Tumor-associated natural killer cell receptor ligands (NKRLs)

Tumor-associated natural killer (NK) cell receptor ligands are a diverse group of cell-surface proteins expressed by malignant cells that serve as critical recognition signals for the innate immune system. These ligands, which include the MHC class I-related molecules (MICA and MICB) and UL16-binding proteins (ULBPs), are typically upregulated in response to cellular stresses such as DNA damage, oxidative stress, or oncogenic transformation. They interact with activating receptors on NK cells, most notably NKG2D, to trigger the release of cytotoxic granules and pro-inflammatory cytokines, thereby facilitating the elimination of transformed cells. Beyond the NKG2D system, other ligands such as B7-H6 and nectins interact with natural cytotoxicity receptors (NCRs) and DNAM-1, respectively, to further modulate NK cell activity. In the context of cancer, tumors frequently employ immune evasion strategies such as the proteolytic shedding of these ligands, which creates soluble decoys that downregulate NK cell receptors and impair anti-tumor immunity. Therapeutic approaches currently under investigation include monoclonal antibodies designed to stabilize surface expression or prevent shedding, bispecific engagers that bridge these ligands to NK cells, and chimeric antigen receptor (CAR) therapies that utilize NK receptor domains to target a broad spectrum of ligand-expressing tumors.

Other names

Natural killer cell receptor ligandsNKG2D ligands (NKG2DL)Natural cytotoxicity receptor (NCR) ligandsStress-induced ligandsInduced-self ligandsMHC class I polypeptide-related sequence A (MICA)MHC class I polypeptide-related sequence B (MICB)UL16-binding proteins (ULBP1-6)B7-H6Poliovirus receptor (CD155)Nectin-2 (CD112)

Drugs targeting these ligands work by either directly binding to them to trigger immune-mediated cytotoxicity (e.g., CAR-T/NK cells and bispecific engagers) or by modulating their expression and stability on the tumor cell surface (e.g., HDAC inhibitors and shedding inhibitors) to enhance NK cell recognition and activation.