Outcomes after Bone Marrow Versus Peripheral Blood Matched Unrelated Donor Allogeneic Hematopoietic Cell Transplantation Using Posttransplant Cyclophosphamide-Based Graft Versus Host Disease Prophylaxis

Background: Allogeneic hematopoietic cell transplantation (HCT) is a potentially curative treatment for various hematologic malignancies and disorders. The choice of graft source, whether bone marrow (BM) or peripheral blood stem cells (PBSC), plays a crucial role in transplantation outcomes. We aim to compare the outcomes of BM versus PBSC grafts in patients undergoing matched unrelated donor (MUD) HCT with posttransplant cyclophosphamide (PT-Cy)-based graft-versus-host disease (GVHD) prophylaxis.

Methods: A retrospective multicenter study was conducted, including patients receiving MUD HCT with PT-Cy-based GVHD prophylaxis from 2013 to 2018, in the publicly available Center for International Blood and Marrow Transplant (CIBMTR) registry dataset (P5646, Ramathan et al). Chi-square and t-test were used to compare categorical and continuous baseline demographics respectively. We examined the impact of graft source on post-transplant outcomes such as overall survival (OS), disease-free survival (DFS), relapse, transplant-related mortality (TRM), acute GVHD (aGVHD), and chronic GVHD (cGVHD), and engraftment. Cox regression analyses were conducted for OS, DFS, relapse, TRM, aGVHD, cGVHD, and platelet and neutrophil engraftment. The hazard ratios (HR) with 95% confidence intervals (CI) were calculated. The multivariate analyses were adjusted for significant variables identified in the univariate analysis. Statistical analysis was conducted using SPSS version 28 and R version 4.16. Significance was considered at p <0.05.

Results: We included 206 MUD HCT recipients receiving PT-Cy-based GVHD prophylaxis, with a median age of 62.5 (48.9-67.3) years, and 121 (58.7%) patients were male. Primary diagnoses were acute myeloid leukemia (AML) in 107 (51.9%) patients, acute lymphocytic leukemia (ALL) in 25 (12.1%) patients, and myelodysplastic syndrome (MDS) in 74 (36%) patients. The Karnofsky performance status (KPS) was 80% in 16% (n=33), 80-89% in 25.2% (n=52), and 90% or higher in 57.3% (n=118) of patients. The Hematopoietic Cell Transplantation-specific Comorbidity Index (HCT-CI) was 0 in 15.5% (n=32), 1-2 in 28.6% (n=59), 3-4 in 39.9% (n=82), and 5 or higher in 16.5% (n=34) of patients. Myeloablative conditioning was used in 54.4% (n=112) of patients. BM graft was used in 32.5% (n=67) patients while 67.5% (n=139) received a PBSC graft. The Cox regression analyses revealed no significant differences in overall survival, relapse, DFS, TRM, aGVHD, and cGVHD between BM and PB graft types. The univariate regression analyses revealed no significant differences in overall survival, relapse, DFS, TRM, aGVHD, and cGVHD between BM and PB graft types after MUD HCT with PT-Cy-based GvHD prophylaxis. However, PB compared to BM grafts was associated with significantly faster neutrophil engraftment (HR 1.56, 95% CI 1.16-2.09, p<0.05) and faster platelet engraftment (HR 1.61, 95% CI 1.18-2.19, p<0.05). In the adjusted multivariate model, PB compared to BM grafts demonstrated significantly faster platelet engraftment (HR 1.89, 95% CI 1.16-3.07, p<0.05).

Conclusion: We observed no significant differences in post-transplant outcomes including overall and disease-free survival, relapse, transplant-related mortality, and acute and chronic GVHD between the bone marrow or peripheral blood stem cell grafts after a matched unrelated donor HCT with PT-Cy-based GVHD prophylaxis; however, faster engraftment was observed with a peripheral blood stem cell graft.