Chronic graft-versus-host disease (GVHD) is a major cause of late death and morbidity following allogeneic hematopoietic cell transplantation (HSCT). Retinoic acid (tamibarotene) exerts multiple effects on cell differentiation and is clinically used for the treatment of acute promyelocytic leukemia. Tamibarotene down-regulates both Th1 and Th17 differentiation in donor T cells after allogeneic HSCT, resulting in attenuation of experimental chronic GVHD. Based on preclinical data, we have launched a phase II study of tamibarotene in patients with steroid-refractory chronic GVHD. This study will clarify whether tamibarotene can exert beneficial effects in patients with steroid-refractory chronic GVHD.