A novel therapeutic regimen to eradicate established solid tumors with an effective induction of tumor-specific immunity

An Update on the Clinical Status, Challenges, and Future Directions of Oncolytic Virotherapy for Malignant Gliomas

OPINION STATEMENT

Malignant gliomas are common central nervous system tumors that pose a significant clinical challenge due to the lack of effective treatments. Glioblastoma (GBM), a grade 4 malignant glioma, is the most prevalent primary malignant brain tumor and is associated with poor prognosis. Current clinical trials are exploring various strategies to combat GBM, with oncolytic viruses (OVs) appearing particularly promising. In addition to ongoing and recently completed clinical trials, one OV (Teserpaturev, Delytact®) received provisional approval for GBM treatment in Japan. OVs are designed to selectively target and eliminate cancer cells while promoting changes in the tumor microenvironment that can trigger and support long-lasting anti-tumor immunity. OVs offer the potential to remodel the tumor microenvironment and reverse systemic immune exhaustion. Additionally, an increasing number of OVs are armed with immunomodulatory payloads or combined with immunotherapy approaches in an effort to promote anti-tumor responses in a tumor-targeted manner. Recently completed oncolytic virotherapy trials can guide the way for future treatment individualization through patient preselection, enhancing the likelihood of achieving the highest possible clinical success. These trials also offer valuable insight into the numerous challenges inherent in malignant glioma treatment, some of which OVs can help overcome.

The need for paradigm shift: prognostic significance and implications of standard therapy-related systemic immunosuppression in glioblastoma for immunotherapy and oncolytic virotherapy

Despite significant advances in our knowledge regarding the genetics and molecular biology of gliomas over the past two decades and hundreds of clinical trials, no effective therapeutic approach has been identified for adult patients with newly diagnosed glioblastoma, and overall survival remains dismal. Great hopes are now placed on combination immunotherapy. In clinical trials, immunotherapeutics are generally tested after standard therapy (radiation, temozolomide, and steroid dexamethasone) or concurrently with temozolomide and/or steroids. Only a minor subset of patients with progressive/recurrent glioblastoma have benefited from immunotherapies. In this review, we comprehensively discuss standard therapy-related systemic immunosuppression and lymphopenia, their prognostic significance, and the implications for immunotherapy/oncolytic virotherapy. The effectiveness of immunotherapy and oncolytic virotherapy (viro-immunotherapy) critically depends on the activity of the host immune cells. The absolute counts, ratios, and functional states of different circulating and tumor-infiltrating immune cell subsets determine the net immune fitness of patients with cancer and may have various effects on tumor progression, therapeutic response, and survival outcomes. Although different immunosuppressive mechanisms operate in patients with glioblastoma/gliomas at presentation, the immunological competence of patients may be significantly compromised by standard therapy, exacerbating tumor-related systemic immunosuppression. Standard therapy affects diverse immune cell subsets, including dendritic, CD4+, CD8+, natural killer (NK), NKT, macrophage, neutrophil, and myeloid-derived suppressor cell (MDSC). Systemic immunosuppression and lymphopenia limit the immune system's ability to target glioblastoma. Changes in the standard therapy are required to increase the success of immunotherapies. Steroid use, high neutrophil-to-lymphocyte ratio (NLR), and low post-treatment total lymphocyte count (TLC) are significant prognostic factors for shorter survival in patients with glioblastoma in retrospective studies; however, these clinically relevant variables are rarely reported and correlated with response and survival in immunotherapy studies (e.g., immune checkpoint inhibitors, vaccines, and oncolytic viruses). Our analysis should help in the development of a more rational clinical trial design and decision-making regarding the treatment to potentially improve the efficacy of immunotherapy or oncolytic virotherapy.

Mathematical modeling predicts pathways to successful implementation of combination TRAIL-producing oncolytic virus and PAC-1 to treat granulosa cell tumors of the ovary

The development of new cancer therapies requires multiple rounds of validation from in vitro and in vivo experiments before they can be considered for clinical trials. Mathematical models assist in this preclinical phase by combining experimental data with human parameters to provide guidance about potential therapeutic regimens to bring forward into trials. However, granulosa cell tumors of the ovary lack a relevant mouse model, complexifying preclinical drug development for this rare tumor. To bridge this gap, we established a mathematical model as a framework to explore the potential of using a tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-producing oncolytic vaccinia virus in combination with the chemotherapeutic agent first procaspase activating compound (PAC-1). We have previously shown that TRAIL and PAC-1 act synergistically on granulosa tumor cells. In line with our previous results, our current model predicts that, although it is unable to stop the tumor from growing in its current form, combination oral PAC-1 with oncolytic virus (OV) provides the best result compared to monotherapies. Encouragingly, our results suggest that increases to the OV infection rate can lead to the success of this combination therapy within a year. The model developed here can continue to be improved as more data become available, allowing for regimen-tailoring via virtual clinical trials, ultimately shepherding effective regimens into trials.

Personalized neoantigen viro-immunotherapy platform for triple-negative breast cancer

BACKGROUND

Triple-negative breast cancer (TNBC) corresponds to approximately 20% of all breast tumors, with a high propensity for metastasis and a poor prognosis. Because TNBC displays a high mutational load compared with other breast cancer types, a neoantigen-based immunotherapy strategy could be effective. One major bottleneck in the development of a neoantigen-based vaccine for TNBC is the selection of the best targets, that is, tumor-specific neoantigens which are presented at the surface of tumor cells and capable of eliciting robust immune responses. In this study, we aimed to set up a platform for identification and delivery of immunogenic neoantigens in a vaccine regimen for TNBC using oncolytic vaccinia virus (VV).

METHODS

We used bioinformatic tools and cell-based assays to identify immunogenic neoantigens in TNBC patients' samples, human and murine cell lines. Immunogenicity of the neoantigens was tested in vitro (human) and ex vivo (murine) in T-cell assays. To assess the efficacy of our regimen, we used a preclinical model of TNBC where we treated tumor-bearing mice with neoantigens together with oncolytic VV and evaluated the effect on induction of neoantigen-specific CD8+T cells, tumor growth and survival.

RESULTS

We successfully identified immunogenic neoantigens and generated neoantigen-specific CD8+T cells capable of recognizing a human TNBC cell line expressing the mutated gene. Using a preclinical model of TNBC, we showed that our tumor-specific oncolytic VV was able to change the tumor microenvironment, attracting and maintaining mature cross-presenting CD8α+dendritic cells and effector T-cells. Moreover, when delivered in a prime/boost regimen together with oncolytic VV, long peptides encompassing neoantigens were able to induce neoantigen-specific CD8+T cells, slow tumor growth and increase survival.

CONCLUSIONS

Our study provides a promising approach for the development of neoantigen-based immunotherapies for TNBC. By identifying immunogenic neoantigens and developing a delivery system through tumor-specific oncolytic VV, we have demonstrated that neoantigen-based vaccines could be effective in inducing neoantigen-specific CD8+T cells response with significant impact on tumor growth. Further studies are needed to determine the safety and efficacy of this approach in clinical trials.

Viral Vector-Based Gene Therapy

Gene therapy is a technique involving the modification of an individual's genes for treating a particular disease. The key to effective gene therapy is an efficient carrier delivery system. Viral vectors that have been artificially modified to lose their pathogenicity are used widely as a delivery system, with the key advantages of their natural high transduction efficiency and stable expression. With decades of development, viral vector-based gene therapies have achieved promising clinical outcomes. Currently, the three key vector strategies are based on adeno-associated viruses, adenoviruses, and lentiviruses. However, certain challenges, such as immunotoxicity and "off-target", continue to exist. In the present review, the above three viral vectors are discussed along with their respective therapeutic applications. In addition, the major translational challenges encountered in viral vector-based gene therapies are summarized, and the possible strategies to address these challenges are also discussed.

Syrian hamster as an ideal animal model for evaluation of cancer immunotherapy

Cancer immunotherapy (CIT) has emerged as an exciting new pillar of cancer treatment. Although benefits have been achieved in individual patients, the overall response rate is still not satisfactory. To address this, an ideal preclinical animal model for evaluating CIT is urgently needed. Syrian hamsters present similar features to humans with regard to their anatomy, physiology, and pathology. Notably, the histological features and pathological progression of tumors and the complexity of the tumor microenvironment are equivalent to the human scenario. This article reviews the current tumor models in Syrian hamster and the latest progress in their application to development of tumor treatments including immune checkpoint inhibitors, cytokines, adoptive cell therapy, cancer vaccines, and oncolytic viruses. This progress strongly advocates Syrian hamster as an ideal animal model for development and assessment of CIT for human cancer treatments. Additionally, the challenges of the Syrian hamster as an animal model for CIT are also discussed.

Application of CRISPR/Cas9 Technology in Cancer Treatment: A Future Direction

Gene editing, especially with clustered regularly interspaced short palindromic repeats associated protein 9 (CRISPR-Cas9), has advanced gene function science. Gene editing's rapid advancement has increased its medical/clinical value. Due to its great specificity and efficiency, CRISPR/Cas9 can accurately and swiftly screen the whole genome. This simplifies disease-specific gene therapy. To study tumor origins, development, and metastasis, CRISPR/Cas9 can change genomes. In recent years, tumor treatment research has increasingly employed this method. CRISPR/Cas9 can treat cancer by removing genes or correcting mutations. Numerous preliminary tumor treatment studies have been conducted in relevant fields. CRISPR/Cas9 may treat gene-level tumors. CRISPR/Cas9-based personalized and targeted medicines may shape tumor treatment. This review examines CRISPR/Cas9 for tumor therapy research, which will be helpful in providing references for future studies on the pathogenesis of malignancy and its treatment.

Preexisting immunity: Barrier or bridge to effective oncolytic virus therapy?

Oncolytic viruses (OVs) represent a highly promising treatment strategy for a wide range of cancers, by mediating both the direct killing of tumor cells as well as mobilization of antitumor immune responses. As many OVs circulate in the human population, preexisting OV-specific immune responses are prevalent. Indeed, neutralizing antibodies (NAbs) are abundantly present in the human population for commonly used OVs, such as Adenovirus type 5 (Ad5), Herpes Simplex Virus-1 (HSV-1), Vaccinia virus, Measles virus, and Reovirus. This review discusses (pre)clinical evidence regarding the effect of preexisting immunity against OVs on two distinct aspects of OV therapy; OV infection and spread, as well as the immune response induced upon OV therapy. Combined, this review provides evidence that consideration of preexisting immunity is crucial in realizing the full potential of the highly promising therapeutic implementation of OVs. Future investigation of current gaps in knowledge highlighted in this review should yield a more complete understanding of this topic, ultimately allowing for better and more personalized OV therapies.

Oncolytic Viruses and Cancer Immunotherapy

PURPOSE OF REVIEW

Oncolytic viruses (OVs) exert their antitumor effect through selective killing of cancer cells and induction of host anti-tumor immunity. This review aims to summarize the recent and current trials with OVs for the treatment of lung cancer.

RECENT FINDINGS

Several OVs have been developed for the treatment of lung cancer including adenovirus, coxsackievirus B3, reovirus, and vaccinia virus and trials have demonstrated a safe toxicity profile. Early-phase trials in lung cancer with OVs have reported antiviral immune responses and evidence of clinical benefit. However, clinical efficacy of OVs in lung cancer either as monotherapy or in combination with chemotherapy has not been confirmed in larger phase II or III trials. Development of OVs in lung cancer has been limited by difficulty in administering OVs in the tumor directly as well as achieving adequate viral load at all tumor sites with systemically administered OVs. Developing novel combinations with OVs, especially checkpoint inhibitors and other immunotherapeutics, may be a strategy to address the limited success seen thus far. Integrating appropriate biomarker studies and meaningful endpoints in future clinical trials will be imperative. Using novel viral delivery systems in addition to increasing tumor specificity through improved genetic modifications in the OVs are other strategies to improve efficacy.

Cancer-associated inflammation: pathophysiology and clinical significance

Purpose

Cancer cells, despite stemming from the own cells of their host, usually elicit an immune response. This response usually enables elimination of cancer at its earliest stages. However, some tumors develop mechanisms of escaping immune destruction and even profiting from tumor-derived inflammation.

Methods

We summarized the roles of different immune cell populations in various processes associated with cancer progression and possible methods of reshaping tumor-associated inflammation to increase the efficacy of cancer therapy.

Results

Changes in various signaling pathways result in attraction of immunosuppressive, pro-tumorigenic cells, such as myeloid-derived suppressor cells, tumor-associated macrophages, and neutrophils, while at the same time suppressing the activity of lymphocytes, which have the potential of destroying cancer cells. These changes promote tumor progression by increasing angiogenesis and growth, accelerating metastasis, and impairing drug delivery to the tumor site.

Conclusion

Due to its multi-faceted role in cancer, tumor-associated inflammation can serve as a valuable therapy target. By increasing it, whether through decreasing overall immunosuppression with immune checkpoint inhibitor therapy or through more specific methods, such as cancer vaccines, oncolytic viruses, or chimeric antigen receptor T cells, cancer-derived immunosuppression can be overcome, resulting in immune system destroying cancer cells. Even changes occurring in the microbiota can influence the shape of antitumor response, which could provide new attractive diagnostic or therapeutic methods. Interestingly, also decreasing the distorted tumor-associated inflammation with non-steroidal anti-inflammatory drugs can lead to positive outcomes.

Win or loss? Combination therapy does improve the oncolytic virus therapy to pancreatic cancer

Pancreatic cancer (PC) is a growing global burden, remaining one of the most lethal cancers of the gastrointestinal tract. Moreover, PC is resistant to various treatments such as chemotherapy, radiotherapy, and immunotherapy. New therapies are urgently needed to improve the prognosis of PC. Oncolytic virus (OV) therapy is a promising new treatment option. OV is a genetically modified virus that selectively replicates in tumor cells. It can kill tumor cells without harming normal cells. The activation of tumor-specific T-cells is a unique feature of OV-mediated therapy. However, OV-mediated mono-therapeutic efficacy remains controversial, especially for metastatic or advanced patients who require systemically deliverable therapies. Hence, combination therapies will be critical to improve the therapeutic efficacy of OV-mediated therapy and prevent tumor recurrence. This review aims to investigate novel combinatorial treatments with OV therapy and explore the inner mechanism of those combined therapies, hopefully providing a new direction for a better prognosis of PC.

Oncolytic Vaccinia Virus in Lung Cancer Vaccines

Therapeutic cancer vaccines represent a promising therapeutic modality via the induction of long-term immune response and reduction in adverse effects by specifically targeting tumor-associated antigens. Oncolytic virus, especially vaccinia virus (VV) is a promising cancer treatment option for effective cancer immunotherapy and thus can also be utilized in cancer vaccines. Non-small cell lung cancer (NSCLC) is likely to respond to immunotherapy, such as immune checkpoint inhibitors or cancer vaccines, since it has a high tumor mutational burden. In this review, we will summarize recent applications of VV in lung cancer treatment and discuss the potential and direction of VV-based therapeutic vaccines.

In silico trials predict that combination strategies for enhancing vesicular stomatitis oncolytic virus are determined by tumor aggressivity

Background

Immunotherapies, driven by immune-mediated antitumorigenicity, offer the potential for significant improvements to the treatment of multiple cancer types. Identifying therapeutic strategies that bolster antitumor immunity while limiting immune suppression is critical to selecting treatment combinations and schedules that offer durable therapeutic benefits. Combination oncolytic virus (OV) therapy, wherein complementary OVs are administered in succession, offer such promise, yet their translation from preclinical studies to clinical implementation is a major challenge. Overcoming this obstacle requires answering fundamental questions about how to effectively design and tailor schedules to provide the most benefit to patients.

Methods

We developed a computational biology model of combined oncolytic vaccinia (an enhancer virus) and vesicular stomatitis virus (VSV) calibrated to and validated against multiple data sources. We then optimized protocols in a cohort of heterogeneous virtual individuals by leveraging this model and our previously established in silico clinical trial platform.

Results

Enhancer multiplicity was shown to have little to no impact on the average response to therapy. However, the duration of the VSV injection lag was found to be determinant for survival outcomes. Importantly, through treatment individualization, we found that optimal combination schedules are closely linked to tumor aggressivity. We predicted that patients with aggressively growing tumors required a single enhancer followed by a VSV injection 1 day later, whereas a small subset of patients with the slowest growing tumors needed multiple enhancers followed by a longer VSV delay of 15 days, suggesting that intrinsic tumor growth rates could inform the segregation of patients into clinical trials and ultimately determine patient survival. These results were validated in entirely new cohorts of virtual individuals with aggressive or non-aggressive subtypes.

Conclusions

Based on our results, improved therapeutic schedules for combinations with enhancer OVs can be studied and implemented. Our results further underline the impact of interdisciplinary approaches to preclinical planning and the importance of computational approaches to drug discovery and development.

Recombinant Orthopoxvirus Primes Colon Cancer for Checkpoint Inhibitor and Cross-Primes T Cells for Antitumor and Antiviral Immunity

Although it is known that oncolytic viruses can inflame and recruit immune cells to otherwise immunosuppressed tumor microenvironments, the influence of the antiviral immune response on antitumor immunity is less clear across viral platforms and tumor types. CF33 is a recombinant orthopoxvirus backbone effective against colon cancer. We tested derivatives of CF33 with and without immune-checkpoint inhibition (anti-PD-L1) in mouse models of colon cancer. Results showed that the efficacy of CF33 backbone with J2R deletion (single-deleted) against colon cancer is not altered by additional deletion of F14.5L in vitro or in vivo CF33 infection upregulated PD-L1 expression on tumor cells and led to an increased influx of lymphocytes and macrophages in tumors. Also, the levels of active CD8⁺ (IFNγ⁺) T cells in the virus-treated tumors were higher than those in control-treated tumors. Furthermore, a combination of CF33 derivatives with anti-PD-L1 resulted in durable tumor regression and long-term survival, resistant to tumor rechallenge. Analysis of immune cells from the treated mice showed that tumor-specific T cell activation occurred more robustly in tumors treated with the virus and that T cells were more strongly activated against the virus than against tumor, in an MHC-I-dependent manner. Our findings warrant further studies on the role of cross-priming of T cells against viral and tumor antigens, in the overall success of viroimmunotherapy.

Oncolytic Adenovirus in Cancer Immunotherapy

Tumor-selective replicating "oncolytic" viruses are novel and promising tools for immunotherapy of cancer. However, despite their first success in clinical trials, previous experience suggests that currently used oncolytic virus monotherapies will not be effective enough to achieve complete tumor responses and long-term cure in a broad spectrum of cancers. Nevertheless, there are reasonable arguments that suggest advanced oncolytic viruses will play an essential role as enablers of multi-stage immunotherapies including established systemic immunotherapies. Oncolytic adenoviruses (oAds) display several features to meet this therapeutic need. oAds potently lyse infected tumor cells and induce a strong immunogenic cell death associated with tumor inflammation and induction of antitumor immune responses. Furthermore, established and versatile platforms of oAds exist, which are well suited for the incorporation of heterologous genes to optimally exploit and amplify the immunostimulatory effect of viral oncolysis. A considerable spectrum of functional genes has already been integrated in oAds to optimize particular aspects of immune stimulation including antigen presentation, T cell priming, engagement of additional effector functions, and interference with immunosuppression. These advanced concepts have the potential to play a promising future role as enablers of multi-stage immunotherapies involving adoptive cell transfer and systemic immunotherapies.

Promising xenograft animal model recapitulating the features of human pancreatic cancer

BACKGROUND

Multiple sites of metastasis and desmoplastic reactions in the stroma are key features of human pancreatic cancer (PC). There are currently no simple and reliable animal models that can mimic these features for accurate disease modeling.

AIM

To create a new xenograft animal model that can faithfully recapitulate the features of human PC.

METHODS

Interleukin 2 receptor subunit gamma (IL2RG) gene knockout Syrian hamster was created and characterized. A panel of human PC cell lines were transplanted into IL2RG knockout Syrian hamsters and severe immune-deficient mice subcutaneously or orthotopically. Tumor growth, local invasion, remote organ metastasis, histopathology, and molecular alterations of tumor cells and stroma were compared over time.

RESULTS

The Syrian hamster with IL2RG gene knockout (named ZZU001) demonstrated an immune-deficient phenotype and function. ZZU001 hamsters faithfully recapitulated most features of human PC, in particular, they developed metastasis at multiple sites. PC tissues derived from ZZU001 hamsters displayed desmoplastic reactions in the stroma and epithelial to mesenchymal transition phenotypes, whereas PC tissues derived from immune-deficient mice did not present such features.

CONCLUSION

ZZU001 hamsters engrafted with human PC cells are a superior animal model compared to immune-deficient mice. ZZU001 hamsters can be a valuable animal model for better understanding the molecular mechanism of tumorigenesis and metastasis and the evaluation of new drugs targeting human PC.

Treatment and Prevention of Lung Cancer Using a Virus-Infected Reprogrammed Somatic Cell-Derived Tumor Cell Vaccination (VIReST) Regime

Lung cancer is one of the most commonly diagnosed cancer and despite therapeutic advances, mortality remains high. The long period of clinical latency associated with lung cancer provides an ideal window of opportunity to administer vaccines to at-risk individuals that can prevent tumor progression and initiate long-term anti-tumor immune surveillance. Here we describe a personalized vaccination regime that could be applied for both therapeutic and prophylactic prevention of lung cancer, based on the derivation of lung cancer cells from induced pluripotent stem cells. Stem cells from healthy mice were modified to express Cre-dependent KRASG12D and Trp53R172H prior to differentiation to lung progenitor cells. Subsequent viral delivery of Cre caused activation of exogenous driver mutations, resulting in transformation and development of lung cancer cells. iPSC-derived lung cancer cells were highly antigenically related to lung cancer cells induced in LSL-KRASG12D/+; Trp53R172H/+ transgenic mice and were antigenically unrelated to original pluripotent stem cells or pancreatic cancer cells derived using the same technological platform. For vaccination, induced lung cancer cells were infected with oncolytic Adenovirus or Vaccinia virus, to act as vaccine adjuvants, prior to delivery of vaccines sequentially to a murine inducible transgenic model of lung cancer. Application of this Virus-Infected, Reprogrammed Somatic cell-derived Tumor cell (VIReST) regime primed tumor-specific T cell responses that significantly prolonged survival in both subcutaneous post-vaccine challenge models and induced transgenic models of lung cancer, demonstrating that stem cell-derived prophylactic vaccines may be a feasible intervention for treatment or prevention of lung cancer development in at-risk individuals.

Immunoscore Guided Cold Tumors to Acquire “Temperature” Through Integrating Physicochemical and Biological Methods

Abstract Immunotherapy for the treatment of tumors has become the most compelling strategy after targeted treatment, especially for lung cancer and melanoma, as well as some blood cancers. For most remaining types of tumors (e.g., pancreatic, colorectal, and breast cancers), abundant immunotherapeutic strategies in the forms of immune checkpoint blockade, cancer vaccines, and CAR-T therapies produce little effect. Furthermore, the immunoreactions induced by various types of cancer and even in individual patients, differ among the single therapeutic immune checkpoint inhibitors, whose pre-existing immunoreaction remains to be optimized for cancer immunotherapy. According to the density of the infiltrating lymphocyte subsets at the invasive margin or core of primary solid tumors, the tumors were classified into four grades using the immunoscore, which is complementary to the tumor node metastasis (TNM) staging system in providing a better prognosis of cancer patients in addition to the classification of immunogenic hot tumors and non-immunogenic cold tumors. This review aimed to outline the features of the most difficult-to-treat and challenging cold tumors and potential approaches to transform “cold” tumors into “hot” tumors, because hot tumors are associated with a higher response rate to immunotherapy. We also summarized the current popular strategies for enhancing T cell trafficking, which may be helpful to provide an etiological basement for a more rational design of drug delivery systems and conquer drug-resistance during cancer therapy.

Comparison of Clinically Relevant Oncolytic Virus Platforms for Enhancing T Cell Therapy of Solid Tumors

Despite some promising results, the majority of patients do not benefit from T cell therapies, as tumors prevent T cells from entering the tumor, shut down their activity, or downregulate key antigens. Due to their nature and mechanism of action, oncolytic viruses have features that can help overcome many of the barriers currently facing T cell therapies of solid tumors. This study aims to understand how four different oncolytic viruses (adenovirus, vaccinia virus, herpes simplex virus, and reovirus) perform in that task. For that purpose, an immunocompetent in vivo tumor model featuring adoptive tumor-infiltrating lymphocyte (TIL) therapy was used. Tumor growth control (p < 0.001) and survival analyses suggest that adenovirus was most effective in enabling T cell therapy. The complete response rate was 62% for TILs + adenovirus versus 17.5% for TILs + PBS. Of note, TIL biodistribution did not explain efficacy differences between viruses. Instead, immunostimulatory shifts in the tumor microenvironment mirrored efficacy results. Overall, the use of oncolytic viruses can improve the utility of T cell therapies, and additional virus engineering by arming with transgenes can provide further antitumor effects. This phenomenon was seen when an unarmed oncolytic adenovirus was compared to Ad5/3-E2F-d24-hTNFa-IRES-hIL2 (TILT-123). A clinical trial is ongoing, where patients receiving TIL treatment also receive TILT-123 (ClinicalTrials.gov: NCT04217473).

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.

A Virus-Infected, Reprogrammed Somatic Cell-Derived Tumor Cell (VIReST) Vaccination Regime Can Prevent Initiation and Progression of Pancreatic Cancer

PURPOSE

Pancreatic cancer remains one of the most lethal cancers, and late detection renders most tumors refractory to conventional therapies. Development of cancer prophylaxis may be the most realistic option for improving mortality associated with this disease. Here, we develop a novel individualized prophylactic and therapeutic vaccination regimen using induced pluripotent stem cells (iPSC), gene editing, and tumor-targeted replicating oncolytic viruses.

EXPERIMENTAL DESIGN

We created a Virus-Infected, Reprogrammed Somatic cell-derived Tumor cell (VIReST) regime. iPSCs from healthy cells were induced to pancreatic tumor cells using in situ gene editing via stable provision of KRas ^G12D and p53 ^R172H tumor driver mutations. These cells were preinfected with oncolytic Adenovirus (AdV) as prime or Vaccinia virus (VV) as boost, to improve vaccine immunogenicity, prior to delivery of vaccines in a sequential regime to young KPC transgenic mice, genetically programmed to develop pancreatic cancer, to prevent and delay disease development.

RESULTS

Tumor cells preinfected with oncolytic AdV as prime or VV as boost were the best regime to induce tumor-specific immunity. iPSC-derived tumor cells were highly related in antigen repertoire to pancreatic cancer cells of KPC transgenic mice, suggesting that an individual's stem cells can provide an antigenically matched whole tumor cell vaccine. The VIReST vaccination primed tumor-specific T-cell responses, resulting in delayed disease emergence and progression and significantly prolonged survival of KPC transgenic mice. Importantly, this regime was well-tolerated and nontoxic.

CONCLUSIONS

These results provide both proof of concept and a robust technology platform for the development of personalized prophylactic cancer vaccines to prevent pancreatic malignancies in at-risk individuals.

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.

Syrian Hamster as an Animal Model for the Study on Infectious Diseases

Infectious diseases still remain one of the biggest challenges for human health. In order to gain a better understanding of the pathogenesis of infectious diseases and develop effective diagnostic tools, therapeutic agents, and preventive vaccines, a suitable animal model which can represent the characteristics of infectious is required. The Syrian hamster immune responses to infectious pathogens are similar to humans and as such, this model is advantageous for studying pathogenesis of infection including post-bacterial, viral and parasitic pathogens, along with assessing the efficacy and interactions of medications and vaccines for those pathogens. This review summarizes the current status of Syrian hamster models and their use for understanding the underlying mechanisms of pathogen infection, in addition to their use as a drug discovery platform and provides a strong rationale for the selection of Syrian hamster as animal models in biomedical research. The challenges of using Syrian hamster as an alternative animal model for the research of infectious diseases are also addressed.

Immune Conversion of Tumor Microenvironment by Oncolytic Viruses: The Protoparvovirus H-1PV Case Study

Cancer cells utilize multiple mechanisms to evade and suppress anticancer immune responses creating a “cold” immunosuppressive tumor microenvironment. Oncolytic virotherapy is emerging as a promising approach to revert tumor immunosuppression and enhance the efficacy of other forms of immunotherapy. Growing evidence indicates that oncolytic viruses (OVs) act in a multimodal fashion, inducing immunogenic cell death and thereby eliciting robust anticancer immune responses. In this review, we summarize information about OV-mediated immune conversion of the tumor microenvironment. As a case study we focus on the rodent protoparvovirus H-1PV and its dual role as an oncolytic and immune modulatory agent. Potential strategies to improve H-1PV anticancer efficacy are also discussed.

Oncolytic viruses: overcoming translational challenges

Oncolytic virotherapy (OVT) is a promising approach in which WT or engineered viruses selectively replicate and destroy tumor cells while sparing normal ones. In the last two decades, different oncolytic viruses (OVs) have been modified and tested in a number of preclinical studies, some of which have led to clinical trials in cancer patients. These clinical trials have revealed several critical limitations with regard to viral delivery, spread, resistance, and antiviral immunity. Here, we focus on promising research strategies that have been developed to overcome the aforementioned obstacles. Such strategies include engineering OVs to target a broad spectrum of tumor cells while evading the immune system, developing unique delivery mechanisms, combining other immunotherapeutic agents with OVT, and using clinically translatable mouse tumor models to potentially translate OVT more readily into clinical settings.

Recent Advances in Oncolytic Virotherapy and Immunotherapy for Glioblastoma: A Glimmer of Hope in the Search for an Effective Therapy?

To date, no targeted drugs, antibodies or combinations of chemotherapeutics have been demonstrated to be more efficient than temozolomide, or to increase efficacy of standard therapy (surgery, radiotherapy, temozolomide, steroid dexamethasone). According to recent phase III trials, standard therapy may ensure a median overall survival of up to 18⁻20 months for adult patients with newly diagnosed glioblastoma. These data explain a failure of positive non-controlled phase II trials to predict positive phase III trials and should result in revision of the landmark Stupp trial as a historical control for median overall survival in non-controlled trials. A high rate of failures in clinical trials and a lack of effective chemotherapy on the horizon fostered the development of conceptually distinct therapeutic approaches: dendritic cell/peptide immunotherapy, chimeric antigen receptor (CAR) T-cell therapy and oncolytic virotherapy. Recent early phase trials with the recombinant adenovirus DNX-2401 (Ad5-delta24-RGD), polio-rhinovirus chimera (PVSRIPO), parvovirus H-1 (ParvOryx), Toca 511 retroviral vector with 5-fluorocytosine, heat shock protein-peptide complex-96 (HSPPC-96) and dendritic cell vaccines, including DCVax-L vaccine, demonstrated that subsets of patients with glioblastoma/glioma may benefit from oncolytic virotherapy/immunotherapy (>3 years of survival after treatment). However, large controlled trials are required to prove efficacy of next-generation immunotherapeutics and oncolytic vectors.

Oncolytic adenovirus: A tool for cancer therapy in combination with other therapeutic approaches

Cancer therapy using oncolytic viruses is an emerging area, in which viruses are engineered to selectively propagate in tumor tissues without affecting healthy cells. Because of the advantages that adenoviruses (Ads) have over other viruses, they are more considered. To achieve tumor selectivity, two main modifications on Ads genome have been applied: small deletions and insertion of tissue- or tumor-specific promoters. Despite oncolytic adenoviruses ability in tumor cell lysis and immune responses stimulation, to further increase their antitumor effects, genomic modifications have been carried out including insertion of checkpoint inhibitors and antigenic or immunostimulatory molecules into the adenovirus genome and combination with dendritic cells and chemotherapeutic agents. This study reviews oncolytic adenoviruses structures, their antitumor efficacy in combination with other therapeutic strategies, and finally challenges around this treatment approach.

A compendium of adenovirus genetic modifications for enhanced replication, oncolysis, and tumor immunosurveillance in cancer therapy

In this review, we specifically focus on genetic modifications of oncolytic adenovirus 5 (Ad5)-based vectors that enhance replication, oncolysis/spread, and virus-mediated tumor immunosurveillance. The finding of negative regulation of minor core protein V by SUMOylation led to the identification of amino acid residues, which when mutated increase adenovirus replication and progeny yield. Suppression of Dicer and/or RNAi pathway with shRNA or p19 tomato bushy stunt protein also results in significant enhancement of adenovirus replication and progeny yield. Truncation mutations in E3-19K or i-leader sequence or overexpression of adenovirus death protein (ADP) potently increase adenovirus progeny release and spread without affecting virus yield. Moreover, E3-19K protein, which was found to inhibit both major histocompatibility complex I (MHCI) and MHC-I chain-related A and B proteins (MICA/MICB) expression on the cell surface, protecting infected cells from T-lymphocyte and natural killer (NK) cell attack, may be tailored to selectively target only MHCI or MICA/MICB, or to lose the ability to downregulate both. At last, E3-19K protein may be exploited to deliver tumor-associated epitopes directly to the endoplasmic reticulum for loading MHCI in the transporter associated with antigen processing (TAP)-deregulated cells.

The Oncolytic Adenovirus XVir-N-31 as a Novel Therapy in Muscle-Invasive Bladder Cancer

Muscle-invasive bladder cancer represents approximately 25% of diagnosed bladder cancer cases and carries a significant risk of death. Oncolytic viruses are novel antitumor agents with the ability to selectively replicate and lyse tumor cells while sparing healthy tissue. We explored the efficiency of the oncolytic YB-1-selective adenovirus XVir-N-31 in vitro and in an orthotopic mouse model for bladder cancer by intramural injection under ultrasound guidance. We demonstrated that XVir-N-31 replicated in bladder cancer cells and induced a stronger immunogenic cell death than wild-type adenovirus by facilitating enhanced release of HMGB1 and exosomal Hsp70. The intratumoral delivery of XVir-N-31 by ultrasound guidance delayed tumor growth in an immunodeficient model, demonstrating the feasibility of this approach to deliver oncolytic viruses directly into the tumor.

Safety of an Oncolytic Myxoma Virus in Dogs with Soft Tissue Sarcoma

Many oncolytic viruses that are efficacious in murine cancer models are ineffective in humans. The outcomes of oncolytic virus treatment in dogs with spontaneous tumors may better predict human cancer response and improve treatment options for dogs with cancer. The objectives of this study were to evaluate the safety of treatment with myxoma virus lacking the serp2 gene (MYXVΔserp2) and determine its immunogenicity in dogs. To achieve these objectives, dogs with spontaneous soft tissue sarcomas were treated with MYXVΔserp2 intratumorally (n = 5) or post-operatively (n = 5). In dogs treated intratumorally, clinical scores were recorded and tumor biopsies and swabs (from the mouth and virus injection site) were analyzed for viral DNA at multiple time-points. In all dogs, blood, urine, and feces were frequently collected to evaluate organ function, virus distribution, and immune response. No detrimental effects of MYXVΔserp2 treatment were observed in any canine cancer patients. No clinically significant changes in complete blood profiles, serum chemistry analyses, or urinalyses were measured. Viral DNA was isolated from one tumor swab, but viral dissemination was not observed. Anti-MYXV antibodies were occasionally detected. These findings provide needed safety information to advance clinical trials using MYXVΔserp2 to treat patients with cancer.

Oncolytic Virus Combination Therapy: Killing One Bird with Two Stones

Over the last 60 years an eclectic collection of microbes has been tested in a variety of pre-clinical models as anti-cancer agents. At the forefront of this research are a number of virus-based platforms that have shown exciting activity in a variety of pre-clinical models and are collectively referred to as oncolytic viruses. Our true understanding of the potential and limitations of this therapeutic modality has been substantially advanced through clinical studies carried out over the last 25 years. Perhaps not surprising, as with all other cancer therapeutics, it has become clear that current oncolytic virus therapeutics on their own are unlikely to be effective in the majority of patients. The greatest therapeutic gains will therefore be made through thoughtful combination strategies built upon an understanding of cancer biology.

Armed oncolytic viruses: A kick-start for anti-tumor immunity

Oncolytic viruses (OVs), viruses that specifically result in killing tumor cells, represent a promising class of cancer therapy. Recently, the focus in the OV therapy field has shifted from their direct oncolytic effect to their immune stimulatory effect. OV therapy can function as a "kick start" for the antitumor immune response by releasing tumor associated antigens and release of inflammatory signals. Combining OVs with immune modulators could enhance the efficacy of both immune and OV therapies. Additionally, genetic engineering of OVs allows local expression of immune therapeutics, thereby reducing related toxicities. Different options to modify the tumor microenvironment in combination with OV therapy have been explored. The possibilities and obstacles of these combinations will be discussed in this review.

Oncolytic Viral Therapy and the Immune System: A Double-Edged Sword Against Cancer

Oncolytic viral therapy is a new promising strategy against cancer. Oncolytic viruses (OVs) can replicate in cancer cells but not in normal cells, leading to lysis of the tumor mass. Beside this primary effect, OVs can also stimulate the immune system. Tumors are an immuno-suppressive environment in which the immune system is silenced in order to avoid the immune response against cancer cells. The delivery of OVs into the tumor wakes up the immune system so that it can facilitate a strong and durable response against the tumor itself. Both innate and adaptive immune responses contribute to this process, producing an immune response against tumor antigens and facilitating immunological memory. However, viruses are recognized by the immune system as pathogens and the consequent anti-viral response could represent a big hurdle for OVs. Finding a balance between anti-tumor and anti-viral immunity is, under this new light, a priority for researchers. In this review, we provide an overview of the various ways in which different components of the immune system can be allied with OVs. We have analyzed the different immune responses in order to highlight the new and promising perspectives leading to increased anti-tumor response and decreased immune reaction to the OVs.

Prospects for combined use of oncolytic viruses and CAR T-cells

With the approval of talimogene laherparepvec (T-VEC) for inoperable locally advanced or metastatic malignant melanoma in the USA and Europe, oncolytic virotherapy is now emerging as a viable therapeutic option for cancer patients. In parallel, following the favourable results of several clinical trials, adoptive cell transfer using chimeric antigen receptor (CAR)-redirected T-cells is anticipated to enter routine clinical practice for the management of chemotherapy-refractory B-cell malignancies. However, CAR T-cell therapy for patients with advanced solid tumours has proved far less successful. This Review draws upon recent advances in the design of novel oncolytic viruses and CAR T-cells and provides a comprehensive overview of the synergistic potential of combination oncolytic virotherapy with CAR T-cell adoptive cell transfer for the management of solid tumours, drawing particular attention to the methods by which recombinant oncolytic viruses may augment CAR T-cell trafficking into the tumour microenvironment, mitigate or reverse local immunosuppression and enhance CAR T-cell effector function and persistence.

Re-designing Interleukin-12 to enhance its safety and potential as an anti-tumor immunotherapeutic agent

Interleukin-12 (IL-12) has emerged as one of the most potent agents for anti-tumor immunotherapy. However, potentially lethal toxicity associated with systemic administration of IL-12 precludes its clinical application. Here we redesign the molecule in such a way that its anti-tumor efficacy is not compromised, but toxic effects are eliminated. Deletion of the N-terminal signal peptide of IL-12 can effect such a change by preventing IL-12 secretion from cells. We use a newly designed tumor-targeted oncolytic adenovirus (Ad-TD) to deliver non-secreting (ns) IL-12 to tumor cells and examine the therapeutic and toxic effects in Syrian hamster models of pancreatic cancer (PaCa). Strikingly, intraperitoneal delivery of Ad-TD-nsIL-12 significantly enhanced survival of animals with orthotopic PaCa and cured peritoneally disseminated PaCa with no toxic side effects, in contrast to the treatment with Ad-TD expressing unmodified IL-12. These findings offer renewed hope for development of IL-12-based treatments for cancer.

Interleukin-12 (IL-12) is a potent immunotherapeutic agent.

Oncolytic Viruses-Interaction of Virus and Tumor Cells in the Battle to Eliminate Cancer

Oncolytic viruses (OVs) are an emerging treatment option for many cancer types and have recently been the focus of extensive research aiming to develop their therapeutic potential. The ultimate aim is to design a virus which can effectively replicate within the host, specifically target and lyse tumor cells and induce robust, long lasting tumor-specific immunity. There are a number of viruses which are either naturally tumor-selective or can be modified to specifically target and eliminate tumor cells. This means they are able to infect only tumor cells and healthy tissue remains unharmed. This specificity is imperative in order to reduce the side effects of oncolytic virotherapy. These viruses can also be modified by various methods including insertion and deletion of specific genes with the aim of improving their efficacy and safety profiles. In this review, we have provided an overview of the various virus species currently being investigated for their oncolytic potential and the positive and negative effects of a multitude of modifications used to increase their infectivity, anti-tumor immunity, and treatment safety, in particular focusing on the interaction of tumor cells and OVs.

Commonly Used Animal Models

This chapter provides an introduction to animals that are commonly used for research. It presents information on basic care topics such as biology, behavior, housing, feeding, sexing, and breeding of these animals. The chapter provides some insight into the reasons why these animals are used in research. It also gives an overview of techniques that can be utilized to collect blood or to administer drugs or medicine. Each section concludes with a brief description of how to recognize abnormal signs, in addition to lists of various diseases.

Prime-boost using separate oncolytic viruses in combination with checkpoint blockade improves anti-tumour therapy

The anti-tumour effects associated with oncolytic virus therapy are mediated significantly through immune-mediated mechanisms, which depend both on the type of virus and the route of delivery. Here, we show that intra-tumoral oncolysis by Reovirus induced the priming of a CD8+, Th1-type anti-tumour response. By contrast, systemically delivered Vesicular Stomatitis Virus expressing a cDNA library of melanoma antigens (VSV-ASMEL) promoted a potent anti-tumour CD4+ Th17 response. Therefore, we hypothesised that combining the Reovirus-induced CD8+ T cell response, with the VSV-ASMEL CD4+ Th17 helper response, would produce enhanced anti-tumour activity. Consistent with this, priming with intra-tumoral Reovirus, followed by an intra-venous VSV-ASMEL Th17 boost, significantly improved survival of mice bearing established subcutaneous B16 melanoma tumours. We also show that combination of either therapy alone with anti-PD-1 immune checkpoint blockade augmented both the Th1 response induced by systemically delivered Reovirus in combination with GM-CSF, and also the Th17 response induced by VSV-ASMEL. Significantly, anti-PD-1 also uncovered an anti-tumour Th1 response following VSV-ASMEL treatment that was not seen in the absence of checkpoint blockade. Finally, the combination of all three treatments (priming with systemically delivered Reovirus, followed by double boosting with systemic VSV-ASMEL and anti-PD-1) significantly enhanced survival, with long-term cures, compared to any individual, or double, combination therapies, associated with strong Th1 and Th17 responses to tumour antigens. Our data show that it is possible to generate fully systemic, highly effective anti-tumour immunovirotherapy by combining oncolytic viruses, along with immune checkpoint blockade, to induce complementary mechanisms of anti-tumour immune responses.

Oncolytic Adenoviruses Armed with Tumor Necrosis Factor Alpha and Interleukin-2 Enable Successful Adoptive Cell Therapy

Adoptive cell therapy holds much promise in the treatment of cancer but results in solid tumors have been modest. The notable exception is tumor-infiltrating lymphocyte (TIL) therapy of melanoma, but this approach only works with high-dose preconditioning chemotherapy and systemic interleukin (IL)-2 postconditioning, both of which are associated with toxicities. To improve and broaden the applicability of adoptive cell transfer, we constructed oncolytic adenoviruses coding for human IL-2 (hIL2), tumor necrosis factor alpha (TNF-α), or both. The viruses showed potent antitumor efficacy against human tumors in immunocompromised severe combined immunodeficiency (SCID) mice. In immunocompetent Syrian hamsters, we combined the viruses with TIL transfer and were able to cure 100% of the animals. Cured animals were protected against tumor re-challenge, indicating a memory response. Arming with IL-2 and TNF-α increased the frequency of both CD4⁺ and CD8⁺ TILs in vivo and augmented splenocyte proliferation ex vivo, suggesting that the cytokines were important for T cell persistence and proliferation. Cytokine expression was limited to tumors and treatment-related signs of systemic toxicity were absent, suggesting safety. To conclude, cytokine-armed oncolytic adenoviruses enhanced adoptive cell therapy by favorable alteration of the tumor microenvironment. A clinical trial is in progress to study the utility of Ad5/3-E2F-d24-hTNFa-IRES-hIL2 (TILT-123) in human patients with cancer.

The Efficacy of Oncolytic Adenovirus Is Mediated by T-cell Responses against Virus and Tumor in Syrian Hamster Model

PURPOSE

Oncolytic adenoviruses (Ad) represent an innovative approach to cancer therapy. Its efficacy depends on multiple actions, including direct tumor lysis and stimulation of antiviral and antitumor immune responses. In this study, we investigated the roles of T-cell responses in oncolytic adenoviral therapy.

EXPERIMENTAL DESIGN

An immunocompetent and viral replication-permissive Syrian hamster tumor model was used. The therapeutic mechanisms of oncolytic Ad were investigated by T-cell deletion, immunohistochemical staining, and CTL assay.

RESULTS

Deletion of T cells with an anti-CD3 antibody completely demolished the antitumor efficacy of oncolytic Ad. Intratumoral injection of Ad induced strong virus- and tumor-specific T-cell responses, as well as antiviral antibody response. Both antiviral and antitumor T-cell responses contributed to the efficacy of oncolytic Ad. Deletion of T cells increased viral replication and extended the persistence of infectious virus within tumors but almost abrogated the antitumor efficacy. Preexisting antiviral immunity promoted the clearance of injected oncolytic Ad from tumors but had no effect on antitumor efficacy. Strikingly, the repeated treatment with oncolytic Ad has strong therapeutic effect on relapsed tumors or tumors insensitive to the primary viral therapy.

CONCLUSIONS

These results demonstrate that T cell-mediated immune responses outweigh the direct oncolysis in mediating antitumor efficacy of oncolytic Ad. Our data have a high impact on redesigning the regimen of oncolytic Ad for cancer treatment. Clin Cancer Res; 23(1); 239-49. ©2016 AACR.

Oncolytic Virus-Mediated Targeting of PGE2 in the Tumor Alters the Immune Status and Sensitizes Established and Resistant Tumors to Immunotherapy

Immunotherapies are highly promising cancer treatments, but understanding the factors mediating their resistance remains critical. Successes in randomized clinical testing have supported the growing appreciation that oncolytic virotherapies primarily act as immunotherapies. Here we identified prostaglandin E2 (PGE2) in the tumor as a key mediator of resistance to immunotherapies, including oncolytic vaccinia virotherapy. Elevated levels of PGE2 coupled to suppressive chemokine profiles and high levels of granulocytic myeloid-derived suppressor cells resulted in loss of immunotherapeutic potential. Viral vectors engineered to target PGE2 were capable of overcoming localized immunosuppression leading to profound changes in the tumor's immune status. This allowed the viral vectors to raise robust anti-tumor adaptive immune responses and sensitized established and previously resistant tumors to immunotherapies.

Oncolytic and immunologic cancer therapy with GM-CSF-armed vaccinia virus of Tian Tan strain Guang9

Targeted oncolytic vaccinia viruses are being developed as a novel strategy in cancer therapy. Arming vaccinia viruses with immunostimulatory cytokines can enhance antitumor efficacy. Such engineered oncolytic viruses, like JX-594, a Wyeth strain vaccinia virus modified with human granulocyte-macrophage colony-stimulating factor (GM-CSF), have shown promising results and have proceeded rapidly in clinical trials. However, the oncolytic potential of the Chinese vaccine strain Tian Tan (VTT) has not been explored. In this study, we constructed a targeted oncolytic vaccinia virus of Tian Tan strain Guang9 (VG9) expressing murine GM-CSF (VG9-GMCSF) and evaluated the antitumor effect of this recombinant vaccinia virus in a murine melanoma model. In vitro, viral replication and cytotoxicity of VG9-GMCSF was as potent as VG9; in vivo, VG9-GMCSF significantly inhibited the growth of subcutaneously implanted melanoma tumors, prolonged the survival of tumor-bearing mice, and produced an antitumor cytotoxic response. Such antitumor effect may be due to the lytic nature of virus as well as the stimulation of immune activity by GM-CSF production. Our results indicate that VG9-GMCSF induces strong tumoricidal activity, providing a potential therapeutic strategy for combating cancer.

Enhanced therapeutic effect using sequential administration of antigenically distinct oncolytic viruses expressing oncostatin M in a Syrian hamster orthotopic pancreatic cancer model

BACKGROUND

The limited efficacy of current treatments against pancreatic cancer has prompted the search of new alternatives such as virotherapy. Activation of the immune response against cancer cells is emerging as one of the main mechanisms of action of oncolytic viruses (OV). Direct oncolysis releases tumor antigens, and viral replication within the tumor microenvironment is a potent danger signal. Arming OV with immunostimulatory transgenes further enhances their therapeutic effect. However, standard virotherapy protocols do not take full advantage of OV as cancer vaccines because repeated viral administrations may polarize immune responses against strong viral antigens, and the rapid onset of neutralizing antibodies limits the efficacy of redosing. An alternative paradigm based on sequential combination of antigenically distinct OV has been recently proposed.

METHODS

We have developed a protocol consisting of sequential intratumor administrations of new Adenovirus (Ad) and Newcastle Disease Virus (NDV)-based OV encoding the immunostimulatory cytokine oncostatin M (OSM). Transgene expression, toxicity and antitumor effect were evaluated using an aggressive orthotopic pancreatic cancer model in Syrian hamsters, which are sensitive to OSM and permissive for replication of both OVs.

RESULTS

NDV-OSM was more cytolytic, whereas Ad-OSM caused higher OSM expression in vivo. Both viruses achieved only a marginal antitumor effect in monotherapy. In addition, strong secretion of OSM in serum limited the maximal tolerated dose of Ad-OSM. In contrast, moderate doses of Ad-OSM followed one week later by NDV-OSM were safe, showed a significant antitumor effect and stimulated immune responses against cancer cells. Similar efficacy was observed when the order of virus administrations was reversed.

CONCLUSION

Sequential administration of oncolytic Ad and NDV encoding OSM is a promising approach against pancreatic cancer.

Treatment strategies for combining immunostimulatory oncolytic virus therapeutics with dendritic cell injections

Oncolytic viruses (OVs) are used to treat cancer, as they selectively replicate inside of and lyse tumor cells. The efficacy of this process is limited and new OVs are being designed to mediate tumor cell release of cytokines and co-stimulatory molecules, which attract cytotoxic T cells to target tumor cells, thus increasing the tumor-killing effects of OVs. To further promote treatment efficacy, OVs can be combined with other treatments, such as was done by Huang et al., who showed that combining OV injections with dendritic cell (DC) injections was a more effective treatment than either treatment alone. To further investigate this combination, we built a mathematical model consisting of a system of ordinary differential equations and fit the model to the hierarchical data provided from Huang et al. We used the model to determine the effect of varying doses of OV and DC injections and to test alternative treatment strategies. We found that the DC dose given in Huang et al. was near a bifurcation point and that a slightly larger dose could cause complete eradication of the tumor. Further, the model results suggest that it is more effective to treat a tumor with immunostimulatory oncolytic viruses first and then follow-up with a sequence of DCs than to alternate OV and DC injections. This protocol, which was not considered in the experiments of Huang et al., allows the infection to initially thrive before the immune response is enhanced. Taken together, our work shows how the ordering, temporal spacing, and dosage of OV and DC can be chosen to maximize efficacy and to potentially eliminate tumors altogether.

Vaccinia virus, a promising new therapeutic agent for pancreatic cancer

The poor prognosis of pancreatic cancer patients signifies a need for radically new therapeutic strategies. Tumor-targeted oncolytic viruses have emerged as attractive therapeutic candidates for cancer treatment due to their inherent ability to specifically target and lyse tumor cells as well as induce antitumor effects by multiple action mechanisms. Vaccinia virus has several inherent features that make it particularly suitable for use as an oncolytic agent. In this review, we will discuss the potential of vaccinia virus in the management of pancreatic cancer in light of our increased understanding of cellular and immunological mechanisms involved in the disease process as well as our extending knowledge in the biology of vaccinia virus.

Quantitative impact of immunomodulation versus oncolysis with cytokine-expressing virus therapeutics

The past century's description of oncolytic virotherapy as a cancer treatment involving specially-engineered viruses that exploit immune deficiencies to selectively lyse cancer cells is no longer adequate. Some of the most promising therapeutic candidates are now being engineered to produce immunostimulatory factors, such as cytokines and co-stimulatory molecules, which, in addition to viral oncolysis, initiate a cytotoxic immune attack against the tumor. This study addresses the combined effects of viral oncolysis and T-cell-mediated oncolysis. We employ a mathematical model of virotherapy that induces release of cytokine IL-12 and co-stimulatory molecule 4-1BB ligand. We found that the model closely matches previously published data, and while viral oncolysis is fundamental in reducing tumor burden, increased stimulation of cytotoxic T cells leads to a short-term reduction in tumor size, but a faster relapse. In addition, we found that combinations of specialist viruses that express either IL-12 or 4-1BBL might initially act more potently against tumors than a generalist virus that simultaneously expresses both, but the advantage is likely not large enough to replace treatment using the generalist virus. Finally, according to our model and its current assumptions, virotherapy appears to be optimizable through targeted design and treatment combinations to substantially improve therapeutic outcomes.

Novel therapeutic strategies in human malignancy: combining immunotherapy and oncolytic virotherapy

Results from randomized clinical trials over the last several years have finally begun to demonstrate the potential of oncolytic viral therapies to treat a variety of cancers. One reason for these successes has been the realization that this platform is most effective when considered primarily as an immunotherapy. Cancer immunotherapy has also made dramatic strides recently with antibodies capable of blocking immune checkpoint inhibitors and adoptive T-cell therapies, notably CAR T-cells, leading a panel of novel and highly clinically effective therapies. It is clear therefore that an understanding of how and when these complementary approaches can most effectively be combined offers the real hope of moving beyond simply treating the disease and toward starting to talk about curative therapies. In this review we discuss approaches to combining these therapeutic platforms, both through engineering the viral vectors to more beneficially interact with the host immune response during therapy, as well as through the direct combinations of different therapeutics. This primarily, but not exclusively focuses on strains of oncolytic vaccinia virus. Some of the results reported to date, primarily in pre-clinical models but also in early clinical trials, are dramatic and hold great promise for the future development of similar therapies and their translation into cancer therapies.

Can oncology recapitulate paleontology? Lessons from species extinctions

Although we can treat cancers with cytotoxic chemotherapies, target them with molecules that inhibit oncogenic drivers, and induce substantial cell death with radiation, local and metastatic tumours recur, resulting in extensive morbidity and mortality. Indeed, driving a tumour to extinction is difficult. Geographically dispersed species of organisms are perhaps equally resistant to extinction, but >99.9% of species that have ever existed on this planet have become extinct. By contrast, we are nowhere near that level of success in cancer therapy. The phenomena are broadly analogous--in both cases, a genetically diverse population mutates and evolves through natural selection. The goal of cancer therapy is to cause cancer cell population extinction, or at least to limit any further increase in population size, to prevent the tumour burden from overwhelming the patient. However, despite available treatments, complete responses are rare, and partial responses are limited in duration. Many patients eventually relapse with tumours that evolve from cells that survive therapy. Similarly, species are remarkably resilient to environmental change. Paleontology can show us the conditions that lead to extinction and the characteristics of species that make them resistant to extinction. These lessons could be translated to improve cancer therapy and prognosis.

Overcoming tumor resistance by heterologous adeno-poxvirus combination therapy

Successful cancer control relies on overcoming resistance to cell death and on activation of host antitumor immunity. Oncolytic viruses are particularly attractive in this regard, as they lyse infected tumor cells and trigger robust immune responses during the infection. However, repeated injections of the same virus promote antiviral rather than antitumor immunity and tumors may mount innate antiviral defenses to restrict oncolytic virus replication. In this article, we have explored if alternating the therapy virus could circumvent these problems. We demonstrate in two virus-resistant animal models a substantial delay in antiviral immune- and innate cellular response induction by alternating injections of two immunologically distinct oncolytic viruses, adenovirus, and vaccinia virus. Our results are in support of clinical development of heterologous adeno-/vaccinia virus therapy of cancer.

8th international conference on oncolytic virus therapeutics

The 8th International Conference on Oncolytic Virus Therapeutics meeting was held from April 10-13, 2014, in Oxford, United Kingdom. It brought together experts in the field of oncolytics from Europe, Asia, Australasia, and the Americas and provided a unique opportunity to hear the latest research findings in oncolytic virotherapy. Presentations of recent work were delivered in an informal and intimate setting afforded by a small group of attendees and an exquisitely focused conference topic. Here we describe the oral presentations and enable the reader to share in the benefits of bringing together experts to share their findings.