Programmed cell death-1 (PD-1) is an immune inhibitory receptor that is expressed transiently on the surface of CD4 and CD8 T cells following immune activation and is highly expressed on T cells chronically exposed to antigen. Signaling through PD-1 can result in T cell exhaustion, a state in which antigen-specific T cells no longer respond to antigen-specific stimulation. As observed in numerous persistent viral infections, including those from HIV, human hepatitis C virus, and murine lymphocytic choriomeningitis virus (LCMV), antibody blockade between PD-1 and its ligands (PD-L1/L2) results in the functional reactivation of "exhausted" antigen-specific T cells. Clinical trials incorporating a PD1 blockade therapy have demonstrated impressive success;highlighting the importance of the expression and regulation of this gene. Our work has shown that PD-1 is regulated at the level of transcription in a complex manner involving nine cis-regulatory elements;a network of positive (NFATc1 and STAT3) and negative (Blimp-1 and LSD1) transcription factors;and a dynamic epigenetic regulatory program, including DNA methylation. Despite this knowledge, the mechanistic details of how the cis-elements, trans-factors, and epigenetic pathways integrate to provide cell type and immune response regulation is not well understood. This understanding is important as PD-1's expression and activity is critical to the development of protective immune responses to infection and cancer. To elucidate the molecular mechanisms that govern PD-1 expression, we propose three aims designed to 1) define the cis- regulatory map and interactions at the PD-1 locus in antigen-specific cells following infection;2) understand the interplay between NFATc1, Blimp-1 and STATs in regulating PD-1 during acute and viral infection conditions;and 3) to understand how the epigenetic silencer LSD1 controls PD-1 expression and DNA methylation at this locus. To investigate these aims, we have established a series of mouse lines that will conditionally delete the cis element CR-C, the transcription factor Blimp-1, or the epigenetic silencer LSD1 in activated CD8 T cells. We have established ex vivo methods to analyze the CD8 T cells and will incorporate an in vivo system of acute and chronic viral infection using LCMV to explore the mechanism by which these factors function to control PD-1. Ultimately our studies will elucidate the molecular genetic and epigenetic programs that control PD-1 expression and will provide new tools to manipulate PD-1 gene expression that could aid in the treatment of infection and cancer.
Despite the success of recent clinical trials to block PD-1 activity and reverse some terminal cancers, little is known how this immune inhibitory receptor is regulated at the molecular level. We have defined some of the rudimentary parameters that define PD-1 expression, including a series of cis-regulatory elements and four groups of transcription factors. The goals of this project are to elucidate the molecular interplay between the factors and elements and to define novel ways in which PD-1 expression may be ultimately manipulated clinically to increase immunity, prevent chronic infections, and treat cancer.