Congratulations to Ryan Zander, PhD, for his NIH R00 grant entitled, "Defining the transcriptional, phenotypic, and functional heterogeneity of virus-specific CD4 T cells during chronic viral infection".  Dr. Zander recently joined the Department and was a Postdoctoral Fellow in Molecular Immunology at the Blood Research Institute in Milwaukee, WI. 

PROJECT SUMMARY:
CD4 T cell “help” in the form of soluble factors and cell-surface ligands is critical to sustain CD8 T cell responses and humoral immunity during chronic viral infection. However, despite their essential role, our understanding of how persistent exposure to antigen and inflammation shapes helper T cell differentiation remains incompletely understood. Using scRNA-seq, we recently demonstrated that CD4 T cells responding to chronic LCMV infection are more heterogenous than previously appreciated, with three transcriptionally distinct subsets dominating the antiviral response: Cxcr6+Th1, Cxcr5+Tfh, and Slamf6+ T memory-like (TML) cells. Notably, our data further indicate that CD4 T cells responding to chronic, but not acute viral infection, preferentially redirect their differentiation towards this TML subset. Interestingly, although Tfh formation is relatively reduced (compared to the TML subset), we recently uncovered that Tfh-secreted IL-21 is critical to sustain Effector CD8 T cell responses, limit T cell exhaustion, and promote viral control. This finding, coupled to the role CD8 T cell exhaustion plays in limiting immunopathology during chronic infection, leads us to speculate that the Tfh response is tightly regulated to prevent an overzealous effector response. Thus, we propose that the acquisition of a quiescent-like TML subset may be beneficial to the host, as it may mitigate potential pathological responses, while also serve as a reservoir to replenish Th1 and Tfh effector cells at the opportune time. Accordingly, an identification of the cellular and molecular factors underlying this altered pattern of CD4 T cell differentiation will be critical to understand how CD4 T cells adapt to sustain antiviral immunity during chronic viral infection. Based on the gene regulatory network formulated by SCENIC (an R package), in Aim 1 of this proposal, we will use CRISPR Cas9 and genetic deletion models to test the contribution of key transcription factors predicted to play a role in regulating CD4 T cell differentiation during chronic viral infection. Additionally, we will manipulate antigen display, antigen-driven TCR-signaling, and inflammatory cytokines known to be overexpressed during chronic infection, including TGF-β, type I IFNs, and IL-10, to directly test how prolonged exposure to these signals impacts the formation and function of CD4 T cells during persistent viral infection. In Aim 2, we will determine whether AT of IL-21-producing Tfh or TML cells, either alone or in conjunction with PD-L1 blockade, can augment ProgenitorEffector CD8 T cell transition, while limiting CD8 T cell exhaustion, thereby improving T cell-mediated antiviral immunity. Overall, knowledge gained from this research will provide mechanistic insights into the functional adaption process CD4 T cells undergo in the face of persistent viral infection. Moreover, completion of this project will lead to the identification of novel strategies aimed at promoting the formation of functional effector CD4 T cells to optimize cellular or humoral mediated immunity.