CD8A and cancer: The relationship between the density and localization of CD8+ T cells and the response to PD-1 blockade in melanoma (16), as well as to PD-L1 blockade in various cancer types (35), has been analyzed, and a higher density of CD8+ T cells, both in the tumor core and in the invasive margin, was shown to correlate with an increased response to PD-1/PD-L1 blockade.