CD4 and graft versus host disease: Transfer of increased ratios of tTreg (PBMC:tTreg 4:1–10:1) blocked the activation, differentiation, and expansion of CD4+ T cells and subsequently prevented all signs of GvHD, demonstrating that this human/mouse chimeric animal model is applicable for the analysis of human tTreg function, and tTreg cellular therapeutics in vivo.