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.