Control of human mesothelin-expressing tumors by DNA vaccines

The Role of Mesothelin Expression in Serous Ovarian Carcinoma: Impacts on Diagnosis, Prognosis, and Therapeutic Targets

Mesothelin (MSLN) is a protein expressed in the mesothelial cell lining of the pleura, peritoneum, and pericardium; its biological functions in normal cells are still unknown. Experimental studies using knockout mice have suggested that this molecule does not play an important role in development and reproduction. In contrast, it has been observed that this molecule is produced in abnormal amounts in several malignant neoplasms, such as mesotheliomas and pancreatic adenocarcinomas. Many molecular studies have also demonstrated that mesothelin is overexpressed in HSOCs. Here, we discuss the current knowledge of mesothelin and focus on its role in clinical and pathological diagnoses, as well as its impact on the prognosis of HSOC. Moreover, regarding the binding of MSLN to the ovarian cancer antigen CA125, which has been demonstrated in many studies, we also report on signal transduction pathways that may play an important role in the spread and neoplastic progression of this lethal neoplasm. Given that mesothelin is overexpressed in many solid tumours and has antigenic properties, this molecule could be considered an antigenic target for the treatment of many malignancies. Consequently, we also review the literature to report on mesothelin-targeting therapies for HSOC that have been recently investigated in many clinical studies.

A tumor-specific neoepitope expressed in homologous/self or heterologous/viral antigens induced comparable effector CD8+ T-cell responses by DNA vaccination

Somatic mutations in tumors often generate neoproteins that contain MHC-I-binding neoepitopes. Little is known if and how efficient tumor-specific neoantigens activate CD8⁺ T cells. Here, we asked whether a de novo generated neoepitope, encoded either within an otherwise conserved and ubiquitously expressed self-antigen or in a chimeric HBV core antigen expression platform, providing heterologous helper functions, induces CD8⁺ T cells in C57Bl/6J mice by DNA immunization. For it, we chose an established D^b/Sp_{244-252/R251H} neoepitope generated in the murine Endophilin-B2/SH3GLB2 (EndoB2-Sp) protein by a single amino acid exchange. We showed that a single injection of EndoB2-Sp expression vectors efficiently primed dimer/pentamer⁺, IFN-γ⁺ and cytolytic D^b/Sp_{244-252/R251H}-specific effector CD8⁺ T cells in C57Bl/6J mice. Priming of D^b/Sp_{244-252/R251H}-specific CD8⁺ T cells proceeded independent from CD4⁺ T-cell help in MHC-II-deficient Aα^-/- mice. As compared to the homologous EndoB2-Sp vaccine, the selective expression of the D^b/Sp_{244-252/R251H} neoepitope in chimeric particle-forming and assembly-deficient HBV core antigens induced comparable frequencies D^b/Sp_{244-252/R251H}-specific CD8⁺ T cells with the same cytolytic effector phenotype. The homologous EndoB2 carrier, but not the nine-residue neoepitope presented on chimeric HBV core particles, induced EndoB2-specific IgG antibody responses. The HBV core expression platform is thus an attractive option to selectively induce neoepitope-specific effector CD8⁺ T cells by DNA vaccination. These novel findings have practical implications for the design of heterologous/self and heterologous/viral cancer vaccines that prime and/or activate neoepitope-specific CD8⁺ T cells.

The Role of Mesothelin as a Diagnostic and Therapeutic Target in Pancreatic Ductal Adenocarcinoma: A Comprehensive Review

Mesothelin is a tumor differentiation antigen, which is highly expressed in several solid neoplasms, including pancreatic cancer. Its selective expression on malignant cells and on only a limited number of healthy tissues has made it an interesting candidate for investigation as a diagnostic and prognostic biomarker and as a therapeutic target. Based on a strong preclinical rationale, a number of therapeutic agents targeting mesothelin have entered clinical trials, including immunotoxins, monoclonal antibodies, antibody-drug conjugates, cancer vaccines, and adoptive T cell therapies with chimeric antigen receptors. In pancreatic cancer, mesothelin has been investigated mainly to address two unmet issues: the urgent need for new laboratory techniques for early tumor detection and the lack of successfully targetable oncogenic alterations for patients' treatment. In this review, we describe the clinicopathological significance of mesothelin expression in pancreatic cancer initiation and progression, we summarize available studies evaluating mesothelin as a potential diagnostic and prognostic biomarker in this disease, and we discuss current evidence and future perspectives of preclinical and clinical studies testing mesothelin as a molecular target for pancreatic cancer treatment.

Development of Anti-Human Mesothelin-Targeted Chimeric Antigen Receptor Messenger RNA-Transfected Peripheral Blood Lymphocytes for Ovarian Cancer Therapy

CD19-targeted chimeric antigen receptor (CAR) engineered T/natural killer (NK)-cell therapies can result in durable clinical responses in B-cell malignancies. However, CAR-based immunotherapies have been much less successful in solid cancers, in part due to "on-target off-tumor" toxicity related to expression of target tumor antigens on normal tissue. Based on preliminary observations of safety and clinical activity in proof-of-concept clinical trials, tumor antigen-specific messenger RNA (mRNA) CAR transfection into selected, activated, and expanded T/NK cells may permit prospective control of "on-target off-tumor" toxicity. To develop a commercial product for solid tumors, mesothelin was selected as an antigen target based on its association with poor prognosis and overexpression in multiple solid cancers. It was hypothesized that selecting, activating, and expanding cells ex vivo prior to mRNA CAR transfection would not be necessary, thus simplifying the complexity and cost of manufacturing. Now, the development of anti-human mesothelin mRNA CAR transfected peripheral blood lymphocytes (CARMA-hMeso) is reported, demonstrating the manufacture and cryopreservation of multiple cell aliquots for repeat administrations from a single human leukapheresis. A rapid, automated, closed system for cGMP-compliant transfection of mRNA CAR in up to 20 × 10⁹ peripheral blood lymphocytes was developed. Here we show that CARMA-hMeso cells recognize and lyse tumor cells in a mesothelin-specific manner. Expression of CAR was detectable over approximately 7 days in vitro, with a progressive decline of CAR expression that appears to correlate with in vitro cell expansion. In a murine ovarian cancer model, a single intraperitoneal injection of CARMA-hMeso resulted in the dose-dependent inhibition of tumor growth and improved survival of mice. Furthermore, repeat weekly intraperitoneal administrations of the optimal CARMA-hMeso dose further prolonged disease control and survival. No significant off-target toxicities were observed. These data support further investigation of CARMA-hMeso as a potential treatment for ovarian cancer and other mesothelin-expressing cancers.

Immuno-modulators enhance antigen-specific immunity and anti-tumor effects of mesothelin-specific chimeric DNA vaccine through promoting DC maturation

As a tumor antigen, mesothelin (MSLN) can be identified in various malignancies. MSLN is potential for antigen-specific cancer vaccines. We generated a novel chimeric DNA vaccine using antigen-specific connective tissue growth factor lined with MSLN (CTGF/MSLN). The anti-tumor effects of the CTGF/MSLN DNA vaccine combined with anti-CD40 Ab and toll-like receptor 3 ligand-poly(I:C) were validated in an MSLN-expressing model. CTGF/MSLN DNA with anti-CD40Ab and poly(I:C) vaccinated mice demonstrated potent anti-tumor effects with longer survival and less tumor volumes. An increase in MSLN-specific CD8⁺ T cells and anti-MSLN Ab titers was also noted in CTGF/MSLN DNA with anti-CD40Ab and poly(I:C) vaccinated mice. The CTGF/MSLN DNA vaccine combined with immuno-modulator EGCG also generated potent anti-tumor effects. Immuno-modulators could enhance the antigen-specific anti-tumor effects of CTGF/MSLN DNA vaccine through promoting the DC maturation. In addition, MSLN-specific cell-based vaccine with AAV-IL-12 and the CTGF/MSLN DNA vaccine with anti-CD40Ab/polyp(I:C) generated more potent anti-tumor effects than the other combinational regimens. The results indicate that an MSLN-specific DNA vaccine combined with immuno-modulators may be an effective immunotherapeutic strategy to control MSLN-expressing tumors including ovarian and pancreastic cancers, and malignant mesothelioma.

Development of improved therapeutic mesothelin-based vaccines for pancreatic cancer

Pancreatic cancer is the 5^th leading cause of cancer deaths, and there are no effective treatments. We developed a poxvirus platform vaccine with improved immunogenicity and inserted the mesothelin gene to create an anti-mesothelin cancer vaccine. Mesothelin expression is mostly restricted to tumors in adult mammals and thus may be a good target for cancer treatment. We show here that the modified vaccinia virus Ankara (MVA) virus expressing mesothelin and the enhanced MVA virus missing the immunosuppressive A35 gene and expressing mesothelin were both safe in mice and were able to induce IFN-gamma secreting T cells in response to mesothelin expressing tumor cells. In addition, the MVA virus has oncolytic properties in vitro as it can replicate in and kill Panc02 pancreatic adenocarcinoma cell line tumor cells, even though it is unable to replicate in most mammalian cells. Deletion of the A35 gene in MVA improved T cell responses as expected. However, we were unable to demonstrate inhibition of Panc02 tumor growth in immunocompetent mice with pre-vaccination of mice, boosts, or even intratumoral injections of the recombinant viruses. Vaccine efficacy may be limited by shedding of mesothelin from tumor cells thus creating a protective screen from the immune system.

Current status of biomarker and targeted nanoparticle development: The precision oncology approach for pancreatic cancer therapy

Pancreatic cancer remains one of the major causes of cancer-related mortality. The majority of pancreatic cancer patients are diagnosed at the advanced stage with unresectable and drug resistant tumors. The new treatments with the combination of chemotherapy, molecular targeted therapy, and immunotherapy have shown modest effects on therapeutic efficacy and survival of the patients. Therefore, there is an urgent need to develop effective therapeutic approaches targeting highly heterogeneous pancreatic cancer cells and tumor microenvironments. Recent advances in biomarker targeted cancer therapy and image-guided drug delivery and monitoring treatment response using multifunctional nanoparticles, also referred to as theranostic nanoparticles, offer a new opportunity of effective detection and treatment of pancreatic cancer. Increasing evidence from preclinical studies has shown the potential of applications of theranostic nanoparticles for designing precision oncology approaches for pancreatic cancer therapy. In this review, we provide an update on the current understanding and strategies for the development of targeted therapy for pancreatic cancer using nanoparticle drug carriers. We address issues concerning drug delivery barriers in stroma rich pancreatic cancer and the potential approaches to improve drug delivery efficiency, therapeutic responses and tumor imaging. Research results presented in this review suggest the development of an integrated therapy protocol through image-guided and targeted drug delivery and therapeutic effect monitoring as a promising precision oncology strategy for pancreatic cancer treatment.

Murine mesothelin: characterization, expression, and inhibition of tumor growth in a murine model of pancreatic cancer

Background

Mesothelin has attracted much interest as a tumor specific antigen; it has been reported to promote tumor development and to be a good target for cancer treatment. Most studies to date have used human mesothelin in immunocompromised mice. Since these models do not allow for study of the natural immune response to mesothelin expressing tumors, we have undertaken the characterization of mouse mesothelin so the effects of this protein can be assessed in immunocompetent mouse strains.

Methods

We analyzed mouse mesothelin expression, tissue distribution, shedding and biochemistry. In addition we constructed stable mesothelin overexpressing lines of the pancreatic cancer line Panc02 by two methods and tested them for growth and tumorigencity in vitro and in vivo.

Results

We show here that mouse mesothelin is similar to human mesothelin in biochemical characteristics, tumor expression and tissue distribution, suggesting the mouse may be a suitable model for study of mesothelin. Stable overexpression of mesothelin in a pancreatic cancer cell line did not increase cell proliferation or anchorage-independent growth in vitro, suggesting that mesothelin is not necessarily a tumor progression factor. Surprisingly overexpression of mesothelin inhibited tumor formation in vivo in immunocompetent mice.

Conclusion

The mouse may be a good model for studying mesothelin in the context of an intact immune response. Mesothelin is not necessarily a tumor progression factor, and indeed mesothelin overexpression inhibited tumor growth in immunocompetent mice.

Mesothelin-specific cell-based vaccine generates antigen-specific immunity and potent antitumor effects by combining with IL-12 immunomodulator

Ovarian cancer is a gynecologic malignancy with a high mortality rate. In the present study, we developed a novel cell-based vaccine, Meso-VAX, to generate mesothelin antigen-specific immune responses and immunotherapy against ovarian cancer. Mesothelin, a secreted protein anchored at the cell membrane, has recently been identified as a potential new tumor antigen for ovarian cancer. In this study, mice vaccinated with Meso-VAX and adeno-associated virus (AAV)-IL-12 exhibited dramatic increases in the number of mesothelin-specific CD4(+) helper and CD8(+) cytotoxic T-cell precursors, higher titers of anti-mesothelin Abs and in vitro tumor killing activity, and all of these mice were tumor-free after 60 days of tumor challenge. In addition, a significant reduction in peritoneal tumors and longer survival were noted in the mice vaccinated with Meso-VAX combined with AAV-IL-12. CD4(+) helper and CD8(+) cytotoxic T lymphocytes were essential for the antitumor effect generated by Meso-VAX combined with AAV-IL-12. The post-vaccination sera of the mice vaccinated with Meso-VAX and AAV-IL-12 also showed mesothelin-specific complement-dependent cell-mediated cytotoxicity. Our results suggest that a Meso-VAX cell-based vaccine combined with AAV-IL-12 can generate antigen-specific immunological responses and antitumor effects on ovarian cancer.

The development, characterization and in vivo anti-ovarian cancer activity of poly(propylene imine) (PPI)-antibody conjugates containing encapsulated paclitaxel

Mesothelin, protein is frequently expressed in ovarian cancers. However, a full understanding of the biological functions of mesothelin is lacking. Here, we investigate the drug targeting potential of antibody conjugated modified half-generation poly (propylene imine) dendrimers i.e. immunodendrimers toward ovarian cancer with a model anti-cancer agent, paclitaxel (PTX). The synthesized plain 4.5G dendrimers as well as immunodendrimers were characterized by FT-IR, (1)H-NMR, TEM, and flow cytometry. Immunodendrimers exhibited considerably reduced hemolytic-, hepato- and nephrotoxicity. MTT cytotoxicity, flow cytometry and cell morphology studies were conducted in OVACAR-3 and A-431 cell. We demonstrate that PTX loaded immunodendrimers reduced the tumor volume significantly. The biodistribution studies further confirmed the targeting efficiency and higher biodistribution of immunodendrimers into the mesothelin protein expressing ovarian cancer cells. The results concluded that the developed immunodendrimers have potential to deliver significantly higher amount of the bioactive and have improved therapeutic outcome.

Direct T cell activation via CD40 ligand generates high avidity CD8+ T cells capable of breaking immunological tolerance for the control of tumors

CD40 and CD40 ligand (CD40L) are costimulatory molecules that play a pivotal role in the proinflammatory immune response. Primarily expressed by activated CD4⁺ T cells, CD40L binds to CD40 on antigen presenting cells (APCs), thereby inducing APC activation. APCs, in turn, prime cytotoxic T lymphocytes (CTLs). Here, two tumor-associated antigen (TAA) animal models, p53-based and GP100-based, were utilized to examine the ability of CD40-CD40L to improve antigen-specific CTL-mediated antitumor immune responses. Although p53 and GP100 are self-antigens that generate low affinity antigen-specific CD8⁺ T cells, studies have shown that their functional avidity can be improved with CD40L-expressing APCs. Therefore, in the current study, we immunized mice with a DNA construct encoding a TAA in conjunction with another construct encoding CD40L via intramuscular injection followed by electroporation. We observed a significant increase in the antigen-specific CTL-mediated immune responses as well as the potent antitumor effects in both models. Antibody depletion experiments demonstrated that CD8⁺ T cells play a crucial role in eliciting antitumor effects in vaccinated mice. Furthermore, we showed that in vitro stimulation with irradiated tumor cells expressing both TAA and CD40L improved the functional avidity of antigen-specific CD8⁺ T cells. Thus, our data show that vaccination with TAA/CD40L DNA can induce potent antitumor effects against TAA-expressing tumors through the generation of better functioning antigen-specific CD8⁺ T cells. Our study serves as an important foundation for future clinical translation.

PD-1 blockade and OX40 triggering synergistically protects against tumor growth in a murine model of ovarian cancer

The co-inhibitory receptor Programmed Death-1 (PD-1) curtails immune responses and prevent autoimmunity, however, tumors exploit this pathway to escape from immune destruction. The co-stimulatory receptor OX40 is upregulated on T cells following activation and increases their clonal expansion, survival and cytokine production when engaged. Although antagonistic anti-PD-1 or agonistic anti-OX40 antibodies can promote the rejection of several murine tumors, some poorly immunogenic tumors were refractory to this treatment. In the present study, we evaluated the antitumor effects and mechanisms of combinatorial PD-1 blockade and OX40 triggering in a murine ID8 ovarian cancer model. Although individual anti-PD-1 or OX40 mAb treatment was ineffective in tumor protection against 10-day established ID8 tumor, combined anti-PD-1/OX40 mAb treatment markedly inhibited tumor outgrowth with 60% of mice tumor free 90 days after tumor inoculation. Tumor protection was associated with a systemic immune response with memory and antigen specificity and required CD4(+) cells and CD8(+) T cells. The anti-PD-1/OX40 mAb treatment increased CD4(+) and CD8(+) cells and decreased immunosuppressive CD4(+)FoxP3(+) regulatory T (Treg) cells and CD11b(+)Gr-1(+) myeloid suppressor cells (MDSC), giving rise to significantly higher ratios of both effector CD4(+) and CD8(+) cells to Treg and MDSC in peritoneal cavity; Quantitative RT-PCR data further demonstrated the induction of a local immunostimulatory milieu by anti-PD-1/OX40 mAb treatment. The splenic CD8(+) T cells from combined mAb treated mice produced high levels of IFN-γ upon tumor antigen stimulation and exhibited antigen-specific cytolytic activity. To our knowledge, this is the first study testing the antitumor effects of combined anti-PD-1/OX40 mAb in a murine ovarian cancer model, and our results provide a rationale for clinical trials evaluating ovarian cancer immunotherapy using this combination of mAb.

Combined TIM-3 blockade and CD137 activation affords the long-term protection in a murine model of ovarian cancer

Background

T-cell immunoglobulin and mucin domain 3 (TIM-3) is known as a negative immune regulator and emerging data have implicated TIM-3 a pivotal role in suppressing antitumor immunity. The co-stimulatory receptor CD137 is transiently upregulated on T-cells following activation and increases their proliferation and survival when engaged. Although antagonistic anti-TIM-3 or agonistic anti-CD137 antibodies can promote the rejection of several murine tumors, some poorly immunogenic tumors were refractory to this treatment. In this study, we sought to evaluate whether combined TIM-3 blockade and CD137 activation would significantly improve the immunotherapy in the murine ID8 ovarian cancer model.

Methods

Mice with established ID8 tumor were intraperitoneally injected with single or combined anti-TIM-3/CD137 monoclonal antibody (mAb); mice survival was recorded, the composition and gene expression of tumor-infiltrating immune cells in these mice was analyzed by flow cytometry and quantitative RT-PCR respectively, and the function of CD8⁺ cells was evaluated by ELISA and cytotoxicity assay.

Results

Either anti-TIM-3 or CD137 mAb alone, although effective in 3 days established tumor, was unable to prevent tumor progression in mice bearing 10 days established tumor, however, combined anti-TIM-3/CD137 mAb significantly inhibited the growth of these tumors with 60% of mice tumor free 90 days after tumor inoculation. Therapeutic efficacy was associated with a systemic immune response with memory and antigen specificity, required CD4⁺ cells and CD8⁺ cells. The 2 mAb combination increased CD4⁺ and CD8⁺ cells and decreased immunosuppressive CD4⁺FoxP3⁺ regulatory T (Treg) cells and CD11b⁺Gr-1⁺ myeloid suppressor cells (MDSC) at tumor sites, giving rise to significantly elevated ratios of CD4⁺ and CD8⁺ cells to Treg and MDSC; This is consistent with biasing local immune response towards an immunostimulatory Th1 type and is further supported by quantitative RT-PCR data showing the increased Th1-associated genes by anti-TIM-3/CD137 treatment. The increased CD8⁺ T cells produced high level of IFN-γ upon tumor antigen stimulation and displayed antigen-specific cytotoxic activity.

Conclusions

To our knowledge, this is the first report investigating the effects of anti-TIM-3/CD137 combined mAb in a murine ovarian cancer model, and our results may aid the design of future trials for ovarian cancer immunotherapy.

Intravenous genetic mesothelin vaccine based on human adenovirus 40 inhibits growth and metastasis of pancreatic cancer

High pancreatic cancer mortality and poor prognosis are caused by the difficulty for early diagnosis and extremely low rates of resection because of metastasis. Mesothelin overexpression in pancreatic cancer is a remarkable biomarker for tumor progression, especially for invasion and metastasis. Here, we generated a novel replication-defective recombinant adenovirus 40 (rAd40), whose gene delivery properties are totally different from a conventional rAd5. In this study, we have identified intravenous administration with rAd40 expressing mouse mesothelin (Msln) as an effective prophylactic cancer vaccine against metastatic lesions of pancreatic cancer in mice. Intravenous administration of rAd40 (rAd40 i.v.) achieved transgene delivery in wider range of organs compared to rAd5 i.v., while rAd5 was distributed mainly to the liver, spleen, and lungs. Additionally, rAd40 i.v. showed less transduction of the liver or inflammatory responses, resulted in reduced liver toxicity compared to rAd5 i.v. Also, more robust systemic antigen-specific immune responses were stimulated by rAd40 i.v. Pretreatment with a single ovalbumin-expressing rAd40 i.v. prevented tumor growth in mouse subcutaneous models of ovalbumin-expressing pancreatic cancer. When used with Msln-expressing rAd40 i.v., Msln protein expression and metastases were suppressed in a syngeneic orthotopic mouse model of pancreatic cancer, corresponding to the detection of Msln- and tumor-specific cytotoxic T lymphocyte (CTL). Our novel methods generated antitumor effects against antigen-expressing tumors through antigen- and tumor-specific CTL-mediated immunity. Thus, our results indicate that a rAd40-based intravenous vaccine provides a new strategy for the effective control of metastatic pancreatic cancer and novel therapy against other cancers and infectious diseases.

Xenogeneic human p53 DNA vaccination by electroporation breaks immune tolerance to control murine tumors expressing mouse p53

The pivotal role of p53 as a tumor suppressor protein is illustrated by the fact that this protein is found mutated in more than 50% of human cancers. In most cases, mutations in p53 greatly increase the otherwise short half-life of this protein in normal tissue and cause it to accumulate in the cytoplasm of tumors. The overexpression of mutated p53 in tumor cells makes p53 a potentially desirable target for the development of cancer immunotherapy. However, p53 protein represents an endogenous tumor-associated antigen (TAA). Immunization against a self-antigen is challenging because an antigen-specific immune response likely generates only low affinity antigen-specific CD8⁺ T-cells. This represents a bottleneck of tumor immunotherapy when targeting endogenous TAAs expressed by tumors. The objective of the current study is to develop a safe cancer immunotherapy using a naked DNA vaccine. The vaccine employs a xenogeneic p53 gene to break immune tolerance resulting in a potent therapeutic antitumor effect against tumors expressing mutated p53. Our study assessed the therapeutic antitumor effect after immunization with DNA encoding human p53 (hp53) or mouse p53 (mp53). Mice immunized with xenogeneic full length hp53 DNA plasmid intramuscularly followed by electroporation were protected against challenge with murine colon cancer MC38 while those immunized with mp53 DNA were not. In a therapeutic model, established MC38 tumors were also well controlled by treatment with hp53 DNA therapy in tumor bearing mice compared to mp53 DNA. Mice vaccinated with hp53 DNA plasmid also exhibited an increase in mp53-specific CD8⁺ T-cell precursors compared to vaccination with mp53 DNA. Antibody depletion experiments also demonstrated that CD8⁺ T-cells play crucial roles in the antitumor effects. This study showed intramuscular vaccination with xenogeneic p53 DNA vaccine followed by electroporation is capable of inducing potent antitumor effects against tumors expressing mutated p53 through CD8⁺ T cells.

Targeted coating with antigenic peptide renders tumor cells susceptible to CD8(+) T cell-mediated killing

The potency of immunotherapies targeting endogenous tumor antigens is hindered by immune tolerance. We created a therapeutic agent comprised of a tumor-homing module fused to a functional domain capable of selectively rendering tumor cells sensitive to foreign antigen-specific CD8(+) T cell-mediated immune attack, and thereby, circumventing concerns for immune tolerance. The tumor-homing module is comprised of a single-chain variable fragment (scFv) that specifically binds to mesothelin (Meso), which is commonly overexpressed in human cancers, including ovarian tumors. The functional domain is comprised of the Fc portion of IgG2a protein and foreign immunogenic CD8(+) T cell epitope flanked by furin cleavage sites (R), which can be recognized and cleaved by furin that is highly expressed in the tumor microenvironment. We show that our therapeutic protein specifically loaded antigenic epitope onto the surface of mesothelin-expressing tumor cells, rendering tumors susceptible to antigen-specific cytotoxic CD8(+) T lymphocytes (CTL)-mediated killing in vitro and in vivo. Our findings have important implications for bypassing immune tolerance to enhance cancer immunotherapy.

Mesothelin regulates growth and apoptosis in pancreatic cancer cells through p53-dependent and -independent signal pathway

Mesothelin, a secreted protein, is overexpressed in some cancers, including pancreatic cancer. Rescent studies have shown that overexpression of mesothelin significantly increased tumor cell proliferation, and downregulation of mesothelin inhibited cell proliferation in pancreatic cancer cells, but its exact function and mechanism remains unclear. The aim of the present study was to evaluate the effects of mesothelin on proliferation and apoptosis in pancreatic cancer cells with different p53 status and to explore its signal pathway. Mesothelin levels were detected by western blot and RT-PCR assay in human pancreatic cancer AsPC-1, HPAC and Capan-2, Capan-1 and MIA PaCa-2 cell lines. Mesothelin was slienced by shRNA in AsPC-1, Capan-2 and Capan-1 cells with rich mesothelin level, and mesothelin was overexpressed in the HPAC and Capan-2 cells with less mesothelin level. We observed that in the AsPC-1 and Capan-1cells with mt-p53, and Capan-2 cells with wt-p53, shRNA mediated sliencing of the mesothelin significantly increased PUMA and Bax expression and caspase-3 activity, and decreased bcl-2 expression, followed by the reduced proliferation and colony forming capability and increased cell apoptosis. When PUMA was slienced by siRNA in the stable mesothelin shRNA transfected cells, proliferative capability was significantly increased, and apoptosis was decreased. However, in the Capan-2 cells with wt-p53, suppression of the mesothelin significantly increased wt-p53 levels. When p53 was blocked by siRNA in the stable mesothelin shRNA transfected Capan-2 cells, PUMA was inhibited, followed by increased proliferative capability and decreased cell apoptosis. In the HPAC and Capan-2 cells with wt-p53 and in the MIA PaCa-2 cells with mt-p53, overexpression of the mesothelin significantly decreased bax levels and increased bcl-2 levels, followed by increased proliferative and colony forming capability. Furthermore, mesothelin-shRNA-transfected cells exhibited a reduced rate of tumor growth under in vivo conditions. However, mesothelin-transfected cells exhibited a increased rate of tumor growth under in vivo conditions. Our data demonstrated that mesothelin promotes proliferation and inhibited apoptosis through p53-dependent pathway in pancreatic cancer cells with wt-p53, and p53-independent pathway in pancreatic cancer cells with mt-p53. Targeting mesothelin by shRNA is the important method for pancreatic cancer therapy.

Mesothelin-targeted agents in clinical trials and in preclinical development

Mesothelin is a tumor differentiation antigen that is highly expressed in several malignant diseases in humans, including malignant mesothelioma and pancreatic, ovarian, and lung adenocarcinomas. The limited expression of mesothelin on normal human tissues and its high expression in many common cancers make it an attractive candidate for cancer therapy. Several agents, including an immunotoxin, monoclonal antibody, antibody drug conjugate, and tumor vaccine, are in various stages of development to treat patients with mesothelin-expressing tumors. This review highlights ongoing clinical trials, as well as other approaches to exploit mesothelin for cancer therapy, that are in preclinical development.

Potential targets for pancreatic cancer immunotherapeutics

Pancreatic adenocarcinoma is the fourth leading cause of cancer death with an overall 5-year survival of less than 5%. As there is ample evidence that pancreatic adenocarcinomas elicit antitumor immune responses, identification of pancreatic cancer-associated antigens has spurred the development of vaccination-based strategies for treatment. While promising results have been observed in animal tumor models, most clinical studies have found only limited success. As most trials were performed in patients with advanced pancreatic cancer, the contribution of immune suppressor mechanisms should be taken into account. In this article, we detail recent work in tumor antigen vaccination and the recently identified mechanisms of immune suppression in pancreatic cancer. We offer our perspective on how to increase the clinical efficacy of vaccines for pancreatic cancer.

The hen model of human ovarian cancer develops anti-mesothelin autoantibodies in response to mesothelin expressing tumors

Objective

Study of the hen immune system led to seminal contributions to basic immunological principles. Recent studies of spontaneous ovarian cancer in the laying hen show strikingly similar tumor types and antigen expression compared to human ovarian cancer, suggesting hens would be valuable for studies of tumor immunology and pre-clinical vaccine development. Circulating mesothelin is a relatively specific marker for human ovarian cancer and autoantibodies to mesothelin were reported. We hypothesized that hen tumors express mesothelin and that circulating anti-mesothelin antibodies occur in response to tumors.

Methods

Mesothelin mRNA expression was analyzed by RT-PCR in hen ovarian tumors and normal ovaries. Mesothelin protein expression was evaluated by immunohistochemistry (IHC) and two-dimensional SDS-PAGE Western blots. Anti-mesothelin antibodies were assessed by immunoassay of sera from hens with normal ovaries and with ovarian tumors.

Results

Significant mesothelin mRNA expression was observed in 57% (12/21) of hen ovarian tumors but not in normal ovaries and was found predominantly in serous tumors as in humans. Mesothelin protein was detected in tumors with mesothelin mRNA by IHC and 2D Western blots, but not in normal ovaries or tumors without mesothelin mRNA. Circulating anti-mesothelin antibodies occurred in 44% (n = 4/9) of hens with ovarian tumors which express mesothelin mRNA and were not found in hens with tumors that did not express mesothelin (n = 0/5) or normal ovaries (n = 0/5).

Conclusion

The results support the utility of the hen as a novel model for preclinical studies of mesothelin as a biomarker and a target for immunotherapy.

Dendritic cells adenovirally-transduced with full-length mesothelin cDNA elicit mesothelin-specific cytotoxicity against pancreatic cancer cell lines in vitro

Mesothelin (MSLN) is an attractive candidate as a molecular target for pancreatic cancer immunotherapy. The purpose of this study was to demonstrate that cytotoxic T lymphocytes (CTLs) generated from peripheral blood mononuclear cells (PBMCs) by stimulation with genetically-modified dendritic cells (DCs) expressing MSLN could produce specific anti-tumor immunity against pancreatic cancer cells endogenously expressing MSLN. MSLN-specific CTLs were generated from PBMCs of healthy donors by in vitro stimulation with DCs adenovirally-transduced with the full-length MSLN gene (DC-AxCAMSLN). The cytotoxic activity was tested using a 4-h (51)Cr-release assay. The pancreatic cancer cell lines (PK1, CfPAC1, AsPC1), a lymphoblastoid cell lines (LCL) transduced with the MSLN gene, and LCL pulsed with MSLN-epitope peptides were used as target cells. MSLN-specific CTLs induced by in vitro stimulation with DC-AxCAMSLN killed pancreatic cancer cell lines expressing MSLN in an HLA-restricted fashion. These CTLs also showed cytotoxic activity against autologous LCL pulsed with multiple MSLN-derived epitope peptides. In addition, CD8(+) T cells, as well as CD4(+) T cells, sorted from these CTLs showed significant production of interferon-γ when stimulated with DC-AxCAMSLN. The in vitro stimulation of PBMCs with DCs transduced with the full-length MSLN gene elicited a potent MSLN-specific cytotoxic activity against pancreatic cancer cell lines endogenously expressing MSLN by recognizing multiple MSLN epitopes and activating both CD8(+) T cells and CD4(+) helper T cells. These results therefore suggest the potential of developing future clinical applications of the vaccines using genetically-modified DCs expressing MSLN.

Anti-viral state segregates two molecular phenotypes of pancreatic adenocarcinoma: potential relevance for adenoviral gene therapy

Background

Pancreatic ductal adenocarcinoma (PDAC) remains a leading cause of cancer mortality for which novel gene therapy approaches relying on tumor-tropic adenoviruses are being tested.

Methods

We obtained the global transcriptional profiling of primary PDAC using RNA from eight xenografted primary PDAC, three primary PDAC bulk tissues, three chronic pancreatitis and three normal pancreatic tissues. The Affymetrix GeneChip HG-U133A was used. The results of the expression profiles were validated applying immunohistochemical and western blot analysis on a set of 34 primary PDAC and 10 established PDAC cell lines. Permissivity to viral vectors used for gene therapy, Adenovirus 5 and Adeno-Associated Viruses 5 and 6, was assessed on PDAC cell lines.

Results

The analysis of the expression profiles allowed the identification of two clearly distinguishable phenotypes according to the expression of interferon-stimulated genes. The two phenotypes could be readily recognized by immunohistochemical detection of the Myxovirus-resistance A protein, whose expression reflects the activation of interferon dependent pathways. The two molecular phenotypes discovered in primary carcinomas were also observed among established pancreatic adenocarcinoma cell lines, suggesting that these phenotypes are an intrinsic characteristic of cancer cells independent of their interaction with the host's microenvironment. The two pancreatic cancer phenotypes are characterized by different permissivity to viral vectors used for gene therapy, as cell lines expressing interferon stimulated genes resisted to Adenovirus 5 mediated lysis in vitro. Similar results were observed when cells were transduced with Adeno-Associated Viruses 5 and 6.

Conclusion

Our study identified two molecular phenotypes of pancreatic cancer, characterized by a differential expression of interferon-stimulated genes and easily recognized by the expression of the Myxovirus-resistance A protein. We suggest that the detection of these two phenotypes might help the selection of patients enrolled in virally-mediated gene therapy trials.

Circulating mesothelin protein and cellular antimesothelin immunity in patients with pancreatic cancer

PURPOSE

Mesothelin is a glycoprotein expressed on normal mesothelial cells and is overexpressed in several histologic types of tumors including pancreatic adenocarcinomas. A soluble form of mesothelin has been detected in patients with ovarian cancer and malignant mesothelioma, and has prognostic value. Mesothelin has also been considered as a target for immune-based therapies. We conducted a study on the potential clinical utility of mesothelin as a biomarker for pancreatic disease and therapeutic target pancreatic cancer.

EXPERIMENTAL DESIGN

Tumor cell-bound and soluble mesothelin in patients was evaluated by immunohistochemistry and ELISA, respectively. The in vitro cellular immune response to mesothelin was evaluated by INF gamma ELISA and intracellular cytokine staining for IFN gamma in CD4(+) and CD8(+) T cells. The level of circulating antibodies to mesothelin was measured by ELISA.

RESULTS

All tumor tissue from patients with pancreatic adenocarcinoma expressed mesothelin (n = 10). Circulating mesothelin protein was detected in patients with pancreatic adenocarcinoma (73 of 74 patients) and benign pancreatic disease (5 of 5) but not in healthy individuals. Mesothelin-specific CD4(+) and CD8(+) T cells were generated from peripheral blood lymphocytes of patients with pancreatic cancer in 50% of patients compared with only 20% of healthy individuals. Antibodies reactive to mesothelin were detected in <3% of either patients or healthy individuals.

CONCLUSIONS

Circulating mesothelin is a useful biomarker for pancreatic disease. Furthermore, mesothelin-specific T cells can be induced in patients with pancreatic cancer. This suggests that mesothelin is a potential target for immune-based intervention strategies in pancreatic cancer.

The human cancer antigen mesothelin is more efficiently presented to the mouse immune system when targeted to the DEC-205/CD205 receptor on dendritic cells

To develop a tumor vaccine directly targeting tumor antigen to dendritic cells in situ, we engineered human mesothelin (MSLN) into an antibody specific for mouse DEC-205, a receptor for antigen presentation. We then characterized both T cell and humoral responses to human MSLN and compared immunizing efficacy of DEC-205-targeted MSLN to nontargeted protein after a single-dose immunization. Targeting human MSLN to DEC-205 receptor induced stronger CD4(+) T-cell responses compared to high doses of mesothelin protein. Approximately 0.5% CD4(+) T cells were primed to produce IFN-gamma, tumor necrosis factor-alpha, and IL-2 via intracellular cytokine staining, and the T cells also could proliferate rapidly. The immune response exhibited breadth because the primed CD4(+) T cells responded to at least three epitopes in the H-2(b) background. Targeting MSLN protein to DEC-205 receptor also resulted in cross-presentation to CD8(+) T cells. Antibody responses against human MSLN were also detected in serum from primed mice by ELISA assays. In summary, targeting of MSLN to DEC-205 improves the induction of CD4(+) and CD8(+) T-cell immunity accompanied by an antibody response. DEC-205-targeting could be valuable for enhancing immunity to MSLN in cancers where this nonmutated protein is expressed.

A novel human monoclonal antibody that binds with high affinity to mesothelin-expressing cells and kills them by antibody-dependent cell-mediated cytotoxicity

Mesothelin is a potential new target for cancer immunotherapy because it is present at relatively low levels only in mesothelial cells of pleura, peritoneum, and pericardium of healthy people, but is significantly elevated in a number of tumors, including mesothelioma, ovarian, pancreatic, and lung cancers. However, all currently available antibodies against mesothelin are either murine or chimeric, which could limit their use because of increased likelihood of immunogenicity compared with fully human antibodies. Here, we report the identification and characterization of a novel fully human monoclonal antibody, m912, which was isolated from a human Fab library by panning against recombinant mesothelin. This antibody in scFv, Fab, and IgG1 formats bound specifically and with high affinity (equilibrium dissociation constant in the nmol/L range) to cell surface-associated human mesothelin and to recombinant mesothelin. It specifically lysed cancer cells engineered to express mesothelin in the presence of peripheral blood mononuclear cells isolated from healthy donors most likely by antibody-dependent cellular cytotoxicity. M912 is the first reported fully human monoclonal antibody to mesothelin, which has potential for cancer treatment and diagnosis.

High mesothelin correlates with chemoresistance and poor survival in epithelial ovarian carcinoma

The objective of this paper is to investigate the mesothelin expression level to the clinicopathological features, chemoresponse, and to the outcome of patients with epithelial ovarian carcinoma (EOC). Mesothelin mRNA was detected by real-time quantitative reverse-transcription PCR in 139 EOC patients. Clinical characteristics, histopathological items, responses to chemotherapy, progression-free survival (PFS), and overall survival (OS) were recorded. Tumours with advanced stages had higher mesothelin than those with early stages. The chemoresistant patients showed significantly higher mesothelin than did chemosensitive patients (2.81 vs 0.43, P<0.001), irrespective of optimal or suboptimal surgery in those with advanced stages. Highly expressed levels of mesothelin were an independent but poor prognostic factor in the PFS (2.03 (1.23-3.37) P=0.006) and OS (3.72 (1.64-8.45), P=0.002) of the 139 EOC patients in multivariate analysis. In addition, patients in advanced stages with highly expressed mesothelin also had significantly worse OS, regardless of whether they had undergone optimal (13.85 (1.76-125.60), P=0.013) or suboptimal (4.47 (1.83-10.88), P=0.001) debulking surgery in multivariate analysis. Out results provide new evidence that mesothelin expression is associated with chemoresistance and with shorter disease-free survival and worse OS of patients with EOC.

Antigen-specific immunotherapy of cervical and ovarian cancer

We contrast the efforts to treat ovarian cancer and cervical cancer through vaccination because of their different pathobiology. A plethora of approaches have been developed for therapeutic vaccination against cancer, many of which target defined tumor-associated antigens (TAAs). Persistent infection with oncogenic human papillomavirus (HPV) types causes cervical cancer. Furthermore, cervical cancer patients frequently mount both humoral and T-cell immune responses to the HPV E6 and E7 oncoproteins, whose expression is required for the transformed phenotype. Numerous vaccine studies target these viral TAAs, including recent trials that may enhance clearance of pre-malignant disease. By contrast, little is known about the etiology of epithelial ovarian cancer. Although it is clear that p53 mutation or loss is a critical early event in the development of epithelial ovarian cancer, no precursor lesion has been described for the most common serous histotype, and even the location of its origin is debated. These issues have complicated the selection of appropriate ovarian TAAs and the design of vaccines. Here we focus on mesothelin as a promising ovarian TAA, because it is overexpressed and immunogenic at high frequency in patients, is displayed on the cell surface, and potentially contributes to ovarian cancer biology.

alpha-Galactosylceramide enhances the protective and therapeutic effects of tumor cell based vaccines for ovarian tumors

Ovarian cancer is one of the leading causes of death from gynecological cancers in the United States. Conventional therapies are unlikely to control advanced stage ovarian cancers, thus requiring innovative alternative therapies. In the current study, we characterized the therapeutic effect of tumor cell-based vaccines combined with the adjuvant, alpha-galactosylceramide (alpha-GalCer) using two different mouse models. Our data suggests that treatment with alpha-GalCer led to an increase in the IFN-gamma serum levels in the presence or absence of irradiated mouse ovarian surface epithelial tumor cells (MOSEC). Furthermore, administration of irradiated MOSEC tumor cells with adjuvant alpha-GalCer generated significant protective and therapeutic antitumor effects against MOSEC tumors in vaccinated C57BL/6 mice. In addition, immune cells expressing CD4, CD8 or NK1.1 markers were found to be important for the protective antitumor effects generated by irradiated tumor cell-based vaccines combined with adjuvant alpha-GalCer. We also found that treatment of a spontaneous ovarian cancer murine model, the Müllerian inhibiting substance type II receptor T antigen (TgMISIIR-TAg) transgenic mice with ovarian tumor cell-based vaccines combined with adjuvant alpha-GalCer led to prolonged survival as well as increased numbers of tumor-specific CD8+ T cells. Therefore, irradiated tumor cell-based vaccines in combination with alpha-GalCer are capable of breaking immune tolerance and generating significant antitumor effects in two different mouse tumor models. Our study serves as a foundation for future clinical translation.

Mesothelin is a specific biomarker of invasive cancer in the Barrett-associated adenocarcinoma progression model: translational implications for diagnosis and therapy

Esophageal adenocarcinoma arises in the backdrop of Barrett metaplasia-dysplasia sequence, with the vast majority of patients presenting with late-stage malignancy. Mesothelin, a glycophosphatidylinositol-anchored protein, is aberrantly overexpressed on the surface of many solid cancers. Mesothelin expression was assessed in esophageal tissue microarrays encompassing the entire histological spectrum of Barrett-associated dysplasia and adenocarcinoma. Mesothelin expression was observed in 24/84 (29%) of invasive adenocarcinomas and in 5/34 (15%) lymph node metastases. In contrast, normal squamous and cardiac mucosa, as well as noninvasive Barrett lesions, failed to label with mesothelin. Mesothelin was expressed in the esophageal adenocarcinoma cell line JH-EsoAd1 but not in primary human esophageal epithelial cells. Anti-mesothelin antibody-conjugated CdSe/CDS/ZnS quantum rods were synthesized, and confocal bioimaging confirmed robust binding to JH-EsoAd1 cells. Anti-mesothelin antibody-conjugated nanoparticles can be useful for the diagnosis and therapy of mesothelin-overexpressing esophageal adenocarcinomas.