CD8A and cancer: There are other cells that play a role in the immune response against cancer such as natural killer (NK) cells which can directly kill cancer cells similar to CD8+ and interact with other cells in TME to promote the anti-tumor effect, and dendritic cells which are one of the main antigen-presenting cells, however, the roles of both these cell types can be negatively impacted by the abnormal metabolic environment in TME (e.g., hypoxia) and inhibitory factors (e.g., TGF-β).