GVHD-free/relapse-free Survival Research Articles

Early Elevation of Absolute Eosinophil Count after Allogeneic Hematopoietic Stem Cell Transplantation Is Associated with Chronic Graft-Versus-Host Disease in Children

BACKGROUND Chronic graft-versus-host disease (cGVHD) is the most frequent late complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and is associated with non-relapse mortality. If recipients with cGVHD are not properly treated at the appropriate time, cGVHD can lead to severe complications. Therefore, early prediction of cGVHD is required to improve quality of life among the pediatric survivors who undergo allo-HSCT. The significance of eosinophilia in peripheral blood after allo-HSCT remains to be elucidated. Previous studies found that eosinophilia after allo-HSCT reduced the risk of relapse of malignancies or non-relapse mortality and was also associated with cGVHD. However, the subjects of these reports were mainly adults and there were limited data focused on eosinophilia after allo-HSCT in children. The aim of this study was to evaluate whether an early elevation of absolute eosinophil count after allo-HSCT was associated with the development of cGVHD in children. METHODS A total of 165 consecutive patients who received allo-HSCT in our institute were included. Patients who had previously received allo-HSCT, relapsed or died before day 100, and did not achieve engraftment, were excluded. Eosinophilia was defined as an eosinophil count of more than 500 /µL in peripheral blood within 60 days of stem cell infusion. The primary outcome of the present study was the development of cGVHD. RESULTS In our cohort, eosinophilia was detected in 67 patients (40.6%), with a median maximum eosinophil count of 1,050 /µL (range, 504 - 7,812 /µL) at a median of 40 days (range, 24 - 59 days), while median maximum eosinophil count in those without eosinophilia was 189 /µL (range, 0 - 495 /µL). There were no significant differences between the patients with or without eosinophilia in disease type, graft source, donor type, conditioning regimen, and GVHD prophylaxis and treatment. The median time from day 0 to the date of diagnosis of cGVHD was 120 days (range, 100 - 1,302 days). The cumulative incidence rate of cGVHD at 3 years in the entire cohort was 39.3% (95% confidence interval: 32.2 - 47.4). Patients with eosinophilia had a higher 3-year cumulative incidence rate of cGVHD, compared with those without eosinophilia (49.1% vs. 32.7%, P = 0.007). Cox proportional hazards model analysis with adjustments for the potential confounding factors of HLA mismatched donor, unrelated donor, aGVHD, use of ATG as conditioning regimen revealed that eosinophilia was associated with an increased risk of cGVHD (adjusted hazard ratio: 2.12; 95% confidence interval: 1.16-3.85, P = 0.014). In the 165 patients who underwent allo-HSCT, there was no significant difference in 5-year overall survival (OS) between the eosinophilia and the non-eosinophilia groups (80.1% vs. 80.5%, P=0.76). In the 121 patients with malignant diseases, there was no significant difference in 5-year OS between the eosinophilia and the non-eosinophilia groups (75.5% vs. 76.3%, P = 0.70). There was also no significant difference in 5-year disease-free survival between the eosinophilia and the non-eosinophilia groups (69.1% vs. 77.1%, P = 0.34). On the other hand, there was a significant difference in 5-year GVHD-free relapse-free survival between the eosinophilia and the non-eosinophilia groups (41.1% vs. 62.4%, P = 0.04). DISCUSSION & CONCLUSION In the present study, we revealed that an early elevation of absolute eosinophil count after allo-HSCT was associated with cGVHD in children. Because eosinophilia after allo-HSCT occurs before the development of cGVHD, early eosinophilia after allo-HSCT may predict the development of cGVHD in children.

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.

Post-transplant сyclophosphamide after matched donor hematopoietic stem cell transplantation in children with acute leukemia.

The data on post-transplant cyclophosphamide (PTCy) in pediatric acute leukemia after matched allo-HSCT are limited to case series. The present study aimed to assess the results of PTCy-based GVHD prophylaxis in a large cohort of children with acute leukemia after matched allo-HSCT. A retrospective analysis of 190 pediatric patients with acute leukemia who had a first allograft between 2008 and 2020 from a matched sibling donor (MSD) or matched unrelated donor (MUD) was carried out. In the MSD setting, GVHD prophylaxis consisted of PTCy alone (n=28) for the study group, and calcineurin inhibitor (CNI)±antimetabolite (n=30) for the control group. In MUD setting, most patients in the study group received GVHD prophylaxis with PTCy+CNI+mycophenolate mofetil (n=42, 66.7%) or PTCy+CNI+sirolimus (n=12, 19%). All patients (n=69) in the control group received ATG+CNI+antimetabolite. After MUD allo-HSCT, the incidences of acute GVHD grade III-IV and moderate/severe chronic GVHD were significantly lower in the PTCy group compared to control (6.6%vs. 35.0% and 12.7%vs. 47.1%, respectively, p<.0001). Five-year GVHD-free, relapse-free survival (GRFS) after MUD allo-HSCT was higher in the PTCy group compared to control (35.1%vs. 7.3%, p<.0001). At the same time, there was no significant difference between both groups after MSD allo-HSCT. In pediatric acute leukemia, PTCy-based GVHD prophylaxis for MUD allo-HSCT is a feasible and effective option that results in a low incidence of GVHD. Compared to the ATG-based approach, PTCy provides better control of GVHD in children. In pediatric allo-HSCT from MSD, PTCy demonstrates comparable effectiveness to conventional GVHD prophylaxis.

How Much Have Post-Transplant Outcomes Improved Since 2000 for Older Patients with Acute Myeloid Leukemia? a Study from the EBMT Acute Leukemia Working Party

Acute myeloid leukemia (AML) is a disease of older patients with a median age at diagnosis of 68 years. Patients older than 65 years historically have performed poorly as not being treated with intensive chemotherapy. Biological age is not the only culprit as other factors also play a role in reducing survival, such as performance status, the presence of comorbid conditions, and most importantly the biology of AML that is usually associated with high risk cytogenetic or molecular aberrations. Despite the increasing use of targeted therapies, allogeneic hematopoietic cell transplantation (allo-HCT) remains an important and potentially curative treatment modality for patients with AML. Over time, significant progress in allo-HCT has resulted in decreased non-relapse mortality (NRM) and allowed the delivery of allo-HCT to older patients. However, little information is available about the global impact of the current standard of care for older AML patients after allo-HCT and about the predictive factors for post-transplant outcomes. To address these challenges, we assessed real-world changes over time in transplant characteristics and post-transplant outcomes in older patients with AML (&amp;gt; 65 years), using a large dataset from the European Society for Blood and Marrow Transplantation registry. We identified 7215 adult patients (40% female; median age 68 years, range 65-80) with AML (secondary AML in 25%) allografted between 2000 and 2021 from a matched sibling donor (MSD; 23%), unrelated donor (UD; 63%) or haploidentical donor (Haplo; 14%). Karyotype risk was intermediate in 71% and adverse in 25%. NPM1 mutation and FLT3 ITD were present in 37% and 30% of patients, respectively.At transplant, 64% of patients were in first complete remission (CR1), 14% in CR2+ and 22% had active disease. Comorbidity index was zero in 43% of patients, 1-2 in 26% and &amp;gt;3 in 31%, while the Karnofsky score was &amp;lt;90 in 35%. Conditioning was reduced intensity (RIC) in 82% of patients. In vivo T cell depletion (TCD) and peripheral blood stem cells (PBSCs) were given to 62% and 93% of patients, respectively. Median follow up calculated by reverse Kaplan Meier was 40 months (interquartile range [IQR] 38-42). We compared changes in patient and transplant characteristics over time in 728 (10%) patients transplanted in 2000-2009, 1775 (25%) patients transplanted in 2010-2014, and 4712 (65%) patients transplanted in 2015-2021. Patients transplanted in recent years (65%) were older, were more likely to be in CR1 and to have an adverse-risk karyotype. Patients transplanted more recently were less likely to have had an MSD but more likely to have had a Haplo, PBSCs and TCD. The 3-year cumulative incidence of relapse (CIR) gradually and significantly decreased from 37% to 31%, then to 30% over the 3 time periods (p=0.001) whereas NRM significantly decreased from 31% and 31% to 27% (p=0.003). The 2-year leukemia free survival (LFS) and overall survival (OS) gradually and significantly improved over time from 32% to 38%, and then to 44% (p=0.001) and from 37% to 42%, and then to 49% (p=0.001), respectively, whereas graft-versus-host disease (GVHD)-free, relapse-free survival (GRFS) improved from 22% to 29%, and then to 34% (p=0.001). In a Cox regression multivariate analysis (MVA), a significant reduction in CIR and increased LFS, OS and GRFS were noted after 2015. LFS, OS and GRFS were also negatively affected by secondary AML, low Karnofsky score, active disease at transplant, and adverse-risk cytogenetics. GRFS was also negatively affected by older age, and positively affected by TCD. RIC positively affected OS whereas PBSCs positively affected LFS and OS. This improvement of post-transplant outcomes over time was observed for patients in CR1 with LFS and OS increasing from 39% to 44% and then to 47% (p=0.005) and from 43% to 48%, and then to 52% (p=0.006) as well as for patients in CR2 with LFS and OS increasing from 29% to 40% and then to 47% (p=0.001) and from 37% to 44% and then to 52% (p= 0.001), respectively. In conclusion, in older patients with AML, we observed an impressive improvement over time in post-transplant outcomes with decreased CIR and improved LFS, OS and GRFS. These large-scale, real-world data can serve as a benchmark for future studies in this setting and indicate that the opportunity for transplant for the elderly should be mandatory and no longer an option.

Risk Factors for CMV Infection, Including HLA Disparity and Ptcy Transplant in the Era of Letermovir Prophylaxis

Reports suggest that post-transplant cyclophosphamide (PTCy) for haploidentical and HLA-matched sibling donor allogeneic stem cell transplant (allo-SCT) is associated with a higher incidence of cytomegalovirus (CMV) infection than calcineurin inhibitor (CNI) for HLA-matched sibling donor allo-SCT. Prophylactic letermovir has been shown effective for CMV seropositive patients, based on the data mostly before the FDA approval of letermovir (2017). We reevaluated the risk of CMV infection in PTCy transplants. We retrospectively analyzed 175 patients after allo-SCT between May 2019-May 2022). CMV infection was monitored at least for the first year by serostatus, viral load over 500 IU/mL, and/or evidence of CMV end-organ disease. Univariate and multivariate Cox regression analyses were used for the factors, including CMV serostatus, use of letermovir, GVHD prophylaxis, and HLA disparities, to affect the risk of CMV infection and graft-versus-host disease (GVHD)-free relapse-free survival (GRFS). Cumulative incidence curves were used to visualize the incidence of CMV infection stratified by HLA match and PTCY use. A landmark analysis at Day +100 was used for GRFS, where patients who had CMV infection beyond Day +100 (N=13) were assigned to the no-infection group. Of the 175 patients, 108 received HLA-matched donors with GVHD prophylaxis, either CNI (N=70) or PTCy (N=38), while 67 received HLA mismatched donors with either CNI (n=6) or PTCy (N=66) ( Table). Letermovir was given to 137 patients (CMV IgG positive N=130, negative N=7) but not to 38 patients (CMV IgG positive N=12, negative N=26). CMV infection occurred in 28 patients (CMV IgG positive N= 28, CMV IgG negative N=0) before or after Day +100 (N=15 or N=13, respectively). CMV IgG positive recipients not receiving letermovir demonstrated a higher risk of infection by Day +100 than those receiving letermovir (Hazard ratio (HR) 10.1 (95% confidence interval (CI) 3.6-28.6), p&amp;lt;0.01). All 13 infections after Day +100 occurred after the cessation of letermovir (median: 82.9 days after cessation). On univariate analysis, PTCy and HLA mismatch donors increased the risk of CMV infection. The risk of infection by Day +100 increased with PTCy (p=0.07). The risk of infection after Day +100 increased with HLA mismatch donors (p=0.05). In addition, it was confirmed that HLA mismatch allo-SCT with PTCy increased the risk of CMV infection over matched allo-SCT with CNI ( Figure, HR 4.6 (95% CI 1.6-11.9), p&amp;lt;0.01), while HLA match allo-SCT with PTCy did not (p=0.3) (Figure 1). The trend was similar when analyzed only in the case of CMV infection by Day +100 (p&amp;lt;0.05) and after Day +100 (p=0.1). In the 130 CMV IgG seropositive patients who received letermovir, multivariate analysis showed that HLA mismatch donors with PTCy increased the risk of CMV infection over HLA match allo-SCT with CNI. When analyzed only for acute myeloid leukemia, acute lymphoblastic leukemia, and myelodysplastic syndrome with letermovir (N=91), HLA mismatch transplant with PTCy increased the risk of CMV infection over HLA match transplant with CNI (p=0.05), but not for HLA match transplant with PTCy. Landmark analysis demonstrated better GRFS in the PTCy group than the CNI group and in patients who received PTCy with CMV infection than those who received CNI without CMV infection (p&amp;lt;0.01). PTCy increased the incidence of CMV infection in HLA mismatch allo-SCT by D+100 but not HLA match allo-SCT in the era of letermovir prophylaxis. Patients with PTCy transplant who overcome CMV infection have improved GRFS, possibly due to the increased graft-versus-leukemia effect. Further analysis is required to confirm the difference in the incidence of CMV infection between HLA match and mismatch transplant with PTCy and to assess the significance of late CMV (after Day +100) infection on GRFS.

Outcome of Allogeneic Stem Cell Transplantation in FLT3-TKD-Mutated AML - a Study on Behalf of the Acute Leukemia Working Party of the EBMT

Introduction The overall prognostic impact of point mutations in the tyrosine-kinase domain 1 of FLT3 (FLT3-TKD mut) in patients (pts) with acute myelogenous leukemia (AML) remains controversial. Furthermore, co-occurrence of FLT3-TKD mut and mutated nucleophosmin-1 (NPM1 mut) was shown to have a favorable prognostic impact on AML pts receiving conventional chemotherapy. However, little is known about the outcome of AML pts with FLT3-TKD mut with or without co-occurring NPM1 mut treated with allogeneic stem cell transplantation (alloSCT). Patients and Methods This is a retrospective study of the acute leukemia working party (ALWP) of the European Society for Blood and Marrow transplantation (EBMT) investigating the outcome of adult AML pts with FLT3-TKD mut with or without NPM1 mut after first alloSCT using matched sibling (MSD), unrelated (UD) or haploidentical (haplo) donors between 2005 and 2022. All patients were in first or second complete remission (CR1 of CR2). Information on cytogenetic risk was necessary for inclusion. No ex-vivo T-cell depletion (TCD) was allowed. The primary endpoint was leukemia-free survival (LFS) at two years after alloSCT. Secondary endpoints were overall survival (OS), cumulative incidence of relapse (RI), non-relapse mortality (NRM), acute and chronic graft-versus-host disease (GVHD) and GVHD-free, relapse free survival (GRFS). One hundred and eighty-two adult AML pts with FLT3-TKD mut were identified, of which 74 (40.7%) had a co-occurring mutation in NPM1. Median age was 55.1 years (range 18.6-79.1) and 46.7% were male. Median follow-up was 21.4 months [IQR 13.6-28.1]. 78% of the pts were in CR1. Cytogentic risk was favorable, intermediate and adverse in 12.6%, 75.3% and 12.1% of pts, respectively. Additional FLT3 internal tandem duplication (FLT3-ITD) was present in 25.8% of pts. Information on measurable residual disease (MRD) was available for 68.7% of pts, being positive in 48% of these. Karnofsky performance score was &amp;lt; 90% in 21.1%, and hematopoietic cell transplantation-specific comorbidity index (HCT-CI) was &amp;gt;=3 in 28.1% of pts. 69.6% of pts were cytomegalovirus (CMV) positive. Conditioning was myeloablative in 52.8% and reduced intensity in 47.2% of pts. Stem cell donors were MSD, UD and haplo in 25.8%, 55.5% and 18.7% of cases. Stem cell source was bone marrow in 10.4%, peripheral blood in 87.4% and both in 2.2%. In-vivo TCD was performed in 59.2% of pts. GVHD prophylaxis was calcineurin inhibitor-based in 92.2% of pts. Results Engraftment was achieved in 99.4% of pts with a day-60 absolute neutrophil count (ANC) &amp;gt;0.5 x 10 9/L of 97.7% [95% CI: 93.7-99.2]. Day-180 rates of acute GVHD (aGVHD) grade II-IV and grade III-IV were 26.2% (95% CI:19.9-32.9) and 8.1% (95% CI:4.6-12.8), respectively. At two years, rates of total chronic GVHD (cGVHD) and extensive cGVHD were 30% (95% CI: 22.5-38) and 16.6% (95% CI:10.6-23.7), respectively. Two-year LFS and OS were 66.1% (95% CI: 57.6-73.2) and 74% (95% CI: 65.4-80.8), respectively. Two-year RI, NRM and GRFS were 22.5% (95% CI:16-29.8), 11.4% (95% CI: 7-17), and 51.1% (95% CI: 42.4-59.1), respectively. Cause of death was original disease in 47.5%, infection in 27.5%, GVHD in 22.5% and non-SCT related in 2.5% of cases. In univariate analysis the only factor with significant impact on LFS was donor type (haplo [n=34] vs. others, p=0.006). For GRFS, patient CMV negativity (p=0.014) and in-vivo TCD (p=0.01) were significant. Interestingly, co-occurring mutations in FLT3 (FLT3-ITD) or NPM1 were not identified as having a significant impact on LFS or GRFS. Moreover, MRD status before alloSCT was also not shown to have a significant impact on these outcomes. In multivariate analysis of LFS and GRFS, only donor type (haplo [n=34] vs. others) was shown to be significant for both endpoints, hazard ratio (HR) 2.54; 95% CI: 1.4-4.6; p=0.002, and HR 2.01; 95% CI: 1.18-3.41; p=0.01, respectively. Conclusion Acknowledging the limitations of our retrospective study in this rare entity results are encouraging given the high-risk population (median age 55.1 years, CR2 in 22%, co-occurring FLT3-ITD in 25.8%, positive MRD in 48%, HCT CI &amp;gt;=3 in 28.1%). LFS, OS and GRFS rates were 66.1%, 74% and 51.1%, respectively, and both RI and NRM were comparably low with rates of 22.5% and 11.4%, respectively. No positive prognostic impact of co-occurring mutations in FLT3-TKD and NPM1 was detected, unlike what was found for conventional chemotherapy.

Post-Transplant Cyclophosphamide Eliminates Disparity in GvHD-Free, Relapse-Free Survival and Overall Survival between 8/8 Matched and 7/8 Mismatched Unrelated Donor Hematopoietic Cell Transplantation in Adults with Hematologic Malignancies

Background: Post-transplant cyclophosphamide (PTCy) has become a standard of care for graft-versus-host disease (GvHD) prophylaxis in recipients of human leukocyte antigen (HLA)-matched and mismatched unrelated donor (MMUD) allografts, generating new opportunities for successful hematopoietic cell transplantation (HCT) regardless of patient ancestry. The National Marrow Donor Program (NMDP)-sponsored 15-MMUD study, which used PTCy-based GvHD prophylaxis (PMID 3390526), demonstrated encouraging overall survival (OS) in adult patients receiving MMUD bone marrow grafts matched at ≤7/8 HLA alleles. Currently, the follow-up ACCESS study (NCT04904588) will determine if similar outcomes can be achieved using MMUD peripheral blood stem cell allografts. As part of its 5-year strategic plan, the NMDP aims to determine the extent of differences in GvHD-free, relapse-free survival (GRFS) between 8/8 and 7/8 URD allografts using PTCy and seeks to develop approaches over time to close the presumed gap in URD outcomes. Methods: The primary objective was to compare GRFS between 8/8 and 7/8 URD HCT using the Center for International Blood &amp; Marrow Transplant Research (CIBMTR) database. After analyzing primary results, secondary objectives were added to compare GRFS, OS, and other clinical outcomes among 8/8 URD, 7/8 URD, and haploidentical-related donor (Haplo) HCT. The study included adult patients (age≥18y) with hematologic malignancies (ALL, AML, MDS) undergoing first URD or Haplo HCT between 2017-2020 using PTCy-based GvHD prophylaxis. Kaplan-Meier curves were used to estimate probability of GRFS and OS. Cox regression examined the independent effect of HLA match controlling for other clinical factors on outcomes referenced to 8/8 URD HCT. A priori clinically selected factors considered as possible confounders in the regression model included disease risk index, comorbidity risk, pre-HCT Karnofsky score, conditioning regimen intensity, graft source, donor/recipient CMV serostatus, year of HCT, donor/recipient age and race/ethnicity. Final models were stratified by factors violating the proportional hazards assumption. Factors were eliminated in a backwards fashion if p-values were &amp;gt;0.10 unless inclusion affected the hazard ratio (HR) of HLA match by more than 10%. Interactions were tested against a p-value of &amp;lt;0.01. Results: Table 1 shows demographics for the three patient cohorts: Haplo (n=2772), 8/8 URD (N=1517), and 7/8 MMUD (N=540). Notable differences among the cohorts included: 8/8 URD recipients had younger, predominantly Caucasian donors and were more likely to receive myeloablative conditioning. Haplo recipients had more donor/recipient CMV seropositivity and received more reduced intensity conditioning. Otherwise patient characteristics were similar. Contrary to our expectations, multivariable regression analysis (MVA) showed no significant differences in either GRFS or OS between recipients of 8/8 and 7/8 URD HCT at 1, 2 and 3-years post-HCT ( Figure 1). Outcomes, including relapse and NRM, between 8/8 and 7/8 URD HCT were similar irrespective of conditioning intensity. However, 8/8 URD HCT associated with lower two-year moderate/severe chronic GvHD than 7/8 URD [1.30 (1.00-1.68), p=0.049]. We next compared GRFS and OS among 8/8 and 7/8 URD and Haplo at 3y after HCT. On MVA, GRFS [HR 1.15 (1.04-1.26), p=0.005] and OS [HR 1.15 (1.03-1.29), p=0.013] were significantly better in 8/8 URD compared to Haplo HCT. Differences between 8/8 URD and Haplo appeared to be driven by significantly higher NRM [HR 1.46 (1.22-1.74), p&amp;lt;0.001)] and two-year moderate/severe chronic GvHD [HR 1.28 (1.07-1.54), p=0.007] in Haplo. No significant differences were seen in GRFS or OS at 3 years when comparing 7/8 URD to Haplo. Causes of death among donor types were similar with primary disease relapse/progression, infection and organ failure being the most frequent. Conclusions: Use of PTCy-based GvHD prophylaxis seems to have resolved previously observed differences in GRFS and OS between 8/8 and 7/8 URD HCT. HCT using an 8/8 URD HCT, if available, continues to be the best option for patients lacking a matched sibling donor. Further studies comparing Haplo to 7/8 URD HCT are warranted, but will require larger numbers of 7/8 URD HCT. Both mismatched donor sources substantially increase access to HCT for patients regardless of their ancestry.

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

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

Predictors of Outcome for Allogeneic Stem Cell Transplantation with a Reduced Intensity Pentostatin/TBI Conditioning Regimen in T-Cell Lymphomas: A Single Center Experience

Background: Allogeneic hematopoietic stem cell transplantation (alloSCT) is a potential curative option for patients with relapsed/refractory T-cell lymphoma (TCL).A reduced intensity conditioning (RIC) regimen of infusional pentostatin and 6 Gy of total body irradiation (TBI) has been shown to be well-tolerated and to have favorable engraftment kinetics 1. We utilized this regimen for patients with aggressive TCL undergoing alloSCT due to the demonstrated activity of pentostatin as a single agent in TCL and its potential impact, along with TBI, on eradicating residual TCL. Methods: This retrospective review includes adult patients with Nodal TCL (PTCL , AITL, ALCL), rare aggressive TCL [(T-ALL, natural killer/T-cell lymphoma (NKTL), adult T-cell leukemia/lymphoma (ATLL), and subcutaneous panniculitis-like T-cell lymphoma (SPTCL)], and T-Prolymphocytic leukemia (TPLL) who underwent alloSCT between 2006 and 2021. The primary objective was to determine transplant related outcomes including grade 3-4 acute graft-versus-host disease (aGVHD), extensive chronic GVHD (cGVHD), relapse, non-relapse mortality (NRM), and overall (OS), relapse-free (RFS), and GVHD-free, relapse-free survival (GRFS) following transplant. A subgroup analysis was conducted to evaluate the impact of disease status at the time of transplant and other factors, including age and subtype of TCL. Results: We report results for 40 patients (Nodal TCL: 21, Rare aggressive TCL: 10, T-PLL: 10) with a median age of 56.6 years ( range 24-71). Seventy-five percent were in clinical CR at the time of transplant. The 1-y cumulative incidence rate (CIN) of aGVHD was 42.5%. The 3-y CIN for cGVHD was 22.9. The median OS was 3.18 years with a 3-y OS rate of 51.9%. The median RFS was 1.24 years, with a 3-year RFS rate of 41.4%. OS and RFS were significantly higher in patients &amp;lt;65 compared to ≥65 (p-value 0.050 and 0.010 respectively), with no difference between the complete response (CR) and non-CR groups or different subtypes of TCL. The median GRFS was 0.52 years, with a 3-year GRFS rate of 20%. There was no statistically significant difference in GRFS or the incidence of GVHD between groups. Renal toxicity was noted in 10 patients. No cases of pulmonary or central nervous system (CNS) toxicities were observed. By day 100, 15 patients had an infection, including 8 bacterial infections and 5 viral infections. A total of 12 patients had reactivation of cytomegalovirus. Twelve patients died within the first year: 4 from relapse, 3 from aGVHD, 3 from infection, 1 from a subdural hematoma after a fall, and 1 from bladder perforation in the setting of hemorrhagic cystitis. Of 13 patients who relapsed, all received salvage therapy and 3 received DLI. Four are alive and in remission. Conclusions: In patients with TCL, RIC for alloSCT was well tolerated and compared favorably with retrospective data from larger groups of patients from CIBMTR and EBMT who were transplanted with different regimens 2. Interestingly, transplant-related outcomes were similar for patients with CR vs partial response (PR) at the time of transplant, and outcomes were better in patients younger than 65. Relapsed patients had a poor outcome despite salvage therapy with only a 30% OS at 3 years. 1. Foss et al, Transfusion 2020 2. Hamadani et al, Blood Advances 2022

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

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

Comparative Study for Haplo, MSD and MUD Allo-Hcts for AML Patients with KMT2A Rearrangement: A Study from the Global Committee and the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation

Background Acute myeloid leukemia (AML) patients with KMT2A rearrangement (KMT2Ar, except for t(9;11)(p21.3;q23.3)/MLLT3::KMT2A) are classified as adverse risk in the 2022 European LeukemiaNet (ELN) classification. There is uncertainty on their outcome following allogeneic cell transplantation (allo-HCT). We compared, in an European Society for Blood and Marrow Transplantation (EBMT) global multi-center registry-based analysis, outcomes following an allogeneic stem cell transplantation (allo-HCT) with either a matched sibling donor (MSD), matched unrelated donor (MUD) or haploidentical donor (HAPLO). Methods Data from 586 AML patients with KMT2Ar receiving a first allo-HCT in 183 EBMT centers from 2010-2022 were analyzed. All patients achieved first complete remission (CR1) before transplantation. Patients with t(9;11), without details on translocation, receiving mismatched UD (&amp;lt;10/10), umbilical cord blood, or grafts with ex-vivo manipulation were excluded. Univariant analysis and Cox regression models were used. Results KMT2A rearranged AML patients received allo-HCT from 201 MSD, 256 10/10 MUD, and 129 HAPLOs. For KMT2Ar type, t(6;11), t(11;19), t(10;11) or other translocations account for 27.8%, 37.5%, 23.9% and 10.8%, respectively. Peripheral blood was the major graft source (83.2%), and myeloablative conditioning accounted for the majority (60.2%) of all allo-HCTs. Engraftment rates were comparable in the three cohorts (MSD 99.5%, MUD 98.4% and HAPLO 96.9% p=0.17). AML relapse was the major cause of death in each donor cohort. On univariate analysis, HAPLO was associated with a lower 2-year relapse incidence (RI) (MSD 41.1%, MUD 37.2%, HAPLO 20%) but a higher 2-year non-relapse mortality (NRM) (MSD 6.1%, MUD 19.3%, HAPLO 21.3%) compared with MSD and MUD. The 180-day cumulative incidence of grade II-IV acute GVHD (aGVHD) was lower in MSD (18.8%) than in MUD (31.3%) or HAPLO groups (26.5%), respectively. The 2-year leukemia-free survival (LFS), overall survival (OS) and GVHD-free/relapse free survival (GRFS) were comparable among the three cohorts. Lower RI was observed in patients with t(11;19) compared with t(6;11) or t(10;11). Complex karyotype (CK) (at least 3 abnormalities) or monosomal karyotype (MK) were both associated with higher RI compared with those without. In addition, in-vivo T cell depletion was related to lower intensive chronic GVHD (cGVHD) incidence. On multivariate analysis, HAPLO HCT was associated with lower RI (hazard ratio [HR=0.46], 95% CI 0.28-0.77; p&amp;lt;0.01) but higher incidence of NRM (HR=2.36, 95% CI 1.17-4.78; p&amp;lt;0.01) compared with MSD, while HAPLO had no significant impact on LFS, OS and GRFS. MUD HCT was associated with higher incidence of grade II-IV aGVHD (HR=1.82, 95% CI 1.19-2,78; p&amp;lt;0.01), NRM (HR=2.73, 95% CI 1.51-4.94; p&amp;lt;0.01), and lower LFS (HR=1.37, 95% CI 1.03-1.83; p&amp;lt;0.05) compared with MSD (reference). Concerning translocation type, t(11;19) was associated with a lower RI (HR=0.64, 95% CI 0.43-0.94; p=0.022), a better LFS (HR=0.66, 95% CI 0.48-0.91; p=0.012), OS (HR=0.63, 95% CI 0.45-0.89; p=0.008) and GRFS (HR=0.75, 95% CI 0.57-1; p=0.049) compared with t(6;11)(reference). Translocations other than t(6;11), t(11;19) or t(10;11) were related to a lower RI (HR=0.45, 95% CI 0.24-0.87) and better OS (HR=0.57, 95% CI 0.34-0.95) compared to t(6;11). MK was associated with higher RI (HR=1.59, 95% CI 1.04-2.45; p&amp;lt;0.05) and lower LFS (HR=1.47, 95% CI 1.01-2.14; p&amp;lt;0.05). Conclusions For AML patients with KMT2Ar, HAPLO HCT was associated with a lower RI but higher NRM, leading to similar LFS, OS and GRFS compared with MUD and MSD HCTs. In the setting of allo-HCT, t(11;19) seems to be associated with favorable outcomes compared with other KMT2Ar.

Efficacy of Cord Blood Transplantation for the Management of Chronic Myelomonocytic Leukemia: A Registry-Based Study in Japan

Introduction Chronic myelomonocytic leukemia (CMML) is a challenging malignancy that shares characteristics with myelodysplastic syndromes and myeloproliferative neoplasms. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only curative option for CMML. Numerous studies have examined transplant outcomes and prognostic factors; however, the focus has primarily been on bone marrow transplantation (BMT) and peripheral blood stem cell transplantation, while cord blood transplantation (CBT) is understudied. To address this knowledge gap, we conducted a nationwide retrospective study to comprehensively compare the outcomes of unrelated BMT and single-unit umbilical CBT in patients with CMML. Methods Data were collected from the Transplant Registry Unified Management Program 2 of the Japanese Data Center for Hematopoietic Cell Transplantation. The inclusion criteria were as follows: age of 16 years or higher, a diagnosis of CMML, and receipt of the first allo-HSCT between 2013 and 2019 through unrelated BMT from a human leukocyte antigen (HLA) 8/8-matched donor (UBMT group) or single-unit umbilical CBT (CBT group). The primary endpoint was overall survival (OS) after allo-HSCT, and the secondary endpoints included progression-free survival (PFS), cumulative incidences of relapse and non-relapse mortality (NRM), neutrophil engraftment, and graft-versus-host (GVHD)-free, relapse-free survival (GRFS). The impact of CBT versus unrelated BMT on outcomes was evaluated using inverse probability of treatment weighting (IPTW) analysis. In this analysis, the Cox proportional hazards regression model for OS, PFS, and GRFS and the Fine-Gray proportional hazards regression model for relapse, NRM, engraftment, and GVHD were used. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated for all outcomes. The propensity score (PS) was calculated via logistic regression by using the following factors: age at allo-HSCT, sex, cytogenetic risk, disease status, days from diagnosis to allo-HSCT, and year of allo-HSCT. For the CBT group, the stabilized weights were calculated by dividing CBT prevalence by each individual's PS. Conversely, for the UBMT group, the weights were calculated by dividing the 1 minus prevalence of CBT by 1 minus each individual's PS. Results Between 2013 and 2021, 238 patients with CMML underwent their first allo-HSCT. Among them, 50 underwent HLA 8/8 allele-matched unrelated BMT (UBMT group) and 68 underwent single-unit umbilical CBT (CBT group). The median age at allo-HSCT was 58.5 (range: 26-75) years; the median follow-up period for survivors was 1,329.5 (range: 100-1,967) days. Intergroup differences in age at allo-HSCT, recipient sex, hematopoietic cell transplantation-specific comorbidity index, Eastern Cooperative Oncology Group performance status, cytogenetic risk, pre-transplant treatment, disease status at allo-HSCT, conditioning intensity, GVHD prophylaxis, and year of allo-HSCT were not significant. The transplantation outcomes are shown in Figure 1. There were no significant differences in the 3-year OS rate (UBMT: 51.0% [95% CI: 34.1-65.5%] vs CBT: 46.2% [95% CI: 33.2-58.1%]; P = 0.60; Figure 1A). IPTW analysis revealed no significant differences between the CBT and UBMT groups (HR: 1.21, 95% CI: 0.69-2.10, P = 0.51). PFS, relapse, NRM, and GRFS were not significantly different between the groups (Figure 1B-E). The neutrophil engraftment rate at 30 days was significantly higher in the UBMT group than in the CBT group (UBMT: 92.0% [95% CI: 78.9-97.1%] vs CBT: 79.4% [95% CI: 67.5-87.4%]; P &amp;lt; 0.01; Figure 1F). These observations associated with the secondary endpoints were concurrently corroborated by the IPTW analysis. Conclusion Our study suggests that CBT can serve as a viable treatment option, demonstrating efficacy comparable to that of unrelated BMT for patients with CMML. These findings underscore the improved outcomes over time after CBT in patients with CMML, which is a treatment previously perceived as inferior to other donor sources (Itonaga et al., Biol Blood Marrow Transplant. 2018;24:840-48). Further investigations are warranted to optimize transplantation strategies and improve outcomes in patients with CMML.

Updated Findings of a Phase II Study of Ruxolitinib Pre-, during- and Post-Hematopoietic Stem Cell Transplantation for Patients with Primary or Secondary Myelofibrosis

Background: Despite tremendous progress in the treatment of myelofibrosis in the last decade, the only curative therapy remains allogeneic hematopoietic cell transplantation (HCT). There are now three FDA-approved JAK inhibitors (JAKi) to treat symptomatic splenomegaly and constitutional symptoms in myelofibrosis, although these agents do not prevent disease progression. Discontinuation of JAKi before (pre) HCT is challenging as patients can experience return of symptoms. Thus, ruxolitinib is often continued during HCT in an off-label fashion; however, little is known about the safety and efficacy of this approach. Furthermore, there is increasing use of ruxolitinib after (post) HCT, following its approval in treating refractory graft-versus-host disease (GVHD). Methods: We previously reported the interim results of a phase II, multicenter, investigator-initiated trial investigating ruxolitinib given pre-, during- and for 1-year post-HCT for patients with primary or secondary MF (NCT03427866). Here we present the results of the study with full accrual of 43 patients. The primary endpoint was 1-year GVHD-free, relapse-free survival (GRFS). Secondary endpoints included overall (OS) and progression free survival (PFS), engraftment, and incidence of acute and chronic GVHD. Patients were treated with reduced intensity conditioning with fludarabine (30mg/m 2/d x 5 days) and melphalan (100 or 140mg/m 2 x 1). Patients received peripheral blood stem cell grafts from either 7/8 or 8/8 HLA-matched donors. GVHD prophylaxis consisted of standard tacrolimus and methotrexate. Results: 44 patients with myelofibrosis were enrolled and 43 underwent HCT between 9/2018 and 5/2023. Median age was 66 (range 46-75), 37% were female (n=16), and most patients had DIPSS intermediate-2/high risk (n=36), 60% (n=27) were receiving ruxolitinib prior to enrolling on the study. Most (n=35) received 8/8 matched unrelated transplants and had measurable splenomegaly by either ultrasound or CT (n=40) prior to HCT. At baseline, 25 patients had JAK2 mutation, 8 had CALR and 5 had MPL mutations, 13 patients had ASXL1 mutations (Figure 1). No differences in outcomes were observed by pre-HCT mutational status. At day 100, all but one patient had undetectable mutations by next generation sequencing. The most common grade 3/4 hematologic adverse events (AE) were anemia (n=12), thrombocytopenia (14), neutropenia (n=11). Non-hematologic grade 3/4 events included hypertriglyceridemia (n=3). Median time to neutrophil engraftment was 15 days (range 4-38), one patient did not engraft. Median time to platelet (&amp;gt;20x10 9) engraftment was 25 days (range 11-145). At day 30, 2 patients had a donor-cell chimerism below 90% (one ultimately relapsed) and at day 100, 2 patients had chimerism below 90 (one ultimately relapsed). With a median follow up among survivors of 13 months (range 0.7 - 26), 1-year GRFS was 74%. OS, PFS and cumulative incidence of NRM and disease relapse were, 86%, 79%, 10%, and 10%, respectively (Figure 2). The cumulative incidence of grade III-IV acute GVHD at 6 months was 2.4%. Only one patient had grade IV acute GVHD. One year moderate/severe chronic GVHD was 11%In univariable analysis, thrombocytopenia of &amp;lt;40 x 10 9/L pre-HCT was associated with worse OS (1-yr OS: 64% vs 92%, p=0.008). Splenomegaly (defined as &amp;gt;17 cm) was associated with worse PFS (1-yr PFS: 100% vs 64%, p=0.046). There was an improvement in OS in patients that received ruxolitinib and achieved response pre-HCT compared to those that did not but this did not achieve statistical significance (1-yr OS 100% vs 74%, p=0.054). Discussion: This study is the first, multicenter trial to test ruxolitinib use pre-, during- and post-HCT in patients with myelofibrosis. Our results demonstrate safety and feasibility of this approach. Favorable rates of engraftment were observed with ongoing ruxolitinib administration even through hematopoietic nadir. We continue to demonstrate favorable outcomes of PFS, OS and GRFS with a low incidence of severe acute and chronic GVHD. Our results strongly support the use of ruxolitinib in the peri- and post-transplant setting for patients with myelofibrosis undergoing HCT.

Impact of Graft Source [Cord Blood Supported By CD34+ Selected Cells (Haplo-Cord) Vs. Matched Donor] on Transplant Outcomes in Myelofibrosis

Introduction: Allogeneic hematopoietic cell transplantation (allo-HCT) is curative for patients with myelofibrosis (MF). Here, we evaluated the impact of donor type [cord blood transplant supported by CD34+ cells (haplo-cord) vs adult matched donor] on outcomes in MF. Methods: All adult patients with primary or secondary (post-ET or post-PV) MF, including those progressing to acute leukemia (AML) who underwent their first allo-HCT at NewYork-Presbyterian Hospital/Weill Cornell Medicine between 01/2015 and 06/2022 were included. Results: 40 patients were transplanted. Median age was 63 years (range 21-77). 23% had a Karnofsky performance scale (KPS) of &amp;lt;80. Two had undergone splenectomy prior to HCT. The median spleen size was 18cm (10-28). Median number of pre-HCT molecular mutations was 2 (range 0-7). 16 (40%) had MF-3 (Table 1). 24 (60%) underwent a matched sibling donor (MSD) (n=9) or unrelated donor (MUD) (n=15) HCT, and 16 (40%) underwent a cord-based (CB) HCT. 39 received Fludarabine/Melphalan +/- low dose total body irradiation (TBI), one underwent myeloablative conditioning with TBI/etoposide based on extensive extramedullary disease. The median time to neutrophil engraftment in the MSD/MUD group was 14 days (IQR 14-18) vs 30 days in the CB group (IQR 15-36) and (p=0.1). The median time to platelet engraftment was 22 days (IQR 17-38) in MSD/MUD vs 49 days (IQR 26-60) in the CB group (P=0.07). The CI of absolute neutrophil count (ANC) and platelet engraftment by day 60 for MSD/MUD vs CB was 92% (95% CI 65-98%) vs 80% (95% CI 45-94%) (p=0.09) and 75% (95% CI 51%- 88%) vs 59% (95% CI 27-81%) (p=0.36), respectively. One patient in the MSD/MUD died without neutrophil engraftment compared to 3 in CB group. 5 patients in each group died without platelet engraftment. Median follow-up for all alive patients was 53 months. Overall survival (OS) for the cohort was 62% at 1 year (95% CI 49-79) and 34% at 3 years (95% CI 21-55). OS at 3 years was similar between MSD/MUD group and CB (32% vs 37%, P=0.9) (figure 1). Graft versus host disease relapse free survival (GRFS) at 3 years was not significantly different in MSD/MUD group, compared to CB group (15% vs 33%, P=0.64). Cumulative incidence of relapse at 3 years in MSD/MUD group was 28% (95% CI 10-49), and 12% (95% CI 1.8-34) in CB group (p=0.356). Non-relapse mortality (NRM) at 1 year was 33% (95% CI 15-52) in MSD/MUD group and 38% (95% CI 15-61) in CB group. NRM at 3 years was 54% (95% CI 29-73) in MSD/MUD group and 48% (95% CI 19-72) on CB group (P=0.95). Discussion: In our small cohort, we showed that OS after haplo-cord transplant was comparable to adult matched donors' grafts (MSD or MUD). While the haplo-cord platforms have been shown to decrease the time to engraftment (11 days for neutrophils and 22 days for platelets) compared with double cord transplants or haploidentical transplants (van Besien K et al . Haematologica 2016, van Besien K et al. Blood Adv 2019), in patients with MF, we saw a trend towards delayed engraftment compared to patients transplanted with adult matched donors' grafts (MSD or MUD). This suggests that the CD34 selected cells may not be able to provide an adequate myeloid bridge and overcome the low cellular content in the CB for adult patients with extensive marrow fibrosis. Larger studies are needed to compare best alternative graft (CB-based versus haploidentical or mismatched unrelated donors) for patients with MF that lack a matched donor.

A Novel Post-Transplant Regimen for Selectively Promoting Unrelated Cord Blood Engraftment in Haploidentical-Cord Transplantation in Childhood Leukemia: A Single-Arm, Dual-Center Trial

Background Our previous studies indicated that complementary transplantation that was combined with a haploidentical peripheral blood stem cell (PBSC) transplant (haplo-SCT) and unrelated cord blood (UCB) transplant using a post-transplant cyclophosphamide (PTCy) regimen was applicable in children with acute leukemia. A better leukemia-free survival (LFS) was found in the UCB engraftment group, however, the engraftment of PBSC or UCB was unpredictable in the setting of complementary transplantation. Here, we conducted a prospective single-arm dual-center trial to investigate the effect of post-transplant cyclophosphamide plus fludarabine regimen for selectively promoting UCB engraftment in haploidentical-cord transplant. Methods This updated conditioning regimen was performed in two hospitals in China, including a total of eligible 78 pediatric patients who were enrolled from September 2019 to October 2022. The median follow-up was 24 months. This study is in progress. Meanwhile, 55 historically consecutive patients from December 2012 to June 2019 were included for comparison. The updated conditioning regimen (PT-Cy/Flu group) consisted of fludarabine (40mg/m 2, d-5 to d-3 and d+3, d+4), busulfan (100mg/m 2, d-6 to d-3), haplo-PBSC (d0), PTCy (50mg/kg, d+3, d+4) and UCB (d+6). The fludarabine was applied at d-6 to d-2 in the original conditioning regimen (PT-Cy group). In addition to PTCy, tacrolimus or cyclosporine and mycophenolate mofetil were administered as prophylaxis of GVHD. The primary aim was the UCB engraftment rate. In addition, the 2-year mid-term inspection included overall survival (OS), LFS, non-relapse mortality (NRM), graft-versus-host disease (GVHD)-free, relapse-free survival (GRFS), and cumulative incidence of acute and chronic GVHD. Results The characteristic of patients were shown in Table 1. In brief, 47 (60.3%) acute myeloid leukemia and 27 (34.6%) acute lymphoblastic leukemia pediatric patients were included. 64 (82.1%) patients achieved first complete remission (CR1) before SCT. The median of PBSC mononuclear cells was 20.0×10 8/kg and CD34 + cells was 12.1×10 6/kg, while the median of CB total nuclear cells was 5.0×10 7/kg and CD34 + cells was 1.8×10 5/kg. Eventually, 73 (93.6%) patients in the PT-Cy/Flu group achieved full UCB engraftment by short tandem repeat (STR) detection, while the UCB engraftment rate was 24 (43.6%) in the PT-Cy group (p&amp;lt;0.001). The OS of the PT-Cy/Flu group was 88.6% ± 4.0% (95%CI 81.2% - 96.7%), which was significantly higher than the PT-Cy group [60.0% ± 6.6% (95%CI 48.4% - 74.5%), p&amp;lt;0.001] (Figure 1A). Of note, the LFS was markedly higher in the PT-Cy/Flu group compared to PT-Cy group [83.2% ± 4.3% (95%CI 75.2% - 92.0%) vs. 54.2% ± 6.8% (95%CI 42.4% - 69.2%), p&amp;lt;0.001] (Figure 1B). However, there was no statistical difference in NRM between the PT-Cy/Flu and PT-Cy groups (7.7% ± 0.1% vs 12.7% ± 0.2%, p=0.326). Moreover, similar cumulative incidence of III-IV acute GVHD and severe chronic GVHD were found between groups (Figure 1C, D). Finally, the GRFS of the PT-Cy/Flu was obviously better than the PT-Cy group [70.1% ± 5.9% (95%CI 59.5% - 82.5%) vs 39.4% ± 7.6% (95%CI 27.0% - 57.5%), p=0.025] (Figure 1E). Conclusion These results suggested that the novel post-transplant cyclophosphamide plus fludarabine regimen can be considered as a strategy for selectively facilitating UCB engraftment and improving LFS in haploidentical-cord transplant in children with acute leukemia.

Allogeneic Hematopoietic Stem Cell Transplantation in Elderly Patients: The Experience of the Spanish Group of Hematopoietic Transplantation and Cell Therapy (GETH-TC)

Introduction Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is associated with significant toxicity and high risk of related mortality in older patients, especially when myeloablative conditioning is used. However, the upper limit of age for this procedure is not clearly defined. The aim of the study is to evaluate the safety and effectiveness of allo-HSCT in a cohort of elderly patients transplanted in Spain, considering non-relapse mortality (NRM), cumulative incidence (CI) of relapse, overall survival (OS) and progression-free survival (PFS). As secondary objectives, we evaluate the potential toxicity of allo-HSCT analyzing the days from infusion to hospital discharge, the number of readmissions within the first year, the CI of graft-versus-host disease (GvHD) and GVHD-free/relapse-free survival (GRFS). Finally, we also looked for prognostic factors significantly impacting OS. Methods We retrospectively analyzed 529 patients ≥65 years of age undergoing a first allo-HSCT between 2011 and 2020 in 17 Spanish centres, regardless of the indication and characteristics of transplantation. Subanalyses were performed according to chronological age (65-69 vs ≥70 years of age) and conditioning intensity (myeloablative vs non-myeloablative). Results Median age was 67.2 years (range 65.0-82.5) and 54 patients were ≥70 years. The most frequent indication was acute leukemia in 260 patients (49.1%). Clinical characteristics are shown in Table 1. Patients ≥70 years were more frequently male and had a lower HCT-CI than patients &amp;lt;70, without any other differences in patients' or transplant characteristics. The median follow-up was 51.2 months (range 9.3-139.6). At 1- and 4-years post-transplant, NRM were 24.3% (95%CI 21-28) and 32.0% (95%CI 28-36), CI of relapse were 21.4% (95%CI 18-25) and 29.1% (95%CI 25-33), OS were 61.2% (95%CI 57-65) and 43.4% (95%CI 39-48) and PFS were 54.3% (95%CI 50-58) and 38.9% (95%CI 35-43), respectively (Figure 1). No differences were found according to age group 65-69 vs ≥70 ( p=0.822, p=0.835, p=0.648 and p=0.743, respectively). Patients who had received myeloablative conditioning had lower CI of relapse (at 4 years post-transplant 19.3% vs. 30.7%, p=0.030), with no differences in NRM ( p=0.308), OS ( p=0.440) or PFS ( p=0.261). Regarding the duration of allo-HSCT admission, 486 patients were discharged alive, with a median number of hospital days from infusion to discharge of 22 (range 8-142). There were no differences based on age group ( p=0.635) or conditioning intensity ( p=0.606). Among 486 patients who were primary discharged, 320 (66.0%) needed a new readmission during the first-year post-transplant, with a median of 1 (range 0-6) up to day +100 and 2 (range 1-10) up to day +365. There were also no differences according to age ( p=0.789 and p=0.779, respectively) or conditioning intensity ( p=0.264 and p=0.818, espectively). Acute GvHD occurred in 265 patients (58.2%), 205 (45.1%) grades I-II and 60 (13.2%) grades III-IV. The CI of acute GvHD grades II-IV and grades III-IV at day +100 was 43.5% and 16.9%, respectively. A total of 174 patients (38.2%) developed chronic GvHD, 66 (14.6%) mild, 49 (10.8%) moderate and 56 (12.4%) severe. The CI of moderate-severe chronic GvHD at 1 and 2 years was 18.2% and 22.4%, respectively. According to age group, there were no differences in the CI of acute GvHD grades II-IV ( p=0.920), acute GvHD grades III-IV ( p=0.853) or chronic moderate-severe GvHD ( p=0.798). At 1- and 4-years after allo-HSCT, GRFS were 37.6% (95%CI 33-42) and 23.7% (95%CI 20-28), with no differences by age group ( p=0.569) or conditioning intensity ( p=0.707). In multivariate analysis, ECOG pretransplant ≥1 (HR 1.32, 95%CI 1-1.7; p=0.028), HCT-CI ≥3 (HR 1.34, 95%CI 1.1-1.7; p=0.016), high/very high DRI (HR 1.62, 95%CI 1.3-2.1; p&amp;lt;0.001) and no development of chronic GvHD (HR 2.99, 95%CI 2.3-3.9; p&amp;lt;0.001) were associated with worse OS. Age, gender, previous lines of treatment or autologous HSCT, donor type, stem cell source, conditioning intensity and development of acute GvHD did not influence OS. Conclusions Allo-HSCT is effective and safe at ages over 65 years, or even 70 years old. Myeloablative conditioning regimen may offer a lower risk of relapse without increasing toxicity. In our experience, ECOG, HCT-CI, DRI and chronic GvHD are more relevant parameters for post-transplant survival than chronological age.

Addition of Myeloablative Doses of Total Marrow Irradiation (TMI) to Myeloablative Fludarabine/Busulfan Conditioning for Allogeneic HSCT in Patients with High-Risk AML, CML, or Myelodysplastic Syndrome: A Phase II Clinical Trial

In allogeneic hematopoietic stem cell transplantation (HSCT) for high-risk myeloid disorders, the intensity of the conditioning regimen correlates with the risk of relapse, but its benefit may be offset by its risk of toxicity. The addition of increasing doses of TMI to myeloablative conditioning was previously shown to have acceptable toxicity in a phase I trial by our group (PMID 25234438), but the efficacy of this strategy remains uncertain. From 2017 to 2023, 31 patients with high-risk acute myeloid leukemia (AML, n=20) or myelodysplastic syndrome (MDS, n=5), or chronic myeloid leukemia (CML, n=3) in accelerated phase or blast crisis, were enrolled into a prospective phase II clinical trial of allogeneic HSCT using myeloablative TMI at 9Gy in combination with standard myeloablative fludarabine (160 mg/m2) and targeted IV busulfan (daily exposure of AUC 4800 μM*min over 3 hours) (FluBu4) chemotherapy. TMI was delivered by using volumetric modulated arc therapy (VMAT) at 1.5Gy twice per day for 3 days for a total of 9Gy. The primary objective of the trial was to achieve &amp;gt;50% Disease-Free Survival (DFS) at 1 year. Here, we report the results on 28 patients who received the TMI-based transplant, whereas among the remaining 3, 1 had not started the conditioning yet and 2 became ineligible due to progression of disease and deterioration of performance status, respectively. The study included patients with matched related donors (MRD, n=9) receiving TMI/FluBu4 as a preparative regimen and patients with matched unrelated (MUD, n=13) or 1-antigen mismatched unrelated (MMUD, n=6) donors receiving conditioning with TMI/FluBu4 + rabbit anti-thymocyte globulin (rATG). Graft-versus-host disease (GVHD) prophylaxis was with methotrexate and tacrolimus, and palifermin was used to prevent severe mucositis. Patients' gender ratio was 16 female/12 male; race was Caucasian in 17 patients, African American in 4, Latino in 7; and median age was 53 years (range: 20-68). The median HCT-Comorbidity Index (HCT-CI) was 3 (range: 0-7). All 20 AML patients were at high risk of relapse because of adverse cytogenetic or molecular profile at diagnosis (n=13), or in second complete remission (CR2) (n=2), or with active disease at the time of transplant (n=5). All patients received peripheral blood stem cells (PBSC) (median CD34+ cell dose: 8.5 x 10 6/kg, range: 2.4-19.9) and fully engrafted. The median time to absolute neutrophil count (ANC) and platelet engraftment was 14 (range: day 9-22) and 15 (range: day 9-43) days, respectively. Grade 3-4 extramedullary toxicities were: mucositis in 57% (n=16), nausea/vomiting in 11% (n=3) and diarrhea in 7% (n=2) of the patients. Acute GVHD grade III-IV was seen in 3 patients (10%). Moderate/severe chronic GVHD was observed in 10 patients (36%). With a median follow-up of 1315 days (range: 158-1925 days) for patients alive, the overall 1 year and current overall survival were 73% and 64%, respectively. GVHD-Free Relapse-Free Survival (GRFS) at 1-year was 54%. Of 5 AML patients transplanted with active disease, 3 were alive and in remission at 1 year and at current date, while 2 died of relapsed disease. Of 28 patients in the study, 6 relapsed/progressed (21%) and 5 of them died of the disease (18%); whereas 5 patients (18%) died of transplant-related mortality (TRM) (2 deaths from septic shock, 1 from disseminated toxoplasmosis, 1 from idiopathic pneumonia and 1 from unknown causes). Kaplan Meyer curves for Overall Survival (OS) and DFS are shown in Figure 1 and 2, respectively. Addition of myeloablative TMI at 9Gy to standard myeloablative targeted FluBu4 was well tolerated and achieved very encouraging results in a group of patients with myeloid malignancies at high risk of relapse (clinicaltrials.gov Identifier: NCT03121014).

The Area Under Tacrolimus Concentrations on Day 14-28 Is the Independent Predictor of the Development of Chronic Gvhd in Patients without Severe Acute Gvhd after Unrelated Allogeneic HSCT

Introduction: In unrelated allogeneic hematopoietic stem cell transplantation (UR-SCT), chronic graft-versus-host disease (GVHD) is a critical complication that affects not only patients' quality of life but also post-transplant outcome. Acute GVHD is a major risk factor for the subsequent development of chronic GVHD. The combination of tacrolimus and short-term methotrexate (TAC+sMTX) has been widely used as a GVHD prophylaxis for UR-SCT in Japan. Previous reports have shown that tacrolimus blood concentrations early after transplantation are associated with the development of acute GVHD, but not with that of chronic GVHD. On the other hand, among UR-SCT recipients who did not develop severe acute GVHD, the relationship between tacrolimus blood concentrations and the development of chronic GVHD remains unclear. Methods: To examine the association between tacrolimus blood concentrations and post-transplant outcomes, the area under the tacrolimus concentration on day 0-14 (AUTC 0-14) and day 14-28 (AUTC 14-28) was calculated simply as the sum of the area of the trapezoid for the corresponding period ( Figure). Tacrolimus was initiated by continuous intravenous administration from day -1 in all patients, and no patients were switched to oral administration prior to day 28. Short-term methotrexate was administered at 10 mg/m 2 on day 1 and 7 mg/m 2 on day 3, day 6, and day 11. Among all 151 adult patients with hematopoietic malignancies who underwent first UR-SCT with GVHD prophylaxis of TAC+sMTX between 2010 and 2022 at the Jikei University Hospital, the following were excluded from the analysis: developing grade III-to-IV acute GVHD, using prednisolone or methyl-prednisolone ≥0.5 mg/kg within day 100, engraftment failure, death before day 100, and relapse before day 100. Results: A total of 68 patients were included in the analysis. Median age was 50.5 (range, 16-68) years. Twenty-seven (40%) patients had acute myeloid leukemia, and 18 (27%) had acute lymphoblastic leukemia. Fifty-five (81%) were in complete remission/chronic phase/early stage. The donor source consisted of 42 (62%) bone marrow transplantation (BMT), 20 (29%) cord blood transplantation (CBT), and 6 (9%) peripheral blood stem cell transplantation (PBSCT). BMT recipients transplanted from 22 (52%) HLA 8/8 matched donor, 19 (45%) HLA 7/8 matched donor, and one (3%) HLA 6/8 matched donor. CBT recipients transplanted from 15 (75%) HLA 4/6 matched donor and 5 (25%) HLA 5/6 matched donor. PBSCT recipients transplanted from 5 (83%) HLA 8/8 matched donor and one (17%) HLA 7/8 matched donor. Fifteen (22%) patients were administered additional low-dose anti-thymocyte globulin (ATG) as GVHD prophylaxis. Fifteen male patients transplanted from female donors (22%). Thirty-nine (57%) patients received myeloablative conditioning regimen. The median time from UR-SCT to neutrophil engraftment was 19 days (range, 11-34). Regarding acute GVHD, 46 patients (68%) developed none, 13 patients (19%) developed grade I, and 9 patients (13%) developed grade II. The median observation period for all 68 patients was 48.2 months (4.0 years). The 4-year cumulative incidence (CI) of chronic GVHD was 51%, of which 24% were moderate-to-severe. The CI of moderate-to-severe chronic GVHD was not associated with age, disease status, donor source, HLA incompatibility, ATG use, female to male, intensity of conditioning regimen, and grade I-to-II acute GVHD development. AUTC 14-28 &amp;lt;200 was the only risk factor (AUTC 14-28&amp;lt;200: 32% vs AUTC 14-28≥200: 11%; p=0.047). Multivariate analysis also showed that AUTC 14-28 &amp;lt;200 was the independent factor for development of moderate-to-severe chronic GVHD ( p=0.04). In all 68 patients, 4-year CI of relapse was 20%, 4-year CI of non-relapse mortality was 10%, 4-year GVHD-free, relapse-free, survival (GRFS) was 50%, and 4-year Overall survival was 80%, all of which did not differ between AUTC 14-28 &amp;lt;200 and AUTC 14-28 ≥200 groups. Conclusion: In UR-SCT, our data showed that AUTC 14-28 &amp;lt;200 may be an independent risk factor for developing moderate-to-severe chronic GVHD, even in patients who did not develop severe acute GVHD.

Improving Outcomes of Peripheral Blood Stem Cell (PBSC) HLA-Mismatched Unrelated Donor (MMUD) Hematopoietic Cell Transplantation (HCT): Effect of Graft Versus Host Disease (GVHD) Prophylaxis

Human leukocyte antigen (HLA) well matched donor (related or unrelated) has remained the preferred donor source for patients undergoing HCT for hematological disease, but the probability of finding a suitable related or unrelated donor has varied based on ethnic groups. HLA-mismatch unrelated donor (MMUD) transplantation has improved access to HCT in underrepresented minority groups and patients of mixed race. Historically, MMUD HCT has been associated with inferior survival outcomes compared to matched unrelated donor HCT when using conventional platforms of GVHD prophylaxis. (PMID: 31449184, 20538804). Efforts to improve outcomes have investigated the addition of a third agent such as anti-thymocyte globulin (ATG), mini-methotrexate (MTX) or mycophenolate mofetil (MMF). More recently, a study by the National Marrow Donor Program (NMDP) demonstrated the feasibility of post-transplant cyclophosphamide (PTCy) based GVHD prophylaxis in MMUD HCT using bone marrow (BM) grafts (PMID: 33905264). Additionally, our group demonstrated promising overall survival (OS) and GVHD-free/relapse-free-survival (GRFS) rates in peripheral blood stem cell (PBSC) MMUD HCT using PTCy based GVHD prophylaxis (PMID: 34156440). Here, we compare outcomes of PBSC MMUD HCT among patients receiving GVHD prophylaxis with either: (1) tacrolimus plus sirolimus (T/S), (2) T/S plus mini-methotrexate (T/S/MTX), or (3) PTCy, MMF, and tacrolimus or sirolimus (PTCy). Patients with various hematologic malignancies that underwent PBSC MMUD HCT (≥5/8 HLA-matched donors) at City of Hope between January 2005 and December 2021 were included in this retrospective review. Of 390 subjects included, GVHD prophylaxis included T/S (n=114), T/S/MTX (n=160), and PTCy (n=116). The median age was 51 (range:15-79), 53.3% of patients belonged to a racial/ethnic minority, and 34.8% (n=136) patients had disease risk index high or very high. Degree of HLA mismatch was 7/8 (91.3%), 6/8 (8.5%), and 5/8 (0.3%). Hematologic diseases included AML (40.3%), ALL (20.3%), MDS/MPN (15.9%), Lymphoma (16.9%), and CML/CMMol (6.7%). Most common conditioning regimens were fTBI-based (34.4%) and melphalan-based (57.2%). HCT comorbidity index was ≥ 3 in 30.8% (n=120), which was most common in PTCy compared to T/S and T/S/MTX: 48.3% vs. 23.7% vs. 23.1%, P&amp;lt;.001. The rate of neutrophil engraftment (15 days vs. 15 days vs 16 days, P=0.002) and platelet engraftment (15 days vs. 16 days vs 27 days, P=0.004) were shorter in T/S compared to T/S/MTX and PTCy, respectively. With median follow-up of 5.4 years (range: 1.0-16.7) the 5-year OS was superior in PTCy (P=0.045) compared to T/S and T/S/MTX: 58.0% (95% CI: 46.6-67.8) vs. 41.1% (95% CI: 31.9-50.1) and 39.6% (95% CI: 32-47.2). The 5-year disease-free survival (DFS) was superior in PTCy (P=0.042) compared to T/S and T/S/MTX: 54.2% (95% CI: 43.3-63.9) vs. 37.1% (95% CI: 28.2-46.0) vs. 37.2% (95% CI: 29.7-44.6), respectively. There was no significant difference in 5-year cumulative incidence of relapse (CIR) in T/S vs. T/S/MTX vs. T/S vs. PTCy: 29.1% (95% CI: 21.0-37.6) vs. 29.5% (95% CI: 22.6-36.7) vs. 22.1% (95% CI: 14.3-31.0), respectively. Additionally, there was no significant difference in 2-year NRM between the cohorts (P=0.459): 24.6% (95% CI: 17.1-32.9) vs. 23.1% (95% CI: 16.9-29.9) vs. 20.4% (95% CI: 13.5-28.4), respectively. The rate of 100-day Grade III-IV acute GVHD were similar between in the cohorts (P=0.321): 19.3% (95% CI: 12.6-27.0) vs. 18.1% (95% CI: 12.6 -24.5) vs. 12.9% (95% CI: 7.6-19.7). When comparing T/S vs. T/S/MTX and PTCy, the incidence of chronic GVHD was less in the PTCy cohort at both 1-year and 2-years (P&amp;lt;.001) with 1-year incidence of 55.0% (95% CI: 45.1-63.7) vs. 61.9% (95% CI: 53.8-68.9) vs. 38.9% (95% CI: 30-47.8), respectively, and 2-year incidence of 58.9% (95% CI: 49.0-67.6) vs. 66.2% (95% CI: 58.3-73.1) vs. 42.7% (95% CI: 33.4-51.6), respectively. To our knowledge, this is the largest reported single center outcome of PBSC MMUD HCT. In this study, we demonstrate the superiority of PTCy based GVHD prophylaxis compared to T/S and T/S/MTX in outcomes of 5-year OS (P=0.045), 5-year DFS (P=0.042), and incidence of chronic GVHD (P&amp;lt;.001). Our experience further supports the superiority of PTCy as the preferred GVHD prophylaxis in the PBSC MMUD HCT setting achieved by lowering chronic GVHD and associated complications.

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

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