VSV oncolytic virotherapy in the B16 model depends upon intact MyD88 signaling

Molecular Circuits of Immune Sensing and Response to Oncolytic Virotherapy

Oncolytic virotherapy is a promising immunotherapy approach for cancer treatment that utilizes viruses to preferentially infect and eliminate cancer cells while stimulating the immune response. In this review, we synthesize the current literature on the molecular circuits of immune sensing and response to oncolytic virotherapy, focusing on viral DNA or RNA sensing by infected cells, cytokine and danger-associated-signal sensing by neighboring cells, and the subsequent downstream activation of immune pathways. These sequential sense-and-response mechanisms involve the triggering of molecular sensors by viruses or infected cells to activate transcription factors and related genes for a breadth of immune responses. We describe how the molecular signals induced in the tumor upon virotherapy can trigger diverse immune signaling pathways, activating both antigen-presenting-cell-based innate and T cell-based adaptive immune responses. Insights into these complex mechanisms provide valuable knowledge for enhancing oncolytic virotherapy strategies.

Chimerization of the Anti-Viral CD8+ T Cell Response with A Broad Anti-Tumor T Cell Response Reverses Inhibition of Checkpoint Blockade Therapy by Oncolytic Virotherapy

Although immune checkpoint inhibition (ICI) has produced profound survival benefits in a broad variety of tumors, a proportion of patients do not respond. Treatment failure is in part due to immune suppressive tumor microenvironments (TME), which is particularly true of hepatocellular carcinoma (HCC). Since oncolytic viruses (OV) can generate a highly immune-infiltrated, inflammatory TME, we developed a vesicular stomatitis virus expressing interferon-ß (VSV-IFNß) as a viro-immunotherapy against HCC. Since HCC standard of care atezolizumab/bevacizumab incorporates ICI, we tested the hypothesis that pro-inflammatory VSV-IFNß would recruit, prime, and activate anti-tumor T cells, whose activity anti-PD-L1 ICI would potentiate. However, in a partially anti-PD-L1-responsive model of HCC, addition of VSV-IFNß abolished anti-PD-L1 therapy. Cytometry by Time of Flight showed that VSV-IFNß expanded dominant anti-viral effector CD8 T cells with concomitant, relative disappearance of anti-tumor T cell populations which are the target of anti-PD-L1. However, by expressing a range of HCC tumor antigens within VSV, the potent anti-viral response became amalgamated with an anti-tumor T cell response generating highly significant cures compared to anti-PD-L1 ICI alone. Our data provide a cautionary message for the use of highly immunogenic viruses as tumor-specific immune-therapeutics by showing that dominant anti-viral T cell responses can inhibit sub-dominant anti-tumor T cell responses. However, by chimerizing anti-viral and anti-tumor T cell responses through encoding tumor antigens within the virus, oncolytic virotherapy can be purposed for very effective immune driven tumor clearance and can generate anti-tumor T cell populations upon which immune checkpoint blockade can effectively work.

Trap and ambush therapy using sequential primary and tumor escape-selective oncolytic viruses

In multiple models of oncolytic virotherapy, it is common to see an early anti-tumor response followed by recurrence. We have previously shown that frontline treatment with oncolytic VSV-IFN-β induces APOBEC proteins, promoting the selection of specific mutations that allow tumor escape. Of these mutations in B16 melanoma escape (ESC) cells, a C-T point mutation in the cold shock domain-containing E1 (CSDE1) gene was present at the highest frequency, which could be used to ambush ESC cells by vaccination with the mutant CSDE1 expressed within the virus. Here, we show that the evolution of viral ESC tumor cells harboring the escape-promoting CSDE1C-T mutation can also be exploited by a virological ambush. By sequential delivery of two oncolytic VSVs in vivo, tumors which would otherwise escape VSV-IFN-β oncolytic virotherapy could be cured. This also facilitated the priming of anti-tumor T cell responses, which could be further exploited using immune checkpoint blockade with the CD200 activation receptor ligand (CD200AR-L) peptide. Our findings here are significant in that they offer the possibility to develop oncolytic viruses as highly specific, escape-targeting viro-immunotherapeutic agents to be used in conjunction with recurrence of tumors following multiple different types of frontline cancer therapies.

Repeated dosing improves oncolytic rhabdovirus therapy in mice via interactions with intravascular monocytes

There is debate in the field of oncolytic virus (OV) therapy, whether a single viral dose, or multiple administrations, is better for tumor control. Using intravital microscopy, we describe the fate of vesicular stomatitis virus (VSV) delivered systemically as a first or a second dose. Following primary administration, VSV binds to the endothelium, initiates tumor infection and activates a proinflammatory response. This initial OV dose induces neutrophil migration into the tumor and limits viral replication. OV administered as a second dose fails to infect the tumor and is captured by intravascular monocytes. Despite a lack of direct infection, this second viral dose, in a monocyte-dependent fashion, enhances and sustains infection by the first viral dose, promotes CD8 T cell recruitment, delays tumor growth and improves survival in multi-dosing OV therapy. Thus, repeated VSV dosing engages monocytes to post-condition the tumor microenvironment for improved infection and anticancer T cell responses. Understanding the complex interactions between the subsequent viral doses is crucial for improving the efficiency of OV therapy and virus-based vaccines.

RIG-I-mediated innate immune signaling in tumors reduces the therapeutic effect of oncolytic vesicular stomatitis virus

BACKGROUND

Oncolytic viral therapy is a promising method for tumor treatment. Currently, several oncolytic viruses (OVs) have been used as tumor therapy at different phases of research and clinical trials. OVs not only directly lyse tumor cells due to viral replication but also initiate host antitumor immune responses. Previous studies have primarily focused on how OVs activate adaptive immune responses in immune cells. However, the role of innate immune responses in tumors induced by OVs remains unclear.

METHODS

To determine the innate immune responses induced by vesicular stomatitis virus (VSV), the mutant VSV^ΔM51 strain was used for the infection and quantitative polymerase chain reaction (qPCR) was employed to measure the transcriptional levels of antiviral genes. The knockdown efficiency of RIG-I was examined by qPCR. Viral titers were measured by plaque assays. Tumor models were established by intradermally implanting RIG-I-knockdown and control LLC cells into the flank of wild type C57BL/6J mice. When the tumors reached approximately 50mm³ , they were infected with VSV^ΔM51 via intratumoral injections to examine its therapeutic effect.

RESULTS

Infection with VSV^ΔM51 triggered remarkable innate immune responses in several tumor cell lines through the cytoplasmic RIG-I sensing pathway. Moreover, we found that intratumoral injection of VSV^ΔM51 effectively reduced tumor growth in murine LCC lung cancer model. Importantly, VSV^ΔM51 -induced antitumor therapy was more effective in murine LLC tumor model established using Rig-I-knockdown cells compared with the tumor model established using control cells.

CONCLUSION

RIG-I-mediated innate immune signaling in tumor cells plays a negative role in regulating antitumor therapy with VSV^ΔM51 virus.

Cutting both ways: the innate immune response to oncolytic virotherapy

Oncolytic viruses (OVs), above and beyond infecting and lysing malignant cells, interact with the immune system in complex ways that have important therapeutic significance. While investigation into these interactions is still in its early stages, important insights have been made over the past two decades that will help improve the clinical efficacy of OV-based management strategies in cancer care moving forward. The inherent immunosuppression that defines the tumor microenvironment can be modified by OV infection, and the subsequent recruitment and activation of innate immune cells, in particular, is central to this. Indeed, neutrophils, macrophages, natural killer cells, and dendritic cells, as well as other populations such as myeloid-derived suppressor cells, are key to the immune escape that allows tumors to survive, but their natural response to infection can be exploited by virotherapy. While stimulation of innate immune cells by OVs can initiate antitumor responses, related antiviral activity can limit virus spread and direct cytopathogenic effects. In this review, we highlight how each innate immune cell population influences this balance of antitumor and antiviral forces during virotherapy, some of the important molecular pathways that have been identified, and specific therapeutic targets that have emerged through this work. We discuss the importance of OV-based combination therapies in optimizing antiviral and antitumor innate immune responses stimulated by virotherapy toward tumor eradication, and how these processes vary depending on the tumor and OV in question. Rather than concentrating on a particular OV species in the review, we present the range of effects that have been documented across OV types to emphasize the context-specific nature of these interactions and how this is important in the design of future OV-based treatment approaches.

Oncolytic virotherapy induced CSDE1 neo-antigenesis restricts VSV replication but can be targeted by immunotherapy

In our clinical trials of oncolytic vesicular stomatitis virus expressing interferon beta (VSV-IFNβ), several patients achieved initial responses followed by aggressive relapse. We show here that VSV-IFNβ-escape tumors predictably express a point-mutated CSDE1P5S form of the RNA-binding Cold Shock Domain-containing E1 protein, which promotes escape as an inhibitor of VSV replication by disrupting viral transcription. Given time, VSV-IFNβ evolves a compensatory mutation in the P/M Inter-Genic Region which rescues replication in CSDE1P5S cells. These data show that CSDE1 is a major cellular co-factor for VSV replication. However, CSDE1P5S also generates a neo-epitope recognized by non-tolerized T cells. We exploit this predictable neo-antigenesis to drive, and trap, tumors into an escape phenotype, which can be ambushed by vaccination against CSDE1P5S, preventing tumor escape. Combining frontline therapy with escape-targeting immunotherapy will be applicable across multiple therapies which drive tumor mutation/evolution and simultaneously generate novel, targetable immunopeptidomes associated with acquired treatment resistance.

Parking CAR T Cells in Tumours: Oncolytic Viruses as Valets or Vandals?

Oncolytic viruses (OVs) and adoptive T cell therapy (ACT) each possess direct tumour cytolytic capabilities, and their combination potentially seems like a match made in heaven to complement the strengths and weakness of each modality. While providing strong innate immune stimulation that can mobilize adaptive responses, the magnitude of anti-tumour T cell priming induced by OVs is often modest. Chimeric antigen receptor (CAR) modified T cells bypass conventional T cell education through introduction of a synthetic receptor; however, realization of their full therapeutic properties can be stunted by the heavily immune-suppressive nature of the tumour microenvironment (TME). Oncolytic viruses have thus been seen as a natural ally to overcome immunosuppressive mechanisms in the TME which limit CAR T cell infiltration and functionality. Engineering has further endowed viruses with the ability to express transgenes in situ to relieve T cell tumour-intrinsic resistance mechanisms and decorate the tumour with antigen to overcome antigen heterogeneity or loss. Despite this helpful remodeling of the tumour microenvironment, it has simultaneously become clear that not all virus induced effects are favourable for CAR T, begging the question whether viruses act as valets ushering CAR T into their active site, or vandals which cause chaos leading to both tumour and T cell death. Herein, we summarize recent studies combining these two therapeutic modalities and seek to place them within the broader context of viral T cell immunology which will help to overcome the current limitations of effective CAR T therapy to make the most of combinatorial strategies.

Remodeling of Tumor Immune Microenvironment by Oncolytic Viruses

Oncolytic viruses (OVs) are potential antitumor agents with unique therapeutic mechanisms. They possess the ability of direct oncolysis and the induction of antitumor immunity. OV can be genetically engineered to potentiate antitumor efficacy by remodeling the tumor immune microenvironment. The present mini review mainly describes the effect of OVs on remodeling of the tumor immune microenvironment and explores the mechanism of regulation of the host immune system and the promotion of the immune cells to destroy carcinoma cells by OVs. Furthermore, this article focuses on the utilization of OVs as vectors for the delivery of immunomodulatory cytokines or antibodies.

Oncolytic Adenovirus ORCA-010 Activates Proinflammatory Myeloid Cells and Facilitates T Cell Recruitment and Activation by PD-1 Blockade in Melanoma

Immune checkpoint inhibitors have advanced the treatment of melanoma. Nevertheless, a majority of patients are resistant, or develop resistance, to immune checkpoint blockade, which may be related to prevailing immune suppression by myeloid regulatory cells in the tumor microenvironment (TME). ORCA-010 is a novel oncolytic adenovirus that selectively replicates in, and lyses, cancer cells. We previously showed that ORCA-010 can activate melanoma-exposed conventional dendritic cells (cDCs). To study the effect of ORCA-010 on melanoma-conditioned macrophage development, we used an in vitro co-culture model of human monocytes with melanoma cell lines. We observed a selective survival and polarization of monocytes into M2-like macrophages (CD14⁺CD80^-CD163⁺) in co-cultures with cell lines that expressed macrophage colony-stimulating factor. Oncolysis of these melanoma cell lines, effected by ORCA-010, activated the resulting macrophages and converted them to a more proinflammatory state, evidenced by higher levels of PD-L1, CD80, and CD86 and an enhanced capacity to prime allogenic T cells and induce a type-1 T cell response. To assess the effect of ORCA-010 on myeloid subset distribution and activation in vivo, ORCA-010 was intratumorally injected and tested for T cell activation and recruitment in the human adenovirus nonpermissive B16-OVA mouse melanoma model. While systemic PD-1 blockade in this model in itself did not modulate myeloid or T cell subset distribution and activation, when it was preceded by i.t. injection of ORCA-010, this induced an increased rate and activation state of CD8α⁺ cDC1, both in the TME and in the spleen. Observed increased rates of activated CD8⁺ T cells, expressing CD69 and PD-1, were related to both increased CD8α⁺ cDC1 rates and M1/M2 shifts in tumor and spleen. In conclusion, the myeloid modulatory properties of ORCA-010 in melanoma, resulting in recruitment and activation of T cells, could enhance the antitumor efficacy of PD-1 blockade.

Cytokines in oncolytic virotherapy

Tumors represent a hostile environment for the effector cells of cancer immunosurveillance. Immunosuppressive receptors and soluble or membrane-bound ligands are abundantly exposed and released by malignant entities and their stromal accomplices. As a consequence, executioners of antitumor immunity inefficiently navigate across cancer tissues and fail to eliminate malignant targets. By inducing immunogenic cancer cell death, oncolytic viruses profoundly reshape the tumor microenvironment. They trigger the local spread of danger signals and tumor-associated (as well as viral) antigens, thus attracting antigen-presenting cells, promoting the activation and expansion of lymphocytic populations, facilitating their infiltration in the tumor bed, and reinvigorating cytotoxic immune activity. The present review recapitulates key chemokines, growth factors and other cytokines that orchestrate this ballet of antitumoral leukocytes upon oncolytic virotherapy.

Characterization of the Impact of Oncolytic Vesicular Stomatitis Virus on the Trafficking, Phenotype, and Antigen Presentation Potential of Neutrophils and Their Ability to Acquire a Non-Structural Viral Protein

Neutrophils are innate leukocytes that mount a rapid response to invading pathogens and sites of inflammation. Although neutrophils were traditionally considered responders to bacterial infections, recent advances have demonstrated that they are interconnected with both viral infections and cancers. One promising treatment strategy for cancers is to administer an oncolytic virus to activate the immune system and directly lyse cancerous cells. A detailed characterization of how the innate immune system responds to a viral-based therapy is paramount in identifying its systemic effects. This study analyzed how administering the rhabdovirus vesicular stomatitis virus (VSV) intravenously at 1 × 10⁹ PFU acutely influenced neutrophil populations. Bone marrow, blood, lungs, and spleen were acquired three- and 24-h after administration of VSV for analysis of neutrophils by flow cytometry. Infection with VSV caused neutrophils to rapidly egress from the bone marrow and accumulate in the lungs. A dramatic increase in immature neutrophils was observed in the lungs, as was an increase in the antigen presentation potential of these cells within the spleen. Furthermore, the potential for neutrophils to acquire viral transgene-encoded proteins was monitored using a variant of VSV that expressed enhanced green fluorescent protein (GFP). If an in vitro population of splenocytes were exposed to αCD3 and αCD28, a substantial proportion of the neutrophils would become GFP-positive. This suggested that the neutrophils could either acquire more virus-encoded antigens from infected splenocytes or were being directly infected. Five different dosing regimens were tested in mice, and it was determined that a single dose of VSV or two doses of VSV administered at a 24-h interval, resulted in a substantial proportion of neutrophils in the bone marrow becoming GFP-positive. This correlated with a decrease in the number of splenic neutrophils. Two doses administered at intervals longer than 24-h did not have these effects, suggesting that neutrophils became resistant to antigen uptake or direct infection with VSV beyond 24-h of activation. These findings implicated neutrophils as major contributors to oncolytic rhabdoviral therapies. They also provide several clear future directions for research and suggest that neutrophils should be carefully monitored during the development of all oncolytic virus-based treatment regimens.

Initial dose of oncolytic myxoma virus programs durable antitumor immunity independent of in vivo viral replication

Background

Oncolytic therapy uses live-replicating viruses to improve the immunological status of treated tumors. Critically, while these viruses are known to self-amplify in vivo, clinical oncolytic therapies still appear to display a strong dose dependence and the mechanisms mediating this dose dependence are not well understood.

Methods

To explore this apparent contradiction, we investigated how the initial dose of oncolytic myxoma virus affected the subsequent ability of treatment to alter the immunological status of tumors as well as synergize with programmed cell death protein 1 (PD1) blockade.

Results

Our results indicate that, due to viral self-amplification in vivo, the overall load of myxoma virus rapidly normalizes within treated tumors despite up to 3-log differences in inoculating dose. Because of this, therapeutic efficacy in the absence of checkpoint blockade is largely dose independent. Despite this rapid normalization, however, treatment with high or low doses of myxoma virus induces distinct immunological changes within treated tumors. Critically, these changes appear to be durably programmed based on the initial oncolytic dose with low-dose treatment failing to induce immunological improvements despite rapidly achieving equivalent viral burdens. Finally, due to the distinct immunological profiles induced by high and low myxoma virus doses, oncolytic efficacy resulting from combination with PD1 blockade therapy displays a strong dose dependence.

Conclusions

Taken together, these data suggest that the ability of oncolytic myxoma virus to immunologically reprogram treated tumors is dependent on initial viral dose. Additionally, this work could provide a possible mechanistic explanation for clinical results observed with other oncolytic viruses.

Transcatheter arterial embolization combined with hypoxia-replicative oncolytic adenovirus perfusion enhances the therapeutic effect of hepatic carcinoma

Purpose

Transcatheter arterial embolization or transcatheter arterial chemoembolization has become a critical therapy for unresectable hepatocarcinoma. Although hypoxia caused by embolization can induce apoptosis and necrosis of the majority of tumor cells, a small proportion of cells can survive with hypoxia and chemotherapy resistance. HIF-1α induced by hypoxia is the key factor rendering surviving tumor cells invasive and metastatic properties. Thus, we generated a synthetic hypoxia-replicative oncolytic adenovirus (HYAD) expecting to further eliminate the surviving tumor cells, which expressed HIF-1α.

Materials and methods

In our study, we detected protein expression, proliferation, apoptosis, and necrosis of hepatic tumor cell line when infected with HYAD under hypoxia and normoxia. And we constructed VX2 hepatic cancer rabbit models to explore the therapeutic effect of transcatheter arterial embolization combined with HYAD perfusion under digital subtraction angiography. Inhibition of tumor growth and invasion was detected by histopathological examination and contrast-enhanced CT scan.

Results

Experiments in vitro verified that HYAD expressed and replicated along with HIF-1α expression or hypoxia. Compared with wild adenovirus type 5 (WT), HYAD expressed much more under hypoxia, which was the main principle of HYAD killing surviving tumor cells posttransarterial embolization. In vivo experiment of VX2 models, HYAD perfusion combined with polyvinyl alcohol (PVA) embolization achieved the highest expression quantity and the longest expression duration compared with simple HYAD perfusion, WT perfusion combined with PVA embolization, and simple WT perfusion. Because adenovirus expression protein E1A had the properties of promoting apoptosis, inhibiting invasion, and inhibiting metastasis, HYAD perfusion combined with PVA embolization group efficiently repressed tumor growth and intrahepatic metastases compared to other processing groups.

Conclusion

HYAD can overcome the hypoxic tumor microenvironment postembolization and target the surviving tumor cells with specificity. In turn, HYAD perfusion combined with PVA embolization can bring out the best effect in each other.

Oncolytic viruses as engineering platforms for combination immunotherapy

To effectively build on the recent successes of immune checkpoint blockade, adoptive T cell therapy and cancer vaccines, it is critical to rationally design combination strategies that will increase and extend efficacy to a larger proportion of patients. For example, the combination of anti-cytotoxic T lymphocyte-associated antigen 4 (CTLA4) and anti-programmed cell death protein 1 (PD1) immune checkpoint inhibitors essentially doubles the response rate in certain patients with metastatic melanoma. However, given the heterogeneity of cancer, it seems likely that even more complex combinations of immunomodulatory agents may be required to obtain consistent, durable therapeutic responses against a broad spectrum of cancers. This carries serious implications in terms of toxicities for patients, feasibility for care providers and costs for health-care systems. A compelling solution is offered by oncolytic viruses (OVs), which can be engineered to selectively replicate within and destroy tumour tissue while simultaneously augmenting antitumour immunity. In this Opinion article, we argue that the future of immunotherapy will include OVs that function as multiplexed immune-modulating platforms expressing factors such as immune checkpoint inhibitors, tumour antigens, cytokines and T cell engagers. We illustrate this concept by following the trials and tribulations of tumour-reactive T cells from their initial priming through to the execution of cytotoxic effector function in the tumour bed. We highlight the myriad opportunities for OVs to help overcome critical barriers in the T cell journey, leading to new synergistic mechanisms in the battle against cancer.

Oncolytic reovirus as a combined antiviral and anti-tumour agent for the treatment of liver cancer

OBJECTIVE

Oncolytic viruses (OVs) represent promising, proinflammatory cancer treatments. Here, we explored whether OV-induced innate immune responses could simultaneously inhibit HCV while suppressing hepatocellular carcinoma (HCC). Furthermore, we extended this exemplar to other models of virus-associated cancer.

DESIGN AND RESULTS

Clinical grade oncolytic orthoreovirus (Reo) elicited innate immune activation within primary human liver tissue in the absence of cytotoxicity and independently of viral genome replication. As well as achieving therapy in preclinical models of HCC through the activation of innate degranulating immune cells, Reo-induced cytokine responses efficiently suppressed HCV replication both in vitro and in vivo. Furthermore, Reo-induced innate responses were also effective against models of HBV-associated HCC, as well as an alternative endogenous model of Epstein-Barr virus-associated lymphoma. Interestingly, Reo appeared superior to the majority of OVs in its ability to elicit innate inflammatory responses from primary liver tissue.

CONCLUSIONS

We propose that Reo and other select proinflammatory OV may be used in the treatment of multiple cancers associated with oncogenic virus infections, simultaneously reducing both virus-associated oncogenic drive and tumour burden. In the case of HCV-associated HCC (HCV-HCC), Reo should be considered as an alternative agent to supplement and support current HCV-HCC therapies, particularly in those countries where access to new HCV antiviral treatments may be limited.

Oncotargeting by Vesicular Stomatitis Virus (VSV): Advances in Cancer Therapy

Modern oncotherapy approaches are based on inducing controlled apoptosis in tumor cells. Although a number of apoptosis-induction approaches are available, site-specific delivery of therapeutic agents still remain the biggest hurdle in achieving the desired cancer treatment benefit. Additionally, systemic treatment-induced toxicity remains a major limiting factor in chemotherapy. To specifically address drug-accessibility and chemotherapy side effects, oncolytic virotherapy (OV) has emerged as a novel cancer treatment alternative. In OV, recombinant viruses with higher replication capacity and stronger lytic properties are being considered for tumor cell-targeting and subsequent cell lysing. Successful application of OVs lies in achieving strict tumor-specific tropism called oncotropism, which is contingent upon the biophysical interactions of tumor cell surface receptors with viral receptors and subsequent replication of oncolytic viruses in cancer cells. In this direction, few viral vector platforms have been developed and some of these have entered pre-clinical/clinical trials. Among these, the Vesicular stomatitis virus (VSV)-based platform shows high promise, as it is not pathogenic to humans. Further, modern molecular biology techniques such as reverse genetics tools have favorably advanced this field by creating efficient recombinant VSVs for OV; some have entered into clinical trials. In this review, we discuss the current status of VSV based oncotherapy, challenges, and future perspectives regarding its therapeutic applications in the cancer treatment.

A classical PKA inhibitor increases the oncolytic effect of M1 virus via activation of exchange protein directly activated by cAMP 1

Oncolytic virotherapy is an emerging and promising treatment modality that uses replicating viruses as selective antitumor agents. Here, we report that a classical protein kinase A (PKA) inhibitor, H89, synergizes with oncolytic virus M1 in various cancer cells through activation of Epac1 (exchange protein directly activated by cAMP 1). H89 substantially increases viral replication in refractory cancer cells, leading to unresolvable Endoplasmic Reticulum stress, and cell apoptosis. Microarray analysis indicates that H89 blunts antiviral response in refractory cancer cells through retarding the nuclear translocation of NF-κB. Importantly, in vivo studies show significant antitumor effects during M1/H89 combination treatment. Overall, this study reveals a previously unappreciated role for H89 and demonstrates that activation of the Epac1 activity can improve the responsiveness of biotherapeutic agents for cancer.

Immune Checkpoint Blockade, Immunogenic Chemotherapy or IFN-α Blockade Boost the Local and Abscopal Effects of Oncolytic Virotherapy

Athough the clinical efficacy of oncolytic viruses has been demonstrated for local treatment, the ability to induce immune-mediated regression of distant metastases is still poorly documented. We report here that the engineered oncolytic vaccinia virus VV_WR-TK^-RR^--Fcu1 can induce immunogenic cell death and generate a systemic immune response. Effects on tumor growth and survival was largely driven by CD8⁺ T cells, and immune cell infiltrate in the tumor could be reprogrammed toward a higher ratio of effector T cells to regulatory CD4⁺ T cells. The key role of type 1 IFN pathway in oncolytic virotherapy was also highlighted, as we observed a strong abscopal response in Ifnar^-/- tumors. In this model, single administration of virus directly into the tumors on one flank led to regression in the contralateral flank. Moreover, these effects were further enhanced when oncolytic treatment was combined with immunogenic chemotherapy or with immune checkpoint blockade. Taken together, our results suggest how to safely improve the efficacy of local oncolytic virotherapy in patients whose tumors are characterized by dysregulated IFNα signaling. Cancer Res; 77(15); 4146-57. ©2017 AACR.

Oncolytic Vesicular Stomatitis Virus as a Viro-Immunotherapy: Defeating Cancer with a "Hammer" and "Anvil"

Oncolytic viruses have gained much attention in recent years, due, not only to their ability to selectively replicate in and lyse tumor cells, but to their potential to stimulate antitumor immune responses directed against the tumor. Vesicular stomatitis virus (VSV), a negative-strand RNA virus, is under intense development as an oncolytic virus due to a variety of favorable properties, including its rapid replication kinetics, inherent tumor specificity, and its potential to elicit a broad range of immunomodulatory responses to break immune tolerance in the tumor microenvironment. Based on this powerful platform, a multitude of strategies have been applied to further improve the immune-stimulating potential of VSV and synergize these responses with the direct oncolytic effect. These strategies include: 1. modification of endogenous virus genes to stimulate interferon induction; 2. virus-mediated expression of cytokines or immune-stimulatory molecules to enhance anti-tumor immune responses; 3. vaccination approaches to stimulate adaptive immune responses against a tumor antigen; 4. combination with adoptive immune cell therapy for potentially synergistic therapeutic responses. A summary of these approaches will be presented in this review.

Murine Tumor Models for Oncolytic Rhabdo-Virotherapy

The preclinical optimization and validation of novel treatments for cancer therapy requires the use of laboratory animals. Although in vitro experiments using tumor cell lines and ex vivo treatment of patient tumor samples provide a remarkable first-line tool for the initial study of tumoricidal potential, tumor-bearing animals remain the primary option to study delivery, efficacy, and safety of therapies in the context of a complete tumor microenvironment and functional immune system. In this review, we will describe the use of murine tumor models for oncolytic virotherapy using vesicular stomatitis virus. We will discuss studies using immunocompetent and immunodeficient models with respect to toxicity and therapeutic treatments, as well as the various techniques and tools available to study cancer therapy with Rhabdoviruses.

Colonization of xenograft tumors by oncolytic vaccinia virus (VACV) results in enhanced tumor killing due to the involvement of myeloid cells

Background

The mechanisms by which vaccinia virus (VACV) interacts with the innate immune components are complex and involve different mechanisms. iNOS-mediated NO production by myeloid cells is one of the central antiviral mechanisms and this study aims to investigate specifically whether iNOS-mediated NO production by myeloid cells, is involved in tumor eradication following the virus treatment.

Methods

Human colon adenocarcinoma (HCT-116) xenograft tumors were infected by VACV. Infiltration of iNOS⁺ myeloid cell population into the tumor, and virus titer was monitored following the treatment. Single-cell suspensions were stained for qualitative and quantitative flow analysis. The effect of different myeloid cell subsets on tumor growth and colonization were investigated by depletion studies. Finally, in vitro culture experiments were carried out to study NO production and tumor cell killing. Student’s t test was used for comparison between groups in all of the experiments.

Results

Infection of human colon adenocarcinoma (HCT-116) xenograft tumors by VACV has led to recruitment of many CD11b⁺ ly6G⁺ myeloid-derived suppressor cells (MDSCs), with enhanced iNOS expression in the tumors, and to an increased intratumoral virus titer between days 7 and 10 post-VACV therapy. In parallel, both single and multiple rounds of iNOS-producing cell depletions caused very rapid tumor growth within the same period after virus injection, indicating that VACV-induced iNOS⁺ MDSCs could be an important antitumor effector component. A continuous blockade of iNOS by its specific inhibitor, L-NIL, showed similar tumor growth enhancement 7–10 days post-infection. Finally, spleen-derived iNOS⁺ MDSCs isolated from virus-injected tumor bearing mice produced higher amounts of NO and effectively killed HCT-116 cells in in vitro transwell experiments.

Conclusions

We initially hypothesized that NO could be one of the factors that limits active spreading of the virus in the cancerous tissue. In contrast to our initial hypothesis, we observed that PMN-MDSCs were the main producer of NO through iNOS and NO provided a beneficial antitumor effect, The results strongly support an important novel role for VACV infection in the tumor microenvironment. VACV convert tumor-promoting MDSCs into tumor-killing cells by inducing higher NO production.

Immunogenicity of self tumor associated proteins is enhanced through protein truncation

We showed previously that therapy with Vesicular Stomatitis Virus (VSV) expressing tumor-associated proteins eradicates established tumors. We show here that when cellular cDNA were cloned into VSV which retained their own poly-A signal, viral species emerged in culture which had deleted the cellular poly-A signal and also contained a truncated form of the protein coding sequence. Typically, the truncation occurred such that a Tyrosine-encoding codon was converted into a STOP codon. We believe that the truncation of tumor-associated proteins expressed from VSV in this way occurred to preserve the ability of the virus to replicate efficiently. Truncated cDNA expressed from VSV were significantly more effective than full length cDNA in treating established tumors. Moreover, tumor therapy with truncated cDNA was completely abolished by depletion of CD4+ T cells, whereas therapy with full length cDNA was CD8+ T cell dependent. These data show that the type/potency of antitumor immune responses against self-tumor-associated proteins can be manipulated in vivo through the nature of the self protein (full length or truncated). Therefore, in addition to generation of neoantigens through sequence mutation, immunological tolerance against self-tumor-associated proteins can be broken through manipulation of protein integrity, allowing for rational design of better self-immunogens for cancer immunotherapy.

Big Data Offers Novel Insights for Oncolytic Virus Immunotherapy

Large-scale assays, such as microarrays, next-generation sequencing and various “omics” technologies, have explored multiple aspects of the immune response following virus infection, often from a public health perspective. Yet a lack of similar data exists for monitoring immune engagement during oncolytic virus immunotherapy (OVIT) in the cancer setting. Tracking immune signatures at the tumour site can create a snapshot or longitudinally analyse immune cell activation, infiltration and functionality within global populations or individual cells. Mapping immune changes over the course of oncolytic biotherapy—from initial infection to tumour stabilisation/regression through to long-term cure or escape/relapse—has the potential to generate important therapeutic insights around virus-host interactions. Further, correlating such immune signatures with specific tumour outcomes has significant value for guiding the development of novel oncolytic virus immunotherapy strategies. Here, we provide insights for OVIT from large-scale analyses of immune populations in the infection, vaccination and immunotherapy setting. We analyse several approaches to manipulating immune engagement during OVIT. We further explore immunocentric changes in the tumour tissue following immunotherapy, and compile several immune signatures of therapeutic success. Ultimately, we highlight clinically relevant large-scale approaches with the potential to strengthen future oncolytic strategies to optimally engage the immune system.

Activation of Cyclic Adenosine Monophosphate Pathway Increases the Sensitivity of Cancer Cells to the Oncolytic Virus M1

Oncolytic virotherapy is a novel and emerging treatment modality that uses replication-competent viruses to destroy cancer cells. Although diverse cancer cell types are sensitive to oncolytic viruses, one of the major challenges of oncolytic virotherapy is that the sensitivity to oncolysis ranges among different cancer cell types. Furthermore, the underlying mechanism of action is not fully understood. Here, we report that activation of cyclic adenosine monophosphate (cAMP) signaling significantly sensitizes refractory cancer cells to alphavirus M1 in vitro, in vivo, and ex vivo. We find that activation of the cAMP signaling pathway inhibits M1-induced expression of antiviral factors in refractory cancer cells, leading to prolonged and severe endoplasmic reticulum (ER) stress, and cell apoptosis. We also demonstrate that M1-mediated oncolysis, which is enhanced by cAMP signaling, involves the factor, exchange protein directly activated by cAMP 1 (Epac1), but not the classical cAMP-dependent protein kinase A (PKA). Taken together, cAMP/Epac1 signaling pathway activation inhibits antiviral factors and improves responsiveness of refractory cancer cells to M1-mediated virotherapy.

Intratumoral immunotherapy for melanoma

Selection of suitable tumor-associated antigens is a major challenge in the development of effective cancer vaccines. Intratumoral (i.t.) immunotherapy empowers the immune system to mount T cell responses against tumor-associated antigens which are most immunogenic. To mediate systemic tumor regression, i.t. immunotherapy must generate systemic T cell responses that can target distant metastases beyond the initially treated tumor mass. Now that promising preclinical results and some initial success in clinical trials have been obtained, we here review i.t. immunotherapy-related preclinical and clinical studies, their mechanisms of action and future prospects.

The profile of tumor antigens which can be targeted by immunotherapy depends upon the tumor's anatomical site

Previously, we showed that vesicular stomatitis virus (VSV) engineered to express a cDNA library from human melanoma cells (ASMEL, Altered Self Melanoma Epitope Library) was an effective systemic therapy to treat subcutaneous (s.c.) murine B16 melanomas. Here, we show that intravenous treatment with the same ASMEL VSV-cDNA library was an effective treatment for established intra-cranial (i.c.) melanoma brain tumors. The optimal combination of antigens identified from the ASMEL which treated s.c. B16 tumors (VSV-N-RAS+VSV-CYTC-C+VSV-TYRP-1) was ineffective against i.c. B16 brain tumors. In contrast, combination of VSV-expressed antigens-VSV-HIF-2α+VSV-SOX-10+VSV-C-MYC+VSV-TYRP1-from ASMEL which was highly effective against i.c. B16 brain tumors, had no efficacy against the same tumors growing subcutaneously. Correspondingly, i.c. B16 tumors expressed a HIF-2α(Hi), SOX-10(Hi), c-myc(Hi), TYRP1, N-RAS(lo)Cytc(lo) antigen profile, which differed significantly from the HIF-2α(lo), SOX-10(lo), c-myc(lo), TYRP1, N-RAS(Hi)Cytc(Hi) phenotype of s.c. B16 tumors, and was imposed upon the tumor cells by CD11b(+) cells within the local brain tumor microenvironment. Combining T-cell costimulation with systemic VSV-cDNA treatment, long-term cures of mice with established i.c. tumors were achieved in about 75% of mice. Our data show that the anatomical location of a tumor profoundly affects the profile of antigens that it expresses.

Oncolytic viruses as anticancer vaccines

Oncolytic virotherapy has shown impressive results in preclinical studies and first promising therapeutic outcomes in clinical trials as well. Since viruses are known for a long time as excellent vaccination agents, oncolytic viruses are now designed as novel anticancer agents combining the aspect of lysis-dependent cytoreductive activity with concomitant induction of antitumoral immune responses. Antitumoral immune activation by oncolytic virus infection of tumor tissue comprises both, immediate effects of innate immunity and also adaptive responses for long lasting antitumoral activity, which is regarded as the most prominent challenge in clinical oncology. To date, the complex effects of a viral tumor infection on the tumor microenvironment and the consequences for the tumor-infiltrating immune cell compartment are poorly understood. However, there is more and more evidence that a tumor infection by an oncolytic virus opens up a number of options for further immunomodulating interventions such as systemic chemotherapy, generic immunostimulating strategies, dendritic cell-based vaccines, and antigenic libraries to further support clinical efficacy of oncolytic virotherapy.

Oncolytic vaccines

Oncolytic viruses are ideal platforms for tumor vaccination because they can mediate the direct in situ killing of tumor cells that release a broad array of tumor antigens and alarmins or danger signals thereby cross-priming antitumor cytotoxic T lymphocytes (CTLs), which mediate the indirect killing of uninfected cells. The balance between the direct and indirect killing phases of oncolytic virotherapy is the key to its success and can be manipulated by incorporating various immunomodulatory genes into the oncolytic virus genome. Recently, the interim analysis of a large multicenter Phase III clinical trial for Talimogene laherparepvec, a granulocyte-macrophage colony stimulating factor-armed oncolytic herpes simplex virus, revealed significant improvement in objective response and durable response rates over control arm and a trend toward improved overall survival. Meanwhile, newer oncolytics are being developed expressing additional immunomodulatory transgenes to further enhance cross-priming and the generation of antitumor CTLs and to block the immunosuppressive actions of the tumor microenvironment. Since oncolytic vaccines can be engineered to kill tumor cells directly, modulate the kinetics of the antitumor immune response and reverse the immunosuppressive actions of the tumor, they are predicted to emerge as the preferred immunotherapeutic anticancer weapons of the future.

The strength of the T cell response against a surrogate tumor antigen induced by oncolytic VSV therapy does not correlate with tumor control

Cancer therapy using oncolytic viruses has gained interest in the last decade. Vesicular stomatitis virus is an attractive candidate for this alternative treatment approach. The importance of the immune response against tumor antigens in virotherapy efficacy is now well recognized, however, its relative contribution versus the intrinsic oncolytic capacity of viruses has been difficult to evaluate. To start addressing this question, we compared glycoprotein and matrix mutants of vesicular stomatitis virus (VSV), showing different oncolytic potentials for B16/B16gp33 melanoma tumor cells in vitro, with the wild-type virus in their ability to induce tumor-specific CD8(+) T cell responses and control tumor progression in vivo. Despite the fact that wild-type and G mutants induced a stronger gp33-specific immune response compared to the MM51R mutant, all VSV strains showed a similar capacity to slow down tumor progression. The effectiveness of the matrix mutant treatment proved to be CD8(+) dependent and directed against tumor antigens other than gp33 since adoptive transfer of isolated CD8(+) T lymphocytes from treated B16gp33-bearing mice resulted in significant protection of naive mice against challenge with the parental tumor. Remarkably, the VSV matrix mutant induced the upregulation of major histocompatibility class-I antigen at the tumor cell surface thus favoring recognition by CD8(+) T cells. These results demonstrate that VSV mutants induce an antitumor immune response using several mechanisms. A better understanding of these mechanisms will prove useful for the rational design of viruses with improved therapeutic efficacy.

MyD88-dependent immunity to a natural model of vaccinia virus infection does not involve Toll-like receptor 2

Although the pattern recognition receptor Toll-like receptor 2 (TLR2) is typically thought to recognize bacterial components, it has been described to alter the induction of both innate and adaptive immunity to a number of viruses, including vaccinia virus (VACV). However, many pathogens that reportedly encode TLR2 agonists may actually be artifactually contaminated during preparation, possibly with cellular debris or merely with molecules that sensitize cells to be activated by authentic TLR2 agonists. In both humans and mice, the most relevant natural route of infection with VACV is through intradermal infection of the skin. Therefore, we examined the requirement for TLR2 and its signaling adaptor MyD88 in protective immunity to VACV after intradermal infection. We find that although TLR2 may recognize virus preparations in vitro and have a minor role in preventing dissemination of VACV following systemic infection with large doses of virus, it is wholly disposable in both control of virus replication and induction of adaptive immunity following intradermal infection. In contrast, MyD88 is required for efficient induction of CD4 T cell and B cell responses and for local control of virus replication following intradermal infection. However, even MyD88 is not required to induce local inflammation, inflammatory cytokine production, or recruitment of cells that restrict virus from spreading systemically after peripheral infection. Thus, an effective antiviral response does require MyD88, but TLR2 is not required for control of a peripheral VACV infection. These findings emphasize the importance of studying relevant routes of infection when examining innate sensing mechanisms.

IMPORTANCE

Vaccinia virus (VACV) provides the backbone for some of the most widely used and successful viral vaccine vectors and is also related to the human pathogens Cantagalo virus and molluscum contagiosum virus that infect the skin of patients. Therefore, it is vital to understand the mechanisms that induce a strong innate immune response to the virus following dermal infection. Here, we compare the ability of the innate sensing molecule Toll-like receptor 2 (TLR2) and the signaling molecule MyD88 to influence the innate and adaptive immune response to VACV following systemic or dermal infection.

Oncolytic viruses as therapeutic cancer vaccines

Oncolytic viruses (OVs) are tumor-selective, multi-mechanistic antitumor agents. They kill infected cancer and associated endothelial cells via direct oncolysis, and uninfected cells via tumor vasculature targeting and bystander effect. Multimodal immunogenic cell death (ICD) together with autophagy often induced by OVs not only presents potent danger signals to dendritic cells but also efficiently cross-present tumor-associated antigens from cancer cells to dendritic cells to T cells to induce adaptive antitumor immunity. With this favorable immune backdrop, genetic engineering of OVs and rational combinations further potentiate OVs as cancer vaccines. OVs armed with GM-CSF (such as T-VEC and Pexa-Vec) or other immunostimulatory genes, induce potent anti-tumor immunity in both animal models and human patients. Combination with other immunotherapy regimens improve overall therapeutic efficacy. Coadministration with a HDAC inhibitor inhibits innate immunity transiently to promote infection and spread of OVs, and significantly enhances anti-tumor immunity and improves the therapeutic index. Local administration or OV mediated-expression of ligands for Toll-like receptors can rescue the function of tumor-infiltrating CD8⁺ T cells inhibited by the immunosuppressive tumor microenvironment and thus enhances the antitumor effect. Combination with cyclophosphamide further induces ICD, depletes Treg, and thus potentiates antitumor immunity. In summary, OVs properly armed or in rational combinations are potent therapeutic cancer vaccines.

Oncolytic vesicular stomatitis virus in an immunocompetent model of MUC1-positive or MUC1-null pancreatic ductal adenocarcinoma

Vesicular stomatitis virus (VSV) is a promising oncolytic agent against various malignancies. Here, for the first time, we tested VSV in vitro and in vivo in a clinically relevant, immunocompetent mouse model of pancreatic ductal adenocarcinoma (PDA). Our system allows the study of virotherapy against PDA in the context of overexpression (80% of PDA patients) or no expression of human mucin 1 (MUC1), a major marker for poor prognosis in patients. In vitro, we tested three VSV recombinants, wild-type VSV, VSV-green fluorescent protein (VSV-GFP), and a safe oncolytic VSV-ΔM51-GFP, against five mouse PDA cell lines that either expressed human MUC1 or were MUC1 null. All viruses demonstrated significant oncolytic abilities independent of MUC1 expression, although VSV-ΔM51-GFP was somewhat less effective in two PDA cell lines. In vivo administration of VSV-ΔM51-GFP resulted in significant reduction of tumor growth for tested mouse PDA xenografts (+MUC1 or MUC1 null), and antitumor efficacy was further improved when the virus was combined with the chemotherapeutic drug gemcitabine. The antitumor effect was transient in all tested groups. The developed system can be used to study therapies involving various oncolytic viruses and chemotherapeutics, with the goal of inducing tumor-specific immunity while preventing premature virus clearance.

Vesicular stomatitis virus variants selectively infect and kill human melanomas but not normal melanocytes

Metastatic malignant melanoma remains one of the most therapeutically challenging forms of cancer. Here we test replication-competent vesicular stomatitis viruses (VSV) on 19 primary human melanoma samples and compare these infections with those of normal human melanocyte control cells. Even at a low viral concentration, we found a strong susceptibility to viral oncolysis in over 70% of melanomas. In contrast, melanocytes displayed strong resistance to virus infection and showed complete protection by interferon. Several recombinant VSVs were compared, and all infected and killed most melanomas with differences in the time course with increasing rates of melanoma infection, as follows: VSV-CT9-M51 < VSV-M51 < VSV-G/GFP < VSV-rp30. VSV-rp30 sequencing revealed 2 nonsynonymous mutations at codon positions P126 and L223, both of which appear to be required for the enhanced phenotype. VSV-rp30 showed effective targeting and infection of multiple subcutaneous and intracranial melanoma xenografts in SCID mice after tail vein virus application. Sequence analysis of mutations in the melanomas used revealed that BRAF but not NRAS gene mutation status was predictive for enhanced susceptibility to infection. In mouse melanoma models with specific induced gene mutations including mutations of the Braf, Pten, and Cdkn2a genes, viral infection correlated with the extent of malignant transformation. Similar to human melanocytes, mouse melanocytes resisted VSV-rp30 infection. This study confirms the general susceptibility of the majority of human melanoma types for VSV-mediated oncolysis.

Natural oncolytic activity of live-attenuated measles virus against human lung and colorectal adenocarcinomas

Lung and colorectal cancers are responsible for approximately 2 million deaths each year worldwide. Despite continual improvements, clinical management of these diseases remains challenging and development of novel therapies with increased efficacy is critical to address these major public health issues. Oncolytic viruses have shown promising results against cancers that are resistant to conventional anticancer therapies. Vaccine strains of measles virus (MV) exhibit such natural antitumor properties by preferentially targeting cancer cells. We tested the ability of live-attenuated Schwarz strain of MV to specifically infect tumor cells derived from human lung and colorectal adenocarcinomas and demonstrated that live-attenuated MV exhibits oncolytic properties against these two aggressive neoplasms. We also showed that Schwarz MV was able to prevent uncontrollable growth of large, established lung and colorectal adenocarcinoma xenografts in nude mice. Moreover, MV oncolysis is associated with in vivo activation of caspase-3 in colorectal cancer model, as shown by immunohistochemical staining. Our results provide new arguments for the use of MV as an antitumor therapy against aggressive human malignancies.

VEGF blockade enables oncolytic cancer virotherapy in part by modulating intratumoral myeloid cells

Understanding the host response to oncolytic viruses is important to maximize their antitumor efficacy. Despite robust cytotoxicity and high virus production of an oncolytic herpes simplex virus (oHSV) in cultured human sarcoma cells, intratumoral (ITu) virus injection resulted in only mild antitumor effects in some xenograft models, prompting us to characterize the host inflammatory response. Virotherapy induced an acute neutrophilic infiltrate, a relative decrease of ITu macrophages, and a myeloid cell-dependent upregulation of host-derived vascular endothelial growth factor (VEGF). Anti-VEGF antibodies, bevacizumab and r84, the latter of which binds VEGF and selectively inhibits binding to VEGF receptor-2 (VEGFR2) but not VEGFR1, enhanced the antitumor effects of virotherapy, in part due to decreased angiogenesis but not increased virus production. Neither antibody affected neutrophilic infiltration but both partially mitigated virus-induced depletion of macrophages. Enhancement of virotherapy-mediated antitumor effects by anti-VEGF antibodies could largely be recapitulated by systemic depletion of CD11b(+) cells. These data suggest the combined effect of oHSV virotherapy and anti-VEGF antibodies is in part due to modulation of a host inflammatory reaction to virus. Our data provide strong preclinical support for combined oHSV and anti-VEGF antibody therapy and suggest that understanding and counteracting the innate host response may help enable the full antitumor potential of oncolytic virotherapy.

[Vesicular stomatitis virus in the fight against cancer]

Cancer is a complex disease that affects more and more people around the world. Unfortunately, existing treatments are only partially efficient and often induce major side effects. Thus, the use of viruses to selectively kill cancer cells is a new promising therapeutic approach. Recently, VSV has been used in oncolytic virotherapy because of its capacity to preferentially infect most human tumor cells. However, despite the availability of good oncolytic VSV mutants, the large variability of tumor cell types and the multiple ways in which they can evade viral infection suggests that therapeutic combinations of various viruses will be necessary to efficiently treat most cancers. A better understanding of the infection mechanisms and immune system recruitment by oncolytic viruses will be of great value for the development of safe and efficient strategies for cancer treatment.

Measles virus causes immunogenic cell death in human melanoma

Oncolytic viruses (OV) are promising treatments for cancer, with several currently undergoing testing in randomised clinical trials. Measles virus (MV) has not yet been tested in models of human melanoma. This study demonstrates the efficacy of MV against human melanoma. It is increasingly recognised that an essential component of therapy with OV is the recruitment of host antitumour immune responses, both innate and adaptive. MV-mediated melanoma cell death is an inflammatory process, causing the release of inflammatory cytokines including type-1 interferons and the potent danger signal HMGB1. Here, using human in vitro models, we demonstrate that MV enhances innate antitumour activity, and that MV-mediated melanoma cell death is capable of stimulating a melanoma-specific adaptive immune response.

Resistance of pancreatic cancer cells to oncolytic vesicular stomatitis virus: role of type I interferon signaling

Oncolytic virus (OV) therapy takes advantage of common cancer characteristics, such as defective type I interferon (IFN) signaling, to preferentially infect and kill cancer cells with viruses. Our recent study (Murphy et al., 2012. J. Virol. 86, 3073-87) found human pancreatic ductal adenocarcinoma (PDA) cells were highly heterogeneous in their permissiveness to vesicular stomatitis virus (VSV) and suggested at least some resistant cell lines retained functional type I IFN responses. Here we examine cellular responses to infection by the oncolytic VSV recombinant VSV-ΔM51-GFP by analyzing a panel of 11 human PDA cell lines for expression of 33 genes associated with type I IFN pathways. Although all cell lines sensed infection by VSV-ΔM51-GFP and most activated IFN-α and β expression, only resistant cell lines displayed constitutive high-level expression of the IFN-stimulated antiviral genes MxA and OAS. Inhibition of JAK/STAT signaling decreased levels of MxA and OAS and increased VSV infection, replication and oncolysis, further implicating IFN responses in resistance. Unlike VSV, vaccinia and herpes simplex virus infectivity and killing of PDA cells was independent of the type I IFN signaling profile, possibly because these two viruses are better equipped to evade type I IFN responses. Our study demonstrates heterogeneity in the type I IFN signaling status of PDA cells and suggests MxA and OAS as potential biomarkers for PDA resistance to VSV and other OVs sensitive to type I IFN responses.

Vesicular stomatitis virus as a flexible platform for oncolytic virotherapy against cancer

Oncolytic virus (OV) therapy is an emerging anti-cancer approach that utilizes viruses to preferentially infect and kill cancer cells, while not harming healthy cells. Vesicular stomatitis virus (VSV) is a prototypic non-segmented, negative-strand RNA virus with inherent OV qualities. Antiviral responses induced by type I interferon pathways are believed to be impaired in most cancer cells, making them more susceptible to VSV than normal cells. Several other factors make VSV a promising OV candidate for clinical use, including its well-studied biology, a small, easily manipulated genome, relative independence of a receptor or cell cycle, cytoplasmic replication without risk of host-cell transformation, and lack of pre-existing immunity in humans. Moreover, various VSV-based recombinant viruses have been engineered via reverse genetics to improve oncoselectivity, safety, oncotoxicity and stimulation of tumour-specific immunity. Alternative delivery methods are also being studied to minimize premature immune clearance of VSV. OV treatment as a monotherapy is being explored, although many studies have employed VSV in combination with radiotherapy, chemotherapy or other OVs. Preclinical studies with various cancers have demonstrated that VSV is a promising OV; as a result, a human clinical trial using VSV is currently in progress.

The efficacy versus toxicity profile of combination virotherapy and TLR immunotherapy highlights the danger of administering TLR agonists to oncolytic virus-treated mice

Injection of oncolytic vesicular stomatitis virus (VSV) into established B16ova melanomas results in tumor regression, in large part by inducing innate immune reactivity against the viral infection, mediated by MyD88- and type III interferon (IFN)-, but not TLR-4-, signaling. We show here that intratumoral (IT) treatment with lipopolysaccharide (LPS), a TLR-4 agonist, significantly enhanced the local therapy induced by VSV by combining activation of different innate immune pathways. Therapy was further enhanced by co-recruiting a potent antitumor, adaptive T-cell response by using a VSV engineered to express the ovalbumin tumor-associated antigen ova, in combination with LPS. However, the combination of IT LPS with systemically delivered VSV resulted in rapid morbidity and mortality in the majority of mice. Decreasing the intravenous (IV) dose of VSV to levels at which toxicity was ameliorated did not enhance therapy compared with IT LPS alone. Toxicity of the systemic VSV + IT LPS regimen was associated with rapidly elevated levels of serum tumor necrosis factor-α (TNF-α) and interleukin (IL)-6, which neither systemic VSV, nor IT LPS, alone induced. These data show that therapy associated with direct IT injections of oncolytic viruses can be significantly enhanced by combination with agonists of innate immune activation pathways, which are not themselves activated by the virus alone. Importantly, they also highlight possible, unforeseen dangers of combination therapies in which an immunotherapy, even delivered locally at the tumor site, may systemically sensitize the patient to a cytokine shock-like response triggered by IV delivery of oncolytic virus.

Systemic combination virotherapy for melanoma with tumor antigen-expressing vesicular stomatitis virus and adoptive T-cell transfer

Oncolytic virotherapy offers the potential to treat tumors both as a single agent and in combination with traditional modalities such as chemotherapy and radiotherapy. Here we describe an effective, fully systemic treatment regimen, which combines virotherapy, acting essentially as an adjuvant immunotherapy, with adoptive cell transfer (ACT). The combination of ACT with systemic administration of a vesicular stomatitis virus (VSV) engineered to express the endogenous melanocyte antigen glycoprotein 100 (gp100) resulted in regression of established melanomas and generation of antitumor immunity. Tumor response was associated with in vivo T-cell persistence and activation as well as treatment-related vitiligo. However, in a proportion of treated mice, initial tumor regressions were followed by recurrences. Therapy was further enhanced by targeting an additional tumor antigen with the VSV-antigen + ACT combination strategy, leading to sustained response in 100% of mice. Together, our findings suggest that systemic virotherapy combined with antigen-expressing VSV could be used to support and enhance clinical immunotherapy protocols with adoptive T-cell transfer, which are already used in the clinic.

Using virally expressed melanoma cDNA libraries to identify tumor-associated antigens that cure melanoma

Multiple intravenous injections of a cDNA library, derived from human melanoma cell lines and expressed using the highly immunogenic vector vesicular stomatitis virus (VSV), cured mice with established melanoma tumors. Successful tumor eradication was associated with the ability of mouse lymphoid cells to mount a tumor-specific CD4(+) interleukin (IL)-17 recall response in vitro. We used this characteristic IL-17 response to screen the VSV-cDNA library and identified three different VSV-cDNA virus clones that, when used in combination but not alone, achieved the same efficacy against tumors as the complete parental virus library. VSV-expressed cDNA libraries can therefore be used to identify tumor rejection antigens that can cooperate to induce anti-tumor responses. This technology should be applicable to antigen discovery for other cancers, as well as for other diseases in which immune reactivity against more than one target antigen contributes to disease pathology.

Vesicular stomatitis virus oncolytic treatment interferes with tumor-associated dendritic cell functions and abrogates tumor antigen presentation

Oncolytic virotherapy is a promising biological approach to cancer treatment that contributes to tumor eradication via immune- and non-immune-mediated mechanisms. One of the remaining challenges for these experimental therapies is the necessity to develop a durable adaptive immune response against the tumor. Vesicular stomatitis virus (VSV) is a prototypical oncolytic virus (OV) that exemplifies the multiple mechanisms of oncolysis, including direct cell lysis, cellular hypoxia resulting from the shutdown of tumor vasculature, and inflammatory cytokine release. Despite these properties, the generation of sustained antitumor immunity is observed only when VSV is engineered to express a tumor antigen directly. In the present study, we sought to increase the number of tumor-associated dendritic cells (DC) in vivo and tumor antigen presentation by combining VSV treatment with recombinant Fms-like tyrosine kinase 3 ligand (rFlt3L), a growth factor promoting the differentiation and proliferation of DC. The combination of VSV oncolysis and rFLt3L improved animal survival in two different tumor models, i.e., VSV-resistant B16 melanoma and VSV-sensitive E.G7 T lymphoma; however, increased survival was independent of the adaptive CD8 T cell response. Tumor-associated DC were actively infected by VSV in vivo, which reduced their viability and prevented their migration to the draining lymph nodes to prime a tumor-specific CD8 T cell response. These results demonstrate that VSV interferes with tumor DC functions and blocks tumor antigen presentation.