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Enterotoxigenic Escherichia coli (ETEC) is the leading cause of traveler's diarrhea. The heat-labile (LT) and heat-stable (ST) toxins mediate ETEC induced diarrhea. ETEC strains may express LT, ST, or both LT and ST, with LT-expressing strains accounting for approximately 50-60% of ETEC-related traveler's diarrhea. Cholera toxin (CT) is80% homologous to LT and vaccination with CT-B subunit (CT-B) -based vaccines elicit a protective immune response against LT-producing ETEC strains. Peru-15 is an oral, single-dose, live-attenuated cholera vaccine candidate that has been investigated in several clinical trials (n400 subjects) and was proven well tolerated, immunogenic, and efficacious. Peru-15 was genetically engineered to express and secrete high levels of CT-B by cloning ctxB onto a glnA balanced-lethal plasmid under the transcriptional control of a strong constitutive promoter, resulting in Peru-15pCTB. In vitro characterization demonstrated that Peru-15pCTB secreted approximately 30-fold more CT-B than Peru-15 and CT-B was stably produced after 40 generations of growth and throughout simulated Seed Bank and FDP (Final Drug Product) production conditions. In preclinical studies, the geometric mean anti-CT-B IgG titer in the sera of mice inoculated intranasally with two doses of Peru-15pCTB was32-fold higher than in mice inoculated with Peru-15. Similarly, rabbits orally inoculated with a single dose of Peru-15pCTB developed titers that were approximately 30-fold higher than rabbits inoculated with a single dose of Peru-15. Sera from Peru-15pCTB vaccinated mice and rabbits neutralized LT toxicity in an in vitro assay. Peru-15pCTB has several promising characteristics of an oral, single-dose, bivalent cholera/ETEC vaccine and is advancing towards a Phase 1 clinical trial.

Eight Salmonella enterica serovar Paratyphi A strains were screened as candidates to create a live attenuated paratyphoid vaccine. Based on biochemical and phenotypic criteria, four strains, RKS2900, MGN9772, MGN9773 and MGN9779, were selected as progenitors for the construction of Δ phoPQ mutant derivatives. All strains were evaluated in vitro for auxotrophic phenotypes and sensitivity to deoxycholate and polymyxin B. All Δ phoPQ mutants were more sensitive to deoxycholate and polymyxin B than their wild-type progenitors, however MGN10028, MGN10044 and MGN10048, required exogenous purine for optimal growth. Purine requiring strains had acquired point mutations in purB during strain construction. All four mutants were evaluated for reactogenicity and immunogenicity in an oral rabbit model. Three strains were reactogenic in a dose-dependent manner, while one strain, MGN10028, was well-tolerated at all doses administered. All Δ phoPQ strains were immunogenic following a single oral dose. The in vitro profile coupled with the favorable reactogenicity and immunogenicity profiles render MGN10028 a suitable live attenuated Paratyphi A vaccine candidate.