Transient Intestinal Colonization by a Live-Attenuated Oral Cholera Vaccine Induces Protective Immune Responses in Streptomycin-Treated Mice

Abstract

Current mouse models for evaluating the efficacy of live oral cholera vaccines (OCVs) have important limitations. Conventionally raised adult mice are resistant to intestinal colonization by Vibrio cholerae, but germ free mice can be colonized and have been used to study OCV immunogenicity. However, germ free animals have impaired immune systems and intestinal physiology; also, live OCVs colonize germ free mice for many months, which does not mimic the clearance kinetics of live OCVs in humans. Here we leverage antibiotic-treated, conventionally raised adult mice to study the effects of transient intestinal colonization by a live OCV V. cholerae strain. In a single dose vaccination regimen, we found that HaitiV, a live-attenuated OCV candidate, was cleared by streptomycin treated adult mice within two weeks after oral inoculation. This transient colonization elicited far stronger adaptive immune correlates of protection against cholera than did inactivated whole-cell HaitiV. Infant mice from HaitiV vaccinated dams were also significantly more protected from choleric disease than pups from inactivated-HaitiV dams. Our findings establish the benefits of antibiotic treated mice for live OCV studies as well as its limitations and underscore the immunogenicity of HaitiV. Importance Oral cholera vaccines (OCVs) are being deployed to combat cholera but current killed OCVs require multiple doses and show little efficacy in young children. Live OCVs have the potential to overcome these limitations but small animal models for testing OCVs have shortcomings. We used an antibiotic treatment protocol for conventional adult mice to study the effects of short-term colonization by a single dose of HaitiV, a live OCV candidate. Vaccinated mice developed vibriocidal antibodies against V. cholerae and delivered pups that were resistant to cholera, whereas mice vaccinated with inactivated-HaitiV did not. These findings demonstrate HaitiV's immunogenicity and suggest that this antibiotic treatment protocol will be useful for evaluating the efficacy of live OCVs.

Nontoxigenic Vibrio cholerae Challenge Strains for Evaluating Vaccine Efficacy and Inferring Mechanisms of Protection

“…In this model, diarrhea and morbidity are dependent on CT activity ( 37 ). A 10 7 CFU oral dose routinely leads to diarrheal disease and death/moribundity within 48 hours with toxigenic V. cholerae strains ( 28 , 37 , 38 ). All pups given ZTox developed diarrhea and became moribund by 35 h postinoculation with a median time to death of 31 hours across 3 independent litters ( Fig.…”

“…Infant mouse lethal dose challenges were performed as previously described ( 37 , 38 ). Five female C57BL/6 dams with 2- to 3-day-old litters (P2 to P3) (Charles River Laboratories) were singly housed with their pups.…”

The Interface of Vibrio cholerae and the Gut Microbiome

“…While long-term protection was not measured, the vaccine exhibits probiotic-like protection, 15 and HaitiV elicits strong correlates of protection in offspring of immunized dams, independent of HaitiV colonization. 236,237…”

Non-toxigenic Vibrio cholerae challenge strains for evaluating vaccine efficacy and inferring mechanisms of protection

“…In this model, diarrhea and morbidity are dependent on CT activity 37 . A 10 7 CFU oral dose routinely leads to diarrheal disease and death/moribundity within 48 hours with toxigenic V. cholerae strains 28,37,38 .…”

“…Infant mouse lethal dose challenges were performed as previously described 37,38 . Five female C57BL/6 dams with 2-3-day old litters (P2-3) (Charles River) were singly housed with their pups.…”