Programmed Death-Ligand 1 (PD-L1) is an immune checkpoint molecule expressed on antigen-presenting cells and various cancer cells, critically involved in modulating T-cell-mediated immune responses. Its interaction with programmed cell death protein 1 (PD-1) on activated T cells delivers inhibitory signals that suppress cytotoxic activity and promote immune tolerance-a mechanism exploited by malignancies to evade immune surveillance. Elevated PD-L1 expression has been documented across multiple tumor types including non-small cell lung carcinoma, melanoma, and gastrointestinal cancers, correlating with advanced disease progression and poorer prognostic outcomes.
VISTA (B7-H5), a member of the B7 immunoglobulin superfamily (IgSF), is an immunoregulatory transmembrane protein encoded by the VSIR gene. Structurally, it comprises three functional domains: (1) An extracellular IgV-like domain critical for ligand-receptor interactions, which enables direct engagement with immune cell receptors such as PSGL-1 to modulate signaling; (2) A hydrophobic transmembrane domain ensuring stable membrane anchoring; (3) A cytoplasmic tail containing conserved motifs potentially involved in intracellular signal transduction, though its precise signaling pathways remain under investigation. Functionally, B7-H5 serves as a potent immune checkpoint molecule that maintains peripheral tolerance under physiological conditions while promoting tumor immune evasion in malignancies. Its immunosuppressive effects manifest through dual mechanisms: direct inhibition of T cell activation/effector function and suppression of NK cell cytotoxicity. Current research focuses on developing anti-B7-H5 monoclonal antibodies and exploring its synergistic potential with existing checkpoint inhibitors to overcome therapeutic resistance.