Cross-priming, a process in which DCs activate CD8 T cells by cross-presenting exogenous antigens onto MHC class I molecules [2,3], plays a critical role in generating CD8 T cell immunity against cancers and viruses, upon vaccination, as well as in the induction of CD8 T cell tolerance (cross-tolerance) [4,5,6,7]. The gene discussed is CD8A; the disease is cancer.