Effect of gut bacteria-derived sphingolipids on oral cholera vaccine responsiveness

PROJECT SUMMARY/ABSTRACT Severe dehydrating diarrhea affects millions of people each year and causes hundreds of thousands of deaths, yet vaccines to protect against bacterial pathogens, such as cholera, provide limited protection. Only half of oral cholera vaccine recipients develop protective immune responses, and reasons for this variation are unknown. We analyzed the microbiota of cholera vaccine responders versus non- responders and found clear relationships between the microbiota and vaccine responsiveness. We found that sphingolipids produced by gut bacteria could recapitulate these differences in a cell culture model of innate immune responses to cholera vaccination. The goal of this study is to explore the association between bacteria-derived sphingolipids and oral cholera vaccine responsiveness. The overall objective is to identify an agent that can be co-administered with oral cholera vaccines to boost responsiveness at the mucosal surface. Our findings could be applied to other oral vaccines. The central hypothesis is that the gut microbiota can impact immune responses to oral vaccines. The rationale for this project is that we observed that the presence of bacteria-derived sphingolipids in stool correlated with long-term protective immune responses to oral cholera vaccines in humans. These responses depend primarily upon the innate immune response to vaccine antigen. Therefore, we tested this experimentally by comparing the innate immune responses generated by a human macrophage model exposed to fecal extracts from cholera vaccine responders and nonresponders from Bangladesh. Responses produced by extracts from vaccine responders were reliably reproduced when we stimulated our model with bacteria-derived sphingolipids. We next established a human tonsillar tissue model for studying oral vaccine responsiveness. This model is rich in diverse immune cell types, accounting for immune cell-cell interactions, and a human-derived model was needed because cholera is a host-restricted pathogen. The next step in this work is to test the effect of sphingolipids on the innate and adaptive immune response to oral vaccination in this multi-cell model. Our central hypothesis will be tested in two Aims: 1) Define the effect of bacteria-derived sphingolipids on innate immune responses in the human tonsil model, and 2) Determine if bacteria-derived sphingolipids impact adaptive immune responses to oral cholera vaccines. This research is innovative because we will study a potential new pathway for enhancing immune responses to oral vaccines. This work is significant because understanding how gut microbes impact vaccine responses may enable new tools for disease prevention, such as the use of microbes or their metabolites as pre- or probiotics to boost responses to oral vaccines.