Graft-versus-Host-Disease (GVHD) is still the major obstacle for the widespread application of allogeneic hematopoietic cell transplantation (HCT). Cytokines from activated and differentiated donor CD4<sup>+</sup> T cells have been shown to play a critical role in the pathogenesis of GVHD by amplifying T cell expansion and mediating host tissue damage. Activated CD4<sup>+</sup> T cells can differentiate into Th1, Th2, and Th17 subsets under different cytokine milieus, and they play different roles in inflammatory response. We recently reported that the lack of donor Th17 led to augmented Th1 differentiation and exacerbated acute GVHD. Absence of IFN-g from donor T cells was also reported by others to induce exacerbated GVHD, but the differentiation status of donor IFN-g deficient donor CD4<sup>+</sup> T cells and their role in GVHD pathogenesis has not been studied. In a MHC-mismatched HCT model of C57BL/6 (H-2<sup>b</sup>) donor to BALB/c (H-2<sup>d</sup>) recipient, we found that wild-type donor CD4<sup>+</sup> T cells predominately differentiate into IFN-g-producing Th1 cells, and mediate GVHD tissue damage in gut, liver, lung, and skin. Absence of IFN-g in donor CD4<sup>+</sup> T cells results in augmented differentiation of Th2 and Th17 and exacerbated GVHD tissue damage in the lung and skin, but ameliorated GVHD tissue damage in the gut and liver. Absence of both IFN-g and IL-17 in donor CD4<sup>+ </sup>T cells leads to further augmentation of Th2 differentiation and lung tissue damage, but reduction of tissue damage in the gut, liver, and skin. These results indicate that donor CD4<sup>+</sup> T cells reciprocally differentiate into Th1, Th2, and Th17 in acute GVHD recipients, and different Th subsets mediate organ-specific tissue damage.