Killer cell lectin-like receptor subfamily K member 1 ligands (NKG2DL)

Killer cell lectin-like receptor subfamily K member 1 (KLRK1) ligands, collectively known as NKG2D ligands (NKG2DL), are a diverse group of MHC class I-related proteins including MICA, MICB, and the ULBP family (ULBP1-6). These proteins are typically absent from the surface of healthy cells but are highly upregulated in response to cellular stressors such as DNA damage, viral infection, or oncogenic transformation. Upon expression, they bind to the NKG2D activating receptor on Natural Killer (NK) cells and CD8+ T cells, serving as a critical 'eat-me' signal that triggers the destruction of the compromised cell. In the context of oncology, many tumors employ immune evasion tactics by proteolytically shedding these ligands from their surface, which not only reduces tumor visibility but also leads to the systemic downregulation of the NKG2D receptor on immune cells. Therapeutic development focuses on stabilizing surface expression, utilizing NKG2D-based CAR-T cells, or employing bispecific antibodies to bridge NKG2DL-expressing tumor cells with effector lymphocytes.

Other names

NKG2D ligandsMHC class I polypeptide-related sequence A (MICA)MHC class I polypeptide-related sequence B (MICB)UL16-binding proteins (ULBP1-6)Retinoic acid early transcripts (RAET1)

Activation of the NKG2D receptor on cytotoxic lymphocytes to induce tumor cell lysis; inhibition of ligand shedding to prevent immune evasion; redirection of T cells via CAR-T or bispecific engagers to ligand-expressing cells.