Chronic graft versus host disease (cGVHD) remains a major problem for long survivors after allogeneic hematopoietic stem cell transplantation (HSCT). Currently, corticosteroid therapy is effective for cGVHD as the first line therapy. However, prolonged therapy with corticosteroids causes various severe adverse events. To develop the new therapeutic strategy of cGVHD, we have launched a multicenter phase I/IIa clinical trial of low dose subcutaneous interleukin-2 (IL-2) for treatment of steroid refractory cGVHD, which is constituted of 2 sequential phases (induction phase and maitanance phase). This study will provide the new therapeutic option for patients with refractory cGVHD after allogeneic HSCT.