Haploidentical vs Mismatched Unrelated Donor Transplants with Posttransplant Cyclophosphamide-based GVHD Prophylaxis

Abstract

Post-transplant cyclophosphamide (PTcy) as a GVHD prevention strategy has provided encouraging results in haploidentical and mismatched unrelated donor (MMUD) transplants. We sought to determine overall survival and GVHD-free relapse-free survival (GRFS) between haploidentical and MMUD using PTcy-contaning GVHD prophylaxis. We retrospectively compared outcomes of 144 adult patients who underwent either haploidentical or MMUD transplants using peripheral blood stem cells, and PTcy, tacrolimus, and mycophenolate for GVHD prophylaxis. Between January 2013 and December 2021, 89 patients received haploidentical and 55 received MMUD transplants. Among MMUD, 87% (n=48) were 7/8 HLA-matched and 13% (n=7) were 6/8 HLA-matched. Median age of the population was 62.5 years, 24% (n=35) were African American, 73% (n=105) had AML, and 20% (n=29) received myeloablative conditioning regimen. Median time to neutrophil engraftment was prolonged in the haploidentical group (18 vs 15 days, p<0.001), while platelet engraftment was similar (23 vs 21 days, p=0.15). Using propensity score-based covariate adjustment, no difference in overall survival and GRFS was noted between both groups. Our study demonstrated that transplant outcomes did not differ between haploidentical and MMUD when PTcy was used for GVHD prophylaxis. In the absence of HLA-matched donors, haploidentical and MMUD appear to provide equivalent outcomes.