The requirement for CD8 cell-intrinsic molecules can be determined by the use of a CD8 T-cell adoptive transfer model. (A) Experimental scheme: K^bD^b double-deficient recipients lacking CD8 T cells were treated with 3 Gy TBI/anti-CD154 mAb followed by infusion of 9 × 10⁶ WT CD8 T cells at the time of T cell–depleted allogeneic BMT. (B) K^bD^b double-deficient recipients were treated as depicted in panel A. For groups A and B, in vivo CD4 depletion was added to demonstrate that the transferred CD8 T cells are capable of rejection; in contrast, the CD4 cell–replete group C shows that these CD8 cells can be tolerized when CD4 cells are present; group D is a control group that did not receive CD8-cell transfer (n = 6-7/group).