Monica V. Goldberg

Immune Inhibitory Molecules LAG-3 and PD-1 Synergistically Regulate T-cell Function to Promote Tumoral Immune Escape

Inhibitory receptors on immune cells are pivotal regulators of immune escape in cancer. Among these inhibitory receptors, CTLA-4 (targeted clinically by ipilimumab) serves as a dominant off-switch while other receptors such as PD-1 and LAG-3 seem to serve more subtle rheostat functions. However, the extent of synergy and cooperative interactions between inhibitory pathways in cancer remain largely unexplored. Here, we reveal extensive coexpression of PD-1 and LAG-3 on tumor-infiltrating CD4(+) and CD8(+) T cells in three distinct transplantable tumors. Dual anti-LAG-3/anti-PD-1 antibody treatment cured most mice of established tumors that were largely resistant to single antibody treatment. Despite minimal immunopathologic sequelae in PD-1 and LAG-3 single knockout mice, dual knockout mice abrogated self-tolerance with resultant autoimmune infiltrates in multiple organs, leading to eventual lethality. However, Lag3(-/-)Pdcd1(-/-) mice showed markedly increased survival from and clearance of multiple transplantable tumors. Together, these results define a strong synergy between the PD-1 and LAG-3 inhibitory pathways in tolerance to both self and tumor antigens. In addition, they argue strongly that dual blockade of these molecules represents a promising combinatorial strategy for cancer.

Cutting Edge: An In Vivo Requirement for STAT3 Signaling in TH17 Development and TH17-Dependent Autoimmunity

STAT3 activation has been observed in several autoimmune diseases, suggesting that STAT3-mediated pathways promote pathologic immune responses. We provide in vivo evidence that the fundamental role of STAT3 signaling in autoimmunity relates to its absolute requirement for generating TH17 T cell responses. We show that STAT3 is a master regulator of this pathogenic T cell subtype, acting at multiple levels in vivo, including TH17 T cell differentiation and cytokine production, as well as induction of RORγt and the IL-23R. Neither naturally occurring TH17 cells nor TH17-dependent autoimmunity occurs when STAT3 is ablated in CD4 cells. Furthermore, ablation of STAT3 signaling in CD4 cells results in increased TH1 responses, indicating that STAT3 signaling skews TH responses away from the TH1 pathway and toward the TH17 pathway. Thus, STAT3 is a candidate target for TH17-dependent autoimmune disease immunotherapy that could selectively inhibit pathogenic immune pathways.

LAG-3 regulates CD8+ T cell accumulation and effector function in murine self- and tumor-tolerance systems

Lymphocyte activation gene-3 (LAG-3) is a cell-surface molecule with diverse biologic effects on T cell function. We recently showed that LAG-3 signaling is important in CD4+ regulatory T cell suppression of autoimmune responses. Here, we demonstrate that LAG-3 maintains tolerance to self and tumor antigens via direct effects on CD8+ T cells using 2 murine systems. Naive CD8+ T cells express low levels of LAG-3, and expression increases upon antigen stimulation. Our data show increased levels of LAG-3 protein on antigen-specific CD8+ T cells within antigen-expressing organs or tumors. In vivo antibody blockade of LAG-3 or genetic ablation of the Lag-3 gene resulted in increased accumulation and effector function of antigen-specific CD8+ T cells within organs and tumors that express their cognate antigen. Most notably, combining LAG-3 blockade with specific antitumor vaccination resulted in a significant increase in activated CD8+ T cells in the tumor and disruption of the tumor parenchyma. A major component of this effect was CD4 independent and required LAG-3 expression by CD8+ T cells. Taken together, these data demonstrate a direct role for LAG-3 on CD8+ T cells and suggest that LAG-3 blockade may be a potential cancer treatment.

A role for the transcription factor Helios in human CD4+CD25+ regulatory T cells

Relative upregulation of the Ikaros family transcription factor Helios in natural regulatory T cells (Tregs) has been reported by several groups. However, a role for Helios in regulatory T cells has not yet been described. Here, we show that Helios is upregulated in CD4(+)CD25(+) regulatory T cells. Chromatin-immunoprecipitation (ChIP) experiments indicated that Helios binds to the FoxP3 promoter. These data were further corroborated by experiments showing that knocking-down Helios with siRNA oligonucleotides results in down-regulation of FoxP3. Functionally, we found that suppression of Helios message in CD4(+)CD25(+) T cells significantly attenuates their suppressive function. Taken together, these data suggest that Helios may play an important role in regulatory T cell function and support the concept that Helios may be a novel target to manipulate Treg activity in a clinical setting.

Tc17 CD8 T Cells: Functional Plasticity and Subset Diversity

IL-17-secreting CD8 T cells (Tc17) have been described in several settings, but little is known regarding their functional characteristics. While Tc1 cells produced IFN-γ and efficiently killed targets, Tc17 cells lacked lytic function in vitro. Interestingly, the small numbers of IFN-γ-positive or IL-17/IFN-γ-double-positive cells generated under Tc17 conditions also lacked lytic activity and expressed a similar pattern of cell surface proteins to IL-17-producing cells. As is the case for Th17 (CD4) cells, STAT3 is important for Tc17 polarization, both in vitro and in vivo. Adoptive transfer of highly purified, Ag-specific IL-17-secreting Tc17 cells into Ag-bearing hosts resulted in near complete conversion to an IFN-γ-secreting phenotype and substantial pulmonary pathology, demonstrating functional plasticity. Tc17 also accumulated to a greater extent than did Tc1 cells, suggesting that adoptive transfer of CD8 T cells cultured in Tc17 conditions may have therapeutic potential for diseases in which IFN-γ-producing cells are desired.

Cyclophosphamide Augments Antitumor Immunity: Studies in an Autochthonous Prostate Cancer Model

To study the immune response to prostate cancer, we developed an autochthonous animal model based on the transgenic adenocarcinoma of the mouse prostate (TRAMP) mouse in which spontaneously developing tumors express influenza hemagglutinin as a unique, tumor-associated antigen. Our prior studies in these animals showed immunologic tolerance to hemagglutinin, mirroring the clinical situation in patients with cancer who are generally nonresponsive to their disease. We used this physiologically relevant animal model to assess the immunomodulatory effects of cyclophosphamide when administered in combination with an allogeneic, cell-based granulocyte-macrophage colony-stimulating factor-secreting cancer immunotherapy. Through adoptive transfer of prostate/prostate cancer-specific CD8 T cells as well as through studies of the endogenous T-cell repertoire, we found that cyclophosphamide induced a marked augmentation of the antitumor immune response. This effect was strongly dependent on both the dose and the timing of cyclophosphamide administration. Mechanistic studies showed that immune augmentation by cyclophosphamide was associated with a transient depletion of regulatory T cells in the tumor draining lymph nodes but not in the peripheral circulation. Interestingly, we also noted effects on dendritic cell phenotype; low-dose cyclophosphamide was associated with increased expression of dendritic cell maturation markers. Taken together, these data clarify the dose, timing, and mechanism of action by which immunomodulatory cyclophosphamide can be translated to a clinical setting in a combinatorial cancer treatment strategy.

Functionally Distinct LAG-3 and PD-1 Subsets on Activated and Chronically Stimulated CD8 T Cells

Lymphocyte Activation Gene-3 (LAG-3) is a transmembrane protein that binds MHC class II, enhances regulatory T cell activity, and negatively regulates cellular proliferation, activation, and homeostasis of T cells. Programmed Death 1 (PD-1) also negatively regulates T cell function. LAG-3 and PD-1 are both transiently expressed on CD8 T cells that have been stimulated during acute activation. However, both LAG-3 and PD-1 remain on CD8 T cells at high levels after stimulation within tolerizing environments. Our previous data demonstrated that blockade of either LAG-3 or PD-1 using mAb therapy in combination with vaccination restores the function of tolerized Ag-specific CD8 T cells in models of self and tumor tolerance. It is unclear whether tolerized CD8 T cells coexpress PD-1 and LAG-3 or whether PD-1 and LAG-3 mark functionally distinct populations of CD8 T cells. In this study, we describe three populations of CD8 T cells activated under tolerizing conditions based on LAG-3 and PD-1 staining, each with distinct phenotypic and functional characteristics. From a mechanistic perspective, both Ag concentration and proinflammatory signals control the expression of LAG-3 and PD-1 phenotypes on CD8 T cells under activating and tolerizing conditions. These results imply that signaling through the PD-1 and LAG-3 pathways have distinct functional consequences to CD8 T cells under tolerizing conditions and manipulation of both Ag and cytokine signaling can influence CD8 tolerance through LAG-3 and PD-1.

LAG-3 in Cancer Immunotherapy

LAG-3 (CD223) is a cell surface molecule expressed on activated T cells (Huard et al. Immunogenetics 39:213-217, 1994), NK cells (Triebel et al. J Exp Med 171:1393-1405, 1990), B cells (Kisielow et al. Eur J Immunol 35:2081-2088, 2005), and plasmacytoid dendritic cells (Workman et al. J Immunol 182:1885-1891, 2009) that plays an important but incompletely understood role in the function of these lymphocyte subsets. In addition, the interaction between LAG-3 and its major ligand, Class II MHC, is thought to play a role in modulating dendritic cell function (Andreae et al. J Immunol 168:3874-3880, 2002). Recent preclinical studies have documented a role for LAG-3 in CD8 T cell exhaustion (Blackburn et al. Nat Immunol 10:29-37, 2009), and blockade of the LAG-3/Class II interaction using a LAG-3 Ig fusion protein is being evaluated in a number of clinical trials in cancer patients. In this review, we will first discuss the basic structural and functional biology of LAG-3, followed by a review of preclinical and clinical data pertinent to a role for LAG-3 in cancer immunotherapy.

Radiotherapy Augments the Immune Response to Prostate Cancer in a Time-Dependent Manner

Cancer immunotherapy refers to an array of strategies intended to treat progressive tumors by augmenting a patients anti‐tumor immune response. As immunotherapy is eventually incorporated into oncology treatment paradigms, it is important to understand how these therapies interact with established cancer treatments such as chemotherapy or Radiotherapy (RT). To address this, we utilized a well‐established, autochthonous murine model of prostate cancer to test whether RT could augment (or diminish) the CD4 T cell response to a tumor vaccine.

Sequencing CTLA-4 blockade with cell-based immunotherapy for prostate cancer

BackgroundThe FDA recently approved an anti-CTLA-4 antibody (Iplimumab) for the treatment of metastatic melanoma. This decision was based on Phase III results, which demonstrate that blocking this immune checkpoint provides a survival advantage in patients with advanced disease. As a single agent, ipilimumab is also being clinically evaluated in advanced (metastatic, castrate-resistant) prostate cancer and two randomized, placebo-controlled Phase III studies have recently completed accrual.MethodsWe used a well-described genetically engineered mouse (GEM), autochronous prostate cancer model (Pro-TRAMP) to explore the relative sequencing and dosing of anti-CTLA-4 antibody when combined with a cell-based, GM-CSF-secreting vaccine (GVAX).ResultsOur results show that combined treatment results in a dramatic increase in effector CD8 T cells in the prostate gland, and enhanced tumor-antigen directed lytic function. These effects are maximized when CTLA-4 blockade is applied after, but not before, vaccination. Additional experiments, using models of metastatic disease, show that incorporation of low-dose cyclophosphamide into this combined treatment regimen results in an additional pre-clinical benefit.ConclusionsTogether these studies define a combination regimen using anti-CTLA-4/GVAX immunotherapy and low-dose chemotherapy for potential translation to a clinical trial setting.