancy, Speakers Bureau; Pfizer: Consultancy, Speakers Bureau. Wermke: Novartis, Roche, Pfizer, BMS: Consultancy, Honoraria, Research Funding. Esteve: Novartis: Consultancy, Research Funding; Bristol Myers Squibb/Celgene: Consultancy; Astellas: Consultancy; Pfizer: Consultancy; Jazz: Consultancy; Abbvie: Consultancy; Novartis: Research Funding. Kontro: Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding. Defilipp: Incyte Corp.: Research Funding; Omeros, Corp.: Consultancy; Syndax Pharmaceuticals, Inc: Consultancy; Regimmune Corp.: Research Funding. Wei: Abbvie, Amgen, Astellas, AstraZeneca, Celgene/BMS, Genentech, Janssen, MacroGenics, Novartis, Pfizer, and Servier: Honoraria; Former employee of Walter and Eliza Hall Institute: Patents & Royalties: Prof. Andrew Wei is a former employee of the Walter and Eliza Hall Institute and is eligible for a fraction of the royalty stream related to Venetoclax; Novartis, Abbvie, Celgene/BMS: Speakers Bureau; Abbvie, Amgen, Astellas, AstraZeneca, Celgene/BMS, Genentech, Janssen, MacroGenics, Novartis, Pfizer, and Servier: Membership on an entity's Board of Directors or advisory committees; Servier: Consultancy; Abbvie, Amgen, AstraZeneca, Celgene/BMS, Novartis, Servier and F. Hoffmann-La Roche: Research Funding. Borate: Takeda: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Daiichi-Sankyo: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Jazz Pharma: Research Funding; Blueprint Medicine: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding; Rampal: Membership on an entity's Board of Directors or advisory committees; Galecto, Inc.: Consultancy; Promedior: Consultancy. OffLabel Disclosure: sabatolimab (mbg453) is an anti-TIM3 antibody under investigation for the treatment of MDS, AML, and CMML.

Background: A major cause of mortality in patients receiving hematopoietic stem cell transplantation (HCT) is acute graft-versus-host disease (GVHD), a multiorgan disorder that includes the skin, liver and gastrointestinal tract. We have previously identified elafin, a protease inhibitor overexpressed in inflamed epidermis, as a diagnostic biomarker of GVHD in the skin, the most commonly involved GVHD organ. However, our initial study was limited to a subset of patients with isolated skin GVHD. The main driver of nonrelapse mortality (NRM) in HCT patients is GI GVHD. Two biomarkers, Regenerating islet-derived 3a (REG3α) and Suppressor of tumorigenesis 2 (ST2), have since been validated as biomarkers of GI GVHD that predict long-term outcomes in patients treated for GVHD. We undertook this study to determine the utility of elafin as a prognostic biomarker of acute GVHD in the general population of previously unstudied acute GVHD patients, and to compare it to ST2 and REG3α. Study Design: 526 patients who received systemic corticosteroid treatment for skin GVHD were analyzed from the Mount Sinai Acute GVHD International Consortium (MAGIC), which includes patients from 25 HCT centers. We used ELISA to measure serum concentrations of elafin, ST2 and REG3α. Patients were divided randomly into equal training and validation sets; and we developed a competing risk regression model for 6-month NRM using elafin concentration in the training set. We developed additional models for 6-month NRM using concentrations of ST2 and REG3α, or the combination of all three biomarkers as predictors. We then constructed ROC curves to evaluate the predictive accuracy of each model and to analyze the ability of each model to stratify patients into high- and low-risk groups. We analyzed the cumulative incidence of 6-month NRM and overall survival in each model and compared the accuracy of each model in the validation set. Results: The area under the receiver operating curve (AUROC) for elafin alone was 0.55 whereas it was 0.75 and statistically superior (P = 0.02) for the combination of ST2 and REG3α. The combination of 3 biomarkers produced an AUROC of 0.76 that was not significantly better than the two biomarker model (P = 0.10). Elafin concentrations, either alone or in combination with ST2 and REG3α, did not produce higher hazard ratios of NRM (data not shown). Patients in the low-risk elafin group paradoxically demonstrated a higher incidence of 6-month NRM, although this difference was not statistically significant (17% vs. 11%, P=0.19), and both overall survival at 6 months (68% vs. 68%, P>0.99) and four-week response (78% vs. 78%, P=0.98) were similar in the low- and high-risk elafin groups (Figure 1). As demonstrated in previous data sets, the combination of ST2 and REG3α divided patients into two groups with a nearly five-fold difference in NRM (6.7% vs. 31%, P Conclusion: We demonstrated that serum elafin concentrations measured at the initiation of systemic treatment for acute GVHD in a multicenter population of patients treated systemically for acute GVHD do not predict 6-month NRM, overall survival, or treatment response. As seen in previous studies, serum concentrations of the GI GVHD biomarkers ST2 and REG3α were significant predictors of NRM and the addition of elafin levels did not improve their accuracy. These results underscore the importance of GI disease in driving NRM in patients who develop acute GVHD. Figure 1. Cumulative incidence of nonrelapse mortality and overall survival in high and low risk groups Six-month cumulative incidences of nonrelapse mortality (NRM) in high (solid line) and low (dotted line) risk groups defined by optimized biomarker thresholds (upper panels) and six-month overall survival estimated using the Kaplan-Meier method (lower panels). (A) Cumulative incidence of NRM (14%) and overall survival (75%) in the total validation set (N=263). (B) Cumulative incidence of NRM in the low (N=150) and high (N=113) elafin group (17% vs. 11%, P=0.19). Overall survival in the low and high elafin group (68% vs. 68%, P > 0.99). (C) Cumulative incidence of NRM in the low (N=175) and high (N=88) ST2 + REG3a group (6.7 vs. 31%, P < 0.001). Overall survival in the low and high ST2 + REG3a group (77% vs. 51%, P < 0.001). (D) Cumulative incidence of NRM in the low (N=180) and high (N=83) elafin + ST2 + REG3a group (7.0 vs. 30%, P < 0.001). Overall survival in the low and high elafin + ST2 + REG3a group (79% vs. 64%, P < 0.001). Figure 1 Figure 1. Disclosures Ozbek: Viracor: Patents & Royalties: GVHD biomarker patent with royalties from Viracor. DeFilipp: Omeros, Corp.: Consultancy; Incyte Corp.: Research Funding; Regimmune Corp.: Research Funding; Syndax Pharmaceuticals, Inc: Consultancy. Grupp: Novartis, Kite, Vertex, and Servier: Research Funding; Jazz Pharmaceuticals: Consultancy, Other: Steering committee, Research Funding; Novartis, Roche, GSK, Humanigen, CBMG, Eureka, and Janssen/JnJ: Consultancy; Novartis, Adaptimmune, TCR2, Cellectis, Juno, Vertex, Allogene and Cabaletta: Other: Study steering committees or scientific advisory boards. Hexner: Blueprint medicines: Membership on an entity's Board of Directors or advisory committees, Research Funding; Tmunity Therapeutics: Research Funding; PharmaEssentia: Membership on an entity's Board of Directors or advisory committees. Kitko: Co-investigator on two NIH grants as part of the cGVHD consortium: Research Funding; Vanderbilt University Medical Center: Current Employment; PER: Other: PER - CME educational talks about GVHD; Horizon: Membership on an entity's Board of Directors or advisory committees. Qayed: Novartis: Honoraria; Mesoblast: Honoraria; Medexus: Honoraria. Reshef: ilead, BMS, Precision, Immatics, Atara, Takeda, Shire, Pharmacyclics, Incyte: Research Funding; Bayer: Consultancy; Gilead and Novartis: Honoraria; BMS, Regeneron, TScan, Synthekine, Atara, Jasper, Bayer: Consultancy. Levine: Incyte: Consultancy, Research Funding; Viracor: Patents & Royalties: GVHD biomarker patent with royalties from Viracor; Mesoblast: Consultancy, Research Funding; Equillium Bio: Membership on an entity's Board of Directors or advisory committees; X4 Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Talaris Therapeutics: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Omeros: Membership on an entity's Board of Directors or advisory committees; Symbio: Membership on an entity's Board of Directors or advisory committees; Biogen: Research Funding; Kamada: Research Funding. Ferrara: Eurofins Viracor: Consultancy, Other: Royalties. Chen: Incyte: Consultancy; Gamida: Consultancy.

Background: Three CD19 directed CAR-T products have gained FDA approval for systemic large B-cell lymphoma. Due to heightened concerns of immune cell associated neurotoxicity syndrome (ICANS), patients with primary CNS lymphoma (PCNSL) were excluded from all pivotal CAR-T studies. Consequently, all three products carry a limitation of use in the PCNSL patient population per their FDA labels . Due to these exclusions, little is known about the treatment-related toxicities and therapeutic potential of the currently available CD19 directed CAR-T products in this challenging patient population with significant unmet need. Methods: Based on our prior experience of tisagenlecleucel in secondary CNS lymphoma (PMID: 31320380) we conducted a pilot study with expansion of tisagenlecleucel in adults with relapsed or refractory PCNSL (NCT04134117). Patients had to be 18 years of age or older and have had progression or relapse following methotrexate-based therapy. All patients needed a confirmed diagnosis of PCNSL without evidence of systemic disease. Patients received a standard regimen of fludarabine (25 mg/m 2) and cyclophosphamide (250 mg/m 2) daily on days -5, -4, and -3 of infusion and a dose of 0.6-6.0 x 10 8 tisagenlecleucel CAR+ T-cells. Patients who had progressed on prior BTKi were allowed to continue given its beneficial effect on CAR-T expansion and function with cessation by month 3. The primary endpoint of this study was tolerability and toxicity including the rate and grade of CRS and ICANS per the 2019 ASTCT (American Society of Transplantation and Cellular Therapy) consensus criteria. Secondary endpoints included overall response rate and complete response rate to tisagenlecleucel per the international PCNSL Collaborative Group (IPCG) criteria which included MRI and CSF assessments. Exploratory endpoints included long-term efficacy, expansion, persistence and phenotype of tisagenlecleucel, cytokine profiling of the blood and CSF and CNS trafficking of CAR-T cells. Results: As of April 1, 2021, 10 subjects (ages 35-70 years) were enrolled and 9 were infused with a median age of 67 years (range, 34-81). Of the 9 infused patients, the median time from leukapheresis to infusion was 30 days (range, 27-37). Patients were heavily pretreated prior to study enrollment and received a median of 4 prior lines of anti-neoplastic therapy. All patients had progressed or failed first line high-dose methotrexate (HD-MTX); two had a history of prior thiotepa based autologous stem cell transplant (ASCT). Eight out of 9 patients had progressed following a prior BTKi and/or an immunomodulatory drug (IMiD) as part of TEDDI-R (temozolomide, etoposide, doxil, dexamethasone, ibrutinib and rituximab, n = 3), ViPOR (venetoclax, ibrutinib, prednisone, obinutuzumab and Revlimid, n = 3), or as monotherapy (n = 5) and 2 patients had received prior stereotactic radiotherapy. All patients had measurable disease at time of lymphodepletion (pre-infusion). Grade 1 CRS was observed in 6 patients with a median onset of 4 days (range, 1-5) following tisagenlecleucel and no patients required intervention for CRS. ICANS developed in 5 out of the 9 patients, only a single case of grade 3 ICANS, with a median time of onset was 5 days (range, 3-11). With a median follow-up of 7.43 months for survivors, 6/9 patients were alive with 4/9 showing ongoing responses (Figure 1). Expansion of tisagenlecleucel was demonstrated in the peripheral blood and CSF. Nanostring and RNA pathway analysis of CSF infiltrates demonstrated higher degrees of CNS CAR-T penetration in responding patients and increased T-cell and macrophage gene signatures. Peripheral and CSF cytokines were assessed. Conclusion: Tisagenlecleucel in r/r PCNSL was safe and efficacious in a highly refractory group of patients with significant unmet need. The majority of patients demonstrated a response per IPCG, including responses beyond 12 months. Tisagenlecleucel was found to expand in the peripheral blood and CNS with CSF gene signatures suggestive of higher CAR-T cell infiltrates in responding patients. Full trial safety data as well as additional follow-up and correlative studies will be presented. Figure 1 Figure 1. Disclosures Frigault: Editas: Consultancy; Iovance: Consultancy; Arcellx: Consultancy; Kite: Consultancy, Research Funding; Takeda: Consultancy; Novartis: Consultancy, Research Funding; BMS: Consultancy. Dietrich: Unum: Consultancy; Blue Earth Diagnostics: Consultancy; Magnolia: Consultancy; Gamaka Bio: Consultancy; Beacon Biosignals: Research Funding; Boehringer Ingelheim: Research Funding; BMS: Research Funding; Medimmune: Research Funding; Acerta: Research Funding; Orbus: Research Funding. Jordan: CereXis: Consultancy; Recursion: Consultancy; Navio Theragnostics: Consultancy. Forst: Eli Lilly: Current holder of individual stocks in a privately-held company. Plotkin: AstraZeneca: Consultancy; Akuous: Consultancy; NFlection Therapeutics: Other: Co-founder; NF2 Therapeutics: Other: Co-founder. Spitzer: Qihan Bio: Consultancy; Bluebird Bio: Consultancy; Jazz Pharmaceuticals: Consultancy; Syneos Health: Consultancy. Defilipp: Omeros, Corp.: Consultancy; Incyte Corp.: Research Funding; Regimmune Corp.: Research Funding; Syndax Pharmaceuticals, Inc: Consultancy. Maus: Tmunity: Consultancy; Novartis: Consultancy; Micromedicine: Consultancy, Current holder of stock options in a privately-held company; Kite Pharma: Consultancy, Research Funding; GSK: Consultancy; Intellia: Consultancy; In8bio (SAB): Consultancy; CRISPR therapeutics: Consultancy; Cabaletta Bio (SAB): Consultancy; BMS: Consultancy; Bayer: Consultancy; Atara: Consultancy; AstraZeneca: Consultancy; Astellas: Consultancy; Arcellx: Consultancy; Agenus: Consultancy; Adaptimmune: Consultancy; tcr2: Consultancy, Divested equity in a private or publicly-traded company in the past 24 months; century: Current equity holder in publicly-traded company; ichnos biosciences: Consultancy, Current holder of stock options in a privately-held company; Torque: Consultancy, Current holder of stock options in a privately-held company; WindMIL: Consultancy. Chen: Gamida: Consultancy; Incyte: Consultancy.

Characterization of molecular alterations in acute myeloid leukemia (AML) has led to development of targeted therapies, including FLT3 and IDH1/2 inhibitors. Maintenance therapy following hematopoietic cell transplantation (HCT) has shown substantial promise. Enasidenib (ENA), a selective IDH2 inhibitor, was associated with impressive rates of response in relapsed/refractory (R/R) AML and is now FDA-approved for this indication. We sought to assess the tolerability and define the maximum tolerated dose (MTD) of ENA as maintenance following HCT for IDH2-mutated myeloid malignancy. HCT-eligible patients (pts) ≥ 18 years with AML in remission, or myelodysplastic syndrome (MDS) with 1000/µL and platelets > 50000/µL). Those with prior HCT, active disease, QTc ≥450ms, and active infections were excluded. ENA was initiated between day 30 and 90 after HCT, at which time the following were required: chimerism ≥70% of donor origin among blood/marrow cells, no acute graft versus host disease (aGVHD) requiring ≥0.5mg/kg/day prednisone or equivalent, and no relapse. ENA was taken orally (po) daily (qd) in 28-day cycles. The period for dose-limiting toxicity (DLT) evaluation was the first cycle, escalation to successive levels was guided by DLT incidence, and 2 levels (50mg,100mg) were studied. Following establishment of MTD or recommended phase 2 dose (RP2D), 10 pts would be enrolled in an expansion cohort. Pts were monitored for relapse and toxicity and continued until disease progression, intolerable toxicity, or receipt of 12 cycles. Nineteen pts have been registered prior to HCT at 3 sites, Massachusetts General Hospital, Dana Farber Cancer Institute, and Johns Hopkins Hospital. Three pts could not initiate ENA following HCT; 2 due to logistic challenges of the COVID pandemic and 1 due to relapse. The remaining 16 pts initiated ENA treatment. The median age was 61 years (range 31-76); 12 (75%) were male, and 13 (81%) were Caucasian. Fourteen (88%) had AML, of which 6 were AML with MDS related changes and 2 had antecedent myeloproliferative neoplasm. Two pts (13%) had MDS. Among these 16 pts, 9 (56%) had IDH2 R140, and 5 (25%) had IDH2 R172 mutations. IDH2 subtype data was unavailable for 2 pts. Of 15 pts with available data from time of diagnosis, 11 (73%) had intermediate-risk and 4 (27%) had adverse-risk cytogenetics. Among these 15 pts, common concurrent mutations were DNMT3A (47%), SRSF2 (33%), and RUNX1 (33%). Eleven AML pts (85%) received intensive versus non-intensive therapies (15%) prior to HCT, and among all pts, 7 (44%) had received ENA prior to HCT. HCT data was available for all 16 pts; 4 pts (25%) received myeloablative, and 12 (75%) received reduced-intensity conditioning. Nine pts (56%) had a matched unrelated, 6 (38%) had haploidentical, and 1 (6%) had a matched related donor HCT. Three pts were enrolled at the 50mg dose level, 6 pts at 100mg, and after no DLTs were detected, the remaining were enrolled in an expansion cohort at 100mg qd. Median follow-up (F/U) for surviving patients is currently 11.7 months (range 1.5-18.9). 2 pts (13%) have relapsed during F/U, at 96 and 364 days post HCT. Additional ≥grade (G) 3 toxicities detected during treatment, possibly or probably related to ENA, included neutropenia, anemia, and bilirubinemia. Six pts (38%) required dose interruptions lasting a median 19 days (range 7-25), 4 required a dose reduction to 50mg, and 1 stopped treatment due to G3 bilirubinemia. In total, 3 pts (18%) discontinued study treatment, 1 for aforementioned G3 bilirubinemia, 1 to pursue a GVHD trial, and 1 for relapse. Six pts have completed the 12-month f/u without relapse, and 7 remain on study. 15 of 16 pts remain alive. Thus far, 3 pts have experienced ≥ G2 aGVHD, and 4 had moderate chronic GVHD. Serial measurement of 2HG is being conducted on samples, and these will be reported. Enasidenib is well-tolerated as post-HCT maintenance therapy for myeloid malignancy at the RP2D of 100mg qd. No DLTs have been detected, and a low rate of post-HCT relapse has been identified to date, although longer f/u is needed. Larger, randomized studies of ENA in the post-SCT setting would determine the true efficacy of this agent as maintenance therapy. Disclosures Fathi: Blueprint: Consultancy; Jazz: Consultancy; Amgen: Consultancy; Newlink Genetics: Consultancy; Pfizer: Consultancy; Abbvie: Consultancy; Seattle Genetics: Consultancy, Research Funding; Agios: Consultancy, Research Funding; PTC Therapeutics: Consultancy; Takeda: Consultancy, Research Funding; Boston Biomedical: Consultancy; Amphivena: Consultancy; BMS/Celgene: Consultancy, Research Funding; Kite: Consultancy; Trovagene: Consultancy; Forty Seven: Consultancy; Novartis: Consultancy; Daiichi Sankyo: Consultancy; Astellas: Consultancy; Trillium: Consultancy; Kura Oncology: Consultancy. Soiffer:Gilead: Consultancy; Novartis: Consultancy; Juno: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; VOR Biopharma: Consultancy; alexion: Consultancy; Rheos Therapeutics: Consultancy; Cugene: Consultancy; Precision Bioscience: Consultancy; Be the Match/ National Marrow Donor Program: Membership on an entity's Board of Directors or advisory committees; Kiadis: Membership on an entity's Board of Directors or advisory committees; Mana Therapeutics: Consultancy. Levis:Menarini: Honoraria; Amgen: Honoraria; FujiFilm: Honoraria, Research Funding; Astellas: Honoraria, Research Funding; Daiichi-Sankyo: Honoraria. Mims:Novartis: Speakers Bureau; Kura Oncology: Membership on an entity's Board of Directors or advisory committees; Leukemia and Lymphoma Society: Other: Senior Medical Director for Beat AML Study; Agios: Consultancy; Syndax Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Other: Data Safety Monitoring Board; Abbvie: Membership on an entity's Board of Directors or advisory committees. Devine:Magenta Therapeutics: Consultancy. Defilipp:Incyte: Research Funding; Regimmune: Research Funding; Syndax Pharmaceuticals: Consultancy. Spitzer:Jazz Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees; Bluebird Bio: Membership on an entity's Board of Directors or advisory committees. Frigault:Celgene: Consultancy; Arcellx: Consultancy; Novartis: Consultancy, Research Funding; Gilead/Kite: Consultancy, Research Funding. Amrein:Amgen: Research Funding; AstraZeneca: Consultancy, Research Funding; Takeda: Research Funding. Hobbs:Incyte: Research Funding; Merck: Research Funding; Bayer: Research Funding; Constellation: Honoraria, Research Funding; Jazz: Honoraria; Celgene/BMS: Honoraria; Novartis: Honoraria. Brunner:Janssen: Research Funding; Acceleron Pharma Inc.: Consultancy; GSK: Research Funding; Xcenda: Consultancy; Takeda: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Jazz Pharma: Consultancy; Forty Seven, Inc: Consultancy; Celgene/BMS: Consultancy, Research Funding; Biogen: Consultancy; Astra Zeneca: Research Funding. Narayan:Genentech: Other: Prior Spouse employment within 24 months and prior spouse equity divested within past 24 months; Takeda: Other: Prior Spouse employment within 24 months; Sanofi-Genzyme: Other: Current Spouse employment . Chen:AbbVie: Other: Data and Safety Monitoring Board Member; Incyte Corporation: Consultancy; Takeda: Consultancy; Actinium: Other: Data and Safety Monitoring Board Member; Equillium: Other: Data and Safety Monitoring Board Member; Magenta: Consultancy; Kiadis: Consultancy. OffLabel Disclosure: Enasidenib as post-transplant maintenance therapy

Allogeneic hematopoietic cell transplantation (HCT) is the only curative therapy for myelofibrosis (MF). In this large multicenter retrospective study, overall survival (OS) in MF patients treated with allogeneic HCT (551 patients) and without HCT (non-HCT) (1377 patients) was analyzed with Cox proportional hazards model. Survival analysis stratified by the Dynamic International Prognostic Scoring System (DIPSS) revealed that the first year of treatment arm assignment, due to upfront risk of transplant-related mortality (TRM), HCT was associated with inferior OS compared with non-HCT (non-HCT vs HCT: DIPSS intermediate 1 [Int-1]: hazard ratio [HR] = 0.26, P < .0001; DIPSS-Int-2 and higher: HR, 0.39, P < .0001). Similarly, in the DIPSS low-risk MF group, due to upfront TRM risk, OS was superior with non-HCT therapies compared with HCT in the first-year post treatment arm assignment (HR, 0.16, P = .006). However, after 1 year, OS was not significantly different (HR, 1.38, P = .451). Beyond 1 year of treatment arm assignment, an OS advantage with HCT therapy in Int-1 and higher DIPSS score patients was observed (non-HCT vs HCT: DIPSS-Int-1: HR, 2.64, P < .0001; DIPSS-Int-2 and higher: HR, 2.55, P < .0001). In conclusion, long-term OS advantage with HCT was observed for patients with Int-1 or higher risk MF, but at the cost of early TRM. The magnitude of OS benefit with HCT increased as DIPSS risk score increased and became apparent with longer follow-up.

The Mount Sinai Acute GVHD International Consortium (MAGIC) algorithm probability (MAP), derived from 2 serum biomarkers, measures damage to crypts in the gastrointestinal tract during graft-versus-host disease (GVHD). We hypothesized that changes in MAP after treatment could validate it as a response biomarker. We prospectively collected serum samples and clinical stages of acute GVHD from 615 patients receiving hematopoietic cell transplantation in 20 centers at initiation of first-line systemic treatment and 4 weeks later. We computed MAPs and clinical responses and compared their abilities to predict 6-month nonrelapse mortality (NRM) in the validation cohort (n = 367). After 4 weeks of treatment, MAPs predicted NRM better than the change in clinical symptoms in all patients and identified 2 groups with significantly different NRM in both clinical responders (40% vs 12%, P < .0001) and nonresponders (65% vs 25%, P < .0001). MAPs successfully reclassified patients for NRM risk within every clinical grade of acute GVHD after 4 weeks of treatment. At the beginning of treatment, patients with a low MAP that rose above the threshold of 0.290 after 4 weeks of treatment had a significant increase in NRM, whereas patients with a high MAP at onset that fell below that threshold after treatment had a striking decrease in NRM that translated into clear differences in overall survival. We conclude that a MAP measured before and after treatment of acute GVHD is a response biomarker that predicts long-term outcomes more accurately than change in clinical symptoms. MAPs have the potential to guide therapy for acute GVHD and may function as a useful end point in clinical trials.

In the absence of prospective studies that examine the effect of conditioning regimen intensity after T-cell–replete haploidentical transplant for acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), and myelodysplastic syndrome (MDS), a retrospective cohort analysis was performed. Of the 1325 eligible patients (AML, n = 818; ALL, n = 286; and MDS, n = 221), 526 patients received a myeloablative regimen and 799 received a reduced-intensity regimen. Graft-versus-host disease prophylaxis was uniform with posttransplant cyclophosphamide, a calcineurin inhibitor, and mycophenolate mofetil. The primary end point was disease-free survival. Cox regression models were built to study the effect of conditioning regimen intensity on transplant outcomes. For patients aged 18 to 54 years, disease-free survival was lower (hazard ratio [HR], 1.34; 42% vs 51%; P = .007) and relapse was higher (HR, 1.51; 44% vs 33%; P = .001) with a reduced-intensity regimen compared with a myeloablative regimen. Nonrelapse mortality did not differ according to regimen intensity. For patients aged 55 to 70 years, disease-free survival (HR, 0.97; 37% vs 43%; P = .83) and relapse (HR, 1.32; 42% vs 31%; P = .11) did not differ according to regimen intensity. Nonrelapse mortality was lower with reduced-intensity regimens (HR, 0.64; 20% vs 31%; P = .02). Myeloablative regimens are preferred for AML, ALL, and MDS; reduced-intensity regimens should be reserved for those unable to tolerate myeloablation.

Allogeneic hematopoietic cell transplantation (allo-HCT) is a potentially curative treatment of chronic myeloid leukemia (CML). Optimal conditioning intensity for allo-HCT for CML in the era of tyrosine kinase inhibitors (TKIs) is unknown. Using the Center for International Blood and Marrow Transplant Research database, we sought to determine whether reduced-intensity/nonmyeloablative conditioning (RIC) allo-HCT and myeloablative conditioning (MAC) result in similar outcomes in CML patients. We evaluated 1395 CML allo-HCT recipients between the ages of 18 and 60 years. The disease status at transplant was divided into the following categories: chronic phase 1, chronic phase 2 or greater, and accelerated phase. Patients in blast phase at transplant and alternative donor transplants were excluded. The primary outcome was overall survival (OS) after allo-HCT. MAC (n = 1204) and RIC allo-HCT recipients (n = 191) from 2007 to 2014 were included. Patient, disease, and transplantation characteristics were similar, with a few exceptions. Multivariable analysis showed no significant difference in OS between MAC and RIC groups. In addition, leukemia-free survival and nonrelapse mortality did not differ significantly between the 2 groups. Compared with MAC, the RIC group had a higher risk of early relapse after allo-HCT (hazard ratio [HR], 1.85; P = .001). The cumulative incidence of chronic graft-versus-host disease (cGVHD) was lower with RIC than with MAC (HR, 0.77; P = .02). RIC provides similar survival and lower cGVHD compared with MAC and therefore may be a reasonable alternative to MAC for CML patients in the TKI era.

Umbilical cord blood transplantation (UCBT) is an alternative for patients who need hematopoietic stem cell transplant (HSCT), but lack HLA-matched adult donors. Rabbit anti-thymoglobulin (ATG) has been used in UCBT conditioning to achieve T cell depletion, but ATG-induced immunosuppression is associated with delayed immune reconstitution, increased infectious complications and higher non-relapse mortality. In a clinical trial of reduced intensity double-unit UCBT (dUCBT), we substituted low dose total body irradiation (TBI) for ATG to determine whether dUCBT without ATG would alter kinetics and quality of immune reconstitution. Thirty-one patients with hematopoietic malignancies and a median age of 58 yr were treated with Flu/Mel/TBI, followed by dUCBT and GVHD prophylaxis with tacrolimus and sirolimus. We examined reconstitution of immune cell populations, thymic regeneration by quantifying T cell receptor excision circles (TREC) and serum cytokines (IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12, IFN-γ, TNF-α, IL-12p70, GM-CSF) using the LUNARISTM Human 11-Plex Cytokine Biochip384 from AYOXXA Biosystems. Assessments were done prior to and at 1, 2, 3, 6, 12 and 24 months after dUCBT. Results are based on 28 evaluable patients. The 2-yr overall survival and progression-free survival were 53% and 48%. Median time to neutrophil and platelet engraftment was 25 and 52 days, respectively. Before UCBT, the median values for most leukocyte subsets were below normal limits, except for monocytes. CD3+ cells remained depressed until 2 months post-transplant when gradually began to re-emerge. However, CD4+ and CD8+ subsets had distinct reconstitution kinetics (Figure 1). CD4+ T cells declined at 1 month but gradually increased and exceeded pre-transplant levels by 9 months after UCBT. In contrast, at 9 months, CD8+ lymphocytes remained depressed to 50% of pre-transplant levels, but increased thereafter and reached normal values by 2-yr. NK cells and monocytes reached normal values at 3 months post-UCBT. B cells were mostly undetectable for the first 6 months, followed by a 10-fold increase at 9 months and exceeded the upper normal limit by 2-yr. TREC, which were within normal range before transplant, decreased after UCBT but remained detectable between 1-6 months and recovered to normal levels by 9 months. Among cytokines, only IL-8, IL-6 and TNF-α displayed significant changes. IL-8 and IL-6 peaked at day 100 and 9 months, and subsequently declined. In contrast, TNF-α increased by day 100 and remained elevated thereafter. To evaluate functional immunity, we assessed correlations between viral reactivation and reconstitution of immune cell populations and thymic function. Nineteen patients experienced 24 clinically significant viral reactivations or infections, with 1-year cumulative incidence of 62%, which was comparable to 53% observed in dUCBT cohorts receiving ATG-containing conditioning. Although there was no difference in CMV, EBV, adenovirus and VZV reactivation, there was a significant increase in the incidence of HHV-6 reactivation. HHV-6 viremia was observed in 24 of 28 (86%) patients during the first month after dUCBT. Six of these 24 (25%) patients developed HHV-6-related encephalitis. There was a correlation between development of encephalitis and HHV-6 viral load ≥50.000 copies/ml (p=0.007). Pre-transplant TREC levels ≥1.200 copies/ml negatively correlated with subsequent HHV-6 reactivation (p=0.04), indicating that baseline reserve of thymic function has a significant role in post-transplant immune reconstitution. On days 30, 60 and 100 post-transplant, higher TREC levels correlated with lack of HHV-6 viremia (p Figure 1 Disclosures Defilipp: Incyte: Research Funding. Politikos:Angiocrine Bioscience Inc: Research Funding. Armand:Otsuka: Research Funding; Roche: Research Funding; Affimed: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Adaptive: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Merck: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Infinity: Consultancy; Sigma Tau: Research Funding; ADC Therapeutics: Consultancy; Tensha: Research Funding; Genentech: Research Funding; Pfizer: Consultancy. Ho:Jazz Pharmaceuticals: Consultancy. Koreth:Amgen: Consultancy; Equillium: Consultancy; Cugene: Consultancy. Avigan:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Research Funding; Juno: Membership on an entity's Board of Directors or advisory committees; Partners Tx: Membership on an entity's Board of Directors or advisory committees; Partner Tx: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy; Parexel: Consultancy; Takeda: Consultancy. Rosenblatt:Celgene: Research Funding; Amgen: Other: Advisory Board; Merck: Other: Advisory Board; BMS: Other: Advisory Board ; Parexel: Consultancy; Imaging Endpoint: Consultancy; Partner Tx: Other: Advisory Board; Dava Oncology: Other: Education; BMS: Research Funding. Chen:Abbvie: Consultancy; Incyte: Consultancy; Magenta: Consultancy; Takeda: Consultancy; Kiadis: Consultancy. Soiffer:Gilead, Mana therapeutic, Cugene, Jazz: Consultancy; Juno, kiadis: Membership on an entity's Board of Directors or advisory committees, Other: DSMB; Mana therapeutic: Consultancy; Kiadis: Other: supervisory board; Jazz: Consultancy; Cugene: Consultancy. Cutler:Kadmon: Consultancy; Incyte: Consultancy; Pharmacyclics: Consultancy; Fate Therapeutics: Consultancy. Ritz:Equillium: Research Funding; Merck: Research Funding; Kite Pharma: Research Funding; Aleta Biotherapeutics: Consultancy; Celgene: Consultancy; Avrobio: Consultancy; LifeVault Bio: Consultancy; Draper Labs: Consultancy; Talaris Therapeutics: Consultancy; TScan Therapeutics: Consultancy.

Systemic glucocorticoids are the principal treatment for acute graft-versus-host disease (GVHD), which remains the major cause of non-relapse mortality (NRM) after allogeneic hematopoietic cell transplantation (HCT). However, there are no validated biomarkers that measure a patient's response to glucocorticoid therapy, and thus response is evaluated by the change in clinical symptom severity. A major weakness in the predictive power of clinical responses is that changes to all organs are weighted equally even though the major driver of NRM is irreversible damage to the crypts of the GI tract. Recent studies from the Mount Sinai Acute GVHD International Consortium (MAGIC) have validated an algorithm probability (MAP) that combines serum concentrations of two biomarkers of GVHD (REG3α and ST2) to generate an estimated probability of 6 month NRM for individual patients. The MAP has been considered a "liquid biopsy" that estimates the damage caused by GVHD to crypts throughout the lower GI tract (Hartwell et al., JCI Insight, 2017; Major-Monfried et al., Blood, 2018). We hypothesized that the change in MAP between start of treatment and 28 days later could serve as a response biomarker for GVHD and might compare favorably to the change in clinical symptoms that measures response to GVHD treatment, which is widely used as a surrogate for long term survival and is the primary endpoint in most GVHD treatment trials (Martin et al., BBMT, 2009; MacMillan et al., Blood, 2010). We prospectively collected serum samples and clinical staging from 368 sequential HCT patients who received systemic treatment for acute GVHD in one of 20 MAGIC centers between January 2016 and February 2018. We measured the serum concentrations of REG3α and ST2 before and after systemic therapy for acute GVHD and computed MAPs, the changes in MAPs, and clinical responses for each patient. MAPs of patients who experienced 6 month NRM showed significantly greater increases than MAPs of patients who survived (p=0.0004). In patients whose MAPs at the start of treatment were low (Ann Arbor 1, MAP < 0.141) or intermediate (Ann Arbor 2, 0.141 ≤ MAP ≤ 0.290), 6 month NRM clustered among those who had the greatest increases in MAP after 28 days (Fig 1A,B). In patients with high MAPs at the start of treatment (Ann Arbor 3, MAP > 0.290), those who survived tended to have the largest decreases in MAP (Fig 1C). These changes in MAP suggested crossing a single threshold could predict risk of mortality. We found that patients whose MAPs rose above a threshold MAP of 0.290 (5% of Ann Arbor 1, 27% of Ann Arbor 2) had significantly worse survival compared to those who remained below it, whereas the large number patients with initially high MAPs that remained above the threshold (66% of Ann Arbor 3) had a large increases in mortality (Fig 2). When measured at day 28, the MAP was significantly more accurate in predicting NRM than the gold standard of the clinical response, with areas under the receiver operating characteristic curve (AUC) of 0.86 and 0.70, respectively (p We conclude that the MAP is, to our knowledge, the first validated laboratory test to serve as response biomarker for the treatment for acute GVHD and a more accurate predictor of survival than clinical response after four weeks of treatment. The MAP may serve as a novel endpoint and an important complement to changes in clinical symptom severity in future trials of GVHD treatment. Disclosures Srinagesh: National Institutes of Health: Research Funding. Ozbek:Viracor: Patents & Royalties: Biomarker Patent. Ayuk:Novartis: Honoraria, Other: Advisory Board, Research Funding. Aziz:Doris Duke Charitable Foundation: Research Funding. Defilipp:Incyte: Research Funding. Grupp:Novartis: Consultancy, Research Funding; Roche: Consultancy; GSK: Consultancy; CBMG: Consultancy; Novartis: Research Funding; Kite: Research Funding; Servier: Research Funding; Jazz: Other: study steering committees or scientific advisory boards; Adaptimmune: Other: study steering committees or scientific advisory boards; Cure Genetics: Consultancy; Humanigen: Consultancy. Hexner:novartis: Research Funding. Kitko:Mallinckrodt: Honoraria; Novartis: Consultancy, Honoraria. Mielke:EBMT/EHA: Other: Travel support; ISCT: Other: Travel support; Miltenyi: Consultancy, Honoraria, Other: Travel and speakers fee (via institution), Speakers Bureau; Jazz Pharma: Honoraria, Other: Travel support, Speakers Bureau; IACH: Other: Travel support; Kiadis Pharma: Consultancy, Honoraria, Other: Travel support (via institution), Speakers Bureau; DGHO: Other: Travel support; Bellicum: Consultancy, Honoraria, Other: Travel (via institution); GILEAD: Consultancy, Honoraria, Other: travel (via institution), Speakers Bureau; Celgene: Honoraria, Other: Travel support (via institution), Speakers Bureau. Merli:Sobi: Consultancy; Amgen: Honoraria; Novartis: Honoraria; Bellicum: Consultancy. Pulsipher:Amgen: Other: Lecture; Miltenyi: Research Funding; Bellicum: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jazz: Other: Education for employees; CSL Behring: Membership on an entity's Board of Directors or advisory committees; Adaptive: Membership on an entity's Board of Directors or advisory committees, Research Funding; Medac: Honoraria. Qayed:Bristol-Myers Squibb: Honoraria. Reshef:Pfizer: Consultancy; Magenta: Consultancy; Kite: Consultancy, Research Funding; Atara: Consultancy, Research Funding; BMS: Consultancy; Pharmacyclics: Consultancy, Research Funding; Incyte: Consultancy, Research Funding; Celgene: Research Funding; Shire: Research Funding. Levine:Incyte: Consultancy, Research Funding; Biogen: Other: non-financial support; Viracor: Patents & Royalties: biomarker patent; Ironwood: Honoraria; bluebird bio: Consultancy; National Cancer Institute: Research Funding; Novartis: Honoraria; Kamada: Research Funding. Ferrara:National Institutes of Health: Research Funding; ViraCor: Consultancy; Incyte: Consultancy; Kamada: Consultancy; Mallinckrodt: Consultancy; Enlivex: Consultancy; Xenikos: Consultancy; CSL Behring: Consultancy.

Post-transplant cyclophosphamide (PTCy) based GVHD prevention regimens are an emerging platform in allogeneic transplantation for hematological malignancies and are being prospectively compared to traditional standards. We present a single-center retrospective series of adult allogeneic bone marrow transplantation with the use of post-transplant cyclophosphamide in the setting of benign hematological conditions. Ten patients were treated between 2013 to 2019. Non-myeloablative conditioning consisted of rATG 0.5mg/kg on day (D) -9, 2mg/kg on D-7,-8 (ATG was in one patient with DBA), fludarabine 30mg/m2 daily from D-6 to D-2, cyclophosphamide 14.5mg/kg D-6 and D-5, and 200cGy of total body irradiation D-1. The bone marrow graft was administered on D0. GVHD prophylaxis consisted of post-transplant cyclophosphamide at 50mg/kg/day IV D+3, and +4 mycophenolate mofetil (MMF) at 15 mg/kg 3 times daily (maximum daily dose 3000 mg) starting on D+5 with taper beginning at D+35 to be off around D+100, and tacrolimus on D+5 with a target trough of 5-10 ng/mL with tapering beginning at D+180 with a goal to be off at D+360 in the absence of any GVHD. The median age at the time of transplantation was 42 (range 24-73) and 4 of 10 were female. Diagnoses include severe aplastic anemia (n=6), Diamond-Blackfan Anemia (n=2), paroxysmal nocturnal hemoglobinuria (n=1), and pure red cell aplasia (n=1). Median Hematopoietic Cell Transplantation-specific Comorbidity Index (HCT-CI) was 0 (range 0-5). Bone marrow donors were haploidentical donors (n=6), fully matched unrelated donors(n=3), and fully matched sibling (n=1). The median donor age was 31 (range 22-53). Donor marrow grafts had a median CD34+ cell count of 4.41 x 106/kg recipient ideal body weight (range 1.12 x 106 to 20.5 x 106). At a median follow-up of 17 months (range 3, 63) after transplantation, all patients are alive, with donor-derived hematopoiesis and free of significant acute or chronic GVHD. Neutrophil and platelet engraftment occurred at a median of 21 (range 16-34) days and 33 (21-65) days, respectively, after transplantation. The patient with pure red cell aplasia developed secondary graft failure and required a second transplant using a peripherally collected graft with the same fully matched unrelated donor. For all recipients, median day +30 unsorted chimerism was 100% (range 71-100%). Patients have not experienced significant acute or chronic GVHD. There were no cases of grade II-IV acute GVHD observed. Chronic GVHD was observed in 3 patients with ocular disease (two mild, one moderate). All patients who are over 12 months after transplantation are off systemic immunosuppression. Three patients experienced CMV reactivation, two required preemptive treatment with oral valganciclovir, while the third had a single positive low level positive CMV PCR that resolved spontaneously. Three patients had low level positive EBV viremia, none of which required pre-emptive treatment. Other significant infectious complications before day +100 included BK cystitis in three patients, influenza, adenovirus cystitis, clostridium difficile colitis, streptococcal and enterococcal polymicrobial endocarditis, and enterococcal bacteremia. Significant non-infectious complications were rare. One patient experienced engraftment syndrome which resolved quickly with systemic steroid administration. Another patient suffered a small spontaneous subdural hemorrhage day +10 after transplantation, but subsequently made a full neurologic recovery. Post-transplant cyclophosphamide based non-myeloablative allogeneic bone marrow transplantation appears safe and effective for patients with non-malignant hematologic conditions and should be prospectively compared to historical regimens. Table 1. Cohort Characteristics. SAA - Severe aplastic anemia, DBA - Diamond Blackfan anemia, ATG- anti-thymocyte globulin, CSA- cyclosporine, Cy-cyclophosphamide, haplo- haploidentical Disclosures Defilipp: Incyte: Research Funding. Frigault:Nkarta: Consultancy; Novartis: Consultancy; Foundation Medicine: Consultancy; Xenetic: Consultancy; Juno/Celgene: Consultancy; Kite/Gilead: Honoraria; Incyte: Consultancy. Chen:Incyte: Consultancy; Magenta: Consultancy; Takeda: Consultancy; Kiadis: Consultancy; Abbvie: Consultancy.

The significance of conditioning regimen intensity on the outcomes of T-cell replete HLA-haploidentical transplants is not known. This study compared outcomes of commonly used myeloablative (MAC) to reduced intensity (RIC) conditioning regimens in 1325 such transplants (AML; n=818; ALL; n=286 and MDS; n=221) in the US between 2008 and 2016. The median age of the study population was 54 years (18 - 70). Most patients (80%) with AML and ALL were in first or subsequent remission; 83% of those with MDS had refractory anemia with excess blasts at transplantation. Fifty-one percent of patients with AML and ALL had intermediate disease risk index (DRI). In contrast, 50% of patients with MDS had high or very high DRI. Patients received MAC (n=526; 40%) or RIC (n=799; 60%) transplant conditioning regimens and a uniform graft-versus-host disease (GVHD) prophylaxis: post-transplant cyclophosphamide, calcineurin inhibitor and mycophenolate. Approximately 50% of patients reported a HCT-CI score of 0-2 in MAC and RIC groups. Sixty-six percent of MAC and 42% of RIC recipients received peripheral blood grafts. Total body irradiation (TBI) + fludarabine (TBI/Flu; 33%) and busulfan with cyclophosphamide with/without Flu (Bu/Cy ± Flu; 36%) were the predominant MAC regimens. Other MAC regimens included TBI/Cy or other agents (10%), Flu/Bu4 (13%), melphalan (140 mg/m2) + Flu ± thiotepa (Flu/Mel ± TT; 9%). TBI (200cGy)/Cy/Flu (84%) was the predominant RIC regimen. Other RIC regimens included TBI 200cGy + Bu or Mel + Flu (7%), Flu/Bu2 (1%) and Flu/Mel (100mg/m2) ± TT (5mg/kg) (8%). The primary endpoint was disease-free survival (relapse or death). Cox regression models were built to study the effect of conditioning regimens on transplant outcomes after adjusting for other factors significantly associated with outcomes. Differences in transplant-outcomes were observed between ages 18-54 years and 55-70 years. The effect of age was further tested within the 18-54 and 55-70 age groups and there were no differences in outcome. In patients aged 18-54 years (n=689), 55% received MAC and 54% received RIC regimens. In patients aged 55-70 years (n=636), 22% received MAC and 78% received RIC regimens. Table 1 shows the effect (hazard ratio; HR) of conditioning regimen intensity in the two age groups adjusted for HCT-CI, recipient CMV serostatus, disease, DRI and graft type and the 2-year probabilities for the outcomes of interest. In patients aged 18-54 years who were equally likely to receive MAC or RIC regimens, relapse risks were higher after RIC regimens that resulted in lower disease-free survival. There were no differences in non-relapse mortality (NRM) or overall survival by conditioning regimen intensity. In patients aged 55-70 years who were more likely to receive RIC regimen, NRM was lower after RIC but without an advantage for relapse, disease-free or overall survival. Figure 1A and 1B show the 2-year probability of disease-free survival by conditioning regimen intensity in patients aged 18-54 and 55-70 years, respectively. Consistent with the main analysis, a subset analysis limited to AML also confirmed higher relapse (HR 1.43, p=0.03) and lower disease-free survival (HR 1.38, p=0.02) after RIC regimens in patients aged 18-54 years but not in patients aged 55-70 years. Acute GVHD (HR 1.01, p=0.94) and chronic GVHD (HR 0.82, p=0.14) did not differ by conditioning regimen intensity. Table 2 compares the effect of TBI- and non-TBI containing MAC and RIC regimens adjusted for age, HCT-CI, recipient CMV serostatus, disease, DRI and graft type. NRM risks were higher after RIC non-TBI compared to RIC TBI regimens. The predominant RIC non-TBI regimen was Flu/Mel (100mg/m2) ± TT (5mg/kg). In conclusion, a MAC regimen offers higher disease-free survival for those aged 18-54 years and can tolerate MAC regimens. For patients who are unable to tolerate MAC regimens, regardless of their age, TBI200 cGy/Cy/Flu is preferred to Flu/Mel ± TT to minimize NRM risks. Disclosures Shah: Juno Pharmaceuticals: Honoraria; Lentigen Technology: Research Funding; Exelexis: Equity Ownership; Geron: Equity Ownership; Miltenyi: Other: Travel funding, Research Funding; Oncosec: Equity Ownership. Brunstein:Gamidacell: Research Funding. Champlin:Otsuka: Research Funding; Sanofi: Research Funding. Hamadani:Celgene Corporation: Consultancy; Merck: Research Funding; Janssen: Consultancy; ADC Therapeutics: Research Funding; Sanofi Genzyme: Research Funding, Speakers Bureau; Cellerant: Consultancy; Takeda: Research Funding; Ostuka: Research Funding; MedImmune: Consultancy, Research Funding. McGuirk:Gamida Cell: Research Funding; Kite Pharma: Honoraria, Other: travel accommodations, expenses, speaker ; Fresenius Biotech: Research Funding; Pluristem Ltd: Research Funding; Bellicum Pharmaceuticals: Research Funding; Astellas Pharma: Research Funding; Novartis Pharmaceuticals Corporation: Honoraria, Other: speaker, Research Funding. Vasu:Boehringer Ingelheim Inc: Membership on an entity's Board of Directors or advisory committees. Waller:Pharmacyclics: Other: Travel Expenses, EHA, Research Funding; Cambium Medical Technologies: Consultancy, Equity Ownership; Celldex: Research Funding; Novartis Pharmaceuticals Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Kalytera: Consultancy.

Background: Allogeneic bone marrow transplantation for patients with hematological malignancies is curative, but the success of the procedure is limited by graft versus host disease (GvHD). Donor T-cells present in the graft are critical for the graft-versus-leukemia effect (GvL) of the transplant and important in facilitating bone marrow reconstitution, but also contribute to development of GvHD, and the risk of GvHD increases dramatically when the donor and recipient are not matched at all of the HLA loci. Hence, there is an urgent need for new approaches to curb GvHD and facilitate transplantation of HLA mismatched grafts to improve patient outcomes. Here, we have used an MHC-mismatched mouse model of GvHD to develop a novel and powerful approach to improve the success of allogeneic bone marrow transplantation by limiting GvHD. We identified a tryptophan metabolite, indole-3-carboxaldehyde (ICA), a dietary component present in foods such as collard greens and broccoli, that prevents lethal GvHD and allows normal engraftment by allogeneic donor bone marrow when fed to transplant recipients for the first few weeks after transplant. Methods: Lethally irradiated B10.BR (H2k) mice were transplanted with 3 x 106 T cell depleted bone marrow cells (TCD-BM) alone or the combination of TCD-BM plus 2 x 106 purified T cells from B6 (H2b) donor mice. Mice received daily gavage with 100 mg/kg or 150 mg/kg ICA or vehicle through day 38 post-transplant. Survival and clinical manifestations of GvHD were monitored through day 62. Histopathology of the gut, cytokines in serum and colon homogenates, intracellular cytokine staining of donor T-cells and bacterial counts in mesenteric lymph nodes (using blood agar plates) were measured in a separate cohort of experimental mice euthanized on day 20. Additionally, a secondary transplant was conducted to test the allo-proliferative capacity (in vivo CFSE dilution assay) and GvHD activity of T-cells from spleens of mice in the TCD-BM + T cells + 150 mg/kg ICA group that survived to day 62, compared to B6 T cells, in combination with fresh B6 TCD-BM, in B10.BR recipients. Results and Conclusion: Figure 1 shows survival curves for mice transplanted with TCD-BM + T-cells that were fed vehicle (red), 100 mg/kg/day of ICA (blue), or 150 mg/kg/day of ICA (green) by oral gavage. Only 7% of the recipients of TCD-BM + T cells treated with vehicle only survived to day 46. ICA administration improved survival in a dose-dependent manner: recipients given 100 mg/kg/day of ICA had 20% survival at day 52 (**p = 0.009) and administration of 150 mg/kg/day of ICA resulted in 83% survival of recipients of TCD-BM + T cells (***p These data indicate that enteral administration of ICA, a natural compound present in food, causes a dramatic reduction of GvHD in a MHC mismatched model of allogeneic bone marrow transplantation. We postulate that this effect is mediated through activation of the aryl hydrocarbon receptor in innate lymphoid cells in the lamina propria of the gut, stimulating regeneration of the gut epithelium and reducing trans-epithelial migration of gut bacteria that contribute to GvHD. Further development and exploration of the mechanism by which ICA treatment reduces GvHD could have a major impact on improving the safety of allogeneic bone marrow transplantation, and increase the availability of donors for those patients who currently lack an HLA matched sibling or volunteer donor. Figure 1 Figure 1. Figure 2 Figure 2. Disclosures No relevant conflicts of interest to declare.