ICOS and graft versus host disease: Although we did not see consistent alteration in major T cell subsets associated with GVHD, we observed significant upregulation in Inducible T cell Costimulator (ICOS) in both CD4+ and CD8α+ T cell subsets in mice developing GVHD compared to those with normal hematopoiesis, and the expression of ICOS was reduced after BRNP treatment (Figure 6).