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

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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PD-L1 on tumor cells is sufficient for immune evasion in immunogenic tumors and inhibits CD8 T cell cytotoxicity

Juneja VR, McGuire KA, Manguso RT, LaFleur MW, Collins N, Haining NW, Freeman GJ, Sharpe AH. PD-L1 on tumor cells is sufficient for immune evasion in immunogenic tumors and inhibits CD8 T cell cytotoxicity. J Exp Med. 2017;214 (4) :895-904.Abstract
It is unclear whether PD-L1 on tumor cells is sufficient for tumor immune evasion or simply correlates with an inflamed tumor microenvironment. We used three mouse tumor models sensitive to PD-1 blockade to evaluate the significance of PD-L1 on tumor versus nontumor cells. PD-L1 on nontumor cells is critical for inhibiting antitumor immunity in B16 melanoma and a genetically engineered melanoma. In contrast, PD-L1 on MC38 colorectal adenocarcinoma cells is sufficient to suppress antitumor immunity, as deletion of PD-L1 on highly immunogenic MC38 tumor cells allows effective antitumor immunity. MC38-derived PD-L1 potently inhibited CD8(+) T cell cytotoxicity. Wild-type MC38 cells outcompeted PD-L1-deleted MC38 cells in vivo, demonstrating tumor PD-L1 confers a selective advantage. Thus, both tumor- and host-derived PD-L1 can play critical roles in immunosuppression. Differences in tumor immunogenicity appear to underlie their relative importance. Our findings establish reduced cytotoxicity as a key mechanism by which tumor PD-L1 suppresses antitumor immunity and demonstrate that tumor PD-L1 is not just a marker of suppressed antitumor immunity.
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Anti-CD48 Monoclonal Antibody Attenuates Experimental Autoimmune Encephalomyelitis by Limiting the Number of Pathogenic CD4+ T Cells

McArdel SL, Brown DR, Sobel RA, Sharpe AH. Anti-CD48 Monoclonal Antibody Attenuates Experimental Autoimmune Encephalomyelitis by Limiting the Number of Pathogenic CD4+ T Cells. J Immunol. 2016;197 (8) :3038-3048.Abstract
CD48 (SLAMF2) is an adhesion and costimulatory molecule constitutively expressed on hematopoietic cells. Polymorphisms in CD48 have been linked to susceptibility to multiple sclerosis (MS), and altered expression of the structurally related protein CD58 (LFA-3) is associated with disease remission in MS. We examined CD48 expression and function in experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. We found that a subpopulation of CD4(+) T cells highly upregulated CD48 expression during EAE and were enriched for pathogenic CD4(+) T cells. These CD48(++)CD4(+) T cells were predominantly CD44(+) and Ki67(+), included producers of IL-17A, GM-CSF, and IFN-γ, and were most of the CD4(+) T cells in the CNS. Administration of anti-CD48 mAb during EAE attenuated clinical disease, limited accumulation of lymphocytes in the CNS, and reduced the number of pathogenic cytokine-secreting CD4(+) T cells in the spleen at early time points. These therapeutic effects required CD48 expression on CD4(+) T cells but not on APCs. Additionally, the effects of anti-CD48 were partially dependent on FcγRs, as anti-CD48 did not ameliorate EAE or reduce the number of cytokine-producing effector CD4(+) T cells in Fcεr1γ(-/-) mice or in wild-type mice receiving anti-CD16/CD32 mAb. Our data suggest that anti-CD48 mAb exerts its therapeutic effects by both limiting CD4(+) T cell proliferation and preferentially eliminating pathogenic CD48(++)CD4(+) T cells during EAE. Our findings indicate that high CD48 expression is a feature of pathogenic CD4(+) T cells during EAE and point to CD48 as a potential target for immunotherapy.
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Type 2 innate lymphoid cell suppression by regulatory T cells attenuates airway hyperreactivity and requires inducible T-cell costimulator-inducible T-cell costimulator ligand interaction

Rigas D, Lewis G, Aron JL, Wang B, Banie H, Sankaranarayanan I, Galle-Treger L, Maazi H, Lo R, Freeman GJ, et al. Type 2 innate lymphoid cell suppression by regulatory T cells attenuates airway hyperreactivity and requires inducible T-cell costimulator-inducible T-cell costimulator ligand interaction. J Allergy Clin Immunol. 2016.Abstract
BACKGROUND: Atopic diseases, including asthma, exacerbate type 2 immune responses and involve a number of immune cell types, including regulatory T (Treg) cells and the emerging type 2 innate lymphoid cells (ILC2s). Although ILC2s are potent producers of type 2 cytokines, the regulation of ILC2 activation and function is not well understood. OBJECTIVE: In the present study, for the first time, we evaluate how Treg cells interact with pulmonary ILC2s and control their function. METHODS: ILC2s and Treg cells were evaluated by using in vitro suppression assays, cell-contact assays, and gene expression panels. Also, human ILC2s and Treg cells were adoptively transferred into NOD SCID γC-deficient mice, which were given isotype or anti-inducible T-cell costimulator ligand (ICOSL) antibodies and then challenged with IL-33 and assessed for airway hyperreactivity. RESULTS: We show that induced Treg cells, but not natural Treg cells, effectively suppress the production of the ILC2-driven proinflammatory cytokines IL-5 and IL-13 both in vitro and in vivo. Mechanistically, our data reveal the necessity of inducible T-cell costimulator (ICOS)-ICOS ligand cell contact for Treg cell-mediated ILC2 suppression alongside the suppressive cytokines TGF-β and IL-10. Using a translational approach, we then demonstrate that human induced Treg cells suppress syngeneic human ILC2s through ICOSL to control airway inflammation in a humanized ILC2 mouse model. CONCLUSION: These findings suggest that peripheral expansion of induced Treg cells can serve as a promising therapeutic target against ILC2-dependent asthma.
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