Grade II-IV Acute GVHD Research Articles

Favorable Outcomes with Low Dose Anti Thymocyte Globulin Based Graft Versus Host Disease Prophylaxis after Mismatched Unrelated Donor Allogenic Hematopoietic Cell Transplantation

DISCUSSION INTRODUCTION Anti thymocyte globulin (ATG) based Graft versus Host disease (GVHD) prophylaxis is widely used for unrelated donor allogeneic hematopoietic cell transplantation (HCT) although the optimal dose remains unclear. Recently, registry based and single centre retrospective analyses have suggested superior outcomes with the PTCy based GVHD prophylaxis regimens when compared to ATG based regimens in mismatched unrelated donor (MMUD) allogeneic HCT, however, these studies all used doses of ATG ≥ 5mg/kg. Outcomes following MMUD allogeneic HCT with lower dose ATG based GVHD prophylaxis regimens have not been extensively studied. Thus, we analysed outcomes of HLA 9/10 MMUD allogeneic HCTs using two low dose ATG based regimens as GVHD prophylaxis at our centre. All adult patients undergoing standard of care allogenic hematopoietic cell transplant at The Ottawa Hospital from January 1 st 2015- December 31, 2022 were included. Data regarding demographics, HLA mismatched allele, conditioning regimen, dose of ATG, time to engraftment, and rates of acute and chronic GVHD was collected. The primary outcome evaluated was overall survival (OS) and secondary outcomes were GVHD-free relapse-free survival (GRFS), cumulative incidence of relapse (CIR) and non-relapse mortality (NRM). Survival outcomes were analyzed using Kaplan Meier analysis. Predictors of survival were identified using Cox-proportional hazards regression model. 77 patients (Males 62.3% (n=48); Median age - 50 years) underwent allogeneic HCT from MMUD. Most common indication for transplant was MDS/AML in 66.2% (n=51) followed by ALL in 11.3% (n=9) patients. Most frequently mismatched locus was HLA A in 37.7% (n= 29) followed by HLA B in 14.3% (n=11). Myeloablative conditioning regimen was received by 76.6% (n=59) while reduced intensity regimens were used in 23.4% (n=18) patients. Rabbit ATG was part of the GVHD prophylaxis regimen in all patients with majority (81%; n=63) receiving 2.5mg/kg and remaining 18.2% (n=14) receiving 4.5mg/kg of the drug. Grade II-IV acute GVHD occurred in 24.7% (n=19) while chronic GVHD occurred in 32.5% (n= 25) patients. After a median follow up of 21 months, relapse occurred in 28.6% (n=22) patients. Two year OS (Fig 1), and GRFS of the whole cohort were 60.6% and 45.3% respectively. 2-year incidence of non-relapse mortality (NRM) and cumulative incidence of relapse (CIR) were 16.9% and 18.2% respectively. Dose of ATG (2.5 mg/kg vs 4.5 mg/kg) was not a predictor of outcomes in either univariate and multivariate analyses. Age more than 50 years, primary diagnosis of lymphoma, reduced intensity conditioning and mismatch in loci other than HLA C were significant predictors of poor OS after univariate analysis. Only primary diagnosis of lymphoma (Hazard Ratio (HR) - 7.76; p=0.045) and mismatch in loci other than HLA C (HR - 9.53; p=0.03) were significant predictors of poor OS after multivariate analysis. When compared to published single centre and registry-based studies using ATG doses ≥ 5 mg/kg, GVHD prophylaxis using ATG doses ≤4.5 mg/kg seems to provide improved outcomes in patients undergoing allogeneic HCT from mismatched unrelated donors (Table 1). Our findings suggest that further studies are needed directly comparing lower dose ATG based regimens to PTCy based regimens to determine the ideal GVHD prophylaxis regimen for patients undergoing allogeneic HCT from HLA mismatched unrelated donors.

Phase II Trial of Reduced-Intensity Fludarabine, Melphalan, and Total Body Irradiation Conditioning Results in Favorable Outcomes with Haploidentical Donor Peripheral Blood Stem Cell Transplant

Introduction High risk hematologic malignancies are curable with allogeneic hematopoietic cell transplant (HCT). Haploidentical (haplo) HCT with post-transplant cyclophosphamide (PTCy) has improved access to transplant in patients lacking an HLA matched donor. However, traditional reduced-intensity conditioning (RIC) with fludarabine/cyclophosphamide/total body irradiation (TBI) for haplo HCT with PTCy is marred by high rates of relapse. This study seeks to optimize the RIC haplo HCT with PTCy platform in older adults with a slight intensification in conditioning and the use of peripheral blood stem cell (PBSCT) grafts in lieu of bone marrow grafts (BMT). Additionally, tacrolimus was substituted by sirolimus based on prior phase II data suggesting favorable rates of graft-versus-host disease (GVHD) after haplo PBSCT with PTCy (Bejanyan, Blood Adv. 2021). We hypothesized that this approach could successfully reduce the risk of relapse and improve disease-free survival (DFS) without substantially increasing non-relapse mortality (NRM). Methods: This single arm, single center phase II trial of haplo PBSCT used a RIC regimen consisting of Melphalan 70 mg/m 2 IV on day -6, fludarabine 30mg/m 2 IV daily on days -6 to -2, and TBI 200 cGy on day -1 (NCT04191187). Subjects received haplo PBSCT with a target dose of 5 x 10 6 CD34+ cells/kg and capped at 7 x 10 6 CD34+ cells/kg. GVHD prophylaxis consisted of PTCy 50 mg/kg on days +3 and +4, mycophenolate mofetfil (MMF) 1 gram three times daily from days +5 to +35, and sirolimus initiated at a target trough of 8-14 ng/mL on day +5 and tapered off between days +100 and +180. Eligibility criteria required a hematologic malignancy as the indication for allogeneic HCT and either age >55 years or a hematopoietic cell transplant comorbidity index (HCT-CI) > 3. The primary endpoint of this study is DFS with a hypothesis that the experimental regimen would have an 18 month DFS of 60% compared to a historic DFS of 40% and 90% power to reject the null hypothesis. Results: A total of 34 subjects were treated on the trial. The median age was 66 years (range: 31-74 years). The HCT-CI score was > 3 in 41%. Acute myeloid leukemia (AML, 44%) was the predominant indication for transplant followed by myelodysplastic syndromes (MDS, 29%). Nine patients (26%) were from underrepresented racial/ethnic minorities (those other than non-Hispanic white). Five patients (15%) received tacrolimus for GVHD prophylaxis before a protocol amendment changed the regimen to sirolimus for the remaining 29 patients (85%). The median follow-up time for 25 surviving patients was 28.5 months . The trial met the primary endpoint with 18-month DFS of 70.5% (90% CI > 59.1%, p=0.002). We observed no primary graft failure events. Neutrophil engraftment by day 30 was achieved in 30 patients (88%), and platelet engraftment by day 60 was achieved in 28 patients (82%). The cumulative incidence of grade II-IV acute GVHD at day 100 was 11.8% (95% CI: 3.6-25.1%). The cumulative incidence of moderate to severe chronic GVHD at 18 months was 9.1% (95% CI: 2.2-22.0%). At 18 months, the cumulative incidence of NRM was 17.7% (95% CI: 7.0-32.2%) and of relapse was 11.9% (3.7-25.4%). GVHD-free relapse-free survival at 18 months was 61.4% (95% CI: 42.9-75.5%) and the overall survival at 18 months was 73.3% (95% CI: 54.9-85.1%). Conclusion: In this completed phase II trial of fludarabine, melphalan 70 mg/m 2, TBI with haplo PBSCT and PTCy/sirolimus/MMF, the primary endpoint was met with an 18-month DFS that was superior to historical control. This was attributable to low rates of relapse without excessive NRM. Acute and chronic GVHD rates were favorable. Pharmacogenomic and pharmacokinetic correlative data is pending and will be included in the final presentation. These promising results merit further investigation to potentially establish this platform as a new standard approach to RIC haplo PBSCT.

Comparative Study for Haplo, MSD and MUD Allo-Hcts for Core-Binding Factor AML Patients in CR2: A Study from the Global Committee and the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation

Background Although core-binding factor acute myeloid leukemia (CBF-AML) generally has a favorable prognosis, relapse occurs in ~40% of cases. Allogeneic hematopoietic cell transplantation (allo-HCT) is recommended when patients achieve second complete remission (CR2). However, transplant outcomes and donor preference for these patients remain unclear. We compared in an EBMT global multi-center registry-based analysis the outcomes following allo-HCT using either haploidentical donors (HAPLO), matched siblings donors (MSD), or 10/10 matched unrelated donors (MUD). Methods Data from 865 de novo adult CBF AML patients in CR2 receiving allo-HCT in 227 EBMT centers from 2010-2022 were analyzed. Transplants from mismatched UD (<10/10), umbilical cord blood or grafts with ex-vivo manipulation were excluded. Univariate analyses and Cox regression models were used. Results Results from 329 MSD, 374 MUD, and 162 HAPLO HCTs were analyzed. For the entire cohort, median age was 43y (range: 18-76). Inv(16)/CBFBMYH11 was detected in 503 patients (58%) and t(8;21)/RUNX1-RUNX1T1 was detected in 362 patients (42%). Peripheral blood was the major graft source (86.1%), and myeloablative conditioning was used for the majority (60.1%) of all allo-HCTs. Female-to-male transplants were more common in the MSD group (25.5%) than in the HAPLO (19.8%) or MUD (14.2%) group, respectively (p<0.01). 83% of patients in the HAPLO group received post transplant cyclophosphamide (PTCy) as graft-versus-host disease (GVHD) prophylaxis. Engraftment rates were higher in the MSD (98.8%) and MUD (98.9%) than in the HAPLO (94.9%) group (p<0.01). Original disease was the major cause of death for the MSD and MUD cohorts, while in the HAPLO group, it was infection. On univariate analysis, HAPLO HCT was associated with a higher 2-year non-relapse mortality (NRM) (MSD 17.1%, MUD 15.3%, HAPLO 25.7%). The 180-day cumulative incidence of grade II-IV acute GVHD was higher in HAPLOs (14.8%) than in MSD (6.8%) or MUD (7.9%) recipients, respectively . No significant difference was observed among the three cohorts for 2-year leukemia-free survival (LFS), overall survival (OS) and GVHD-free/relapse free survival (GRFS). CBF-AML with inv(16) was associated with lower relapse incidence RI (18.1%) than with t(8;21) (28.3%), which contributed to better OS (75.7% vs 59.8% at 2 years), LFS (65.8% vs 51.2%) and GRFS (50.8% vs 38.5%) . Older patient age i.e., above the median age, was associated with a higher NRM (22.4% vs 13.3%) and a lower OS (63.8% vs 74.8%) than younger age i.e., below the median age. Peripheral blood grafts were associated with higher incidences of chronic GVHD (41.5% vs 25.8%) and extensive cGVHD (21.6% vs 9.7%) than bone marrow grafts. On multivariate analysis, no significant difference was observed among HAPLO, MSD and MUD allo-HCTs on NRM. HAPLO HCT was associated with lower RI compared to MSD (hazard ratio [HR]=0.56, 95% CI 0.32-0.97; p<0.05) and MUD (HR=0.57, 95% CI: 0.33-0.99, p<0.05) while there was no significant differences between the 3 types of donors on LFS, OS and GRFS. CBF-AML with t(8;21) was associated with both higher RI (HR=1.79, 95% CI 1.3-2.47; p<0.01) and higher NRM (HR=1.58, 95% CI 1.1-2.27; p<0.01) than CBF-AML with inv(16), which led to worse LFS, OS and GRFS. Higher age (per 10 year) was associated with higher risk of NRM (HR=1.29, 95% CI 1.11-1.5; p<0.01) and worse OS (HR=1.13, 95% CI 1.01-1.27; p=0.03). Conclusions For CBF-AML patients in CR2, haploidentical HCTs were associated with a lower RI compared to MSD and MUD allo-HCTs. HAPLO achieved similar LFS, OS and GRFS to MSD or MUD, respectively. In addition, CBF AML with inv(16) had better outcomes than with t(8;21) after allo-HCT.

Post-Transplant Cyclophosphamide-Based Graft-Versus-Host Disease Prophylaxis in HLA-Matched and Haploidentical Donor Transplants for Patients with Hodgkin disease: A Comparative Study of the LWP EBMT

INTRODUCTION Post-transplant cyclophosphamide (PTCy) has proven to be a highly effective strategy in preventing graft-versus-host disease (GVHD) in haploidentical (haplo) hematopoietic stem cell transplantation (HSCT), but it is being increasingly used in HLA-matched transplants. The outcomes of haplo HSCT with PTCY in various hematologic malignancies, particularly in relapsed/refractory Hodgkin disease (HD), have shown promising results, challenging those obtained in transplant patients from HLA-matched donors without PTCy. However, there is limited information on the impact of donor types on the outcomes of patients with HD undergoing allogenic HSCT when using homogeneous GVHD prophylaxis with PTCy. To address this knowledge gap, we have conducted an extensive study using the Lymphoma Working Party of the European Society for Blood and Marrow Transplantation (LWP-EBMT) registry. The aim of this study was to compare the outcomes of patients with HD undergoing HSCT from both HLA-matched donors, which include matched sibling donors (MSD) and matched unrelated donors (MUD), and haplo donors, using PTCy as GVHD prophylaxis approach in all cohorts. PATIENTS AND METHODS Inclusion criteria All adults (≥ 18 years) patients diagnosed with HD who underwent their first HSCT between January 2010 and December 2020 from either a MSD, MUD or haplo, and whose data were reported to the EBMT registry were included. For the purposes of this study, only transplants who received PTCy-based as GVHD prophylaxis were considered. Statistical Analysis The study utilized statistical methods such as Kaplan-Meier estimation, Log-Rank test, competing risks analysis, and Cox proportional hazards regression. The analyses included OS, PFS, NRM, aGVHD, cGVHD, and graft failure. The statistical software R and packages were used. RESULTS Patient and Transplantation Characteristics Patient, disease and transplant-related characteristics of the 860 patients are summarized in Table 1. Engraftment The cumulative incidence (Cum Inc) of neutrophil recovery at day 30 was 95% (95% CI, 93-96) in the HLA-matched group and 96% (95% CI, 91-98) in the haplo cohort (p=0.18). The 60-day Cum Inc of platelet recovery in similar order was 94% (95% CI, 88-97) and 86% (95% CI, 83-88) (p<0.001). GVHD The Cum Inc of acute GVHD grade II-IV at 100 days in the HLA-matched and the haplo cohorts was 24% (95% CI, 17-31) and 34% (95% CI, 30-37), respectively (p=0.01), whereas for grade III-IV it was 8% (95% CI, 4-13) and 10% (95% CI, 8-13), (p=0.44). In multivariable analysis (table 2), haplo was associated with an increased risk of acute GVHD grades II-IV, when compared with HLA-matched (HR 0.65; 95% CI, 0.46-0.93; p=0.01). Other variables are shown in table 2. The 2-year Cum Inc of chronic GVHD in the HLA-matched and haplo cohorts was 26% (95% CI, 19-33) and 27% (95% CI, 24-31), respectively (p=0.75). Other variables are shown in table 2. NRM and relapse The Cum Inc of NRM at 2 years was 10% (95% CI; 6-16) for HLA-matched and 18% (95% CI; 15-21) for haplo (p=0.02). In multivariable analysis (table 2), haplo was associated with an increased risk of NRM, when compared to HLA-matched (HR 0.5; 95% CI, 0.28-0.89; p=0.01). Other variables are shown in table 2. The Cum Inc of relapse at 2 years was 22% (95% CI; 15-29) for HLA-matched and 24% (95% CI; 20-27) for haplo (p=0.81). Other variables are shown in table 2. Survival The 2-year OS for the HLA-matched and haplo cohorts was 82% (95% CI; 75-88) and 70% (95% CI; 67-74), respectively (p=0.002). In multivariable analysis (table 2), compared to HLA-matched, haplo (HR, 0.51; 95% CI, 0.34-0.77; p=0.001) was associated with worse survival. Other variables are shown in table 2. The 2-year PFS was similar between HLA-matched and haplo (66%; 95% CI, 58-74; and 58%; 95% CI, 54-62, respectively; p=0.17). Other variables are shown in table 2. Comparison of outcomes for MSD and MUD With regards to the donor type, most posttransplant outcomes did not exhibit significant differences, except for a higher incidence of grades II-IV acute GVHD in the MUD group (33%; 95% CI, 32-44) compared to the MSD group (17%; 95% CI, 10-25) (p=0.01). CONCLUSION Our study shows that in patients with HD undergoing HSCT with PTCy for GVHD prophylaxis, no significant differences in 2-year PFS were observed between HLA-matched and haplo. A higher risk of acute GVHD and NRM is associated with haplo, leading to lower OS compared to HLA-matched transplantation.

Mismatched Unrelated Donor Transplantation with Ptcy-Based Gvhd Prophylaxis Is Associated with Better Survival Than Double Unit Umbilical Cord Blood Transplantation in Patients with AML in First CR: A Study from the ALWP of the EBMT

Background: The best donor option for acute myeloid leukemia (AML) patients lacking an HLA-matched donor has remained unknown. The recently reported BNT CTN 1101 trial observed higher non-relapse mortality (NRM) and lower overall survival (OS) in patients randomized to double-unit unrelated umbilical cord blood transplantation (dCBT) in comparison to those randomized to HLA-haploidentical bone marrow transplantation with post-transplant cyclophosphamide (PTCy)-based graft-versus-host disease (GVHD) prophylaxis 1. In addition, recent registry studies observed at least as good transplantation outcomes in AML patients given grafts from 9/10 HLA-matched unrelated donor (UD 9/10) with PTCy-based GVHD prophylaxis as those given grafts from HLA-haploidentical donors 2,3. These observations prompted us to perform a retrospective registry study comparing hematopoietic cell transplantation (HCT) outcomes between UD 9/10 and dCBT. Methods: Inclusion criteria consisted of adult patient, AML in CR1 at transplantation, either peripheral blood stem cells (PBSC) from UD 9/10 with PTCy as GVHD prophylaxis or dCBT, transplantation between 2013 and 2021, and no in vivo T-cell depletion. Results: A total of 208 dCBT patients and 270 UD 9/10 allo-HCT were included. The 180-day cumulative incidence of grade II-IV acute GVHD was 29% in UD 9/10 versus 44% in dCBT recipients (P=0.001). The 2-year cumulative incidences of relapse and of NRM were 23.5% and 12.5%, respectively, in UD 9/10 recipients versus 27% (P=0.39) and 18% (P=0.07), respectively in dCBT recipients. Two-year OS and LFS were 70% and 64%, respectively, in UD 9/10 recipients versus 60% (P=0.016) and 55% (P=0.028), respectively in dCBT recipients. In multivariate analyses, in comparison with UD 9/10 recipients, dCBT patients had a higher non-relapse mortality (HR=2.35, 95% CI: 1.23-4.48; P=0.01), comparable relapse incidence (HR=1.12, 95% CI: 0.67-1.86; P=0.66), lower leukemia-free survival (HR=1.5, 95% CI: 1.01-2.23; P=0.047), and lower overall survival (HR=1.66, 95% CI: 1.08-2.55; P=0.02). Conclusions: In summary, our results suggest that transplantation outcomes are better with UD 9/10 with PTCy-based GVHD prophylaxis than with dCBT for AML patients in CR1. These data might support the use of UD 9/10 with PTCy-based GVHD prophylaxis in AML patients lacking an HLA-matched donor. References Fuchs, E. J. et al. Double unrelated umbilical cord blood vs HLA-haploidentical bone marrow transplantation: the BMT CTN 1101 trial. Blood 137, 420-428 (2021).Baron, F. et al. Comparison of HLA-mismatched unrelated donor transplantation with post-transplant cyclophosphamide versus HLA-haploidentical transplantation in patients with active acute myeloid leukemia. Bone Marrow Transplant. 57, 1657-1663 (2022).Battipaglia, G. et al. Post-transplant cyclophosphamide in one-antigen mismatched unrelated donor transplantation versus haploidentical transplantation in acute myeloid leukemia: a study from the Acute Leukemia Working Party of the EBMT. Bone Marrow Transplant. 57, 562-571 (2022).

Reconstitution Dynamics and Impact on Clinical Outcomes of Mucosal-Associated Invariant T-Cells in Pediatric Patients Receiving Allogeneic Hematopoietic Stem Cell Transplantation

Background Understanding the reconstitution of all immune system components after allogeneic hematopoietic stem cell transplantation (HSCT) is crucial to optimize the prevention of infections, leukemia relapse and graft-versus-host disease (GvHD), thus improving patient's outcome. Mucosal-associated invariant T (MAIT) cells have received major interest in the field for their ability to respond to fungal and bacterial infections and control mucosal homeostasis in the GvHD context. However, the impact of MAIT cell recovery on T-cell immunity and on patient outcomes after HSCT remains not fully characterized. Patients and study design We retrospectively analyzed 156 consecutive patients (median age 8.5 years, range 0.6-24.7) affected by malignant hemopathies undergoing HSCT between April 2019 to May 2022, fully engrafted at day+30 after receiving the graft from an unrelated matched (MUD) or mismatched (mMUD) donor (n=52 and n=11, respectively) or from an HLA-haploidentical (Haplo) donor (n= 93) after alpha-beta T-/CD19-cell depletion. Conditioning regimen was myeloablative, TBI- (n=120) or chemo-based (n=36) in all patients. GvHD prophylaxis included short course methotrexate, anti-thymocyte globulin, cyclosporin with or without abatacept 10mg/kg at day -1,+5,+14,+28,+42,+60 for patients transplanted from mMUD or MUD, respectively. Haplo-HSCT patients did not receive any post-HSCT pharmacological prophylaxis. Patient characteristics are listed in Table 1. We investigated T and, in particular, MAIT cell recovery up to 2 years after HSCT and their correlation with clinical outcomes. Results With a median follow-up of 27 months (range 2-49), the overall survival (OS), disease-free survival (DFS) and non-relapse mortality (NRM) of the entire cohort were 78,5% (95%CI 70-84), 70% (95%CI 62-77) and 6% (95%CI 3-11), respectively. The cumulative incidence (CI) of relapse was 23% (95%CI 17-31). CI of grade II-IV acute GvHD (aGvHD) was 19.7% (95%CI 14-27), while CI of chronic GvHD (cGvHD) was 15% (95%CI 10-22) with a CI of moderate-severe cGvHD of 10% (95% CI 6-16), resulting in a cGvHD-free, relapse-free survival (GRFS) of 63% (95%CI 54-69). CI of post-HSCT CMV reactivation was 35% (95%CI 28-43); 13 and 22 patients experienced pre-engraftment or late blood stream infections (BSI) (CI 8%, 95%CI 5-13 and 14%, 95%CI 9-20, respectively). While total abT cells reached normal levels between 1 and 2 years post-transplantation, MAIT cells showed prolonged impaired reconstitution up to 2 years post-HSCT. Compared to UD-HSCT, MAIT cell recovery after Haplo-HSCT was significantly delayed. Interestingly, across all time points analyzed, we observed that a large fraction of MAIT cells were negative for CD161, a marker canonically expressed on MAIT cells. We also found that MAIT cells showed prolonged functional impairment as demonstrated by the increased expression of the activation (CD25, CD38), exhaustion (PD1, TIM3) and senescence (CD57) markers, as well as by the suboptimal response to ex vivo T-cell activation 1 year post HSCT. OS, DFS and NRM were not influenced by the absolute number and proportion of MAIT cells when assessed 30 days post-HSCT. Interestingly, higher absolute count of MAIT at +30 was associated with higher CI of aGvHD (27% vs 11%, p=0.04) in univariate analysis. Furthermore, an higher proportion of MAIT cells at the same time point, as well as the use of mMUD as donor, were associated as independent factors with a higher CI of all grades of cGvHD (25% vs 8%, p=0.01 and 74% vs 12%, p<0.001, respectively) and moderate-severe cGvHD (17% vs 4% p=0.024 and 59% vs 8% p=0.017, respectively), resulting in lower GRFS in patients with an higher proportion of MAIT cells at +30 (72% vs 52%, p=0.019) (Fig. 1). Univariate analysis also showed that patients with higher absolute values of MAIT had a lower CI of late BSI (17% vs 35%, p=0.05) but experienced more frequently CMV reactivation (44% vs 26%, p= 0.029) which occurred more in Haplo- and mMUD-recipients compared to MUD-patients (41.2% and 45.4% vs 21.2%, p=0.029). Conclusions Our study shows that MAIT cell recovery is significantly impaired in terms of absolute number and function in patients receiving HSCT. Evaluation of MAIT cells at early time points after HSCT may represent a useful parameter to identify patients at risk of late BSI, cGvHD and CMV reactivation. Additional studies are needed to further assess the biological function of MAIT cells.

Maintenance Ruxolitinib Is Associated with Low Rates of Chronic Gvhd Requiring Systemic Treatment in Older Adults with AML/MDS Undergoing Allogeneic HCT: Results of a Phase II Multicenter Trial

Introduction: Despite recent advances in graft-versus-host disease (GVHD) prophylaxis, novel approaches to effective prevention of chronic GVHD remain of utmost importance. This is particularly true for older transplant recipients,for whom high-dose cyclophosphamide or prolonged treatment with corticosteroids is challenging. Ruxolitinib, an oral selective inhibitor of JAK1/2, is FDA-approved for the treatment of refractory acute and chronic GVHD. However, the clinical efficacy of JAK inhibition in preventing severe chronic GVHD is not well characterized. Methods: In this prospective, multicenter phase II trial (NCT03286530), older adult subjects (age 60-80) with AML in CR1 or MDS undergoing RIC allogeneic HCT were enrolled. Transplants could be conducted from HLA-matched related donors or 7/8 or 8/8 HLA-matched unrelated donors. Transplants were required to use busulfan- or melphalan-based reduced intensity conditioning and peripheral blood stem cells. Standard GVHD prophylaxis consisted of tacrolimus and methotrexate (5-10 mg/m 2 on Days +1, +3, and +6 ± +11). Subjects were enrolled prior to transplant. Ruxolitinib therapy could begin between Day +30 and Day +100, after meeting pre-treatment criteria, which included: donor engraftment, ongoing remission confirmed by biopsy, adequate hematopoietic recovery (Hgb ≥8 g/dL, PLT ≥50K/uL), and the absence of progressive acute GVHD. Ruxolitinib was administered at 10 mg BID continuously in 28-day cycles (allowing for dose reductions due to drug interactions or cytopenias), for up to 24 cycles. The primary objective was to evaluate the GRFS at 1-year after HCT. Key secondary objectives included the cumulative incidence of chronic GVHD, acute GVHD, and relapse, as well as overall survival. Results: Seventy-eight subjects were enrolled, and 63 subjects received ruxolitinib on trial. The reasons for not initiating ruxolitinib were acute GVHD (n=4), physician discretion (n=3), disease relapse (n=2), low chimerism (n=2), death (n=2), primary graft failure (n=1), and subject withdrawal (n=1). In the treated subjects, the median age was 68 years (range, 61-79). Fifty-five (87.3%) subjects had AML and 8 (12.7%) had MDS. Transplants were performed from HLA-matched related (n=16, 25.4%) or unrelated (n=47, 74.6%) donors with either Fludarabine/Melphalan (n=34, 54%) or Fludarabine/Busulfan (n=29, 46%). The median start date of ruxolitinib after HCT was day 45 (range, 32-93). The median follow-up of survivors was 19 months (range, 3-64) at last cutoff (2/14/23). At the time of analysis, the median number of cycles on treatment is 14 (range, 1-24). 17 subjects remain on therapy; the reasons for discontinuation include completed treatment (n=21), disease relapse (n=13), adverse events (n=7), and physician discretion (n=5). The most common (severe grade ≥3) adverse events experienced while on ruxolitinib were neutropenia (n=18, 29% of subjects), thrombocytopenia (n=17, 27% of subjects), and anemia (n=16, 25% of subjects). Seven subjects experienced grade ≥3 infectious events; no fungal infections have occurred. In subjects receiving ruxolitinib, the 6-month cumulative incidence of Grade II-IV acute GVHD was 14% (95%CI, 7-24) and Grade III-IV acute GVHD was 4.8% (95%CI, 1.3-12), with three cases of grade II-IV GVHD occurring prior to initiation of ruxolitinib. While the 12-month incidence of all cases of chronic GVHD is 27% (95%CI, 17-39), the 12-month incidence of chronic GVHD requiring systemic therapy is 8.4% (95%CI, 3.1-17). The 18-month cumulative incidence of NRM is 5.6% (95%CI, 1.4-14); with only one death attributed to GVHD and one death due to infection (COVID-19), thus far. The 18-month cumulative incidence of disease relapse is 27% (95%CI, 16-39). The 12-month GRFS (primary endpoint) is 70% (95%CI, 56-80). The 18-month OS, PFS, and CRFS are 78% (95%CI, 64-88), 68% (95%CI, 53-78) and 64% (95%CI, 50-76), respectively ( Figure 1). Conclusion: Prolonged administration of ruxolitinib following allogeneic HCT is associated with low rates of chronic GVHD requiring systemic treatment. The incidence of relapse is comparable to historical rates, suggesting no compromise of GVL effect. Despite the anticipated cytopenias with therapy, most subjects were able to remain on treatment. The incorporation of JAK inhibition into GVHD prevention approaches warrants further investigation.

Haematopoietic Stem Cell Transplantation for Hepatitis-Associated Aplastic Anaemia: Clinical Characteristics, Outcomes and Risk Factors

Introduction: Hepatitis-associated aplastic anaemia (HAAA) is a severe and life-threatening condition that requires effective treatment approaches. Hematopoietic stem cell transplantation (HSCT) has emerged as a promising therapeutic option for HAAA patients. In this retrospective study, we aimed to investigate the clinical characteristics, outcomes, and prognostic factors associated with HSCT in HAAA patients at a prominent Chinese blood disease hospital between 2008 and 2022. Methods: A comprehensive review of 35 HAAA patients who underwent HSCT was conducted, and clinical data were analyzed to determine the treatment's efficacy and safety. The patients were primarily categorized into those with severe AA (28.6%) and very severe AA (65.7%), with a predominant male representation (68.6%) and a median onset age of 23 years (range, 9-44). Both haploidentical and matched sibling donors were utilized in comparable proportions. Results: The study revealed a promising 5-year overall survival (OS) rate of 74.0% after HSCT, underscoring the effectiveness of this treatment approach in HAAA patients. However, certain factors significantly impacted survival rates and treatment outcomes. Prolonged intervals from diagnosis to HSCT (>=75 days), acute graft-versus-host disease (GVHD), and post-HSCT liver events, such as hepatic GVHD and a three-fold increase in aminotransferase or bilirubin, were found to worsen 5-year OS. Interestingly, higher doses of mononuclear cell count, CD34+, CD3+, CD4+, and CD8+ cells in allografts were associated with poorer OS or graft failure-free survival (GFFS), suggesting that pursuit of higher cell counts in certain cases may be counterproductive. Furthermore, a close examination of the multivariate models revealed that recipients who received sex-matched grafts experienced better OS, while those with younger male donors had a lower incidence of grade II-IV acute GVHD. Moreover, a higher HLA matching degree (HLA >=7/10) between the recipient and donor emerged as an independent prognostic factor associated with better OS and GFFS. Conclusion: This study highlights the safety and efficacy of HSCT as a treatment modality for HAAA patients. Early transplantation, careful donor selection, and efforts to improve post-transplant liver events were identified as crucial factors to optimize treatment outcomes. While the use of certain cells in higher doses may have a negative impact on survival, the importance of achieving a high HLA matching degree cannot be overstated. Moving forward, these findings can serve as valuable insights in guiding the management and treatment decisions for HAAA patients undergoing HSCT. Further research and continuous improvement in transplantation protocols will undoubtedly advance the success rates and long-term prognosis for individuals afflicted with this challenging condition.

JAK2/mTOR Inhibition Fails to Prevent Acute Gvhd Despite Reduced Th1/Th17 Cells: Final Phase II Trial Results

Introduction: Our phase I graft-versus-host disease (GVHD) prevention trial of pacritinib (recommended phase II dose: 100mg po BID day 0 to +70, dose level 2) plus sirolimus (8-14ng/ml) and tacrolimus (3-7ng/ml) (PAC/SIR/TAC) demonstrated the regimen was safe and free of pan-JAK myelosuppression after allogeneic hematopoietic cell transplantation (alloHCT). PAC inhibits JAK2 with no activity against JAK1, avoiding off-target suppression of IL-2 required by Tregs. JAK2/STAT3 activity mediates IL-6, IL-12, and IL-23 receptor signaling and subsequent pathogenic Th1 and Th17 differentiation. JAK2/mTOR blockade supports Treg potency, providing further rationale for the PAC/SIR/TAC combination. Herein we report on our completed phase II trial of PAC/SIR/TAC after 8/8-HLA matched alloHCT. Methods: This single-arm phase II trial (NCT02891603) was powered to determine if PAC/SIR/TAC suppressed %pSTAT3 + CD4 + T cells at day +21 (primary endpoint: %pSTAT3 + CD4 + T cells ≤ 35%) and determine the cumulative incidence of grade II-IV acute GVHD by day +100. We also evaluated the impact of PAC/SIR/TAC on CD4 T cell differentiation (Treg, Th1, Th17) and related CD28 (pS6 and pH3ser10) and IL-2 receptor (pSTAT5) signal transduction after alloHCT. Eligible patients (n=28) received alloHCT for AML, MDS, ALL, and MF. Reduced (n=21) or myeloablative (n=7) intensity conditioning was permitted. HLA-A, -B, -C, and -DRB1 matched-related (n=7) or unrelated donors (n=21) were allowed. Adequate vital organ function and Karnofsky performance status (KPS ≥ 80%) were required. Results: PAC/SIR/TAC (PAC 100mg BID) met the primary endpoint of the phase II study, reducing %pSTAT3 + CD4 + T cells to 9.62% at day +21 ( Figure 1A). PAC/SIR/TAC significantly improved CD4 + T cell STAT5 phosphorylation at day +21, increasing the ratio of pSTAT5 + to pSTAT3 + CD4 + T cells (ratio 80.7 v 1.71 P<0.0001) compared to dose level 1 PAC/SIR/TAC of the phase I trial that lacked effective JAK2 blockade (PAC 100mg daily, day +21 %pSTAT3 + CD4 + T cells 59.5%). Partial CD28 signaling blockade was achieved by PAC/SIR/TAC compared to dose level 1, with suppression of mTOR (%pS6 + CD4 + T cells 7.67 v 22.5% P=0.0009) but only modest inhibition of Aurora kinase A activity (%pH3ser10 + CD4 + T cells 71.3 v 98.6% P<0.0001), a pathway for escape alloreactivity. Th1 (0.01 v 0.03 k/µl P=0.026) and Th17 (0.016 v 0.032 P=0.031) cells were reduced at day +21, increasing the ratio of Tregs to Th1 and Th17 cells (0.84 v 0.21 P=0.043) with PAC/SIR/TAC compared to dose level 1. Like JAK2 KO murine T cells, Th2 cells at day +21 were increased with PAC/SIR/TAC (0.056 v 0.001 k/µl P=0.036), compared to dose level 1. T, B, and NK cell engraftment at day +21 was comparable to dose level 1. Despite suppression of Th1 and Th17 cells, the cumulative incidence of grade II-IV acute GVHD by day +100 with PAC/SIR/TAC was similar to historic SIR/TAC values (46.4 v 43%) ( Figure 1B). Acute GVHD onset did not correlate with duration of PAC therapy, depth of pSTAT3 inhibition, or burden of circulating Th1, Th17, or Th2 cells. Conclusions: While PAC/SIR/TAC successfully reduced pSTAT3, increased pSTAT5, and suppressed Th1 and Th17 cells, the regimen did not reduce acute GVHD risk. Completed phase II and III trials testing tocilizumab (anti-IL-6 monoclonal antibody, ACTRN12612000726853, ACTRN12614000266662) and now PAC reveal a biologic disconnect between effective IL-6/JAK2/pSTAT3 axis blockade and a disappointing lack of clinical improvement in acute GVHD prevention. We surmise uncontrolled T cell Aurora kinase A activity contributed to acute GVHD via CD28 costimulation in this trial. As PAC polarizes the pSTAT5:pSTAT3 CD4 + T cell ratio and targets IRAK1 and CSFR1, it may have activity in refractory chronic GVHD. This concept is now being tested by others (NCT05531786).

Outcomes after Bone Marrow Versus Peripheral Blood Haploidentical Hematopoietic Stem Cell Transplantation Using Post-Transplant Cyclophosphamide-Based Gvhd Prophylaxis

Background: Patients who do not have a human leukocyte antigen (HLA)-matched donor can undergo hematopoietic stem cell transplantation (HSCT) by utilizing haploidentical (haplo) family donors and post-transplant cyclophosphamide (PTCy) for Graft-versus-host disease (GVHD) prophylaxis. Originally, Haplo transplants utilized a bone marrow (BM) source because of concern of higher incidence of GVHD with peripheral blood stem cells (PBSC) graft. Recent years have seen an increase in PBSC graft utilization. Some published studies have reported comparable survival between the two graft sources. These studies also reported lower rate of chronic GVHD and higher quality of life with BM and a lower relapse rate and faster engraftment with PBSCs. We aimed to investigate the outcomes following BM versus PBSC haplo HSCT using (PT-Cy)-based GVHD prophylaxis. Methods: In this single-center retrospective study, we included all (n=176) adult patients who underwent haplo HSCT from August 2016 to July 2021 and had at least one year of follow-up. Bivariate analyses, using the chi-square and t-test, were performed. Kaplan-Meier and regression analyses were conducted. Data were analyzed using SPSS version 28. Statistical significance was considered at p<0.05. Results: The study included 176 haplo transplants including 65% peripheral blood and 35% bone marrow grafts. The median age was 54 (18-74) years and 68% of recipients were males. Ethnic minorities comprised 30% of recipients. Hematologic diagnoses included myeloid disease (65%), lymphoid disease (29%), and others (6%). 31 % of the patients underwent a Myeloablative transplant. Hematopoietic cell transplantation comorbidity index of 3 or higher was noted in 53% of patients. With a Median follow-up 21 (0-73) months, Overall survival (OS) and disease-free survival (DFS) was not reached in either BM or PBSC haplo HSCT group. 1-year OS of 75% and 74% (p-0.898) and 1-year DFS of 63% and 63% (p-0.994) were noted in BM and PBSC group respectively. In PBSC versus BM haplo recipients, an earlier neutrophil engraftment (17 days vs 18 days, p=0.022) was seen. Similar incidences of grade II-IV acute GVHD (50% vs 51%, p=0.875), relapse (22% vs 26%, p=0.579), non-relapse mortality (NRM, 17% vs 20%, p=0.682), platelet engraftment (28 vs 31 days, p<0.092) and 1- year chronic GVHD (35% vs 38%, p=0.410) were noted. Conclusions: In this study, Haploidentical allogeneic hematopoietic stem cell transplant recipients demonstrated similar rates of overall and disease-free survival, relapse, non-relapse mortality, acute and chronic GVHD, and platelet engraftment regardless of graft source. Neutrophil engraftment was observed one day earlier in peripheral stem cell recipients. This supports the use of either PBSC or Bone marrow as the preferred source of Haploidentical transplants.

Higher CD34+ Cell Doses Correlate with Reduced Incidence of Relapse and Better Event-Free Survival after KIR-Ligand Mismatch Cord Blood Transplantation for Childhood Acute Myeloid Leukemia

Introduction In children with acute myeloid leukemia (AML), hematopoietic stem cell transplantation (HSCT) is an important treatment, and cord blood units from unrelated donors provide a well-established source of stem cells for HSCT. The main advantages of using cord blood include rapid availability, allowance of greater HLA disparities due to a relatively low risk of severe graft-versus-host disease (GVHD), and possibly a greater graft-versus-leukemia (GVL) effect. Killer cell immunoglobulin-like receptors (KIRs) are the main receptors on natural killer cells that play an important role in GVL after HSCT. Previous studies on the effects of KIR-ligand (KIR-L) incompatibility in unrelated cord blood transplantation (CBT) for leukemia have resulted in conflicting results, and in some studies, this has led to an increased incidence of acute GVHD. Furthermore, the impact of KIR-L mismatch on outcomes in children with AML remains poorly understood. In this study, we explored the association of KIR-L incompatibility and other clinical factors with patient outcomes in children with AML who received CBT. Methods Data were collected from the Transplant Registry Unified Management Program sponsored by the Japanese Society for Transplantation and Cellular Therapy and the Japanese Data Center for Hematopoietic Cell Transplantation. The patients were selected according to the following criteria: (1) de novo non-M3 AML, (2) age < 16 years and CR1 or CR2 at the time of receiving HSCT, (3) no prior HSCT, and (4) HSCT performed between 2000 and 2021. Patients without information on survival and disease recurrence or those with Down syndrome were excluded. KIR-L mismatch in the graft-versus-host direction was defined as lacking a donor KIR-L group (HLA-C1, C2, Bw4, or A3/A11) in a recipient. A myeloablative conditioning regimen was defined as total-body irradiation (TBI) at > 8 Gy, melphalan at > 140 mg/m 2, or busulfan at ≥ 9 mg/kg. All other regimens were analyzed as reduced-intensity conditioning regimens. Adverse cytogenetics were defined as previously described [Creutzig et al. Blood, 2012]. Results A total of 299 patients were included. The median age at HSCT was 5 years (range, 0-15), and the median follow-up period for survivors was 7.2 years (range, 0.1-22.4). The median total nucleated cell and CD34+ cell doses were 6.7 x 10 7/kg (range 0.01-12.3) and 1.9 x 10 5/kg (range 0.01-59.4), respectively. The study cohort consisted of 240 patients in the KIR-L match group and 59 patients in the KIR-L mismatch group. The background characteristics of these two groups did not differ significantly, except for a trend indicating that the KIR-L mismatch group received CBT more recently ( p = 0.063). The cumulative incidence rates of neutrophil recovery at Day 42 were 93.3% (95% CI, 89.3-95.9%) and 91.5% (95% CI, 80.0-96.5%) ( p = 0.980), and the cumulative incidence rates of platelet engraftment at 6 months were 91.5% (95% CI, 87.1-94.5%) and 89.8% (95% CI, 77.9-95.5%) ( p = 0.314) for the KIR-L match and mismatch groups, respectively. The cumulative incidence rates of grade II-IV acute GVHD at Day 100 were 40.9% (95% CI, 34.6-47.1%) and 40.7% (95% CI, 28.0-52.9%) ( p = 0.709), whereas those of chronic GVHD at one year after transplantation were 15.6% (95% CI, 11.2-20.6%) and 15.9% (95% CI, 7.8-26.6%) ( p = 0.914) for the KIR-L match and mismatch groups, respectively. In univariate analyses, the 5-year event-free survival (EFS) was 70.1% (95% CI, 63.6-75.6%) for the KIR-L match group and 72.9% (95% CI, 59.0-82.8%) for the KIR-L mismatch group ( p = 0.609). Stratification by CD34+ cell doses showed a significant correlation between higher CD34+ cell doses and better EFS in the KIR-L mismatch group (Figure 1), attributed not only to reduced nonrelapse mortality but also to a lower incidence of relapse. In multivariate analysis of EFS, KIR-L mismatch with high CD34+ cell doses (> the median doses) was identified as an independent favorable prognostic factor (Table 1; hazard ratio = 0.21, p = 0.037). Conclusion Our study demonstrates that higher CD34+ cell doses were associated with a lower relapse rate and better EFS in KIR-L mismatch CBT for childhood AML. This finding is noteworthy, as previous literature has primarily emphasized the role of higher CD34+ cell doses in reducing nonrelapse mortality. Our results suggest that higher CD34+ cell doses are also crucial for achieving a high GVL effect in the context of KIR-L mismatch CBT.

Score to Guide Donor Choice in Haploidentical Stem Cell Transplant Using Post-Transplant Cyclophosphamide for Patients with Acute Myeloid Leukemia: A Study from the Acute Leukemia Working Party of the EBMT

Introduction: There is paucity of information to guide selection of the most appropriate stem cell donor for haploidentical (Haplo) hematopoietic stem cell transplant (HSCT). Patients and Methods: We retrospectively analyzed the characteristics of haploidentical family donors that may affect transplant outcomes in patients with acute myeloid leukemia (AML) who received graft-versus-host disease (GVHD) prophylaxis with postransplant cyclophosphamide (PTCy) registered in the EBMT database. The primary endpoint was GVHD and relapse-free survival (GRFS). Results: Overall, 2200 patients were included with a median age of 56 years (range, 18-75); 1742 (79%) were in complete remission and 1246 (56.6) received reduced intensity conditioning. Regarding donors, the median age was 37 years (range, 8-71), 820 (37%) were females of which 458 (21%) were used for male recipients, 1252 (57%) had positive CMV serostatus, 1631 (74%) donated peripheral blood (PB) and 1638 (75%) had ≥ 4/8 HLA mismatch with the recipient. 100-day acute GVHD grade II-IV and III-IV and 2-year chronic and chronic extensive GVHD were 28% (95% CI 26-30), 11% (95% CI 10-12), 33% (95% CI 31-35) and 14% (95% CI 12-15), respectively. After median follow-up of 24 months, the cumulative incidence of relapse and non-relapse mortality (NRM) and the probability of leukemia-free survival (LFS), overall survival (OS) and GRFS were 26% (95% CI 24-28), 22% (95% CI 20-24), 52% (95% CI 50-55), 57% (95% CI 55-60) and 41% (95% CI 39-43), respectively. In multivariable analysis, donor-related risk factors with a negative impact on GRFS were older age (HR 1.1; 95% CI 1.04-1.15), use of PB (HR 1.19; 95% CI 1.04-1.37), and female donors to male recipients (HR 1.25; 95% CI 1.09-1.43). We further developed a score that distinguished 4 groups with 0 (241), 1 (913), 2 (863) or 3 (183) donor-related risk factors. GRFS was 57% (95% CI 50-63), 43% (95% CI 39-46), 37% (95% CI 33-40), and 30% (95% CI 23-38), respectively (P < 0.001) (Figure 1). The score was also able to stratify risk groups for acute and chronic GVHD, NRM, LFS and OS. Conclusion: Donor variables have an important impact on AML patient's outcome after Haplo-HSCT using PTCy. With three simple donor characteristics, age, gender and stem cell source, we were able to generate a score that may help to select the most appropriate donor in clinical practice.

PB CD8 T N and CD4 T EM on day30 after Allo-HSCT Is a Predictive Marker for the Development of aGVHD

Introduction ： Acute GVHD (aGVHD) is a common complication 20-60 days after allo-HSCT and can be life-threatening in some cases. It has been reported to be associated with T-cell immune reconstitution, but the detailed mechanisms are not clear. Early post-transplant lymphocyte recovery is mainly due to homeostatic peripheral expansion (HPE), which is variable depending on various factors such as donor source, recipient's age. T cell-related cytokines, such as sIL-2R , IL-7 and TNFr1 are known biomarkers for the aGVHD, but there are few reports that predict the aGVHD incidence rate using the peripheral blood (PB) lymphocyte subset. We evaluated the effect of PB lymphocyte subset in early post-transplant period on aGVHD. Methods ： We retrospectively analyzed 83 patients (40 in AML, 12 in ALL, 1 in MPAL, 13 in MDS, 2 in MPN, 9 in malignant lymphoma/LPD and 3 in AA) who underwent the allo-HSCT in our hospital from 2013 to 2023. The median age of patients was 44 years (range:17-66). Sixteen received BM, 47 received PB (including 28 with haploidentical (9 with ATG, 19 with PTCY)), and 20 received CB. GVHD prophylaxis was FK506+MTX in 61 patients, CyA+MTX in 3 and MMF+FK506+CY in 19. The median observation period was 495 [38-2983] days. PB lymphocyte subset (Naïve Tcell (T N):CD45RA+CD62L+, Central memory Tcell (T CM) :CD45RA-CD62L+, Effector memory Tcell (T EM) :CD45RA-CD62L-, Effector memory Tcell re-expressed CD45RA (T EMRA) :CD45RA+CD62L-, Th1:CD3+4+CXCR3+CCR6-, Th2:CD3+4+CXCR3-CCR6-, Th17:CD3+4+CXCR3-CCR6+) at day30 (range:28-35) after transplantation were analyzed by FCM. Results ： Twenty-five patients had grade II-IV aGVHD, and 11 had grade Ⅲ-IV aGVHD. Patients with Grade II-IV aGVHD exhibited significantly lower proportion of CD8+T N as compared to non aGVHD groups (GVHD+: 17.7 ± 13.3%; GVHD-: 30.9 ± 16.3%; p < 0.001) . In contrast, the proportion of CD4+T EM and CD8+T EM were higher in the Grade II-IV acute GVHD group (GVHD+: 30.9 ± 23.1%; GVHD-: 21.9 ± 15.6%; p=0.04, GVHD+: 36.1 ± 16.2%; GVHD-: 22.7 ± 14.7%; p < 0.001, respectively). We found a strong statistical correlation between the proportion of CD8+T N and CD8+T EM. The cumulative incidences of Grade II-IV and III -IV acute GVHD at day + 100 for CD8+T N <20% group was 56.9% and 29.6% compared with 14.2% and 6.3% for the CD8+T N >20% group (p < 0.001 and p < 0.01). Similarly, the cumulative incidences of Grade II-IV and III -IV acute GVHD at day + 100 for CD4+T EM >30% group was 48.1% and 32.6% compared with 22.2% and 5.9% for the CD4+T EM <30% group (p= 0.02 and p < 0.01). Two-year NRM was higher in the CD8+T N <20% group than in the CD8+T N >20% group (26.3% vs 4.2%, p=0.008). The two-year cumulative incidence of relapse (CIR) was comparable between the two groups, but tended to be lower in the mismatched CR group (CD8+T N <20%: 33.1% versus CD8+T N >20%: 43.4%, p=0.31). Conclusion ： PB CD8 T N and CD4 T EM fraction on day30 is a predictive biomarker for the development of acute GVHD.

Donor NK Cell Education By KIR3DL1 and HLA-B Associates with Reduced Relapse in Unrelated Bone Marrow Transplantation for Adult T-Cell Leukemia

Background: Adult T-cell leukemia/lymphoma (ATL) derives from human T-cell leukemia virus-1 (HTLV-1)-infected T cells, and its prognosis is still dismal. Whereas allogeneic stem cell transplant (allo-HSCT) may lead to long-term remission, 1-year relapse rate is still high at 35-47% (Muranushi et al, Bone Marrow Transplant. 2021). As for NK cell modulation against ATL, polymorphisms of killer-cell immunoglobulin-like receptors (KIRs) are of interest. NK cell inhibition by donor KIR/patient HLA interaction and NK cell education status have been reported to affect the prognosis of allo-HSCT, but no consensus has been reached. Furthermore, the effects of entire KIR haplotypes have not been extensively studied. Aim: Using high-resolution genotyping of all 15 functional KIR genes based on long-range PCR and long-read sequencer, correlations between KIR/HLA polymorphisms and relapses in unrelated bone marrow transplantation (UR-BMT) for ATL were evaluated. Methods: DNAs and clinical data of 264 transplants performed between 2007 and 2016 were obtained. Alleles of 15 KIRs, HLA-A, B, C, DRB1, DPB1 and DQB1 were genotyped for patients and donors. Prognostic factors for relapse were evaluated using the Fine-Gray proportional-hazards models. Results: Donor KIR3DL1 and patient HLA-B combination predictive of strong interaction (n=74) showed a trend for a lower relapse rate than weak or non-interactive combinations (n=145) (HR, 0.64; p=0.100), raising the beneficial impact of donor NK cell education at KIR3DL1/HLA-B interaction. Comprehensive analysis focusing on amino acids of donors' KIRs/HLAs specified combinations of HLA-B isoleucine 80 (80I)/ KIR3DL2 aspartic acid 42 and HLA-B threonine 80 (80T)/ KIR3DL2 glutamic acid 42 (n=76) associated with decreased relapse (HR, 0.35; 95%CI, 0.19-0.65; p=0.00087). On the other hand, combinations of HLA-B glutamic acid 152 (152E)/ KIR2DL4 cysteine 30 and HLA-B valine 152 (152V)/ KIR2DL4 tyrosine 30 (n=27) were associated with increased relapse (HR, 11.79; 95%CI, 1.6-86.58; p=0.015). Given that KIR3DL2/ KIR2DL4 do not bind HLA-B and are closely linked to KIR3DL1/S1 in KIR haplotypes, specific KIR3DL1/S1 alleles were further explored by subgroup analyses. As a result, combinations of HLA-B 80I/ KIR3DL1*015& KIR3DL2*002 and HLA-B 80T/ KIR3DL1∗001, ∗005, ∗007, ∗020, ∗038, ∗097 (n=60) were defined as the group at low risk for relapse (adjusted HR, 0.21; 95%CI, 0.09-0.48; p=0.00026) (Figure 1A), and combinations of HLA-B 152E/ KIR3DS1 and HLA-B 152V/ KIR3DL1∗001, ∗007, ∗015, ∗020, ∗029, ∗038 (n=176) were defined as the group at high-risk for relapse (adjusted HR, 5.31; 95%CI, 1.72-16.39; p=0.0037) (Figure 1B). The cases in the low-risk group and/or not in the high-risk group (n=84) had a lower relapse rate (adjusted HR, 0.20; 95%CI, 0.10-0.40; p=0.0000059) (Figure 1C) and a higher overall survival (adjusted HR, 0.66; 95%CI, 0.46-0.95; p=0.0265389) (Figure 1D) than the remaining cases (n=130). In spite of reduced relapse rate, the former showed a lower rate of grades II-IV acute GVHD (HR 0.65; p=0.049). Finally, CD107a degranulation of NK cells was measured following coincubation of HLA-null K562 cells and PBMCs from healthy donors with or without genotypes of the low-risk group. KIR3DL1(+) NK cells showed increased CD107a degranulation compared with KIR3DL1(−) NK cells in healthy donors with the low-risk group genotype (p=0.031), but this difference was not apparent in healthy donors without the low-risk group genotype (p=0.28) (Figure 2). Conclusions: Allelic genotyping of KIRs enabled to specify donors associated with reduced relapses. Donor NK cell education status at HLA-B/KIR3DL1 interaction might confer enhanced GVT effects and better prognosis in UR-BMT against ATL.

A Multi-Center Retrospective Analysis of Outcomes Post Allogeneic Stem Cell Transplantation in AML Patients with TET2 Mutations: A Study on Behalf of the Global Committee and the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation

Background Mutations in TET2 present in about 15% of adult AML are reported in some limited series as an adverse prognostic factor for overall survival. However the impact of allogeneic hematopoietic cell transplantation (allo-HCT) for the treatment of these patients remains unclear. We addressed this issue in a EBMT global multi-center registry-based study. Patients and Methods 644 adult AML patients with TET2 mutations receiving first non ex-vivo depleted allo-HCT from 2013-2022 in 127 centers were analyzed. All patients achieved first complete remission (CR1) before allo-HCT. Results The median age of the 644 AML patients was 59.4 (range, 18.1-86.3) years. 556 patients (86.3%) had de novo, and 88 (13.7%) had secondary AML, respectively. 367 (57.2%) patients were male. The median interval from diagnosis to allo-HCT was 4.9 (IQR, 3.8-6.2) months. Patients were categorized into favorable -(N=23, 3.9%), intermediate-(N=475, 79.8%) and adverse (N=97, 16.3%) risk categories according to cytogenetic characteristics. Conditioning regimen was myeloablative (MAC) in 46.7% of patients. 149 patients (23.1%) received a matched-sibling donor, 176 (27.3%) a haploidentical donor (Haplo), 268 (41.6%) a 10/10 unrelated donor (UD) and 51 (7.9%) a 9/10 UD allo-HCT, respectively. For the entire cohort, with a median follow-up of 1.9 years, the 30-day cumulative incidence of engraftment was 97.6%. The 100-day cumulative incidence of grade II-IV aGVHD was 22.9% and the 2-year cumulative incidence of extensive cGVHD was 13.7%. In addition, the 2-year relapse incidence and NRM were 23.2% and 12.8%, respectively. Finally, the 2-year OS, LFS and GRFS were 69.8%, 63.9% and 49.8%, respectively. In multivariable analyses, a donor type 9/10 UD was associated with a higher RI (HR=2.33, 95% CI 1.21-4.48; p=0.01), a lower LFS (HR=2.20, 95% CI 1.31-3.70; p<0.01) and OS (HR=2.29, 95% CI 1.33-3.96; p<0.01) as compared to MSD as reference. Compared to MSD, 10/10 UD and Haplo had similar outcomes. The adverse-cytogenetic group was associated with higher RI (HR=1.85, 95% CI 1.19-2.86; p<0.01), and higher incidence of grade II-IV acute GVHD (HR=1.74, 95% CI 1.14-2.64; p=0.01) as compared to other groups combined as reference. Compared to de novo AML (reference), secondary AML was associated with lower LFS (HR=1.49, 95% CI 1.03-2.15; p<0.05) and OS (HR=1.68, 95% CI 1.15-2.45; p<0.01). When age increased, patients faced higher RI (HR for 10y increment=1.24, 95% CI 1.01-1.53; p<0.05) and extensive chronic GVHD (HR=1.34, 95% CI 1.02-1.77; p<0.05), which translated into higher NRM (HR=1.66, 95% CI 1.23-2.24; p<0.01), lower LFS (HR=1.36, 95% CI 1.14-1.62; p<0.01) and OS (HR=1.60, 95% CI 1.31-1.96; p<0.01). Later year of transplantation was associated with lower incidence of II-IV acute GVHD (HR for 2y increment=0.76, 95% CI 0.63-0.92; p<0.01), chronic GVHD (HR=0.67, 95% CI 0.54-0.83; p<0.01) and extensive chronic GVHD (HR=0.72, 95% CI 0.52-0.99; p<0.05). Female to male, patient CMV status and interval between diagnosis and HCT did not affect significantly the transplant outcomes in multivariable analysis. Conclusion No significant difference was observed in outcomes of AML patients with TET2 mutations following MSD, HAPLO and 10/10 UD allo-HCTs, while 9/10 UD was associated with higher relapse incidence and lower survival outcomes. Higher patient age, secondary AML and adverse cytogenetics predicted worse transplant outcomes. GVHD prevention improved with time for these patients.

Reduced Intensity Haploidentical Bone Marrow Transplantation in Adults with Severe Sickle Cell Disease: BMT CTN 1507

Background: Allogeneic hematopoietic stem-cell transplantation has curative potential for sickle cell disease (SCD). Event-free survival (EFS) in children with SCD is >90% after a bone marrow transplant (BMT) from a myeloablative matched sibling donor (MSD). Unfortunately, <15% of patients with SCD have MSD, and myeloablative conditioning can be prohibitively toxic in adults with SCD. Reduced intensity HLA-haploidentical BMT with post-transplant cyclophosphamide (PTCy) has been shown in small studies to expand the donor pool with encouraging results. Still, concerns about graft failure and graft-versus-host disease (GVHD) persist. We present the results of a Blood and Marrow Transplant Clinical Trials Network (BMT CTN) 1507, multi-center single-arm, phase-II, prospective clinical trial (clinicaltrials.gov #NCT03263559) of haploidentical-BMT with PTCy to estimate EFS at 2-years in adults with severe SCD. Pediatric stratum data is not included in the data presentation and will be available in 2-years. Study Design and Methods: Eligibility: SCD patients aged 15.00-45.99 years with prior stroke, recurrent ACS or pain, chronic transfusion regimen, or tricuspid valve regurgitant jet velocity (TRJV) ≥2.7 m/sec were eligible. Participants were required to have an HLA-haploidentical first-degree relative donor, willing and able to donate bone marrow. The primary objective was EFS (survival without primary or secondary graft failure or second infusion of stem cells) at 2 years after haploidentical-BMT. Secondary objectives included determining the impact on clinical and laboratory manifestations of SCD and other transplant outcomes at 2 years post haploidentical-BMT. The protocol was opened for enrollment on 10/5/2017, completed accrual on 01/6/2021, and data are current as of 8/2023. Preconditioning with hydroxyurea (HU) 30mg/kg/day (Day-70 to Day-10); Conditioning regimen included Thymoglobulin (rATG), Thiotepa, Fludarabine, Cyclophosphamide, and Total Body Irradiation (TBI). GVHD prophylaxis included PTCy, sirolimus, and mycophenolate mofetil, figure. Results: A total of 54 eligible participants enrolled from 19 sites; 42 (78%) proceeded to transplant. Amongst enrolled participants, 59.3% are male, 92.6% are Black, and 3.7% are Hispanic. 10 participants started HU but did not proceed to BMT, and 2 did not start HU or proceed to BMT. Reasons included donor issues (n=4), withdrawal of consent (n=2), insurance coverage (n=2), death (n=1), and other (n=3). 38/42 (90%) participants completed the study as planned; 2 participants withdrew consent, and 2 were lost to follow-up. The median age was 22.8 years at enrollment; 47/54 (87%) of enrolled participants had Hemoglobin SS disease, 40/54 (74.1%) had a Lansky/Karnofsky score of 90-100 at baseline, and 41/54 (75.9%) had an HLA match score of 4/8. Recurrent vaso-occlusive pain episodes (38.9%), acute chest syndrome (16.8%), and overt stroke (16.7%) were the most common indications for transplant. Only 13 (31%) participants achieved the intended 30 mg/kg/day dosing of HU preconditioning. Estimated 2-year EFS is 88% (95% CI: 73.5%, 94.8%); all except one qualifying event occurred within 12 months. The 2-year overall survival (OS) post-HU was 93.0% (95% CI: 79.8%, 97.7%), and the 2-year OS post-transplant was 95.0% (95% CI: 81.5%, 98.7%); 2 (4.8%) participants had primary graft failure, and 1 (2.4%) had secondary graft failure before day +100. The cumulative incidence of grades II-IV acute GVHD at day 100 was 26.2% (95% CI: 14.0%, 40.2%), and grades III-IV acute GVHD at day 100 was 4.8% (95% CI: 0.9%, 14.4%). There were two deaths in the first year post-BMT (1 -organ failure; 1-ARDS), none in the second year; 33 (78.6%) participants reported at least one re-admission post-BMT, mainly due to either bacterial infection (n=41) or viral reactivation (n=36), table. Conclusion: This multi-center phase-II trial of a reduced intensity haploidentical-BMT in adults with SCD shows durable donor engraftment at 2-years with low mortality. The 2-year EFS and OS are comparable to that reported after MSD myeloablative BMT. These results support haploidentical BMT with PTCy as a suitable and tolerable curative therapy for adults with SCD and severe end-organ toxicity such as stroke and pulmonary hypertension, a population typically excluded from participating in myeloablative gene therapy and gene editing trials.

Sirolimus Is an Acceptable Alternative to Tacrolimus for Graft-versus-Host Disease Prophylaxis after Haploidentical Peripheral Blood Stem Cell Transplantation with Post-Transplantation Cyclophosphamide

Graft-versus-host disease (GVHD) prophylaxis with post-transplantation cyclophosphamide (PTCy), tacrolimus (Tac), and mycophenolate mofetil (MMF) for allogeneic haploidentical donor (haplo) hematopoietic cell transplantation (HCT) results in comparable outcomes to matched unrelated donor HCT. A phase II study from the Moffitt Cancer Center substituting sirolimus (Siro) for Tac in this prophylactic regimen reported comparable rates of grade II-IV acute GVHD (aGVHD). Many centers have substituted Siro for Tac in this setting based on a preferable side effect profile, although comparative data are limited. In this study, we retrospectively compared outcomes in haplo-HCT with PTCy/Siro/MMF versus haplo-HCT with PTCy/Tac/MMF. The study cohort included all consecutive patients receiving haploidentical donor T cell-replete peripheral blood stem cell (PBSC) HCT for hematologic malignancies at Moffitt Cancer Center or the City of Hope National Medical Center between 2014 and 2019. A total of 423 patients were included, of whom 84 (20%) received PTCy/Siro/MMF and 339 (80%) received PTCy/Tac/MMF. The median age for the entire cohort was 54 years (range, 18 to 78 years), and the median follow-up was 30 months. The Siro group had a higher proportion of patients age ≥60 years (58% versus 34%; P < .01), and the groups also differed in diagnosis type, conditioning regimen, and cytomegalovirus serostatus. There were no significant differences in the rates of grade II-IV aGVHD (45% versus 47%; P = .6) at day +100 or chronic GVHD (cGVHD) (47% versus 54%; P = .79) at 2 years post-HCT. In multivariate analysis, neutrophil engraftment at day +30 was significantly better in the Tac group (odds ratio, .30; 95% confidence interval, .1 to .83; P = .02), with a median time to engraftment of 17 days versus 18 days in the Siro group, but platelet engraftment was similar in the 2 groups. Otherwise, in multivariate analysis, GVHD prophylaxis type had no significant influence on aGVHD or cGVHD, nonrelapse mortality, relapse, GVHD-free relapse-free survival, disease-free survival, or overall survival after PBSC haplo-HCT. These findings suggest that Siro is a comparable alternative to Tac in combination with PTCy/MMF for GVHD prophylaxis, with overall similar clinical outcomes despite delayed engraftment after peripheral blood stem cell haplo-HCT. Although Tac remains the standard of care, Siro may be substituted based on the side effect profile of these medications, with consideration of patient medical comorbidities at HCT.

Safety and Efficacy of Outpatient Myeloablative Busulfan Conditioning in Allogeneic Stem Cell Transplantation

INTRODUCTION: Busulfan-based regimens are the backbone of myeloablative conditioning (MAC) in allogeneic hematopoietic stem cell transplant (allo-HSCT), particularly for patients (pts) with Acute Myelogenous Leukemia (AML). However, literature on busulfan conditioning administered in the outpatient (OP) setting is limited. Here, we investigate the safety and efficacy of OP busulfan as compared to standard inpatient (IP) administration. METHODS: Pts &amp;gt; 18 years of age who received pharmacokinetically dose adjusted IV busulfan (130 mg/m2 x 4 days) conditioning prior to HSCT between January 2019 and April 2023 at our institution were included in this retrospective analysis. Pts who received non-myeloablative conditioning or who underwent a haploidentical HSCT were excluded. All pts undergoing HSCT were classified as having low-, intermediate-, or high-risk disease by the Disease Risk Index. Pts with AML were classified as having favorable, intermediate, or adverse disease by 2022 ELN classification. CIBMTR guidelines were used to determine neutrophil and platelet engraftment. Oral mucositis was graded per the World Health Organization scale. Clinical grading of acute graft-vs-host disease (AGVHD) was assigned per standard criteria. Adverse events (AEs) were reported in accordance with the CTCAE, v.5. Categorical variables were compared using the Fisher's Exact test. Continuous variables were compared using the Wilcoxon Rank-Sum test. Overall survival (OS) was defined as time from HSCT to time of death from all-cause mortality. Relapse-free survival (RFS) was defined as time from HSCT to time of relapse or non-relapse mortality. The Kaplan-Meier method was used to estimate OS and RFS. Survival differences between cohorts were compared using the Log-rank test. All hypothesis testing was two-sided and conducted at a significance level of 0.05. RESULTS: In total, 54 pts met eligibility criteria; 43 IP and 11 OP. The OP cohort was younger than the IP cohort (35 years vs 47 years median age; p=0.0284). All other patient, disease, and transplant characteristics were similar between cohorts. The majority of pts were male (IP: 56%, OP: 55%) and White/Caucasian (IP: 100%, OP: 91%). AML (IP: 88%, OP: 82%) was the most common indication for HSCT. Most pts were in CR1 (IP: 74%, OP: 89%) and had intermediate risk disease by both DRI (IP: 84%, OP: 64%) and 2022 ELN classification (IP: 62%, OP: 67%). PBSCT (IP: 88%, OP: 91%) and 10/10 MUD (IP: 67%, OP: 45%) were the most common types of HSCT. The majority of pts received a conditioning regimen of Flu/Bu4 (IP: 58%, OP: 55%). The use of PTCy was comparable between groups (p=0.6593). Of the 11 pts who received OP busulfan, 1 had to complete their conditioning IP after experiencing a seizure in the setting of prior meningitis. Between the 2 cohorts, there was no significant difference in the incidence of AEs &amp;gt; grade 2 (p=1), grade 2 AEs (p=0.8695), grade 3 AEs (p=0.7592), grade 4 AEs (p=0.2487), and grade 5 AEs (p=0.6457) within 30 days of conditioning. Incidences of transplant-related GI toxicities, including nausea (p=1), vomiting (p=0.4979), diarrhea/enteritis (p=1), and mucositis (oral: p=0.6102, GI: p=0.2821) were similar. There was no difference in time to neutrophil (p=0.1606) or platelet engraftment (p=0.9742). Length of hospitalization was shorter in the OP vs IP cohort (18 vs 24 days; p&amp;lt;0.0001). During hospitalization, there was no difference in the incidences of neutropenic fever (p=1), infection (p=0.5104), ICU transfer (p=1), or engraftment syndrome (p=0.7076). Number of infections per patient during hospitalization were comparable (p=0.3764). D30 chimerism was similar IP vs OP. Within 180 days of HSCT, there was no difference in the incidence of AGVHD (p=0.5152) or Grade II-IV AGVHD (p=1). Differences in 2-year OS (LR=0.2200) and 4-year RFS (LR=0.3144) were not significant. CONCLUSION: In pts undergoing MAC allo-HSCT with IV busulfan,OP administration shortens the length of hospitalization without delaying engraftment or increasing the risk of toxicity, neutropenic fever, infection, or ICU admission. Additionally, D30 chimerism, rates of engraftment syndrome and AGVHD, and survival were not affected. This makes OP busulfan an attractive option for transplant centers and their pts.

Post-Transplant Cyclophosphamide (PTCY) Compared to ATG in Patients with Myelodysplastic Neoplasms Allografted with an Unrelated Donor: A Registry Study of the Chronic Malignancies Working Party of the EBMT

Background Prospective randomized trials have reported a benefit for ATG-based GVHD prophylaxis in the setting of allogeneic hematopoietic stem cell transplantation (alloHSCT) with an unrelated donor (UD). However, the best GVHD prophylaxis has been recently challenged by the use of PTCY, first in haplo-identical transplant and then in HLA mismatched or matched unrelated transplantation. We here present the outcomes of PTCY vs ATG as GVHD prophylaxis in MDS patients from the EBMT registry transplanted with an unrelated donor. Method A total of 969 patients transplanted from 2012 to 2019 in 92 participating centers, receiving either PTCY or ATG, were included in this study. The primary outcomes were progression free survival (PFS) and overall survival (OS). Competing risks analyses were performed to analyze non-relapse mortality (NRM) with competing event relapse, and acute GvHD grade II-IV, chronic GvHD and neutrophil engraftment with competing events relapse and death. Cox proportional hazards regression with a predefined covariate constellation (age, IPSS-R cytogenetics, donor HLA matching, age, hypomethylating agents (HMA) prior to transplantation, comorbidity score and MDS classification (MDS with or without excess blast, EB) was used to obtain adjusted effect estimates of ATG compared to PTCY for OS and PFS. Results Overall, 214 patients received PTCY and 755 received ATG as GVHD prophylaxis for UD alloHSCT. Patients of the ATG group were older (60.1 year-old [IQR: 50.6-65.2] vs 57.2 year-old [IQR: 46.4-61.1], p=0.008). Disease characteristics were similar in both group: there were a total of 583 MDS with EB at diagnosis, 510 MDS-EB at transplantation, and 207 patients transformed into AML. Among patients with available data for IPSS-R at MDS diagnosis (n=760) 44 (5.8%) were Very Low, 114 (15%) Low, 209 (27.5%) Intermediate, 232 (30.5%) High and 161 (21.2%) Very High. Patients of the PTCY group received more frequently HMA before transplantation (72.4% vs 57.3%, p=0.001) and were preferentially transplanted from an HLA mismatched 9/10 donor (37.9% vs 21.6%, p&amp;lt;0.001). Conditioning regimen was more frequently myeloablative in the PTCY group (55.4% vs 38.7%, p&amp;lt;0.001). Neutrophil engraftment at 28 days was significantly better with ATG (93% vs 84%, p&amp;lt;0.001). With a median follow-up of 4.4 (95% CI 4.2 - 4.8) years, five-year OS was 57% (49-64) with PCTY and 49% (95% 46-53%) in ATG group, p=0.127. Five-year cumulative incidence of relapse was similar in both groups (22%, 95%CI 16-29 in PTCY vs 25%, 95%CI 22-28 in ATG; p=0.28). Notably, 5-year PFS was marginally higher for PTCY with 52% (95%CI 44-59) vs 44% (95%CI 40-48) for ATG, p=0.075, whereas 5-year NRM was 26% (95% CI 20-32%) vs 31% (95% CI 27-34) in PTCY and ATG, respectively, p=0.28. Grade II-IV acute GVHD incidence was lower using PTCY (22% [95% CI 17-28%] vs 30% [95% CI 26-33%]), p=0.035 while there was no difference for chronic GVHD (36% (29-43% with PTCY vs 38% (34-41%) in ATG at 5 years). Multivariable analyses confirmed a better OS and PFS for PTCY, with a HR of ATG of 1.34 (95% CI 1.02-1.76), p=0.04, and a better PFS for PTCY with a HR for ATG of 1.31 (95%CI 1.01-1.69) (Table 1). There was no apparent interaction between GvHD prophylaxis and IPSS-R or HLA matching, suggesting an effect exclusive to the type of GVHD prophylaxis used. Conclusion: This EBMT registry study suggests that MDS patients who received a transplant from an unrelated donor had a better OS and PFS using PTCY compared to ATG. This confirms that PTCY instead of ATG in this setting is a valid option.

Comparison of Non-Relapse Mortality after Haploidentical Hematopoietic Stem Cell Transplantation with Post-Transplant Cyclophosphamide Versus Single Umbilical Cord Blood Transplantation for Hematologic Disease

Introduction: Unrelated cord blood transplantation (UCBT) and haploidentical stem cell transplantation with post-transplant cyclophosphamide as graft-versus-host disease (GVHD) prophylaxis (PTCy-haplo) are alternative options for patients with hematologic disease lacking a human leukocyte antigen (HLA)-matched donor. Non-relapse mortality (NRM) after UCBT may vary depending on the cord blood CD34+ cell count, but no study has accounted for CD34+ cell count when comparing the outcomes after UCBT and PTCy-haplo. Therefore, we analyzed transplant outcomes after UCBT and PTCy-haplo in patients with hematologic disease from data of a nationwide registry that included cord blood CD34+ cell count. Methods: Patients with hematologic disease receiving first UCBT or PTCy-haplo between 2014 and 2020 were identified from the nationwide registration data of the Japanese Data for Hematopoietic Cell Transplantation. Acute GVHD-related mortality was defined as death caused primarily by GVHD or occurred secondary to GVHD, and infection-related mortality as death due to graft failure or infection but not acute GVHD. Patients treated by UCBT were stratified by the median CD34+ cell count for comparison (0.84 × 10 5/kg). Results: A total of 7,499 patients were enrolled and classified into 3 groups: PTCy-haplo (n = 1,142), UCBT with high CD34+ cell count (UCB-H; ≥ 0.84 × 10 5/kg, n = 3,185), and UCBT with low CD34+ cell count (UCB-L; &amp;lt; 0.84 × 10 5/kg, n = 3,172). Patients in the PTCy-haplo group were slightly younger than UCB-H and UCB-L patients (median age: 54 vs. 56 and 55 years). The PTCy-haplo group also included a greater proportion of males than the UCB-H group (62.4% vs. 50.0%) but not the UCB-L group (64.2%). A greater proportion of PTCy-haplo patients had a PS score of 0 (53.2% vs. 46.2% and 45.6%), a hematopoietic cell transplantation-specific comorbidity index of 0 (57.6% vs. 52.7% and 54.4%) and donor-specific anti-HLA antibody (2.7% vs. 1.0% and 1.6%), received reduced-intensity conditioning (58.0% vs. 40.5% and 41.6%), calcineurin inhibitor with mycophenolate mofetil (88.5% vs. 38.6% and 38.4%), and underwent transplantation in the later period (82.0% vs. 54.6% and 50.7%). There were no significant differences in disease-risk index between groups. At 2 years post-transplantation, NRM and overall survival (OS) were significantly better in the PTCy-haplo group than the UCB-H and UCB-L groups (NRM: 18.8% vs. 21.6% and 25.3%, P &amp;lt; 0.001; OS: 56.2% vs. 53.3% vs. 49.6%, P &amp;lt; 0.001). Neutrophil engraftment rate at 42 days was also significantly higher in the PTCy-haplo group than the UCB-H and UCB-L groups (93.7% vs. 87.5% and 82.9%, P &amp;lt; 0.001). The PTCy-haplo group less frequently developed grade II-IV (26.4% vs. 37.3% and 34.4%, P &amp;lt; 0.001) and III-IV acute GVHD (7.0% vs. 12.2% and 10.5%, P &amp;lt; 0.001). While neither the differences in NRM nor that in OS remained significant between PTCy-haplo and UCB-H groups in multivariable analysis (NRM: hazard ratio [HR], 1.18, 95% confidence interval [CI], 0.99-1.41, P = 0.073; OS: HR, 1.05, 95% CI, 0.94-1.17, P = 0.42), significant differences were maintained between PTCy-haplo and UCB-L groups (NRM: HR, 1.35, 95% CI, 1.13-1.61, P = 0.001; OS: HR, 1.12, 95% CI, 1.00-1.26, P = 0.042). Regarding the cause-specific mortality, infection-related mortality was also significantly lower in the PTCy-haplo group compared to UCB-H and UCB-L groups (8.1% vs. 11.1% and 13.6%, P &amp;lt; 0.001) while GVHD-related mortality did not differ among groups (5.0% vs. 5.2% and 4.9%, P = 0.69). Conclusion: UCBT-H resulted in similar NRM and OS as patients receiving PTCy-haplo, whereas outcomes were worse in UCBT-L. These findings indicate that high CD34+ cell count in cord blood is a critical criterion for alternative donor selection.