Haploidentical Peripheral Stem Cell Transplantation for Young Patients with Severe Aplastic Anemia Using Post-Transplantation Cyclophosphamide and Methotrexate.

Severe aplastic anemia (SAA) is a serious bone marrow failure disorder that is often cured with hematopoietic stem cell transplantation (HSCT). The absence of a matched related donor is common, however, and thus novel approaches are needed to safely expand the donor pool to include alternative donors, especially haploidentical related donors, for patients with SAA. This study aimed to explore a novel approach to HSCT for patients with SAA without an available HLA-identical sibling or a matched unrelated donor, termed haploidentical peripheral blood stem cell transplantation (haplo-PBSCT), using a conditioning regimen comprising cyclophosphamide, busulfan, and fludarabine (CBF) and a graft-versus-host disease (GVHD) prophylaxis regimen with post-transplantation cyclophosphamide (PTCy), low-dose methotrexate (LD-MTX), and calcineurin inhibitors. This prospectively designed nonrandomized study included 29 patients with SAA who underwent haplo-PBSCT between November 2017 and May 2020. The median patient age was 17 years (range, 14 to 30 years), and the median time to neutrophil recovery was 13 days (range, 13 to 15 days). There was 1 primary graft failure (GF) in the group receiving PTCy at a dose of 50 mg/kg and no GFs in the group receiving PTCy at a dose of 100 mg/kg. The median duration of follow-up was 736 days (95% confidence interval, 512 to 879 days). The estimated 1-year overall survival and disease-free survival were 91.7 ± 5.7% and 89.7 ± 5.7%, respectively. Only 1 of the 27 patients developed grade II acute GVHD. Four patients developed limited and mild chronic GVHD, involving only the skin or/and oral mucosa. Haplo-PBSCT following CBF and followed by PTCy and LD-MTX represents a novel approach for safely expanding the donor pool to include alternative donors for young patients with SAA.