7. PROJECT SUMMARY Vibrio cholerae is endemic in 47 countries and causes 3 million cases of cholera and 100,000 deaths annually. In addition, V. cholerae also causes large epidemics of disease. However, while oral cholera vaccines (OCVs) are increasingly being used to prevent cholera epidemics, there has not yet been a systematic effort to use vaccines in endemic areas which account for over 95% of the global cholera burden. One reason for the hesitancy to widely implement vaccination as a public health strategy is that current cholera vaccines have significant immunologic limitations. For example, a recent trial of a killed OCV in Bangladesh demonstrated a 37% protective efficacy. In contrast, natural infection with V. cholerae provides over 90% protection against re-infection. One potential reason for this is that natural infection, and potentially live-attenuated but not killed OCVs, generate antibody responses to in vivo expressed proteins which contribute to long term protection. This is supported by our preliminary data which shows that despite induction of comparable vibriocidal antibody responses following infection and vaccination, V. cholerae infection generates responses to novel protein antigens, which are not likely to be induced by killed oral cholera vaccines. In this proposal, we will test this by comparing the V. cholerae-antigen repertoire following infection and vaccination using a V. cholerae-antigen microarray which our team has recently developed. We will then determine whether responses to any antigens are associated with protection against cholera. Finally, we will build on this knowledge to identify the function of protective antibodies to cholera. The results of these studies will improve our understanding of host-pathogen interactions during cholera, result in better immunologic correlates of vaccine protection, and impact strategies for improving vaccines for cholera and potentially other mucosal infections.