This PPG competing renewal application is driven by the fundamental and therapeutic importance of costimulatory pathways in regulating T cell activation, tolerance, and exhaustion and builds upon our significant progress since initial award of this PPG in 2003. Synergy in our PPG is highlighted by 118 publications, 43 co- authored by multiple PPG investigators. Our PPG also has had a significant role in fostering development of junior faculty,and sharing novel mAbs and mouse strains with the broader scientific community has resulted in better understanding of costimulation above and beyond our PPG aims. Our overarching goal is to develop a comprehensive understanding of how positive and negative second signals regulate T cell activation, tolerance and exhaustion. Working together, we have discovered that the PD-1 pathway has multifaceted immunoregulatory functions. We have determined novel roles for the PD-1 pathway in regulating humoral immunity and in controlling T cell differentiation and function. We also have discovered two new coinhibitory molecules, identifying repulsion guidance molecule b (RGMb) as a PD-L2 ligand and regulator of respiratory tolerance, and Protein C receptor (PROCR) as a novel regulator of Th17 cells. These discoveries demonstrate ongoing synergy within our PPG. The sharing of unpublished results and discussion of data have inspired hypotheses and experiments bidirectionally in all PPG projects, which drive the focus of our renewal application. Our major goals are to investigate: 1) Roles of PD-1, PD-L1 and PD-L2 in regulating protective and pathogenic humoral immune responses, 2) Roles of the PD-1 pathway in regulating the balance between protective and pathogenic subsets of T cells, 3) Function of RGMb in controlling T cell activation, tolerance and exhaustion, and 4) Relationships between PD-1 and PROCR in controlling Th17 cells and exhausted CD8 T cells, using models of infection, chronic graft versus host disease (cGVHD) and autoimmunity. Our proposed Program will consist of 3 highly integrated and interactive Projects, supported by 3 Cores. Project 1 (Sharpe/Ahmed) will focus on the roles of PD-1, PD-L1, PD-L2, RGMb and PROCR in controlling protective immunity during acute and chronic viral infections. Project 2 (Blazar/Turka) will investigate how PD-1 pathway members, PROCR and CD28 regulate cGVHD. Project 3 (Kuchroo/ Sharpe) will study how PROCR and PD-1 influence pathogenic vs. non-pathogenic Th17 cells and thus regulate autoimmune diseases. Administrative Core A (Sharpe) will provide administrative and scientific coordination. Antibody/Ig fusion protein Core B (Freeman) will provide novel mAbs and Ig fusion proteins. Transgenic/Knockout Core C (Sharpe) will provide a unique and important set of mouse strains. The use of the same standardized tools makes it possible to compare and contrast results in different settings and disease models. Mechanistic insights from our proposed studies should guide translation into new immunotherapies targeting costimulatory and coinhibitory pathways for human chronic viral infections, cancer, autoimmune diseases and transplantation.

Public Health Relevance

These studies will provide the basis for understanding how, where and when costimulatory and coinhibitory molecules regulate chronic viral infection, chronic-graft versus-host disease, and organ-specific autoimmunity. These studies have implications for developing novel immunotherapies based on targeting costimulatory pathways for human chronic viral infections, cancer, autoimmune diseases and transplantation. Project 1: Costimulation and Regulation of Anti-viral Immunity Project Leader (PL): Sharpe, Arlene H. DESCRIPTION (as provided by applicant): Anti-microbial T cell responses play a major role in determining the outcome of infection. Chronic infections are often distinguished by T cell responses that are not able to fully eliminate the pathogen. The mechanisms that explain this failure of T cell effector responses are only beginning to be understood. During the current funding period, we have used the lymphocytic choriomeningitis virus (LCMV) model to investigate how the PD-1 pathway regulates T cell responses during chronic infection. We have found that the PD-1 pathway has multifaceted roles in protective immunity. We discovered that in addition to PD-L1, PD-L2 limits responses of exhausted T cells. We also have shown that PD-L1 has distinct roles on hematopoietic and non-hematopoietic cells during chronic infection. However, we lack a mechanistic understanding of PD-L1 and PD-L2 functions on specific cell types. A major goal of this proposal is to elucidate mechanisms by which PD-1 and its ligands regulate CD8 T cell exhaustion, issues of fundamental and translational importance, given the therapeutic promise of this pathway. In addition, we have discovered a new function for the PD-1 pathway in protective immunity. We have identified a role for PD-1 in regulating humoral immunity by inhibiting the generation and function of T follicular regulatory cells. Thus, we will not only address how the PD-1 pathway regulates CD8 T cell exhaustion, but also how it controls humoral immunity. In addition, we will study roles of two novel coinhibitory molecules identified by PPG investigators in anti-microbial immunity: repulsion guidance molecule b (RGMb) and protein C receptor (PROCR). Dr. Freeman (Core B) identified RGMb as a second binding partner for PD-L2. The rescue of T cell exhaustion in PD-L2 deficient mice leads us to study RGMb function during chronic infection. Dr. Kuchroo (PI, Project 3) has identified protein C receptor (PROCR) as a novel coinhibitory molecule;in collaboration we have found that PROCR is highly expressed on exhausted CD8 T cells. We will study if PROCR regulates T cell exhaustion. Our main hypothesis is that PD-1 pathway members and PROCR regulate protective immunity during acute and chronic infections. To test this hypothesis, our Specific Aims are to: 1) Analyze how PD-1 and its ligands regulate humoral immunity during acute mucosal/localized viral infection (influenza) versus systemic infection (LCMV). 2) Investigate roles of the PD-1 and PROCR pathways in controlling exhausted CD8 T cells during chronic LCMV infection. Our goals are to determine how to optimally modulate the PD-1 and PROCR pathways therapeutically in chronic infection, and develop new strategies to promote protective immunity during acute viral infections.

National Institute of Health (NIH)
Research Program Projects (P01)
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Special Emphasis Panel (ZAI1)
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Lapham, Cheryl K
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Harvard Medical School
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Flynn, Ryan; Du, Jing; Veenstra, Rachelle G et al. (2014) Increased T follicular helper cells and germinal center B cells are required for cGVHD and bronchiolitis obliterans. Blood 123:3988-98
Penaloza-MacMaster, Pablo; Kamphorst, Alice O; Wieland, Andreas et al. (2014) Interplay between regulatory T cells and PD-1 in modulating T cell exhaustion and viral control during chronic LCMV infection. J Exp Med 211:1905-18
Sawitzki, Birgit; Brunstein, Claudio; Meisel, Christian et al. (2014) Prevention of graft-versus-host disease by adoptive T regulatory therapy is associated with active repression of peripheral blood Toll-like receptor 5 mRNA expression. Biol Blood Marrow Transplant 20:173-82
Dubovsky, Jason A; Flynn, Ryan; Du, Jing et al. (2014) Ibrutinib treatment ameliorates murine chronic graft-versus-host disease. J Clin Invest 124:4867-76
Xiao, Yanping; Yu, Sanhong; Zhu, Baogong et al. (2014) RGMb is a novel binding partner for PD-L2 and its engagement with PD-L2 promotes respiratory tolerance. J Exp Med 211:943-59
Porichis, Filippos; Hart, Meghan G; Zupkosky, Jennifer et al. (2014) Differential impact of PD-1 and/or interleukin-10 blockade on HIV-1-specific CD4 T cell and antigen-presenting cell functions. J Virol 88:2508-18
Mott, Kevin R; Allen, Sariah J; Zandian, Mandana et al. (2014) Inclusion of CD80 in HSV targets the recombinant virus to PD-L1 on DCs and allows productive infection and robust immune responses. PLoS One 9:e87617
Joller, Nicole; Lozano, Ester; Burkett, Patrick R et al. (2014) Treg cells expressing the coinhibitory molecule TIGIT selectively inhibit proinflammatory Th1 and Th17 cell responses. Immunity 40:569-81
Alexander, Kylie A; Flynn, Ryan; Lineburg, Katie E et al. (2014) CSF-1-dependant donor-derived macrophages mediate chronic graft-versus-host disease. J Clin Invest 124:4266-80
Ding, Zhi-Chun; Lu, Xiaoyun; Yu, Miao et al. (2014) Immunosuppressive myeloid cells induced by chemotherapy attenuate antitumor CD4+ T-cell responses through the PD-1-PD-L1 axis. Cancer Res 74:3441-53

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