Malki, Monzr M. Al

ACCESS is a prospective, multicenter phase II trial evaluating peripheral blood stem cell (PBSC) transplantation using 4-7/8 HLA-mismatched unrelated donors (MMUD) with post-transplant cyclophosphamide (PTCy), tacrolimus, and mycophenolate. Adults undergoing first HCT with myeloablative (MAC) or reduced-intensity/nonmyeloablative (RIC/NMA) conditioning were enrolled, with donors aged 18-35 years and matched at 4/8-7/8 HLA loci by high-resolution typing. This expanded analysis includes all enrolled adult PBSC recipients, including the protocol-specified RIC/NMA cohort expansion, to improve precision of outcome estimates and provide descriptive analyses by HLA match level. Among 268 adults, 183 received 7/8 and 85 received <7/8 MMUD grafts; 82.4% of the <7/8 cohort received 6/8 grafts. Median follow-up among survivors was 11.9 months. At 1-year, overall survival was 78.6% (95% CI, 71.9-83.9) in the 7/8 cohort and 85.6% (95% CI, 76.0-91.5) in the <7/8 cohort. One-year relapse, non-relapse mortality, and GVHD-free relapse-free survival were 17.1%, 13.7%, and 51.1% versus 22.8%, 8.4%, and 54.6%, respectively. The cumulative incidence of grade II-IV and grade III-IV acute GVHD by day 100 was 36.6% and 7.7% in the 7/8 cohort versus 28.3% and 5.9% in the <7/8 cohort. Moderate-to-severe chronic GVHD at 1 year was 11.3% versus 7.7%, respectively. Among adult ACCESS recipients treated on a uniform young-donor PBSC/PTCy platform, short-term outcomes with predominantly 6/8 MMUD transplantation were encouraging. Because donor match level was not prospectively assigned and between-group comparisons were exploratory, these findings are descriptive and should not be interpreted as establishing equivalence with 7/8 MMUD transplantation. (Registered as NCT04904588 at CT.gov)

Importance Allogeneic hematopoietic cell transplant (HCT) is curative for hematologic cancers, yet access remains inequitable for racially and ethnically underrepresented and socioeconomically disadvantaged populations, making the goal of having a suitable donor for every patient who needs a transplant challenging. The ACCESS trial broadened access by enrolling patients without matched donors, who instead received an HCT from a mismatched unrelated donor. Objective To compare baseline characteristics of ACCESS trial participants with participants enrolled in a similar clinical trial and a patient-reported outcome (PRO) protocol cohort. Design, Setting, and Participants This cross-sectional study included adult participants (aged ≥18 years) from 3 cohorts—the ACCESS trial (2021-2024), BMT CTN 1703 trial (2019-2021), and Center for International Blood and Marrow Transplant Research (CIBMTR) PRO Protocol observational study (2020-2025)—who completed a baseline PRO survey. The ACCESS and PRO Protocol cohorts were stratified by conditioning intensity (myeloablative [MAC] vs reduced-intensity and nonmyeloablative [RIC/NMA]); all BMT CTN 1703 participants received RIC/NMA. Exposure Hematopoietic cell transplant. Main Outcomes and Measures Racial and ethnic diversity, insurance type, education, and income were compared among cohorts using counts and percentages, and socioeconomic and structural disadvantage were measured using the Social Vulnerability Index and Comprehensive Score for Financial Toxicity–Functional Assessment of Chronic Illness Therapy. Results Baseline surveys were completed by 208 participants in the ACCESS trial (median [range] age at transplant, 62.3 [20.4-78.9] years; 108 male [51.9%]), 122 participants in the PRO Protocol study (median [range] age at transplant, 63.9 [21.1-78.0] years; 67 male [54.9%]), and 342 participants in the BMT CTN 1703 trial (median [range] age at transplant, 66.9 [20.7-78.6] years; 218 male [63.7%]). Participants in ACCESS were more racially and ethnically diverse, with 15 (7.2%), 25 (12.1%), 46 (22.2%), 110 (53.1%), and 11 (5.3%) of Asian, Black or African American, Hispanic or Latino, White, and other race and ethnicity, respectively, compared with 4 (3.3%), 2 (1.6%), 8 (6.6%) 104 (85.2%), and 4 (3.3%), respectively, in the PRO Protocol and 10 (3.0%), 0, 16 (4.8%), 302 (91.0%), and 4 (1.2%), respectively, in the BMT CTN 1703 trial. Participants in ACCESS were more likely to have Medicaid (36 [18.1%]) vs PRO Protocol (8 [6.7%]) and BMT CTN 1703 (16 [5.1%]) participants and reported lower education (some college or an associate’s degree: 103 [49.5%] vs 73 [59.8%] in the PRO Protocol; postcollege education: 34 [17.3%] vs 35 [29.2%] in the PRO Protocol) and household income (<$40 000 annually: 25 [24.0%] vs 8 [11.6%] in the PRO Protocol and 7 [38.9%] in the BMT CTN 1703 trial). Median Social Vulnerability Index scores were highest among participants in the ACCESS MAC group (median [range], 0.72 [0.01-0.97] vs 0.61 [0.16-0.78] in the PRO Protocol MAC group), and 16 participants [27.6%] in the ACCESS MAC group reported moderate to severe financial toxicity. The ACCESS participants lived closer to transplant centers, especially in the RIC/NMA group (median [IQR], 28 [14-75] miles vs 47 [16-96] miles for BMT CTN 1703 participants and 49 [21-104] miles for PRO Protocol participants). Conclusions and Relevance This cross-sectional study of clinical trial participants and a clinical cohort found that the ACCESS trial enrolled a more racially and ethnically diverse and socioeconomically disadvantaged population. Trial designs that broaden eligibility could expand access to HCT, highlighting the need for systemic interventions to ensure equity.

Abstract Allogeneic hematopoietic cell transplantation (allo-HCT) is a potentially curative treatment for many hematological malignancies, but graft-versus-host disease (GVHD) is a common complication. Low gut microbiome diversity is associated with higher GVHD risk and shorter survival in multiple studies. Recently, the BMT CTN 1703 clinical trial demonstrated superiority of a GVHD-prophylaxis regimen including post-transplant cyclophosphamide (PTCy) compared to the standard prophylaxis (tacrolimus and methotrexate, Tac/MTX) in terms of GVHD-free, relapse-free survival at one year among reduced intensity conditioning allo-HCT recipients. However, the effect of PTCy on the gut microbiome and its association with clinical outcome have not been described. Here, we report on a companion randomized clinical controlled trial (BMT CTN 1801), which collected 2575 longitudinal stool samples from 304 study participants. Samples were obtained up to weekly up to day 84 post allo-HCT and at less frequent intervals thereafter, up to 2 years. Microbiome diversity and absolute microbial load were lower in the PTCy group compared to the Tac/MTX group on days 14–28 post-HCT. However, diversity at the timepoint closest to neutrophil engraftment was not significantly associated with non-relapse mortality after one year or other clinical outcomes, contrary to expectations from previous studies. Microbial domination events, when a single species exceeds 30% relative abundance, were comparable across treatment arms and reflected both pathogen blooms as well as less severe disruptions of the microbial community. Clostridium scindens and secondary bile acid metabolism pathways were less prevalent in the PTCy arm than in the Tac/MTX arm post-HCT, yet presence of secondary bile acid metabolism pathways was associated with a lower risk of chronic GVHD. Given that PTCy was associated with a greater disruption of the microbiome as measured by diversity, absolute microbial abundance, and bile acid metabolism capability, but better clinical outcomes overall, these data suggest that the importance of the microbiome in modulating the host immune systems after allo-HCT is specific to different types of GVHD prophylaxis.

Abstract Background: A randomized multicenter trial (BMT CTN 1703) demonstrated that after reduced intensity conditioning HCT, PT-Cy-based GVHD prophylaxis led to significant reductions in acute and chronic GVHD, but was associated with significantly more Grade 2 (moderate) infections and similar overall survival vs Tac/MTX. A linked mechanistic study (BMT CTN 1801) found that PT-Cy led to pan-T cell depletion and reduced T cell receptor (TCR) repertoire diversity vs Tac/MTX. To discover the molecular mechanisms driving the association of PT-Cy with increased infections, we examined pathogen-specific T cell reconstitution in BMT CTN 1801 patients (n=165 PT-Cy, n=159 Tac/MTX). Methods: We performed deep TCR sequencing on 2,369 blood samples collected pre-HCT (recipient baseline) and on Days +7, 14, 28, 63, 100, 180, 270, 365, 730, and from the graft infusion product. We then applied a novel set of TCR classifiers (Adaptive Biotechnologies) capable of identifying pathogen-specific clones associated with CMV, EBV, SARS-CoV-2, HSV-1, HSV-2, parvovirus, RSV, influenza A, rhinovirus, adenovirus, HHV-6B, norovirus and Toxoplasma. Single-cell (sc) TCR/RNA-sequencing on a sample subset (n=26) was performed to determine the phenotype of pathogen-specific T cells. Results. By linking scRNA-seq with pathogen-specific TCR barcoding, we identified CD4 and CD8 memory T cells as their predominant T cell reservoir. We found that the total number of pathogen-specific singleton TCRs was significantly lower with PT-Cy, starting early post-HCT and persisting through 2 years. For example, at Day +14, PT-Cy patients had 7.8-fold fewer pathogen-specific singleton TCRs vs Tac/MTX (mean of 6.9 vs 54.1, p<0.001). Consistent differences between PT-Cy and Tac/MTX were observed for TCRs specific for each pathogen individually. Patients who developed Grade 3 (severe) viral infections had significantly fewer pathogen-specific singleton TCRs at Day +14 compared to those who had no viral infections (mean of 4.0 vs 32.5, p=0.03). Leveraging intrinsic TCR barcoding of the HCT infusion (“graft”) and of the patient's baseline samples (“recipient”), we could assign the graft/recipient origin of the pathogen-specific cells with high fidelity. This analysis revealed pronounced differences in the origin of pathogen-specific T cells with PT-Cy vs Tac/MTX, especially prior to Day +100. The absolute number of pathogen-specific TCRs originating from the graft was significantly higher with Tac/MTX vs PT-Cy. This difference was observed from day +7 through 6 months post-HCT, with up to 7.1-fold more graft-derived pathogen-specific TCRs in Tac/MTX vs PT-Cy (p<0.001 at each timepoint before day +100). Within patients who received Tac/MTX, the balance of graft vs recipient pathogen-specific clones significantly favored graft clones (for example, a mean of 14.9 graft vs 8.6 recipient pathogen-specific TCRs at Day+14, p=0.02). By contrast, with PT-Cy, in addition to having substantially fewer pathogen-specific TCRs overall, the proportion of these TCRs was not significantly different between graft and recipient clones (mean of 2.1 graft vs 3.3 recipient pathogen-specific TCRs at Day+14, p=0.42). These data uncover that, in addition to the reduction in pathogen-specific T cells with PT-Cy, there was a relative skewing of the anti-microbial T cell reservoir towards recipient cells that persisted after conditioning. Conclusions: PT-Cy led to in vivo T cell depletion across all T cell subsets, which prominently included clones tracked from the allograft itself into the HCT recipient, with a relative sparing of recipient T cell clones that survived transplant conditioning. While the mechanism for relative sparing of recipient cells has not yet been determined, these conditioning-exposed cells may be less proliferative than newly infused graft T cells. The depletion of graft T cells included CD4 and CD8 memory cells specific for infections, which may have contributed to relative deficits in protective immunity against infection in patients receiving PT-Cy. Importantly, these data suggest that with PT-Cy, persisting recipient TCRs may play a key role in preserving anti-infectious immunity. Taken together, these results provide a mechanistic basis for key post-transplant clinical outcomes of the landmark BMT CTN 1703 study. They also underscore the importance of recipient immune status with PT-Cy, creating the opportunity for targeted infection risk assessment in these patients.

Abstract 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.

Abstract Allogeneic hematopoietic cell transplantation (HCT) using an HLA mismatched unrelated donor (MMUD) with calcineurin inhibitor-based graft versus host disease (GVHD) prophylaxis results in increased incidence of non-relapse mortality (NRM) and lower survival compared to matched donor HCT. The NMDP sponsored 15-MMUD study demonstrated that post-transplant cyclophosphamide (PTCy)-based prophylaxis following bone marrow derived MMUD HCT resulted in reduced incidence of GVHD and favorable survival. Because marrow grafts can be difficult to procure and vary in quality, we conducted a phase II, prospective, multicenter study to evaluate PTCy-based GVHD prophylaxis in adult recipients of MMUD using peripheral blood stem cell (PBSC) allografts. The primary study aim was to estimate the probability of one-year overall survival (OS) post HCT. Secondary aims were to assess other key clinical endpoints and determine the rate of severe infections. Initial results of the first 70 recipients who received reduced intensity conditioning (RIC) were previously reported by Al Malki et al (JCO 2025) demonstrating a 1-year OS of 78.6% (95% CI, 67% to 86.5%). Here, we report results from a planned expansion of the study that included 123 additional RIC recipients, with updated results from the initial cohort of 70 patients (total N = 193 subjects) treated at 33 centers. Study participants received cyclophosphamide 50 mg/kg (ideal body weight) administered on days 3 and 4 post HCT with tacrolimus and mycophenolate mofetil as previously described (Al Malki, JCO, 2025). The median study participant age was 65.0 (range: 22.9-78.9); 92 (47.7%) of participants were male, and 84 (43.5%) identified as having other than non-Hispanic white ancestry. The HCT comorbidity index was high-risk (>3) in 65 (33.7%). Underlying histologic diagnosis was AML in 96 (49.7%) participants, MDS in 43 (22.3%), ALL in 20 (10.4%), lymphoma or CLL in 24 (12.4%), and CML/other leukemias in 10 (5.2%). Conditioning regimens used were fludarabine and melphalan (100 or 140 mg/m2) (N=120; 62.2%), 2-day busulfan and fludarabine (N=38; 19.7%), and fludarabine, cyclophosphamide and total body irradiation (200 cGy) (N=32; 16.6%). Donor HLA matching (considering HLA-A, -B, -C, and -DRB1) was 7/8 in 131 (67.9%) of participants, 6/8-matched in 51 (26.4%), and 4-5/8-matched in 11 (5.7%) participants. Median donor age was 25.5 years (range: 18.7-35.7). The one-year overall OS estimate was 79.6% (95% confidence interval [CI]: 73.2-84.7). Survival was similar among HLA 7/8-matched donor recipients (77.8%, 69.7-84%) and <7/8 matched donor recipients (83.7%, 71.8-90.9%). The one-year GVHD-free, relapse-free survival (GRFS) was 49.9% (42.6-56.9%) and the one-year progression-free survival was 70.2% (63.2-76.2%). The one-year cumulative incidence (CI) rates of NRM and relapse were 12.5% (8.3-17.6%) and 17.3%(12.3-23%), respectively. The 6-month CI of grade II-IV and grade III-IV acute GVHD were 40.0% (33.0-46.8%) and 7.8% (4.6-12.1%), respectively. The one-year incidence of all chronic GVHD and severe chronic GVHD were 15.6% (10.7-21.2%) and 3.7% (1.6-7%), respectively, by NIH consensus criteria. The CI of grade 1-4 cytokine release syndrome (CRS) by day 7 post HCT was 28.0% (21.8-34.9%), and grade 3-4 CRS was 0.5% (0-2.9%). Primary engraftment failure occurred in 9 (4.7%) participants. Among 145 evaluated participants, 85.5% were >95% donor in blood chimerism at day 100 post HCT. Within the first 100 days after HCT, CTCAE grade 2-5 infections occurred in 113 (58.5%) of participants and grade 3-5 infections occurred in 59 (30.6%) of participants. The most common etiologies of grade 2-5 infections were bacterial (N=78), followed by viral (N=48). The most common grade 3-5 non-infectious toxicities were cardiac disorders, which occurred in 4 (2.1%) of participants. In conclusion, the results including this expansion cohort demonstrate encouraging 1-year OS, NRM and relapse rates in RIC recipients of PTCy-based GVHD prophylaxis and PBSC allografts from MMUDs. This larger cohort of 193 recipients re-affirm the results from the initial cohort with greater robustness.Measures to mitigate infection risk are likely to further improve outcomes. Reducing the dose of PTCy is a candidate approach currently being tested in the ongoing OPTIMIZE trial (NCT 06001385).These results support the extension of PBSC MMUD using PTCy to individuals who lack an HLA-matched donor and require RIC HCT.

Abstract Allogeneic hematopoietic cell transplantation (HCT) remains inaccessible to many patients, particularly those of non-European ancestry, due to the limited availability of matched unrelated donors (URD). While single-HLA mismatched donors (7/8) often yield acceptable outcomes, URD HCT mismatched at ≥ 2 HLA alleles (<7/8) has historically been associated with poor survival and prohibitive toxicity. Post-transplant cyclophosphamide (PTCy) has improved outcomes following mismatched unrelated donor (MMUD) HCT, potentially enabling less stringent donor matching. Whether the degree of donor-recipient HLA disparity remains prognostic after MMUD HCT when PTCy is used is unknown. The ACCESS trial (NCT04904588) was conducted by the Center for International Blood and Marrow Transplant Research Clinical Research Organization and prospectively evaluated PTCy-based graft versus host disease (GVHD) prophylaxis in adult recipients of 4–7/8 (HLA-A, -B, -C and -DRB1) MMUD peripheral blood stem cells (PBSC) from donors age ≤35 years old following either myeloablative (MAC) or reduced intensity/non-myeloablative (RIC/NMA) conditioning. This analysis focused on all adult recipients of <7/8 grafts enrolled on the study across both conditioning strata, with descriptive comparison to patients who received 7/8 MMUD PBSC grafts. The primary endpoint was 1-year overall survival (OS). Secondary endpoints included primary graft failure (PGF), non-relapse mortality (NRM), relapse, acute and chronic GVHD, and GVHD-free relapse-free survival (GRFS). A total of 268 adults received MMUD PBSC grafts: 85 with <7/8 matches (MAC: n=23; RIC/NMA: n=62) and 183 with 7/8 matches (MAC: n=52; RIC/NMA: n=131). Among <7/8 recipients, median age was 57 years old (range, 24–78), 49% were male, with diagnoses of acute myeloid leukemia (AML) (55%), myelodysplastic syndromes (MDS) (15%), and lymphoma (14%). HLA mismatch distribution in the <7/8 group was 6/8 in 82%, 5/8 in 14%, and 4/8 in 4%. Most received fludarabine/melphalan (44%) or myeloablative busulfan/fludarabine (21%). Median CD34+ cell dose was 5.5 ×10^6/recipient kg (range: 3.2-8.0) and 75% of grafts were cryopreserved prior to infusion. Median donor age was 25.8 (range: 18.7-35.7) in the 7/8 group and 25.0 (range: 18.3-34.8) in the <7/8 group. The <7/8 cohort was racially and ethnically diverse, with 61% identifying as other than non-Hispanic white. The 7/8 cohort had a median age of 63 years old (range, 20–79), with 52% male. Disease distribution, conditioning intensity, and infused cell doses were similar to the <7/8 group. A smaller proportion of grafts were cryopreserved (61%), and 47% of patients identified as other than non-Hispanic White. One-year OS for <7/8 recipients was 86% (95% CI: 76–92%), compared to 79% (95% CI: 72–84%) in 7/8 recipients. One-year incidence of relapse was 23% (95% CI: 14–33%) in the <7/8 group and 17% (95% CI: 12–23%) in 7/8 recipients; NRM was 8% (95% CI: 4–16%) and 14% (95% CI: 9–19%), respectively. GRFS was 55% (95% CI: 43–65%) for <7/8 and 51% (95% CI: 44–58%) for 7/8 recipients. PGF occurred in 8% (95% CI: 3–18%) of <7/8 RIC recipients and 3% (95% CI: 1–8%) of 7/8 RIC recipients; no MAC recipients had PGF. At 6 months post-HCT, grade II–IV acute GVHD occurred in 34% (95% CI: 24–44%) of <7/8 patients and 39% (95% CI: 32–46%) of 7/8; grade III–IV acute GVHD was observed in 7% (95% CI: 3–14%) and 8% (95% CI: 5–13%), respectively. Moderate to severe chronic GVHD (NIH consensus criteria) at one year occurred in 8% (95% CI: 3–15%) of <7/8 recipients and 11% (95% CI: 7–16%) of 7/8 recipients. When grouped by conditioning intensity, 1-year outcomes within the <7/8 cohort were: OS 91% after MAC and 84% after RIC/NMA; relapse in 32% after MAC and 20% after RIC/NMA, respectively; GRFS was 53% for MAC and 55% for RIC/NMA; and NRM remained low at 9% after MAC and 8% after RIC/NMA. In this cohort of adult recipients of <7/8 MMUD PBSC grafts with PTCy-based GVHD prophylaxis enrolled on the ACCESS study, 1-year OS exceeded 80% and was comparable to 7/8 recipients. Relapse, NRM, and GVHD rates were similarly favorable and consistent with outcomes reported in 7/8 donor recipients. These findings support extending suitable MMUD match considerations to include 4-6/8 in the context of PTCy, potentially enabling near-universal donor access, while allowing for optimization of other non-HLA donor factors.

Abstract Introduction: Graft Failure (GF) is a rare but devastating outcome of HCT. Primary GF (PGF), defined as a failure of neutrophil recovery by Day+28, is straightforward to diagnose. Diagnosing secondary GF (SGF) is more challenging, with its broad time-range, multiple confounding diagnoses, and lack of predictive biomarkers. In BMT CTN1703/1801, we analyzed patients receiving RIC HCT for heme malignancies with either Tac/MTX (n=159) or PT-Cy (n=165) GVHD prophylaxis. SGF was defined as donor chimerism <5% after initial donor engraftment. With Tac/MTX, there were 3 PGF and 1 SGF diagnoses. With PT-Cy, there were 4 PGF and 6 SGF. Median SGF diagnosis was Day +64 (range: Day+28-215). There were too few Tac/MTX patients to analyze SGF, but sufficient events with PT-Cy. To identify PT-Cy SGF predictors, we leveraged lymphocyte, T, B, and NK cell reconstitution analysis. In SGF we found an early, profound deficit in the reconstitution of all major lymphocyte populations, including total lymphocytes, T, B, and NK cells, as early as Day+28. This enabled the modeling of a SGF risk classifier based on the Absolute Lymphocyte Count (ALC). Methods: Clinical ALC measurements were performed on all SGF patients (n=6) and on non-GF controls with ALCs available (146 of 155 non-GF patients). Flow cytometry was performed on all PT-Cy SGF patients (n = 6) and from a subset of non-GF controls (n = 18: controls were chosen as patients without relapse or severe GVHD, to reduce confounders introduced by immunologic interventions, and for whom all samples, including from the graft infusion, were available). T, B, and NK counts, as well as T cell subsets, were compared (using Welch's T test) on Days 7, 14, 21, 28, 42, 63, 98, 180, 270, 365, 730, with SGF patients censored on the day of GF diagnosis. To interrogate the optimal ALC cutoff, the cumulative incidence of SGF was computed at Days +28 and +42, with death without GF as a competing risk. Results: We have previously demonstrated that, compared to Tac/MTX, PT-Cy patients exhibited an early decrease in reconstitution of all T cell populations (with normal NK and B cell reconstitution). Here we focused specifically on PT-Cy patients with or without SGF. Graft CD34 counts/kg were not different between SGF patients and non-GF patients (mean CD34/kg = 1.38 x10e6 (SGF) vs 0.67 x10e6 (non-GF, p = 0.61) However, even amidst the overarching early suppression in T cell reconstitution with PT-Cy, SGF patients could be easily distinguished from the larger PT-Cy cohort, based on more profound deficits in ALC, T, B and NK cells reconstitution, measured using 2 strategies: (1) SGF patients demonstrated significant early (Day +28) quantitative defects in the reconstitution of the ALC (mean +/- SEM 262+/-32 cells/µL (non-GF) vs 60 +/- 25 (SGF, p<0.0001), CD4 T cells (62 +/- 12 cells/µL vs 19+/-15, p=0.048), CD8 T cells (15 +/-3 cells/µL vs 3.5 +/-1 p=0.0009), all CD8 T cell subpopulations, as well as NK cells (116+/-31 cells/µL vs 2.9+/-1.4 cells/µL, p= 0.002) and B cells (3.5 +/-1.4 cells/µL vs 0.16+/-0.07 p =0.03). (2) In SGF, there was a significant deficit in the rate of rise of all major lymphocyte populations between Days 28-42-60 vs non-GF, including CD4 T cells (p<0.0001), CD8 T cells (p = 0.0002), B cells (p<0.0001), and NK cells (p =0.048). These discoveries suggested that a classifier could be identified to risk-stratify patients for SGF. We explored an ALC cutpoint, amenable to standard clinical lab analysis. A statistically significant threshold was identified at both Days+28 and +42, with Day+42 being most predictive: A threshold of 120 cells/µL was identified as optimal, with landmark analysis documenting a SGF rate of 34.7% below the cutpoint, and SGF of 1% above it (HR = 45.9, 95% CI 5.7 - 366). Conclusions: Despite the small number of events, PT-Cy patients with SGF demonstrated a distinctive reconstitution trajectory that encompassed an early, substantial, and sustained deficit in all lymphocyte counts, as well as a lack of their longitudinal expansion. This enabled the discovery of a candidate ALC biomarker cutpoint at Day+42 that could distinguish patients who were more likely to develop SGF. If confirmed, these data could generate a predictive biomarker for SGF, which would enable the design of trials evaluating early interventions (e.g. CD34+ boosts, DLI, modification of immunosuppression) to improve outcomes for these patients.

Abstract The antiapoptotic protein, myeloid cell leukemia-1 (Mcl-1), contributes to the pathophysiology of acute myeloid leukemia (AML) and certain B-cell malignancies. Tumor dependence on Mcl-1 is associated with resistance to venetoclax. Voruciclib, an oral cyclin-dependent kinase (CDK) inhibitor targeting CDK9, indirectly decreases Mcl-1 protein expression and synergizes with venetoclax in preclinical models. This dose escalation study evaluated voruciclib in patients with previously treated hematologic malignancies. Initially, voruciclib was administered daily, continuously, on a 28-day cycle (group 1). After 2 patients with prior allogeneic stem cell transplantation had a dose-limiting toxicity (DLT) of interstitial pneumonitis at 100 mg, voruciclib administration was changed to days 1 to 14 of a 28-day cycle (group 2). Forty patients, 21 with AML and 19 with B-cell malignancies, were enrolled. Patients had a median of 3 prior lines of therapy (range, 1-8). Dose escalation in group 2 was stopped at 200 mg, a dose that achieved plasma concentrations sufficient for target inhibition, without DLTs observed. The most common adverse events were diarrhea (30%), nausea (25%), anemia (22%), fatigue (22%), constipation (17%), dizziness (15%), and dyspnea (15%). In AML, 1 patient achieved a morphologic leukemia-free state, and 2 had stable disease. Voruciclib treatment led to a decrease in MCL1 messenger RNA expression, downregulation of myelocytomatosis (MYC) and NF-κB transcriptional gene sets, and reduced phosphorylation of RNA polymerase 2. Voruciclib on intermittent dosing was well tolerated, with no DLTs, paving the way for evaluation of the combination of voruciclib with venetoclax for patients with previously treated AML. This trial was registered at www.clinicaltrials.gov as #NCT03547115.

Abstract Clonal cytopenia of undetermined significance (CCUS) represents a distinct disease entity characterized by myeloid-related somatic mutations with a variant allele fraction of ≥2% in individuals with unexplained cytopenia(s) but without a myeloid neoplasm (MN). Notably, CCUS carries a risk of progressing to MN, particularly in cases featuring high-risk mutations. Understanding CCUS requires dedicated studies to elucidate its risk factors and natural history. Our analysis of 357 patients with CCUS investigated the interplay between clonality, cytopenia, and prognosis. Multivariate analysis identified 3 key adverse prognostic factors: the presence of splicing mutation(s) (score = 2 points), platelet count of <100 × 109/L (score = 2.5), and ≥2 mutations (score = 3). Variable scores were based on the coefficients from the Cox proportional hazards model. This led to the development of the clonal cytopenia risk score (CCRS), which stratified patients into low- (score of <2.5 points), intermediate- (score of 2.5 to <5), and high-risk (score of ≥5) groups. The CCRS effectively predicted 2-year cumulative incidence of MN for low- (6.4%), intermediate- (14.1%), and high-risk (37.2%) groups, respectively, by the Gray test (P < .0001). We further validated the CCRS by applying it to an independent CCUS cohort of 104 patients, demonstrating a c-index of 0.64 (P = .005) in stratifying the cumulative incidence of MN. Our study underscores the importance of integrating clinical and molecular data to assess the risk of CCUS progression, making the CCRS a valuable tool that is practical and easily calculable. These findings are clinically relevant, shaping the management strategies for CCUS and informing future clinical trial designs.