Tumor cell ligands for Natural cytotoxicity triggering receptor 2 (NKp44) (NKp44L)

Tumor cell ligands for Natural cytotoxicity triggering receptor 2 (NKp44) are a heterogeneous group of molecules expressed on the surface of malignant cells that interact with the NKp44 receptor on activated natural killer (NK) cells. The most prominent activating ligand is a specific 21-kDa isoform of the mixed-lineage leukemia protein 5 (MLL5), often referred to as NKp44L, which is selectively expressed on various tumor types but absent in most healthy tissues (Frontiers in Immunology, 2019). Other ligands include the proliferating cell nuclear antigen (PCNA), which acts as an inhibitory ligand when expressed on the cell surface, and soluble factors like PDGF-DD and Nidogen-1 (Journal of Experimental Medicine, 2019). These interactions play a critical role in tumor immunosurveillance, where activating ligands trigger NK cell-mediated lysis and cytokine production, while inhibitory ligands facilitate tumor immune evasion (Blood, 2013). Therapeutic strategies targeting these ligands include NKp44-based chimeric antigen receptor (CAR) T cells and monoclonal antibodies designed to enhance NK cell activity or directly target tumor cells (Clinical Cancer Research, 2008). Targeting the NKp44-ligand axis aims to either enhance the activating signals or block the inhibitory pathways to restore effective anti-tumor immunity.

Other names

NKp44 ligandsNCR2 ligands21spe-MLL5MLL5 isoformSurface PCNABAG6BAT3Nidogen-1PDGF-DDGalectin-3Heparan sulfate proteoglycans

Binding of activating ligands (e.g., MLL5 isoform) to NKp44 triggers NK cell cytotoxicity and cytokine release via DAP12 signaling, while binding of inhibitory ligands (e.g., surface PCNA) suppresses NK cell activity through ITIM-mediated signaling.