Immunological heterogeneity has long been the major challenge in developing broadly effective
vaccines to protect humans and animals against bacterial and
viral infections. Enterotoxigenic Escherichia coli (ETEC) strains, the leading bacterial cause of
diarrhea in humans, express at least 23 immunologically different
colonization factor antigens (CFAs) and two distinct
enterotoxins [heat-labile toxin (LT) and heat-stable toxin type Ib (STa or hSTa)]. ETEC strains expressing any one or two CFAs and either toxin cause
diarrhea, therefore
vaccines inducing broad immunity against a majority of CFAs, if not all, and both toxins are expected to be effective against ETEC. In this study, we applied the multiepitope fusion
antigen (MEFA) strategy to construct ETEC
antigens and examined
antigens for broad anti-CFA and
antitoxin immunogenicity. CFA MEFA CFA/I/II/IV [CVI 2014, 21(2):243-9], which carried
epitopes of seven CFAs [CFA/I, CFA/II (CS1, CS2, CS3), CFA/IV (CS4, CS5, CS6)] expressed by the most prevalent and virulent ETEC strains, was genetically fused to LT-STa
toxoid fusion monomer 3xSTaA14Q-dmLT or 3xSTaN12S-dmLT [IAI 2014, 82(5):1823-32] for CFA/I/II/IV-STaA14Q-dmLT and CFA/I/II/IV-STaN12S-dmLT MEFAs. Mice intraperitoneally immunized with either CFA/I/II/IV-STa-
toxoid-dmLT MEFA developed
antibodies specific to seven CFAs and both toxins, at levels equivalent or comparable to those induced from co-administration of the CFA/I/II/IV MEFA and
toxoid fusion 3xSTaN12S-dmLT. Moreover, induced
antibodies showed in vitro adherence inhibition activities against ETEC or E. coli strains expressing these seven CFAs and neutralization activities against both toxins. These results indicated CFA/I/II/IV-STa-
toxoid-dmLT MEFA or CFA/I/II/IV MEFA combined with 3xSTaN12S-dmLT induced broadly protective anti-CFA and
antitoxin immunity, and suggested their potential application in broadly effective ETEC
vaccine development. This MEFA strategy may be generally used in
multivalent vaccine development.