Insights into Vibrio cholerae vaccine development and physiology from small animal models of intestinal colonization and disease

Abstract

The Gram-negative human bacterial pathogen Vibrio cholerae causes cholera, a severe diarrheal disease that continues to pose a significant public health threat. V. cholerae robustly colonizes the human small intestine and relies on a suite of virulence factors, including its signature secreted cholera toxin, to cause disease. Since its identification in 1854, many animal models for V. cholerae colonization and disease have been developed. These models vary widely in species, age, route of infection, and translational potency. This thesis leverages three major V. cholerae animal models – infant rabbits, infant mice, and adult germ-free mice – to advance cholera vaccine development and understanding of the pathogen’s biology and virulence. Chapters 2 and 3 describe the pre-clinical characterization of a new live oral cholera vaccine (OCV) candidate, HaitiV. We developed a new mouse model for OCV evaluation that takes advantage of the differential colonization and disease susceptibilities of adult germfree and infant mice to V. cholerae. With this model, we showed that HaitiV stimulates strong anti-V. cholerae protective adaptive immune responses. We further engineered HaitiV’s O-antigen (the determinant of serotype) to probe how vaccine surface antigens representative of co-circulating pandemic V. cholerae strains impact protective immunity, a critical and long-standing question for understanding OCV development and V. cholerae pathogenesis. This work directly advances HaitiV towards a Phase I first-in-human clinical trial. Chapter 4 presents data from ongoing studies of VCA0040, a protein of unknown function identified in an infant rabbit transposon screen for V. cholerae intestinal colonization factors. We found that VCA0040 is required for V. cholerae cell shape maintenance in alkaline pH. Inactivating mutations in the sodium motive force-dependent accessory Sec complex secDF1, but not the proton motive force-dependent secDF2, suppressed the defects of Δvca0040 V. cholerae. We propose that VCA0040 supports V. cholerae alkaline fitness in vivo and in vitro by supporting bioenergetic homeostasis and downstream envelope proteome remodeling. Collectively, these studies provide compelling evidence of how appropriate implementation of specific animal models can advance our understanding of V. cholerae cell biology and the development of next-generation therapeutics to combat cholera.