What We Do

The Sharpe laboratory investigates T cell costimulatory pathways and their immunoregulatory functions. We focus on the roles of these pathways in regulating pathogenic and protective immune responses needed for the induction and maintenance of T cell tolerance and the prevention of autoimmunity, as well as effective antimicrobial and antitumor immunity. We are also involved in studies aimed at translating the fundamental understanding of T cell costimulation into new therapies for autoimmune diseases, chronic viral infections, and cancer. Manipulation of T cell costimulatory pathways is of great therapeutic interest as it may provide a means to enhance immune responses to promote anti-microbial and tumor immunity, or to terminate immune responses to control autoimmune diseases and achieve tolerance for organ transplantation.

Recent Publications

Inhibitors of the PD-1 Pathway in Tumor Therapy

LaFleur MW, Muroyama Y, Drake CG, Sharpe AH. Inhibitors of the PD-1 Pathway in Tumor Therapy. J Immunol. 2018;200 (2) :375-383.Abstract
The programmed death 1 (PD-1) pathway delivers inhibitory signals that function as a brake for immune responses. This pathway limits the initiation and duration of immune responses, thereby protecting tissues from immune-mediated damage and autoimmune diseases. However, the PD-1 pathway also inhibits immune responses to tumors. The critical role of PD-1 in preventing antitumor immunity is demonstrated by the transformative effects of PD-1 pathway blockade in a broad range of cancers with the hallmark of durability of response. Despite this success, most patients do not respond to PD-1 monotherapy, and some patients experience adverse events. In this review, we discuss the functions of the PD-1 pathway and its translation to cancer immunotherapy. We also consider current challenges and opportunities for PD-1 cancer immunotherapy, including mechanisms of response and resistance, identification of biomarkers of response to PD-1 therapy, characterization and treatment of PD-1 therapy-related adverse events, and development of safe and effective combination therapies.
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PD-L1 Prevents the Development of Autoimmune Heart Disease in Graft-versus-Host Disease

Juchem KW, Sacirbegovic F, Zhang C, Sharpe AH, Russell K, McNiff JM, Demetris AJ, Shlomchik MJ, Shlomchik WD. PD-L1 Prevents the Development of Autoimmune Heart Disease in Graft-versus-Host Disease. J Immunol. 2018;200 (2) :834-846.Abstract
Effector memory T cells (TEM) are less capable of inducing graft-versus-host disease (GVHD) compared with naive T cells (TN). Previously, in the TS1 TCR transgenic model of GVHD, wherein TS1 CD4 cells specific for a model minor histocompatibility Ag (miHA) induce GVHD in miHA-positive recipients, we found that cell-intrinsic properties of TS1 TEM reduced their GVHD potency relative to TS1 TN Posttransplant, TS1 TEM progeny expressed higher levels of PD-1 than did TS1 TN progeny, leading us to test the hypothesis that TEM induce less GVHD because of increased sensitivity to PD-ligands. In this study, we tested this hypothesis and found that indeed TS1 TEM induced more severe skin and liver GVHD in the absence of PD-ligands. However, lack of PD-ligands did not result in early weight loss and colon GVHD comparable to that induced by TS1 TN, indicating that additional pathways restrain alloreactive TEM TS1 TN also caused more severe GVHD without PD-ligands. The absence of PD-ligands on donor bone marrow was sufficient to augment GVHD caused by either TEM or TN, indicating that donor PD-ligand-expressing APCs critically regulate GVHD. In the absence of PD-ligands, both TS1 TEM and TN induced late-onset myocarditis. Surprisingly, this was an autoimmune manifestation, because its development required non-TS1 polyclonal CD8+ T cells. Myocarditis development also required donor bone marrow to be PD-ligand deficient, demonstrating the importance of donor APC regulatory function. In summary, PD-ligands suppress both miHA-directed GVHD and the development of alloimmunity-induced autoimmunity after allogeneic hematopoietic transplantation.
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B Cells Drive Autoimmunity in Mice with CD28-Deficient Regulatory T Cells

Zhang R, Sage PT, Finn K, Huynh A, Blazar BR, Marangoni F, Mempel TR, Sharpe AH, Turka LA. B Cells Drive Autoimmunity in Mice with CD28-Deficient Regulatory T Cells. J Immunol. 2017;199 (12) :3972-3980.Abstract
Follicular regulatory T (TFR) cells are a newly defined regulatory T cell (Treg) subset that suppresses follicular helper T cell-mediated B cell responses in the germinal center reaction. The precise costimulatory signal requirements for proper TFR cell differentiation and function are still not known. Using conditional knockout strategies of CD28, we previously demonstrated that loss of CD28 signaling in Tregs caused autoimmunity in mice (termed CD28-ΔTreg mice), characterized by lymphadenopathy, accumulation of activated T cells, and cell-mediated inflammation of the skin and lung. In this study, we show that CD28 signaling is required for TFR cell differentiation. Treg-specific deletion of CD28 caused a reduction in TFR cell numbers and function, which resulted in increased germinal center B cells and Ab production. Moreover, residual CD28-deficient TFR cells showed a diminished suppressive capacity as assessed by their ability to inhibit Ab responses in vitro. Surprisingly, genetic deletion of B cells in CD28-ΔTreg mice prevented the development of lymphadenopathy and CD4+ T cell activation, and autoimmunity that mainly targeted skin and lung tissues. Thus, autoimmunity occurring in mice with CD28-deficient Tregs appears to be driven primarily by loss of TFR cell differentiation and function with resulting B cell-driven inflammation.
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Rescue of exhausted CD8 T cells by PD-1-targeted therapies is CD28-dependent

Kamphorst AO, Wieland A, Nasti T, Yang S, Zhang R, Barber DL, Konieczny BT, Daugherty CZ, Koenig L, Yu K, et al. Rescue of exhausted CD8 T cells by PD-1-targeted therapies is CD28-dependent. Science. 2017;355 (6332) :1423-1427.Abstract
Programmed cell death-1 (PD-1)-targeted therapies enhance T cell responses and show efficacy in multiple cancers, but the role of costimulatory molecules in this T cell rescue remains elusive. Here, we demonstrate that the CD28/B7 costimulatory pathway is essential for effective PD-1 therapy during chronic viral infection. Conditional gene deletion showed a cell-intrinsic requirement of CD28 for CD8 T cell proliferation after PD-1 blockade. B7-costimulation was also necessary for effective PD-1 therapy in tumor-bearing mice. In addition, we found that CD8 T cells proliferating in blood after PD-1 therapy of lung cancer patients were predominantly CD28-positive. Taken together, these data demonstrate CD28-costimulation requirement for CD8 T cell rescue and suggest an important role for the CD28/B7 pathway in PD-1 therapy of cancer patients.
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