Outcomes of Peripheral Blood Haploidentical Stem Cell Transplantation With Post-Transplant Cyclophosphamide and Earlier Initiation of Immunosuppression.

Introduction: Peripheral blood (PB) grafts are increasingly used in haploidentical hematopoietic stem cell transplantation (haplo-HSCT) with post-transplant cyclophosphamide (PT-Cy). The optimal timing for initiation of immunosuppression (IS) with calcineurin inhibitors (CNI) and mycophenolate mofetil (MMF) in PB haplo-HSCT is unclear. This study evaluates the outcomes of early initiation of IS prior to PT-Cy.

Methods: Medical records of adult patients with hematologic malignancies who received PB haplo-HSCT with PT-Cy between 2017 and 2022 were retrospectively reviewed. IS with CNI and MMF were started on day 0 and 1 postinfusion. Statistical analyses for survival outcomes were performed using the Kaplan-Meier method, and cumulative incidence (CI) models were used to account for competing risks for relapse, and nonrelapse mortality (NRM).

Results: A total of 51 patients were included, with a median age of 37 years (range: 19-63) and a median follow-up of 44 months (range: 37.8-53 months). Neutrophil and platelet engraftment were achieved in 98% and 96% of patients, respectively. CRS occurred in 35.3% of patients, predominantly grade I, with only 1 patient developing grade II CRS. At 3 years, overall survival (OS) and progression free survival (PFS) were 51.8% and 50.2%, respectively, and GVHD-relapse free survival (GFRS) was 43.1%. The CI of relapse and NRM at 3 years were 28.2% and 21.6%, respectively.

Conclusion: Early initiation of IS in PB haplo-HSCT was associated with high rates of engraftment, low rates of CRS, and favorable long-term survival outcomes. Prospective studies are needed to validate these findings and refine IS timing.