In contrast, recipients of IFN-γ−/−CD8+ T co-housed with non-GVHD recipients of WT CD8+ T cells showed significant reduction in Gut-aGVHD severity with reduction of diarrhea and higher bodyweight and survival (Fig. 7a) and lower prevalence of E. coli but higher prevalence of Lactobacillus and Clostridiaceae (Fig. 7b). The gene discussed is IFNG; the disease is graft versus host disease.