Immune Mechanisms Regulating the Development of Systemic and Mucosal Antigen-specific B Cells After Vaccination and Challenge in Humans

CCHI Research Project 2 – Abstract Shigellosis and salmonellosis continue to be serious public health problems affecting primarily young children in developing countries; however, adults are also susceptible to these pathogens. The emergence of multi-drug and extensively drug-resistant Shigella and Salmonella strains has created a sense of urgency for the development of effective vaccines. However, the lack of information on the development of mucosal immunity has hindered novel vaccine design. To date, it is unclear to what extend the immunity measured in peripheral blood is representative of the gut mucosal immunity. Recent studies have shown that immunity in local tissues is critical for protection from disease. The recently described resident memory B cells are likely the first line of defense against re-infection at the tissue level. The overall goal of Research Project (RP2) is to characterize and compare the mechanisms that drive the development of systemic and mucosal B cell immunity to human- restricted enteric pathogens using state-of-the-art immunological and genomics methods. To this end, unique human specimens (Core 1) will be used including a) PBMC from volunteers immunized parenterally with conjugate vaccines against Salmonella (TSCV) and Shigella (SF2s-TT15); b) PBMC from volunteers immunized with oral vaccines against Salmonella (Ty21a) and Shigella (CVD 1208S-122); c) PBMC from S. flexneri 2a challenge studies; d) PBMC and terminal ileum biopsies from adult Ty21a vaccinees; and e) PBMC from children immunized with Ty21a. Our overall hypothesis is that antigen-specific mucosal B cell responses differ in magnitude and characteristics to those in peripheral blood and that oral immunization favors responses associated with protection and these responses are also age dependent. In Aim 1, we will characterize Shigella- and Salmonella-specific B cells in PBMC after parenteral and oral immunizations. Aim 2 will characterize B cell immunity (PBMC) after a wt Shigella challenge. Aim 3 will characterize Salmonella-specific B cell responses after oral vaccination at the systemic (PBMC) and local (gut mucosa) levels. Aim 4 will explore Salmonella- specific B cell responses (PBMC) in children (<18 yo). In all aims, the mechanisms involved will be studied by evaluating changes in phenotype, gene expression (transcriptome), epigenome (EpiTOF), and/or BCR- sequence profiles (LIBRA-seq) in bacteria-specific B cells after vaccination/challenge. Additionally, Aim 3 will incorporate imaging mass cytometry (Core 3) to study Salmonella-specific B cells and their interaction(s) with other immune cells at the tissue level. Bacteria-specific B cells will be identified using a unique set of reagents developed to study enteric pathogens (e.g., bacteria with fluorescent tags). The rich data sets will be analyzed, compared and integrated in collaboration with the Systems Biology and Biostatistics Core (Core 2). Data integration will include results from RP1-3, so we will provide unprecedented information on the development of immunity to human-restricted enteric pathogens to aid vaccine design and determine correlates of protection.