CD8A and cancer: Moreover, the critical role of NKG2D-mediated tumor surveillance are supported by the proof that NK and CD8+ T cells could rapidly eradicate the tumor cells that were transfected with NKG2D ligands and injected into mice [40], and many clinical retrospective observations have presented the prognostic value of NKG2D ligands in different cancer types and they might be viable targets for developing effective cancer immunotherapy [41, 42].