NKG2D ligand (Natural Killer Group 2 Member D ligand) (NKG2DL)

NKG2D ligands (NKG2DLs) are a diverse group of stress-induced cell surface proteins, including MHC class I polypeptide-related sequence A (MICA), MICB, and the UL16-binding protein (ULBP1-6) family (PMID: 31110339). These ligands are typically absent from healthy cells but are upregulated in response to DNA damage, oncogenic transformation, or viral infection, acting as molecular signals for immune recognition (PMID: 29463950). They function by binding to the NKG2D (KLRK1) activating receptor expressed on natural killer (NK) cells, CD8+ T cells, and gamma-delta T cells, which triggers the release of cytotoxic granules and cytokines to eliminate the target cell (UniProt P26718). In many cancers, tumor cells overexpress these ligands, making them a primary target for novel immunotherapies such as NKG2D-based CAR-T cells (e.g., CYAD-01) and bispecific engagers (PMID: 30206131). However, tumors often employ immune evasion strategies, such as the proteolytic shedding of NKG2DLs into soluble forms (sNKG2DL), which act as decoys to desensitize immune cells (PMID: 28636053). Therapeutic development focuses on targeting these ligands to restore immune surveillance while managing potential on-target off-tumor toxicities in tissues with low-level basal expression (PMID: 33432103).

Other names

MHC class I polypeptide-related sequence A (MICA)MHC class I polypeptide-related sequence B (MICB)UL16-binding proteins (ULBP1-6)RAET1 proteinsStress-induced ligands

Drugs targeting NKG2D ligands typically utilize the extracellular domain of the NKG2D receptor or specific antibodies to recognize and bind these ligands on the surface of tumor cells. This binding facilitates the direct killing of the target cell by engineered immune cells (like CAR-T or CAR-NK) or by recruiting endogenous immune effectors through bispecific engagers or antibody-dependent cellular cytotoxicity (ADCC) (PMID: 31110339, PMID: 30206131).