Our previous studies using BMT mouse models suggested that host iNKT cells were indispensable for the induction of immune tolerance after a single injection of lipo α‐GC.12, 28, 29 Other studies using murine acute BMT models also showed that host‐derived iNKT cells played a critical role in aqueous α‐GC‐induced immune tolerance, mediated by the production of IL‐4 and IL‐10.9, 10 Our study showed the preventive effect of sclerodermatous GVHD by lipo α‐GC was canceled by anti‐IL‐4 antibody, suggesting that the tolerogenic activity of iNKT cells is in an IL‐4‐dependent manner. Here, IL4 is linked to graft versus host disease.