We assessed Ceacam1 regulation of GHVD on donor T cells or recipients in two well-described major histocompatibility complex (MHC) class I/II-disparate models C57BL/6 (B6, H-2 b )RBALB/ c (H-2 d ) and BALB/cRB10.BR (H-2 k ). We used Ceacam1 2/2 B6 mice [28] , Ceacam1-transgenic (Tg) B6 mice (described in Figure  S1 ), and Ceacam1 2/2 BALB/c mice [28] as the source of donor T cells or recipients. In all experiments, recipients received splitdose lethal irradiation (BALB/c: 8.5 Gy, B10.BR: 11 Gy) and a graft of 5610 6 allogeneic T cell depleted bone marrow (TCD-BM) of wildtype (WT) origin, with or without splenic T cells.