Jose I. Quetglas

Cancer Immunotherapy with Immunomodulatory Anti-CD137 and Anti–PD-1 Monoclonal Antibodies Requires BATF3-Dependent Dendritic Cells

UNLABELLED Weak and ineffective antitumor cytotoxic T lymphocyte (CTL) responses can be rescued by immunomodulatory mAbs targeting PD-1 or CD137. Using Batf3(-/-) mice, which are defective for cross-presentation of cell-associated antigens, we show that BATF3-dependent dendritic cells (DC) are essential for the response to therapy with anti-CD137 or anti-PD-1 mAbs. Batf3(-/-) mice failed to prime an endogenous CTL-mediated immune response toward tumor-associated antigens, including neoantigens. As a result, the immunomodulatory mAbs could not amplify any therapeutically functional immune response in these mice. Moreover, administration of systemic sFLT3L and local poly-ICLC enhanced DC-mediated cross-priming and synergized with anti-CD137- and anti-PD-1-mediated immunostimulation in tumor therapy against B16-ovalbumin-derived melanomas, whereas this function was lost in Batf3(-/-) mice. These experiments show that cross-priming of tumor antigens by FLT3L- and BATF3-dependent DCs is crucial to the efficacy of immunostimulatory mAbs and represents a very attractive point of intervention to enhance their clinical antitumor effects. SIGNIFICANCE Immunotherapy with immunostimulatory mAbs is currently achieving durable clinical responses in different types of cancer. We show that cross-priming of tumor antigens by BATF3-dependent DCs is a key limiting factor that can be exploited to enhance the antitumor efficacy of anti-PD-1 and anti-CD137 immunostimulatory mAbs.

Focusing and sustaining the antitumor CTL effector killer response by agonist anti-CD137 mAb

Significance Immunotherapy of cancer with immunomodulatory agents is achieving significant efficacy in an important fraction of patients. The stimulatory inducible receptor of T and NK lymphocytes known as CD137 or 4-1BB is being stimulated with agonist antibodies to enhance antitumor immunity in clinical trials. In addition, the intracellular signaling domain of CD137 is crucial as a component of successful anti-leukemia therapies with chimeric antigen receptors transduced into adoptively transferred T lymphocytes. In this study the marked synergistic effects of adoptive T cell and agonist anti-CD137 mAb therapies are studied, providing in vivo evidence for improved, more sustained and focused tumoricidal functions of antitumor cytotoxic T lymphocytes when under the influence of CD137-targeted pharmacological stimulation with immunostimulatory monoclonal antibodies. Cancer immunotherapy is undergoing significant progress due to recent clinical successes by refined adoptive T-cell transfer and immunostimulatory monoclonal Ab (mAbs). B16F10-derived OVA-expressing mouse melanomas resist curative immunotherapy with either adoptive transfer of activated anti-OVA OT1 CTLs or agonist anti-CD137 (4-1BB) mAb. However, when acting in synergistic combination, these treatments consistently achieve tumor eradication. Tumor-infiltrating lymphocytes that accomplish tumor rejection exhibit enhanced effector functions in both transferred OT-1 and endogenous cytotoxic T lymphocytes (CTLs). This is consistent with higher levels of expression of eomesodermin in transferred and endogenous CTLs and with intravital live-cell two-photon microscopy evidence for more efficacious CTL-mediated tumor cell killing. Anti-CD137 mAb treatment resulted in prolonged intratumor persistence of the OT1 CTL-effector cells and improved function with focused and confined interaction kinetics of OT-1 CTL with target cells and increased apoptosis induction lasting up to six days postadoptive transfer. The synergy of adoptive T-cell therapy and agonist anti-CD137 mAb thus results from in vivo enhancement and sustainment of effector functions.

Immunotherapeutic synergy between anti-CD137 mAb and intratumoral administration of a cytopathic Semliki Forest virus encoding IL-12.

Intratumoral injection of Semliki Forest virus encoding interleukin-12 (SFV-IL-12) combines acute expression of IL-12 and stressful apoptosis of infected malignant cells. Agonist antibodies directed to costimulatory receptor CD137 (4-1BB) strongly amplify pre-existing cellular immune responses toward weak tumor antigens. In this study, we provide evidence for powerful synergistic effects of a combined strategy consisting of intratumoral injection of SFV-IL-12 and systemic delivery of agonist anti-CD137 monoclonal antibodies (mAbs), which was substantiated against poorly immunogenic B16 melanomas (B16-OVA and B16.F10) and TC-1 lung carcinomas. Effector CD8(β)(+) T cells were sufficient to mediate complete tumor eradications. Accordingly, there was an intensely synergistic in vivo enhancement of cytotoxic T lymphocytes (CTL)-mediated immunity against the tumor antigens OVA and tyrosine-related protein-2 (TRP-2). This train of phenomena led to long-lasting tumor-specific immunity against rechallenge, attained transient control of the progression of concomitant tumor lesions that were not directly treated with SFV-IL-12 and caused autoimmune vitiligo. Importantly, we found that SFV-IL-12 intratumoral injection induces bright expression of CD137 on most tumor-infiltrating CD8(+) T lymphocytes, thereby providing more abundant targets for the action of the agonist antibody. This efficacious combinatorial immunotherapy strategy offers feasibility for clinical translation since anti-CD137 mAbs are already undergoing clinical trials and development of clinical-grade SFV-IL-12 vectors is in progress.

Semliki Forest Virus Expressing Interleukin-12 Induces Antiviral and Antitumoral Responses in Woodchucks with Chronic Viral Hepatitis and Hepatocellular Carcinoma

ABSTRACT A vector based on Semliki Forest virus (SFV) expressing high levels of interleukin-12 (SFV-enhIL-12) has previously demonstrated potent antitumoral efficacy in small rodents with hepatocellular carcinoma (HCC) induced by transplantation of tumor cells. In the present study, the infectivity and antitumoral/antiviral effects of SFV vectors were evaluated in the clinically more relevant woodchuck model, in which primary HCC is induced by chronic infection with woodchuck hepatitis virus (WHV). Intratumoral injection of SFV vectors expressing luciferase or IL-12 resulted in high reporter gene activity within tumors and cytokine secretion into serum, respectively, demonstrating that SFV vectors infect woodchuck tumor cells. For evaluating antitumoral efficacy, woodchuck tumors were injected with increasing doses of SFV-enhIL-12, and tumor size was measured by ultrasonography following treatment. In five (83%) of six woodchucks, a dose-dependent, partial tumor remission was observed, with reductions in tumor volume of up to 80%, but tumor growth was restored thereafter. Intratumoral treatment further produced transient changes in WHV viremia and antigenemia, with ≥1.5-log10 reductions in serum WHV DNA in half of the woodchucks. Antitumoral and antiviral effects were associated with T-cell responses to tumor and WHV antigens and with expression of CD4 and CD8 markers, gamma interferon, and tumor necrosis factor alpha in peripheral blood mononuclear cells, suggesting that immune responses against WHV and HCC had been induced. These experimental observations suggest that intratumoral administration of SFV-enhIL-12 may represent a strategy for treatment of chronic HBV infection and associated HCC in humans but indicate that this approach could benefit from further improvements.

Virotherapy with a Semliki Forest Virus–Based Vector Encoding IL12 Synergizes with PD-1/PD-L1 Blockade

Quetglas and colleagues report that intratumoral injection of cytolytic nonreplicative Semliki Forest virus vector expressing IL12, along with systemic administration of anti-PD-1/PD-L1 antibodies, induced regression of both virally injected and distal tumors and synergistically prolonged survival in mouse tumor models. Virotherapy and checkpoint inhibitors can be combined for the treatment of cancer with complementarity and potential for synergistic effects. We have developed a cytolytic but nonreplicative viral vector system based on Semliki Forest virus that encodes IL12 (SFV-IL12). Following direct intratumoral injection, infected cells release transgenic IL12, die, and elicit an inflammatory response triggered by both abundantly copied viral RNA and IL12. In difficult-to-treat mouse cancer models, such as those derived from MC38 and bilateral B16-OVA, SFV-IL12 synergized with an anti–PD-1 monoclonal antibody (mAb) to induce tumor regression and prolong survival. Similar synergistic effects were attained upon PD-L1 blockade. Combined SFV-IL12 + anti–PD-1 mAb treatment only marginally increased the elicited cytotoxic T-lymphocyte response over SFV-IL12 as a single agent, at least when measured by in vivo killing assays. In contrast, we observed that SFV-IL12 treatment induced expression of PD-L1 on tumor cells in an IFNγ-dependent fashion. PD-L1–mediated adaptive resistance thereby provides a mechanistic explanation of the observed synergistic effects achieved by the SFV-IL12 + anti–PD-1 mAb combination. Cancer Immunol Res; 3(5); 449–54. ©2015 AACR.

A novel system for the production of high levels of functional human therapeutic proteins in stable cells with a Semliki Forest virus noncytopathic vector

Semliki Forest virus (SFV) vectors lead to high protein expression in mammalian cells, but expression is transient due to vector cytopathic effects, inhibition of host cell proteins and RNA-based expression. We have used a noncytopathic SFV mutant (ncSFV) RNA vector to generate stable cell lines expressing two human therapeutic proteins: insulin-like growth factor I (IGF-I) and cardiotrophin-1 (CT-1). Therapeutic genes were fused at the carboxy-terminal end of Puromycin N-acetyl-transferase gene by using as a linker the sequence coding for foot-and-mouth disease virus (FMDV) 2A autoprotease. These cassettes were cloned into the ncSFV vector. Recombinant ncSFV vectors allowed rapid and efficient selection of stable BHK cell lines with puromycin. These cells expressed IGF-I and CT-1 in supernatants at levels reaching 1.4 and 8.6 microg/10(6)cells/24 hours, respectively. Two cell lines generated with each vector were passaged ten times during 30 days, showing constant levels of protein expression. Recombinant proteins expressed at different passages were functional by in vitro signaling assays. Stability at RNA level was unexpectedly high, showing a very low mutation rate in the CT-1 sequence, which did not increase at high passages. CT-1 was efficiently purified from supernatants of ncSFV cell lines, obtaining a yield of approximately 2mg/L/24 hours. These results indicate that the ncSFV vector has a great potential for the production of recombinant proteins in mammalian cells.

Safety and antitumor effect of oncolytic and helper-dependent adenoviruses expressing interleukin-12 variants in a hamster pancreatic cancer model

Gene transfer of potent immunostimulatory cytokines such as interleukin-12 (IL-12) is a potential treatment for advanced cancer. Different vectors and IL-12 modifications have been developed to avoid side effects associated with high serum levels of the cytokine, while preserving its antitumor properties. Here we have evaluated two alternative strategies using the Syrian hamster as a model for pancreatic cancer metastatic to the liver. Local administration of an oncolytic adenovirus (OAV) expressing a single-chain version of IL-12 caused transient, very intense elevations of IL-12 in serum, resulting in severe toxicity at sub-therapeutic doses. Anchoring IL-12 to the membrane of infected cells by fusion with the transmembrane domain of CD4 reduced systemic exposure to IL-12 and increased the tolerance to the OAV. However, only a modest increase in the therapeutic range was achieved because antitumor potency was also reduced. In contrast, systemic administration of a helper-dependent adenoviral vector (HDAd) equipped with a Mifepristone-inducible expression system allowed sustained and controlled IL-12 production from the liver. This treatment was well tolerated and inhibited the progression of hepatic metastases. We conclude that HDAds are safer than OAVs for the delivery of IL-12, and are promising vectors for immunogene therapy approaches against pancreatic cancer.

Strict Requirement for Vector-Induced Type I Interferon in Efficacious Antitumor Responses to Virally Encoded IL12

Host responses are increasingly considered important for the efficacious response to experimental cancer therapies that employ viral vectors, but little is known about the specific nature of host responses required. In this study, we investigated the role of host type I interferons (IFN-I) in the efficacy of virally delivered therapeutic genes. Specifically, we used a Semliki Forest virus encoding IL12 (SFV-IL12) based on its promise as an RNA viral vector for cancer treatment. Intratumoral injection of SFV-IL12 induced production of IFN-I as detected in serum. IFN-I production was abolished in mice deficient for the IFNβ transcriptional regulator IPS-1 and partially attenuated in mice deficient for the IFNβ signaling protein TRIF. Use of bone marrow chimeric hosts established that both hematopoietic and stromal cells were involved in IFN-I production. Macrophages, plasmacytoid, and conventional dendritic cells were each implicated based on cell depletion experiments. Further, mice deficient in the IFN-I receptor (IFNAR) abolished the therapeutic activity of SFV-IL12, as did a specific antibody-mediated blockade of IFNAR signaling. Reduced efficacy was not caused by an impairment in IL12 expression, because IFNAR-deficient mice expressed the viral IL12 transgene even more strongly than wild-type (WT) hosts. Chimeric host analysis for the IFNAR involvement established a strict requirement in hematopoietic cells. Notably, although tumor-specific CD8 T lymphocytes expanded robustly after intratumoral injection of WT mice with SFV-IL12, this did not occur in mice where IFNAR was inactivated genetically or pharmacologically. Overall, our results argued that the antitumor efficacy of a virally based transgene therapeutic relied strongly on a vector-induced IFN-I response, revealing an unexpected mechanism of action that is relevant to a broad array of current translational products in cancer research.

Eradication of Liver-Implanted Tumors by Semliki Forest Virus Expressing IL-12 Requires Efficient Long-Term Immune Responses

Semliki Forest virus vectors expressing IL-12 (SFV–IL-12) were shown to induce potent antitumor responses against s.c. MC38 colon adenocarcinomas in immunocompetent mice. However, when MC38 tumors were implanted in liver, where colon tumors usually metastasize, SFV–IL-12 efficacy was significantly reduced. We reasoned that characterization of immune responses against intrahepatic tumors in responder and nonresponder animals could provide useful information for designing more potent antitumor strategies. Remarkably, SFV–IL-12 induced a high percentage of circulating tumor-specific CD8 T cells in all treated animals. Depletion studies showed that these cells were essential for SFV–IL-12 antitumor activity. However, in comparison with nonresponders, tumor-specific cells from responder mice acquired an effector-like phenotype significantly earlier, were recruited more efficiently to the liver, and, importantly, persisted for a longer period of time. All treated mice had high levels of functional specific CD8 T cells at 8 d posttreatment reflected by both in vivo killing and IFN-γ–production assays, but responder animals showed a more avid and persistent IFN-γ response. Interestingly, differences in immune responses between responders and nonresponders seemed to correlate with the immune status of the animals before treatment and were not due to the treatment itself. Mice that rejected tumors were protected against tumor rechallenge, indicating that sustained memory responses are required for an efficacious therapy. Interestingly, tumor-specific CD8 T cells of responder animals showed upregulation of IL-15Rα expression compared with nonresponders. These results suggest that SFV–IL-12 therapy could benefit from the use of strategies that could either upregulate IL-15Rα expression or activate this receptor.

A Semliki Forest virus vector engineered to express IFNα induces efficient elimination of established tumors

Semliki Forest virus (SFV) represents a promising gene therapy vector for tumor treatment, because it produces high levels of recombinant therapeutic proteins while inducing apoptosis in infected cells. In this study, we constructed a SFV vector expressing murine interferon alpha (IFNα). IFNα displays antitumor activity mainly by enhancing an antitumor immune response, as well as by a direct antiproliferative effect. In spite of the antiviral activity of IFNα, SFV–IFN could be produced in BHK cells at high titers. This vector was able to infect TC-1 cells, a tumor cell line expressing E6 and E7 proteins of human papillomavirus, leading to high production of IFNα both in vitro and in vivo. When injected into subcutaneous TC-1 tumors implanted in mice, SFV–IFN was able to induce an E7-specific cytotoxic T lymphocyte response, and to modify tumor infiltrating immune cells, reducing the percentage of T regulatory cells and activating myeloid cells. As a consequence, SFV–IFN was able to eradicate 58% of established tumors treated 21 days after implantation with long-term tumor-free survival and very low toxicity. SFV–IFN was also able to induce significant antitumor responses in a subcutaneous tumor model of murine colon adenocarcimoma. These data suggest that local production of IFNα by intratumoral injection of recombinant SFV–IFN could represent a potent new strategy to treat tumors in patients.