Natural cytotoxicity triggering receptor 2 ligand (NKp44L)

Natural cytotoxicity triggering receptor 2 ligands (NKp44L) are a heterogeneous group of molecules expressed on the surface of tumor cells, virally infected cells, and cells under physiological stress. These ligands interact with the NKp44 (NCR2) receptor, an activating receptor primarily expressed on activated Natural Killer (NK) cells (UniProt O95944). Key identified ligands include a specific tumor-associated splice variant of the MLL5 protein, surface-expressed Proliferating Cell Nuclear Antigen (PCNA), and certain heparan sulfate proteoglycans (Baychelier et al., 2013, Blood; Hecht et al., 2009, Journal of Cytometry). While the interaction with the MLL5-derived ligand typically triggers NK cell-mediated lysis of the target cell, the interaction with surface PCNA has been shown to paradoxically inhibit NK cell activity, serving as a mechanism for tumor immune evasion (Rosental et al., 2011, Journal of Immunology). NKp44L expression is highly restricted in healthy tissues but significantly upregulated in various malignancies, including breast, lung, and colon cancers, as well as in HIV-infected CD4+ T cells (Vieillard et al., 2005, PNAS). This restricted expression profile makes NKp44L a promising target for selective cancer immunotherapy. Current therapeutic strategies under investigation include the use of NKp44-Fc fusion proteins to block inhibitory interactions or trigger ADCC, and the development of CAR-NK cells and bispecific antibodies designed to engage NK cells against NKp44L-positive targets. Additionally, soluble forms of NKp44L can be detected in the sera of patients, potentially serving as a biomarker for disease progression and treatment efficacy.

Other names

NCR2 ligandNKp44 ligandMLL5 isoformSurface PCNAHeparan sulfateBAG6BAT3

Modulation of Natural Killer (NK) cell activity through interaction with the NKp44 (NCR2) activating receptor to induce or inhibit cytotoxicity.