Customized Viral Immunotherapy for HPV-Associated Cancer

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.

Personalizing Oncolytic Immunovirotherapy Approaches

Development of successful cancer therapeutics requires exploration of the differences in genetics, metabolism, and interactions with the immune system among malignant and normal cells. The clinical observation of spontaneous tumor regression following natural infection with microorganism has created the premise of their use as cancer therapeutics. Oncolytic viruses (OVs) originate from viruses with attenuated virulence in humans, well-characterized vaccine strains of known human pathogens, or engineered replication-deficient viral vectors. Their selectivity is based on receptor expression level and post entry restriction factors that favor replication in the tumor, while keeping the normal cells unharmed. Clinical trials have demonstrated a wide range of patient responses to virotherapy, with subgroups of patients significantly benefiting from OV administration. Tumor-specific gene signatures, including antiviral interferon-stimulated gene (ISG) expression profile, have demonstrated a strong correlation with tumor permissiveness to infection. Furthermore, the combination of OVs with immunotherapeutics, including anticancer vaccines and immune checkpoint inhibitors [ICIs, such as anti-PD-1/PD-L1 or anti-CTLA-4 and chimeric antigen receptor (CAR)-T or CAR-NK cells], could synergistically improve the therapeutic outcome. Creating response prediction algorithms represents an important step for the transition to individualized immunovirotherapy approaches in the clinic. Integrative predictors could include tumor mutational burden (TMB), inflammatory gene signature, phenotype of tumor-infiltrating lymphocytes, tumor microenvironment (TME), and immune checkpoint receptor expression on both immune and target cells. Additionally, the gut microbiota has recently been recognized as a systemic immunomodulatory factor and could further be used in the optimization of individualized immunovirotherapy algorithms.

Therapeutic efficacy of a VSV-GP-based human papilloma virus vaccine in a murine cancer model

Human papilloma virus (HPV) infections are associated with almost all cervical cancers and to a lower extend also with anogenital or oropharyngeal cancers. HPV proteins expressed in HPV-associated tumors are attractive antigens for cancer vaccination strategies as self-tolerance, which is associated with most endogenous tumor-associated antigens, does not need to be overcome. In this study, we generated a live attenuated cancer vaccine based on the chimeric vesicular stomatitis virus VSV-GP, which has previously proven to be a potent vaccine vector and oncolytic virus. Genes at an earlier position in the genome more to the 3' end are expressed stronger compared to genes located further downstream. By inserting an HPV16-derived antigen cassette consisting of E2, E6 and E7 into VSV-GP either at first (HPVp1) or fifth (HPVp5) position in VSV-GP's genome we aimed to analyze the effect of vaccine antigen position and consequently expression level on viral fitness, immunogenicity, and anti-tumoral efficacy in a syngeneic mouse tumor model. HPVp1 expressed higher amounts of HPV antigens compared to HPVp5 in vitro but had a slightly delayed replication kinetic which overall translated into increased HPV-specific T cell responses upon vaccination of mice. Immunization with both vectors protected mice in prophylactic and in therapeutic TC-1 tumor models with HPVp1 being more effective in the prophylactic setting. Taken together, VSV-GP is a promising candidate as therapeutic HPV vaccine and first position of the vaccine antigen in a VSV-derived vector seems to be superior to fifth position.

Oncolytic ImmunoViroTherapy: A long history of crosstalk between viruses and immune system for cancer treatment

Cancer Immunotherapy relies on harnessing a patient's immune system to fine-tune specific anti-tumor responses and ultimately eradicate cancer. Among diverse therapeutic approaches, oncolytic viruses (OVs) have emerged as a novel form of cancer immunotherapy. OVs are a naturally occurring or genetically modified class of viruses able to selectively kill cancer cells, leaving healthy cells unharmed; in the last two decades, the role of OVs has been redefined to act beyond their oncolytic activity. Indeed, the immunogenic cancer cell death mediated by OVs induces the release of tumor antigens that in turn induces anti-tumor immunity, allowing OVs to act as in situ therapeutic cancer vaccines. Additionally, OVs can be engineered for intratumoral delivery of immunostimulatory molecules such as tumor antigens or cytokines to further enhance anti-tumor response. Moreover, OVs can be used in combination with other cancer immunotherapeutic approaches such as Immune Checkpoint Inhibitors and CAR-T cells. The current review first defines the three main mechanisms of action (MOA) of OVs currently used in cancer therapy that are: i) Oncolysis, ii) OV-induced cancer-specific immune activation, and iii) Exploiting pre-existing anti-viral immunity to enhance cancer therapy. Secondly, we focus on how OVs can induce and/or improve anti-cancer immunity in a specific or unspecific fashion, highlighting the importance of these approaches. Finally, the last part of the review analyses OVs combined with other cancer immunotherapies, revising present and future clinical applications.

A New Generation of Vaccines in the Age of Immunotherapy

PURPOSE OF REVIEW

Cancer vaccines are one of the most extensively studied immunotherapy type in solid tumors. Despite favorable presuppositions, so far, the use of cancer vaccines has been associated with disappointing results. However, a new generation of vaccines has been developed, promising to revolutionize the immunotherapy field.

RECENT FINDINGS

In this review, we aim to highlight the advances in cancer vaccines and the remaining hurdles to overcome. Cancer vaccination has experienced tremendous progress in the last decade, with myriad promising developments. Future efforts should focus on optimization of target identification, streamlining of most appropriate vaccination strategies, and adjuvant development, as well as predictive biomarker identification. Cautious optimism is warranted in the face of early successes seen in recent clinical trials for oncolytic vaccines. If an approach were to prove successful, it could revolutionize cancer therapy the way ICIs did in the previous decade.

A modular self-adjuvanting cancer vaccine combined with an oncolytic vaccine induces potent antitumor immunity

Functional tumor-specific cytotoxic T cells elicited by therapeutic cancer vaccination in combination with oncolytic viruses offer opportunities to address resistance to checkpoint blockade therapy. Two cancer vaccines, the self-adjuvanting protein vaccine KISIMA, and the recombinant oncolytic vesicular stomatitis virus pseudotyped with LCMV-GP expressing tumor-associated antigens, termed VSV-GP-TAA, both show promise as a single agent. Here we find that, when given in a heterologous prime-boost regimen with an optimized schedule and route of administration, combining KISIMA and VSV-GP-TAA vaccinations induces better cancer immunity than individually. Using several mouse tumor models with varying degrees of susceptibility for viral replication, we find that priming with KISIMA-TAA followed by VSV-GP-TAA boost causes profound changes in the tumor microenvironment, and induces a large pool of poly-functional and persistent antigen-specific cytotoxic T cells in the periphery. Combining this heterologous vaccination with checkpoint blockade further improves therapeutic efficacy with long-term survival in the spectrum. Overall, heterologous vaccination with KISIMA and VSV-GP-TAA could sensitize non-inflamed tumors to checkpoint blockade therapy.

Successful cancer immune therapy correlates with a T cell-inflamed tumour microenvironment. Authors show here that co-administration of a self-adjuvanting protein vaccine and an antigen-expressing oncolytic virus in an optimised regimen strongly enhances T cell immunogenicity and may turn non-inflamed tumours proinflammatory and less resistant to checkpoint blockade therapy.

Tumor Immunity and Immunotherapy for HPV-Related Cancers

Human papillomavirus (HPV) infection drives tumorigenesis in the majority of cervical, oropharyngeal, anal, and vulvar cancers. Genetic and epidemiologic evidence has highlighted the role of immunosuppression in the oncogenesis of HPV-related malignancies. Here we review how HPV modulates the immune microenvironment and subsequent therapeutic implications. We describe the landscape of immunotherapies for these cancers with a focus on findings from early-phase studies exploring antigen-specific treatments, and discuss future directions. Although responses across these studies have been modest to date, a deeper understanding of HPV-related tumor biology and immunology may prove instrumental for the development of more efficacious immunotherapeutic approaches. SIGNIFICANCE: HPV modulates the microenvironment to create a protumorigenic state of immune suppression and evasion. Our understanding of these mechanisms has led to the development of immunomodulatory treatments that have shown early clinical promise in patients with HPV-related malignancies. This review summarizes our current understanding of the interactions of HPV and its microenvironment and provides insight into the progress and challenges of developing immunotherapies for HPV-related malignancies.

Mechanisms that allow vaccination against an oncolytic vesicular stomatitis virus-encoded transgene to enhance safety without abrogating oncolysis

Vaccination can prevent viral infections via virus-specific T cells, among other mechanisms. A goal of oncolytic virotherapy is replication of oncolytic viruses (OVs) in tumors, so pre-existing T cell immunity against an OV-encoded transgene would seem counterproductive. We developed a treatment for melanomas by pre-vaccinating against an oncolytic vesicular stomatitis virus (VSV)-encoded tumor antigen. Surprisingly, when the VSV-vectored booster vaccine was administered at the peak of the primary effector T cell response, oncolysis was not abrogated. We sought to determine how oncolysis was retained during a robust T cell response against the VSV-encoded transgene product. A murine melanoma model was used to identify two mechanisms that enable this phenomenon. First, tumor-infiltrating T cells had reduced cytopathic potential due to immunosuppression. Second, virus-induced lymphopenia acutely removed virus-specific T cells from tumors. These mechanisms provide a window of opportunity for replication of oncolytic VSV and rationale for a paradigm change in oncolytic virotherapy, whereby immune responses could be intentionally induced against a VSV-encoded melanoma-associated antigen to improve safety without abrogating oncolysis.

Immunotherapy and Gene Therapy for Oncoviruses Infections: A Review

Immunotherapy has been shown to be highly effective in some types of cancer caused by viruses. Gene therapy involves insertion or modification of a therapeutic gene, to correct for inappropriate gene products that cause/may cause diseases. Both these types of therapy have been used as alternative ways to avoid cancers caused by oncoviruses. In this review, we summarize recent studies on immunotherapy and gene therapy including the topics of oncolytic immunotherapy, immune checkpoint inhibitors, gene replacement, antisense oligonucleotides, RNA interference, clustered regularly interspaced short palindromic repeats Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-based gene editing, transcription activator-like effector nucleases (TALENs) and custom treatment for Epstein-Barr virus, human T-lymphotropic virus 1, hepatitis B virus, human papillomavirus, hepatitis C virus, herpesvirus associated with Kaposi's sarcoma, Merkel cell polyomavirus, and cytomegalovirus.

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.

The Role of Bcl-xL Protein in Viral Infections

Bcl-xL represents a family of proteins responsible for the regulation of the intrinsic apoptosis pathway. Due to its anti-apoptotic activity, Bcl-xL co-determines the viability of various virally infected cells. Their survival may determine the effectiveness of viral replication and spread, dynamics of systemic infection, and viral pathogenesis. In this paper, we have reviewed the role of Bcl-xL in the context of host infection by eight different RNA and DNA viruses: hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency virus (HIV), influenza A virus (IAV), Epstein-Barr virus (EBV), human T-lymphotropic virus type-1 (HTLV-1), Maraba virus (MRBV), Schmallenberg virus (SBV) and coronavirus (CoV). We have described an influence of viral infection on the intracellular level of Bcl-xL and discussed the impact of Bcl-xL-dependent cell survival control on infection-accompanying pathogenic events such as tissue damage or oncogenesis. We have also presented anti-viral treatment strategies based on the pharmacological regulation of Bcl-xL expression or activity.

New viral vectors for infectious diseases and cancer

Since the discovery in 1796 by Edward Jenner of vaccinia virus as a way to prevent and finally eradicate smallpox, the concept of using a virus to fight another virus has evolved into the current approaches of viral vectored genetic vaccines. In recent years, key improvements to the vaccinia virus leading to a safer version (Modified Vaccinia Ankara, MVA) and the discovery that some viruses can be used as carriers of heterologous genes encoding for pathological antigens of other infectious agents (the concept of 'viral vectors') has spurred a new wave of clinical research potentially providing for a solution for the long sought after vaccines against major diseases such as HIV, TB, RSV and Malaria, or emerging infectious diseases including those caused by filoviruses and coronaviruses. The unique ability of some of these viral vectors to stimulate the cellular arm of the immune response and, most importantly, T lymphocytes with cell killing activity, has also reawakened the interest toward developing therapeutic vaccines against chronic infectious diseases and cancer. To this end, existing vectors such as those based on Adenoviruses have been improved in immunogenicity and efficacy. Along the same line, new vectors that exploit viruses such as Vesicular Stomatitis Virus (VSV), Measles Virus (MV), Lymphocytic choriomeningitis virus (LCMV), cytomegalovirus (CMV), and Herpes Simplex Virus (HSV), have emerged. Furthermore, technological progress toward modifying their genome to render some of these vectors incompetent for replication has increased confidence toward their use in infant and elderly populations. Lastly, their production process being the same for every product has made viral vectored vaccines the technology of choice for rapid development of vaccines against emerging diseases and for 'personalised' cancer vaccines where there is an absolute need to reduce time to the patient from months to weeks or days. Here we review the recent developments in viral vector technologies, focusing on novel vectors based on primate derived Adenoviruses and Poxviruses, Rhabdoviruses, Paramixoviruses, Arenaviruses and Herpesviruses. We describe the rationale for, immunologic mechanisms involved in, and design of viral vectored gene vaccines under development and discuss the potential utility of these novel genetic vaccine approaches in eliciting protection against infectious diseases and cancer.

The Changing Landscape of Therapeutic Cancer Vaccines-Novel Platforms and Neoantigen Identification

Therapeutic cancer vaccines, an exciting development in cancer immunotherapy, share the goal of creating and amplifying tumor-specific T-cell responses, but significant obstacles still remain to their success. Here, we briefly outline the principles underlying cancer vaccine therapy with a focus on novel vaccine platforms and antigens, underscoring the renewed optimism. Numerous strategies have been investigated to overcome immunosuppressive mechanisms of the tumor microenvironment (TME) and counteract tumor escape, including improving antigen selection, refining delivery platforms, and use of combination therapies. Several new cancer vaccine platforms and antigen targets are under development. In an effort to amplify tumor-specific T-cell responses, a heterologous prime-boost antigen delivery strategy is increasingly used for virus-based vaccines. Viruses have also been engineered to express targeted antigens and immunomodulatory molecules simultaneously, to favorably modify the TME. Nanoparticle systems have shown promise as delivery vectors for cancer vaccines in preclinical research. T-win is another platform targeting both tumor cells and the TME, using peptide-based vaccines that engage and activate T cells to target immunoregulatory molecules expressed on immunosuppressive and malignant cells. With the availability of next-generation sequencing, algorithms for neoantigen selection are emerging, and several bioinformatic platforms are available to select therapeutically relevant neoantigen targets for developing personalized therapies. However, more research is needed before the use of neoepitope prediction and personalized immunotherapy becomes commonplace. Taken together, the field of therapeutic cancer vaccines is fast evolving, with the promise of potential synergy with existing immunotherapies for long-term cancer treatment.

Live-attenuated lymphocytic choriomeningitis virus-based vaccines for active immunotherapy of HPV16-positive cancer

Infection with human papillomavirus (HPV) is associated with a variety of cancer types and limited therapy options. Therapeutic cancer vaccines targeting the HPV16 oncoproteins E6 and E7 have recently been extensively explored as a promising immunotherapy approach to drive durable antitumor T cell immunity and induce effective tumor control. With the goal to achieve potent and lasting antitumor T cell responses, we generated a novel lymphocytic choriomeningitis virus (LCMV)-based vaccine, TT1-E7E6, targeting HPV16 E6 and E7. This replication-competent vector was stably attenuated using a three-segmented viral genome packaging strategy. Compared to wild-type LCMV, TT1-E7E6 demonstrated significantly reduced viremia and CNS immunopathology. Intravenous vaccination of mice with TT1-E7E6 induced robust expansion of HPV16-specific CD8⁺ T cells producing IFN-γ, TNF-α and IL-2. In the HPV16 E6 and E7-expressing TC-1 tumor model, mice immunized with TT1-E7E6 showed significantly delayed tumor growth or complete tumor clearance accompanied with prolonged survival. Tumor control by TT1-E7E6 was also achieved in established large-sized tumors in this model. Furthermore, a combination of TT1-E7E6 with anti-PD-1 therapy led to enhanced antitumor efficacy with complete tumor regression in the majority of tumor-bearing mice that were resistant to anti-PD-1 treatment alone. TT1-E7E6 vector itself did not exhibit oncolytic properties in TC-1 cells, while the antitumor effect was associated with the accumulation of HPV16-specific CD8⁺ T cells with reduced PD-1 expression in the tumor tissues. Together, our results suggest that TT1-E7E6 is a promising therapeutic vaccine for HPV-positive cancers.

Enhanced immunotherapeutic profile of oncolytic virus-based cancer vaccination using cyclophosphamide preconditioning

Despite a sizeable body of research, the efficacy of therapeutic cancer vaccines remains limited when applied as sole agents. By using a prime:boost approach involving two viral cancer vaccines, we were able to generate large tumor-specific CD8⁺ T-cell responses in a murine model of disseminated pulmonary melanoma. Significant increases in the number and quality of circulating effector T-cells were documented when low-dose cyclophosphamide (CTX) was administered pre-vaccination to tumor-bearing but not tumor-free hosts. Interestingly, tumor-bearing mice receiving CTX and co-primed with a melanoma differentiation antigen together with an irrelevant control antigen exhibited significantly enhanced immunity against the tumor, but not the control antigen, in secondary lymphoid organs. This result highlighted an increased cancer-specific reactivity of vaccine-induced T-cell responses following CTX preconditioning. Additionally, an acute reduction of the frequency of peripheral regulatory T-cells (Tregs) was noticeable, particularly in the proliferating, presumably tumour-reactive, subset. Enhanced infiltration of lungs with multifunctional T-cells resulted in overt reduction in metastatic burden in mice pretreated with CTX. Despite doubling the median survival in comparison to untreated controls, most vaccinated mice ultimately succumbed to cancer progression. However, preconditioning of the virus-based vaccination with CTX resulted in a remarkable improvement of the therapeutic activity leading to complete remission in the majority of the animals. Collectively, these data reveal how CTX can potentiate specific cellular immunity in an antigen-restricted manner that is only observed in vaccinated tumor-bearing hosts while depleting replicating Tregs. A single low dose of CTX enhances antitumor immunity and the efficacy of this potent prime:boost platform by modulating the kinetics of the vaccine-specific responses. Clinical assessment of CTX combined with next-generation cancer vaccines is indicated.

Combination therapy with oncolytic viruses and immune checkpoint inhibitors

Introduction: Immune checkpoint inhibitors (ICI) have dramatically improved the outcome for cancer patients across multiple tumor types. However the response rates to ICI monotherapy remain relatively low, in part due to some tumors cultivating an inherently 'cold' immune microenvironment. Oncolytic viruses (OV) have the capability to promote a 'hotter' immune microenvironment which can improve the efficacy of ICI.Areas covered: In this article we conducted a literature search through Pubmed/Medline to identify relevant articles in both the pre-clinical and clinical settings for combining OVs with ICIs and discuss the impact of this approach on treatment as well as changes within the tumor microenvironment. We also explore the future directions of this novel combination strategy.Expert opinion: The imminent results of the Phase 3 study combining pembrolizumab with or without T-Vec injection are eagerly awaited. OV/ICI combinations remain one of the most promising avenues to explore in the success of cancer immunotherapy.

Measles Vaccines Designed for Enhanced CD8+ T Cell Activation

Priming and activation of CD8⁺ T cell responses is crucial to achieve anti-viral and anti-tumor immunity. Live attenuated measles vaccine strains have been used successfully for immunization for decades and are currently investigated in trials of oncolytic virotherapy. The available reverse genetics systems allow for insertion of additional genes, including heterologous antigens. Here, we designed recombinant measles vaccine vectors for priming and activation of antigen-specific CD8⁺ T cells. For proof-of-concept, we used cytotoxic T lymphocyte (CTL) lines specific for the melanoma-associated differentiation antigen tyrosinase-related protein-2 (TRP-2), or the model antigen chicken ovalbumin (OVA), respectively. We generated recombinant measles vaccine vectors with TRP-2 and OVA epitope cassette variants for expression of the full-length antigen or the respective immunodominant CD8⁺ epitope, with additional variants mediating secretion or proteasomal degradation of the epitope. We show that these recombinant measles virus vectors mediate varying levels of MHC class I (MHC-I)-restricted epitope presentation, leading to activation of cognate CTLs, as indicated by secretion of interferon-gamma (IFNγ) in vitro. Importantly, the recombinant OVA vaccines also mediate priming of naïve OT-I CD8⁺ T cells by dendritic cells. While all vaccine variants can prime and activate cognate T cells, IFNγ release was enhanced using a secreted epitope variant and a variant with epitope strings targeted to the proteasome. The principles presented in this study will facilitate the design of recombinant vaccines to elicit CD8⁺ responses against pathogens and tumor antigens.

Oncolytic Viruses: Priming Time for Cancer Immunotherapy

New immuno-oncology therapies are improving cancer treatments beyond the former standard of care, as evidenced by the recent and continuing clinical approvals for immunotherapies in a broad range of indications. However, a majority of patients (particularly those with immunologically cold tumors) still do not benefit, highlighting the need for rational combination approaches. Oncolytic viruses (OV) both directly kill tumor cells and inflame the tumor microenvironment. While OV spread can be limited by the generation of antiviral immune responses, the initial local tumor cell killing can reverse the immunosuppressive tumor microenvironment, resulting in more effective release of tumor-associated antigens (TAAs), cross-presentation, and antitumoral effector T cell recruitment. Moreover, many OVs can be engineered to express immunomodulatory genes. Rational combination approaches to cancer immunotherapy include the use of OVs in combination with immune checkpoint inhibitors (ICIs) or adoptive T cell therapy (ACT) to promote sustained antitumoral immune responses. OV combinations have additive or synergistic efficacy in preclinical tumor models with ICIs or ACT. Several preclinical studies have confirmed systemic reactivation and proliferation of adoptively transferred antitumoral T cells in conjunction with oncolytic OVs (expressing cytokines or TAAs) resulting from the specific tumor cell killing and immunostimulation of the tumor microenvironment which leads to increased tumor trafficking, activity, and survival. Recent clinical trials combining OVs with ICIs have shown additive effects in melanoma. Additional clinical data in an expanded range of patient indications are eagerly awaited. The relative timings of OV and ICI combination remains under-studied and is an area for continued exploration. Studies systematically exploring the effects of systemic ICIs prior to, concomitantly with, or following OV therapy will aid in the future design of clinical trials to enhance efficacy and increase patient response rates.

Considerations for Clinical Translation of MG1 Maraba Virus

Oncolytic viral immunotherapy based on the MG1 Maraba platform has undergone extensive preclinical evaluation, resulting in the advancement of two programs into clinical trials. MG1 Maraba encoding tumor antigens (tumor associated antigens or viral antigens) are used to boost antitumor immunity, while MG1 Maraba infects tumors, causes oncolysis and transforms the tumor microenvironment. An overview of MG1 Maraba clinical development is outlined here, along with general considerations relating to the design of clinical trials for complex biologic products such as oncolytic viral immunotherapies. These include choice of patient population, optimized treatment regimen, and endpoints which provide early signals of activity and inform the late-stage development path of these agents with novel mechanisms of action.

Detection of Tumor Antigen-Specific T-Cell Responses After Oncolytic Vaccination

Oncolytic vaccines, which consist of recombinant oncolytic viruses (OV) encoding tumor-associated antigens (TAAs), have demonstrated potent antitumor efficacy in preclinical models and are currently evaluated in phase I/II clinical trials. On one hand, oncolysis of OV-infected malignant entities reinstates cancer immunosurveillance. On the other hand, overexpression of TAAs in infected cells further stimulates the adaptive arm of antitumor immunity. Particularly, the presence of tumor-specific CD8⁺ T lymphocytes within the tumor microenvironment, as well as in the periphery, has demonstrated prognostic value for cancer treatments. These effector CD8⁺ T cells can be detected through their production of the prototypical Tc1 cytokine: IFN-γ. The quantitative and qualitative assessment of this immune cell subset remains critical in the development process of efficient cancer vaccines, including oncolytic vaccines. The present chapter will describe a single-cell immunological assay, namely the intracellular cytokine staining (ICS), that allows the enumeration of IFN-γ-producing TAA-specific CD8⁺ T cells in various tissues (tumor, blood, lymphoid organs) following oncolytic vaccination.

Design and application of oncolytic viruses for cancer immunotherapy

The approval of the first oncolytic virus (OV) for the treatment of metastatic melanoma and the recent discovery that the use of oncolytic viruses may enhance cancer immunotherapies targeted against various immune checkpoint proteins have attracted great interest in the field of cancer virotherapy. OVs are designed to target and kill cancer cells leaving normal cell unharmed. OV infection and concomitant cancer cell killing stimulate anti-tumour immunity and modulates tumour microenvironment towards less immunosuppressive phenotype. The intrinsic capacity of OVs to turn immunologically cold tumours into immunologically hot tumours, and to increase immune cell and cytokine infiltration, can be further enhanced by arming OVs with transgenes that increase their immunostimulatory activities and direct immune responses specifically towards cancer cells. These OVs, specifically engineered to be used as cancer immunotherapeutics, can be synergized with other immune modulators or cytotoxic agents to achieve the most potent immunotherapy for cancer.

Immunology of Adenoviral Vectors in Cancer Therapy

Adenoviruses are a commonly utilized virus for gene therapy platforms worldwide. Since adenovirus components are characterized as highly immunogenic, their immunogenicity inhibits the widespread use of adenoviral vectors to treat genetic disorders. However, stimulation of the immune response can be exploited for cancer immunotherapy platforms, and thus adenoviral vectors are used for therapeutic gene transfer, vaccines, and oncolytic agents in the cancer gene therapy field. It is now accepted that the generation of anti-tumor immune responses induced by oncolytic adenovirus treatments is critical for their anti-tumor efficacy. As such, in cancer immunotherapy with adenoviral vectors, a balance must be struck between induction of anti-adenoviral and anti-tumor immune responses. The recent trend in adenoviral-based cancer gene therapy is the development of adenoviral vectors to enhance immune responses and redirect them toward tumors. This review focuses on anti-adenoviral immunity and how adenovirotherapies skew the immune response toward an anti-tumor response.

Updates on Oncolytic Virus Immunotherapy for Cancers

The 2018 annual Cambridge Healthtech Institute's International Immuno-Oncology Summit in Boston, MA convened late August, and academic and industry researchers were allowed to debate and discuss oncolytic virology during the virus immunotherapy portion of the conference. The breakthrough agent, TVEC/IMLYGIC, as well as most other oncolytic viruses (OVs) in clinical trials, are demonstrating an immense synergy with T cell checkpoint inhibitors. To this extent, the marriage of T cell checkpoint inhibitors and OV is now vastly accepted, indicating the next phase in OVs is the recruitment of the immune system, and tailoring the immune response toward tumor clearance is a far better strategy than directly lysing the tumor outright with virus. The next field-shaping question for OVs is how to convert a patient's immune response against their tumor. The talks this year focused on whether OVs can cause the emergence of a strong anti-tumor immunity intrinsically or whether vectors, which educate the immune system to detect tumor antigens, were more efficacious. Speakers presented novel transgenes to arm OVs and systems biology approaches to discover the best viral backbones to engineer into vectors. Here we summarize the meeting's keynote talks, thematic principles running through the summit, and current developments in the OV field.

Development and applications of oncolytic Maraba virus vaccines

Oncolytic activity of the MG1 strain of the Maraba vesiculovirus has proven efficacy in numerous preclinical cancer models, and relied not only on a direct cytotoxicity but also on the induction of both innate and adaptive antitumor immunity. To further expand tumor-specific T-cell effector and long-lasting memory compartments, we introduced the MG1 virus in a prime-boost cancer vaccine strategy. To this aim, a replication-incompetent adenoviral [Ad] vector together with the oncolytic MG1 have each been armed with a transgene expressing a same tumor antigen. Immune priming with the Ad vaccine subsequently boosted with the MG1 vaccine mounted tumor-specific responses of remarkable magnitude, which significantly prolonged survival in various murine cancer models. Based on these promising results, we validated the safety profile of the Ad:MG1 oncolytic vaccination strategy in nonhuman primates and initiated clinical investigations in cancer patients. Two clinical trials are currently under way (NCT02285816; NCT02879760). The present review will recapitulate the discoveries that led to the development of MG1 oncolytic vaccines from bench to bedside.

Preclinical evaluation of a MAGE-A3 vaccination utilizing the oncolytic Maraba virus currently in first-in-human trials

Multiple immunotherapeutics have been approved for cancer patients, however advanced solid tumors are frequently refractory to treatment. We evaluated the safety and immunogenicity of a vaccination approach with multimodal oncolytic potential in non-human primates (NHP) (Macaca fascicularis). Primates received a replication-deficient adenoviral prime, boosted by the oncolytic Maraba MG1 rhabdovirus. Both vectors expressed the human MAGE-A3. No severe adverse events were observed. Boosting with MG1-MAGEA3 induced an expansion of hMAGE-A3-specific CD4⁺ and CD8⁺ T-cells with the latter peaking at remarkable levels and persisting for several months. T-cells reacting against epitopes fully conserved between simian and human MAGE-A3 were identified. Humoral immunity was demonstrated by the detection of circulating MAGE-A3 antibodies. These preclinical data establish the capacity for the Ad:MG1 vaccination to engage multiple effector immune cell populations without causing significant toxicity in outbred NHPs. Clinical investigations utilizing this program for the treatment of MAGE-A3-positive solid malignancies are underway (NCT02285816, NCT02879760).

Trial Watch: Oncolytic viro-immunotherapy of hematologic and solid tumors

Oncolytic viruses selectively target and kill cancer cells in an immunogenic fashion, thus supporting the establishment of therapeutically relevant tumor-specific immune responses. In 2015, the US Food and Drug Administration (FDA) approved the oncolytic herpes simplex virus T-VEC for use in advanced melanoma patients. Since then, a plethora of trials has been initiated to assess the safety and efficacy of multiple oncolytic viruses in patients affected with various malignancies. Here, we summarize recent preclinical and clinical progress in the field of oncolytic virotherapy.

CXCL9 promotes prostate cancer progression through inhibition of cytokines from T cells

Chemokines have been demonstrated to serve an important role in a variety of diseases, particularly in tumor progression. There have been numerous studies that have reported that T cells serve major roles in tumor progression. However, the function of CXC motif chemokine ligand 9 (CXCL9) in prostate cancer remains unknown. The present study aimed to investigate the role of CXCL9 in prostate cancer. A prostate cancer mouse model was generated by treating C57/BL‑6 and B6.Cg‑Selplgtm1Fur/J mice with 3,2'‑dimethyl 4‑aminobiphenyl (DMAB). Hematoxylin and eosin staining detected the histopathological alterations of mouse prostate tissues. Immunohistochemistry (IHC) staining determined cell proliferation of the mice. Flow cytometry was used to detect the alterations of T cells in C57+DMAB or CXCL9+DMAB mice. Immunofluorescence revealed that there was positive expression of interleukin‑6 (IL‑6) and transforming growth factor (TGF)‑β in the mouse tissues. The survival rates of C57+DMAB and CXCL9+DMAB mice was analyzed. The association of CXCL9 expression and clinical stages was also evaluated. Results revealed that prostate cancer pathology and cell proliferation in CXCL9+DMAB mice were significantly greater compared with the C57+DMAB mice. Compared with C57+DMAB mice, the number of T cells in peripheral blood and spleen of CXCL9+DMAB mice was significantly reduced. IHC demonstrated that the expression of IL‑6 and TGF‑β was significantly downregulated in the CXCL9+DMAB mice. The survival rate of CXCL9+DMAB mice was significantly decreased compared with the C57+DMAB mice. In addition, reverse transcription‑quantitative polymerase chain reaction analysis demonstrated that CXCL9 mRNA expression in clinical samples was positively associated with clinical pathological stages of prostate cancer. In conclusion, CXCL9 may promote prostate cancer progression via inhibition of cytokines from T cells.

Preclinical Development of Oncolytic Immunovirotherapy for Treatment of HPVPOS Cancers

Immunotherapy for HPV^POS malignancies is attractive because well-defined, viral, non-self tumor antigens exist as targets. Several approaches to vaccinate therapeutically against HPV E6 and E7 antigens have been adopted, including viral platforms such as VSV. A major advantage of VSV expressing these antigens is that VSV also acts as an oncolytic virus, leading to direct tumor cell killing and induction of effective anti-E6 and anti-E7 T cell responses. We have also shown that addition of immune adjuvant genes, such as IFNβ, further enhances safety and/or efficacy of VSV-based oncolytic immunovirotherapies. However, multiple designs of the viral vector are possible—with respect to levels of immunogen expression and method of virus attenuation—and optimal designs have not previously been tested head-to-head. Here, we tested three different VSV engineered to express a non-oncogenic HPV16 E7/6 fusion protein for their immunotherapeutic and oncolytic properties. We assessed their profiles of efficacy and toxicity against HPV^POS and HPV^NEG murine tumor models and determined the optimal route of administration. Our data show that VSV is an excellent platform for the oncolytic immunovirotherapy of tumors expressing HPV target antigens, combining a balance of efficacy and safety suitable for evaluation in a first-in-human clinical trial.

Rhabdoviruses as vaccine platforms for infectious disease and cancer

The family Rhabdoviridae (RV) comprises a large, genetically diverse collection of single-stranded, negative sense RNA viruses from the order Mononegavirales. Several RV members are being developed as live-attenuated vaccine vectors for the prevention or treatment of infectious disease and cancer. These include the prototype recombinant Vesicular Stomatitis Virus (rVSV) and the more recently developed recombinant Maraba Virus, both species within the genus Vesiculoviridae. A relatively strong safety profile in humans, robust immunogenicity and genetic malleability are key features that make the RV family attractive vaccine platforms. Currently, the rVSV vector is in preclinical development for vaccination against numerous high-priority infectious diseases, with clinical evaluation underway for HIV/AIDS and Ebola virus disease. Indeed, the success of the rVSV-ZEBOV vaccine during the 2014-15 Ebola virus outbreak in West Africa highlights the therapeutic potential of rVSV as a vaccine vector for acute, life-threatening viral illnesses. The rVSV and rMaraba platforms are also being tested as 'oncolytic' cancer vaccines in a series of phase 1-2 clinical trials, after being proven effective at eliciting immune-mediated tumour regression in preclinical mouse models. In this review, we discuss the biological and genetic features that make RVs attractive vaccine platforms and the development and ongoing testing of rVSV and rMaraba strains as vaccine vectors for infectious disease and cancer.

Transforming the prostatic tumor microenvironment with oncolytic virotherapy

Prostate cancer (PCa) was estimated to have the second highest global incidence rate for male non-skin tumors and is the fifth most deadly in men thus mandating the need for novel treatment options. MG1-Maraba is a potent and versatile oncolytic virus capable of lethally infecting a variety of prostatic tumor cell lines alongside primary PCa biopsies and exerts direct oncolytic effects against large TRAMP-C2 tumors in vivo. An oncolytic immunotherapeutic strategy utilizing a priming vaccine and intravenously administered MG1-Maraba both expressing the human six-transmembrane antigen of the prostate (STEAP) protein generated specific CD8+ T-cell responses against multiple STEAP epitopes and resulted in functional breach of tolerance. Treatment of mice with bulky TRAMP-C2 tumors using oncolytic STEAP immunotherapy induced an overt delay in tumor progression, marked intratumoral lymphocytic infiltration with an active transcriptional profile and up-regulation of MHC class I. The preclinical data generated here offers clear rationale for clinically evaluating this approach for men with advanced PCa.

Preclinical development of peptide vaccination combined with oncolytic MG1-E6E7 for HPV-associated cancer

Human papilloma virus (HPV)-associated cancer is a significant global health burden and despite the presence of viral transforming antigens within neoplastic cells, therapeutic vaccinations are ineffective for advanced disease. HPV positive TC1 cells are susceptible to viral oncolysis by MG1-E6E7, a custom designed oncolytic Maraba virus. Epitope mapping of mice vaccinated with MG1-E6E7 enabled the rational design of synthetic long peptide (SLP) vaccines against HPV16 and HPV18 antigens. SLPs were able to induce specific CD8+ immune responses and the magnitude of these responses significantly increased when boosted by MG1-E6E7. Logically designed vaccination induced multi-functional CD8+ T cells and provided complete sterilising immunity of mice challenged with TC1 cells. In mice bearing large HPV-positive tumours, SLP vaccination combined with MG1-E6E7 was able to clear tumours in 60% of mice and these mice were completely protected against a long term aggressive re-challenge with the TC1 tumour model. Combining conventional SLPs with the multi-functional oncolytic MG1-E6E7 represents a promising approach against advanced HPV positive neoplasia.