Cluster of differentiation 4 (CD4) (CD4)

Cluster of differentiation 4 (CD4) is a transmembrane glycoprotein and a member of the immunoglobulin superfamily that serves as a vital co-receptor for the T-cell receptor (TCR) (UniProt P01730). It is primarily expressed on the surface of T helper cells, where it facilitates the recognition of antigens presented by Major Histocompatibility Complex (MHC) class II molecules on antigen-presenting cells (PubMed: 15549124). The binding of CD4 to MHC class II stabilizes the immunological synapse and recruits the tyrosine kinase Lck to the TCR complex, which is essential for initiating T-cell activation and the subsequent adaptive immune response (StatPearls: T-Cell Receptor). In the context of the FK-GI101 immunotherapy platform developed by CellVax Therapeutics, patient-derived tumor cells are ex vivo modified to express MHC class II, transforming them into Tumor Presenting Cells that directly engage the CD4 co-receptor on T cells (CellVax Therapeutics; Cellipont Bioservices). This interaction is designed to overcome tumor-mediated immune evasion and trigger a personalized, multi-antigenic immune attack against gastrointestinal cancers such as gastric, pancreatic, and colon cancer (PRNewswire, July 2025). Additionally, CD4 is clinically significant as the primary entry receptor for the Human Immunodeficiency Virus (HIV), making it a target for both oncological and anti-viral therapeutic strategies (NIH: HIV/AIDS Research).

Other names

T-cell surface glycoprotein CD4T-cell surface antigen T4/Leu-3CD4 receptorCD4 co-receptor

FK-GI101 is an autologous cell therapy where tumor cells are modified to express MHC Class II, which then binds to the CD4 co-receptor on T helper cells to initiate a targeted immune response against the tumor.