We transferred equal numbers (1:1 ratio) of congenically-marked antigen-specific gene-deleted naive CD8+ T cells and control cells to an unmanipulated host that was subsequently challenged with viral infection or tumor (Fig. 3a and Supplementary Fig. 2d) to compare the phenotype and function of the gene-deleted and control T cells in the same microenvironment. This evidence concerns the gene CD8A and neoplasm.