Natural killer cell activating ligand (NKG2DL)

Natural killer (NK) cell activating ligands, primarily the NKG2D ligands such as MICA, MICB, and the ULBP family, are proteins that are typically absent or minimally expressed on healthy cells but become highly upregulated during cellular stress, malignant transformation, or viral infection [1][2]. These ligands serve as critical "danger signals" recognized by the activating receptor NKG2D, which is expressed on NK cells, CD8+ T cells, and γδ T cells [2]. Upon binding, these ligands trigger a potent cytotoxic response and cytokine production, facilitating the elimination of the stressed or tumor cell [1]. In many cancers, tumors evolve to evade this immune surveillance by proteolytically shedding these ligands from the cell surface, creating soluble decoys that desensitize immune cells and promote tumor progression [3]. Therapeutic strategies targeting these ligands include chimeric antigen receptor (CAR) therapies that utilize the NKG2D extracellular domain to recognize a broad spectrum of cancers, as well as monoclonal antibodies designed to stabilize surface expression and prevent shedding [3][4]. While promising due to their broad expression across various malignancies, challenges include the potential for off-target effects on non-malignant stressed tissues and the immunosuppressive environment created by soluble ligand isoforms [1][2]. Sources: [1] Duan, S., et al. (2019). "NKG2D ligands: promising targets for cancer immunotherapy." Cellular & Molecular Immunology. [2] Zingoni, A., et al. (2018). "NKG2D and Its Ligands: One Step Ahead." Frontiers in Immunology. [3] de Andrade, L. F., et al. (2018). "Antibody therapy targeting the MICA/B alpha3 domain prevents shedding and promotes antitumor immunity." Science. [4] ClinicalTrials.gov (NCT03018405 for CYAD-01).

Other names

NKG2D ligandsStress-induced ligandsMHC class I polypeptide-related sequence A (MICA)MHC class I polypeptide-related sequence B (MICB)UL16-binding proteins (ULBP1-6)RAET1 proteins

Binding to the NKG2D activating receptor on NK cells and cytotoxic T cells to trigger degranulation, cytokine production, and lysis of the ligand-expressing cell.