Post-transplant high-dose cyclophosphamide after HLA-matched vs haploidentical hematopoietic cell transplantation for AML

Post-transplant cyclophosphamide (PT-Cy) is the backbone of GvHD prophylaxis following haploidentical hematopoietic cell transplantation (haplo-HCT). PT-Cy has also been used in matched related (MRD) and unrelated (MUD) settings. It is not known whether outcomes are similar between haplo-HCT and MRD/MUD HCT when PT-Cy is used. We performed a retrospective analysis of 83 patients with AML who underwent HCT (using PT-Cy-based GvHD prophylaxis) from MRD, MUD or haploidentical donors. The groups were similar in baseline characteristics with the exception of older age in the MRD/MUD group (P=0.012). In multivariate analysis, the effect of donor type (MRD/MUD vs haploidentical) on transplant outcomes was not significant in any of the models except for faster neutrophil recovery after MRD/MUD transplants (hazard ratio: 2.21; 95% confidence interval: 1.31-3.72, P=0.002). In conclusion, we showed similar outcomes in MRD/MUD vs haploidentical HCT (except slower count recovery following haplo-HCT) when PT-Cy is used for GvHD prophylaxis. Although slower count recovery following haplo-HCT (compared with MRD/MUD transplants without PT-Cy) has been attributed to using PT-Cy, our results suggest that HLA disparity is the primary cause of this difference. Furthermore, our analysis supports PT-Cy as a viable option for GvHD prophylaxis after MRD/MUD transplants.