CEACAM1 and graft versus host disease: Although integrin α4β7 is important for GVHD pathogenesis, and we have previously shown that β7−/− T cells cause a sustained decrease in acute systemic and intestinal GVHD [31], differential expression of integrin α4β7 by Ceacam1−/− T cells is almost certainly only one part of how Ceacam1 regulates target organ GVHD.