CD226 and neoplasm: Vδ2+ T cells are activated by cells that accumulate HMBPP and/or IPP and can also be stimulated through receptors NKG2D and DNAM-1 of various stress-induced molecules expressed on tumor cells including MICA/B, UL16-binding proteins (ULBP1–6), Nectin-2, and PVR, respectively [39,40].