Epitope and mechanistic correlates of broadly protective human antibodies for pneumococcal infection

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Streptococcus pneumoniae is a leading infectious pathogen, causing pneumonia, bacteremia, meningitis, acute otitis media, and nearly one million deaths worldwide each year. S. pneumoniae can be carried in the nasopharynx asymptomatically, which contributes to pathogen spread, as pneumococcal carriage often precedes active infection. Infections occur with increased frequency in high-risk populations, such as individuals with diabetes, asthma, chronic obstructive pulmonary disease, cardiovascular disease, and HIV. Several vaccines are currently in use to prevent pneumococcal infection; however, several factors warrant further research, including limited serotype coverage of current vaccines, limited vaccine efficacy against some vaccine- included serotypes, increased incidence of colonization and infection with non-vaccine serotypes, and widespread drug and multidrug antibiotic resistance among non-vaccine serotypes. This R01 proposal will address these limitations by defining the structural determinants mediating the serotype breadth and protective efficacy of broadly-reactive human mAbs that prevent and treat pneumococcal infection. The scientific premise of this proposal is that mAbs to conserved pneumococcal antigens that are broadly reactive could serve as priority or adjunctive therapies for pneumococcal disease management. This proposal will focus on mAbs to pneumococcal antigens that are highly conserved and are targets of B cells during pneumococcal colonization and infection. Our work will advance the field by generating new therapeutic options for the prevention and treatment of pneumococcal infection for diverse serotypes, including encapsulated and nonencapsulated serotypes, and by identifying protective epitopes on pneumococcal surface proteins. Our innovative hypothesis is that human mAbs targeting conserved pneumococcal surface proteins will exhibit substantial serotype breadth, can treat pneumococcal infection, and that mAb protective efficacy and serotype breadth is correlated to epitope specificity. Our data will provide new findings for the pneumococcal protein vaccine field. In Aim 1, the serotype breadth and protective efficacy of human mAbs targeting conserved protein antigens will be determined in models of both primary and secondary (following influenza virus infection) pneumococcal infection. In Aim 2, we will define the epitopes mediating the protective efficacy of the human mAbs using X-ray crystallography and cryo-EM, which will be critical to the field by informing the development of protein-based pneumococcal vaccines, as we have shown in our preliminary data that the epitope on pneumococcal proteins impacts mAb breadth and protective efficacy. In Aim 3, we will conduct in depth in vitro and in vivo mechanistic studies to assess mAb functions, including opsonophagocytic and agglutination activity, and inhibition of bacterial growth, adhesion, invasion, and biofilm formation. We will also assess the specific immunological pathways important for mAb-mediated bacterial clearance. Overall, our work is both practically and conceptually innovative, and will challenge current treatment paradigms for pneumococcal infection.