B-F5

B-F5 is a murine IgG1 monoclonal antibody that targets the CD4 antigen on T lymphocytes. Developed by Diaclone and investigated in clinical trials during the 1990s, it was explored as an immunosuppressive agent for the treatment of severe refractory Crohn's disease, rheumatoid arthritis, and psoriasis. B-F5 binds to the CD4 molecule, a co-receptor for the T-cell receptor (TCR), thereby inhibiting T-cell activation and the subsequent inflammatory cascade. Notably, B-F5 was reported to induce immunosuppression without causing significant or sustained depletion of CD4+ T cells, suggesting a mechanism of functional modulation rather than cytolysis. However, clinical development of the murine B-F5 antibody was limited by its immunogenicity, leading to the development of a humanized version known as torgalizumab (BT-061) by Biotest AG.