Interleukin-12 induces an effective antitumor response in malignant mesothelioma

Fusion peptide is superior to co-expressing subunits for arming oncolytic herpes virus with interleukin 12

BACKGROUND

G47∆ is a triple-mutated oncolytic herpes simplex virus type 1 (HSV-1) recently approved as a new drug for malignant glioma in Japan. As the next-generation, we develop armed oncolytic HSV-1 using G47∆ as the backbone. Because oncolytic HSV-1 elicits specific antitumor immunity, interleukin 12 (IL-12) can function as an effective payload to enhance the efficacy.

METHODS

We evaluate the optimal methods for expressing IL-12 as a payload for G47∆-based oncolytic HSV-1. Two new armed viruses are generated for evaluation by employing different methods to express IL-12: T-mfIL12 expresses murine IL-12 as a fusion peptide, with the genes of two subunits (p35 and p40) linked by bovine elastin motifs, and T-mIL12-IRES co-expresses the subunits, with the two genes separated by an internal ribosome entry site (IRES) sequence.

RESULTS

T-mfIL12 is significantly more efficient in producing IL-12 than T-mIL12-IRES in all cell lines tested, whereas the expression methods do not affect the replication capabilities and cytopathic effects. In two syngeneic mouse subcutaneous tumor models of Neuro2a and TRAMP-C2, T-mfIL12 exhibits a significantly higher efficacy than T-mIL12-IRES when inoculated intratumorally. Furthermore, T-mfIL12 shows a significantly higher intratumoral expression of functional IL-12, causing stronger stimulation of specific antitumor immune responses than T-mIL12-IRES.

CONCLUSIONS

The results implicate that a fusion-type expression of IL-12 is a method superior to co-expression of separate subunits, due to higher production of functional IL-12 molecules. This study led to the creation of triple-mutated oncolytic HSV-1 armed with human IL-12 currently used in phase 1/2 trial for malignant melanoma.

How Our Continuing Studies of the Pre-clinical Inbred Mouse Models of Mesothelioma Have Influenced the Development of New Therapies

Asbestos-induced preclinical mouse models of mesothelioma produce tumors that are very similar to those that develop in humans and thus represent an ideal platform to study this rare, universally fatal tumor type. Our team and a number of other research groups have established such models as a stepping stone to new treatments, including chemotherapy, immunotherapy and other approaches that have been/are being translated into clinical trials. In some cases this work has led to changes in mesothelioma treatment practice and over the last 30 years these models and studies have led to trials which have improved the response rate in mesothelioma from less than 10% to over 50%. Mouse models have had a vital role in that improvement and will continue to play a key role in the future success of mesothelioma immunotherapy. In this review we focus only on these original inbred mouse models, the large number of preclinical studies conducted using them and their contribution to current and future clinical therapy for mesothelioma.

Lactate dehydrogenase-elevating virus enhances natural killer cell-mediated immunosurveillance of mouse mesothelioma development

Background

Viral infections can reduce early cancer development through enhancement of cancer immunosurveillance. This study was performed to analyse this effect of viral infection in a mouse model of solid tumor.

Methods

The experimental model used was the effect of BALB/c mouse infection by lactate dehydrogenase-elevating virus on AB1 mesothelioma cancer development.

Results

Acute infection with lactate dehydrogenase-elevating virus strongly reduced in vivo early AB1 mesothelioma growth and death resulting from cancer development. This effect was not due to a direct cytolytic effect of the virus on AB1 cells, but to an in vivo activation of natural killer cells. Gamma-interferon production rather than cytotoxic activity against AB1 cells mediated this protective effect. This gamma-interferon production by natural killer cells was dependent on interleukin-12 production.

Conclusions

Together with other reported effects of infectious agents on cancer development, this observation may support the hypothesis that enhancement of innate immunosurveillance against tumors may result from infection with common infectious agents through modulation of the host immune microenvironment.

Murine mesothelioma induces locally-proliferating IL-10(+)TNF-α(+)CD206(-)CX3CR1(+) M3 macrophages that can be selectively depleted by chemotherapy or immunotherapy

We used a murine model to monitor changes to myeloid cell subsets, i.e., myeloid-derived suppressor cells (MDSCs), M1 macrophages that secrete pro-inflammatory cytokines and express CD40 and CD80 and suppressive M2 macrophages that secrete anti-inflammatory cytokines and express CD206 and CX3CR1, during mesothelioma progression and during chemotherapy or immunotherapy-induced tumor regression. In vitro studies showed that mesothelioma-conditioned media generated CD206(-)CX3CR1(+)MCP-1(+)TGF-β(+) macrophages that induced T cell proliferation but prevented T cell IFNγ production. In vivo studies showed that co-inoculation of macrophages with mesothelioma cells led to faster tumor growth, and depleting macrophages using anti-F4/80 antibody induced tumor regression. Flow cytometry revealed increasing levels of different suppressive myeloid cells in lymphoid organs: MDSCs dominated bone marrow (BM) and spleens, M2 macrophages dominated tumor-draining lymph nodes (DLN) and a mixed IL-10(+)TNF-α(+)CD206(-)CX3CR1(+) M1/M2 (M3) macrophage subset dominated the mesothelioma microenvironment. Ki67 staining and cell cycle analysis showed that tumor-associated M1 and M3, but not M2, macrophages were proliferating in situ, with M1 cells arrested in the G1 phase while M3 cells progressed to mitosis. Immunohistochemistry showed that M1 and M3 cells were co-located supporting the hypothesis that M1 cells transition to M3 cells during proliferation. Gemcitabine reduced tumor-associated M3 and MDSCs, but not M2 macrophages, the latter likely contributing to the tumor outgrowth seen following treatment cessation. In contrast, IL-2/agonist anti-CD40 antibody therapy reduced M3 cells and polarized macrophages into M1 cells coinciding with tumor regression. These data show that myeloid cells, particularly M3 cells, represent a therapeutic target for the generation of antitumor immunity.

Activation of CD1d-restricted natural killer T cells can inhibit cancer cell proliferation during chemotherapy by promoting the immune responses in murine mesothelioma

We studied the impact of natural killer T (NKT) cell activation by alpha-galactocysylceramide (α-GalCer, α-GC) on cancer cell repopulation during chemotherapy in murine mesothelioma. The number of NKT cells was found to be increased during the development of murine mesothelioma. NKT cells specifically recognize α-GC through CD1d resulting in their activation and expansion. Tumor-bearing mice were treated with chemotherapy once weekly, and α-GC was followed after each cycle of chemotherapy. Anti-tumor effect was evaluated on wild-type (WT) and CD1d knockout (CD1dKO) mice. Cancer cell proliferation and apoptosis were evaluated by Ki67 and TUNEL immunohistochemistry. CD4(+) and CD8(+) T cell proportion and activation in tumor, spleen, draining lymph node and peripheral blood were determined by flow cytometry, and gene expression of activated T cell-related cytokines was quantified by reverse transcription PCR. NKT cells were identified by CD1d-α-GC-tetramer staining. In WT mice, tumor growth delay was achieved by cisplatin (Cis), and this effect was improved in combination with α-GC, but α-GC alone had little effect. Cancer cell proliferation during chemotherapy was significantly inhibited by α-GC, while cancer cell death was significantly upregulated. α-GC following chemotherapy resulted in NKT cell expansion and an increase of interferon-γ production in the draining lymph node, blood and spleen. Gene expression of immune-associated cytokines was upregulated. Strikingly, the percentage of inducible T cell co-stimulator(+)CD4 T cells, Th17/Tc17 cells increased in splenocytes. In CD1d KO mice, however, Cis alone was less effective and Cis + α-GC provided no additional benefit over Cis alone. α-GC alone had minimal effect in both mice. NKT activation between cycles of chemotherapy could improve the outcome of mesothelioma treatment.

The "Trojan Horse" approach to tumor immunotherapy: targeting the tumor microenvironment

Most anticancer therapies including immunotherapies are given systemically; yet therapies given directly into tumors may be more effective, particularly those that overcome natural suppressive factors in the tumor microenvironment. The “Trojan Horse” approach of intratumoural delivery aims to promote immune-mediated destruction by inducing microenvironmental changes within the tumour at the same time as avoiding the systemic toxicity that is often associated with more “full frontal” treatments such as transfer of large numbers of laboratory-expanded tumor-specific cytotoxic T lymphocytes or large intravenous doses of cytokine. Numerous studies have demonstrated that intratumoural therapy has the capacity to minimizing local suppression, inducing sufficient “dangerous” tumor cell death to cross-prime strong immune responses, and rending tumor blood vessels amenable to immune cell traffic to induce effector cell changes in secondary lymphoid organs. However, the key to its success is the design of a sound rational approach based on evidence. There is compelling preclinical data for local immunotherapy approaches in tumor immunology. This review summarises how immune events within a tumour can be modified by local approaches, how this can affect systemic antitumor immunity such that distal sites are attacked, and what approaches have been proven most successful so far in animals and patients.

Novel immunocytokine IL12-SS1 (Fv) inhibits mesothelioma tumor growth in nude mice

Mesothelin is a glycosylphosphatidylinositol-anchored glycoprotein that is highly expressed on the cell surface of malignant mesothelioma. Monoclonal antibodies against mesothelin are being evaluated for the treatment of mesothelioma. Immunocytokines represent a novel class of armed antibodies. To provide an alternative approach to current mesothelin-targeted antibody therapies, we have developed a novel immunocytokine based on interleukin-12 (IL12) and the SS1 Fv specific for mesothelin. IL12 possesses potent anti-tumor activity in a wide variety of solid tumors. The newly-developed recombinant immunocytokine, IL12-SS1 (Fv), was produced in insect cells using a baculovirus-insect cell expression system. The SS1 single-chain Fv was fused to the C terminus of the p35 subunit of IL12 through a short linker (GSADGG). The single-chain IL12-SS1 (Fv) immunocytokine bound native mesothelin proteins on malignant mesothelioma (NCI-H226) and ovarian (OVCAR-3) cells as well as recombinant mesothelin on A431/H9 cells. The immunocytokine retained sufficient bioactivity of IL12 and significantly inhibited human malignant mesothelioma (NCI-H226) grown in the peritoneal cavity of nude mice and showed comparable anti-tumor activity to that of the SS1P immunotoxin. IL12-SS1 (Fv) is the first reported immunocytokine to mesothelin-positive tumors and may be an attractive addition to mesothelin-targeted cancer therapies.

Immune responses and immunotherapeutic interventions in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive, primary pleural malignancy with poor prognosis, hypothesized to originate from a chronic inflammatory state within the pleura. Similar to what has been observed in other solid tumors (melanoma, ovarian and colorectal cancer), clinical and pre-clinical MPM investigations have correlated anti-tumor immune responses with improved survival. As such, a better understanding of the complex MPM tumor microenvironment is imperative in strategizing successful immunotherapies. Herein, we review the immune responses vital to the development and progression of MPM, as well as assess the role of immunomodulatory therapies, highlighting recent pre-clinical and clinical immunotherapy investigations.

Inflammation precedes the development of human malignant mesotheliomas in a SCID mouse xenograft model

Asbestos fibers cause chronic inflammation that may be critical to the development of malignant mesothelioma (MM). Two human MM cell lines (Hmeso, PPM Mill) were used in a SCID mouse xenograft model to assess time-dependent patterns of inflammation and tumor formation. After intraperitoneal (IP) injection of MM cells, mice were euthanized at 7, 14, and 30 days, and peritoneal lavage fluid (PLF) was examined for immune cell profiles and human and mouse cytokines. Increases in human MM-derived IL-6, IL-8, bFGF, and VEGF were observed in mice at 7 days postinjection of either MM line, and a striking neutrophilia was observed at all time points. Free-floating tumor spheroids developed in mice at 14 days, and both spheroids and adherent MM tumor masses occurred in all mice at 30 days. Results suggest that inflammation and cytokine production precede and may be critical to the development of MMs.

Cytokine-armed vaccinia virus infects the mesothelioma tumor microenvironment to overcome immune tolerance and mediate tumor resolution

Intratumoral (i.t.) administration of cytokine genes expressed by viral vectors represents a rational approach that induces cytokine secretion at the site they are needed, and i.t. vaccinia virus (VV) has shown promise in mesothelioma patients. However, we and others have shown that the mesothelioma tumor microenvironment includes macrophages, dendritic cells (DCs), and T cells. Therefore, we investigated which of these cell types are infected after exposure to VV or Fowlpox virus (FPV)-cytokine gene constructs. In vitro studies showed that mesothelioma tumor cells were resistant to FPV infection yet highly permissive to infection by VV vectors resulting in significant cytokine production and impaired proliferation. Macrophages secreted low levels of cytokine suggestive of resistance to overt infection. DCs transiently secreted virally derived cytokines, but did not mature during VV infection. VV inhibition of T cell proliferation was rescued by the interleukin (IL)-2 and IL-12 VV constructs. In vivo studies of murine mesotheliomas showed that i.t. injection of the parent VV could not hinder tumor progression. In contrast, the VV-cytokine constructs induced profound tumor regression. These data suggest that i.t. VV-cytokine gene constructs retard tumor growth by infecting mesothelioma cells and targeting the immune system through tumor-infiltrating DC and T cells.

What's the place of immunotherapy in malignant mesothelioma treatments?

Malignant pleural mesothelioma (MPM) is a rare malignancy of the pleura with a very poor prognosis. Treatments evaluated for malignant mesothelioma, including chemotherapy, radiotherapy and surgery are of limited efficacy. However, the fact that the tumors of some patients with MPM regress spontaneously or respond to immunotherapy suggests that the immune system may respond to MPM under some circumstances. In this respect, animal studies have demonstrated immunoreactivity of MPM to different immunotherapies. In the case of MPM, several clinical studies have demonstrated a correlation between the presence of a lymphocyte infiltrate and a better prognosis and humoral response directed against specific antigens related to tumor. Thus, MPM immunotherapy is undoubtedly a highly promising but also very challenging approach to the treatment of this disease that has slipped through the defense lines of the immune system. This article reviews past and recent developments of the clinical strategies that concern immunotherapy of mesothelioma.

New diagnostic and molecular characteristics of malignant mesothelioma

Malignant mesothelioma is a primary cancer of the serosal cavities, an anatomic site that is also frequently affected by metastatic disease, predominantly from primary carcinomas of the lung, breast, and ovary. Advances in immunohistochemistry have resulted in improved diagnostic sensitivity and specificity in the differential diagnosis between metastatic adenocarcinoma and malignant mesothelioma in both cytological and histological material. Recently, the author's group applied high throughput technology to the identification of new markers that may aid in differentiating malignant mesothelioma from ovarian and peritoneal serous carcinoma, tumors with closely related histogenesis and antigenic profile. In addition to the improved tools available for serosal cancer diagnosis, knowledge regarding the biology of malignant mesothelioma has been accumulating in recent years. This review presents current data regarding the diagnostic and biological aspects of malignant mesothelioma.

Prophylactic IL-12 treatment reduces postoperative metastasis: mediation by increased numbers but not cytotoxicity of NK cells

Despite a promising potential, interleukin-12 immunotherapy has yielded limited clinical success while causing perilous toxicities. Here we study a context in which IL-12 may prove clinically beneficial--the removal of the primary tumor, when cell-mediated immunity (CMI) may eradicate minimal residual disease (MRD), but is inhibited by postoperative immunosuppression, potentially leading to enhanced malignant progression. F344 rats were preoperatively treated with IL-12 and inoculated postoperatively with syngeneic MADB106 tumor cells. An optimal regimen of eight-day sustained exposure to IL-12 was developed (1 microg/rat/day), which caused mild side effects, increased baseline resistance to experimental MADB106 metastasis, and abolished the promotion of metastasis by laparotomy and other immunosuppressive paradigms. Depletion of NK cells indicated their major role in controlling MADB106 metastasis in naïve and IL-12 treated rats. Studying NK cytotoxicity, we found that IL-12 did not potentiate activity per NK cell, nor protected it from suppression by surgery. However, IL-12 increased the numbers of NK cells in the circulation and marginating pulmonary pool of naïve and operated rats, and correspondingly increased total NK activity in these compartments. Therefore, this study indicates anti-tumor effects of IL-12 based on increased numbers of strategically located NK cells, and advocates a prophylactic approach against the potential metastasis-promoting effects of surgery.

Expression of Cancer-Associated Molecules in Malignant Mesothelioma

Malignant mesothelioma (MM) is a malignant tumor derived from mesothelial cells, native cells of the body cavities. Exposure to asbestos is the most strongly established etiologic factor, predominantly for the most common disease form, pleural mesothelioma. The pathogenesis of MM involves the accumulation of extensive cytogenetic changes, as well as cancer-related phenotypic alterations that facilitate tumor cell survival, invasion and metastasis. This review presents current knowledge regarding the biological characteristics of this disease that are linked to the so-called hallmarks of cancer. In addition, data suggesting that the anatomic site (solid tumor vs. effusion) affects the expression of metastasis-associated and regulatory molecules in MM are presented. Finally, recent work in which high-throughput methodology has been applied to MM research is reviewed. The data obtained in the reviewed research may aid in defining new prognostic markers and therapeutic targets for this aggressive disease in the future.

Recombinant GM-CSF plus autologous tumor cells as a vaccine for patients with mesothelioma

Treatments evaluated for malignant mesothelioma (MM), including chemotherapy, radiotherapy and surgery are of limited efficacy. Immunotherapy has shown some promise in MM but optimal vaccination conditions are yet to be defined. Autologous tumour vaccines have the advantage of containing both 'self'- and 'neo'-tumor antigens but they are not commonly used in any cancer, and never in MM. We therefore evaluated the effect of an autologous MM tumor cell lysate, given s.c. with recombinant granulocyte-macrophage colony stimulating factor (GM-CSF), on anti-tumor immunity in patients with MM.

PATIENTS AND METHODS

An autologous tumor lysate vaccine was manufactured from surgically resected tumor and administered subcutaneously together with GM-CSF. Induction of tumor specific cellular immunity was assessed by delayed type hypersensitivy (DTH) skin testing using autologous tumor tissue and of humoral immune responses to shared MM antigens by western blotting of patients' sera against a panel of allogeneic human MM cell lines. CT scanning was used to evaluate tumor progression.

RESULTS

Twenty-two patients were enrolled onto the trial. Of these five developed positive delayed type hypersensitivity skin tests and five showed evidence of altered antibody specificities by western blotting. A total of seven patients developed at least one type of anti-MM immune response. On an intention-to-treat basis the median survival of all patients was 11.5 months, and the 1- and 2-year survival rates were 50% and 27%, respectively. Complete or partial CT responses were not seen, however seven patients had stable disease for the duration of the trial. Vaccination was safe with no severe adverse reactions.

CONCLUSION

Vaccination with autologous MM tumor cell lysate with GM-CSF induced tumor specific immunity in 32% of patients, was safe and was associated with stable disease but no major tumour regressions.

Gene therapy for malignant mesothelioma: beyond the infant years

Mesothelioma may be particularly well suited for gene therapy treatment owing to its accessibility, allowing both intrapleural and intratumoral gene delivery. At least four gene therapy trials have been carried out in mesothelioma patients, using different vector systems (adenovirus, vaccinia virus, irradiated tumor cells), and different transgenes (herpes simplex virus thymidine kinase (HSVtk) combined with ganciclovir, IL-2, IFN-beta). Although small in scale, these trials have given an inkling of hope for therapeutic efficacy. However, it is clear that gene therapy protocols need to be optimized further. This paper will review progress made in (i) vector development, (ii) defining optimal transgenes, and (iii) gene delivery. Adenoviruses are the most commonly used vectors for gene therapy, and are continuously being improved. With respect to the nature of the transgenes, five categories can be distinguished: (i) 'suicide' or sensitivity genes (e.g., HSVtk), (ii) cytokines and other immune modulators, (iii) replacements for mutant tumor suppressor genes (e.g., p53), (iv) antiangiogenic proteins and (v) tumor antigens. It seems clear that expression of a single transgene is unlikely to be sufficient to eradicate a tumor, such as mesothelioma, that is diagnosed late in disease progression. Hence, multimodality therapy, including conventional therapy (chemo- and radiotherapy, surgery) with one or more transgenes has a higher chance of success.

Gene Therapy for Malignant Pleural Mesothelioma

Gene therapy for mesothelioma is currently in its adolescence. The expansion of knowledge regarding molecular aspects of mesothelioma carcinogenesis has facilitated the development of promising gene therapy modalities that target specific oncoproteins and mutant tumor suppressor genes. Although implementation of any of these gene therapy approaches as part of standard medical care for patients who have mesothelioma remains years in the future, the field is finally progressing toward more definitive phase II/III efficacy studies. Unfortunately, the marginal benefits garnered from standard anticancer treatments in mesothelioma argue strongly for continued participation in clinical studies of various experimental approaches, particularly gene therapy. These trials serve multiple purposes: to establish safety, determine proper dosing, evaluate for efficacy, and, in an iterative fashion, guide future avenues of laboratory investigation.

Intratumoral Poly-N-Acetyl Glucosamine-Based Polymer Matrix Provokes a Prolonged Local Inflammatory Response That, When Combined with IL-2, Induces Regression of Malignant Mesothelioma in a Murine Model

The authors have previously shown that cytokines delivered directly into malignant mesothelioma (MM) tumors can retard tumor growth and mediate tumor regression under certain conditions. In this report the authors compared the efficacy of serial intratumoral injections of three cytokines, GM-CSF, IL-12, and IL-2, to their sustained release using a single injection in a poly-N-acetyl glucosamine gel. IL-2 combined with the polymer gel gave optimal antitumor results when MM tumors were accessible as either subcutaneous deposits or as masses spread throughout the peritoneal cavity. The gel acted not only as a slow-release cytokine depot but also as a trigger for inflammation and recruited several immune cell types to the gel/tumor interface; when combined with IL-2 (but not with GM-CSF or IL-12), it acted as a selective reservoir for infiltrating CD8+ T cells. Hence, the IL-2/gel may provide a microenvironment that allows intratumoral T cells to proliferate and retain their cytolytic functions as they encounter their cognate antigens expressed by tumor cells.

Immunotherapy of Murine Malignant Mesothelioma Using Tumor Lysate–pulsed Dendritic Cells

RATIONALE

Exploiting the immunostimulatory capacities of dendritic cells holds great promise for cancer immunotherapy. Currently, dendritic cell-based immunotherapy is evaluated clinically in a number of malignancies, including melanoma and urogenital and lung cancer, showing variable but promising results.

OBJECTIVE

To evaluate if pulsed dendritic cells induce protective immunity against malignant mesothelioma in a mouse model.

METHODS

Malignant mesothelioma was induced in mice by intraperitoneal injection of the AB1 mesothelioma cell line, leading to death within 28 days. For immunotherapy, dendritic cells were pulsed overnight either with AB1 tumor cell line lysate, AB1-derived exosomes, or ex vivo AB1 tumor lysate, and injected either before (Days -14 and -7) at the day of (Day 0) or after (Days +1 and +8) tumor implantation.

MAIN RESULTS

Mice receiving tumor lysate-pulsed dendritic cells before tumor implantation demonstrated protective antitumor immunity with prolonged survival (> 3 months) and even resisted secondary tumor challenge. Tumor protection was associated with strong tumor-specific cytotoxic T-lymphocyte responses. Adoptive transfer of splenocytes or purified CD8+ T lymphocytes transferred tumor protection to unimmunized mice in vivo. When given after tumor implantation in a therapeutic setting, pulsed dendritic cells prevented mesothelioma outgrowth. With higher tumor load and delayed administration after tumor implantation, dendritic cells were no longer effective.

CONCLUSIONS

We demonstrate in this murine model that immunotherapy using pulsed dendritic cells may emerge as a powerful tool to control mesothelioma outgrowth. In the future, immunotherapy using dendritic cells could be used as adjuvant to control local recurrence after multimodality treatment for malignant mesothelioma.

Malignant pleural mesothelioma--an update

Exposure to asbestos is the most frequent, but not exclusive, cause of malignant mesothelioma. Clinical features include dyspnea, cough, nonspecific chest pain, weight loss and night sweats. Diagnosis may be complicated by histologic difficulties. Thoracoscopic techniques are proving beneficial, but no one method of imaging has proven superior, and disease staging is inconsistent. Conventional treatments such as chemotherapy, surgery, and radiotherapy have had variable impacts, although chemotherapy is useful in palliation and can improve both survival and quality of life. There is hope for new antimetabolite agents. The role of radical surgery is yet to be evaluated in a large trial. New radiotherapeutic techniques to improve local control are promising. Multimodality treatments appear to be the most successful for management of potentially resectable disease. It is likely that biological markers will improve accuracy in staging and prognosis. With new treatments based on better understanding of the biology of the disease, there is cautious optimism for the future for patients with malignant pleural mesothelioma.

Cytotoxic T Cell Responses against Mesothelioma by Apoptotic Cell-pulsed Dendritic Cells

Malignant pleural mesothelioma is an uncommon tumor largely confined to the thoracic cavity, which is resistant to conventional therapies, therefore prompting an intensive search for effective treatment alternatives. This study focuses on dendritic cell (DC) vaccination for malignant pleural mesothelioma and evaluates the in vitro efficacy of antigen-loaded DC-based vaccines for the induction of major histocompatibility complex Class I-restricted antimesothelioma cytotoxic T lymphocyte responses. The source of tumor-associated antigens for HLA-A2(+) DCs from healthy donors was apoptotic HLA-A2(-) mesothelioma cells either lacking or expressing heat shock protein 70 according to whether tumor cells were heat shocked or not before ultraviolet-mediated apoptosis. Our results show that both apoptotic preparations were equivalent regarding the responsiveness of DCs to combined treatment with tumor necrosis factor-alpha and poly(inosinic-cytidylic) acid, as determined by similar increased expression of costimulatory molecules and interleukin-12 production. However, only DCs loaded with apoptotic heat shock protein 70-expressing cells were found to be potent in vitro inducers of cytotoxic T lymphocyte activity against HLA-A2(+) mesothelioma cells. Such elicited cytotoxic T lymphocytes also exhibit cytotoxic activity against an HLA-A2(+) melanoma cell line, suggesting recognition of shared antigens. These findings therefore carry the potential of offering an alternative, promising approach for the therapy of patients with malignant pleural mesothelioma.

IL-2 intratumoral immunotherapy enhances CD8+ T cells that mediate destruction of tumor cells and tumor-associated vasculature: a novel mechanism for IL-2

Therapeutic use of IL-2 can generate antitumor immunity; however, a variety of different mechanisms have been reported. We injected IL-2 intratumorally (i.t.) at different stages of growth, using our unique murine model of mesothelioma (AE17; and AE17 transfected with secretory OVA (AE17-sOVA)), and systematically analyzed real-time events as they occurred in vivo. The majority of mice with small tumors when treatment commenced displayed complete tumor regression, remained tumor free for >2 mo, and survived rechallenge with AE17 tumor cells. However, mice with large tumors at the start of treatment failed to respond. Timing experiments showed that IL-2-mediated responses were dependent upon tumor size, not on the duration of disease. Although i.t. IL-2 did not alter tumor Ag presentation in draining lymph nodes, it did enhance a previously primed, endogenous, tumor-specific in vivo CTL response that coincided with regressing tumors. Both CD4(+) and CD8(+) cells were required for IL-2-mediated tumor eradication, because IL-2 therapy failed in CD4(+)-depleted, CD8(+)-depleted, and both CD4(+)- and CD8(+)-depleted C57BL/6J animals. Tumor-infiltrating CD8(+) T cells, but not CD4(+) T cells, increased in association with a marked reduction in tumor-associated vascularity. Destruction of blood vessels required CD8(+) T cells, because this did not occur in nude mice or in CD8(+)-depleted C57BL/6J mice. These results show that repeated doses of i.t. (but not systemic) IL-2 mediates tumor regression via an enhanced endogenous tumor-specific CTL response concomitant with reduced vasculature, thereby demonstrating a novel mechanism for IL-2 activity.

IL-12/IL-2 combination cytokine therapy for solid tumours: translation from bench to bedside

A broad range of approaches are under active investigation for the biological therapy of cancer, in particular, strategies directed at host immune response potentiation. These efforts have been fuelled by studies demonstrating the presence of an endogenous, but ineffective, host antitumour immune response and a greater understanding of the key factors which regulate this response. These mechanisms involve complex interactions between various effector cell populations, soluble factors and the tumour itself and are determined by the timing and relative intensity of positive and negative autoregulatory pathways, as well as a variety of immunosuppressive effects capable of mediating tumour self-defence. Based on these observations, immunotherapeutic regimens have been developed to potentiate antigen-specific sensitisation of effector cells with tumour vaccines/adjuvants, expand and amplify the number and function of effector cells, and to counteract suppressive pathways engaged by tumour cells themselves. Significant effort has focused on evaluating the use of exogenous cytokines, administered either systemically or locally into the tumour site via gene therapy. Several cytokines have demonstrated unique activity in the preclinical setting, including IL-2 and IFN-alpha -inducing cytokines such as IL12 and IL18. Most notably, later studies have now attempted to build on the clinical efficacy of IL-2 alone, to define combinations of agents with synergistic immunoregulatory and/or antitumour efficacy. Several lines of evidence suggest that IL-12 and IL-2 provide complementary immunoregulatory signals and have now shown that in combination, these two cytokines mediate synergistic antitumour activity in preclinical tumour models. This paper will review existing data regarding mechanisms of interaction between IL-2 and IL-12 in vitro and in preclinial models and describe future opportunities for the investigation of these potentially promising cytokines in the treatment of cancer.

Cancer testis antigens expression in mesothelioma: role of DNA methylation and bioimmunotherapeutic implications

Recent evidences suggest that malignant mesothelioma may be sensitive to immunotherapy; however, little is known about malignant mesothelioma-associated tumour antigens. Focusing on cancer/testis antigens, the expression of well-characterised immunogenic tumour-associated antigens was investigated in malignant mesothelioma cells. At variance with MAGE-4 and NY-ESO-1, malignant mesothelioma cells frequently expressed MAGE-1, -2 and -3, GAGE 1-2, GAGE 1-6, SSX-2 and SSX 1-5, and distinct malignant mesothelioma cells concomitantly expressed at least four cancer/testis antigens. Additionally, the tumour-associated antigens RAGE-1 was expressed at high levels in both benign and malignant mesothelial cells. Lastly, treatment with the DNA hypomethylating agent 5-aza-2'-deoxycytidine induced and up-regulated the expression of the cancer/testis antigen examined in malignant mesothelioma cells. Overall, these findings strongly suggest that cancer/testis antigens-based immunotherapy may represent a suitable therapeutic approach to malignant mesothelioma, and foresee the clinical use of 5-aza-2'-deoxycytidine to design new chemo-immunotherapeutic strategies in malignant mesothelioma patients.

New approaches for mesothelioma: biologics, vaccines, gene therapy, and other novel agents

Although malignant mesothelioma is not a classically immunogenic cancer, there is abundant evidence for immune recognition. The relative ease of obtaining tumor tissue makes mesothelioma ideal for studying surrogate biomarkers such as lymphocytic infiltration or expression of transduced genes. There is evidence that malignant mesothelioma patients as well as asbestos-exposed persons without mesothelioma have impaired immune responsiveness. Substantial progress has been made in animal models using several biological and immunological techniques, but clinical application has been problematic. Systems studied have included lysis by interleukin-2 (IL-2)-activated lymphokine-activated killer (LAK) cells, tumor necrosis factor-alpha (TNF-alpha), a p16-expressing adenovirus vector, suicide gene therapy using the herpes simplex virus-tyrosine kinase (HSV-tk) followed by ganciclovir, and immunomodulatory gene therapy with IL-2, IL-4, interferon-gamma (IFN-gamma), IFN-alpha, TNF-alpha, granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-6, and IL-1beta transfected into tumors. Vaccinia virus has been studied as a vector for cytokine gene transfer. Suicide gene therapy has been combined with a tumor vaccine. The University of Western Australia is initiating a pilot study of autologous vaccination in malignant mesothelioma. Novel agents under study include the angiogenesis inhibitors SU5416, bevacizumab, and thalidomide. ZD1839, an orally administered, highly selective inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase, is being tested in a phase II trial. Since platelet-derived growth factor (PDGF) is thought to be an autocrine growth factor for mesothelioma STI-571 (Gleevec; Novartis, Basel, Switzerland), a highly selective inhibitor of the PDGF receptor tyrosine kinase, is being tested in a phase II trial. The development of more active cytotoxic combinations in this disease should facilitate further studies of chemoimmunotherapy. It seems likely that no single treatment modality will be effective by itself.

Localised spontaneous regression in mesothelioma -- possible immunological mechanism

Malignant mesothelioma (MM) is an aggressive tumor usually associated with asbestos exposure. Although it can remain stable for prolonged periods, it has not been described to spontaneously regress. MM tumors are thought to be immunogenic based both on animal studies and on the good responses in some humans treated with immunotherapy. Here we present a case of pleural MM in which a transient spontaneous regression was associated with tumor tissue infiltration with mononuclear cells and serological evidence of anti-MM reactivity. The patient's tumor eventually progressed and with this progression there was evidence of loss of serological reactivity to some, but not all, of her MM antigens. The patient survived for 20 months and, in contrast to her initial biopsy, no significant lymphoid infiltrate was detected in her MM tissue at post mortem examination.

Management of malignant pleural mesothelioma: a critical review

Malignant mesothelioma remains a uniformly fatal disease and best supportive care continues to be the standard treatment. Neither chemotherapy nor surgery has been shown to prolong survival. Radiotherapy is not curative but is useful for prophylaxis against needle-track metastases and for symptom palliation. Combinations of therapies have been tried but most studies were uncontrolled and selection bias makes the results impossible to interpret. The combination of extrapleural pneumonectomy, chemotherapy, and radiotherapy attracted much interest, but the subsequent results were disappointing in a highly selected group of patients. Randomized controlled trials are desperately needed to provide definitive information on experimental treatments. It is also important to develop better measures of disease response and to assess quality of life issues in clinical trials. If patients are to receive therapies other than palliation, they should only do so in the setting of randomized controlled trials under approved protocols.

Gene Therapy for Lung Cancer

Gene therapy is emerging as a promising modality for the treatment of lung cancer. Diverse strategies employing gene therapy for lung cancer have been investigated in vitro and in animal models, and a number of these approaches have met with promising results. Several phase I and II clinical trials have been undertaken, and early results suggest that it may be safe to administer gene therapy to lung cancer patients. It remains to be determined whether this modality will be efficacious as primary or adjunctive therapy in the setting of lung cancer.

Cross-presentation of tumour antigens: evaluation of threshold, duration, distribution and regulation

The development of technology to measure antigen presentation in the secondary lymphoid system has provided the opportunity of analysing components of the host antitumour immune response that have, until now, been unavailable for study. In particular, this technology has enabled us to evaluate threshold levels of tumour antigen required for cross-presentation in draining lymph nodes, the duration of this antigen presentation and processes that regulate tumour antigen presentation. Thus, we have been able to dissect out the relationship between antigen presentation and the resultant development of effector function in class I-restricted T cells, as well as the role of regulatory CD4 cells. We have also used this technology to evaluate the effects of antitumour therapy on local antigen cross-presentation.

Cytokine gene therapy of mesothelioma. Immune and antitumor effects of transfected interleukin-12

Malignant mesothelioma (MM) is a solid tumor of the mesothelium for which there is no curative treatment. MM appears to be sensitive to immunotherapeutic approaches, and one of the most powerful immunomodulatory cytokines with antitumor effects is interleukin (IL)-12. We have previously shown in a murine model of MM that systemic administration of recombinant IL-12 induces a potent anti-MM immune response. The nature and accessibility of MM tumors means that they are suitable candidates for direct cytokine and gene-transfer therapeutic approaches. Therefore, we undertook a study to assess the antitumor effects induced by the local production of IL-12 within MM tumors by transfecting a murine MM line with the genes for IL-12. The IL-12 transfectant (AB1-IL-12) did not produce tumors in normal mice, but did so in athymic nude mice, implicating T cells in the prevention of MM tumor growth. In mixing experiments, paracrine IL-12 production inhibited growth of untransfected MM cells provided that cells producing IL-12 represented more than 50-80% of the inoculum. Furthermore, BALB/c mice previously challenged with AB1-IL-12 were protected against rechallenge with parental AB1 tumor, indicating that the transfectant induced long-term immunity. AB1-IL-12 induced systemic immunity that was effective at reducing the incidence of parental AB1 tumor at a distal site, but its effects were dose-dependent. Though both CD4(+) and CD8(+) cells infiltrated the rejecting tumor, CD8(+) effector cells were essential for protection against development of parental AB1 tumor. This study shows that paracrine secretion of IL-12, generated by gene transfer, can induce immunity against MM that can act locally and also at a distant site. In addition, there was no evidence of toxicity, which has been associated with the systemic administration of IL-12, indicating that this cytokine is a good candidate for experimental gene therapy in MM.

Tumor Antigens are Constitutively Presented in the Draining Lymph Nodes

Tumor growth is rarely associated with a strong specific CTL response, suggesting that the immune system is ignorant of the presence of tumor because the Ags are not readily available to or are sequestered from potential effector cells. We studied the in vivo activation of naive TCR transgenic hemagglutinin (HA)-specific CD8+ T cells adoptively transferred into mice bearing HA-expressing tumor using 5,6-carboxy-succinimidyl-fluorescein-ester labeling, which allows the identification of proliferating HA-specific T cells. We demonstrate that tumor Ags are constitutively presented in the lymph nodes draining tumors and are powerfully mitogenic for responding T cells despite the absence of anti-tumor CTL responses. Importantly, this proliferative signal occurs throughout tumor growth and is still detectable 6 mo after tumor inoculation when tumor is not palpable. These results provide the first evidence that there is constitutive presentation of tumor Ags in draining lymph nodes.