CD8A and neoplasm: The reasons of unresponsive to immunotherapy are attributed to multiple factors, such as (i) insufficient infiltration of activated CD8+ T cells into the non-inflamed types of tumor microenvironment that retards anti-PD-1 targetability (Spranger et al., 2016), (ii) variable population of CD8+ T cells from edge to core of the tumors due to tumor heterogeneity, hypoxia, and variability in mutations of specific oncogene pathways (Gajewski et al., 2013).