Post-Transplant Cyclophosphamide Is Associated with Improved Clinical Outcomes in HLA-Mismatched Unrelated Donor Hematopoietic Cell Transplantation

The current standard of care to prevent graft versus host disease (GVHD) after HLA mismatched unrelated donor (URD) allogeneic hematopoietic cell transplantation (HCT) is tacrolimus, methotrexate (MTX) and anti-thymocyte globulin (ATG). Recently, an approach based on administration of post-transplant cyclophosphamide (PT-Cy) demonstrated promise in a prospective trial for HLA mismatched URD HCT. Here, we compared tacrolimus/MTX/ATG (ATG group) treatment, with that of PT-Cy, mycophenolate mofetil, and tacrolimus or sirolimus (PT-Cy group) after HLA mismatched URD HCT, at two academic centers with similar peri-transplant supportive care practices. Subjects that underwent HCT from a URD mismatched at one or more loci among HLA-A, -B, -C, and -DRB1 from 2010-2020 were included. The primary endpoint of our study was one-year GVHD-free, relapse-free survival (GRFS). Of 128 total subjects included (ATG: 46; PT-Cy: 82), the median age was 54.7 (range: 21.0 - 72.0) in the ATG group and 60.3 (21.0 - 75.2) in the PT-Cy group. Notably, 74 subjects (57.8%) belonged to a racial/ethnic minority, while 53 (41.4%) received a bone marrow (BM) graft, and 26 (20.3%) received a highly mismatched (i.e.,