Natural killer group 2 member D (NKG2D) receptor-ligand complex (NKG2D-MICA/B-ULBP)

The Natural killer group 2 member D (NKG2D) receptor-ligand complex, often referred to as the NKG2D–MICA/B–ULBP immune synapse, is a fundamental mechanism for immune surveillance against stressed, infected, or malignant cells [1]. NKG2D (encoded by KLRK1) is a potent activating receptor expressed on natural killer (NK) cells, CD8+ T cells, and certain subsets of γδ T cells [4]. Its ligands include the MHC class I polypeptide-related sequences A and B (MICA and MICB) and the UL16-binding proteins (ULBP1-6), which are typically absent on healthy cells but are upregulated in response to cellular stress, DNA damage, or oncogenic transformation [2]. In many cancers, tumor cells evade immune detection by proteolytically shedding MICA and MICB from their surface, which not only reduces ligand density but also generates soluble decoys that internalize and desensitize the NKG2D receptor [3]. Therapeutic interventions targeting this synapse include monoclonal antibodies designed to inhibit ligand shedding, bispecific antibodies that recruit NK cells to tumor antigens, and chimeric antigen receptor (CAR) therapies utilizing the NKG2D extracellular domain [1, 3]. While these therapies show promise in restoring anti-tumor immunity, they also present challenges such as potential off-target toxicity against healthy tissues expressing stress ligands and the risk of cytokine release syndrome [1]. Sources: [1] Dhar, P., & Wu, J. D. (2018). NKG2D and its ligands in cancer. Journal of Hematology & Oncology, 11(1), 114. [2] Schmiedel, D., & Mandelboim, O. (2018). NKG2D Ligands-Critical Targets for Cancer Immune Escape and Therapy. Frontiers in Immunology, 9, 2040. [3] Ferrari de Andrade, L., et al. (2018). Antibody-mediated inhibition of MICA and MICB shedding promotes antitumor immunity. Science, 359(6383), 1537-1542. [4] UniProt Consortium. (2024). UniProtKB - P26712 (KLRK1_HUMAN).

Other names

NKG2D–MICA/B–ULBP immune synapseKLRK1-MICA/B-ULBP axisNKG2D-ligand axisNKG2D receptor-ligand systemKLRK1-ligand complex

Agonism of NKG2D signaling or stabilization of surface ligands (MICA/B) to enhance anti-tumor cytotoxicity; or antagonism of the NKG2D receptor to suppress pathological immune activation in autoimmune diseases.