STAT6 drives the expression of anti-tumor effector proteins, such as IFNγ or FasL, and directly stimulates the expression of other anti-tumor effectors, such as granzyme A or granzyme B. Last, STAT6 activates donor T cell Th2 pathway and regulatory cytokine production and thereby has an impact on generation/expansion of GVHD-regulating donor T lymphocytes. This evidence concerns the gene STAT6 and graft versus host disease.