IL17A and graft versus host disease: Ultimately, a study investigating IL-4, IL-5, IL-9, and IL-13 quadruple cytokine-deficient T cells in a well-established mouse model demonstrated that combined Th2 cytokine deficiency resulted in enhanced T cell proliferation, higher TNF-α, IL-2, IFN-γ and IL-17a serum levels and overall aggravated GVHD (101).