P501-AS15 vaccine

P501-AS15 vaccine is a therapeutic cancer vaccine developed by GSK. It consists of the CPC-P501 protein (also known as prostatic acid phosphatase or PAP) formulated with the immunostimulant adjuvant AS15. The vaccine was designed to stimulate an immune response against prostate-specific antigens in patients with prostate cancer, particularly those who are hormone-sensitive and show rising PSA levels after primary tumor treatment. The mechanism of action involves immunostimulation—AS15 is a complex adjuvant system containing QS-21 Stimulon (a saponin-based adjuvant), monophosphoryl lipid A (MPL), and CpG7909 (a TLR9 agonist) in a liposomal formulation, which together enhance both humoral and cellular immune responses against the target antigen[1][8][10]. Clinical development reached up to phase 2 trials for prostate cancer but has since been discontinued[1].