In MHC-mismatched murine models, the absence of CEACAM1 on donor T cells exacerbates GVHD, with higher alloreactive T cell infiltration in the gut (28); loss of Ceacam1 in the host also leads to increased sensitivity to radiation damage and increased infiltration of donor T cells in the lower GI tract of GVHD recipients (28). Here, CEACAM1 is linked to graft versus host disease.