TILs isolated from tumors in many model systems, as well as humans with certain types of tumors, show skewed CD4+:CD8+ cell ratios with increased numbers of CD8+ T cells within the tumor, but not in the periphery [105,106,107] (recall that normal peripheral CD4+:CD8+ ratios are about 2.5:1). This evidence concerns the gene CD8A and neoplasm.