CD274 and neoplasm: Apart from the PD-1/PD-L1 and CTLA-4/CD86 immune checkpoint axes, other non-conventional checkpoint receptors [killer Ig-like inhibitory receptors (KIRs), Ig-like transcript 2 (ILT-2), and NKG2A] can be expressed on Vγ9Vδ2+ T cells, inhibit their cytotoxic function, and prevent tumor cell lysis upon recognition of specific HLA class I ligands on tumor cells (195–203).