CD8A and neoplasm: Therapeutic vaccines can improve anti-tumor CD8+ T cell responses, in general, through two distinct mechanisms: (i) either by de novo priming CD8+ T cells that were not recruited into the initial response due to inefficient or absent presentation of their respective target peptides on professional antigen-presenting cells or (ii) by re-priming/stimulation of antigen-experienced CD8+ T cells to undergo further proliferation.