Outcomes of salvage haploidentical transplantation using posttransplant cyclophosphamide for graft failure following allogeneic hematopoietic stem cell transplantation.

Haploidentical donors have emerged as an alternative donor source for salvage stem cell transplantation (SCT) after graft failure; however, data regarding salvage haploidentical SCT using posttransplant cyclophosphamide (PTCy) are limited. Using nationwide data (2011-2019), we retrospectively investigated transplant outcomes after salvage haploidentical SCT using PTCy for graft failure (n = 33, median age 34 years). The total dose of PTCy was 75-100 mg/kg (standard dose) in 26 patients (78.8%) and 40-50 mg/kg (lower dose) in 5 patients (15.2%). The neutrophil engraftment rate at 30 days was 81.8%. One-year overall survival (OS) and non-relapse mortality (NRM) rates were 47.4% and 46.0%, respectively. The standard-dose group exhibited better OS (61.1% vs. 0.0% at 1 year, P = 0.022) and NRM (35.1% vs. 80.0% at 1 year, P = 0.052) than the lower-dose group. Moreover, the standard-dose group was less prone to both grades II-IV (11.5% vs. 40.0%) and III-IV (0.0% vs. 40.0%) acute graft-versus-host disease (GVHD). Use of cyclophosphamide in previous SCT and conditioning did not affect OS or NRM. In conclusion, haploidentical salvage SCT using PTCy offers promising survival outcomes. Prospective studies are required to validate the efficacy of salvage haploidentical SCT using PTCy.