A cross protective multivalent vaccine for Shigella and ETEC

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Project Summary: Even though Shigella and enterotoxigenic Escherichia coli (ETEC) are the two most important bacterial causes of moderate-to-severe diarrhea in children in developing countries and in international travelers, there are currently no licensed vaccines for these infections. The goal of this application is the development of an injectable combination vaccine to protect from these two bacterial enteric infections. To accomplish this, we developed an ETEC vaccine candidate (MecVax) using the epitope- and structure- based vaccinology platform, MEFA (Multi-Epitope Fusion Antigen) which results in a polyvalent fusion protein with multiple epitopes on a single protein. MecVax includes two proteins, one to stimulate immunity to the colonization factor antigens (CFAs) of ETEC and another to stimulate immunity to the two enterotoxins. The first has epitopes for the seven most common CFAs while the second has epitopes for the heat-labile enterotoxin (LT) and the heat stable enterotoxin (STa). Animals immunized with MecVax develop functional antibodies to the CFAs and the two toxins and are protected when challenged with ETEC. Developing a safe and immunogenic antigen for STa is innovative since this small protein (19AA) is not naturally immunogenic. To extend protection to shigellosis, we developed a MEFA for Shigella which includes epitopes for the different virulence proteins that are common among all strains of Shigella and invasive E. coli. To further extend protection, the Shigella MEFA also includes epitopes for shiga toxins (including shiga toxin producing E coli - STEC). Because this vaccine is based on the virulence proteins which are common to all strains, this MEFA is expected to protect against all Shigella species and serotypes and not be limited by serotype as are the other vaccines which are based solely on the LPS antigen. There is no single animal model which can effectively evaluate the protective immune responses to the MEFA vaccines; thus, we use a combination of assays to determine the immune responses to the MEFA vaccines. Antibody responses in mice quantitate the responses to the specific epitopes in MEFA fusion while we use functional antibody assays to determine if the antibodies block adhesion (for ETEC), invasion (for Shigella) and neutralize toxins (for LT, STa and Shiga toxins). We then determine protection in animal models using a rabbit colonization model (both ETEC and Shigella) and protection against disease in a pig model (for ETEC) and a mouse lethal pulmonary challenge model (for Shigella). Using a combination of these assays and animal models, we will build the preclinical evidence for the combined ETEC-Shigella combination vaccine. The central hypothesis is that unlike current oral vaccine candidates, an injectable Shigella-ETEC MEFA vaccine will stimulate higher serum antibody titers and protect when the subject is most vulnerable and that natural exposure will boost local intestinal immunity. An effective Shigella-ETEC vaccine will prevent hundreds of millions diarrhea clinical cases and save > 200,000 lives annually.