Mesothelin is a cell-surface glycoprotein present on mesothelial cells and elicits T-cell responses in a variety of cancers including pancreatic and ovarian cancer. Breast cancer is not known to express mesothelin. We postulated that mesothelin may be a unique tumor associated antigen in triple negative breast cancer (TNBC), a less common breast cancer subtype which may have been underrepresented in prior studies that characterized mesothelin expression. Therefore, we screened 99 primary breast cancer samples by immunohistochemistry analysis using formalin fixed paraffin embedded archival tumor tissues subtypes and confirmed that mesothelin was overexpressed in the majority of TNBC (67%) but only rarely in < 5% ER(+) or Her2-neu (+) breast cancer respectively. To determine whether mesothelin may be exploited as a novel immunotherapy target in breast cancer, an in vitro cell killing assay was performed to compare the ability of genetically modified T cells expressing a chimeric antibody receptor (CAR) specific for mesothelin (mesoCAR T-cells) or non-transduced T-cells to kill mesothelin-expressing primary breast cancer cells. A significantly higher anti-tumor cytotoxicity by mesoCAR T-cells was observed (31.7% vs. 8.7%, p<0.001). Our results suggest that mesothelin has promise as a novel immunotherapy target for TNBC for which effective targeted therapy is lacking to date.
Malignant cells drive the generation of a desmoplastic and immunosuppressive tumor microenvironment. Cancer-associated stromal cells (CASCs) are a heterogeneous population that provides both negative and positive signals for tumor cell growth and metastasis. Fibroblast activation protein (FAP) is a marker of a major subset of CASCs in virtually all carcinomas. Clinically, FAP expression serves as an independent negative prognostic factor for multiple types of human malignancies. Prior studies established that depletion of FAP+ cells inhibits tumor growth by augmenting anti-tumor immunity. However, the potential for immune-independent effects on tumor growth have not been defined. Herein, we demonstrate that FAP+ CASCs are required for maintenance of the provisional tumor stroma since depletion of these cells, by adoptive transfer of FAP-targeted chimeric antigen receptor (CAR) T cells, reduced extracellular matrix proteins and glycosaminoglycans. Adoptive transfer of FAP-CAR T cells also decreased tumor vascular density and restrained growth of desmoplastic human lung cancer xenografts and syngeneic murine pancreatic cancers in an immune-independent fashion. Adoptive transfer of FAP-CAR T cells also restrained autochthonous pancreatic cancer growth. These data distinguish the function of FAP+ CASCs from other CASC subsets and provide support for further development of FAP+ stromal cell-targeted therapies for the treatment of solid tumors.
Chimeric antigen receptors (CAR) bearing an antigen-binding domain linked in cis to the cytoplasmic domains of CD3ζ and costimulatory receptors have provided a potent method for engineering T-cell cytotoxicity towards B-cell leukemia and lymphoma. However, resistance to immunotherapy due to loss of T-cell effector function remains a significant barrier, especially in solid malignancies. We describe an alternative chimeric immunoreceptor design in which we have fused a single-chain variable fragment for antigen recognition to the transmembrane and cytoplasmic domains of KIR2DS2, a stimulatory killer immunoglobulin-like receptor (KIR). We show that this simple, KIR-based CAR (KIR-CAR) triggers robust antigen-specific proliferation and effector function in vitro when introduced into human T cells with DAP12, an immunotyrosine-based activation motifs (ITAM)-containing adaptor. T cells modified to express a KIR-CAR and DAP12 exhibit superior antitumor activity compared to standard first and second generation CD3ζ-based CARs in a xenograft model of mesothelioma highly resistant to immunotherapy. The enhanced antitumor activity is associated with improved retention of chimeric immunoreceptor expression and improved effector function of isolated tumor-infiltrating lymphocytes. These results support the exploration of KIR-CARs for adoptive T-cell immunotherapy, particularly in immunotherapy-resistant solid tumors.
immunotherapy; cancer; T cell; CAR; immunoreceptor
Immunotherapy using vaccines or adoptively transferred tumor infiltrating lymphocytes (TILs) is limited by T cell functional inactivation within the solid tumor microenvironment. The purpose of this study was to determine if a similar tumor-induced inhibition occurred with genetically-modified cytotoxic T cells expressing chimeric antibody receptors (CARs) targeting tumor-associated-antigens.
Human T cells expressing CAR targeting mesothelin or fibroblast activation protein and containing CD3ζ and 4-1BB cytoplasmic domains were intravenously injected into immunodeficient mice bearing large, established human mesothelin- expressing flank tumors. CAR TILs were isolated from tumors at various time points and evaluated for effector functions and status of inhibitory pathways.
CAR T cells were able to traffic into tumors with varying efficiency and proliferate. They were able to slow tumor growth, but did not cause regressions or cures. The CAR TILs underwent rapid loss of functional activity that limited their therapeutic efficacy. This hypofunction was reversible when the T cells were isolated away from the tumor. The cause of the hypofunction appeared to be multifactorial and was associated with upregulation of intrinsic T cell inhibitory enzymes (diacylglycerol kinase and SHP-1) and the expression of surface inhibitory receptors (PD-1, LAG3, TIM3, 2B4).
Advanced generation human CAR T cells are reversibly inactivated within the solid tumor microenvironment of some tumors by multiple mechanisms. The model described here will be an important tool for testing T cell-based strategies or systemic approaches to overcome this tumor-induced inhibition. Our results suggest that PD-1 pathway antagonism may augment human CAR T cell function.
Neutrophils are important innate immune cells involved in microbial clearance at the sites of infection. However, their role in cancer development is unclear. We hypothesized that neutrophils mediate antitumor effects in early tumorigenesis. To test this, we first studied the cytotoxic effects of neutrophils in vitro. Neutrophils were cytotoxic against tumor cells, with neutrophils isolated from tumor-bearing mice trending to have increased cytotoxic activities. We then injected an ELR+ CXC chemokine-producing tumor cell line into C57BL/6 and Cxcr2−/− mice, the latter lacking the receptors for neutrophil chemokines. We observed increased tumor growth in Cxcr2−/− mice. As expected, tumors from Cxcr2−/− mice contained fewer neutrophils. Surprisingly, these tumors also contained fewer CD8+ T cells, but more IL-17-producing cells. Replenishment of functional neutrophils was correlated with decreased IL-17-producing cells, increased CD8+ T cells, and decreased tumor size in Cxcr2−/− mice, while depletion of neutrophils in C57BL/6 mice showed the opposite effects. Results from a non-ELR+ CXC chemokine producing tumor further supported that functional neutrophils indirectly mediate tumor control by suppressing IL-17A production. We further studied the correlation of IL-17A and CD8+ T cells in vitro. IL-17A suppressed proliferation and IFNγ production of CD8+ T cells, while CD11b+Ly6G+ neutrophils did not suppress CD8+ T cell function. Taken together, these data demonstrate that, while neutrophils could control tumor growth by direct cytotoxic effects, the primary mechanism by which neutrophils exert antitumor effects is to regulate IL-17 production, through which they indirectly promote CD8+ T cell responses.
CD11b+Ly6G+Cells, Neutrophils, Tumor, IL-17 and CD8+T cells
Recent clinical trials have shown promise in the use of chimeric antigen receptor(CAR)-transduced T cells; however, augmentation of their activity may broaden their clinical utility and improve their efficacy. We hypothesized that, since CAR action requires proteins essential for TCR signal transduction, deletion of negative regulators of these signaling pathways would enhance CAR signaling and effector T cell function. We tested CAR activity and function in T cells that lacked one or both isoforms of diacylglycerol kinase (dgk) expressed highly in T cells, dgkα and dgkζ, enzymes that metabolize the second messenger diacylglycerol (DAG) and limit Ras/ERK activation. We found that primary murine T cells transduced with CARs specific for the human tumor antigen mesothelin demonstrated greatly enhanced cytokine production and cytotoxicity when co-cultured with a murine mesothelioma line that stably expresses mesothelin. Additionally, we found that dgk-deficient CAR-transduced T cells were more effective in limiting the growth of implanted tumors, both concurrent with and after establishment of tumor. Consistent with our studies in mice, pharmacologic inhibition of dgks also augments function of primary human T cells transduced with CARs. These results suggest that deletion of negative regulators of TCR signaling enhances the activity and function of CAR-expressing T cells and identify dgks as potential targets for improving the clinical potential of CARs.
diacylglycerol kinase; chimeric antigen receptor; T cell receptor; tumor; mesothelin
Thymidylate synthase (TS) is a potential predictor of outcome after pemetrexed (Pem) in patients with malignant pleural mesothelioma (MPM), and assays measuring TS levels are commercially marketed. The goal of this study was to further evaluate the value of TS and to study another potential biomarker of response, the enzyme, folyl-polyglutamate synthase (FPGS), which activates Pem intracellularly.
Patients and Methods
Levels of TS and FPGS were semi-quantitatively determined immunohistochemically using H-scores on tissue samples from 85 MPM patients receiving Pem as primary therapy. H-score was correlated with radiographic disease control rate (DCR), time to progression (TTP) and overall survival (OS). In addition, expression levels of TS and FPGS in MPM cell lines were determined using immunoblotting and correlated with their sensitivity to Pem-induced cell death.
H-scores from patients with disease control versus progressive disease showed extensive overlap. There were no significant correlations of DCR, TTP, or OS to either TS levels (p = 0.73, 0.93, and 0.59, respectively), FPGS levels (p = 0.95, 0.77 and 0.43 respectively) or the ratio of FPGS/TS using the median scores of each test as cutoffs. There was no correlation between TS or FPGS expression and chemosensitivity of mesothelioma cells to Pem in vitro.
Although previous retrospective data suggest that TS and FPGS expression might be potential markers of Pem efficacy in MPM, our data indicate these markers lack sufficient predictive value in individual patients and should not be used to guide therapeutic decisions in the absence of prospective studies.
Foxp3+ T-regulatory (Treg) cells maintain immune homeostasis and limit autoimmunity, but can also curtail host immune responses to various types of tumors1,2. Foxp3+ Tregs are therefore considered promising targets to enhance anti-tumor immunity, and efforts are underway to develop approaches for their therapeutic modulation. However, while studies showing that Foxp3+ Treg depletion experimentally can enhance anti-tumor responses provide proof-of-principle, they lack clear translational potential and have various shortcomings. Histone/protein acetyltransferases (HATs) promote chromatin accessibility, gene transcription and the function of multiple transcription factors and non-histone proteins3,4. We now report that conditional deletion or pharmacologic inhibition of one HAT, p300 (Ep300, KAT3B), in Foxp3+ Tregs, increased TCR-induced apoptosis in Tregs, impaired Treg suppressive function and peripheral Treg induction, and limited tumor growth in immunocompetent, but not in immunodeficient, hosts. Our data thereby demonstrate that p300 is important for Foxp3+ Treg function and homeostasis in vivo and in vitro, and identify novel mechanisms by which appropriate small molecule inhibitors can diminish Treg function without overtly impairing T-effector (Teff) cell responses or inducing autoimmunity. Collectively, these data suggest a new approach for cancer immunotherapy.
Effector T cells become rapidly inactivated after antigen exposure due to extracellular as well as intrinsic signals. We have recently demonstrated that the deletion of diacylglycerol kinases, intrinsic inhibitors of T-cell signaling, enhances the activity of adoptively transferred T cells expressing a chimeric antigen receptor (CAR) specific for a tumor-associated antigen.
Chimeric Antigen Receptor; T cell hypofunction; diacylglycerol kinase; tumor immunosuppression; tumor microenvironment
Progression of premalignant lesions is restrained by oncogene-induced senescence. Oncogenic Ras triggers senescence in many organs, including the lung, which exhibits high levels of the angiogenesis inhibitor thrombospondin-1 (TSP-1). The contribution of TSP-1 upregulation to the modulation of tumorigenesis in the lung is unclear. Using a mouse model of lung cancer, we have shown that TSP-1 plays a critical and cell-autonomous role in suppressing Kras-induced lung tumorigenesis independent of its antiangiogenic function. Overall survival was decreased in a Kras-driven mouse model of lung cancer on a Tsp-1–/– background. We found that oncogenic Kras–induced TSP-1 upregulation in a p53-dependent manner. TSP-1 functioned in a positive feedback loop to stabilize p53 by interacting directly with activated ERK. TSP-1 tethering of ERK in the cytoplasm promoted a level of MAPK signaling that was sufficient to sustain p53 expression and a senescence response. Our data identify TSP-1 as a p53 target that contributes to maintaining Ras-induced senescence in the lung.
Adoptive T cell immunotherapy (ACT) with tumor infiltrating lymphocytes or genetically-modified T cells has yielded dramatic results in some cancers. However, T cells need to traffic properly into tumors in order to adequately exert therapeutic effects.
The chemokine CCL2 was highly secreted by malignant pleural mesotheliomas (MPM) (a planned tumor target), but the corresponding chemokine receptor (CCR2) was minimally expressed on activated human T cells transduced with a chimeric antibody receptor (CAR) directed to the MPM tumor antigen mesothelin (mesoCAR T cells). The chemokine receptor CCR2b was thus transduced into mesoCAR T cells using a lentiviral vector and the modified T cells were used to treat established mesothelin-expressing tumors.
CCR2b transduction led to CCL2-induced calcium flux and increased transmigration, as well as augmentation of in vitro T cell killing ability. A single intravenous injection of 20 million mesoCAR + CCR2b T cells into immunodeficient mice bearing large, established tumors (without any adjunct therapy) resulted in a 12.5-fold increase in T cell tumor infiltration by Day 5 compared to mesoCAR T cells. This was associated with significantly increased anti-tumor activity.
CAR T cells bearing a functional chemokine receptor can overcome the inadequate tumor localization that limits conventional CAR targeting strategies and can significantly improve anti-tumor efficacy in vivo.
The small molecule anti-tumor agent, 5, 6-dimethylxanthenone-4-acetic acid (DMXAA, now called Vadimezan) is a potent macrophage and dendritic cell activating agent that, in the murine system, results in the release of large amounts of cytokines and chemokines. The mechanisms by which this release is mediated have not been fully elucidated. The mitogen-activated protein kinase (MAPK) pathways plays an important role in the regulation of proinflammatory cytokines, such as, TNFα, IL-1β, as well as the responses to extracellular stimuli, such as, lipopolysaccharide (LPS). The results of this study demonstrate that DMXAA activates three members of mitogen-activated protein kinase (MAPK) superfamily, namely p38 MAPK, extracellular signal-regulated kinases 1 and 2 (ERK1 and ERK2), and c-Jun N-terminal kinases (JNKs) via a RIP2-independent mechanism in murine macrophages. By using selective inhibitors of MAPKs, this study confirms that both activated p38/MK2 pathways and ERK1/2 MAPK play a significant role in regulation of both TNF-α and IL-6 protein production induced by DMXAA at the post-transcriptional level. Our findings also show that Interferon-γ priming can dramatically augment TNF-α protein secretion induced by DMXAA through enhancing activation of multiple MAPKs pathways at the post-transcriptional level. This study expands current knowledge on mechanisms of how DMXAA acts as a potent anti-tumor agent in murine system and also provides useful information for further study on the mechanism of action of this potential anti-tumor compound in human macrophages.
MAPK; post-transcriptional regulation; TNFα; DMXAA; proinflammatory cytokines
Drugs that can rapidly inhibit respiratory infection from influenza or other respiratory pathogens are needed. One approach is to engage primary innate immune defenses against viral infection, such as activating the IFN pathway. In this study, we report that a small, cell-permeable compound called 5,6-di-methylxanthenone-4-acetic acid (DMXAA) can induce protection against vesicular stomatitis virus in vitro and H1N1 influenza A virus in vitro and in vivo through innate immune activation. Using the mouse C10 bronchial epithelial cell line and primary cultures of nasal epithelial cells, we demonstrate DMXAA activates the IFN regulatory factor-3 pathway leading to production of IFN-β and subsequent high-level induction of IFN-β–dependent proteins, such as myxovirus resistance 1 (Mx1) and 2′,5′-oligoadenylate synthetase 1 (OAS1). Mice treated with DMXAA intranasally elevate mRNA/protein expression of Mx1 and OAS1 in the nasal mucosa, trachea, and lung. When challenged intranasally with a lethal dose of H1N1 influenza A virus, DMXAA reduced viral titers in the lungs and protected 80% of mice from death, even when given at 24 hours before infection. These data show that agents, like DMXAA, that can directly activate innate immune pathways, such as the IFN regulatory factor-3/IFN-β system, in respiratory epithelial cells can be used to protect from influenza pneumonia and potentially in other respiratory viral infections. Development of this approach in humans could be valuable for protecting health care professionals and “first responders” in the early stages of viral pandemics or bioterror attacks.
innate immunity; interferon; influenza; pneumonia; bronchial epithelium
The role of chemokines in the pathogenesis of lung cancer has been increasingly appreciated. Monocyte chemoattractant protein–1 (MCP-1, also known as CCL2) is secreted from tumor cells and associated tumor stromal cells. The blockade of CCL2, as mediated by neutralizing antibodies, was shown to reduce tumorigenesis in several solid tumors, but the role of CCL2 in lung cancer remains controversial, with evidence of both protumorigenic and antitumorigenic effects. We evaluated the effects and mechanisms of CCL2 blockade in several animal models of non–small-cell lung cancer (NSCLC). Anti-murine–CCL2 monoclonal antibodies were administered in syngeneic flank and orthotopic models of NSCLC. CCL2 blockade significantly slowed the growth of primary tumors in all models studied, and inhibited lung metastases in a model of spontaneous lung metastases of NSCLC. In contrast to expectations, no significant effect of treatment was evident in the number of tumor-associated macrophages recruited into the tumor after CCL2 blockade. However, a change occurred in the polarization of tumor-associated macrophages to a more antitumor phenotype after CCL2 blockade. This was associated with the activation of cytotoxic CD8+ T lymphocytes (CTLs). The antitumor effects of CCL2 blockade were completely lost in CB-17 severe combined immunodeficient mice or after CD8 T-cell depletion. Our data from NSCLC models show that CCL2 blockade can inhibit the tumor growth of primary and metastatic disease. The mechanisms of CCL2 blockade include an alteration of the tumor macrophage phenotype and the activation of CTLs. Our work supports further evaluation of CCL2 blockade in thoracic malignancies.
tumor immunology; CCL2; lung cancer; mesothelioma; tumor-associated macrophages
Since an immuno-inhibitory environment exists within tumors, successful vaccines will likely require additional approaches to alter the tumor microenvironment. Monocyte chemoattractant proteins (such as CCL2) are produced by many tumors and have both direct and indirect immuno-inhibitory effects. We hypothesized that CCL2 blockade would reduce immunosuppression and augment vaccine immunotherapy. Anti-murine-CCL2/CCL12 monoclonal antibodies were administered in three immunotherapy models: one aimed at the HPV-E7 antigen expressed by a non-small cell lung cancer line, one targeted to mesothelin expressed by a mesothelioma cell line, and one using an adenovirus expressing Interferon-α to treat a non-immunogenic, non-small cell lung cancer line. We evaluated the effect of the combination treatment on tumor growth and assessed the mechanism of these changes by evaluating cytotoxic T cells, immunosuppressive cells, and the tumor microenvironment. Administration of anti-CCL2/CCL12 antibodies along with the vaccines markedly augmented efficacy with enhanced reduction in tumor volume and cures of approximately half of the tumors. The combined treatment generated more total intra-tumoral CD8+ T-cells that were more activated and more anti-tumor antigen specific, as measured by tetramer evaluation. Another important potential mechanism was reduction in intratumoral T-regulatory (T-reg) cells. CCL2 appears to be a key proximal cytokine mediating immunosuppression in tumors. Its blockade augments CD8+ T cell immune response to tumors elicited by vaccines via multifactorial mechanisms. These observations suggest that combining CCL2 neutralization with vaccines should be considered in future immunotherapy trials.
CCL2; Cancer immunotherapy; Lung Cancer; Mesothelioma; T-lymphocytes
Vesicular stomatitis virus (VSV) has shown promise as an oncolytic agent, although unmodified VSV can be neurotoxic. To avoid toxicity, a vector was created by introducing the interferon-β (IFN-β) gene (VSV.IFN-β). We conducted this study to determine the ability of VSV.IFN-β to lyse human cancer (mesothelioma) cells and to evaluate the potential of this recombinant virus for clinical translation. Four normal human mesothelial and 12 mesothelioma cell lines were tested for their susceptibility to VSV vectors in vitro. VSV.hIFN-β did not cause cytotoxicity in any normal lines. Only 4 of 12 lines were effectively lysed by VSV.hIFN-β. In the eight resistant lines, pretreatment with IFN-β prevented lysis of cells by VSV.GFP, and VSV infection or addition of IFN-β protein resulted in the upregulation of double-stranded RNA-dependent protein kinase (PKR), myxovirus resistance A (MxA), and 2′,5′-oligo-adenylate-synthetase (2′5′-OAS) mRNA. In the susceptible lines, there was no protection by pretreatment with IFN-β protein and no IFN- or VSV-induced changes in PKR, MxA, and 2′5′-OAS mRNA. This complete lack of IFN responsiveness could be explained by marked downregulation of interferon alpha receptors (IFNARs), p48, and PKR in both the mesothelioma cell lines and primary tumor biopsies screened. Presence of p48 in three tumor samples predicted responsiveness to IFN. Our data indicate that many mesothelioma tumors have partially intact IFN pathways that may affect the efficacy of oncolytic virotherapy. However, it may be feasible to prescreen individual susceptibility to VSV.IFN-β by immunostaining for the presence of p48 protein.
The signaling pathway(s) and molecular target(s) for 5,6-dimethylxanthenone-4-acetic acid (DMXAA), a tumor vascular disrupting agent in late stages of clinical development, are still undefined. As an approach toward identifying potential targets for DMXAA, a tritiated azido-analog of DMXAA was used to probe for cellular binding proteins. More than 20 cytosolic proteins from murine splenocytes, RAW 264.7 cells, and the HECPP immortalized endothelial cells were photoaffinity-labeled. Although no protein domain, fold, or binding site for a specific ligand was found to be shared by all the candidate proteins, essentially all were noted to be oxidizable proteins, implicating a role for redox signaling in the action of DMXAA. Consistent with this hypothesis, DMXAA caused an increase in concentrations of reactive oxygen species (ROS) in RAW264.7 cells during the first 2 hours. This increase in ROS was suppressed in the presence of the antioxidant, N-acetyl-l-cysteine, which also suppressed DMXAA-induced cytokine production in the RAW 264.7 cells with no effects on cell viability. Short interfering RNA (siRNA)-mediated knockdown of one of the photoaffinity-labeled proteins, superoxide dismutase 1, an ROS scavenger, resulted in an increase in tumor necrosis factor-α production by RAW 264.7 cells in response to DMXAA compared with negative or positive controls transfected with nontargeting or lamin A/C-targeting siRNA molecules, respectively. The results from these lines of study all suggest that redox signaling plays a central role in cytokine induction by DMXAA.
5,6-Dimethylxanthenone-4-acetic acid (DMXAA) acts through tumor vascular disruption and cytokine production and is the first of its class to enter phase 3 trials. We characterized leukocytes and cytokines in murine Colon 38 tumors before and after DMXAA treatment. Tumor mass declined 50% 24 hours after DMXAA administration, but the leukocyte count per gram of tumor increased threefold owing to a large influx of Ly6G+CD11b+F4/80- cells with the morphology of neutrophils. However, B and T lymphocytes, natural killer cells, and macrophages in the tumor all decreased in numbers. Seven chemokines were substantially induced in the tumor, spleen, and serum 4 hours after DMXAA administration. Using cultured spleen cell subpopulations, CD11b+ cells (largely monocytes and macrophages) were shown to be the primary producers of tumor necrosis factor α, interleukin 6 (IL-6), and macrophage inflammatory 1α (MIP-1α). CD49b+ natural killer cells produced IP-10, whereas CD45R+ B lymphocytes produced regulated upon activation normal T cell express sequence. T lymphocytes were not major producers of cytokines in the response to DMXAA. Murine peripheral blood leukocytes (PBLs) produced a similar panel of cytokines in culture to that detected in mouse serum after DMXAA treatment. Cytokines in human PBL cultures were subsequently measured with the aim of identifying potential serum markers of the human response to DMXAA. IP-10 (P < .001), monocyte chemoattractant protein 1 (P < .001), and sCD40L (P < .01) were decreased, whereas IL-8 (P < .001) and MIP-1α (P = .03) were increased in DMXAA-treated compared with untreated PBL cultures from a group of 12 donors.