We believe that the reprogramming of cytotoxic CD8+ T cells into innocuous cells results from what we have termed “defensive tolerance.” Our further understanding of how this reprogramming is accomplished in some allografts or tumors has implications for designing more effective, clinically applicable treatment protocols for achieving allotransplant tolerance, as well as giving us an understanding of tumor immunobiology. The gene discussed is CD8A; the disease is neoplasm.