HLA-haploidentical transplantation with post-transplant cyclophosphamide

Recently, post-transplant cyclophosphamide (PTCy) -based HLA-haploidentical stem cell transplantation (PTCy-haploSCT) has been increasingly performed. The mechanism of GVHD prevention by PTCy is selective depletion of proliferating alloreactive T cells, while preserving non-alloreactive T cells. Several studies have reported that the incidence of non-relapse mortality, relapse, disease-free survival, and overall survival after PTCy-haploSCT are equivalent to those after HLA-matched SCT. Furthermore, the incidence of GVHD, especially chronic GVHD, after PTCy-haploSCT was lower than that of HLA-matched SCT. In Japan, we have conducted several prospective, multicenter, phase II studies since 2013. To reduce relapse, several strategies have been developed. In the first study (Haplo13), we used peripheral blood stem cells and added busulfan (BU) to the original non-myeloablative regimen developed by a Johns Hopkins group. In the second study, we used a BU- or TBI-based myeloablative conditioning regimen (Haplo14 MAC). In the third study, we reduced the dose of PTCy (Haplo16 RIC). In the latest study (Haplo17), we reduced the dose and/or duration of MMF and tacrolimus. We hope that these studies improve the outcome of PTCy-haploSCT.