Background Acute graft-versus-host disease (GVHD) is a major cause of non-relapse mortality (NRM) after allogeneic hematopoietic cell transplantation (HCT). High-dose steroids are standard first-line therapy for grade II–IV acute GVHD, whereas systemic treatment (tx) is generally not recommended for grade I. However, in practice many patients (pts) with grade I GVHD receive systemic steroids. A prior GITMO randomized trial (n=173) of grade I GVHD to either systemic steroid tx or “watch and wait” found that preemptive steroid tx reduced progression to grade II but not grade III/IV GVHD, increased serious infections, and resulted in similar chronic GVHD, NRM and survival (Bacigalupo, Haematologica 2017). In this study we analyzed real world evidence for early systemic steroid use and the potential impact of serum biomarkers in grade I GVHD. Methods We analyzed clinical data and serum samples from pts with grade I acute GVHD at 24 Mount Sinai Acute GVHD International Consortium (MAGIC) centers between 2014 and 2022 who were treated according to physician discretion. Pts were divided into a preemptive steroid tx group or a watch-and-wait group (systemic steroids administered only if progression to grade II–IV GVHD). Preemptive steroid use was treated as a time-dependent covariate and a frailty proportional hazards model with random effects was used to adjust for center effects to account for possible heterogeneity in clinical practices across transplant centers. Serum samples collected at the diagnosis of grade I GVHD were analyzed for ST2 and REG3α to calculate validated Ann Arbor (AA) scores (1, 2, 3). Results Grade I GVHD was diagnosed in 1143 pts; 591 (52%) received preemptive tx and 552 (48%) were treated by a watch-and-wait strategy. In the preemptive tx group, steroids were initiated at a median of 0 days and within 7 days for >90%. The median initial dose of steroids was 1 mg/kg of prednisone or its equivalent. In the watch and wait group, only 184 pts (33%) required systemic steroids for progression to grade II-IV GVHD at a median of 14 days from grade I diagnosis. Preemptive steroid tx reduced the risk of grade II–IV acute GVHD (HR, 0.71; 95% CI, 0.56–0.89; P=0.003), but not the risk of grade III/IV acute GVHD (HR, 1.03; 95% CI, 0.69–1.52; P=0.899) or chronic GVHD (HR, 1.03; 95% CI, 0.69–1.52; P=0.899), consistent with the GITMO trial. The 12-month incidence of NRM was higher for preemptive tx vs. watch and wait (13% vs 7%, P=0.002). In multivariate analysis preemptive steroid use independently predicted an increased risk of NRM (HR, 1.63; 95% CI, 1.06–2.50; P=0.026) as did several other known risk factors (older recipient age, umbilical cord blood donor, HCT-CI ≥3, and myeloablative conditioning). Greater NRM in the preemptive tx group was driven primarily by 3-fold more infectious deaths; deaths due to uncontrolled GVHD were similar for both tx groups. The risk for relapse was unexpectedly lower in the preemptive tx group (HR 0.64; 95% CI 0.47-0.88; P=0.006) and overall survival was therefore not different between groups, but risk factors for relapse such as minimal residual disease status were not available precluding further analysis of this finding. Serum was collected in 871 (76%) pts at onset of grade I GVHD for retrospective biomarker analysis. AA scores were AA1 (80%), AA2 (15%), and AA3 (5%). AA scores were highly predictive of progression to grade III/IV GVHD (AA1 vs AA2 vs AA3: 9% vs 14% vs 44%, all P<0.001) and the risk of 12-month NRM (8% vs 16% vs 39%, all P<0.001); this pattern was observed in both tx groups. The negative effect of preemptive steroid tx was most pronounced in pts with grade I/AA1 GVHD who experienced 5-fold more infectious related deaths compared to pts managed with a watch and wait approach. Conclusion Treatment of grade I GVHD with systemic steroids did not reduce the incidence of grade III/IV GVHD or deaths due to uncontrolled GVHD and instead increased the risk of NRM from infections compared to pts who were treated only after GVHD progressed. Importantly, 2/3 of the watch and wait pts never needed systemic steroid tx. These findings remained robust after adjusting for multiple confounders, including center effects, and were consistent with the GITMO trial. MAGIC biomarkers at the onset of grade I GVHD predicted outcomes and a watch and wait strategy may be best for the 80% of pts with AA1 GVHD. Better treatment options are needed for the 20% of pts with grade I and AA2/3 GVHD.

Obesity is increasing in prevalence and has been linked to inflammation, leading to worse outcomes in various disease states. Preclinical studies have demonstrated deleterious effects of obesity on graft-versus-host disease (GVHD). Several retrospective clinical studies have investigated the impact of obesity on allogeneic hematopoietic cell transplantation (HCT); however, with varying results and more limited data on the impact on chronic GVHD. We aimed to investigate the association of obesity on organ involvement, severity, and response to chronic GVHD therapy in a multicenter cohort of patients with chronic GVHD, as well as its impact on overall survival (OS), nonrelapse mortality (NRM), failure-free survival (FFS), and quality of life (QOL). We conducted a retrospective study of patients enrolled from 2007 to 2019 in two prospective longitudinal observational studies from the Chronic GVHD Consortium. Obesity was defined as a body mass index (BMI) ≥ 30, as calculated based on height and weight at the time of enrollment. Grade, organ involvement, and response to chronic GVHD therapy were compared between obese (BMI ≥ 30) and nonobese (BMI < 30) patients. Secondary outcomes included OS, NRM, FFS, and QOL measurement with the Lee symptom scale, Functional Assessment of Cancer Therapy, and Medical Outcomes Study Short Form 36. Among 487 patients identified with newly diagnosed chronic GVHD within 3 mo of study enrollment, 114 (23.4%) had BMI ≥ 30. The only significant difference between obese and nonobese patients was the presence of diabetes as a comorbidity. There were no significant differences in affected organs, grade, overall response to treatment, or organ-specific response to treatment between obese and nonobese patients. Chronic lung GVHD was more common in obese compared to nonobese patients (24.6% versus 13.9% for mild, 5.3% versus 4.8% for moderate, and 0.9% versus 0.8% for severe lung GVHD, P = .047), however, small case numbers and the lack of between group differences in OS, NRM, or FFS limit this interpretation. QOL analyses revealed greater patient-reported symptom burden and worse QOL in obese patients at enrollment and after 6 mo. We found obesity is associated with worse QOL but not with chronic GVHD phenotypes, responsiveness to treatment, or survival outcomes in a multicenter cohort of allogeneic HCT recipients. Given the increasing evidence of a multi-factorial role for obesity as a modulator of immune processes, additional studies investigating more accurate measures of obesity and body composition are needed to further understand their role in chronic GVHD.

Background: Graft-versus-host disease (GVHD) remains a significant complication following allogeneic HCT. At lower doses, histone deacetylase (HDAC) inhibition (vorinostat) has been shown to reduce GVHD through immunomodulation and may potentially offer neuroprotective effects. We conducted a phase I/II prospective, multi-site, open-label clinical trial combining vorinostat with standard immunosuppression for GVHD prevention in children and AYA patients undergoing allogeneic HCT (NCT03842696). Methods: Eligible patients were 3–39 years old, diagnosed with a hematologic malignancy, had Lansky/Karnofsky scores >70% without organ dysfunction, and were undergoing allogenic transplant from either a fully HLA-matched (8/8 allelic match at the HLA-A, -B, -C, and -DRB1 loci) or haploidentical donor. In matched-donor transplants, patients received standard GVHD prophylaxis (tacrolimus and methotrexate) plus vorinostat (60 mg/m2 twice daily) from day -10 through day +30 post-HCT. In haploidentical-donor transplants, patients received post-transplant cyclophosphamide, mycophenolate mofetil, and tacrolimus, with vorinostat (60 mg/m2 twice daily) initiated on day +5 and continued through day +30 post-HCT. The primary endpoint was the incidence of grade 2–4 acute GVHD by day 100 post-HCT. Forty-three patients were needed to achieve 80% power to detect a reduction in grade 2–4 acute GVHD incidence of 50% to 28%, with a Type I error rate of 5%. Secondary endpoints included the incidence of relapse, non-relapse mortality (NRM), and overall survival (OS). Data were analyzed using intention-to-treat analysis. All patients were considered for toxicity through day 180, for acute GVHD through day 100, and secondary endpoints through day 365. Exploratory endpoints included neurocognitive assessments, pharmacokinetic analyses, and laboratory correlatives. Neurocognition was assessed using the NIH toolbox cognitive battery, Wide Range Achievement Test (WRAT), and Wechsler Abbreviated Scale of Intelligence (WASI). Scores were standardized based on normative data by age, with outcomes reported as standard scores (mean=100, SD=15). Results: Between 2020–2025, 43 patients were enrolled (median age 19 years [range 3-39]; 27 males and 16 females); with diagnoses of MDS/AML (n=29) or ALL (n=14). Transplants included 25 HLA-matched unrelated donors, 7 HLA-matched related donors, and 11 haploidentical donors. Neutrophil engraftment occurred at a median of 14.5 days with no primary graft failures. No dose-limiting toxicities definitely attributable to the study drug were observed in the phase I or II portions of the study. The cumulative incidence of grade 2–4 acute GVHD was 16.2% [95% confidence interval (CI), 0.07-0.29] and 6.9% [95% CI, 0.02-0.17] for grade 3–4. The cumulative incidence of chronic GVHD requiring systemic immunosuppression was 20.9% [95% CI, 0.10-0.34]. At 1-year post-HCT, 6 patients (14.3% [95% CI, 0.0572-0.266]) experienced relapse and 4 patients (9.3%) died with a 4.6% [95% CI, 0.008- 0.14] 1-year NRM. One-year OS was 90.5% [95% CI, 0.82-0.99]. Baseline neurocognitive assessments showed significant impairments compared to the normative population.Specifically, the overall NIH Toolbox composite score was significantly lower (P<0.001), as were performances on individual subtests of processing speed (P<0.05), attention (P<0.001), and executive functioning (P<0.001). Scores of the WRAT Math subtest were also significantly lower than the normative population (P<0.001). By one-year post-HCT, there were universal upward trends across all cognitive domains. There was no longer significant impairment in overall cognitive functioning among transplant patients compared to normal controls. However, individual impairments persisted on tests of attention (P<0.001) and executive functioning (P<0.01). Conclusions: Vorinostat for GVHD prophylaxis was well-tolerated with a low incidence of acute and chronic GVHD and encouraging 1-year OS in children and AYA patients. No dose-limiting toxicities or SAEs/AEs definitely attributable to vorinostat were observed. If validated in a larger cohort, vorinostat may serve as a promising option for acute GVHD prevention in both HLA-matched and haploidentical donor transplants, without increasing relapse rates . Additionally, our findings highlight significant neurocognitive effects that children and AYA patients bring into allogeneic HCT. Pharmacokinetic and laboratory correlative analyses are ongoing.

Acute graft versus host disease (aGVHD) is a complication seen following allogeneic hematopoietic cell transplantation (allo-HCT) that contributes to significant morbidity and mortality. To our knowledge, no validated bedside model for predicting the risk of developing aGVHD following allo-HCT is currently available. Secondly, whether a machine learning based risk score can achieve superior performance compared to traditional statistical models is currently unknown. We aimed to develop and validate a clinical risk score to identify patients with significantly different risk for developing aGVHD grades 2-4 and 3-4 by day 100 post-transplant. Additionally, we compared the performance of the machine learning technique Bayesian additive regression trees (BART) with traditional logistic regression model. This analysis included adult patients who underwent allo-HCT between 2008 and 2019. Eligibility criteria were inclusive of a wide range of transplant indications, donor types, graft types, conditioning regimens, and GVHD prophylaxis regimens. The final cohort included 21,796 patients and was randomly split into training and validation sets consisting of 15,258 (70%) and 6,538 (30%) patients respectively. The training and validation sets were highly comparable across key characteristics. The most common categories for several key characteristics are shown in Table 1. Patient-related variables analyzed included age, race and ethnicity, Karnofsky performance status, and hematopoietic cell transplantation-specific comorbidity index. Disease-related factors included disease type, cytogenetics, and disease status at allo-HCT. Transplant-related variables included conditioning regimen, donor and graft type, donor age (unrelated donors only), donor-recipient ABO matching, donor-recipient sex matching, donor-recipient CMV serostatus, GVHD prophylaxis, and in-vivo T-cell depletion status. The primary outcome was aGVHD grade 2-4 and the secondary outcome was aGVHD grade 3-4, both summarized as event rate by day 100 post-transplant. Models were created using the training set. Logistic regression with a stepwise selection procedure was used to select prognostic factors for each outcome. Weighted scores were assigned to variables associated with each outcome based on the magnitude of their odds ratios. Risk scores were categorized into four groups using the 25th, 50th and 75th percentiles from the training set as cutting points, and association of the risk scores was tested using the independent validation cohort. Using the same training and validation sets, BART model was implemented to fit the training data and make predictions on the validation data. From logistic regression, the odds of developing aGVHD 2-4 by day 100 post-transplant were 1.50 (95% confidence intervals [CI] 1.29-1.75, p <.0001) for the 25th to 50th percentile group, 2.0 (95% CI 1.78-2.40, p <.0001) for the 50th to 75th percentile group, and 3.1 (95% CI 2.72-3.65, p <.0001) for the >75th percentile group when compared to the ≤25th percentile group in the validation cohort. The adjusted day-100 probability of aGVHD 2-4 was 26% in the ≤ 25th percentile group and 53% in the >75th percentile group. The odds of developing aGVHD 3-4 by day 100 post-transplant were 1.4 (95% CI 1.11-1.74, p=0.0043) in the 25th to 50th percentile group, 2.0 (95% CI 1.61-2.49, p <.0001) in the 50th to 75th percentile group, and 3.2 (95% CI 2.64-3.98, p <.0001) in the >75th percentile group when compared to the ≤ 25th percentile group in the validation cohort. The adjusted day-100 probability of aGVHD 3-4 was 9% in the ≤25th percentile group and 24% in the >75th percentile group. Cumulative incidence of aGVHD 2-4 and 3-4 in the training and validation sets using a stratified Fine-Gray model are shown in Figure 1. When comparing the performance of BART based models to logistic regression-based models using concordance index, there were no significant differences for aGVHD 2-4 (p=0.078) or aGVHD 3-4 (p=0.99). Here we have created the first validated clinical risk score for the risk of developing aGVHD 2-4 and 3-4 following allo-HCT, with wide eligibility criteria and inclusiveness. This risk score can guide personalized clinical decision making, patient counseling, and design of clinical trials for testing novel prophylactic interventions. Finally, the BART-based models showed similar performance to the traditional statistical-based models. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

HCT is a well-established standard therapy for children and young adults (CYA) with very high-risk/relapsed B-ALL. Recent studies have shown pre-HCT positive MRD by multichannel flow cytometry (MFC) leads to poorer outcomes, namely lower relapse-free and overall survival, with many centers delaying HCT if any detectable MRD by MFC is present. NGS has emerged as a methodology to detect MRD 2-3 logs lower than MFC (as low as 10-7 vs. 10-4). A subset analysis of the Children's Oncology Group ASCT0431 trial showed improved predictive power of NGS for relapse, event-free survival (EFS), and overall survival (OS) compared to MFC pre- and post-HCT (Pulsipher, 2015). Based upon these findings, we performed a prospective correlative biology study as part of the NCI-funded PTCTC ONC1401 trial. Samples from 9 US centers with patients transplanted between 2015 to 2021 were obtained for BM and PB NGS testing pre- and post-HCT at pre-specified time points. We hypothesized that BM NGS pre- and post-HCT would be highly predictive of relapse, relapse-free survival (RFS), and non-relapse mortality (NRM) in patients undergoing HCT for B-ALL and would be superior to BM MFC. A secondary hypothesis was that PB NGS would outperform BM MFC and may be a reasonable post-HCT relapse monitoring approach. Our cohort consisted of 121 CYA with B-ALL and a median age of 12 (range <1-27.0) years; 29.8%, 41.3%, and 14.9% were CR1, CR2, CR3+, respectively. Over half (59.5%) were male and 46.3% identified as Hispanic/Latino. Few (8.3%) received matched sibling BM, with the majority (50.4%) receiving haploidentical grafts. NGS MRD values were centrally performed using Clonoseqassay (NGS study results were not available to clinical teams). Pre-HCT BM and PB NGS results were available for 61.2% and 71.9% of patients, respectively, and multiple imputations were completed for missing values. Only 9.1% of patients had positive BM MFC MRD pre-HCT while 27.3% were positive by NGS BM MRD, showing higher sensitivity of NGS. Univariable and multivariable Cox proportional hazards models were used to assess RFS, with the multivariable model adjusting for age, conditioning type, and donor type. Univariable and multivariable Fine and Gray competing risk models were applied to evaluate relapse and NRM, treating mortality and relapse as competing events, respectively. Model predictive performance was assessed using the concordance index (C-index). All MRD methods predicted relapse on univariable analysis, but subdistribution hazard ratios (SHR) for NGS BM were much more predictive for relapse (3.46, 95% confidence interval: 1.45, 8.28) and RFS (hazard ratio (HR) 2.20 (1.19, 4.06)) compared to NGS PB and BM MFC. NGS PB was more predictive than BM MFC (SHR 2.12 (0.87, 5.15) vs. 1.63 (0.46, 5.81) for relapse and HR 1.94 (0.97, 3.86) vs. 0.77 (0.24, 2.51) for RFS), but statistical power was low, likely due to fewer patients who had positive MRD pre-HCT using PB NGS and MFC (13.2% and 9.1%, respectively). In addition, current practice is to intervene with a variety of approaches post-HCT for pre-HCT MFC MRD+ patients to prevent relapse. These interventions likely led to better than expected RFS for those who were MFC MRD+ pre-HCT. Using multivariable models, NGS BM clearly predicted a higher risk for relapse and inferior RFS than NGS PB and BM MFC (SHR 3.58 (1.33, 9.60) vs. 1.83 (0.65, 5.20) vs. 1.58 (0.44, 5.71) for relapse, respectively, and HR 2.00 (1.03, 3.87) vs. 1.67 (0.79, 3.55) vs. 0.68 (0.21, 2.24) for RFS). This was also demonstrated by higher C-index for NGS BM compared to the other methods (0.64 vs. 0.58 vs. 0.54 for relapse and 0.60 vs. 0.56 vs. 0.51 for RFS). A total of 24 patients relapsed post-HCT. Pre-HCT flow was positive for 3/24 (12.5%) of those who relapsed, while PB NGS was positive for 7/24 (29.2%), and BM NGS was positive for 17/24 (70.8%). NGS MRD from the BM predicted relapse 5.7x more often than BM MFC and 2.4x more often than PB NGS. The high level of sensitivity of BM NGS MRD at defining relapse risk could facilitate planned post-HCT interventions to prevent relapse. Ongoing analyses to be presented at the meeting include assessment of the predictive power of post-HCT BM and PB NGS versus BM MFC MRD and an assessment of the effect of graft-versus-host disease (GvHD) on outcomes; notably, preliminary analyses showed a key role for acute GvHD in mitigating relapse in MRD+ patients, which will be further defined through ongoing landmark analyses.

Background: Related haploidentical bone marrow transplant (haplo-BMT) with posttransplant cyclophosphamide is a potentially curative treatment for patients with sickle cell disease (SCD) who traditionally have limited donor options. The presence of donor-specific, anti-human leukocyte antigens (HLA) antibodies or DSA has been associated with a significantly increased risk of graft failure following haploidentical stem-cell transplantation (Ciurea et al. Transplantation, 2009). Development of DSA is common in SCD secondary to sensitization through blood transfusion. We evaluated the efficacy of our desensitization strategy in patients with SCD with prohibitive DSA undergoing haplo-BMT. Methods: The study was conducted as part of a multi-institutional Vanderbilt Haploidentical Learning Collaborative, which opened in October 2013, with institutional specific IRB and the primary objective of optimizing haplo-BMT for SCD. Patients and donors were high resolution HLA typed at the HLA-A, B, C, DRB1, DRB3-5, DQB1, and DPB1 loci. Patients' sera were tested for HLA-antibodies against the donor using solid-phase immunoassays on the Luminex platform using the LABScreen Single Antigen Kit (One Lambda, Canoga Park, CA, USA) at the time of initial evaluation and within 30 days prior to start of conditioning. The crossmatch techniques used were standard complement dependent cytotoxicity assays and/or flow cytometric crossmatch tests. A mean fluorescence intensity (MFI) of 3000 Units (U) was used as the cut-off for clinical relevance and considered moderate-to-severe DSA level for both anti-HLA class I and class II antibodies. Desensitization was initiated in patients with DSA MFI ≥3000 U and with no other donors identified. Each patient underwent desensitization based on modified Johns Hopkins approach (Gladstone et al. BBMT 2013), and common haplo-BMT conditioning (de la Fuente et al. BBMT 2019), figure 1. Desensitization included alternate-day, single-volume plasmapheresis (PP), performed using the COBE Spectra (TerumoBCT, Lakewood, CO), replacing 100% volume with 5% albumin, anti-CMV hyper-intravenous immune immunoglobulin (IVIg) (100 mg/kg), tacrolimus (1 mg, IV per day or 2 mg, po twice daily) and mycophenolate mofetil (1 g, twice daily) starting 1 to 2 weeks prior to start of haplo-BMT conditioning, with 1 additional treatment on the day before infusion of stem cells. Most patients also received a single dose of rituximab 375 mg/kg at least 1 week prior to start of PP/IVIg. HLA antibodies were measured on day 0 before the infusion of bone marrow and if the MFI had not decreased to <3000 U, two additional cycles of PP/IVIg were given on days +1 and day +2 post-transplant. Results: Eight haploidentical patients had moderate-to-severe DSA levels (Table). All had DSA to HLA class I, patient #7 had DSA to two class I antigens, and patient #8 to 2 class I and 2 class II antigens. Donors were all first-degree relatives (4-maternal, 2-paternal and 2-sibling). Mean age of patients was 12.25 years (range 3-25), 5 patients were female. Patient #6 underwent a second haplo-BMT from paternal donor after a previous graft failure from a maternal haploidentical donor 18 months prior. A paired t-test showed a statistically significant difference between baseline DSA level (mean (M)= 14187.25, standard deviation (SD)= 6782.55) and day-0 DSA level (M= 3849.63, SD= 3704.21); [t(7) = 5.54, p=0.0008]. The 95% confidence interval of the difference between the means ranged from 5926.3 to 14749. Desensitization was well tolerated without serious adverse events in all patients. Four patients required additional cycles of PP/IVIg on days +1 and +2. DSA was undetectable or <1000 U in 3 of 4 patients who required PP/IVIg on D+1 and D+2. Median time to neutrophil engraftment was 20.5 days (range 15-28); all patients engrafted by day +28, though 4 patients had initial mixed chimerism in the T cell fraction. Patient #8 had persistent DSA to class II on Day +2, developed poor graft function despite having primary engraftment and died of pulmonary hemorrhage on Day + 45. Conclusion: The combination of rituximab, PP/IVIg and pre-transplant immunosuppression is an effective desensitization strategy for patients with SCD and high DSA titer undergoing haplo-BMT. The risk of graft failure is reduced, enabling transplantation when no other donor exists. Larger prospective studies are needed to further validate this approach. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Introduction: Since October 2021, there have been two Food and Drug Administration (FDA) approved CD19 CAR-T products (tisagenlecleucel (tisa-cel) and brexucabtagene autoleucel (brexu-cel)) for adolescents and young adults (AYA) aged 18 to 25 with B-cell acute lymphoblastic leukemia (B-ALL). Only a small number of AYAs were treated on both registration studies. Comparison across these single arm studies is not possible with differences in demographics and clinical management. We aim to understand prescriber preferences and rationale when deciding between products in the AYA population with B-ALL and inform future clinical investigations. Methods: We conducted a 21-question electronic survey of CAR-T prescribers through the Pediatric Transplantation and Cellular Therapy Consortium (PTCTC). (Note: PTCTC did not formally approve this work but assisted with survey conduct.) The survey consisted of questions about practice demographics and logistics, prescriber opinion and preferences regarding the two FDA approved CAR-T products based on literature data. Results: There was a total of 13 completed surveys from 10 centers at the time of analysis. Most respondents primarily treat patients with hematological malignancies who are 18 years of age or younger (85%). The median FDA approved CAR-T volume among the centers were 1-5 and ranged from 0 to >20. Close to half of respondents (46%) reported their institution requiring committee discussion and approval for all CAR-T cases. Ninety-two percent prescribed tisa-cel for any indication; 23% prescribed brexu-cel for any indication. Within the past year, over half of the respondents treated at least 16 patients with B-ALL (62%) and prescribed at least one CAR-T product. Approximately 31% of the respondents discuss both CAR-T products as treatment options for AYA with B-ALL, and respondents from two centers reported that their center is only certified to prescribe tisa-cel. Since October 2021, 69% of respondents had prescribed tisa-cel for B-ALL while only 15% had prescribed brexu-cel for B-ALL. Regarding current practice, close to half (46%) reported general consensus among their institutional practice is to prescribe tisa-cel for AYA with B-ALL. No one planned to routinely prescribe brexu-cel for AYA with B-ALL, although 31% report planning to consider either CAR-T product on a case-by-case basis. The remaining 23% has no general plan: 15% not having discussed both CAR-T products as an option and 8% is unsure. When asked the clinical data for deciding tisa-cel vs brexu-cel for AYA with B-ALL, some respondents reported more data and experience with tisa-cel, including longer follow-up and better persistence with 4-1BB costimulatory domain. For patients who need CAR-T treatment more urgently, some would consider brexu-cel for the shorter vein to vein time. The respondents were then presented with hypothetical clinical scenarios using published data without revealing the product name and asked to select CAR-T product A (tisa-cel), B (brexu-cel) or if both would be reasonable. When presented with the CR/CRi rate and the 4-1BB vs CD28 co-stimulatory CAR constructs in a blinded fashion, the percent of respondents willing to consider both products as reasonable options were comparable as that reported in practice (close to 31%, with the remaining favoring tisa-cel). However, when presented with reported OS data from both products in blinded fashion, close to 69% of the respondents selected that both products are reasonable options. When presented with product manufacturing turnaround time, 42% of respondents preferred brexu-cel while the remaining 58% respondents felt both products were reasonable. Conclusions: AYA with B-ALL requiring CAR-T therapy are eligible for both tisa-cel and brexu-cel and there exists clinical equipoise as to which product is best for different clinical scenarios given the lack of head-to-head comparison. Most CAR-T prescribers at the time of this survey favored tisa-cel given its availability and familiarity as well as its 4-1BB costimulatory domain. However, some prescribers may favor brexu-cel if there was rapid clinical decline requiring expedited turnaround time. Some changes in product preference when clinical data was presented in a blinded manner were seen, suggesting providers' willingness and feasibility to design a pragmatic study comparing tisa-cel and brexu-cel in real world practice in the AYA population.

Introduction: Controlling both GVHD and disease relapse is essential for allogeneic hematopoietic cell transplantation (alloHCT) success. For three decades, the standard GVHD prophylaxis strategy has been a calcineurin inhibitor such as tacrolimus (Tac) plus methotrexate (MTX). Although several approaches have been tried in recent years to improve upon Tac/MTX, intensifying immunosuppression frequently comes with an increased risk of serious infections or relapse and usually no effect on chronic GVHD even if acute GVHD is reduced. The Blood and Marrow Transplant Clinical Trials Network (BMT CTN) previously completed a phase II study comparing three novel GVHD prophylaxis regimens to contemporaneous controls receiving Tac/MTX (BMT CTN 1203) in order to determine the most promising novel GVHD prophylaxis approach with reduced intensity conditioning (RIC). The most promising GVHD prophylaxis regimen in BMT CTN 1203 was a 3-drug combination of post-transplant cyclophosphamide (PTCy), tacrolimus, and mycophenolate mofetil (PTCy/Tac/MMF). Here, we report the results of the randomized phase III study comparing outcomes of alloHCT in those randomized to receive PTCy/Tac/MMF versus standard Tac/MTX. Patients and Methods: Eligible adults (age 18+) with hematologic malignancies undergoing RIC alloHCT with an 6/6 matched related (N=128), 8/8 matched unrelated (N=288), or 7/8 single mismatch (N=15) peripheral blood stem cell donor, satisfactory organ function, and adequate performance status were randomized 1:1 to receive PTCy/Tac/MMF (N=214) or Tac/MTX (N=217), stratified by transplant center and Disease Risk Index (DRI). The primary endpoint of the study was GVHD/relapse or progression-free survival (GRFS), a time-to-event outcome defined as grade III-IV acute GVHD, chronic GVHD requiring systemic immune suppression, disease relapse or progression, or death by any cause. The primary hypothesis was that PTCy/Tac/MMF has a ≥15% higher GRFS at 1 year than Tac/MTX in the intent-to-treat population. Secondary endpoints included the incidence/severity of acute and chronic GVHD, engraftment/chimerism, relapse/progression, infections, and survival. Results: The 2 study arms were well balanced by patient sex, age, Karnofsky performance status, disease risk, comorbidities, donor match, conditioning regimen, and post-transplant maintenance therapy (Figure panel A). In the multivariate Cox regression model of the primary endpoint, the PTCy treatment group had a significantly lower hazard of GRFS than Tac/MTX (hazard ratio 0.641, 95% confidence interval [CI] 0.492 to 0.835, p=0.001). The adjusted 1-year GRFS rate was 52.7% (95% CI: 45.8%, 59.2%) for the PTCy arm and 34.9% (95% CI: 28.6%, 41.3%) for the control arm, Figure panel B). The lower proportion of GRFS events in the PTCy arm was due to a reduction in both acute and chronic GVHD. The Day 100 grade III-IV acute GVHD was 6.3% vs 14.7% (p=0.001), and chronic GVHD rate at 1 year was 21.9% vs 35.1% (p=0.005) for PTCy vs Tac/MTX, respectively. There was no difference in the relapse/progression rate at 1 year (20.8% vs 20.2%, p=0.9), or OS rate at 1 year post transplant (76.8% vs 72.6% , p=0.3), in PTCy vs Tac/MTX. The cumulative incidence of engraftment was lower for PTCy for neutrophils ≥ 500/mm3 by day +28 (90.3% vs 93.4%, p=0.03), platelets ≥ 50,000/mm3 by day +100 (79.5% vs 83.7%, p<0.001), and lymphocytes ≥ 1000/mm3 by 1 year (47.1% vs 63.2%, p<0.001). Grade 3 infection rates were similar between the arms (12.2% for PTCy vs 13.3%, p=0.8) but grade 2 infections were greater for PTCy (33.7% vs 23.5%, p=0.002). There was no difference in CMV reactivation between the treatment arms (7.3% for PTCy vs 7.1%, p=0.8). There was no significant difference in proportion of chimerism at day +100 (>95% donor in 68.6% for PTCy vs 67.8%, p=0.2) or secondary graft failure between the arms (2.9% for PTCy vs 0.9%, p=0.2). Conclusions: BMT CTN 1703 met its primary endpoint, demonstrating a higher 1-year GRFS with PTCy/Tac/MMF compared to Tac/MTX owing to significant improvements in GVHD risk without increased risk of relapse or death. PTCy/Tac/MMF, which has become standard of care for mismatched transplants, should also become the standard of care for GVHD prophylaxis from closely-matched donors receiving reduced intensity conditioning. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Introduction: Global application of bone marrow transplant (BMT) for sickle cell disease (SCD) requires a protocol that addresses the core limitations of this approach - namely donor availability, graft-versus-host disease (GVHD) and engraftment. To meet these demands, we developed the Vanderbilt Haploidentical Learning Collaborative across 10 countries and 22 sites with a common related HLA-haploidentical (haploBMT) reduced intensity platform. Our phase II trial (ClinicalTrials.gov identifier NCT01850108) was successfully employed with a probability of overall survival of 96.7% (95% CI 87.1- 99.2%) at one year, but a high rate of graft failure (GF) in pediatric patients (<18 years), prompting us to perform an in-depth analysis of engraftment kinetics. Methods: Seven Institutional Review Board approved sites enrolled patients undergoing a haploBMT for SCD from 8/14/2014-2/28/2022. Common conditioning included: thymoglobulin 4.5 mg/kg, thiotepa 10 mg/kg, fludarabine 150 mg/m2, cyclophosphamide 29 mg/kg and TBI 2Gy. GVHD prophylaxis included post-transplant cyclophosphamide 100 mg/kg, mycophenolate mofetil, and sirolimus (de la Fuente et al. BBMT 2019). Hydroxyurea and hypertransfusion to lower the percentage hemoglobin S <30% for at least 60 days pre-conditioning was variably employed. Primary GF was defined as <5% donor myeloid/lymphoid or whole blood (WB) chimerism at one-month (M1) post-haploBMT. Secondary GF was defined <5% donor myeloid/lymphoid or WB chimerism with prior documentation of >5% donor cells at M1. Categorical variables were compared using Fisher's exact test. Continuous variables were compared using Wilcoxon rank sum test. Results: A total of 41 pediatric and 39 adult subjects were enrolled for data analysis. GF was only noted in the pediatric cohort with 4 (10%) and 6 (15%) developing primary and secondary GF, respectively. Primary GF was associated with lack of a hypertransfusion pre-conditioning (0% vs 54%) and CMV reactivation (75% vs 21%) compared to engrafted patients. For secondary GF, we evaluated the mechanisms of prolonged tolerance including early donor T-cell engraftment. Although our data was limited by only 28% (n=22) having lymphocyte subsets at M1, pediatric patients had lower T-cell counts (median 45.0 cells/µL, IQR: 6.50-118) compared to adults (median 723 cells/µL, IQR 618-1325) (Figure). Older recipient age and positive recipient CMV status were the only variables significantly associated with both CD4+ plus CD8+ count >100 cells/µL and donor CD3+ chimerism >90% (Table). Pediatric T-cell engraftment matched adult values at later time points except in patients with secondary GF and improvement in T-cell counts above 500 cells/µL at M2 was associated with a higher TNC dose (median 4.57x108 cells/µL, IQR 2.86-5.75 vs 1.74x108 cells/µL, IQR 1.55-2.24). We next evaluated the impact of low donor T-cell engraftment at M1. Patients with low donor T-cell engraftment had significantly higher rates of immune-mediated complications including secondary GF (CD3+ chimerism <90%: 42.9% vs 0%, p=0.001) and chronic GVHD (CD4+ plus CD8+ <100 cells/µL: 63.6% vs 9.1%, p=0.024). Incidence of viral reactivation was not different between cohorts. Disease and GVHD-free survival positively trended with donor T-cell engraftment (Table), and patients with both CD4+ plus CD8+ count <100 cells/µL and donor CD3+ chimerism <90% at M1 had severe immune-mediated complications, implicating an association of inadequate immune control with poor early donor T-cell engraftment. Conclusions: This analysis illustrates the importance of early T-cell engraftment in developing bi-directional immune tolerance following haploBMT. Although our study identified recipient age and CMV status as important factors in T-cell engraftment, the mechanism behind these factors, such as age-associated differences in drug metabolism and the role of CMV in promoting donor T-cell expansion, and how donor T cells promote tolerance require additional investigation. Our study demonstrates the importance of monitoring T-cell counts and sorted chimerism early post haploBMT and raises the question of how best to intervene in patients with low donor T-cell engraftment at M1. Our consortium plans to prospectively evaluate immune tolerance, including regulatory T-cell dynamics and impact of immune interventions at M1, to answer these important questions. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

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.

Consensus on the need for antibacterial prophylaxis in patients with acute graft-vs.-host disease (AGVHD) has not been established with practices varying across centers. The aim of this study was to determine the risk for bacterial bloodstream infections (BSI) from neutrophil engraftment through day 100 post-hematopoietic cell transplant (HCT) in patients with AGVHD and whether organ involvement and severity impact this risk.

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. 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: 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.

MRD detected by flow cytometry (FC) or PCR has been associated with key outcomes after HCT for ALL. In a prospective multicenter trial (NCT02646839; Pediatric Blood and Marrow Transplant Consortium [PBMTC] ONC1401), we performed a planned analysis of NGS-MRD to predict outcomes pre- and post-HCT for ALL patients (n=57, median follow-up 523 [range 58-1198] days post-HCT).We evaluated baseline blast samples from 74 patients for dominant BCR/TCR rearrangements and to follow MRD by NGS. Dominant clones were identified in 100% of B-ALL patients, 96.8% (61/63) in BCR and 3.2% in TCR gamma. For T-ALL patients, clones were identified in 62.7% (7/11), with the remaining 37.3% being polyclonal. Patients proceeded to HCT only if they were in morphological remission.Pre-HCT NGS-MRD from bone marrow (BM) was highly predictive of EFS (n=29 P=0.027, Figure 1) and NGS-MRD from peripheral blood (PB) trended similarly (n=27, P=0.17, Figure 2). In BM NGS-MRD negative patients, relapse was exceptionally low with all events due to transplant related mortality (TRM). There did not appear to be a benefit of acute (Figure 3) or chronic graft-vs-host-disease (GVHD) in NGS-MRD- patients.Pre-HCT, 10% of the BM samples were MRD+ by FC, but 35% were MRD+ by NGS. Direct comparison of NGS-MRD in BM and PB with FC MRD pre- and post-HCT showed improvements in positive and negative predictive power.Αβ-T and B-cell depleted haploidentical grafts had similar outcomes to other stem cell sources (Figure 4) with decreased incidence of GVHD [aGVHD > grade 2: n=1 (3.3%) and extensive cGVHD: n=1(3.3%)]. TBI (total body irradiation) based myeloablative conditioning (TBI/TT [Thiotepa]/CY [Cyclophosphamide], TBI/CY, or TBI/VP16; ± anti-thymocyte globulin [ATG]) and non-TBI reduced toxicity (Flu [Fludarabine]/Mel [Melphalan]/TT; ± ATG) had similar EFS (P= 0.31). TRM was very low 8.7% (n=5) in this population (n=57)) and rescue of relapse was high for the duration of follow up to date, resulting in similar OS for MRD- vs. MRD+ patients (P= 0.15), likely due to rescue with cell/immunotherapy.We examined the interaction of obesity, using body mass index (BMI) based on height/weight, pre-HCT, in the context of NGS-MRD on EFS. The BMI was converted to a percentile through population norms for age, gender, and defined thresholds published by the Centers for Disease Control and prevention (CDC). Lean patients (< 85th percentile [%]) overall had better survival than the overweight (OW)/obese (85-94%/≥95%) (Figure 5: P=0.016). Among the lean patients, NGS-MRD was prognostic, with NGS-MRD+ patients having worse EFS. This was also observed with the OW/obese group, where being NGS MRD+ led to dismal survival. Overweight/Obese patients who were pre-HCT MRD- had survival similar lean/MRD+ patients. Thus, both factors, weight category and NGS-MRD influenced EFS (Figure 6: P= 0.02). MRD detected by flow cytometry (FC) or PCR has been associated with key outcomes after HCT for ALL. In a prospective multicenter trial (NCT02646839; Pediatric Blood and Marrow Transplant Consortium [PBMTC] ONC1401), we performed a planned analysis of NGS-MRD to predict outcomes pre- and post-HCT for ALL patients (n=57, median follow-up 523 [range 58-1198] days post-HCT). We evaluated baseline blast samples from 74 patients for dominant BCR/TCR rearrangements and to follow MRD by NGS. Dominant clones were identified in 100% of B-ALL patients, 96.8% (61/63) in BCR and 3.2% in TCR gamma. For T-ALL patients, clones were identified in 62.7% (7/11), with the remaining 37.3% being polyclonal. Patients proceeded to HCT only if they were in morphological remission. Pre-HCT NGS-MRD from bone marrow (BM) was highly predictive of EFS (n=29 P=0.027, Figure 1) and NGS-MRD from peripheral blood (PB) trended similarly (n=27, P=0.17, Figure 2). In BM NGS-MRD negative patients, relapse was exceptionally low with all events due to transplant related mortality (TRM). There did not appear to be a benefit of acute (Figure 3) or chronic graft-vs-host-disease (GVHD) in NGS-MRD- patients. Pre-HCT, 10% of the BM samples were MRD+ by FC, but 35% were MRD+ by NGS. Direct comparison of NGS-MRD in BM and PB with FC MRD pre- and post-HCT showed improvements in positive and negative predictive power. Αβ-T and B-cell depleted haploidentical grafts had similar outcomes to other stem cell sources (Figure 4) with decreased incidence of GVHD [aGVHD > grade 2: n=1 (3.3%) and extensive cGVHD: n=1(3.3%)]. TBI (total body irradiation) based myeloablative conditioning (TBI/TT [Thiotepa]/CY [Cyclophosphamide], TBI/CY, or TBI/VP16; ± anti-thymocyte globulin [ATG]) and non-TBI reduced toxicity (Flu [Fludarabine]/Mel [Melphalan]/TT; ± ATG) had similar EFS (P= 0.31). TRM was very low 8.7% (n=5) in this population (n=57)) and rescue of relapse was high for the duration of follow up to date, resulting in similar OS for MRD- vs. MRD+ patients (P= 0.15), likely due to rescue with cell/immunotherapy. We examined the interaction of obesity, using body mass index (BMI) based on height/weight, pre-HCT, in the context of NGS-MRD on EFS. The BMI was converted to a percentile through population norms for age, gender, and defined thresholds published by the Centers for Disease Control and prevention (CDC). Lean patients (< 85th percentile [%]) overall had better survival than the overweight (OW)/obese (85-94%/≥95%) (Figure 5: P=0.016). Among the lean patients, NGS-MRD was prognostic, with NGS-MRD+ patients having worse EFS. This was also observed with the OW/obese group, where being NGS MRD+ led to dismal survival. Overweight/Obese patients who were pre-HCT MRD- had survival similar lean/MRD+ patients. Thus, both factors, weight category and NGS-MRD influenced EFS (Figure 6: P= 0.02). Figure 2Pre-HCT MRD-PB by NGS.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 3GVHD through D+100.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 4Alpha/beta depleted haploidentical grafts had similar outcomes to other stem cell sources.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 5Weight category pre-HCT.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 6Pre-HCT BM NGS-MRD and weight category.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Background Post-transplant cyclophosphamide (PTCy) enables allogeneic hematopoietic cell transplant (Allo-HCT) across the human leukocyte antigen barrier. Allo-HCT for severe transfusion dependent thalassemia is restricted in its application due to limited donor availability, graft rejection, and regimen-related toxicities. We explored the use of a common non-myeloablative (NMA) conditioning regimens with PTCy based graft-versus-host disease (GvHD) prophylaxis for matched related, haploidentical, and unrelated donors in the setting of a collaborative consortium. Methods A multicenter learning collaboration involving 3 centers used an augmented NMA conditioning with PTCy developed by John Hopkins group (Bolaños-Meade, Blood 2012). All patients received common conditioning regimen consisting of ATG 4.5 mg/kg, fludarabine 150 mg/m2, cyclophosphamide 29 mg/kg, thiotepa (10 mg/kg on day -7) and TBI 200 cGy. Graft versus host disease (GvHD) prophylaxis was PTCy 50 mg/kg on days +3 and +4, MMF, and sirolimus. To improve engraftment rates, all patients received preconditioning with hydroxyurea 30mg/kg x 60 days (Figure 1). Most patients received G-primed bone marrow as stem cell source. Two patients received matched related donor (MRD), 4 patients haploidentical, and 3 patients matched unrelated donor (I-MUD, 2-mismatched MUD) bone marrow transplants (Figure 2). Results A total of 9 patients with transfusion dependent thalassemia were included with a median follow-up time of 371 days. One case of primary graft failure was seen in the haploidentical cohort at D+32; 89% (8/9) patients successfully engrafted. Two cases each of mild gut and skin acute GvHD and one case each of limited gut and skin chronic GvHD were seen in transplanted patients. No cases of grades III-IV acute or severe, chronic GvHD were seen. All patients are alive, thalassemia free survival (TFS) was 100% in the MRD and M/MUD recipients, but 75% (3/4) in the haploidentical cohort. There was no statistical difference between groups in regards to neutrophil or platelet engraftment, age, TNC or CD34+ cell dose. No engrafted patient required long-term immunosuppression therapy, and all remain transfusion independent. Conclusion We have shown the feasibility of NMA conditioning with PTCy plus thiotepa for severe transfusion dependent thalassaemia. A phase II study will help determine the optimal regimen with least toxicity and improved thalassaemia free survival.