Natural killer group 2 member D–Natural killer group 2 member D ligand complex (NKG2D–NKG2DL complex) (NKG2D–NKG2DL complex)

The Natural killer group 2 member D (NKG2D)–Natural killer group 2 member D ligand (NKG2DL) complex is a pivotal immunological synapse formed between the activating receptor NKG2D (encoded by KLRK1) and its stress-induced ligands, such as MICA, MICB, and the ULBP family (UniProt P26718, Q29983). In humans, these ligands are typically absent on healthy cells but are upregulated on the surface of tumor cells in response to DNA damage, oxidative stress, or oncogenic transformation (PubMed: 21737333). Binding of NKG2D to its ligands triggers the activation of Natural Killer (NK) cells and provides a potent costimulatory signal to CD8+ T cells, facilitating the targeted lysis of malignant cells (PubMed: 11777960). However, tumors frequently employ immune evasion strategies such as the proteolytic shedding of ligands by metalloproteinases, which results in soluble ligands that can systemically downregulate NKG2D expression and impair anti-tumor immunity (PubMed: 29593235). Therapeutic approaches targeting this complex include NKG2D-based chimeric antigen receptor (CAR) T-cell therapies, such as CYAD-01, and monoclonal antibodies designed to inhibit ligand shedding, thereby restoring the visibility of tumor cells to the immune system (ClinicalTrials.gov: NCT03018405).

Other names

NKG2D–NKG2DL axisKLRK1–MICA/B complexCD314–ULBP complexNKG2D–MICA/B complexNKG2D–ULBP complex

Activation of cytotoxic immune cells via chimeric antigen receptors (CARs); inhibition of proteolytic shedding of MICA/B to maintain surface ligand density; bispecific engagement of NKG2D-expressing cells with tumor-associated antigens.