Haploidentical transplant with posttransplant cyclophosphamide vs matched related and unrelated donor transplant in acute myeloid leukemia and myelodysplastic neoplasm

Abstract Hematopoietic cell transplantation from haploidentical donors (haploHCT) has facilitated treatment of AML and MDS by increasing donor availability and became more feasible since the introduction of post-transplant cyclophosphamide (ptCY). In our single-center retrospective analysis including 213 patients with AML or MDS, we compare the outcome of haploHCT (n=40) with ptCY with HCT from HLA-identical MRD (n=105) and MUD (n=68). At 2 years after transplantation, overall survival (OS) after haploHCT was not significantly different (0.59; 95% confidence interval 0.44 - 0.79) compared to MRD (0.77; 0.67 - 0.88) and MUD transplantation (0.72; 0.64 - 0.82, p = 0.51). While progression-free survival (PFS) was also not significantly different (haploHCT: 0.60; 0.46 - 0.78, MRD: 0.55; 0.44 - 0.69, MUD: 0.64; 0.55 - 0.74, p = 0.64), non-relapse mortality (NRM) was significantly higher after haploHCT (0.18; 0.08 - 0.33) vs. MRD (0.029; 0.005 - 0.09) and MUD (0.06; 0.02 - 0.12, p<0.05). Higher NRM was mainly caused by a higher rate of fatal infections, while deaths related to GvHD or other non-relapse reasons were rare in all groups. As most fatal infections occurred early and were bacterial related, one potential risk factor among many was identified in the significantly longer time to neutrophil engraftment after haploHCT with a median of 16 days (interquartile range; 14.8 - 20.0) vs. 12 days (10.0 - 13.0) for MRD and 11 days (10.0 - 13.0) for MUD (p=0.01).