Indeed, recent adoptive transfer studies have reported that the administration of purified donor‐type iNKT cells, or even third‐party iNKT cells, potently suppressed GVHD.31, 32 Furthermore, similar results were observed in a systemic lupus erythematosus model, in addition to GVHD models.33, 34 In this study, we found that the proportion of donor Tregs among CD4+ T cells was much higher than that of host Tregs, and donor Tregs were indispensable for the prevention of cGVHD symptoms. Here, CD4 is linked to graft versus host disease.