Based on our previous studies, the helminthic regulation of GVHD is dependent on Th2 cytokine IL4 generation by recipient cells, which in our further studies in IL4Rα-/-, T cell-specific IL4Rα-/- and STAT6-/- BMT recipients [6,10,11] appears to act on other BMT recipient cells (more specifically on recipient cell IL4 receptor and STAT6) to condition the host and regulate GVHD. This evidence concerns the gene STAT6 and graft versus host disease.