Itacitinib (INCB039110), a selective JAK1 inhibitor, disrupts the JAK1/STAT3 signaling pathway and was shown to improve GVHD outcomes and survival in various mouse models, partially by reduction of CD4 and CD8 T cell numbers in the inflamed colon tissue, indicating a loss of Th17 phenotype (178–180). This evidence concerns the gene JAK1 and graft versus host disease.