Development and preclinical evaluation of safety and immunogenicity of an oral ETEC vaccine containing inactivated E. coli bacteria overexpressing colonization factors CFA/I, CS3, CS5 and CS6 combined with a hybrid LT/CT B subunit antigen, administered alone and together with dmLT adjuvant

Abstract

A first-generation oral inactivated whole-cell enterotoxigenic Escherichia coli (ETEC) vaccine, comprising formalin-killed ETEC bacteria expressing different colonization factor (CF) antigens combined with cholera toxin B subunit (CTB), when tested in phase III studies did not significantly reduce overall (generally mild) ETEC diarrhea in travelers or children although it reduced more severe ETEC diarrhea in travelers by almost 80%. We have now developed a novel more immunogenic ETEC vaccine based on recombinant non-toxigenic E. coli strains engineered to express increased amounts of CF antigens, including CS6 as well as an ETEC-based B subunit protein (LCTBA), and the optional combination with a nontoxic double-mutant heat-labile toxin (LT) molecule (dmLT) as an adjuvant. Two test vaccines were prepared under GMP: (1) A prototype E. coli CFA/I-only formalin-killed whole-cell+LCTBA vaccine, and (2) A "complete" inactivated multivalent ETEC-CF (CFA/I, CS3, CS5 and CS6 antigens) whole-cell+LCTBA vaccine. These vaccines, when given intragastrically alone or together with dmLT in mice, were well tolerated and induced strong intestinal-mucosal IgA antibody responses as well as serum IgG and IgA responses to each of the vaccine CF antigens as well as to LT B subunit (LTB). Both mucosal and serum responses were further enhanced (adjuvanted) when the vaccines were co-administered with dmLT. We conclude that the new multivalent oral ETEC vaccine, both alone and especially in combination with the dmLT adjuvant, shows great promise for further testing in humans.

Delivery strategies to enhance oral vaccination against enteric infections

“…The over-expression of ETEC antigens by non-pathogenic E. coli is one strategy which has delivered promising pre-clinical and phase I human trial results [101][102][103]. Additionally, novel strains of V. cholerae expressing multiple surface antigens have been generated and hold promise for future trials [104].…”

“…These issues were however later addressed by the production of the ORCVAX® formulation in India by Shantha Biotechnics under GMP conditions and it is marketed under the trade name Shanchol®. Therefore the ability to produce a vaccine under GMP is an important early consideration to make and one that is exemplified by the current oral ETEC vaccine candidate undergoing clinical trials where all components are produced under GMP [101].…”

E. coli Bacteremia Strains - High diversity and Associations with Agerelated Clinical Phenomena

“…Vaccine development aiming at the most common enteropathogenic E. coli, the enterotoxigenic E. coli (ETEC), is therefore of imperative importance. Experimental studies of a second generation ETEC vaccine are promising [22]. E. coli causes the majority of urinary tract infections [23], a considerable part of blood stream infections [2], and is a commonly found bacterial species in infections of the central nervous system of newborns and patients with anatomic or surgical defects [24].…”

Vaccines for viral and bacterial pathogens causing acute gastroenteritis: Part II: Vaccines forShigella,Salmonella,enterotoxigenicE. coli(ETEC) enterohemorragicE. coli(EHEC) andCampylobacter jejuni

“…103 This new version includes 1 £ 10 9 inactivated bacteria, containing 10 g CFA/I, 38 mg CS3, 6.4 mg CS5 and 1.5 mg CS6, plus 13 mg LT/CT and 25 mg dmLT. Vaccination of BALB/c and C57/BL6 mice elicited immune responses to all components included in the formulation.…”