Cholera conjugates designed to prevent colonization and induce B cell memory

Dartmouth College, Hanover NH

Investigators

Abstract

During the last 3 centuries and before, Vibrio cholerae (Vc), a Gram negative bacterium has plagued humans, causing 7 pandemics of the disease, cholera. Cholera in both epidemic and endemic form, features intracta- ble diarrhea and high mortality if not treated. Endemic cholera in Africa and the Haiti epidemic underscore the unresolved issue of how to control cholera. One short term cholera control approach is a universal vaccine. The main challenge of a universal cholera vaccine is to provide immunity quickly to the most susceptible co- hort: young children (2-5 years old). The consensus is that the current oral cholera vaccine (OCV) with its 42% protective efficacy for young children does not accomplish this. We will expand and improve our experimental conjugate cholera vaccine by introducing a new clinically relevant carrier. The current BSA carrier is not ap- propriate for human vaccines. The conjugates we developed contain a highly immunogenic form of acid- detoxified Inaba LPS (pmLPS) that induces vibriocidal titers with one dose and highly protective Ab with a sec- ond. We need to optimize the pmLPS conjugate to reach our goal of a one dose cholera vaccine for young children. Individual Vc flagellar proteins (FlaPr) will serve as carriers. Synthesis of existing data in the cholera literature suggest a hypothesis: a purified, recombinant, Vc FlaPr will induce protective antibodies (Abs) and also serve as a TLR5 agonists required for optimal Ab induction. The literature indicates the two pro- tective Ag in pm-LPS-FlaPr conjugates will prompt synergistic Ab effects thus providing the final component of a one dose, pediatric cholera vaccine. Following oral or intranasal administration, FlaPr-based vaccine and a killed, whole-cell Vc vaccine will be compared for immunogenicity, induction of protective immunity, and B cell memory. Adult mice will serve for initial immunogenicity studies but in select studies, the vaccine response of neonatal mice will be compared to adults. Like young children, neonatal mice immunized with native LPS are poor repsonders. We propose to overcome this defect by using a conjugate vaccine that preferentially target neonatal follicular B cells rather than marginal zone B cells that mainly make anti-LPS IgM Abs. The redirected response should enhance class switching and induce LPS-specific memory B cells. In our studies, if adult and neonatal mice produce similar Ab responses to the conjugates, but only adults respond to the LPS, it would supply a critical piece of evidence showing the value of the conjugates and the utility of the neonatal mouse model. The use of pmLPS-FlaPr conjugates to overcome non-responsiveness to LPS epitopes in neonatal mice is decidedly novel for cholera vaccine research. In the clinic, capsular polysaccharides are the typical pro- tective epitopes of the conjugate vaccine that are used extensively for childhood vaccination (e.g., pneumo- coccal). Capsular conjugate vaccines are so effective they have reconfigured the circulating serotypes of childhood pathogens. pmLPS-conjugates could have the same effect.