GSK2904545A + AS01B

GSK2904545A + AS01B is a combination vaccine candidate developed by GSK to prevent *Clostridium difficile* infection (CDI). It contains the **F2 antigen**—a fusion protein composed of the C-terminal regions of TcdA and TcdB toxins from *C. difficile*—formulated with the **AS01B adjuvant system**. AS01B is a liposome-based adjuvant containing 3-O-desacyl-4’-monophosphoryl lipid A and QS-21 (licensed from Antigenics/Agenus) designed to boost the vaccine’s immunogenicity by activating innate immune responses. The vaccine is administered by intramuscular injection and aims to induce neutralizing antibodies against TcdA and TcdB, thus preventing primary and recurrent CDI. Clinical trials have shown that this combination is well tolerated and generates robust functional humoral responses against both toxins, particularly in older adults[1][3][5].