CD4 and graft versus host disease: Although both have previously been associated with cGVHD [25], it has been shown that IL-17A is capable of suppressing the production and secretion of IL-17F [26] and that IL-17A-producing CD4 T (Th17) cells induce GVHD, whereas the IL-17A cytokine is protective in GVHD after allogeneic bone marrow transplantation [27].