Protein-based vaccine candidate MecVax broadly protects against enterotoxigenic Escherichia coli intestinal colonization in a rabbit model

There are no vaccines licensed against enterotoxigenic Escherichia coli (ETEC), a leading cause of children's diarrhea and the most common cause of travelers' diarrhea. Multivalent vaccine candidate MecVax unprecedentedly targets two ETEC enterotoxins (heat-stable toxin, STa; heat-labile toxin, LT) and the seven most prevalent ETEC adhesins (colonization factor antigen, CFA/I, coli surface antigens, CS1-CS6) and has been demonstrated preclinically to protect against STa- and LT-mediated ETEC clinical diarrhea and prevent intestinal colonization from ETEC strain H10407 (CFA/I, STa, LT). However, it is unattested whether MecVax broadly protects against intestinal colonization from ETEC strains producing the other six adhesins (CS1-CS6) also targeted by this product. In this study, we immunized rabbits with MecVax and challenged them with heterogeneous ETEC strains that express CS1-CS6 adhesins to evaluate MecVax's efficacy against bacterial intestinal colonization, thus providing broad vaccine protection against ETEC infection. Data revealed that rabbits intramuscularly immunized with MecVax developed robust responses to both ETEC enterotoxins (STa, LT) and seven adhesins (CFA/I, CS1-CS6), and when challenged with ETEC isolates expressing CS1/CS3, CS2/CS3, CS4/CS6, CS5/CS6, or CS6 adhesin, the immunized rabbits prevented over two logs (>99%) of bacteria from colonization in small intestines. Additionally, compared to a CFA-toxoid fusion protein, which is another potential ETEC vaccine antigen to target two ETEC enterotoxins and the seven adhesins, MecVax exhibited better protection against ETEC intestinal colonization. These results, in conjunction with the protection data from early studies, evidenced that MecVax is broadly protective, validating MecVax's candidacy as an effective vaccine against ETEC-associated diarrhea and accelerating ETEC vaccine development.