Sigle Agent of Posttransplant Cyclophosphamide Without Calcineurin Inhibitor Controls Severity of Experimental Chronic GVHD

Chronic graft-versus-host disease (GVHD) is a major cause of late death and morbidity following allogeneic hematopoietic cell transplantation (HCT), but its pathogenesis remains unclear. Recently, haplo-identical HCT with post-transplant cyclophosphamide (Haplo-HCT with PTCY) was found to achieve a low incidence rate of acute GVHD and chronic GVHD. However, while the pathogenesis of acute GVHD following Haplo-HCT with PTCY has been well investigated, that of chronic GVHD remains to be elucidated, especially in HLA-matched HCT with PTCY. Based on its safety profile, PTCY is currently applied for the human leucocyte antigen (HLA)-matched HCT setting. Here, we investigated the mechanisms of chronic GVHD following HLAmatched HCT with PTCY using a well-defined mouse chronic GVHD model. PTCY attenuated clinical and pathological chronic GVHD by suppressing effector T-cells and preserving regulatory T-cells compared with a control group. Additionally, we demonstrated that cyclosporine A (CsA) did not show any additional positive effects on attenuation of GVHD in PTCY-treated recipients. These results suggest that monotherapy with PTCY without CsA could be a promising strategy for the prevention of chronic GVHD following HLA-matched HCT.