Identifying novel regulators of Tfh cell differentiation that can be targeted to improve humoral immunity during chronic viral infection - SUMMARY T follicular helper (Tfh) cells are a subset of CD4+ T cells that specialize in communicating with germinal center (GC) B cells to facilitate B cell differentiation into either Memory B cells or Plasma cells that secrete high-affinity class-switched antibodies. As a key regulator of both antibody quantity and quality, coupled to the crucial role antibodies play in mediating pathogen control following immunization or infection, or in driving autoimmune or allergic diseases respectively, Tfh cells directly contribute to either protective or pathological B cell responses depending on the context of the disease. Notably, Tfh cells play an especially important role during chronic viral infections, such as during HIV-1 and hepatitis C virus infection, or during chronic lymphocytic choriomeningitis (LCMV) infection in mice, all of which critically depend on Tfh-mediated antibody responses for viral control. Moreover, recent evidence indicates that Tfh cell-derived IL-21 functions to sustain the effector function of CD8+ T cells during chronic viral infection and cancer. However, despite their essential role, the precise molecular circuits underpinning Tfh cell differentiation remain unclear. Moreover, in settings of persistent infection, the development of neutralizing antibodies is often delayed for several months, and the initial wave of antibodies that do develop are often of low-affinity and poor quality. Furthermore, hypergammaglobulinemia, or the overproduction of non-specific antibodies, and impaired FCγ receptor effector functions are hallmarks of chronic viral infections in both mice and humans, indicating that dysregulated humoral immunity is a generalizable feature of persistent viral infection. We hypothesize that persistent exposure to antigen and inflammation perturbs functional Tfh cell responses, thereby resulting in insufficient “help” signals to both B cells and CD8+ T cells, suboptimal antibody responses and impaired viral control during chronic infection. Herein, I will employ cutting-edge technologies, including single cell profiling of T cell transcriptomes and epigenomes, innovative bioinformatic pipelines, and CRISPR/Cas9 screening and genetic mouse models to identify novel and conserved regulators of Tfh cell differentiation across different infections and species, as well as determine how persistent exposure to antigen and inflammation perturbs the transcriptional and epigenetic program of Tfh cells and their functional capacity to provide “help” to B cells. Additionally, using computational approaches to integrate publicly available single-cell RNA-sequencing datasets containing human CD4+ T cell populations, accompanied by a creative in vitro Tfh:B cell co-culture system, we will extend our findings from experimental models to further delineate critical regulators of human Tfh cells. Successful completion of this project will provide mechanistic insight into the molecular circuitry underpinning Tfh cell development and aid in the identification of novel strategies aimed at targeting Tfh cells to modulate their function for therapeutic benefit during chronic viral infection and/or other diseases.
