Studies have shown that tumor-infiltrating CD39+CD8+ T cells show less cytotoxicity compared with those of CD39−CD8+ T cells, which are characterized by the production of IFN-γ, tumor necrosis factor (TNF)-α, and granzyme B, suggesting that tumor-infiltrating CD8+ T cells with high CD39 expression exhibited features of exhaustion [67]. The gene discussed is CD8A; the disease is neoplasm.