Comparison of total body irradiation-based conditioning regimens vs chemotherapy-based protocols in haploidentical stem cell transplants in a Pakistani cohort – A single-center experience

Abstract

Objective: To compare the outcomes of total body irradiation (TBI)-based and chemotherapy (CT)-based conditioning regimens in patients undergoing haploidentical hematopoietic stem cell transplantation (Haplo-HSCT).

Methodology: This retrospective single-center comparative study included 50 consecutive patients who underwent Haplo-HSCT at Shifa International Hospital, Islamabad, between January 2016 and September 2023. Patients received either TBI-based conditioning (n=21) or CT-based conditioning (n=29). Primary endpoints were overall survival (OS), progression-free survival (PFS), and graft-versus-host disease/relapse-free survival (GRFS). Secondary outcomes included neutrophil and platelet engraftment, transplant-related mortality (TRM), non-relapse mortality (NRM), relapse, engraftment failure, and graft-versus-host disease (GvHD). Survival outcomes were analyzed using Kaplan-Meier methods.

Results: The mean age was 23.4±12.2 years in the TBI group and 28.7±11.9 years in the CT group; 76% of patients were male. Median follow-up was 11.5 months. Two-year OS was 37.0% in the TBI group and 41.4% in the CT group, while two-year PFS was 37.0% and 41.4%, respectively. GRFS was similarly low in both groups (12.7% vs. 13.8%). Neutrophil engraftment occurred significantly earlier with TBI-based conditioning (median Day +13 vs. Day +14; p=0.032), whereas platelet engraftment was comparable. TRM (38.1% vs. 41.4%), NRM (14.3% vs. 13.7%), relapse (14.3% vs. 13.7%), and acute or chronic GvHD rates were similar between groups. Primary engraftment failure occurred only in the TBI group (9.5%).

Conclusion: TBI- and CT-based conditioning regimens produced comparable survival outcomes following Haplo-HSCT. Although TBI-based conditioning resulted in significantly faster neutrophil engraftment, it was associated with a higher incidence of primary engraftment failure. Larger prospective multicenter studies are needed to confirm these findings.