We next asked whether T cells overexpressing Ceacam1 would cause less disease, and transplanted BALB/c recipients with 0.5610 6 or 1610 6 donor WT or Ceacam 1-Tg T cells. At both doses, recipients of Ceacam1-Tg T cells showed attenuated mortality ( Figure 1B) . Finally, we assessed the role of Ceacam1 on tissues of allo-BMT recipients, and transferred TCD-BM+T cells into WT vs. Cea-cam1 2/2 BALB/c recipients. This revealed that Ceacam1 2/2 recipients had increased early (but not overall) mortality, with nearly 50% of mice succumbing within the first week ( Figure 1C ).