Reduced Intensity Conditioning Research Articles

Outcomes after Bone Marrow Versus Peripheral Blood Stem Cell Matched Unrelated Donor Hematopoietic Stem Cell Transplantation

Background: Matched unrelated donors (MUD) have become an acceptable alternative donor for patients requiring potentially curative hematopoietic stem cell transplantation (HSCT) and lacking a matched sibling donor. Patients may undergo a bone marrow (BM) or peripheral blood stem cell (PBSC) graft, with previous studies showing similar survival outcomes. However, BM grafts have shown a lower incidence of chronic graft-versus-host disease (GVHD) but a higher relapse rate and slower engraftment. We aimed to compare the outcomes of BM versus PBSC in patients undergoing MUD HSCT. Methods: For this retrospective single-center study, we included all (n=276) adult MUD HSCT recipients at the University of Kansas Medical Center who had at least one year of follow-up (August 2016 to July 2021). We conducted a bivariate analysis using chi-squared and ANOVA tests. The Kaplan-Meier and regression analyses were also performed. Data analyses were conducted using SPSS version 28. Statistical significance was considered at p<0.05. Results: Our study included 276 MUD patients including 110 PBSC (40%) and 166 BM (60%) grafts. The median age was 55 (range 21-77) years, and 158 patients (57%) were males. Eighteen patients (6%) were ethnic minorities, and 89 (32%) patients had a Karnofsky performance status of ≥90%. 118 (43%) patients had a hematopoietic cell transplantation-specific comorbidity index of 3 or higher. Hematologic diseases included acute myeloid leukemia (n=119, 43%), myeloid disorders (n=77, 28%), acute lymphoblastic leukemia (ALL) (n=35, 13%), Lymphoma (n=15, 5%), and others (n=30, 11%). Sixty-two percent of patients were in complete remission at the time of transplantation, and patients not in remission included myelodysplastic syndrome, myelofibrosis, and lymphoma patients. Reduced-intensity conditioning (RIC, n=162, 58%) and myeloablative conditioning (MAC) (n=114, 41%) were used. The median follow-up was 55 (21-73) months. Overall survival (OS) was not reached in either BM or PBSC MUD HSCT group, while a median disease-free survival of 45 and 49 months was noted in PBSC and BM groups respectively (p=0.915). We observed similar rates of relapse (25% vs 27%, p=0.413), one-year overall survival (75% vs 72%, p=0.679), one-year disease-free survival (63% vs 62%, p=1.00), and one-year non-relapsed morality (NRM, 23% vs 21%, p=0.779) after PBSC or BM graft. Bone marrow graft recipients had delayed engraftment of neutrophils (20 days vs 16 days, p<0.001) and platelets (>20 K/uL: 24 days vs 16 days, p<0.001; >50 K/uL: 28 days vs 18 days, p=0.006) compared to PBSC recipients. Bone marrow graft recipients had similar rates of grade II-IV acute GVHD (50% vs 52%, p=0.714) and grade III-IV GVHD (12% vs 11%, p=0.847), but lower rates of 1-year chronic GVHD (39 % vs 55%, p=0.014) compared to PBSC recipients. In the subgroup analysis stratified by conditioning intensity, faster engraftment of neutrophils (median 16 vs 21 days, p<0.001) and platelets (>20 K/uL: 18 days vs 27 days, p<0.001; >50 K/uL: 18 days vs 33 days, p<0.001) was observed with PBSC as compared to BM graft in myeloablative transplant recipients, while there was no statistically significant association with the rates of acute or chronic GVHD, NRM, Relapse, DFS, and OS after a PBSC or BM graft. Among the RIC transplant recipients, faster neutrophil engraftment (mean 17 vs 20 days, p<0.001) and higher 1-year extensive chronic GVHD (52% vs 32%, p=0.015) were observed with PBSC compared to BM graft whereas no statistically significant difference was noted in platelet engraftment, acute GVHD, NRM, Relapse, DFS, and OS after a BM or PBSC graft. Conclusions: Allogeneic matched unrelated donor hematopoietic stem cell transplant recipients had similar rates of overall and disease-free survival, relapse, non-relapse mortality, and acute GVHD after a bone marrow or peripheral blood stem cell graft; however, delayed neutrophil and platelet engraftment with a lower incidence of chronic GVHD was noted after a bone marrow graft compared to peripheral blood stem cell graft.

Development of a Stacked Ensemble Model for Risk Stratification of Chronic Gvhd after Allogeneic HSCT: Trump Cohort Study

Background Effective risk stratification is vital for selecting donors and developing treatment strategies for allogeneic hematopoietic stem cell transplantation (allo-HSCT). Several pretransplant risk models have been proposed to predict post-transplant patient outcomes from pretransplant risk factors. However, it is still challenging to predict mid-to-long-term prognosis. To establish a novel and user-friendly tool for predicting chronic graft-versus-host disease (cGVHD), non-relapse mortality (NRM) and overall survival (OS), we used a Stacked Ensemble Model (SEM) designed to handle right-censored data and competing risk events (Iwasaki et al., 2021). Methods Using Japanese registry data, the Japanese Transplant Registry Unified Management Program, we analyzed 21,840 patients who underwent their first allo-HSCT between 2010 and 2018 for hematologic malignancies. Of these, 14,430 patients were alive without cGVHD and relapse on day 100 post-transplantation. Primary endpoint was cGVHD and secondary endpoints were NRM and OS. Data were randomly split into the training set (70% of the dataset) and the validation set (30%). We treated patient age and time from diagnosis to transplant as continuous variables and performance status, ABO type matching, sex matching, disease/status groups based on refined Disease Risk Index, Hematopoietic Cell Transplantation-specific Comorbidity Index, usage of total body irradiation, conditioning intensity, T cell depletion in vivo, human leukocyte antigen (HLA) locus matching, the number of HLA mismatching and CMV serostatus as categorical variables. To evaluate predictive accuracy at day 30, 60 and 100 posttransplant, we considered acute graft-versus-host disease (aGVHD) and its treatment, including grade 2 to 4 aGVHD occurrence, grade 3 to 4 aGVHD occurrence, stage of aGVHD before and after treatment, corticosteroid treatment, anti-thymocyte globulin treatment and treatment response of 1 st line therapy for aGVHD. Results The median age of the patients at transplantation was 51 years (inter quartile range (IQR): 39 - 60). The sources of stem cells were HLA-matched related bone marrow (BM) in 967 patients, HLA-matched related peripheral blood (PB) in 1,998 patients, haploidentical BM in 172 patients, haploidentical PB in 778 patients, unrelated BM in 5,539 patients, unrelated PB in 366 patients, and cord blood in 4,237 patients. Myeloablative conditioning was administered in 9,390 patients and reduced-intensity conditioning in 5,040 patients. The most common indication of HSCT was intermediate-risk acute myeloid leukemia (AML) in complete remission (CR, n=3,233) followed by acute lymphoblastic leukemia in first CR (n=2,164) and intermediate-risk AML in non-CR (n=1,618). Median follow-up period of survivors was 2.2 years (IQR: 0.9-4.5). The overall performance of SEM was superior across the endpoints evaluated, cGVHD, NRM and OS, while XGBoost showed a slightly higher C-index for cGVHD, demonstrating its robustness and reliability (Table 1, the C-index for cGVHD/NRM/OS-SEM: 0.567/0.635/0.607, Cox-PH: 0.550/0.624/0.602, Random Survival Forest: 0.555/0.632/0.597, XGBoost: 0.573/0.624/0.604, and Dynamic Deephit: 0.549/0.614/0.589). C-index of SEM for cGVHD, NRM, and OS were gradually improved as time goes by (Table 1, the C-index for cGVHD/NRM/OS: at day 30-0.589/0.643/0.635, at day 60-0.598/0.655/0.640, at day 100-0.598/0.688/0.640). Kaplan-Meier curves 100-day post-transplantation confirmed the accuracy of our predictions, effectively stratifying patients into four risk groups (Figure 1). SHapley Additive Explanations showed contribution of variables for predicting specific outcomes. Grade 3 to 4 aGVHD and stage of aGVHD after treatment influenced non-relapse mortality. Particularly, grade 3 to 4 aGVHD showed significant impact on OS in line with pretransplant risk factors including sex matching, donor source and disease/status groups. Grade 2 to 4 aGVHD and treatment response of 1 st line therapy for aGVHD influenced cGVHD. Conclusion Our study emphasizes the importance of aGVHD events in mid-to-long-term post-transplantation outcomes and presents SEM-based prediction models that account for early-phase post-transplantation events. We are currently developing a user-friendly web application tool for cGVHD, aiming to enhance post-transplant risk stratification and preemptive therapy for cGVHD.

Outcomes of Attenuated Dose Fludarabine and Melphalan Based Conditioning Regimen in Patients Undergoing Allogeneic Hematopoietic Stem Cell Transplant for Acute Leukemia and Myelodysplastic Syndrome

Introduction: Fludarabine combined with melphalan 140 mg/m2 (FluMel140) is a commonly used reduced-intensity conditioning (RIC) regimen in patients undergoing matched related (MRD) and unrelated donor (MUD) allogeneic stem cell transplant (alloSCT). Ciurea et al Blood 2020, described outcomes of Flu 160 mg/m2 and Mel 100 mg/m2. In this study, we describe our experience of attenuated melphalan dosing 100-120 mg/m2 versus 140 mg/m2 with fludarabine 125 mg/m2 (attenuated FluMel versus regular dose FluMel). Methods: We retrospectively reviewed patients from November 2016 to April 2023 with AML, ALL or MDS undergoing alloSCT who received fludarabine and melphalan. Patients who received the lower dose of melphalan were considered to be the attenuated FluMel cohort, whereas patients receiving the melphalan 140 mg/m2 were considered to be the control cohort. Kaplan-Meier and log-rank tests were used to estimate OS. NRM and relapse incidence (RI) was calculated using competing risk analysis. R 4.2.0 (R Foundation for Statistical Computing) was used for statistical analyses. Results: A total of 134 patients [92 (68.7%) males] were evaluated. Thirty-seven (27.6%) patients received attenuated FluMel and 97 (72.4%) patients received regular dose FluMel (controls). Among the patients in the attenuated FluMel cohort, 5 (13.5%) patients also received fludarabine at doses less than 125 mg/m 2 [median 20 mg/m 2 (range 87.5-112.5 mg/m 2]. Median age at transplant was 65 years (range 30 - 76 years). The most common disease was AML [75 (56.0%) patients] ( Table 1). Patients in the attenuated FluMel group had comparable iothalamate clearance compared to control cohort (clearance <65 ml/min/1.73 m2: 18.9% vs. 12.4%, P = 0.52). Patients in the attenuated FluMel group had comparable rates of high/very high DRI to those in control cohort (51.4% vs. 43.3%, P = 0.91). Compared to the control cohort, patients in the attenuated FluMel group were less likely to have a matched related donor (21.6% vs. 45.4%, P = 0.02) and were more likely to receive PTCy for GVHD prophylaxis (37.8% vs. 16.5%, P = 0.02). Among the patients receiving attenuated FluMel, the median melphalan dose administered was 100 mg/m2. The median time to neutrophil engraftment was 19 days (IQR 16-21 days), and median time to platelet engraftment was 18 days (range 12-25 days). Eleven (29.7%) patients developed post-alloSCT mucositis, and 3 (8.1%) patients developed grade 3-4 mucositis. All the patients in the attenuated FluMel group achieved 100% CD33 donor chimerism at day +30 (n=35) and day +100 (n=28) after alloSCT. Similarly, 26 (74.3%, n = 35) patients achieved ≥ 95% CD3 donor chimerism at day +30 after alloSCT and 23 (82.1%, n = 28) patients achieved ≥ 95% CD3 donor chimerism at day +100 after alloSCT. Median follow-up of the entire cohort after alloSCT was 2.3 years (95% CI 2.1-2.5 years). Median follow-up was 1.5 years in the attenuated FluMel cohort and 2.5 years for the control cohort ( P<0.001) . Survival was similar among patients receiving attenuated FluMel vs. control cohort (2-year OS 74.7% vs. 65.0%, P = 0.28). At 2 years post-alloSCT, the attenuated FluMel and control cohort had similar non-relapse mortality (19.9% vs. 24.4%, P=0.58) and relapse (22% vs. 15.2%, P=0.51). The attenuated FluMel was not associated with an increased incidence of relapse (HR 1.36, 95% CI 0.50-3.73, P=0.55) or NRM (HR 0.74, 95% CI 0.28-1.95, P = 0.55). GVHD-free relapse free (GRFS) survival was also similar among the attenuated Flu/Mel and control cohort (1-year GRFS rate 41.1% vs. 45.6%, P = 0.8). Among the patients receiving PTCy for GVHD prophylaxis, the 2-year OS in patients receiving attenuated FluMel was higher than the control group, but it was not statistically significant (2-year OS rate: 90% vs. 55%, P=0.37, Figure 1). Compared to the control group, the attenuated FluMel group had similar rates of NRM at 100 days (10% vs. 12.5%), 1 year (NA vs. 25%) and at 2 years after alloSCT (NA vs. 25%, P=0.54). GRFS at 1 year was also similar between the attenuated FluMel and control group (68.6% vs. 43.8%, P = 0.69). Conclusion: The attenuated dosed FluMel conditioning is a safe and effective regimen for elderly patients with acute leukemia and MDS, and is non-inferior to regular dose FluMel. Among patients receiving PTCy for GVHD prophylaxis, the lower dose of melphalan was non-inferior to regular dose FluMel for survival outcomes. Larger studies are needed to confirm our findings.

Large-Scale Post-Transplant TCR Deep Sequencing Reveals a Major T Cell Diversity Bottleneck with Post-Transplant Cyclophosphamide with Implications for Both Efficacy and Toxicity: Results of the BMT CTN 1801 Study

Background: BMT CTN 1703 was a Phase 3 trial comparing Tac/MTX (n = 217) to post-transplant cyclophosphamide (PT-Cy)/Tac/MMF (n = 214) GVHD prophylaxis after reduced intensity conditioning unrelated donor hematopoietic cell transplant (HCT). PT-Cy significantly improved GVHD-free Relapse-Free Survival (Bolanos-Meade et al NEJM 2023). However overall survival was not significantly different and the # of Grade 2 infections was higher with PT-Cy. To investigate its biologic underpinnings 1703 was linked to a mechanistic study, BMT CTN 1801, which co-enrolled 324 pts (159 CNI/MTX 165 PT-Cy). The resulting dataset enabled an analysis of post-HCT T cell reconstitution at an unprecedented level of detail. Methods: Samples were collected from the HCT infusion and on D+7, 14, 28, 63, 98, 180, 270, 1- and 2-yr. We extracted DNA (2,225 samples) and performed Adaptive Biotech β-strand T Cell Receptor (TCR) Immunosequencing (TCR-Seq). We profiled 44,077 (median) TCRs/sample resulting in 215,155,719 T cells analyzed. We evaluated multiple TCR diversity measures longitudinally and before/after cGVHD and infections. Each measure evaluates a specific aspect of TCR diversity, including Simpsons Clonality (focuses on the most expanded clones) Diversity Slope (mid-range clones) Richness (both mid-range and less-expanded clones) and Singletons (the TCR-Seq equivalent of naïve T cells). This analysis was robust to the full range (1000-50,000) of down-sampled TCRs sequenced. Results: We identified major differences in TCR reconstitution in Tac/MTX vs PT-Cy that begin early and persist through 2 yr post-HCT. These resulted in a significantly less diverse TCR repertoire with PT-Cy with substantial implications for its efficacy and toxicity. The most salient differences are: (1) PT-Cy caused significant in-vivo T cell depletion early post-HCT (% T cells/total WBC at D+28: 8.2% (Tac/MTX) vs 2.2% (PT-Cy) p=2.2x10 -23). (2) The remaining donor T cells in PT-Cy undergo substantial clonal expansion ( Fig 1) resulting in significantly constrained TCR diversity measured by Clonality, Slope, Richness, Singletons (not shown) and Singletons/Richness ( Fig 2) which began early (D+14) and persisted for 2 yr. (3) Linked T cell depletion and clonal expansion resulted in a TCR diversity bottleneck after PT-Cy ( Fig 1). Due to the bottleneck, while the fraction of T cells originating from the transplant infusion at =/> 1 yr was similar between arms (18% vs 24%, p=0.7) there were significantly fewer Singleton TCRs in PT-Cy, suggesting a reduction in naïve T cells ( Fig 2), an outcome that has critical consequences for both cGVHD and infection. Thus while cGVHD onset with Tac/MTX was linked to a significant drop in TCR diversity due to singleton clonal expansion (median log-2 fold change in singletons with Tac/MTX = -0.25 p = 0.01) this drop was not observed with PT-Cy (log-2 fold change = -0.05, p = 0.1). Along with the significantly decreased # singletons at all time-points in PT-Cy ( Fig 2) this suggests that while cGVHD after Tac/MTX is linked to substantial naïve T cell expansion, the same is not true with PT-Cy, identifying a novel mechanism for cGVHD control with PT-Cy. The substantially fewer singletons in PT-Cy vs Tac/MTX may also increase the risk of Grade 2+ infections. T cell responses to new infections rely on antigen recognition/effector maturation of naïve (singleton TCR) T cells. After infection, the TCR repertoire became less diverse for both Tac/MTX and PT-Cy (log-2-fold singleton change -0.17 and -1.2 p = 0.0006 and 0.01) indicating that singletons in both cohorts were capable of expanding to pathogens. However the markedly decreased # singletons in PT-Cy at all timepoints was associated with significantly fewer singletons prior to infection (mean 3979 at 5K read-depth for Tac/MTX vs 2820 for PT-Cy p<0.001). This singleton deficit would place PT-Cy patients at higher risk of missing the critical mass of TCRs required to respond effectively to infections, consistent with their increased rate of Gr 2 infections. Conclusions: We performed longitudinal TCR-Seq on >200 million T cells from 324 HCT patients, representing the largest post-HCT TCR-Seq analysis in the history of the field, and enabling novel insights into TCR dynamics. These data identify a previously unappreciated global TCR diversity bottleneck with PT-Cy that simultaneously protects patients from cGVHD and places them at higher risk of infectious complications.

The Effect of Allogeneic Hematopoietic Stem Cell Transplantation on Sickle Cell Disease-Related Organ Damage: A Systematic Review and Meta-Analysis

Background Allogeneic hematopoietic stem cell transplantation (HSCT) is the only established curative treatment option for patients with sickle cell disease (SCD). One of the main indications for HSCT is SCD-related organ damage, which is a major cause of morbidity and early mortality. However, whether HSCT is effective in recovering SCD-related organ dysfunction has not been systematically reviewed. Methods This is a systematic review and meta-analysis investigating the effects of HSCT on organ function in patients with SCD. We performed a comprehensive search in MEDLINE/PubMed and EMBASE up to June 2023, focusing on studies reporting pulmonary, cardiac, renal, splenic, and/or cerebral function parameters, as well as retinopathy and/or avascular osteonecrosis (AVN) before and after HSCT. Continuous data were analyzed using the weighted inverse-variance random effects meta-analyses, reported as standardized mean difference (SMD) and 95% confidence intervals (95%-CI). Binomial data were analyzed using the Mantel-Haenszel random effects meta-analyses, reported as risk ratio (RR) and 95%-CI. A negative SMD indicates an improvement and a positive SMD indicates a worsening of the measured parameter post-HSCT. A RR <1 indicates a result in favor of the transplantation and a RR >1 indicates a worsening of the measured parameter after HSCT. The ‘Newcastle-Ottawa Quality Assessment Scale’ and the ‘Clinical Diversity in Meta-analysis’ (CDIM) tool were used to assess the quality and the clinical heterogeneity of the studies. Results Thirty-two of 476 studies met our inclusion criteria, of which 17 were used for the meta-analyses and 15 for the qualitative part of the review. Of the studies that were included in the meta-analyses, 4 comprised adult patients (n=184) and 13 pediatric and/or young adults <22 years old (n=591). The majority of donors were matched sibling donors (86.4%), and studies with both myeloablative and/or reduced intensity conditioning regimens were included. The CDIM score was low or moderate for all performed meta-analyses, suggesting fair clinical comparability among the studies. Summary plots of the meta-analyses are shown in Figure 1. Pulmonary function test parameters remained stable following HSCT (SMD -0.08, p=0.64 for forced expiratory volume in 1 second; SMD -0.13, p=0.35 for forced vital capacity; and SMD -0.95, p=0.30 for diffusing capacity). Mean tricuspid regurgitation velocity (TRV) did not change significantly in the meta-analysis (SMD -0.34, p=0.14). However, 3 studies used for the qualitative review reported normalization in patients with prior elevated TRV. Whole brain cerebral blood flow improved significantly after transplantation (SMD -1.39, p=<0.01). Several studies reported an absent or very low incidence of new (silent) cerebral infarcts and a decrease of transcranial Doppler velocities following successful HSCT. In pediatric patients, creatinine clearance decreased significantly after HSCT (SMD -0.80, p=0.01) and the presence of proteinuria increased (RR 2.00, p=<0.01). Furthermore, splenic uptake ( 99mTc) and phagocytic function of the spleen improved (RR 0.31, p=<0.01 and RR 0.23, p=<0.01, respectively). Retinopathy and AVN before and after HSCT were investigated in only 1 study in children with SCD, both showing no significant changes post-HSCT. Discussion and Conclusion Allogeneic HSCT has the potential to stabilize or recover pulmonary and cardiac function parameters in SCD patients. In pediatric patients, splenic function parameters showed impressive improvement following HSCT. On the other hand, creatinine clearance decreased significantly in children. This might be a reflection of either normalization of SCD-related hyperfiltration or transplantation-related toxicity, which may also have contributed to the increased prevalence of proteinuria after HSCT. With respect to cerebral damage, cerebral perfusion parameters improved and progression of silent cerebral infarctions was prevented following HSCT. Last, we demonstrate a paucity of evidence regarding the course of renal function, retinopathy, and AVN in adult SCD transplant recipients. More research is needed to define which patients with SCD-related organ damage might benefit most from HSCT and which organs are less likely to recover.

Post-Transplant Cyclophosphamide, Tacrolimus or Cyclosporine a and Mycophenolate Mofetil Compared to Anti-Thymocyte Globulin tacrolimus or Cyclosporine a and Methotrexate Combinations As Graft- versus -Host Disease Prophylaxis Post Allogeneic Stem Cell Transplantation from Sibling and Unrelated Donors in Patients with Acute Myeloid Leukemia: a Study on Behalf of the Acute Leukemia Working Party of the European Society for Blood and Marrow

Background: Recently, the BMT CTN 1703 phase III study compared post-transplant cyclophosphamide with tacrolimus with mycophenolate mofetil (PTCy/TAC/MMF) to TAC /methotrexate (MTX) as graft- versus-host disease (GVHD) prophylaxis post allogeneic transplantation (HSCT), demonstrating a lower incidence of severe acute (a) GVHD and chronic (c) GVHD and better GVHD-free, relapse-free survival (GRFS). The control arm did not include anti-thymocyte globulin (ATG), used in many centers for GVHD prophylaxis. Methods: The study aim was to compare PTCy with TAC or cyclosporine A (CSA) and MMF (PTCy/TAC or CSA & MMF) to ATG combined with TAC or CSA and MTX (ATG/TAC or CSA & MTX) in acute myeloid leukemia (AML) patients (pts) undergoing HSCT from matched siblings (MSD) or 9-10/10 unrelated donor (UD) in first complete remission (CR1). Statistical tests included a multivariate analysis (MVA) adjusting for potential confounding factors using a Cox proportional-hazards regression model for main outcomes. . Results: 6050 pts met the inclusion criteria, 402 received PTCy/TAC or CSA & MMF and 5648 received ATG/TAC or CSA & MTX as GVHD prophylaxis. Median follow-up was 23.4 (IQR, 20.3-24.9) and 41.8 (IQR, 39.6-43.3) months (p<0.0001). The median year of the transplant was 2018 (2010-2020) and 2016 (2007-2020) (p<0.0001). Pts in the PTCy/TAC or CSA & MMF group were younger, with a median age of 48.7 (range 18-5.6) versus 51.5 (8-77.8) years (p=0.024). The diagnosis was de novo AML in 84.1% vs 85.3% and secondary (s) AML in 15.9% vs. 14.7% (p=0.49). The cytogenetic risk was categorized as intermediate (70.9% vs. 67.1%), adverse (22.2% vs. 25.7 %), and favorable (6.9% vs. 7.2%) for pts in the PTCy/TAC or CSA & MMF and ATG/TAC or CSA & MTX groups, respectively (p=0.35) (data missing for 2214 pts). Karnofsky performance status (KPS) did not differ between the groups. There was a higher frequency of pt cytomegalovirus (CMV) seropositivity and female (F) donor to male (M) pt combination in the PTCy/TAC or CSA & MMF group, 77.8% vs. 71.8% (p=0.009) and 18.4% vs. 14.4% (p=0.029). More pts in the PTCy/TAC or CSA & MMF group received reduced intensity conditioning (RIC) 51.5% versus 41.1% in the ATG/TAC or CSA & MTX group, respectively (p<0001). Day 60 neutrophil engraftment (ANC >0.5 x 10 9/L) was 98.7% vs. 98.6% (p=0.84). Day 180 incidence of a GVHD grade II-IV and III-IV was 21.2% vs. 20.4% (p=0.92) and 8.1% vs. 6% (p=0.1), in pts receiving PTCy/TAC or CSA & MMF versus the ATG/TAC or CSA & MTX GVHD prophylaxis, respectively. The 2-year (y) total and extensive chronic (c) GVHD were 33.7% vs. 30% (p=0.09) and 10.7 % vs. 11.2% (p=0.81), respectively. GVHD was the cause of death in 11.6% vs. 13.9% of pts who died. In the MVA, both aGVHD (grade II-IV or III-IV) and cGVHD (total or extensive) did not differ between the groups with hazard ratios (HRs) =1.15 (95% CI 0.86-1.53, p=0.35), HR=0.87 (95% CI 0.56-1.34, p=0.52), HR=0.91 (95% CI 0.7-1.18, p=0. 47 and HR=1.51 (95% CI 0.96-2.36, p=0.074). Two-y NRM was significantly lower in pts that received PTCy/TAC or CSA & MMF versus ATG/TAC or CSA & MTX for GVHD prophylaxis, HR=1.57 (95% CI 1.07-2.3, p=0.022). Other HSCT outcome parameters did not differ between the groups. The HR for 2-y RI was 0.99 (95% CI 0.77-127, p=0. 93). The HRs for 2-y leukemia-free survival (LFS), overall survival (OS), and GRFS were HR=1.15 (95% CI 0.94-1.42, p<0.18), HR=1.18 (95% CI 0.94-1.49, p=0.16) and HR=1.12 (95% CI 0.93-1.36, p=0.22), respectively. Donor type and conditioning regimen were poor prognostic factors for grade II-IV, III-IV aGVHD, and total and extensive cGVHD. For cGVHD, additional poor prognostic factors were F donor to M pt combination and pt CMV seropositivity. Poor prognostic factors for LFS, OS, and GRFS were 9/10 UD, age (by 10 y), sAML, adverse-risk cytogenetics, lower KPS, and pt CMV seropositivity. For NRM, factors were the same apart from cytogenetics risk which was not a prognostic factor. In addition, time from diagnosis to HSCT was a prognostic factor for NRM and RI. Other poor prognostic factors for RI were lower KPS and pt CMV seropositivity. Conclusions: In this registry-based retrospective analysis, comparing PTCy in combination with TAC or CSA and MMF to ATG in combination with TAC or CSA and MTX as GVHD prophylaxis, we observed a similar incidence and severity of both aGVHD and cGVHD. NRM was significantly lower with the PTCy-based GVHD prophylaxis, while all other transplant outcome parameters were similar.

Abatacept-Prophylaxis Based Haploidentical Transplantation May Allow Sustained Engraftment and Offset Gvhd in Non-Malignant Disorders

Introduction: Non-malignant disorders (NMD) derive no benefit from graft-versus-host disease (GVHD) after allogeneic hematopoietic transplantation (HCT). Transplantation designed to optimize engraftment and immune reconstitution while minimizing GVHD and organ toxicities is desirable. Post-transplant cyclophosphamide (PTCy) decreases severe chronic GVHD risk in radiation-containing regimens for NMD when combined with serotherapy (anti-thymocyte globulin) (PMID: 22955919; PMID: 30500440). Abatacept effectively offsets GVHD following unrelated donor (URD) HCT (PMID: 33449816; PMID: 32813873). Based on these reports, NCT03128996 was developed for haploidentical transplantation in NMD after radiation-free reduced intensity conditioning (RIC) combining PTCy + Abatacept for GVHD prophylaxis. Serotherapy does not contribute to GVHD prophylaxis in this RIC approach. Outcomes focused on safety and GVHD- free donor engraftment in children with NMD and no better donor options. Method: Conditioning included alemtuzumab (day -22 to -19), fludarabine (day -8 to -4), melphalan (day -3) and thiotepa (day -4) as previously published (hydroxyurea prior to RIC was used in proliferative marrow disorders) (PMID: 32813873). Stem cell source was bone marrow (BM) or CD34-selected peripheral blood cells with a fixed CD3 cell dose of 1x10^6/kg recipient weight. GVHD prophylaxis included tacrolimus (day -1, with wean beginning 6-9 months post-HCT), PTCy on days +3 and +4, mycophenolate mofetil until day +28, and monthly abatacept doses until 13 months post-HCT. Survival, safety, donor chimerism, GVHD incidence, and incidence of post HCT infection were primary outcome measures. Results: Eleven patients 6 to 24 years old (median 9 years) underwent HCT for adrenoleukodystrophy ( 2), sickle cell disease (SCD) ( 6), aplastic anemia ( 1), second transplant for severe combined immunodeficiency ( 1) and STAT 5B gain-of-function mutation ( 1). Eight were trial participants and 3 treated according to trial guidelines. All patients tolerated abatacept infusions and engrafted with neutrophil recovery (>500/cu mm) at a median of 17 days (range 15-24 days). As of 7/31/2023, median follow up is 411 days (range 83-1979 days). The mean myeloid and T-cell chimerisms at D100 (n=10) and 1 year (n=6) were 97.8%+/- 5.3 and 96.3% +/- 6.4 and 98.6% +/- 3.3 and 95% +/-8.7, respectively. One patient with SCD has low myeloid engraftment (24%) at 7 months post-HCT (lymphoid 91%); a stem cell boost is planned after immune suppression with fludarabine/Cytoxan/ATG (PMID: 35798858). Viral reactivation was noted in 4 patients, none developed CMV disease or EBV post-transplant lymphoproliferation. One patient developed grade 1 acute GVHD. Of 6 evaluable patients, one developed localized chronic skin GVHD. This patient remains on systemic immune suppression beyond 13 months (ruxolitinib). The overall and GVHD-free survival at 1-year post HCT in evaluable patients (N=6) is 100 % and 83%, respectively. Conclusion: Promising preliminary results in this cohort support continuation of the trial with longer term follow-up. The effective suppression of GVHD without serious infectious complications in the first year post-HCT is encouraging. Virus reactivation was however noted early post-HCT and requires monitoring and prophylaxis. Incorporating abatacept into GVHD prophylaxis was successful in achieving desired outcomes; the phase 1 portion of the study is completed and the phase 2 trial and follow-up are ongoing.

Cerebral Oxygen Metabolism Improves Following Hematopoietic Cell Transplantation in Children with Sickle Cell Disease

Introduction: Allogeneic hematopoietic cell transplantation (HCT) is potentially curative for patients with sickle cell disease (SCD). It is often recommended for patients with severe SCD, including those at risk of, or with a history of stroke. There has been limited investigation into the direct impact of HCT on cerebral hemodynamics. Quantitative biomarkers of cerebral hemodynamics, including oxygen extraction fraction (OEF) and cerebral blood flow (CBF), can provide an objective assessment of therapeutic efficacy of HCT as well as other emerging therapies. We have previously shown that CBF improves after HCT in patients with SCD (Sharma A, et al. Suppl 1, Blood 2021). Here, we performed a prospective evaluation using magnetic resonance imaging (MRI) to measure the OEF of the whole brain and the superior sagittal sinus (SSS), to compare cerebral oxygen metabolism in SCD patients before and after HCT. Methods: We performed anatomical and hemodynamic MRI of the brain prior to, and at 6 months after HCT in children with SCD undergoing a reduced intensity conditioning based HCT on a clinical trial (NCT04362293). Patients were receiving either hydroxyurea (HU) or chronic transfusion therapy (CTT) before HCT. MRI brain scanning was performed for all patients in a 3 Tesla MRI imaging system (Siemens MAGNETOM Prisma, Erlangen, Germany) with a 16-channel phased-array coil. Quantitative susceptibility map (QSM) imaging was performed through a 3D multi-echo gradient echo sequence with flow compensation and reconstructed with the morphology-enabled dipole inversion (MEDI) method (Liu T, et al. MRM 2013). The oxygen extraction fraction was calculated utilizing the established formula incorporating clinically measured hematocrit, tissue susceptibility, and hemoglobin susceptibility values quantified through quantitative susceptibility mapping (QSM), as previously delineated (Fan A, et al. JCBFM 2020) for the segmented vessels from the whole brain and the SSS. Results: The median age at HCT was 15.6 years (N=11). Hematocrit as well as global and regional (SSS) OEF of the patients were quantified and compared between baseline and at 6 months after HCT (Fig 1). All patients experienced a decrease in OEF after HCT. We then stratified the patients into those who were receiving HU or CTT prior to HCT. In patients receiving HU prior to HCT (n=7), there was a small decrease in OEF for the whole brain (42.4% vs. 39.9%, P = 0.40) and SSS (33.1% vs. 31.3%, P =0.12) at 6 months after HCT compared to baseline. However, in patients receiving CTT prior to HCT (n=4) both the global OEF (50.0% vs. 34.4 %, P < 0.01) and regional OEF (31.8% vs. 26.7 %, P < 0.05) decreased significantly at 6 months after HCT. All patients exhibited an increased hematocrit following HCT (Fig 2). Specifically, the HU cohort improved from a mean of 27.4% to 37.5% ( P<0.01), while the CTT cohort increased from 26.2% to 39.6% ( P<0.01) after HCT. Conclusions: Our results demonstrate the feasibility of global and regional OEF quantification using MRI in patients undergoing HCT for SCD. We observed that the OEF of the whole brain and SSS exhibited a similar downward trend after HCT in patients receiving either HU or CTT. This indicates an overall improvement in oxygen delivery after HCT. OEF decrease was marked after HCT in the CTT group, suggesting that HCT provided better cerebral hemodynamic outcomes than at baseline for this group. In contrast, the cohort of patients receiving HU showed a subtle decrease in OEF after HCT, perhaps implying that these patients had milder cerebral hemodynamic compromise than the CTT group. Both pretreatment groups demonstrated significantly higher hemoglobin concentrations after HCT compared to before treatment which may have contributed to the improvement in OEF. Our study presents objective physiologic comparisons of different clinical therapies on cerebral hemodynamics, providing early data on the effects of cerebral oxygen delivery in pediatric patients with SCD. Further studies with larger patient numbers are warranted to confirm the trends observed in oxygen metabolism and understand the mechanisms underlying differential responses to HCT and other disease-modifying therapies. These imaging biomarkers may also help assess different genetic therapies currently in development.

Intent to Treat Allogeneic Stem Cell Transplantation Outcomes in Relapsed/Refractory T-Cell Lymphomas

Introduction T-cell lymphomas (TCL) are a heterogeneous group of lymphoproliferative malignancies with an overall poor prognosis. Despite aggressive first-line therapy, most patients experience disease relapse or progression. Allogeneic stem cell transplant (AlloSCT) is a standard of care for relapsed/refractory (R/R) TCL. However, many patients do not receive this potentially curative therapy. There is a paucity of data regarding the frequency of and barriers to undergoing AlloSCT in R/R TCL. To address this knowledge gap, we conducted a retrospective analysis of R/R TCL patients intending to undergo AlloSCT and hypothesized the primary barrier to AlloSCT to be lack of effective disease control. Methods We identified patients with a primary diagnosis of R/R TCL seen at the University of Washington/Fred Hutchinson Cancer Center (UW/FHCC) between 1/2008 and 6/2023 and linked these patients with the UW/FHCC bone marrow transplant (BMT) database to identify those who were intended for transplant. Intention to transplant (ITT) was defined as undergoing human leukocyte antigen (HLA) typing for purposes of AlloSCT. Patients with T-cell lymphoblastic leukemia/lymphoma were excluded. The primary endpoint was the rate of patients who underwent AlloSCT. Secondary endpoints included progression-free (PFS) and overall survival (OS) in patients who underwent AlloSCT and specific barriers to AlloSCT. Results Overall, 163 patients met ITT criteria. Males comprised 66% of patients. Median age was 65 (range 34-81) years and the median number of treatment regimens prior to HLA typing was 3 (range 1-10). The majority of patients (60%) were non-Hispanic whites (NHW), with Asians/Pacific Islanders (API), Hispanics/Latinos (HL), African Americans (AA) and Alaskan Natives/American Indians (ANAI) contributing 17%, 12%, 7% and 4%, respectively. Sixty-four patients (39%) had peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), 23 (14%) had angioimmunoblastic TCL (AITL), 17 (10%) had anaplastic large cell lymphoma (ALCL; 6 with ALK+), 16 (10%) had NK/TCL, 11 (7%) had hepatosplenic TCL, 12 (7%) had T-cell prolymphocytic leukemia, 5 (3%) had adult T-cell leukemia/lymphoma and 12 (7%) had primary cutaneous TCL. Twenty-two (13%) patients had secondary CNS involvement and 27 (17%) had previous autologous stem cell transplant. Of all patients who received HLA typing, 154 (94%) had a transplant consult, 54 (33%) initiated pre-AlloSCT workup and 51 (31%) underwent AlloSCT. Barriers to AlloSCT included progressive disease, patient preference, inability to identify a donor, indolent disease, poor functional status/multiple comorbidities and lack of a caregiver in 55%, 9%, 8%, 5%, 3% and 1%, respectively (Figure 1A). Six (5%) patients are currently receiving salvage therapy with plans for subsequent AlloSCT. AlloSCT occurred in NHW, API, HL, AA and ANAI patients at rates of 35%, 11%, 26%, 36% and 50%, respectively. All patients who were unable to undergo transplant due to lack of a donor were from groups other than NHW. AlloSCT rates were 30%, 39% and 17% in PTCL-NOS, AITL and ALCL, respectively. At a median follow-up time of 24.2 months, 101 (63%) patients are deceased with 83 (82%) due to disease. Twenty (39%), 17 (33%), 11 (22%) and 3 (6%) patients received an AlloSCT with a matched unrelated, matched related, mismatched unrelated and haploidentical donor, respectively. Fifteen (29%) patients underwent a myeloablative while 36 (71%) underwent a reduced intensity conditioning regimen. None of the 51 patients who underwent AlloSCT had pre-transplant measurable disease. Of transplanted patients, median PFS was 55.7 months and OS was 62.4 months (Figure 1B). Sixteen (31%) patients had eventual disease relapse. Eighty percent of relapses occurred within 3 months after AlloSCT. Seven (13%) and 6 (12%) of the transplanted patients were deceased within 12 months after AlloSCT due to disease relapse and complications of AlloSCT, respectively. Conclusions Although AlloSCT may be highly effective for R/R TCL achieving a CR, only a small minority of patients are able to undergo AlloSCT and the outcomes for the ITT population is dismal. Common barriers to undergoing AlloSCT include progressive disease and inability to identify suitable donors, particularly in minority populations. More effective pre-transplant salvage therapies and alternative AlloSCT donors are greatly needed.

The Frailty Syndrome As Predictor of Allogeneic Hematopoietic Cell Transplantation Outcomes. Prospective Study on Behalf of the Grupo Español De Trasplante Hematopoyético y Terapia Celular

INTRODUCTION Including frailty in the evaluation of patients before HCT is recommended, but more needs to be done to reach a consensus on how to evaluate and manage this syndrome in clinical practice. Since 2021, sixteen institutions members of the Grupo Español de Trasplante Hematopoyético y Terapia Celular (GETH-TC) have participated in a multicenter and prospective study with the purpose of investigating the state of frailty of adult patient candidates to HCT and evaluate the effect of frailty in transplant outcomes. METHODS All Spanish institutions members of the Group were invited to participate in the study and finally 16 of them were actively involved in it. All patient candidates for HCT were eligible to be included in the study after providing informed consent. Frailty was evaluated at first consultation, at admission, and after the stem cell infusion, using the HCT Frailty Scale (Salas et al. BMT 2023) as described in Table 1. According to their respective total frailty score, patients were classified into three levels of frailty: fit, pre-frail, and frail. The frailty assessment was made by the hematologists and nurse team as part of the clinical practice, utilizing existing human resources and without requiring additional medical appointments for patients. The median time to complete the evaluation ranged from 8 to 10 minutes. The evaluation of physical frailty was complemented with the Mini-Cog test. The results obtained from the frailty assessment were not used to determine HCT eligibility and/or to design the HCT process. This study did not have external funding. RESULTS Between February 2021 and May 2023, 916 consecutive adult candidates for HCT in any of the participating institutions were included in the project. Of all of them, the results reported here correspond only to the 341 adult candidates for allogeneic (allo)-HCT. Median patients' age was 56 (range, 18-76); 65.3% were males; the most prevalent baseline diagnosis was myeloid malignancies (57.5%). Prior to HCT, 36.8% adults had an KPS<90% and 11.5% an HCT-CI>3, 53.1% patients received reduced intensity conditioning regimens, 25.5% alternative donor grafts, and 61.6% received PTCY-based prophylaxis. At the first consultation, 94 (27.6%) adults were classified as fit, 203 (59.5%) as pre-frail, and 44 (12.9%) as frail. Frail patients were more likely to have a KPS<90% (OR 2.80, p<0.01) and an abnormal result of the Mini-Cog test (<3) (OR 8.21, P<0.001). The probability of being frail was independent of age (continuous) (p=0.654), sex (p=0.323), and comorbidities (HCT-CI>3) (p=0.196) (multivariate binary regression analysis). As shown in Table 1, the state of frailty changed throughout the study period, confirming the dynamic nature of the frailty syndrome. A total of 59 (17.3%) patients went through a pre-transplant rehabilitation (pre-hab) program. With this information, the dynamics of frailty of these patients was compared with that of patients who did not join a pre-hab program. At HCT admission, the distribution of patients across the frailty categories was different between the two groups (p=0.028). The proportion of fit patients was higher in the pre-hab group (55.1% vs. 26.7%) because part of the pre-frail patients changed to the fit category. The power of the HCT Frailty Scale to predict OS was evaluated in the subsample of 216 patients that had a minimum follow-up of 120 days among survivors. Table 1 shows that the probability of OS at 1-year increases with the level of fitness of the patients at first consultation, as follows: 35.6% (frail), 70.5% (pre-frail) and 72% (fit), (p<0.001). Secondly, the effect of the level of fitness in the probability of 1-year OS was higher with frailty measured at the time of HCT admission; respectively, 20%, 66.8% and 78.9%. (p<0.001) ( Figure 1). The difference is explained by the improvement in fitness of the patients that participated in a pre-hab program between first consultation and admission. CONCLUSIONS This study validates the applicability of the HCT Frailty Scale at HCT institutions that are part of a health care system different from that where it was first implemented. The HCT Frailty Scale classifies adult patients to allo-HCT in three categories of frailty, frail that have predictive power over transplant outcomes. Frailty syndrome is independent of age and comorbidities and can be improved through pre-hab programs with the positive result of improving the OS of transplanted patients.

Role of Splenic Irradiation Prior to Transplant for Myelofibrosis: A Global Collaboration

JAK inhibitors and novel agents have shown promising reduction of spleen size in newly diagnosed myelofibrosis. However, not all patients will respond or they eventually progress at some point. Despite hematopoietic cell transplantation (HCT) being the only curative treatment option to date, splenomegaly prior to HCT remains a particular challenge. On the other hand, numbers of patients eligible for HCT continue to increase worldwide, and thus management of splenomegaly becomes more and more relevant. One approach to reduce spleen size prior to HCT could be splenic irradiation. However, evidence on its role remains scarce. We took advantage of a global collaboration between European, US, and Latin American centers to investigate the role of splenic irradiation as part of the HCT platform for patients with myelofibrosis. Radiation therapy had to be given within 3 months prior to or be part of conditioning therapy for HSCT. Detailed information on irradiation as well as post-HCT safety profiles was collected in addition to usual patient-, disease-, and transplant-related variables. This global collaborative study included 52 patients, of whom 71% had primary myelofibrosis, 17% post polycythemia vera and 12% post essential thrombocythemia myelofibrosis. Median age at HCT was 60 years (range, 32-76). Risk category according to DIPSS prior to irradiation was intermediate-1 in 20%, intermediate-2 in 52%, and high in 28%. Driver mutation status was JAK2 in 44%, CALR in 40%, MPL in 4%, and triple negative in 12%. Four patients had portal vein thrombosis before irradiation. Ruxolitinib before irradiation was received by 76% and 4% received fedratinib. Reduced intensity conditioning HCT was received by 73% and 85% were matched related or matched unrelated donor transplants. Median time from irradiation to HCT was 2 weeks (range, 0.9-12 weeks) and median spleen size prior to irradiation was 23 cm (range, 14-35). Spleen size was measured by ultrasound in 70%, CT scan in 20%, and physical examination in 10%. Median total irradiation dose was 7 Gy (range, 3-12), fractionated in a median of 5 administrations (range, 2-12). Splenic irradiation resulted in a significant spleen reduction prior to HCT but was also associated with significant reduction in platelet and leukocyte counts ( Table). Spleen size did not correlate with blood counts prior or after irradiation. Higher platelet count prior to irradiation correlated with higher counts after irradiation (r=0.83; P<0.001). There was no correlation between irradiation dose and post-irradiation hematological toxicities. Only 1 patient had non-hematological adverse events (tumor lysis syndrome). Neutrophil engraftment was achieved by 90% within a median of 18 days after HCT and platelet engraftment was achieved by 81% within a median of 38 days. Median follow-up of the total cohort was 2.7 years and 3-year overall survival was 66% (95% CI, 52-80%; Figure). Non-relapse mortality was 27% (95% CI, 15-39%) and cumulative incidence of relapse was 11% (95% CI, 2-20%; Figure). Incidence of acute GVHD grade II-IV and chronic GVHD was 25% and 38%, respectively. Increased spleen size (as continuous variable) prior to irradiation was associated with worse outcome (P=0.05), showing 3-year survival of 73% for spleen ≤25cm vs 42% for >25cm, and non-relapse mortality of 58% vs 14%, respectively (P=0.02). No effect of spleen size after irradiation on outcomes was observed. All 4 patients with portal vein thrombosis died (2-year survival 25%). A multivariable model showed that larger spleen size before irradiation, lower hemoglobin levels, CALR/MPL-unmuated driver mutation genotype, and presence of portal vein thrombosis were significantly associated with worse survival ( Table). This first international and largest study to date on splenic irradiation as part of the HCT algorithm for patients with myelofibrosis and splenomegaly showed a significant impact of spleen size on overall survival and non-relapse mortality, while relapse rates were low. In addition, lower hemoglobin levels and presence of portal vein thrombosis at time of irradiation predicted worse outcomes.

Day 100 Risk Assessment Tool Predicts 1 Year Survival in Allogeneic Hematopoietic Cell Transplant Patients

Introduction Allogeneic hematopoietic cell transplant (HCT) is a potentially curative therapy for many advanced malignancies; however, it is associated with a significant risk of non-relapse mortality. Several validated measures have been developed to estimate 1-year overall survival (OS) and non-relapse mortality (NRM), but these rely solely on pre-transplant factors to estimate risk. We previously described a “Day 100 risk assessment tool” (PMID 34628474) that aimed to identify the most effective way to deliver high quality care. The score is based on factors primarily occurring within the first 100 days of HCT, demonstrating that, independent of traditional pre-transplant variables, factors identified at day 100 significantly impacted longer term outcomes. This previous analysis included 163 patients who were transplanted from 2015-2018. We now aim to validate our scoring system in a larger, more contemporary cohort. Methods The Day 100 risk tool includes 11 binary variables: HCT-comorbidity index ≥ 3, distance from transplant center > 1 hour, day 100 ECOG performance status (PS > 2), acute GVHD requiring systemic corticosteroids, infection requiring intravenous antibiotics, concerns regarding caregiver support, coping skills, substance use, poor health literacy, medication compliance, and “other” concerns from the care team. Patients were given a point for each factor (0 or 1) and total points were summed as the risk score for analysis. Patients who survived at least 100 days were included in analysis. One year survival estimates were analyzed using the Kaplan-Meier method (overall survival [OS]) and cumulative incidence methods (non-relapse mortality [NRM]). Prognostic factors were identified with Cox regression (OS) or Fine and Gray regression (NRM). All patients who died after 1-year were censored at 12 months. Results From 1/2018-7/2022, 407 patients underwent first allogeneic HCT and survived at least 100 days without progression of disease. Median age of patients was 61 years old (range 20 - 76) and the majority of patients were: Male (54.3%, N=221), White (88.7%, N=361), diagnosed with acute myelogenous leukemia (AML) (45%, N=183), received peripheral blood stem cells (72%, n=294) had a matched unrelated donor (62.7%, n=255), underwent reduced intensity conditioning (64%, n=259), and received post-transplant cyclophosphamide graft-versus-host disease prophylaxis (52.6%, n=214). Stratified according to best fit for survival, 46.7% (n=190) were classified as “low risk” (0-1), 42.5% (n=173) “intermediate risk” (2-3), and 10.8% (n=44) as “high risk” (≥4) based on Day 100 score. One-year OS was significantly worse for the high risk ≥4) compared to low risk (0-1) and intermediate risk (2-3) (Figure 1). Multivariable analysis demonstrated that the high-risk Day 100 score was significantly associated with 1-year OS and NRM (Table 1). Conclusion In a larger contemporary cohort, we validate our Day 100 risk assessment tool as prognostic for 1-year outcomes. Future dynamic scoring systems incorporating post-transplant events may help to identify high risk patients and potential interventions to improve longer-term outcomes.

How Much Have Post-Transplant Outcomes Improved Since 2000 for Patients with Philadelphia-Positive Acute Lymphoblastic Leukemia in First Remission? a Study from the EBMT Acute Leukemia Working Party

Background Allogeneic hematopoietic cell transplantation (allo-HCT) remains an important curative modality for patients with Philadelphia-positive acute lymphoblastic leukemia (Ph+ ALL) in first complete remission (CR1). Recent years have witnessed an improvement in transplant techniques and increased use of post-transplant pharmacological interventions aimed at reducing the risk of relapse. However, recent results using the combination of blinatumomab and second or third-generation tyrosine kinase inhibitors (TKI) have challenged the role of allo-HCT in CR1. To address these challenges, we assessed real-world changes over time in transplant characteristics and post-transplant outcomes in adult patients with Ph+ ALL in CR1, using a large dataset from the European Society for Blood and Marrow Transplantation (EBMT) registry. Methods We identified 3292 adult patients (45% female; median age 45 years, range 18-76) with Ph+ ALL allografted between 2001 and 2020 in CR1 from a matched sibling (38%), unrelated (54%) or haploidentical donor (8%).At transplant, 41% of patients were measurable disease (MRD) positive (pos). The comorbidity index (CI) was zero in 63% of patients with available data. Conditioning was myeloablative (MAC) in 77% of patients, and included total body irradiation (TBI) in 64% of patients. In vivo T cell depletion (TCD) and peripheral blood stem cells (PBSC) were given to 52% and 86% of patients, respectively. Most patients (66%) and donors (55%) were cytomegalovirus (CMV) positive. Median follow-up for live patients was 56 months (interquartile range [IQR] 28-32). Results We compared changes in patient and transplant characteristics over time in 245 patients transplanted in 2001-2005, 679 patients transplanted in 2006-2010, 1035 patients transplanted in 2011-2015, and 1333 patients transplanted in 2016-2020. Patients transplanted in recent years were older, were less likely to be MRDpos, and more likely to receive PBSC and TCD. The 3-year cumulative incidence of relapse (CIR) gradually and significantly decreased from 41% to 32%, 27%, and 19% over the 4 time periods (p=0.001), and non-relapse mortality (NRM) significantly decreased as well from 25% to 24%, 23% and 17% (p=0.001). The 3-year leukemia-free survival (LFS) and overall survival (OS) gradually and significantly improved over time from 34% to 44%, 50%, and 64% (p=0.001) and from 47% to 56%, 65%, and 75% (p=0.001), respectively. Finally, graft-versus-host disease (GVHD)-free, relapse-free survival (GRFS) improved from 26% to 34%, 37%, and 49% (p=0.001). In a Cox regression multivariate analysis (MVA), a progressive and significant improvement in all transplant outcomes was noted including reduced acute and chronic GVHD, reduced CIR and NRM, and increased LFS, OS, and GRFS. LFS was also negatively affected by older age, male gender of both patients and donors, MRDpos pretransplant, and the use of reduced intensity conditioning while positively affected by the use of TBI. OS was also positively affected by younger age, female gender of patients, matched sibling donor, TBI, and TCD. This improvement in post-transplant outcomes over time was observed both in MRDpos but also in MRD negative (neg) patients. In MRDneg patients, 3-year CIR decreased from 34% to 30%, 24%, and 17% (p=0.001) over the 4 time periods whereas LFS improved from 41% to 46%, 52%, and 66% (p=0.001). Similarly, in MRD-positive patients, CIR decreased from 48% to 34%, 32%, and 23% (p=0.001) over the 4 time periods whereas LFS improved from 27% to 42%, 47% and 60% (p=0.001). Conclusion In patients with Ph+ ALL, we observed an impressive improvement over time in post-transplant outcomes with decreased CIR and NRM and improved LFS, OS, and GRFS, both in MRDpos and MRDneg patients. These large-scale, real-world data can serve as a benchmark for future studies in this setting, including those testing the combination of TKI and blinatumomab as an alternative to transplant.

Safety and Efficacy of Orca-Q with Haploidentical Donors for the Treatment of Advanced Hematologic Malignancies without the Use of Post-Transplant Cyclophosphamide

Srour, Salhotra, Lowsky and Abedi contributed equally as authors BACKGROUND Allogeneic stem cell transplantation (SCT) can be curative for several high-risk hematologic malignancies, but access was previously limited to patients with a fully matched donor. The introduction of post-transplant cyclophosphamide (PTCy) GvHD prophylaxis has increased the use of haploidentical donors (haplo) for patients who lack an HLA-matched donor. However, clinical outcomes associated with PTCy-based regimens remain challenging due to increased relapse rates (particularly in the setting of reduced intensity conditioning) and the adverse event profile including higher incidence of mucositis, cytokine release syndrome (CRS), delayed engraftment & T cell reconstitution, infections, early cardiotoxicity events and death from organ failure (Dulery 2021, Abboud 2021, Nagler 2022, Hoover 2022, Bolaños-Meade 2023). Additionally, the incidence of chronic GvHD after haplo SCT with PTCy is 24 - 33% at 1 year in various historical cohorts. Orca-Q -an investigational precision engineered cell therapy biologic- represents an alternative strategy which may be administered with single agent prophylaxis and does not require PTCy. The cellular composition of Orca-Q includes enriched CD34+ stem cells, combined with specific T-cell subsets, and is intended to reconstitute the blood and immune systems. METHODS Adult patients with high-risk hematologic malignancies eligible for MAC SCT were enrolled on the haplo donor dose expansion arm of a multicenter phase1 study of Orca-Q (NCT03802695). Haplo was defined as ≥ 4/8 but < 7/8 matched related donor at HLA-A, -B, -C, and -DRB1 typed using DNA-based high-resolution. Patients received MAC conditioning and single agent GVHD prophylaxis with tacrolimus (starting on day -1 and taper day +60). Orca-Q was manufactured centrally at Orca Bio Manufacturing Site in Sacramento, CA from G-CSF mobilized peripheral blood apheresis. RESULTS Orca-Q was successfully manufactured and delivered to all subjects with a vein-to-vein time (time between end of donor apheresis to start of recipient's Orca-T infusion) of < 72 hours. A total of 33 patients (21 AML, 10 ALL, 2 CML) were included. Median age was 43 (range, 21 - 63) years, 73% were male. Median follow-up was 375 (range, 73 - 1384) days. Sixteen patients received TBI-based MAC; 17 received busulfan-based MAC (Table). All patients engrafted with median time of 12.0 (range, 8 - 25) and 15.5 (range, 8 - 79) days for neutrophil and platelet engraftment, respectively. Two patients had secondary graft failure. Two patients had Grade 1 CRS; 1 patient had Grade 2 CRS. Grade 2+ aGvHD through Day 180+ occurred in 15% of patients. Grade 3-4 acute GvHD (aGvHD) was rare with only 1 event of grade 3 aGvHD and no grade 4 aGvHD. No patients had moderate-to-severe cGvHD. Estimated incidence of CTCAE grade 2 and > grade 3 infections were 9% and 15% at 1 year, respectively. 5 patients died (2 from relapsed disease) during the study period. NRM was 9% at 1 year. The 1-year relapse-free survival, GvHD-and-relapse free survival (Figure), and overall survival at 1 year was 82%. CONCLUSIONS Our findings reveal promising safety and efficacy outcomes using Orca-Q cell therapy for haplo-SCT despite the use of MAC with only single-agent tacrolimus, and without PTCy. With median follow-up of approximately 1 year, no patients experienced moderate or severe cGvHD, the low AE profile in the haplo setting remains favorable, and 1 year GvHD-free, relapse-free survival of 83% is very encouraging. This phase 1 study continues to enroll patients across the US. REFERENCES Abboud R, Wan F, Mariotti J, et al. Bone Marrow Transplant. 2021;56(11):2763-2770. Bolaños-Meade GM, Hamadani M, Wu J. N Engl J Med. 2023; 388(25):2338-2348. Duléry R, Mohty R, Labopin M, et al. JACC CardioOncol. 2021; 3(2):250-259. Hoover A, O'Leary D, Cao Q, et al. Blood. 2022; 140 (Supplement 1):282-283 Nagler A, Tsirigotis P. Bone Marrow Transplant. 2022; 57(11):1640-1641.

Favorable Outcomes for High-Risk MDS and Oligoblastic AML with MDS-Related Changes with Reduced Intensity Allogeneic Bone Marrow Transplantation with Post-Transplantation Cyclophosphamide

Introduction: Newer classification systems label myelodysplastic syndrome (MDS) with 10-20% blasts and acute myeloid leukemia (AML) with MDS-related changes (AML-MR) on a continuum as they share common biologic features. The prognostic implication of blast percentage is less clinically relevant particularly in diseases with high-risk molecular features such as MDS/AML with TP53 mutations. The recently introduced Molecular International Prognostic Scoring System (IPSS-M) allows for a more personalized prognosis for MDS patients (pts) than the prior revised IPSS (IPSS-R), but it is less clear if this translates to better therapeutic choices or outcomes for pts. Allogeneic bone marrow transplantation (BMT) remains the only potentially curative approach. Increasingly clinical trials of novel compounds combined with hypomethylating agents (HMAs) have not shown improved efficacy over single agent HMAs, necessitating further study of BMT approaches for durable disease control across the spectrum of disease biology. No uniform approach to the conditioning regimen and GVHD prophylaxis for this pt population has proven superior. In the current study, we describe the outcomes of BMT with post-transplant cyclophosphamide (PTCy) for patients with high-risk MDS and oligoblastic AML-MR, and analyze the prognostic implication of their chromosomal and molecular profiles within the international scoring systems. Patients and methods: This is a retrospective analysis of patients with 5-30% blasts and IPSS-R ≥3 who underwent BMT with PTCy at Johns Hopkins Hospital between 1/2013 and 12/2020. Next generation sequencing (NGS) was performed within 12 months of diagnosis. Kaplan-Meier analysis was performed to evaluate overall survival (OS) and relapse-free survival (RFS). Competing risks analysis was performed to evaluate the incidence of relapse and non-relapse mortality (NRM). Cox-regression models were performed in univariate analyses with false discovery rate adjustment and then subsequently conducted for multivariable analyses to identify statistically significant and independent prognostic factors. Results: Ninety-four consecutive patients (65% male) were identified with a median age of 61 (range 22 - 75) years at diagnosis. Median follow-up was 4.8 years (range 5 days-9.6 years) post BMT. Two-thirds (63%) underwent haploidentical transplantation, and 91% received reduced intensity conditioning with Fludarabine, Cyclophosphamide, and TBI. Median age at BMT was 65 years (range 22 - 76). The median time from diagnosis to BMT was 7.9 months. 52 (57%) received HMA based treatment and 36 (39%) intensive chemotherapy prior to BMT. Graft failure occurred in 6 patients (6.4%) The 5-year OS rate was 53% (95% CI: 43%-65%), the 5-year RFS rate was 47% (95% CI: 38%-59%) ( Figure 1A). The incidence of relapse was 21% (95% CI: 13% - 30%) at 1 year and 31% (95% CI: 21% - 40%) at 2 years after BMT ( Figure 1B). NRM rate in the first-year was 7% (95% CI: 2%-13%) and 11% (95% CI: 4%-17%) in the first two years ( Figure 1B). The incidence of acute GVHD (aGVHD) grades 3 to 4 was 3.2%, whereas chronic GVHD (cGVHD) presented in 12 patients (12.7%) with only 2 patients (2.1%) having moderate to severe disease based on the NIH grading criteria. Univariate analysis showed that higher IPSS-R (HR 1.68, 95% CI 1.39 - 2.04), poor or very poor karyotype risk (HR 7.48, 95% CI 3.49 - 16.02), complex karyotype (HR 3.72, 95% CI 2.01 - 6.88), higher IPSS-M (HR 1.72, 95% CI 1.38 - 2.14), TP53 mutations (HR 6.53, 95% CI 3.36 - 12.7) and RAS mutations (HR 4.96, 95% CI 1.7 - 14.5) were associated with worse OS. IPSS-R was significantly correlated with the patients' response to bridge therapy (OR 1.34, P=0.036). IPSS-R, IPSS-M, poor or very poor karyotype risk, complex karyotype, TP53 and any RAS mutations and response to bridge therapy were independently associated with worse OS and RFS ( Table 1, Figure 1C). Conclusion: This retrospective analysis supports that BMT with PTCy is a durable approach for patients with high-risk MDS and oligoblastic AML-MR leading to high OS and RFS associated with a promising safety profile with low NRM and severe GVHD incidence. IPSS-R, IPSS-M, karyotype and response to bridge therapy are independent predictors of OS and RFS post-BMT. The presence of TP53 and/or RAS mutations defines a sub-group of patients with dismal outcomes representing an unmet need within this patient population.

Outcomes of Allogeneic Hematopoietic Cell Transplantation in Patients with Active Primary Malignancy at HCT - a Bi-Institutional Retrospective Cohort Analysis

Background: Patients diagnosed with hematologic malignancies may be candidates to proceed to allogeneic hematopoietic cell transplantation (HCT). In those with active solid malignancy, given the cumulative toxicity associated with additional chemotherapy and the intensive immunosuppression required after HCT, there has been a concern that outcomes of HCT would be suboptimal. Specifically, prior malignancy may relapse early after HCT or transform to a more aggressive phenotype. We aimed to evaluate the bi-directional relationship between HCT and active solid malignancy. Methods: We retrospectively reviewed charts of patients in 2 large transplant centers who received first allogeneic HCT between 2012 and 2022 with concurrent active solid malignancy (defined as receiving any treatment for solid malignancy within 5 years prior to HCT). Hematologic relapse was treated as a competing event in time-to-event analyses of graft vs. host disease (GVHD) and non-relapse mortality (NRM). Analysis of chronic GVHD was performed only among patients who survived more than 3 months post HCT. Mortality was treated as a competing event in the analysis of relapse of solid malignancy. Modified GVHD-relapse free survival (mGRFS) was defined as survival with no prior GVHD and/or relapse of either solid or hematology malignancies. This trial was approved by the hospital ethic committee. Results: Between 01/2012 and 12/2022 we identified 45 patients (females, 62%) who fulfilled the eligibility criteria. Median age was 63 (range, 21-74) years and median post HCT follow-up was 41 (range, 7.1-122.5) months. Acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) (n=35 and n=6, respectively) were the most common hematologic malignancies. Status of hematologic malignancy at HCT was complete remission (n=27, 60%), partial remission (n=1, 2%) and stable/progressive disease (n=17, 38%). Most common diagnoses of active solid malignancies were breast cancer (n=22, 49%) and colon cancer (n=6, 13%) with 24% patients receiving active treatment at HCT and 7% with progressive disease at HCT. HCT comorbidity index (HCT-CI) was 3-5 in 82% (>5, 18%). Majority received reduced intensity conditioning (n=29, 64%) with an allograft mainly derived from unrelated donors (n=31, 69%). Early HCT complications included severe mucositis (16%), bacteremia (20%), and invasive fungal infections (4%). There were no cases of sinusoidal obstruction syndrome. 27% resumed maintenance treatment for solid malignancies post HCT with no significant toxicity. Incidences of grade 2-4 and 3-4 acute GVHD at day 200 were 48% and 3%, respectively. Incidences of overall and moderate-severe chronic GVHD at 3 years were 53% and 24%, respectively. Hematologic relapse incidence at 6 months, 1 and 3 years were 31%, 37%, and 48%, respectively with no impact of conditioning intensity (p=.95). Incidences of NRM at 3 months, 1 and 3 years were 7%, 15%, and 25%, respectively. Cumulative progression of solid malignancies at 3 years was 12%, Figure 1A. Incidence of mRGFS at 1 year was 16%. Overall survival at 3 years was 53% in all cohort, 54% in patients with AML/MDS and 61% in patients with concomitant breast cancer, Figure 1B. Cox regression model identified both progressive solid and hematologic malignancy to be associated with increased risk of mortality (HR=4.3, p=.049 and HR=1.8, p=.028, respectively), while sex, age, conditioning intensity and HCT-CI did not impact survival. Conclusions: HCT is safe and efficacious in patients with active solid malignancy. However relapse incidence of hematologic malignancy is high and mGRFS is low. Progression of the solid malignancy after HCT is in fact uncommon. Therefore in this specific patient cohort, improved transplantation techniques to better control the hematologic disease post-transplant are warranted to make HCT more effective and long lasting.

A Phase IB/II Study of Blinatumomab in Patients with B-Cell Acute Lymphoblastic Leukemia (ALL) and B-Cell Non-Hodgkin Lymphoma (NHL) As Post-Allogeneic Blood or Marrow Transplant (alloBMT) Remission Maintenance

Background: AlloBMT can be curative as consolidation for high risk B ALL and NHL. However, transplant-related toxicity and disease relapse limit survival. Post-transplantation cyclophosphamide (PTCy) as graft-versus-host disease (GVHD) prophylaxis limits GVHD and facilitates alternative allograft sources. Following PTCy, cellular immune reconstitution is favorable for strategies to augment anti-tumor immunity. Blinatumomab (blina) is effective in the treatment of CD19+ ALL and NHL. Blina leads to T cell activation that may enhance post-transplant tumor-specific T cell responses, leading to a more potent graft-versus-tumor effect. A study of 21 B ALL pts demonstrated the feasibility of post-transplant blina but did not improve survival when pts universally remained on immunosuppression for at least 1 cycle of treatment (Gaballa. Blood. 2022). We present results of a phase Ib/II trial to assess the tolerability and preliminary efficacy of blina as post-alloBMT remission maintenance in B-cell ALL and NHL in pts off immunosuppression. Methods: Pts ≥1 month-old with high risk CD19+ B ALL or ≥18 years-old with NHL who underwent alloBMT with PTCy were eligible. Pts had to be 60-180 days post-transplant with count recovery and in remission. Pts had to be off immunosuppression for ≥4 weeks prior to treatment, and without a history of grade ≥3 acute GVHD or severe chronic GVHD. Pts could receive 2 cycles of blina if they had evidence of disease (including MRD) at their pre- and/or post-transplant evaluations but otherwise received 1 cycle. Blina was given as a continuous infusion at 9 mcg/day on C1D1-7 and 28 mcg/day on C1D8-28 and C2D1-28. Results: The study closed to accrual on January 31, 2023 following enrollment of 42 pts (26 male/16 female) with a median age of 54 (Range 30-73). Among enrolled pts, 19 had Ph-negative B ALL and 23 had B-cell NHL. All pts underwent reduced-intensity conditioning alloBMT using a regimen of fludarabine, cyclophosphamide, and total body irradiation. Median prior lines of therapy were 2 (range 1-6). Additional transplant details are presented in Table 1. All B ALL pts were in an MRD-negative CR by flow cytometry at a sensitivity of 0.01% at alloBMT. All pts received a single cycle of therapy. Pts started blina a median of 137 days post-transplant (range, 90-182). Four pts failed to complete a full cycle due to G4 transaminitis (1), G4 neutropenia (1), relapse (1), and patient preference in the setting of tremors (1). Grade 3 or 4 adverse events felt to be at least possibly related to the study drug included G3 neutropenia (7%), G4 neutropenia (19%), anemia (5%), G3 ALT (5%), G4 AST (2%), G3 AST (2%), and neurotoxicity (7%). Two pts (5%) developed chronic GVHD following blina requiring the resumption of immunosuppression. At a median follow-up of 40 months post-alloBMT, the 3-year relapse-free survival is 73% (95% CI 54-85%) due to a 24% (95% CI 12-39%) incidence of relapse and a 4% (95% CI 0-17%) incidence of non-relapse mortality, as shown in Figure 2. All 3 (100%) relapsed B ALL pts and 2/6 (33%) relapsed B NHL pts presented with CNS involvement. Four pts with CNS relapse (80%) had CNS involvement prior to alloBMT. Among 2 pts who died without relapse, 1 was unrelated to alloBMT, while the other died of therapy-related myeloid neoplasm. Data on biomarkers including changes in T cell subpopulations in both BM and PB, and co-signaling molecule expression will be presented. Conclusions: Post-alloBMT maintenance therapy with blina is feasible with minimal toxicity in pts off immunosuppression. Initial survival outcomes are promising with the majority of relapses involving the CNS. A randomized trial of maintenance with blina after alloBMT with PTCy is needed to confirm efficacy in this high-risk population.

Prospective Evaluation of Patient-Reported Outcome up to 10 Years after Allogeneic Stem Cell Transplantation Using FACT-G/BMT and EORTC-QLQ30 Questionnaires

Introduction Increasing outpatient care in all medical departments will pose a challenge for daily routines and force us to rethink established processes. In hemato-oncology there is good evidence for the continuous improvement of overall survival after allogeneic stem cell transplantation (allo-HCT) during the last decades. However, the chronic character of the underlying hematopoietic malignancy and the accompanying long-lasting consequences of an allo-HCT are often not properly addressed in follow-up care. The health care status of this population should be determined on physical and mental condition and serious longer-term sequelae need to be monitored more closely than on quarterly basis. Patient-reported outcome measurements (PROMs) are able to address this issue in clinical routine and capture the multidimensional construct of quality of life (QoL). PROMs focus mainly on how a patient survives after a treatment, and not only on whether she/he survives and how long. Patients and Methods We performed a cross-sectional survey including all adult allo-HCT recipients who attended follow-up care in the period from March to July 2023 at the University Hospital Tübingen, Germany. Eligible participants completed both, the EORTC Core Quality of Life questionnaire (EORTC QLQ-C30) and the Functional Assessment of Cancer Therapy General (FACT-G) with the subscale for Bone Marrow Transplantation (FACT-BMT). We built 8 cohorts (day 30, day 100, month 6, month 12, year 3, year 5, year 10 and >10 years) to evaluate QoL after allo-HCT and to identify predictors like age, performance status (PS), conditioning regime, graft-versus-host disease (GvHD) development and relapse. Results We included 200 recipients (93 women, average age 54.2 years) who received allo-HCT between 2004 and 2022. The majority was treated for acute leukemia (n=95), followed by chronic leukemia (n=16), myelofibrosis (n=25), myelodysplastic neoplasm (n=20), lymphoma/myeloma (n=14) and others (n=30). 82.5% (n=165) received reduced-intensity conditioning (RIC) and 17.5% (n=35) myeloablative conditioning (MAC). 75.5% (n=151) of allogeneic donors were HLA-matched, 14.5% (n=29) HLA-mismatched and 8.5% (n=17) haplo-identical. The median follow-up was 43.4 months with the following patient numbers in the 8 cohorts: n=25 (d30), n=21 (d100), n=24 (m6), n=34 (m12), n=32 (y3), n=30 (y5), n=23 (y10) and n=11 (>10y). 73% (n=146) showed complete remission at last follow up, 14% (n=28) relapsed. Acute GvHD was observed in 39% (n=78) with additional 6.5% (n=13) suspected to have one. Chronic GvHD was observed in 39.5% (n=79). Average GHS in the EORTC QLQ-30 was 59.2%, average total scores in the FACT-G and FACT-BMT were 77.68 (max. score 108) and 105.37 (max. score 148), respectively. Both PROMs (EORTC QLQ30, FACTs) demonstrated the same biphasic course with a significant QoL recovery over time (Figure 1), comparing for example the global health status (GHS) on d30 (50%) with y10 (68,8%, p=0.07). Interestingly, allo-HCT recipients again experience a drastic decrease achieving y3, mainly caused by worse emotional and physical well-being. The median ECOG PS before allo-HCT was 0 and degraded to 1 in all cohorts until y10, where a return to baseline was seen. Current PS and PRO results showed a significant correlation (p<0.001). No correlations between QoL and age, GvHD or conditioning regime were found. Conclusion Allo-HCT recipients manage to regain a good QoL in long-term follow-up over 10 years but experience a significant low around y3. PROMs are able to detect such developments and can help to improve patient management. As indicated by our data, a higher degree of support in y3 could improve QoL and well-being of allo-HCT patients. However, until today, we lack the implementation of efficient strategies to do so in clinical routine.

Analysis of the Impact of Whole Blood and T-Cell Donor Chimerism after Allogeneic Stem Cell Transplant

Background: Allogeneic stem cell transplant (alloSCT) is one of the few currently available therapies to cure acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Positive outcomes are dependent on engraftment of donor cells to provide hematopoiesis as well as a graft-versus-tumor effect. Measurement of whole blood (WB) and T-cell (TC) chimerism at routine intervals post alloSCT allows for monitoring of engraftment. Development of mixed donor chimerism (MC) may indicate impending graft failure or disease relapse. The ideal frequency for chimerism measurements as well as the role of WB versus TC chimerism remains unclear. In this study, we analyzed the impact of WB versus TC mixed chimerism on survival outcomes in patients with AML and MDS. Furthermore, we studied baseline factors associated with the development of MC. Methods: In this retrospective analysis, adults with AML or MDS who received an alloSCT between January 1, 2016 and February 1, 2022 that had at least 1 donor chimerism measured on Day 30 (D30), Day 60 (D60), Day 90 (D90) at Juravinski Hospital and Cancer Centre (Hamilton, ON, Canada). Baseline demographic and transplant-related characteristics were collected. AML and MDS diagnoses were based on WHO 2016 classification of myeloid neoplasm and acute leukemia. Conditioning intensities were classified according to CIBMTR definitions. A total of 271 transplants were completed during the study period for AML or MDS. 128 were excluded from the analysis (chimerism testing not performed (n=121), second transplants (n=7)). We analyzed a total of 143 patients with median age of 63 years (19 - 76) who were transplanted for AML (n=105) and MDS (n=38). Donors were HLA-matched siblings (MRD, n=26), unrelated donors (MUD (8/8 or 7/8), n=85) or haploidentical related donor (MMRD, n=32). All patients except one received peripheral blood stem cell grafts. For alloSCT, 20 % of patients received myeloablative conditioning (MAC) and 80% received reduced-intensity conditioning (RIC). Complete chimerism (CC) was defined as ≥95%, whereas MC was defined as ≤95%. All chimerism measurements were measured using a PowerPlex® 16 System (Promega) (Hamilton Regional Laboratory Medicine Program, Hamilton, ON). Results: In our cohort, OS at 2 years was 57% and RFS 49%. Of the baseline factors, only disease-risk based on ELN 2022 for RFS with a hazard ratio (HR) of 1.43, 95% CI [0.83, 2.49] for adverse risk and HR 0.53 95% CI [0.23, 1.03] (p=0.03) for favourable risk. WB MC was detected in 22%, 22%, 23% of patients on D30, D60, and D90, respectively. TC MC was detected in 48%, 46%, and 43% of patients on D30, D60, and D90, respectively. WB MC had a strong negative impact on RFS, with a HR of 2.81, 95% CI [1.69, 4.66; p<0.001] on D30, 3.07, 95% CI [1.67, 5.66; p<0.001] on D60 and 4.77, 95% CI [2.47, 9.22; p<0.001] on D90. The influence of TC MC on RFS was also significant at all time points. Of 101 patients who were alive and did not have a relapse prior to D90 and had D30 chimerism and D90 chimerism evaluated, the patients who had a mixed WB and TC chimerism on D90 had a HR of 6.13, 95% CI [2.23, 16.85] and HR 2.73, 95% CI [1.24, 5.98] for RFS, which was statistically significant even after adjusting for known information of D30 WB/TC chimerism status (Table 1). WB MC had a strong negative impact on OS with a HR of 2.67, 95% CI (1.54, 4.64; p=0.001) on D30, 2.81, 95% CI (1.47, 5.38; p=0.002) on D60 and 4.78, 95% CI (2.47, 9.24; p<0.001) on D90. Again, the later time points remained statistically significant, when adjusting for known D30 chimerism status. The influence of TC MC on OS was also significant at all time points, however only a non-significant trend remained at later time points when adjusting for D30 TC chimerism (Table 2). We analyzed baseline factors predictive for D30 chimerism. For WB chimerism, only donor source remained statistically significant (p=0.038) with MMRD having a lower HR for MC 0.39, 95% CI [0.11, 1.41] and MRD having a higher HR for MC 2.33, 95% CI [0.9 - 5.99]. Conclusions: Our data confirm that a mixed chimerism as early as D30 post-alloSCT can have a detrimental impact on outcomes (RFS and OS) in alloSCT. Patients receiving haploidentical alloSCT had a lower risk to develop mixed chimerism in our cohort. These dismal outcomes of patients with mixed chimerism in our cohort provides a strong rationale to study interventions such as novel maintenance strategies or donor-lymphocyte infusions in this patient group.

Clinical Evaluation of a Functional Combinatorial Precision Medicine Platform to Predict Patient-Specific Treatment Outcomes in Acute Myeloid Leukemia

Introduction: Acute myeloid leukemia (AML) is an aggressive form a leukemia that remains difficult to treat, often with rapid and frequent disease relapse due to drug-resistant clonal selection. A range of combination therapies have been designed to overcome this hurdle, however, identifying the most appropriate combination therapy at each line of treatment remains a challenge. Functional precision medicine platforms that use ex vivo drug sensitivity data from primary patient samples have shown potential to guide treatments in a range of cancers. We have recently developed an ex vivo combinatorial drug sensitivity platform, quadratic phenotypic optimization platform (QPOP), that analyses a predesigned array of 155 test combinations performed on a primary patient sample to rank and compare all possible therapeutic combinations from a 12-drug set. In this study, we evaluated the use of QPOP to predict treatment outcomes in an AML cohort treated with a variety of combination therapies. Furthermore, we also explored QPOP's combination therapy ranking function to identify novel or under-utilized combinations that may benefit larger groups of AML patients when appropriately guided. Methods: Prospective clinical feasibility study of QPOP in AML was performed at National University Hospital (NUH) in Singapore. Peripheral blood or bone marrow aspirations were collected from AML patients, recruited between 26 th November 2019 and June 15 th 2023. Following CD34+ cell selection, the enriched malignant blast population was subjected to an array of 155 test combinations derived from an orthogonal array composite design. Phenotypic cell viability data from this test was subsequently used by QPOP to derive drug combination scores and rankings for all possible combinations. Median turnaround time for QPOP patient-specific reports was 8 (±2.1) days. Patients were treated with current standard of care options as guided by the clinician. The primary outcomes of this study were to determine the concordance between treatment outcomes as guided by clinicians and QPOP drug combination scores and rankings. Secondary outcomes of this study were to identify high-ranking, potentially effective combinations that may be nover or under-utilized for future studies. Results: 40 patients were recruited to the study with 49 samples analyzed by QPOP. Samples collected until 21 January 2022 were also used to refined ex vivo drug dosing levels for 12-drug, 3-level test combination arrays. Excluding patients diagnosed as non-AML and patient without available clinical concordance data, QPOP response concordance was evaluable for 19 patients. A 75% positive predictive value (PPV) and a 72.7% negative predictive value (NPV) was determined for a QPOP normalized cell viability (NCV) cutoff of 0.65. The area under the curve of the receiver operator curve, AUC = 0.75, suggesting acceptable predictivity. Concordance analysis of with samples (n = 10) collected after 21January 2022 demonstrated an 80% PPV, 80% NPV, AUC = 0.80 for an NCV cutoff of 0.62, suggesting that current ex vivo dosage settings for test array can further improve test accuracy. Combination therapy with the BCL2 inhibitor venetoclax and hypomethylating agent azacytidine is standard-of-care for AML. QPOP NCV cutoff of 0.62 also exhibited 100% concordance (5/5) with venetoclax+azacytidine treatment further demonstrating the accuracy of QPOP to predict treatment outcomes in AML. Amongst top ranked QPOP-derived combinations, venetoclax/fludarabine was amongst the most frequently reoccurring top-ranked combinations. With appropriate functional combinatorial precision medicine testing, patients who may benefit from addition of venetoclax to fludarabine-based chemotherapy regimens, such as fludarabine/busulfan reduced-intensity conditioning chemotherapy, may be accurately identified. Conclusions: This clinical study demonstrates the feasibility of QPOP to predict treatment outcomes and accurately identify both response and resistance to combination therapy. Following platform workflow optimization, initial concordance analysis suggests excellent predictivity. Expansion of this clinical study is needed to confirm these results. This study also suggests that underutilized combinations may be effective across a larger population of AML patients with appropriate ex vivo drug testing and deserve further clinical interrogation.