We first transplanted irradiated BALB/c mice with B6 TCD-BM with WT or Ceacam1 2/2 T cells, and observed that recipients of Ceacam1 2/2 T cells had significantly increased mortality compared to recipients of WT T cells ( Figure 1A , left). We confirmed this in a second MHC-disparate allo-BMT model, BALB/cRB10.BR ( Figure 1A, right) .