CD8A and neoplasm: There are other important factors that need to be considered in the context of the therapeutic response to immunotherapies in the brain that have not been discussed in this review, such as lower abundance of DCs and CD8+ T cells in BrM as compared to extracranial tumors [57, 58], differences in molecular profiles between BrM and extracranial disease [59], which may impact on anti-tumor immune responses, the presence of the blood-tumor barrier that originates from the specialized blood-brain barrier [60], and brain-resident stroma including microglia and astrocytes [2].