HLA-haploidentical stem cell transplantation using posttransplant cyclophosphamide

Abstract

 Human leukocyte antigen (HLA)-haploidentical stem cell transplantation using posttransplant cyclophosphamide (PTCy-haplo) is rapidly increasing worldwide. In Japan, the number of HLA-haploidentical stem cell transplantations exceeded that of related HLA-matched transplantations in 2020. In 2024, PTCy was approved for insurance coverage. Recent retrospective studies using Japanese registry data demonstrated that the transplantation outcomes of PTCy-haplo are comparable to those of HLA-matched unrelated and cord blood transplantations. PTCy-haplo was initially developed for bone marrow transplantation after non-myeloablative conditioning; however, it has become widely used in peripheral blood stem cell transplantation and myeloablative conditioning. Several strategies have been attempted to improve transplantation outcomes with PTCy-haplo, including using peripheral blood stem cells, increasing the number of infused CD34-positive cells, younger donors, HLA class Ⅱ mismatches, HLA-B leader matching, reduced PTCy dose, early initiation of calcineurin inhibitors, and posttransplant maintenance therapy. Furthermore, PTCy has shown efficacy in HLA-matched and HLA 1-2 allele mismatched transplantations, with favorable results reported in a prospective Japanese phase Ⅱ trial. We aim to achieve safer allogeneic transplantation by sufficiently suppressing GVHD using PTCy.