Reovirus virotherapy overrides tumor antigen presentation evasion and promotes protective antitumor immunity

The role of interleukin 17 in cancer: a systematic review

Interleukin 17 (IL17) is a cytokine involved in immune regulation and has been increasingly recognized for its role in cancer progression. This systematic review aims to integrate data on IL17's role in various tumors to better understand its implications for cancer prognosis and treatment. The review included 105 studies (27.6% experimental and 72.4% clinical). Clinical studies involved 9266 patients: 31.2% males, 60.0% females, and 8.8% with undefined gender. IL17A and IL17 were the most studied subtypes (36.2% and 33.3%, respectively). Breast cancer (26.7%), colorectal carcinoma (13.3%), and hematologic malignancies (10.5%) were the most researched neoplasms. IL17A promoted tumor growth in breast cancer and correlated with poor outcomes in colorectal, breast, and lung cancers. IL17 also played a significant role in immune modulation in gliomas and other tumors. IL17A significantly influences tumor growth and prognosis across various cancers, with notable roles in immune modulation and poor outcomes in multiple cancer types.

Microbubble-Protected Oncolytic Virotherapy Targeted by Sonoporation Induces Tumor Necrosis and T-Lymphocyte Infiltration in Humanized Mice Bearing Triple-Negative Breast Cancer

Oncolytic virotherapy has shown great promise in mediating targeted tumor destruction through tumor-selective replication and induction of anti-tumor immunity; however, obstacles remain for virus candidates to reach the clinic. These include avoiding neutralizing antibodies, preventing stimulation of the adaptive immune response during intravenous administration, and inducing sufficient apoptosis and immune activation so that the body's defense can work to eradicate systemic disease. We have developed a co-formulation of oncolytic viruses (OVs) with Imagent® lipid-encapsulated, perfluorocarbon microbubbles (MBs) to protect the OVs from the innate and adaptive immune system. Once inside the MB, the viral particles become acoustically active such that external ultrasound can target the delivery of the virus locally within the tumor. Humanized NSG female mice (Hu-CD34+ NSG-SGM3) engrafted in their flanks with MDA-MB-231-Luc triple-negative breast cancer (TNBC) cells were transduced with MB/OVs, with or without adjuvant Pembrolizumab treatment, and tumor sizes and tumor necrosis were assessed. The presence of CD8+ (cytotoxic T-cells), CD4+ (helper T-cells), and CD25+ (Tregs) tumor-infiltrating lymphocytes (TILs) was quantified in the tumor samples by immunohistochemistry. In an in vivo model of humanized mice engrafted with a human immune system, we observed significantly greater tumor necrosis and smaller tumor mass in human TNBC xenografts systemically treated with MB/OV complexes in the presence or absence of pembrolizumab adjuvant treatment, compared to controls. Additionally, we observed a low ratio of CD4+/CD8+ TILs and a high ratio of CD8+/CD25+ TILs in the MDA-MB-231 xenografts treated with MB/OVs complexes with or without pembrolizumab adjuvant treatment, compared to controls. Our study demonstrated the feasibility of using MBs to target OVs to TNBC through diagnostic ultrasound, which decreased tumor mass by increasing tumor necrosis and stimulated a local and systemic antitumoral immune response by increasing intratumoral CD8+ T-cytotoxic lymphocyte infiltration and decreasing CD25+ Treg cells.

Tutorial: design, production and testing of oncolytic viruses for cancer immunotherapy

Oncolytic viruses (OVs) represent a novel class of cancer immunotherapy agents that preferentially infect and kill cancer cells and promote protective antitumor immunity. Furthermore, OVs can be used in combination with established or upcoming immunotherapeutic agents, especially immune checkpoint inhibitors, to efficiently target a wide range of malignancies. The development of OV-based therapy involves three major steps before clinical evaluation: design, production and preclinical testing. OVs can be designed as natural or engineered strains and subsequently selected for their ability to kill a broad spectrum of cancer cells rather than normal, healthy cells. OV selection is further influenced by multiple factors, such as the availability of a specific viral platform, cancer cell permissivity, the need for genetic engineering to render the virus non-pathogenic and/or more effective and logistical considerations around the use of OVs within the laboratory or clinical setting. Selected OVs are then produced and tested for their anticancer potential by using syngeneic, xenograft or humanized preclinical models wherein immunocompromised and immunocompetent setups are used to elucidate their direct oncolytic ability as well as indirect immunotherapeutic potential in vivo. Finally, OVs demonstrating the desired anticancer potential progress toward translation in patients with cancer. This tutorial provides guidelines for the design, production and preclinical testing of OVs, emphasizing considerations specific to OV technology that determine their clinical utility as cancer immunotherapy agents.

Oncolytic virotherapy in cancer treatment: challenges and optimization prospects

Oncolytic viruses (OVs) are emerging cancer therapeutics that offer a multifaceted therapeutic platform for the benefits of replicating and lysing tumor cells, being engineered to express transgenes, modulating the tumor microenvironment (TME), and having a tolerable safety profile that does not overlap with other cancer therapeutics. The mechanism of OVs combined with other antitumor agents is based on immune-mediated attack resistance and might benefit patients who fail to achieve durable responses after immune checkpoint inhibitor (ICI) treatment. In this Review, we summarize data on the OV mechanism and limitations of monotherapy, which are currently in the process of combination partner development, especially with ICIs. We discuss some of the hurdles that have limited the preclinical and clinical development of OVs. We also describe the available data and provide guidance for optimizing OVs in clinical practice, as well as a summary of approved and promising novel OVs with clinical indications.

Oncolytic viral therapy as promising immunotherapy against glioma

Glioma is a common primary central nervous system malignant tumor in clinical, traditional methods such as surgery and chemoradiotherapy are not effective in treatment. Therefore, more effective treatments need to be found. Oncolytic viruses (OVs) are a new type of immunotherapy that selectively infects and kills tumor cells instead of normal cells. OVs can mediate antitumor immune responses through a variety of mechanisms, and have the ability to activate antitumor immune responses, transform the tumor microenvironment from “cold” to “hot,” and enhance the efficacy of immune checkpoint inhibitors. Recently, a large number of preclinical and clinical studies have shown that OVs show great prospects in the treatment of gliomas. In this review, we summarize the current status of glioma therapies with a focus on OVs. First, this article introduces the current status of treatment of glioma and their respective shortcomings. Then, the important progress of OVs of in clinical trials of glioma is summarized. Finally, the urgent challenges of oncolytic virus treatment for glioma are sorted out, and related solutions are proposed. This review will help to further promote the use of OVs in the treatment of glioma.

Chimeric Antigen Receptor-T Cell and Oncolytic Viral Therapies for Gastric Cancer and Peritoneal Carcinomatosis of Gastric Origin: Path to Improving Combination Strategies

Precision immune oncology capitalizes on identifying and targeting tumor-specific antigens to enhance anti-tumor immunity and improve the treatment outcomes of solid tumors. Gastric cancer (GC) is a molecularly heterogeneous disease where monoclonal antibodies against human epidermal growth factor receptor 2 (HER2), vascular endothelial growth factor (VEGF), and programmed cell death 1 (PD-1) combined with systemic chemotherapy have improved survival in patients with unresectable or metastatic GC. However, intratumoral molecular heterogeneity, variable molecular target expression, and loss of target expression have limited antibody use and the durability of response. Often immunogenically "cold" and diffusely spread throughout the peritoneum, GC peritoneal carcinomatosis (PC) is a particularly challenging, treatment-refractory entity for current systemic strategies. More adaptable immunotherapeutic approaches, such as oncolytic viruses (OVs) and chimeric antigen receptor (CAR) T cells, have emerged as promising GC and GCPC treatments that circumvent these challenges. In this study, we provide an up-to-date review of the pre-clinical and clinical efficacy of CAR T cell therapy for key primary antigen targets and provide a translational overview of the types, modifications, and mechanisms for OVs used against GC and GCPC. Finally, we present a novel, summary-based discussion on the potential synergistic interplay between OVs and CAR T cells to treat GCPC.

Regional Immunotherapy for Peritoneal Carcinomatosis in Gastroesophageal Cancer: Emerging Strategies to Re-Condition a Maladaptive Tumor Environment

Peritoneal carcinomatosis originating from gastric/gastroesophageal junction cancer (GC-PC) occurs in a defined subset of gastric cancer patients with unique clinical, pathologic, molecular and immunologic characteristics that create significant obstacles to effective treatment with modern therapy. Although systemic chemo- and immuno- therapy have yielded disappointing results in GC-PC, recent advances in the characterization of GC-PC and peritoneal immune biology present new opportunities for targeted therapeutics. In this review article, we discuss the distinct properties of GC-PC and the peritoneal immune environment as they pertain to current and investigative treatment strategies. We discuss pre-clinical studies and clinical trials relevant to the modulation of the peritoneal environment as a therapeutic intervention in GC-PC. Finally, we present a road map for future combinatorial strategies based on the conception of the peritoneal cavity as a bioreactor. Within this isolated compartment, prevailing immunosuppressive conditions can be altered through regional interventions toward an adaptive phenotype that would support the effectiveness of regionally delivered cellular therapy products. It is hoped that novel combination strategies would promote efficacy not only in the sequestered peritoneal environment, but also via migration into the circulation of tumor-reactive lymphocytes to produce durable systemic disease control, thereby improving oncologic outcome and quality of life in patients with GC-PC.

Creation and characterization of a recombinant mammalian orthoreovirus expressing σ1 fusion proteins encoding human epidermal growth factor receptor 2 peptides

Mammalian orthoreovirus (MRV) is an oncolytic virus that has been tested in over 30 clinical trials. Increased clinical success has been achieved when MRV is used in combination with other onco-immunotherapies. This has led the field to explore the creation of recombinant MRVs which incorporate immunotherapeutic sequences into the virus genome. This work focuses on creation and characterization of a recombinant MRV, S1/HER2nhd, which encodes a truncated σ1 protein fused in frame with three human epidermal growth factor receptor 2 (HER2) peptides (E75, AE36, and GP2) known to induce HER2 specific CD8+ and CD4+ T cells. We show S1/HER2nhd expresses the σ1 fusion protein containing HER2 peptides in infected cells and on the virion, and infects, replicates in, and reduces survival of HER2+ breast cancer cells. The oncolytic properties of MRV combined with HER2 peptide expression holds potential as a vaccine to prevent recurrences of HER2 expressing cancers.

Reovirus infection of tumor cells reduces the expression of NKG2D ligands, leading to impaired NK-cell cytotoxicity and functionality

In recent years, reoviruses have been of major interest in immunotherapy because of their oncolytic properties. Preclinical and clinical trials, in which reovirus was used for the treatment of melanoma and glioblastoma, have paved the way for future clinical use of reovirus. However, little is known about how reovirus infection affects the tumor microenvironment and immune response towards infected tumor cells. Studies have shown that reovirus can directly stimulate natural killer (NK) cells, but how reovirus affects cellular ligands on tumor cells, which are ultimately key to tumor recognition and elimination by NK cells, has not been investigated. We tested how reovirus infection affects the binding of the NK Group-2 member D (NKG2D) receptor, which is a dominant mediator of NK cell anti-tumor activity. Using models of human-derived melanoma and glioblastoma tumors, we demonstrated that NKG2D ligands are downregulated in tumor cells post-reovirus-infection due to the impaired translation of these ligands in reovirus-infected cells. Moreover, we showed that downregulation of NKG2D ligands significantly impaired the binding of NKG2D to infected tumor cells. We further demonstrated that reduced recognition of NKG2D ligands significantly alters NK cell anti-tumor cytotoxicity in human primary NK cells and in the NK cell line NK-92. Thus, this study provides novel insights into reovirus-host interactions and could lead to the development of novel reovirus-based therapeutics that enhance the anti-tumor immune response.

Hypoxia effects on oncolytic virotherapy in Cancer: Friend or Foe?

Researchers have tried to find novel strategies for cancer treatment in the past decades. Among the utilized methods, administering oncolytic viruses (OVs) alone or combined with other anticancer therapeutic approaches has had promising outcomes, especially in solid tumors. Infecting the tumor cells by these viruses can lead to direct lysis or induction of immune responses. However, the immunosuppressive tumor microenvironment (TME) is considered a significant challenge for oncolytic virotherapy in treating cancer. Based on OV type, hypoxic conditions in the TME can accelerate or repress virus replication. Therefore, genetic manipulation of OVs or other molecular modifications to reduce hypoxia can induce antitumor responses. Moreover, using OVs with tumor lysis capability in the hypoxic TME may be an attractive strategy to overcome the limitations of the therapy. This review summarizes the latest information available in the field of cancer virotherapy and discusses the dual effect of hypoxia on different types of OVs to optimize available related therapeutic methods.

Tumor Microenvironment as a Therapeutic Target in Melanoma Treatment

The role of the tumor microenvironment in tumor growth and therapy has recently attracted more attention in research and drug development. The ability of the microenvironment to trigger tumor maintenance, progression, and resistance is the main cause for treatment failure and tumor relapse. Accumulated evidence indicates that the maintenance and progression of tumor cells is determined by components of the microenvironment, which include stromal cells (endothelial cells, fibroblasts, mesenchymal stem cells, and immune cells), extracellular matrix (ECM), and soluble molecules (chemokines, cytokines, growth factors, and extracellular vesicles). As a solid tumor, melanoma is not only a tumor mass of monolithic tumor cells, but it also contains supporting stroma, ECM, and soluble molecules. Melanoma cells are continuously in interaction with the components of the microenvironment. In the present review, we focus on the role of the tumor microenvironment components in the modulation of tumor progression and treatment resistance as well as the impact of the tumor microenvironment as a therapeutic target in melanoma.

Oncolytic Virus-Driven Biotherapies from Bench to Bedside

With advances in cancer biology and an ever-deepening understanding of molecular virology, oncolytic virus (OV)-driven therapies have developed rapidly and become a promising alternative to traditional cancer therapies. In recent years, satisfactory results for oncolytic virus therapy (OVT) are achieved at both the cellular and organismal levels, and efforts are being increasingly directed toward clinical trials. Unfortunately, OVT remains ineffective in these trials, especially when performed using only a single OV reagent. In contrast, integrated approaches, such as using immunotherapy, chemotherapy, or radiotherapy, alongside OVT have demonstrated considerable efficacy. The challenges of OVT in clinical efficacy include the restricted scope of intratumoral injections and poor targeting of intravenous administration. Further optimization of OVT delivery is needed before OVs become a viable therapy for tumor treatment. In this review, the development process and antitumor mechanisms of OVs are introduced. The advances in OVT delivery routes to provide perspectives and directions for the improvement of OVT delivery are highlighted. This review also discusses the advantages and limitations of OVT monotherapy and combination therapy through the lens of recent clinical trials and aims to chart a course toward safer and more effective OVT strategies.

Mammalian orthoreovirus infection in human epidermal growth factor receptor 2 positive (HER2+) breast cancer cells

Mammalian orthoreovirus (MRV) is a clinically benign oncolytic virus which has been investigated for use in multiple cancer types, including breast cancer (BC). In human clinical trials, MRV has been shown to be safe, and multiple BC patients have shown partial responses to intratumoral and intravenous virus delivery. Combination therapies inclusive of MRV and current FDA approved BC chemotherapies are being investigated to target metastatic, early BC, and triple negative BC. Though MRV is being tested clinically, we still do not fully understand the highly variable patient responses to MRV therapy. One of the most aggressive BC subtypes is HER2+ BC, in which human epidermal growth factor receptor 2 (HER2) is dysregulated, resulting in increased growth, survival, and metastasis of cancer cells. FDA approved therapies, trastuzumab and pertuzumab, target HER2 to prevent signaling of the phosphoinositide 3-kinase (PI3K) pathway. However, recent findings show that accumulation of hypoxia inducible factor-1 alpha (HIF-1α) in HER2+ BC cells contributes to trastuzumab resistance. In this work, we provide evidence that MRV infects, replicates in, and kills HER2 overexpressing cells. MRV infection is also found to have variable effects on signaling pathways that activate or are activated by HER2 expression. Finally, we show that MRV reduces HIF-1α accumulation in all the cell lines tested, including a HER2+ BC cell line. These studies provide further evidence that MRV holds promise for use in conjunction with trastuzumab to treat HER2+ BC patients.

Immunotherapy for Peritoneal Carcinomatosis: Challenges and Prospective Outcomes

Peritoneal metastasis, also known as peritoneal carcinomatosis (PC), is a refractory cancer that is typically resistant to conventional therapies. The typical treatment for PC is a combination of cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC). Recently, research in this area has seen significant advances, particularly in immunotherapy as an alternative therapy for PC, which is very encouraging. Catumaxomab is a trifunctional antibody intraperitoneal (IP) immunotherapy authorized in Europe that can be used to diminish malignant ascites by targeting EpCAM. Intraperitoneal (IP) immunotherapy breaks immunological tolerance to treat peritoneal illness. Increasing T-cell responses and vaccination against tumor-associated antigens are two methods of treatment. CAR-T cells, vaccine-based therapeutics, dendritic cells (DCs) in combination with pro-inflammatory cytokines and NKs, adoptive cell transfer, and immune checkpoint inhibitors are promising treatments for PC. Carcinoembryonic antigen-expressing tumors are suppressed by IP administration of CAR-T cells. This reaction was strengthened by anti-PD-L1 or anti-Gr1. When paired with CD137 co-stimulatory signaling, CAR-T cells for folate receptor cancers made it easier for T-cell tumors to find their way to and stay alive in the body.

Viral Vectors in Gene Therapy: Where Do We Stand in 2023?

Viral vectors have been used for a broad spectrum of gene therapy for both acute and chronic diseases. In the context of cancer gene therapy, viral vectors expressing anti-tumor, toxic, suicide and immunostimulatory genes, such as cytokines and chemokines, have been applied. Oncolytic viruses, which specifically replicate in and kill tumor cells, have provided tumor eradication, and even cure of cancers in animal models. In a broader meaning, vaccine development against infectious diseases and various cancers has been considered as a type of gene therapy. Especially in the case of COVID-19 vaccines, adenovirus-based vaccines such as ChAdOx1 nCoV-19 and Ad26.COV2.S have demonstrated excellent safety and vaccine efficacy in clinical trials, leading to Emergency Use Authorization in many countries. Viral vectors have shown great promise in the treatment of chronic diseases such as severe combined immunodeficiency (SCID), muscular dystrophy, hemophilia, β-thalassemia, and sickle cell disease (SCD). Proof-of-concept has been established in preclinical studies in various animal models. Clinical gene therapy trials have confirmed good safety, tolerability, and therapeutic efficacy. Viral-based drugs have been approved for cancer, hematological, metabolic, neurological, and ophthalmological diseases as well as for vaccines. For example, the adenovirus-based drug Gendicine® for non-small-cell lung cancer, the reovirus-based drug Reolysin® for ovarian cancer, the oncolytic HSV T-VEC for melanoma, lentivirus-based treatment of ADA-SCID disease, and the rhabdovirus-based vaccine Ervebo against Ebola virus disease have been approved for human use.

Dendritic cells and natural killer cells: The road to a successful oncolytic virotherapy

Every type of cancer tissue is theoretically more vulnerable to viral infection. This natural proclivity has been harnessed as a new anti-cancer therapy by employing oncolytic viruses (OVs) to selectively infect and destroy cancer cells while providing little or no harm with no toxicity to the host. Whereas the primary oncolytic capabilities of OVs initially sparked the greatest concern, the predominant focus of research is on the association between OVs and the host immune system. Numerous OVs are potent causal agents of class I MHC pathway-related chemicals, enabling early tumor/viral immune recognition and cytokine-mediated response. The modified OVs have been studied for their ability to bind to dendritic cells (DCs) by expressing growth factors, chemokines, cytokines, and defensins inside the viral genome. OVs, like reovirus, can directly infect DCs, causing them to release chemokines and cytokines that attract and excite natural killer (NK) cells. In addition, OVs can directly alter cancer cells' sensitivity to NK by altering the expression levels of NK cell activators and inhibitors on cancerous cells. Therefore, NK cells and DCs in modulating the therapeutic response should be considered when developing and improving future OV-based therapeutics, whether modified to express transgenes or used in combination with other drugs/immunotherapies. Concerning the close relationship between NK cells and DCs in the potential of OVs to kill tumor cells, we explore how DCs and NK cells in tumor microenvironment affect oncolytic virotherapy and summarize additional information about the interaction mentioned above in detail in this work.

Gene Therapy Cargoes Based on Viral Vector Delivery

Viral vectors have been proven useful in a broad spectrum of gene therapy applications due to their possibility to accommodate foreign genetic material for both local and systemic delivery. The wide range of viral vectors has enabled gene therapy applications for both acute and chronic diseases. Cancer gene therapy has been addressed by the delivery of viral vectors expressing anti-tumor, toxic, and suicide genes for the destruction of tumors. Delivery of immunostimulatory genes such as cytokines and chemokines has also been applied for cancer therapy. Moreover, oncolytic viruses specifically replicating in and killing tumor cells have been used as such for tumor eradication or in combination with tumor killing or immunostimulatory genes. In a broad meaning, vaccines against infectious diseases and various cancers can be considered gene therapy, which has been highly successful, not the least for the development of effective COVID-19 vaccines. Viral vector-based gene therapy has also demonstrated encouraging and promising results for chronic diseases such as severe combined immunodeficiency (SCID), muscular dystrophy, and hemophilia. Preclinical gene therapy studies in animal models have demonstrated proof-of-concept for a wide range of disease indications. Clinical evaluation of drugs and vaccines in humans has showed high safety levels, good tolerance, and therapeutic efficacy. Several gene therapy drugs such as the adenovirus-based drug Gendicine® for non-small-cell lung cancer, the reovirus-based drug Reolysin® for ovarian cancer, lentivirus-based treatment of SCID-X1 disease, and the rhabdovirus-based vaccine Ervebo against Ebola virus disease, and adenovirus-based vaccines against COVID-19 have been developed.

Fundamentals of utilizing microbes in advanced cancer therapeutics: Current understanding and potential applications

One of the biggest health related issues in the twenty-first century is cancer. The current therapeutic platforms have not advanced enough to keep up with the number of rising cases. The traditional therapeutic approaches frequently fail to produce the desired outcomes. Therefore, developing new and more potent remedies is crucial. Recently, investigating microorganisms as potential anti-cancer treatments have garnered a lot of attention. Tumor-targeting microorganisms are more versatile at inhibiting cancer than the majority of standard therapies. Bacteria preferentially gather and thrive inside tumors, where they can trigger anti-cancer immune responses. They can be further trained to generate and distribute anticancer drugs based on clinical requirements using straightforward genetic engineering approaches. To improve clinical outcomes, therapeutic strategies utilizing live tumor-targeting bacteria can be used either alone or in combination with existing anticancer treatments. On the other hand, oncolytic viruses that target cancer cells, gene therapy via viral vectors, and viral immunotherapy are other popular areas of biotechnological investigation. Therefore, viruses serve as a unique candidate for anti-tumor therapy. This chapter describes the role of microbes, primarily bacteria and viruses in anti-cancer therapeutics. The various approaches to utilizing microbes in cancer therapy are discussed and examples of microorganisms that are now in use or that are undergoing experimental research are briefly discussed. We further point out the hurdles and the prospects of microbes-based remedies for cancer treatment.

Immunovirotherapy: The role of antibody based therapeutics combination with oncolytic viruses

Despite the fact that the new drugs and targeted therapies have been approved for cancer therapy during the past 30 years, the majority of cancer types are still remain challenging to be treated. Due to the tumor heterogeneity, immune system evasion and the complex interaction between the tumor microenvironment and immune cells, the great majority of malignancies need multimodal therapy. Unfortunately, tumors frequently develop treatment resistance, so it is important to have a variety of therapeutic choices available for the treatment of neoplastic diseases. Immunotherapy has lately shown clinical responses in malignancies with unfavorable outcomes. Oncolytic virus (OV) immunotherapy is a cancer treatment strategy that employs naturally occurring or genetically-modified viruses that multiply preferentially within cancer cells. OVs have the ability to not only induce oncolysis but also activate cells of the immune system, which in turn activates innate and adaptive anticancer responses. Despite the fact that OVs were translated into clinical trials, with T-VECs receiving FDA approval for melanoma, their use in fighting cancer faced some challenges, including off-target side effects, immune system clearance, non-specific uptake, and intratumoral spread of OVs in solid tumors. Although various strategies have been used to overcome the challenges, these strategies have not provided promising outcomes in monotherapy with OVs. In this situation, it is increasingly common to use rational combinations of immunotherapies to improve patient benefit. With the development of other aspects of cancer immunotherapy strategies, combinational therapy has been proposed to improve the anti-tumor activities of OVs. In this regard, OVs were combined with other biotherapeutic platforms, including various forms of antibodies, nanobodies, chimeric antigen receptor (CAR) T cells, and dendritic cells, to reduce the side effects of OVs and enhance their efficacy. This article reviews the promising outcomes of OVs in cancer therapy, the challenges OVs face and solutions, and their combination with other biotherapeutic agents.

GOBLET: a phase I/II study of pelareorep and atezolizumab +/- chemo in advanced or metastatic gastrointestinal cancers

Most gastrointestinal (GI) cancers have microsatellite-stable (MSS) tumors, which have an immunologically 'cold' phenotype with fewer genetic mutations, reduced immune cell infiltration and downregulated immune checkpoint proteins. These attributes make MSS tumors resistant to conventional immunotherapy including checkpoint blockade therapy. Pelareorep is a naturally occurring, nongenetically modified reovirus. Upon intravenous administration, pelareorep selectively kills tumor cells and promotes several immunologic changes that prime tumors to respond to checkpoint blockade therapy. Given its demonstrated synergy with checkpoint blockade, as well as its encouraging efficacy in prior GI cancer studies, pelareorep plus atezolizumab will be evaluated in the GOBLET study in multiple GI cancer indications.

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.

Advances in DNA- and RNA-Based Oncolytic Viral Therapeutics and Immunotherapies

The role of viruses has been studied extensively for use as curative cancer therapies. However, the natural immunogenicity of viruses and their interaction with the host’s immune system needs to be examined to determine the full effectiveness of the viral treatment. The prevalence of cancer is increasing globally, and treatments are needed to support the increasing body of patient care. Oncolytic viral therapies used existing pathogenic viruses, which are genetically modified to not cause disease in humans when administered using a vaccine viral vector. Immunotherapies are another avenue of recent interest that has gained much traction. This review will discuss oncolytic viral approaches using three DNA-based viruses, including herpes simplex virus (HSV), vaccinia virus, and adenovirus; as well as four RNA-based viruses, including reovirus, Newcastle disease virus (NDV), poliovirus, and measles virus (MV). It also examines the novel field of cancer-based immunotherapies.

Engineering strategies to enhance oncolytic viruses in cancer immunotherapy

Oncolytic viruses (OVs) are emerging as potentially useful platforms in treatment methods for patients with tumors. They preferentially target and kill tumor cells, leaving healthy cells unharmed. In addition to direct oncolysis, the essential and attractive aspect of oncolytic virotherapy is based on the intrinsic induction of both innate and adaptive immune responses. To further augment this efficacious response, OVs have been genetically engineered to express immune regulators that enhance or restore antitumor immunity. Recently, combinations of OVs with other immunotherapies, such as immune checkpoint inhibitors (ICIs), chimeric antigen receptors (CARs), antigen-specific T-cell receptors (TCRs) and autologous tumor-infiltrating lymphocytes (TILs), have led to promising progress in cancer treatment. This review summarizes the intrinsic mechanisms of OVs, describes the optimization strategies for using armed OVs to enhance the effects of antitumor immunity and highlights rational combinations of OVs with other immunotherapies in recent preclinical and clinical studies.

Oncolytic Virotherapy in Peritoneal Metastasis Gastric Cancer: The Challenges and Achievements

Gastric cancer (GC) is the fourth most common cancer and the second leading cause of cancer death globally. Although the mortality rate in some parts of the world, such as East Asia, is still high, new treatments and lifestyle changes have effectively reduced deaths from this type of cancer. One of the main challenges of this type of cancer is its late diagnosis and poor prognosis. GC patients are usually diagnosed in the advanced stages of the disease, which is often associated with peritoneal metastasis (PM) and significantly reduces survival. This type of metastasis in patients with GC poses a serious challenge due to limitations in common therapies such as surgery and tumor resection, as well as failure to respond to systemic chemotherapy. To solve this problem, researchers have used virotherapy such as reovirus-based anticancer therapy in patients with GC along with PM who are resistant to current chemotherapies because this therapeutic approach is able to overcome immune suppression by activating dendritic cells (DCs) and eventually lead to the intrinsic activity of antitumor effector T cells. This review summarizes the immunopathogenesis of peritoneal metastasis of gastric cancer (PMGC) and the details for using virotherapy as an effective anticancer treatment approach, as well as its challenges and opportunities.

Immune Checkpoint Blockade Augments Changes Within Oncolytic Virus-induced Cancer MHC-I Peptidome, Creating Novel Antitumor CD8 T Cell Reactivities

The combination cancer immunotherapies with oncolytic virus (OV) and immune checkpoint blockade (ICB) reinstate otherwise dysfunctional antitumor CD8 T cell responses. One major mechanism that aids such reinstatement of antitumor CD8 T cells involves the availability of new class I major histocompatibility complex (MHC-I)-bound tumor epitopes following therapeutic intervention. Thus, therapy-induced changes within the MHC-I peptidome hold the key to understanding the clinical implications for therapy-reinstated CD8 T cell responses. Here, using mass spectrometry-based immuno-affinity methods and tumor-bearing animals treated with OV and ICB (alone or in combination), we captured the therapy-induced alterations within the tumor MHC-I peptidome, which were then tested for their CD8 T cell response-stimulating activity. We found that the oncolytic reovirus monotherapy drives up- as well as downexpression of tumor MHC-I peptides in a cancer type and oncolysis susceptibility dependent manner. Interestingly, the combination of reovirus + ICB results in higher numbers of differentially expressed MHC-I-associated peptides (DEMHCPs) relative to either monotherapies. Most importantly, OV+ICB-driven DEMHCPs contain biologically active epitopes that stimulate interferon-gamma responses in cognate CD8 T cells, which may mediate clinically desired antitumor attack and cancer immunoediting. These findings highlight that the therapy-induced changes to the MHC-I peptidome contribute toward the reinstated antitumor CD8 T cell attack established following OV + ICB combination cancer immunotherapy.

Challenges and Future Perspectives of Immunotherapy in Pancreatic Cancer

Simple Summary

Immunotherapeutic agents harness the patient’s immune system to fight cancer cells. Especially immune checkpoint inhibitors, a certain group of immunotherapeutic agents, have recently improved treatment options for many cancer types. Unfortunately, clinical trials testing of these agents in pancreatic cancer patients have not confirmed promising results from laboratory experiments. Several characteristics of pancreatic cancer biology, especially the profound tumour microenvironment that inhibits the successful identification and elimination of tumour cells by immune cells seems to be responsible for the lacking efficacy of immunotherapeutics in pancreatic cancer. We summarise recently published clinical trials investigating immunotherapeutic strategies in pancreatic cancer patients and available data on how these treatments influence pancreatic cancer biology. Moreover, we identify potential strategies to improve experimental and clinical studies in order to generate more conclusive data and improve patient outcomes in the future.

Abstract

To date, extensive efforts to harness immunotherapeutic strategies for the treatment of pancreatic ductal adenocarcinoma (PDAC) have yielded disappointing results in clinical trials. These strategies mainly focused on cancer vaccines and immune checkpoint inhibitors alone or in combination with chemotherapeutic or targeted agents. However, the growing preclinical and clinical data sets from these efforts have established valuable insights into the immunological characteristics of PDAC biology. Most notable are the immunosuppressive role of the tumour microenvironment (TME) and PDAC’s characteristically poor immunogenicity resulting from tumour intrinsic features. Moreover, PDAC tumour heterogeneity has been increasingly well characterized and may additionally limit a “one-fits-all” immunotherapeutic strategy. In this review, we first outline mechanisms of immunosuppression and immune evasion in PDAC. Secondly, we summarize recently published data on preclinical and clinical efforts to establish immunotherapeutic strategies for the treatment of PDAC including diverse combinatorial treatment approaches aiming at overcoming this resistance towards immunotherapeutic strategies. Particularly, these combinatorial treatment approaches seek to concomitantly increase PDAC antigenicity, boost PDAC directed T-cell responses, and impair the immunosuppressive character of the TME in order to allow immunotherapeutic agents to unleash their full potential. Eventually, the thorough understanding of the currently available data on immunotherapeutic treatment strategies of PDAC will enable researchers and clinicians to develop improved treatment regimens and to design innovative clinical trials to overcome the pronounced immunosuppression of PDAC.

Comparison of oncolytic virotherapy and nanotherapy as two new miRNA delivery approaches in lung cancer

Lung cancer is known as the second leading cause of cancer death. Finding ways to detect early-stage lung cancer can remarkably increase the survival rate. Biomarkers such as microRNAs can be helpful in cancer diagnosis, predicting its prognosis, and patients' chances of survival. Numerous studies have confirmed the correlation between microRNA expression and the likelihood of patients surviving after treatment. Consequently, it is necessary to study the expression profile of microRNAs during and after treatment. Oncolytic virotherapy and nanotherapy are two neoteric methods that use various vectors to deliver microRNAs into cancer cells. Although these treatments have not yet entered into the clinical trials, much progress has been made in this area. Analyzing the expression profile of microRNAs after applying nanotherapy and oncolytic virotherapy can evaluate the effectiveness of these methods. This review refers to the studies conducted about these two approaches. The advantages and disadvantages of these methods in delivery and affecting microRNA expression patterns are discussed below.

Beyond cancer cells: Targeting the tumor microenvironment with gene therapy and armed oncolytic virus

Cancer gene therapies are usually designed either to express wild-type copies of tumor suppressor genes or to exploit tumor-associated phenotypic changes to endow selective cytotoxicity. However, these approaches become less relevant to cancers that contain many independent mutations, and the situation is made more complex by our increased understanding of clonal evolution of tumors, meaning that different metastases and even regions of the same tumor mass have distinct mutational and phenotypic profiles. In contrast, the relatively genetically stable tumor microenvironment (TME) therefore provides an appealing therapeutic target, particularly since it plays an essential role in promoting cancer growth, immune tolerance, and acquired resistance to many therapies. Recently, a variety of different TME-targeted gene therapy and armed oncolytic strategies have been explored, with particular success observed in strategies targeting the cancer stroma, reducing tumor vasculature, and repolarizing the immunosuppressive microenvironment. Herein, we review the progress of these TME-targeting approaches and try to highlight those showing the greatest promise.

Role of Myeloid Cells in Oncolytic Reovirus-Based Cancer Therapy

Oncolytic reovirus preferentially targets and kills cancer cells via the process of oncolysis, and additionally drives clinically favorable antitumor T cell responses that form protective immunological memory against cancer relapse. This two-prong attack by reovirus on cancers constitutes the foundation of its use as an anticancer oncolytic agent. Unfortunately, the efficacy of these reovirus-driven antitumor effects is influenced by the highly suppressive tumor microenvironment (TME). In particular, the myeloid cell populations (e.g., myeloid-derived suppressive cells and tumor-associated macrophages) of highly immunosuppressive capacities within the TME not only affect oncolysis but also actively impair the functioning of reovirus-driven antitumor T cell immunity. Thus, myeloid cells within the TME play a critical role during the virotherapy, which, if properly understood, can identify novel therapeutic combination strategies potentiating the therapeutic efficacy of reovirus-based cancer therapy.

Oncolytic Reovirus-Mediated Recruitment of Early Innate Immune Responses Reverses Immunotherapy Resistance in Prostate Tumors

Prostate cancers are considered "cold" tumors characterized by minimal T cell infiltrates, absence of a type I interferon (IFN) signature, and the presence of immunosuppressive cells. This non-inflamed phenotype is likely responsible for the lack of sensitivity of prostate cancer patients to immune checkpoint blockade (ICB) therapy. Oncolytic virus therapy can potentially overcome this resistance to immunotherapy in prostate cancers by transforming cold tumors into "hot," immune cell-infiltrated tumors. We investigated whether the combination of intratumoral oncolytic reovirus, followed by targeted blockade of Programmed cell death protein 1 (PD-1) checkpoint inhibition and/or the immunomodulatory CD73/Adenosine system can enhance anti-tumor immunity. Treatment of subcutaneous TRAMP-C2 prostate tumors with combined intratumoral reovirus and anti-PD-1 or anti-CD73 antibody significantly enhanced survival of mice compared with reovirus or either antibody therapy alone. Only combination therapy led to rejection of pre-established tumors and protection from tumor re-challenge. This therapeutic effect was dependent on CD4+ T cells and natural killer (NK) cells. NanoString immune profiling of tumors confirmed that reovirus increased tumor immune cell infiltration and revealed an upregulation of the immune-regulatory receptor, B- and T-lymphocyte attenuator (BTLA). This expression of BTLA on innate antigen-presenting cells (APCs) and its ligand, Herpesvirus entry mediator (HVEM), on T cells from reovirus-infected tumors was in keeping with a role for the HVEM-BTLA pathway in promoting the potent anti-tumor memory response observed.

Research and application of hydrostatic high pressure in tumor vaccines (Review)

It is well known that hydrostatic pressure (HP) is a physical parameter that is now regarded as an important variable for life. High hydrostatic pressure (HHP) technology has influenced biological systems for more than 100 years. Food and bioscience researchers have shown great interest in HHP technology over the past few decades. The development of knowledge related to this area can better facilitate the application of HHP in the life sciences. Furthermore, new applications for HHP may come from these current studies, particularly in tumor vaccines. Currently, cancer recurrence and metastasis continue to pose a serious threat to human health. The limited efficacy of conventional treatments has led to the need for breakthroughs in immunotherapy and other related areas. Research into tumor vaccines is providing new insights for cancer treatment. The purpose of this review is to present the main findings reported thus far in the relevant scientific literature, focusing on knowledge related to HHP technology and tumor vaccines, and to demonstrate the potential of applying HHP technology to tumor vaccine development.

Enhancing the Efficacy of Tumor Vaccines Based on Immune Evasion Mechanisms

Tumor vaccines aim to expand tumor-specific T cells and reactivate existing tumor-specific T cells that are in a dormant or unresponsive state. As such, there is growing interest in improving the durable anti-tumor activity of tumor vaccines. Failure of vaccine-activated T cells to protect against tumors is thought to be the result of the immune escape mechanisms of tumor cells and the intricate immunosuppressive tumor microenvironment. In this review, we discuss how tumor cells and the tumor microenvironment influence the effects of tumor infiltrating lymphocytes and summarize how to improve the efficacy of tumor vaccines by improving the design of current tumor vaccines and combining tumor vaccines with other therapies, such as metabolic therapy, immune checkpoint blockade immunotherapy and epigenetic therapy.

Boiling histotripsy and in-situ CD40 stimulation improve the checkpoint blockade therapy of poorly immunogenic tumors

Background: Advanced stage cancers with a suppressive tumor microenvironment (TME) are often refractory to immune checkpoint inhibitor (ICI) therapy. Recent studies have shown that focused ultrasound (FUS) TME-modulation can synergize ICI therapy, but enhancing survival outcomes in poorly immunogenic tumors remains challenging. Here, we investigated the role of focused ultrasound based boiling histotripsy (HT) and in-situ anti-CD40 agonist antibody (αCD40) combinatorial therapy in enhancing therapeutic efficacy against ICI refractory murine melanoma. Methods: Unilateral and bilateral large (~330-400 mm3) poorly immunogenic B16F10 melanoma tumors were established in the flank regions of mice. Tumors were exposed to single local HT followed by an in-situ administration of αCD40 (HT+ αCD40: HT40). Inflammatory signatures post treatment were assessed using pan-cancer immune profiling and flow cytometry. The ability of HT40 ± ICI to enhance local and systemic effects was determined by immunological characterization of the harvested tissues, and by tumor growth delay of local and distant untreated tumors 4-6 weeks post treatment. Results: Immune profiling revealed that HT40 upregulated a variety of inflammatory markers in the tumors. Immunologically, HT40 treated tumors showed an increased population of granzyme B+ expressing functional CD8+ T cells (~4-fold) as well as an increased M1 to M2 macrophage ratio (~2-3-fold) and CD8+ T: regulatory T cell ratio (~5-fold) compared to the untreated control. Systemically, the proliferation rates of the melanoma-specific memory T cell population were significantly enhanced by HT40 treatment. Finally, the combination of HT40 and ICI therapy (anti-CTLA-4 and anti-PD-L1) caused superior inhibition of distant untreated tumors, and prolonged survival rates compared to the control. Conclusions: Data suggest that HT40 reprograms immunologically cold tumors and sensitizes them to ICI therapy. This approach may be clinically useful for treating advanced stage melanoma cancers.

Improving antitumor efficacy via combinatorial regimens of oncolytic virotherapy

As a promising therapeutic strategy, oncolytic virotherapy has shown potent anticancer efficacy in numerous pre-clinical and clinical trials. Oncolytic viruses have the capacity for conditional-replication within carcinoma cells leading to cell death via multiple mechanisms, including direct lysis of neoplasms, induction of immunogenic cell death, and elicitation of innate and adaptive immunity. In addition, these viruses can be engineered to express cytokines or chemokines to alter tumor microenvironments. Combination of oncolytic virotherapy with other antitumor therapeutic modalities, such as chemotherapy and radiation therapy as well as cancer immunotherapy can be used to target a wider range of tumors and promote therapeutic efficacy. In this review, we outline the basic biological characteristics of oncolytic viruses and the underlying mechanisms that support their use as promising antitumor drugs. We also describe the enhanced efficacy attributed to virotherapy combined with other drugs for the treatment of cancer.

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.

Piscine orthoreovirus: Biology and distribution in farmed and wild fish

Piscine orthoreovirus (PRV) is a common and widely distributed virus of salmonids. Since its discovery in 2010, the virus has been detected in wild and farmed stocks from North America, South America, Europe and East Asia in both fresh and salt water environments. Phylogenetic analysis suggests three distinct genogroups of PRV with generally discrete host tropisms and/or regional patterns. PRV-1 is found mainly in Atlantic (Salmo salar), Chinook (Oncorhynchus tshawytscha) and Coho (Oncorhynchus kisutch) Salmon of Europe and the Americas; PRV-2 has only been detected in Coho Salmon of Japan; and PRV-3 has been reported primarily in Rainbow Trout (Oncorhynchus mykiss) in Europe. All three genotypes can establish high-load systemic infections by targeting red blood cells for principal replication. Each genotype has also demonstrated potential to cause circulatory disease. At the same time, high-load PRV infections occur in non-diseased salmon and trout, indicating a complexity for defining PRV's role in disease aetiology. Here, we summarize the current body of knowledge regarding PRV following 10 years of study.

Oncolytic poxvirus CF33-hNIS-ΔF14.5 favorably modulates tumor immune microenvironment and works synergistically with anti-PD-L1 antibody in a triple-negative breast cancer model

Triple-negative breast cancer is the most aggressive subtype of breast cancer and is difficult to treat. Breast cancer is considered to be poorly immunogenic and hence is less responsive to immunotherapies. We tested whether the oncolytic poxvirus CF33-hNIS-ΔF14.5 could modulate tumor immune microenvironment and make the tumors responsive to the immune checkpoint inhibitor anti-PD-L1. We found that virus infection causes the upregulation of PD-L1 levels on triple-negative breast cancer cells in vitro as well as in vivo in mice. In a mouse model of orthotopic triple-negative breast cancer, the virus was found to increase tumor infiltration by CD8+ T cells. Likewise, in mice treated with CF33-hNIS-ΔF14.5 high levels of proinflammatory cytokines IFNγ and IL-6 were found in the tumors but not in the serum. The levels of immune modulation were even higher in mice that were treated with a combination of the virus and anti-PD-L1 antibody. While CF33-hNIS-ΔF14.5 and anti-PD-L1 antibody failed to exert significant anti-tumor effect as a single agent, a combination of the two agents resulted in significant anti-tumor effect with 50% mice experiencing complete tumor regression when both agents were injected intra-tumorally. Furthermore, the ‘cured’ mice did not develop tumor after re-challenge with the same cancer cells suggesting that they developed immunity against those cancer cells. Taken together, our study shows that CF33-hNIS-ΔF14.5 favorably modulates tumor immune microenvironment in triple-negative breast cancer model making them responsive to the immune checkpoint inhibitor anti-PD-L1, and hence warrants further studies to determine the clinical applicability of this combination therapy.

Pembrolizumab in Combination with the Oncolytic Virus Pelareorep and Chemotherapy in Patients with Advanced Pancreatic Adenocarcinoma: A Phase Ib Study

PURPOSE

Pelareorep is an intravenously delivered oncolytic reovirus that can induce a T-cell-inflamed phenotype in pancreatic ductal adenocarcinoma (PDAC). Tumor tissues from patients treated with pelareorep have shown reovirus replication, T-cell infiltration, and upregulation of PD-L1. We hypothesized that pelareorep in combination with pembrolizumab and chemotherapy in patients with PDAC would be safe and effective.

PATIENTS AND METHODS

A phase Ib single-arm study enrolled patients with PDAC who progressed after first-line treatment. Patients received pelareorep, pembrolizumab, and either 5-fluorouracil, gemcitabine, or irinotecan until disease progression or unacceptable toxicity. Study objectives included safety and dose-limiting toxicities, tumor response, evaluation for reovirus replication, and immune analysis in peripheral blood and tumor biopsies.

RESULTS

Eleven patients were enrolled. Disease control was achieved in three of the 10 efficacy-evaluable patients. One patient achieved partial response for 17.4 months. Two additional patients achieved stable disease, lasting 9 and 4 months, respectively. Treatment was well tolerated, with mostly grade 1 or 2 treatment-related adverse events, including flu-like symptoms. Viral replication was observed in on-treatment tumor biopsies. T-cell receptor sequencing from peripheral blood revealed the creation of new T-cell clones during treatment. High peripheral clonality and changes in the expression of immune genes were observed in patients with clinical benefit.

CONCLUSIONS

Pelareorep and pembrolizumab added to chemotherapy did not add significant toxicity and showed encouraging efficacy. Further evaluation of pelareorep and anti-PD-1 therapy is ongoing in follow-up studies. This research highlights the potential utility of several pretreatment and on-treatment biomarkers for pelareorep therapy warranting further investigation.

Therapy-Induced MHC I Ligands Shape Neo-Antitumor CD8 T Cell Responses during Oncolytic Virus-Based Cancer Immunotherapy

Oncolytic viruses (OVs), known for their cancer-killing characteristics, also overturn tumor-associated defects in antigen presentation through the MHC class I pathway and induce protective neo-antitumor CD8 T cell responses. Nonetheless, whether OVs shape the tumor MHC-I ligandome remains unknown. Here, we investigated if an OV induces the presentation of novel MHC I-bound tumor antigens (termed tumor MHC-I ligands). Using comparative mass spectrometry (MS)-based MHC-I ligandomics, we determined differential tumor MHC-I ligand expression following treatment with oncolytic reovirus in a murine ovarian cancer model. In vitro, we found that reovirus changes the tumor ligandome of cancer cells. Concurrent multiplexed quantitative proteomics revealed that the reovirus-induced changes in tumor MHC-I ligand presentation were mostly independent of their source proteins. In an in vivo model, tumor MHC-I ligands induced by reovirus were detectable not only in tumor tissues but also the spleens (a source of antigen-presenting cells) of tumor-bearing mice. Most importantly, therapy-induced MHC-I ligands stimulated antigen-specific IFNγ responses in antitumor CD8 T cells from mice treated with reovirus. These data show that therapy-induced MHC-I ligands may shape underlying neo-antitumor CD8 T cell responses. As such, they should be considered in strategies promoting the efficacy of OV-based cancer immunotherapies.

Inhibition of Pyruvate Dehydrogenase Kinase Enhances the Antitumor Efficacy of Oncolytic Reovirus

Oncolytic viruses (OV) such as reovirus preferentially infect and kill cancer cells. Thus, the mechanisms that dictate the susceptibility of cancer cells to OV-induced cytotoxicity hold the key to their success in clinics. Here, we investigated whether cancer cell metabolism defines its susceptibility to OV and if OV-induced metabolic perturbations can be therapeutically targeted. Using mass spectrometry-based metabolomics and extracellular flux analysis on a panel of cancer cell lines with varying degrees of susceptibility to reovirus, we found that OV-induced changes in central energy metabolism, pyruvate metabolism, and oxidative stress correlate with their susceptibility to reovirus. In particular, reovirus infection accentuated Warburg-like metabolic perturbations in cell lines relatively resistant to oncolysis. These metabolic changes were facilitated by oxidative stress-induced inhibitory phosphorylation of pyruvate dehydrogenase (PDH) that impaired the routing of pyruvate into the tricarboxylic acid cycle and established a metabolic state unsupportive of OV replication. From the therapeutic perspective, reactivation of PDH in cancer cells that were weakly sensitive for reovirus, either through PDH kinase (PDK) inhibitors dichloroacetate and AZD7545 or short hairpin RNA-specific depletion of PDK1, enhanced the efficacy of reovirus-induced oncolysis in vitro and in vivo. These findings identify targeted metabolic reprogramming as a possible combination strategy to enhance the antitumor effects of OV in clinics. SIGNIFICANCE: This study proposes targeted metabolic reprogramming as a valid combinatorial strategy to enhance the translational efficacy of oncolytic virus-based cancer therapies.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/15/3824/F1.large.jpg.

Systemically Administered Reovirus-Induced Downregulation of Hypoxia Inducible Factor-1α in Subcutaneous Tumors

Reovirus, which possesses a 10-segmented double-stranded RNA genome, mediates superior antitumor effects via not only virus replication in a tumor cell-specific manner but also other mechanisms distinct from virus replication. Several groups, including ours, reported the reovirus-mediated downregulation of hypoxia inducible factor-1α (HIF-1α) following infection in cultured tumor cells; however, it remained to be clarified whether reovirus downregulates the expression of HIF-1α and its target genes in tumor-bearing hosts. We found that reovirus induced significant downregulation of protein levels of HIF-1α and its target genes in the subcutaneous tumors at 120 h post-systemic administration. Expression of reovirus capsid protein σ3 was found in the pimonidazole-positive hypoxic area in the tumor. Significant levels of tumor cell apoptosis were not found in the tumors of reovirus-treated mice at this time point, suggesting that reovirus-mediated tumor cell killing did not largely contribute to the downregulation of HIF-1α protein levels in the tumors. UV-inactivated reovirus did not induce downregulation of HIF-1α expression in the tumors, indicating that virus replication was indispensable for downregulation of HIF-1α expression in the subcutaneous tumors. This study provides important information for the development of reovirus-mediated virotherapy against various types of tumors.

Early Investigations and Recent Advances in Intraperitoneal Immunotherapy for Peritoneal Metastasis

Peritoneal metastasis (PM) is an advanced stage malignancy largely refractory to modern therapy. Intraperitoneal (IP) immunotherapy offers a novel approach for the control of regional disease of the peritoneal cavity by breaking immune tolerance. These strategies include heightening T-cell response and vaccine induction of anti-cancer memory against tumor-associated antigens. Early investigations with chimeric antigen receptor T cells (CAR-T cells), vaccine-based therapies, dendritic cells (DCs) in combination with pro-inflammatory cytokines and natural killer cells (NKs), adoptive cell transfer, and immune checkpoint inhibitors represent significant advances in the treatment of PM. IP delivery of CAR-T cells has shown demonstrable suppression of tumors expressing carcinoembryonic antigen. This response was enhanced when IP injected CAR-T cells were combined with anti-PD-L1 or anti-Gr1. Similarly, CAR-T cells against folate receptor α expressing tumors improved T-cell tumor localization and survival when combined with CD137 co-stimulatory signaling. Moreover, IP immunotherapy with catumaxomab, a trifunctional antibody approved in Europe, targets epithelial cell adhesion molecule (EpCAM) and has shown considerable promise with control of malignant ascites. Herein, we discuss immunologic approaches under investigation for treatment of PM.

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 virus immunotherapies in ovarian cancer: moving beyond adenoviruses

Ovarian cancer is the 5th most common cancer in UK women with a high relapse rate. The overall survival for ovarian cancer has remained low for decades prompting a real need for new therapies. Recurrent ovarian cancer remains confined in the peritoneal cavity in >80% of the patients, providing an opportunity for locoregional administration of novel therapeutics, including gene and viral therapy approaches. Immunotherapy is an expanding field, and includes oncolytic viruses as well as monoclonal antibodies, immune checkpoint inhibitors, and therapeutic vaccines. Oncolytic viruses cause direct cancer cell cytolysis and immunogenic cell death and subsequent release of tumor antigens that will prime for a potent tumor-specific immunity. This effect may be further enhanced when the viruses are engineered to express, or coadministered with, immunostimulatory molecules. Currently, the most commonly used and well-characterized vectors utilized for virotherapy purposes are adenoviruses. They have been shown to work synergistically with traditional chemotherapy and radiotherapy and have met with success in clinical trials. However, pre-existing immunity and poor in vivo models limit our ability to fully investigate the potential of oncolytic adenovirus as effective immunotherapies which in turn fosters the need to develop alternative viral vectors. In this review we cover recent advances in adenovirus-based oncolytic therapies targeting ovarian cancer and recent advances in mapping immune responses to oncolytic virus therapies in ovarian cancer.

A Phase II Study of Pelareorep (REOLYSIN®) in Combination with Gemcitabine for Patients with Advanced Pancreatic Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) has a poor prognosis, with 1 and 5-year survival rates of ~18% and 7% respectively. FOLFIRINOX or gemcitabine in combination with nab-paclitaxel are standard treatment options for metastatic disease. However, both regimens are more toxic than gemcitabine alone. Pelareorep (REOLYSIN®), a proprietary isolate of reovirus Type 3 Dearing, has shown antitumor activity in clinical and preclinical models. In addition to direct cytotoxic effects, pelareorep can trigger antitumor immune responses. Due to the high frequency of RAS mutations in PDAC, we hypothesized that pelareorep would promote selective reovirus replication in pancreatic tumors and enhance the anticancer activity of gemcitabine. Chemotherapy-naïve patients with advanced PDAC were eligible for the study. The primary objective was Clinical Benefit Rate (complete response (CR) + partial response (PR) + stable disease (SD) ≥ 12 weeks) and secondary objectives include overall survival (OS), toxicity, and pharmacodynamics (PD) analysis. The study enrolled 34 patients; results included one partial response, 23 stable disease, and 5 progressive disease. The median OS was 10.2 months, with a 1- and 2-year survival rate of 45% and 24%, respectively. The treatment was well tolerated with manageable nonhematological toxicities. PD analysis revealed reovirus replication within pancreatic tumor and associated apoptosis. Upregulation of immune checkpoint marker PD-L1 suggests future consideration of combining oncolytic virus therapy with anti-PD-L1 inhibitors. We conclude that pelareorep complements single agent gemcitabine in PDAC.

Oncolytic Reovirus Inhibits Immunosuppressive Activity of Myeloid-Derived Suppressor Cells in a TLR3-Dependent Manner

Oncolytic reovirus, which possesses 10 segments of dsRNA genome, mediates antitumor effects via not only virus replication in a tumor cell-specific manner, but also activation of antitumor immunity; however, the mechanism(s) of reovirus-induced activation of antitumor immunity have not been fully elucidated. Recent studies have demonstrated that overcoming an immunosuppressive environment in tumor-bearing hosts is important to achieve efficient activation of antitumor immunity. Among the various types of cells involved in immunosuppression, it has been revealed that myeloid-derived suppressor cells (MDSCs) are significantly increased in tumor-bearing hosts and play crucial roles in the immunosuppression in tumor-bearing hosts. In this study, we examined whether reovirus inhibits the immunosuppressive activity of MDSCs, resulting in efficient activation of immune cells after in vivo administration. The results showed that splenic MDSCs recovered from PBS-treated tumor-bearing mice significantly suppressed the Ag-specific proliferation of CD8⁺ T cells. In contrast, the suppressive activity of MDSCs on T cell proliferation was significantly reduced after reovirus administration. Reovirus also inhibited the immunosuppressive activity of MDSCs in IFN-β promoter stimulator-1 knockout (KO) mice and in wild-type mice. In contrast, the immunosuppressive activity of MDSCs in TLR-3 KO mice was not significantly altered by reovirus treatment. The activation levels of CD4⁺ and CD8⁺ T cells were significantly lower in TLR3 KO mice than in wild-type mice after reovirus administration. These results indicate that reovirus inhibits the immunosuppressive activity of MDSCs in a TLR3, but not IFN-β promoter stimulator-1, signaling-dependent manner.

Immunotherapy for thoracic oncology gone viral

Immune therapy has now been incorporated into the standard of care for non-small-cell lung cancer based on randomized trials showing superiority of anti-PD1 antibodies compared with chemotherapy. Thus there is a renewed interest in immune approaches to treating lung cancer. One promising approach is with oncolytic viruses that either naturally or through engineering, preferentially infect or kill cancer cells. In preclinical models of different thoracic cancers, it has been found that these viruses can induce immune responses through multiple mechanisms. Thus, in addition to their direct cytolytic effects, oncolytic viruses can also promote antitumor immunity. This review will discuss the immune effects of oncolytic viruses lung cancers and the approaches that are underway to augment immune therapy in clinical testing.

Potentiating prostate cancer immunotherapy with oncolytic viruses

The clinical effectiveness of immunotherapies for prostate cancer remains subpar compared with that for other cancers. The goal of most immunotherapies is the activation of immune effectors, such as T cells and natural killer cells, as the presence of these activated mediators positively correlates with patient outcomes. Clinical evidence shows that prostate cancer is immunogenic, accessible to the immune system, and can be targeted by antitumour immune responses. However, owing to the detrimental effects of prostate-cancer-associated immunosuppression, even the newest immunotherapeutic approaches fail to initiate the clinically desired antitumour immune reaction. Oncolytic viruses, originally used for their preferential cancer-killing activity, are now being recognized for their ability to overturn cancer-associated immune evasion and promote otherwise absent antitumour immunity. This oncolytic-virus-induced subversion of tumour-associated immunosuppression can potentiate the effectiveness of current immunotherapeutics, including immune checkpoint inhibitors (for example, antibodies against programmed cell death protein 1 (PD1), programmed cell death 1 ligand 1 (PDL1), and cytotoxic T lymphocyte antigen 4 (CTLA4)) and chemotherapeutics that induce immunogenic cell death (for example, doxorubicin and oxaliplatin). Importantly, oncolytic-virus-induced antitumour immunity targets existing prostate cancer cells and also establishes long-term protection against future relapse. Hence, the strategic use of oncolytic viruses as monotherapies or in combination with current immunotherapies might result in the next breakthrough in prostate cancer immunotherapy.

A randomized phase II study of pelareorep and docetaxel or docetaxel alone in men with metastatic castration resistant prostate cancer: CCTG study IND 209

BACKGROUND

Pelareorep is an oncolytic virus with activity in many cancers including prostate. It has in vitro synergism with microtubule-targeted agents. We undertook a clinical trial evaluating pelareorep in mCRPC patients receiving docetaxel.

PATIENTS AND METHODS

In this randomized, open-label phase II study, patients received docetaxel 75mg/m2 on day 1 of a 21-day cycle and prednisone 5mg twice daily, in combination with pelareorep (arm A) or alone (arm B). The primary endpoint was 12 weeks lack of disease progression rate (LPD).

RESULTS

Eighty-five pts were randomized. Median age was 69, ECOG performance status was 0/1/2 in 31%/66%/3% of patients. Bone/regional lymph node/liver metastases were present in 98%/24%/6%. The median prognostic score was slightly higher in Arm A (144 vs. 129 p= 0.005). Adverse events were as expected but more prevalent in arm A. The 12-week LPD rate was 61% and 52.4% in arms A/B (p=0.51). Median survival was 19.1 on Arm A and 21.1 months on Arm B (HR 1.83; 95% CI 0.96 to 3.52; p=0.06). No survival benefit of pelareorep was found.

CONCLUSION

Pelareorep with docetaxel was tolerable with comparable LPD in both arms but response and survival were inferior and so this combination does not merit further study.