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.
Vibrio cholerae (Vc) infections cause cholera, a major threat to human health even after 200+ years of research. More people die from cholera than die waiting for an organ transplant in the USA. Transplant research is funded in the hundreds of millions of dollars ? not so for cholera vaccine development. It is time to normalize the research efforts to the number of people that are dying and or acutely ill rather than those who can pay for the biomedical research derived services. A glaring unmet need for cholera vaccines is a one dose vaccine that effectively immunize the young. Dr. R. Hall, NIH, Program Officer, laments the lack of new idea being studied or proposed in cholera vaccine research. This critique does not include my group. We are investigating pediatric cholera vaccines based on a novel LPS epitope that is part of a conjugate vaccine formulation. Our current proposal aims to take advantage of the adjuvant properties of Vc flagellar proteins that bind toll like receptor 5 (TLR5) and induce pro-inflammatory cytokines that enhance antigen presentation. This is often a difficult first step of the immune response non-invasive pathogens like Vc ? how to get the right antigen in, in immunogenic form. Vc flagellins are immunogenic in people and induce protective antibodies in animal. Purified Vc flagella and LPS are additive or synergistic at preventing colonization of the gut because both inhibit motility which is required for Vc access to the epithelium.
