How Could HLA‑G Revolutionize Immunotherapies?

The HLA‑G complex is a little‑known immune system molecule with surprising potential. Unlike classic MHC proteins, HLA‑G does not present antigens to trigger defenses, but rather “hides” them, promoting calm among immune cells. This ability is crucial during pregnancy, when the fetus must be accepted by the mother’s body.\n\nRecent studies show that HLA‑G can modulate both innate immunity – such as natural killer cells – and adaptive immunity, influencing T and B lymphocytes. Its action is “context‑dependent”: in transplants or autoimmune diseases it helps reduce immune attacks, while in tumors or infections it can aid malignant cells or pathogens in evading detection.\n\nThe key to this versatility lies in multiple isoforms, each with a unique binding profile, and interactions with other non‑classical MHC molecules. Researchers are harnessing these traits to design new immunotherapies. Some approaches insert the HLA‑G gene into stem cells or T‑cells, making them “invisible” to rejection. Others aim to block HLA‑G in tumors, re‑activating the immune response against cancer.\n\nIn short, HLA‑G acts as a “peace regulator” of our immune system, and its manipulation could open the door to safer, more targeted treatments for both autoimmune disorders and cancer.

HLA‑G belongs to the non‑classical MHC‑class I gene family, characterized by low tissue expression and high isoform diversity generated through alternative splicing and proteolytic processing. Membrane‑bound isoforms (HLA‑G1, G2, G3, G4) and soluble forms (HLA‑G5, G6) differ in the presence of α1‑α3 domains and in their ability to form dimers or oligomers, influencing binding to immune receptors such as LILRB1, LILRB2 and KIR2DL4.\n\nBinding of HLA‑G to LILRB1/2, inhibitory receptors expressed on NK cells, monocytes, dendritic cells and T lymphocytes, triggers ITIM phosphorylation and activation of SHP‑1/2, leading to inhibition of cellular activation cascades. Interaction with KIR2DL4, present on uterine NK cells, promotes angiogenic factor production and maternal‑fetal tolerance.\n\nTherapeutically, CAR‑T cells engineered to express HLA‑G display reduced immunogenicity in pre‑clinical transplant models, suggesting potential for treating autoimmune diseases without adverse immune reactions. Conversely, anti‑HLA‑G monoclonal antibodies (e.g., TTX‑080) are in clinical trials to block tumor‑induced immunosuppression, aiming to boost checkpoint inhibitor efficacy.\n\nAnother frontier involves nanoparticles coated with HLA‑G‑derived peptides, designed to induce antigen‑specific tolerance in organ‑rejection models. Finally, HLA‑G expression profiling via RNA‑seq and mass‑spectrometry proteomics is uncovering molecular signatures linked to immune response phenotypes, paving the way for predictive biomarkers to personalize immunomodulatory therapies.