Oncolytic herpes simplex virus interactions with the host immune system

Safety of non-replicative and oncolytic replication-selective HSV vectors

Herpes simplex virus type 1 (HSV-1) is a DNA virus and human pathogen used to construct promising therapeutic vectors. HSV-1 vectors fall into two classes: replication-selective oncolytic vectors for cancer therapy and defective non-replicative vectors for gene therapy. Vectors from each class can accommodate ≥30 kb of inserts, have been approved clinically, and demonstrate a relatively benign safety profile. Despite oncolytic HSV (oHSV) replication in tumors and elicited immune responses, the virus is well tolerated in cancer patients. Current non-replicative vectors elicit only limited immune responses. Seropositivity and immune responses against HSV-1 do not eliminate either the vector or infected cells, and the vectors can therefore be re-administered. In this review we highlight vectors that have been translated to the clinic and host-virus immune interactions that impact on the safety and efficacy of HSVs.

Molecular insights and promise of oncolytic virus based immunotherapy

Discovering a therapeutic that can counteract the aggressiveness of this disease's mechanism is crucial for improving survival rates for cancer patients and for better understanding the most different types of cancer. In recent years, using these viruses as an anticancer therapy has been thought to be successful. They mostly work by directly destroying cancer cells, activating the immune system to fight cancer, and expressing exogenous effector genes. For the treatment of tumors, oncolytic viruses (OVs), which can be modified to reproduce only in tumor tissues and lyse them while preserving the healthy non-neoplastic host cells and reinstating antitumor immunity which present a novel immunotherapeutic strategy. OVs can exist naturally or be created in a lab by altering existing viruses. These changes heralded the beginning of a new era of less harmful virus-based cancer therapy. We discuss three different types of oncolytic viruses that have already received regulatory approval to treat cancer as well as clinical research using oncolytic adenoviruses. The primary therapeutic applications, mechanism of action of oncolytic virus updates, future views of this therapy will be covered in this chapter.

Oncolytic α-herpesvirus and myeloid-tropic cytomegalovirus cooperatively enhance systemic antitumor responses

Oncolytic virotherapy aims to activate host antitumor immunity. In responsive tumors, intratumorally injected herpes simplex viruses (HSVs) have been shown to lyse tumor cells, resulting in local inflammation, enhanced tumor antigen presentation, and boosting of antitumor cytotoxic lymphocytes. In contrast to HSV, cytomegalovirus (CMV) is nonlytic and reprograms infected myeloid cells, limiting their antigen-presenting functions and protecting them from recognition by natural killer (NK) cells. Here, we show that when co-injected into mouse tumors with an oncolytic HSV, mouse CMV (mCMV) preferentially targeted tumor-associated myeloid cells, promoted the local release of proinflammatory cytokines, and enhanced systemic antitumor immune responses, leading to superior control of both injected and distant contralateral tumors. Deletion of mCMV genes m06, which degrades major histocompatibility complex class I (MHC class I), or m144, a viral MHC class I homolog that inhibits NK activation, was shown to diminish the antitumor activity of the HSV/mCMV combination. However, an mCMV recombinant lacking the m04 gene, which escorts MHC class I to the cell surface, showed superior HSV adjuvanticity. CMV is a potentially promising agent with which to reshape and enhance antitumor immune responses following oncolytic HSV therapy.

Tumor Microenvironment: A Niche for Cancer Stem Cell Immunotherapy

Tumorigenic Cancer Stem Cells (CSCs), often called tumor-initiating cells (TICs), represent a unique subset of cells within the tumor milieu. They stand apart from the bulk of tumor cells due to their exceptional self-renewal, metastatic, and differentiation capabilities. Despite significant progress in classifying CSCs, these cells remain notably resilient to conventional radiotherapy and chemotherapy, contributing to cancer recurrence. In this review, our objective is to explore novel avenues of research that delve into the distinctive characteristics of CSCs within their surrounding tumor microenvironment (TME). We will start with an overview of the defining features of CSCs and then delve into their intricate interactions with cells from the lymphoid lineage, namely T cells, B cells, and natural killer (NK) cells. Furthermore, we will discuss their dynamic interplay with myeloid lineage cells, including macrophages, neutrophils, and myeloid-derived suppressor cells (MDSCs). Moreover, we will illuminate the crosstalk between CSCs and cells of mesenchymal origin, specifically fibroblasts, adipocytes, and endothelial cells. Subsequently, we will underscore the pivotal role of CSCs within the context of the tumor-associated extracellular matrix (ECM). Finally, we will highlight pre-clinical and clinical studies that target CSCs within the intricate landscape of the TME, including CAR-T therapy, oncolytic viruses, and CSC-vaccines, with the ultimate goal of uncovering novel avenues for CSC-based cancer immunotherapy.

Advancements and challenges in oncolytic virus therapy for gastrointestinal tumors

BACKGROUND

Tumors of the gastrointestinal tract impose a substantial healthcare burden due to their prevalence and challenging prognosis.

METHODS

We conducted a review of peer-reviewed scientific literature using reputable databases (PubMed, Scopus, Web of Science) with a focus on oncolytic virus therapy within the context of gastrointestinal tumors. Our search covered the period up to the study's completion in June 2023.

INCLUSION AND EXCLUSION CRITERIA

This study includes articles from peer-reviewed scientific journals, written in English, that specifically address oncolytic virus therapy for gastrointestinal tumors, encompassing genetic engineering advances, combined therapeutic strategies, and safety and efficacy concerns. Excluded are articles not meeting these criteria or focusing on non-primary gastrointestinal metastatic tumors.

RESULTS

Our review revealed the remarkable specificity of oncolytic viruses in targeting tumor cells and their potential to enhance anti-tumor immune responses. However, challenges related to safety and efficacy persist, underscoring the need for ongoing research and improvement.

CONCLUSION

This study highlights the promising role of oncolytic virus therapy in enhancing gastrointestinal tumor treatments. Continued investigation and innovative combination therapies hold the key to reducing the burden of these tumors on patients and healthcare systems.

Clinical advances in oncolytic virus therapy for malignant glioma: a systematic review

PURPOSE

In the past decade, there has been little progress in the treatment of malignant glioma. Recently, oncolytic virus has made great progress in glioma treatment, and a number of clinical trials have shown their potential of prolonging the survival time of glioma patients. Our objective is to evaluate effectiveness and safety of oncolytic virus (OV) in malignant glioma treatment.

METHODOLOGY

Based upon PRISMA, we collected relevant published clinical trials by searching medical databases up to January 16, 2023, applying the language restrictions in English and Chinese. We cross-searched the terms: 'glioma', 'glioblastoma', 'oncolytic viruses', 'oncolytic virotherapy' with filter 'clinical trial'. Two researchers independently extracted the data regarding case definitions, published years, trial phase, characteristics of patients, administration of drug, overall survival (OS), and adverse events.

RESULTS

19 published clinical trials in OV treatment of malignant glioma were included in the further systematic review analysis. None of them induced irresistible adverse effects attributing to OV treatment, median overall survival varied from 3.25 to 20.2 months after treatments. According to trials providing patient's detailed molecular diagnosis, we find that the effectiveness of OV treatment has no significant difference in patients with different IDH or MGMT status.

CONCLUSIONS

Current clinical trials have initially shown the potential of oncolytic virotherapy as a new treatment for malignant glioma. Besides development of virus types, the strategy of OV use is an urgent problem to be solved in future clinical application, such as repeated administrations, innovative drug delivery systems, and biomarkers.

Viral Vectors Expressing Interleukin 2 for Cancer Immunotherapy

Interleukin 2 (IL-2) plays a crucial role in T cell growth and survival, enhancing the cytotoxic activity of natural killer and cytotoxic T cells and thus functioning as a versatile master proinflammatory anticancer cytokine. The FDA has approved IL-2 cytokine therapy for the treatment of metastatic melanoma and metastatic renal cell carcinoma. However, IL-2 therapy has significant constraints, including a short serum half-life, low tumor accumulation, and life-threatening toxicities associated with high doses. Oncolytic viruses (OVs) offer a promising option for cancer immunotherapy, selectively targeting and destroying cancer cells while sparing healthy cells. Numerous studies have demonstrated the successful delivery of IL-2 to the tumor microenvironment without compromising safety using OVs such as vaccinia, Sendai, parvo, Newcastle disease, tanapox, and adenoviruses. Additionally, by engineering OVs to coexpress IL-2 with other anticancer transgenes, the immune properties of IL-2 can be further enhanced. Preclinical and clinical studies have shown promising antitumor effects of IL-2-expressing viral vectors, either alone or in combination with other anticancer therapies. This review summarizes the therapeutic potential of IL-2-expressing viral vectors and their antitumor mechanisms of action.

Oncolytic viruses-modulated immunogenic cell death, apoptosis and autophagy linking to virotherapy and cancer immune response

Recent reports have revealed that oncolytic viruses (OVs) play a significant role in cancer therapy. The infection of OVs such as oncolytic vaccinia virus (OVV), vesicular stomatitis virus (VSV), parvovirus, mammalian reovirus (MRV), human adenovirus, Newcastle disease virus (NDV), herpes simplex virus (HSV), avian reovirus (ARV), Orf virus (ORFV), inactivated Sendai virus (ISV), enterovirus, and coxsackievirus offer unique opportunities in immunotherapy through diverse and dynamic pathways. This mini-review focuses on the mechanisms of OVs-mediated virotherapy and their effects on immunogenic cell death (ICD), apoptosis, autophagy and regulation of the immune system.

Targeting TMEM205 mediated drug resistance in ovarian clear cell carcinoma using oncolytic virus

BACKGROUND

Ovarian clear cell carcinoma (OCCC) accounts for approximately 8-10% of epithelial ovarian cancers in the United States. Although it is rare, OCCC usually presents with treatment challenges and the overall prognosis is far worse than high grade serous ovarian cancer HGSOC. The objective of this study was to examine the therapeutic relevance of combining oncolytic virus with cisplatin for ovarian cancer clear cell carcinoma (OCCC).

RESULTS

We identified that TMEM205, a recently discovered transmembrane protein, contributes to chemoresistance in OCCC cells via the exosomal pathway. Mechanistically, TMEM205 undergoes ligand-independent constitutive endocytosis and co-localizes with Rab11 to contribute to the late recycling endosomes in a clathrin-independent manner. Further, we observed that oncolytic virus (oHSV) pretreatment followed by treatment with cisplatin decreases TMEM205 expression and sensitizes cells to cisplatin in a synergistic manner in OCCC cells. TMEM205 interacts with glycoprotein-C of oHSV post-infection; both of these proteins undergo ubiquitination and ultimately get shuttled outside the cell via exosomes. Thus, we demonstrate the mechanotransduction pathway of TMEM205-mediated chemoresistance along with targeting this pathway using oHSV and cisplatin as a powerful therapeutic strategy for OCCC. oHSV combination with cisplatin inhibits OCCC tumor growth in vivo in immunodeficient and immunocompetent mice models.

CONCLUSION

Our results suggest that the combination of oHSV and cisplatin in immunocompetent as well as immune deficient OCCC tumor bearing mice reduces overall tumor burden as well as metastatic disease thereby providing survival benefit. Additionally, the detection of TMEM205 in exosomal cargo early in OCCC development has potential to be exploited as a biomarker.

Optimal timing of PD-1 blockade in combination with oncolytic virus therapy

Anti-PD-1 and oncolytic viruses (OVs) have non-overlapping anti-tumor mechanisms, since each agent works at different steps of the cancer-immunity cycle. Evidence suggests that OVs improve therapeutic responses to anti-PD-1 therapy by reversing immunosuppressive factors, increasing the number and diversity of infiltrating lymphocytes, and promoting PD-L1 expression in both injected and non-injected tumors. Many studies in preclinical models suggest that the timing of anti-PD-1 administration influences the therapeutic success of the combination therapy (anti-PD-1 + OV). Therefore, determining the appropriate sequencing of agents is of critical importance to designing a rationale OV-based combinational clinical trial. Currently, the combination of anti-PD-1 and OVs are being delivered using various schedules, and we have classified the timing of administration of anti-PD-1 and OVs into five categories: (i) anti-PD-1 lead-in → OV; (ii) concurrent administration; (iii) OV lead-in → anti-PD-1; (iv) concurrent therapy lead-in → anti-PD-1; and (v) OV lead-in → concurrent therapy. Based on the reported preclinical and clinical literature, the most promising treatment strategy to date is hypothesized to be OV lead-in → concurrent therapy. In the OV lead-in → concurrent therapy approach, initial OV treatment results in T cell priming and infiltration into tumors and an immunologically hot tumor microenvironment (TME), which can be counterbalanced by engagement of PD-L1 to PD-1 receptor on immune cells, leading to T cell exhaustion. Therefore, after initial OV therapy, concurrent use of both OV and anti-PD-1 is critical through which OV maintains T cell priming and an immunologically hot TME, whereas PD-1 blockade helps to overcome PD-L1/PD-1-mediated T cell exhaustion. It is important to note that the hypothetical conclusion drawn in this review is based on thorough literature review on current understanding of OV + anti-PD-1 combination therapies and rhythm of treatment-induced cancer-immunity cycle. A variety of confounding factors such as tumor types, OV types, presence or absence of cytokine transgenes carried by an OV, timing of treatment initiation, varying dosages and treatment frequencies/duration of OV and anti-PD-1, etc. may affect the validity of our conclusion that will need to be further examined by future research (such as side-by-side comparative studies using all five treatment schedules in a given tumor model).

The gamble between oncolytic virus therapy and IFN

Various studies are being conducted on oncolytic virotherapy which one of the mechanisms is mediating interferon (IFN) production by it exerts antitumor effects. The antiviral effect of IFN itself has a negative impact on the inhibition of oncolytic virus or tumor eradication. Therefore, it is very critical to understand the mechanism of IFN regulation by oncolytic viruses, and to define its mechanism is of great significance for improving the antitumor effect of oncolytic viruses. This review focuses on the regulatory mechanisms of IFNs by various oncolytic viruses and their combination therapies. In addition, the exerting and the producing pathways of IFNs are briefly summarized, and some current issues are put forward.

Single agent Talimogene Laherparepvec for stage IIIB-IVM1c melanoma patients: A systematic review and meta-analysis

Single-agent Talimogene Laherparepvec (T-VEC) was developed for treatment of unresectable and injectable stage III-IV melanoma. Since its approval and reimbursement, studies have reported varying response rates. The purpose of this systematic review and meta-analysis was to investigate the efficacy and safety of T-VEC. Of 341 publications that were identified, eight studies with a total of 642 patients were included. In patients with stage IIIB-IVM1a, the pooled complete- and overall response rate (CRR and ORR) were 41% and 64%, respectively. In patients with stage IIIB-IVM1c, the pooled CRR and ORR were 30% and 44%, respectively. In patients with stage IVM1b and IVM1c, the pooled CRR and ORR were 4% and 9%, respectively. Adverse events (AEs) were seen in 41-100% of all patients and 0-11% of AEs were severe. In conclusion, single agent T-VEC achieves the highest response rates in patients with early metastatic melanoma and is well-tolerated with generally only mild toxicities.

T-SIGn tumor reengineering therapy and CAR T cells synergize in combination therapy to clear human lung tumor xenografts and lung metastases in NSG mice

Although chimeric antigen receptor (CAR) T cells have emerged as highly effective treatments for patients with hematologic malignancies, similar efficacy has not been achieved in the context of solid tumors. There are several reasons for this disparity including a) fewer solid tumor target antigens, b) heterogenous target expression amongst tumor cells, c) poor trafficking of CAR T cells to the solid tumor and d) an immunosuppressive tumor microenvironment (TME). Oncolytic viruses have the potential to change this paradigm by a) directly lysing tumor cells and releasing tumor neoantigens, b) stimulating the local host innate immune response to release cytokines and recruit additional innate and adaptive immune cells, c) carrying virus-encoded transgenes to “re-program” the TME to a pro-inflammatory environment and d) promoting an adaptive immune response to the neoantigens in this newly permissive TME. Here we show that the Tumor-Specific Immuno-Gene (T-SIGn) virus NG-347 which encodes IFNα, MIP1α and CD80 synergizes with anti-EGFR CAR T cells as well as anti-HER-2 CAR T cells to clear A549 human tumor xenografts and their pulmonary metastases at doses which are subtherapeutic when each is used as a sole treatment. We show that NG-347 changes the TME to a pro-inflammatory environment resulting in the recruitment and activation of both CAR T cells and mouse innate immune cells. We also show that the transgenes encoded by the virus are critical as synergy is lost in their absence.

Oncolytic Viro-Immunotherapy: An Emerging Option in the Treatment of Gliomas

The prognosis of malignant gliomas remains poor, with median survival fewer than 20 months and a 5-year survival rate merely 5%. Their primary location in the central nervous system (CNS) and its immunosuppressive environment with little T cell infiltration has rendered cancer therapies mostly ineffective, and breakthrough therapies such as immune checkpoint inhibitors (ICIs) have shown limited benefit. However, tumor immunotherapy is developing rapidly and can help overcome these obstacles. But for now, malignant gliomas remain fatal with short survival and limited therapeutic options. Oncolytic virotherapy (OVT) is a unique antitumor immunotherapy wherein viruses selectively or preferentially kill tumor cells, replicate and spread through tumors while inducing antitumor immune responses. OVTs can also recondition the tumor microenvironment and improve the efficacy of other immunotherapies by escalating the infiltration of immune cells into tumors. Some OVTs can penetrate the blood-brain barrier (BBB) and possess tropism for the CNS, enabling intravenous delivery. Despite the therapeutic potential displayed by oncolytic viruses (OVs), optimizing OVT has proved challenging in clinical development, and marketing approvals for OVTs have been rare. In June 2021 however, as a genetically engineered OV based on herpes simplex virus-1 (G47Δ), teserpaturev got conditional and time-limited approval for the treatment of malignant gliomas in Japan. In this review, we summarize the current state of OVT, the synergistic effect of OVT in combination with other immunotherapies as well as the hurdles to successful clinical use. We also provide some suggestions to overcome the challenges in treating of gliomas.

β-adrenergic receptor inhibition enhances oncolytic herpes virus propagation through STAT3 activation in gastric cancer

Background

Oncolytic viruses (OVs) are considered a promising therapeutic alternative for cancer. However, OVs could activate the host innate immunity, then impair the viral propagation in tumor cells. In this study, we explored the effect of propranolol, a non-selective β-blocker, on the antitumor efficacy of T1012G virus in gastric cancer models.

Methods

The proliferation of gastric cancer cells treated with monotherapy or combination treatment was detected by CCK8 cell proliferation assay. The effect of propranolol was further evaluated by in vitro viral replication assays. In vivo tumor xenograft experiments were used to observe the effect of combination therapy on gastric cancer growth in mice. The expression levels of viral proteins and interferon responsive genes were detected in the gastric cancer cell lines treated with combined treatment by western blot. The impact of propranolol on IFN-α/β-mediated inhibition of viral propagation and the expression of antiviral gene PKR was detected by viral replication assays and western blot.

Results

Cell viability assay detected a 97.9% decrease of T1012G IC50 in HGC-27 when it was pretreated with propranolol along with a sevenfold increase of virus titers compared with T1012G only group (P < 0.001). Moreover, propranolol pretreatment caused sustained tumor regression (335.3 ± 36.92 mm³ vs. 1118 ± 210.0 mm³, P < 0.01) and enhanced the viral propagation (fourfold increase, P < 0.01) compared with T1012G only group. Propranolol pretreatment significantly enhanced the p-STAT3 (2.9-fold, P < 0.05) and suppressed p-PKR (65.94% ± 10.11%, P < 0.05) compared with T1012G only group. In addition, propranolol could counteract IFN-α/β-mediated inhibition of viral propagation (compared with IFNα: 5.1-fold, P < 0.001; IFNβ: 4.6-fold, P < 0.01) or enhancement of PKR activation (IFNα: 92.57% ± 1.77%, P < 0.001, IFNβ: 99.34% ± 0.13% decrease, P < 0.001).

Conclusions

In summary, β-blocker pretreatment could improve the propagation and therapeutic efficacy of T1012G in human gastric cancer by regulating STAT3-PKR signaling cascade, even in the presence of type I IFNs. These data support new strategies of improving the efficacy of OVs in gastric cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00687-1.

Using oncolytic viruses to ignite the tumour immune microenvironment in bladder cancer

The advent of immune checkpoint inhibition (ICI) has transformed the treatment paradigm for bladder cancer. However, despite the success of ICI in other tumour types, the majority of ICI-treated patients with bladder cancer failed to respond. The lack of efficacy in some patients could be attributed to a paucity of pre-existing immune reactive cells within the tumour immune microenvironment, which limits the beneficial effects of ICI. In this setting, strategies to attract lymphocytes before implementation of ICI could be helpful. Oncolytic virotherapy is thought to induce the release of damage-associated molecular patterns, eliciting a pro-inflammatory cytokine cascade and stimulating the activation of the innate immune system. Concurrently, oncolytic virotherapy-induced oncolysis leads to further release of neoantigens and subsequent epitope spreading, culminating in a robust, tumour-specific adaptive immune response. Combination therapy using oncolytic virotherapy with ICI has proven successful in a number of preclinical studies and is beginning to enter clinical trials for the treatment of both non-muscle-invasive and muscle-invasive bladder cancer. In this context, understanding of the mechanisms underpinning oncolytic virotherapy and its potential synergism with ICI will enable clinicians to effectively deploy oncolytic virotherapy, either as monotherapy or as combination therapy in the different clinical stages of bladder cancer.

Temozolomide antagonizes oncolytic immunovirotherapy in glioblastoma

BACKGROUND

Temozolomide (TMZ) chemotherapy is a current standard of care for glioblastoma (GBM), however it has only extended overall survival by a few months. Because it also modulates the immune system, both beneficially and negatively, understanding how TMZ interacts with immunotherapeutics is important. Oncolytic herpes simplex virus (oHSV) is a new class of cancer therapeutic with both cytotoxic and immunostimulatory activities. Here, we examine the combination of TMZ and an oHSV encoding murine interleukin 12, G47Δ-mIL12, in a mouse immunocompetent GBM model generated from non-immunogenic 005 GBM stem-like cells (GSCs.

METHODS

We first investigated the cytotoxic effects of TMZ and/or G47Δ-IL12 treatments in vitro, and then the antitumor effects of combination therapy in vivo in orthotopically implanted 005 GSC-derived brain tumors. To improve TMZ sensitivity, O⁶-methylguanine DNA methyltransferase (MGMT) was inhibited. The effects of TMZ on immune cells were evaluated by flow cytometery and immunohistochemistry.

RESULTS

The combination of TMZ+G47Δ-IL12 kills 005 GSCs in vitro better than single treatments. However, TMZ does not improve the survival of orthotopic tumor-bearing mice treated with G47Δ-IL12, but rather can abrogate the beneficial effects of G47Δ-IL12 when the two are given concurrently. TMZ negatively affects intratumor T cells and macrophages and splenocytes. Addition of MGMT inhibitor O⁶-benzylguanine (O6-BG), an inactivating pseudosubstrate of MGMT, to TMZ improved survival, but the combination with G47Δ-IL12 did not overcome the antagonistic effects of TMZ treatment on oHSV therapy.

CONCLUSIONS

These results illustrate that chemotherapy can adversely affect oHSV immunovirotherapy. As TMZ is the standard of care for GBM, the timing of these combined therapies should be taken into consideration when planning oHSV clinical trials with chemotherapy for GBM.

Dual roles of a novel oncolytic viral vector-based SARS-CoV-2 vaccine: preventing COVID-19 and treating tumor progression

The ongoing coronavirus disease 2019 (COVID-19) pandemic is caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Cancer patients are usually immunocompromised and thus are particularly susceptible to SARS-CoV-2 infection resulting in COVID-19. Although many vaccines against COVID-19 are being preclinically or clinically tested or approved, none have yet been specifically developed for cancer patients or reported as having potential dual functions to prevent COVID-19 and treat cancer. Here, we confirmed that COVID-19 patients with cancer have low levels of antibodies against the spike (S) protein, a viral surface protein mediating the entry of SARS-CoV-2 into host cells, compared with COVID-19 patients without cancer. We developed an oncolytic herpes simplex virus-1 vector-based vaccine named oncolytic virus (OV)-spike. OV-spike induced abundant anti-S protein neutralization antibodies in both tumor-free and tumor-bearing mice, which inhibit infection of VSV-SARS-CoV-2 and wild-type (WT) live SARS-CoV-2 as well as the B.1.1.7 variant in vitro. In the tumor-bearing mice, OV-spike also inhibited tumor growth, leading to better survival in multiple preclinical tumor models than the untreated control. Furthermore, OV-spike induced anti-tumor immune response and SARS-CoV-2-specific T cell response without causing serious adverse events. Thus, OV-spike is a promising vaccine candidate for both preventing COVID-19 and enhancing the anti-tumor response.

One Sentence Summary

A herpes oncolytic viral vector-based vaccine is a promising vaccine with dual roles in preventing COVID-19 and treating tumor progression.

The Current State of Oncolytic Herpes Simplex Virus for Glioblastoma Treatment

Glioblastoma (GBM) is a lethal primary malignant brain tumor with no current effective treatments. The recent emergence of immuno-virotherapy and FDA approval of T-VEC have generated a great expectation towards oncolytic herpes simplex viruses (oHSVs) as a promising treatment option for GBM. Since the generation and testing of the first genetically engineered oHSV in glioma in the early 1990s, oHSV-based therapies have shown a long way of great progress in terms of anti-GBM efficacy and safety, both preclinically and clinically. Here, we revisit the literature to understand the recent advancement of oHSV in the treatment of GBM. In addition, we discuss current obstacles to oHSV-based therapies and possible strategies to overcome these pitfalls.

Pathogenetic Features and Current Management of Glioblastoma

Glioblastoma (GBM) is the most common form of primary malignant brain tumor with a devastatingly poor prognosis. The disease does not discriminate, affecting adults and children of both sexes, and has an average overall survival of 12-15 months, despite advances in diagnosis and rigorous treatment with chemotherapy, radiation therapy, and surgical resection. In addition, most survivors will eventually experience tumor recurrence that only imparts survival of a few months. GBM is highly heterogenous, invasive, vascularized, and almost always inaccessible for treatment. Based on all these outstanding obstacles, there have been tremendous efforts to develop alternative treatment options that allow for more efficient targeting of the tumor including small molecule drugs and immunotherapies. A number of other strategies in development include therapies based on nanoparticles, light, extracellular vesicles, and micro-RNA, and vessel co-option. Advances in these potential approaches shed a promising outlook on the future of GBM treatment. In this review, we briefly discuss the current understanding of adult GBM's pathogenetic features that promote treatment resistance. We also outline novel and promising targeted agents currently under development for GBM patients during the last few years with their current clinical status.

Modification of Extracellular Matrix Enhances Oncolytic Adenovirus Immunotherapy in Glioblastoma

PURPOSE

Extracellular matrix (ECM) component hyaluronan (HA) facilitates malignant phenotypes of glioblastoma (GBM), however, whether HA impacts response to GBM immunotherapies is not known. Herein, we investigated whether degradation of HA enhances oncolytic virus immunotherapy for GBM.

EXPERIMENTAL DESIGN

Presence of HA was examined in patient and murine GBM. Hyaluronidase-expressing oncolytic adenovirus, ICOVIR17, and its parental virus, ICOVIR15, without transgene, were tested to determine if they increased animal survival and modulated the immune tumor microenvironment (TME) in orthotopic GBM. HA regulation of NF-κB signaling was examined in virus-infected murine macrophages. We combined ICOVIR17 with PD-1 checkpoint blockade and assessed efficacy and determined mechanistic contributions of tumor-infiltrating myeloid and T cells.

RESULTS

Treatment of murine orthotopic GBM with ICOVIR17 increased tumor-infiltrating CD8+ T cells and macrophages, and upregulated PD-L1 on GBM cells and macrophages, leading to prolonged animal survival, compared with control virus ICOVIR15. High molecular weight HA inhibits adenovirus-induced NF-κB signaling in macrophages in vitro, linking HA degradation to macrophage activation. Combining ICOVIR17 with anti-PD-1 antibody further extended the survival of GBM-bearing mice, achieving long-term remission in some animals. Mechanistically, CD4+ T cells, CD8+ T cells, and macrophages all contributed to the combination therapy that induced tumor-associated proinflammatory macrophages and tumor-specific T-cell cytotoxicity locally and systemically.

CONCLUSIONS

Our studies are the first to show that immune modulatory ICOVIR17 has a dual role of mediating degradation of HA within GBM ECM and subsequently modifying the immune landscape of the TME, and offers a mechanistic combination immunotherapy with PD-L1/PD-1 blockade that remodels innate and adaptive immune cells.

Nucleic Acid-Based Approaches for Tumor Therapy

Within the last decade, the introduction of checkpoint inhibitors proposed to boost the patients' anti-tumor immune response has proven the efficacy of immunotherapeutic approaches for tumor therapy. Furthermore, especially in the context of the development of biocompatible, cell type targeting nano-carriers, nucleic acid-based drugs aimed to initiate and to enhance anti-tumor responses have come of age. This review intends to provide a comprehensive overview of the current state of the therapeutic use of nucleic acids for cancer treatment on various levels, comprising (i) mRNA and DNA-based vaccines to be expressed by antigen presenting cells evoking sustained anti-tumor T cell responses, (ii) molecular adjuvants, (iii) strategies to inhibit/reprogram tumor-induced regulatory immune cells e.g., by RNA interference (RNAi), (iv) genetically tailored T cells and natural killer cells to directly recognize tumor antigens, and (v) killing of tumor cells, and reprograming of constituents of the tumor microenvironment by gene transfer and RNAi. Aside from further improvements of individual nucleic acid-based drugs, the major perspective for successful cancer therapy will be combination treatments employing conventional regimens as well as immunotherapeutics like checkpoint inhibitors and nucleic acid-based drugs, each acting on several levels to adequately counter-act tumor immune evasion.

Combining Oncolytic Viruses With Cancer Immunotherapy: Establishing a New Generation of Cancer Treatment

The recent successes of tumor immunotherapy approaches, such as immune checkpoint blockade (ICB) and chimeric antigen receptor T cell (CAR-T) therapy, have revolutionized cancer treatment, improving efficacy and extending treatment to a larger proportion of cancer patients. However, due to high heterogeneity of cancer, poor tumor cell targeting, and the immunosuppressive status of the tumor microenvironment (TME), combinatorial agents are required to obtain more effective and consistent therapeutic responses in a wide range of cancers. Oncolytic viruses (OVs) are able to selectively replicate in and destroy tumor cells and subsequently induce systematic anti-tumor immune responses. Thus, they are ideal for combining with cancer immunotherapy. In this review, we discuss the current understanding of OVs, as well as the latest preclinical and clinical progress of combining OVs with cancer immunotherapies, including ICB, CAR-T therapy, bispecific T cell engagers (BiTEs), and cancer vaccines. Moreover, we consider future directions for applying OVs to personalized cancer immunotherapies, which could potentially launch a new generation of cancer treatments.

Enhancing Antitumor Efficacy of Heavily Vascularized Tumors by RAMBO Virus through Decreased Tumor Endothelial Cell Activation

Vascularization is a common pathology for many solid tumors, and therefore anti-angiogenic strategies are being investigated as a therapeutic target for treatment. Numerous studies are also being conducted regarding the effects of oncolytic viruses, including Imlygic^TM, an FDA approved oncolytic herpes simplex virus-1 (oHSV) for the treatment of highly vascularized tumors such as Kaposi sarcoma (NCT04065152), and brain tumors. To our knowledge, the effects of combining oncolytic HSV with angiogenesis inhibition on endothelial cell activation has not been previously described. Here, we tested the effects of Rapid Antiangiogenesis Mediated By Oncolytic Virus (RAMBO), an oHSV which expresses a potent anti-angiogenic gene Vasculostatin on endothelial cell activation in heavily vascularized solid tumors. oHSV treatment induces endothelial cell activation, which inhibits virus propagation and oncolysis in adjacent tumor cells in vitro. Consistently, this was also observed in intravital imaging of intracranial tumor-bearing mice in vivo where infected tumor endothelial cells could efficiently clear the virus without cell lysis. Quantitative real-time PCR (Q-PCR), leukocyte adhesion assay, and fluorescent microscopy imaging data, however, revealed that RAMBO virus significantly decreased expression of endothelial cell activation markers and leukocyte adhesion, which in turn increased virus replication and cytotoxicity in endothelial cells. In vivo RAMBO treatment of subcutaneously implanted sarcoma tumors significantly reduced tumor growth in mice bearing sarcoma compared to rHSVQ. In addition, histological analysis of RAMBO-treated tumor tissues revealed large areas of necrosis and a statistically significant reduction in microvessel density (MVD). This study provides strong preclinical evidence of the therapeutic benefit for the use of RAMBO virus as a treatment option for highly vascularized tumors.

Oncolytic Herpes Simplex Virus Encoding IL12 Controls Triple-Negative Breast Cancer Growth and Metastasis

Triple-negative breast cancer (TNBC) is a difficult-to-treat disease with high rates of local recurrence, distant metastasis, and poor overall survival with existing therapies. Thus, there is an unmet medical need to develop new treatment regimen(s) for TNBC patients. An oncolytic herpes simplex virus encoding a master anti-tumor cytokine, interleukin 12, (designated G47Δ-mIL12) selectively kills cancer cells while inducing anti-tumor immunity. G47Δ-mIL12 efficiently infected and killed murine (4T1 and EMT6) and human (HCC1806 and MDA-MB-468) mammary tumor cells in vitro. In vivo in the 4T1 syngeneic TNBC model, it significantly reduced primary tumor burden and metastasis, both at early and late stages of tumor development. The virus-induced local and abscopal effects were confirmed by significantly increased infiltration of CD45⁺ leukocytes and CD8⁺ T cells, and reduction of granulocytic and monocytic MDSCs in tumors, both treated and untreated contralateral, and in the spleen. Significant trafficking of dendritic cells (DCs) were only observed in spleens of virus-treatment group, indicating that DCs are primed and activated in the tumor-microenvironment following virotherapy, and trafficked to lymphoid organs for activation of immune cells, such as CD8⁺ T cells. DC priming/activation could be associated with virally enhanced expression of several antigen processing/presentation genes in the tumor microenvironment, as confirmed by NanoString gene expression analysis. Besides DC activation/priming, G47Δ-mIL12 treatment led to up-regulation of CD8⁺ T cell activation markers in the tumor microenvironment and inhibition of tumor angiogenesis. The anti-tumor effects of G47Δ-mIL12 treatment were CD8-dependent. These studies illustrate the ability of G47Δ-mIL12 to immunotherapeutically treat TNBC.

Oncolytic Virus Encoding a Master Pro-Inflammatory Cytokine Interleukin 12 in Cancer Immunotherapy

Oncolytic viruses (OVs) are genetically modified or naturally occurring viruses, which preferentially replicate in and kill cancer cells while sparing healthy cells, and induce anti-tumor immunity. OV-induced tumor immunity can be enhanced through viral expression of anti-tumor cytokines such as interleukin 12 (IL-12). IL-12 is a potent anti-cancer agent that promotes T-helper 1 (Th1) differentiation, facilitates T-cell-mediated killing of cancer cells, and inhibits tumor angiogenesis. Despite success in preclinical models, systemic IL-12 therapy is associated with significant toxicity in humans. Therefore, to utilize the therapeutic potential of IL-12 in OV-based cancer therapy, 25 different IL-12 expressing OVs (OV-IL12s) have been genetically engineered for local IL-12 production and tested preclinically in various cancer models. Among OV-IL12s, oncolytic herpes simplex virus encoding IL-12 (OHSV-IL12) is the furthest along in the clinic. IL-12 expression locally in the tumors avoids systemic toxicity while inducing an efficient anti-tumor immunity and synergizes with anti-angiogenic drugs or immunomodulators without compromising safety. Despite the rapidly rising interest, there are no current reviews on OV-IL12s that exploit their potential efficacy and safety to translate into human subjects. In this article, we will discuss safety, tumor-specificity, and anti-tumor immune/anti-angiogenic effects of OHSV-IL12 as mono- and combination-therapies. In addition to OHSV-IL12 viruses, we will also review other IL-12-expressing OVs and their application in cancer therapy.

Therapeutic Application of PARP Inhibitors in Neuro-Oncology

In response to a variety of cellular stresses, poly(ADP-ribose) polymerase 1 (PARP1) has vital roles in orchestrating DNA damage repair and preserving genomic integrity. Clinical activity of PARP inhibitors (PARPis) in BRCA1/2 mutant cancers validated the concept of synthetic lethality between PARP inhibition and deleterious BRCA1/2 mutations, leading to clinical approval of several PARPis. Preclinical and clinical studies aiming to broaden the therapeutic application of PARPis identified sensitivity biomarkers and rationale combination strategies that can target BRCA wild-type and homologous recombination (HR) DNA repair-proficient cancers, including central nervous system (CNS) malignancies. In this review, we summarize recent progress in PARPi therapy in brain tumors, and discuss current opportunities for, and challenges to, the use of PARPis in neuro-oncology.

Immunohistochemistry for Tumor-Infiltrating Immune Cells After Oncolytic Virotherapy

Immunohistochemistry (IHC) is an integral laboratory staining technique, which is used for the detection of immune cells in mouse/human tissues or tumors. Oncolytic herpes simplex virus (oHSV) treatment or virotherapy of solid tumors results in antitumor immune responses and infiltration of a variety of immune cells into the tumor. Here, we describe a step-by-step chromogen/substrate-based single- and dual-color IHC protocol to stain immune cells in formalin-fixed, paraffin-embedded mouse glioblastoma (GBM) brain tumor sections after oHSV virotherapy. Tumor sections are deparaffinized with xylene, then gradually rehydrated using ethanol, followed by heat-mediated antigen retrieval using appropriate buffers. Tumor sections are incubated with primary antibodies, which detect a specific immune cell antigen, then incubated with peroxidase- or phosphatase-labeled secondary antibodies, followed by incubation with a color-producing substrate and color visualization (of immune cells) by light microscopy. The protocol described herein is also applicable to detect immune cells in other mouse and human tumors or organs after other forms of immunotherapy.

Oncolytic HSV therapy increases trametinib access to brain tumors and sensitizes them in vivo

BACKGROUND

Hyperactivation of the RAS-RAF-MEK-ERK signaling pathway is exploited by glioma cells to promote their growth and evade apoptosis. MEK activation in tumor cells can increase replication of ICP34.5-deleted herpes simplex virus type 1 (HSV-1), but paradoxically its activation in tumor-associated macrophages promotes a pro-inflammatory signaling that can inhibit virus replication and propagation. Here we investigated the effect of blocking MEK signaling in conjunction with oncolytic HSV-1 (oHSV) for brain tumors.

METHODS

Infected glioma cells co-cultured with microglia or macrophages treated with or without trametinib were used to test trametinib effect on macrophages/microglia. Enzyme-linked immunosorbent assay, western blotting, and flow cytometry were utilized to evaluate the effect of the combination therapy. Pharmacokinetic (PK) analysis of mouse plasma and brain tissue was used to evaluate trametinib delivery to the CNS. Intracranial human and mouse glioma-bearing immune deficient and immune competent mice were used to evaluate the antitumor efficacy.

RESULT

Oncolytic HSV treatment rescued trametinib-mediated feedback reactivation of the mitogen-activated protein kinase signaling pathway in glioma. In vivo, PK analysis revealed enhanced blood-brain barrier penetration of trametinib after oHSV treatment. Treatment by trametinib, a MEK kinase inhibitor, led to a significant reduction in microglia- and macrophage-derived tumor necrosis factor alpha (TNFα) secretion in response to oHSV treatment and increased survival of glioma-bearing mice. Despite the reduced TNFα production observed in vivo, the combination treatment activated CD8+ T-cell mediated immunity and increased survival in a glioma-bearing immune-competent mouse model.

CONCLUSION

This study provides a rationale for combining oHSV with trametinib for the treatment of brain tumors.

Oncolytic herpes simplex virus immunovirotherapy in combination with immune checkpoint blockade to treat glioblastoma

Oncolytic viruses, such as oncolytic herpes simplex virus (oHSV), are a new class of cancer therapeutic, which selectively replicate and kill cancer cells, while inducing an inflammatory microenvironment, immunovirotherapy. Recently, an oHSV (talimogene laherparepvec) has been approved for the treatment of advanced melanoma. Glioblastoma (GBM) is an almost always lethal primary tumor in the brain that is highly immunosuppressive, and posited to contain GBM stem-like cells (GSCs). Immune checkpoint blockade has revolutionized therapy for some cancers, but not GBM. We have used a syngeneic GSC-derived orthotopic GBM model (005) to develop immunotherapeutic strategies. Curative therapy required oHSV expressing IL-12 in combination with two checkpoint inhibitors, anti-PD-1 and anti-CTLA-4. This response required CD4⁺ and CD8⁺ T cells, and macrophages in a complex interplay.

Oncolytic herpes simplex virus and immunotherapy

BACKGROUND

Oncolytic viruses have been proposed to be employed as a potential treatment of cancer. Well targeted, they will serve the purpose of cracking tumor cells without causing damage to normal cells. In this category of oncolytic viral drugs human pathogens herpes simplex virus (HSV) is especially suitable for the cause. Although most viral infection causes antiviral reaction in the host, HSV has multiple mechanisms to evade those responses. Powerful anti-tumor effect can thus be achieved via genetic manipulation of the HSV genes involved in this evading mechanism, namely deletions or mutations that adapt its function towards a tumor microenvironment. Currently, oncolytic HSV (oHSV) is widely use in clinical; moreover, there's hope that its curative effect will be further enhanced through the combination of oHSV with both traditional and emerging therapeutics.

RESULTS

In this review, we provide a summary of the HSV host antiviral response evasion mechanism, HSV expresses immune evasion genes such as ICP34.5, ICP0, Us3, which are involved in inducing and activating host responses, so that the virus can evade the immune system and establish effective long-term latent infection; we outlined details of the oHSV strains generated by removing genes critical to viral replication such as ICP34.5, ICP0, and inserting therapeutic genes such as LacZ, granulocyte macrophage colony-stimulating factor (GM-CSF); security and limitation of some oHSV such G207, 1716, OncoVEX, NV1020, HF10, G47 in clinical application; and the achievements of oHSV combined with immunotherapy and chemotherapy.

CONCLUSION

We reviewed the immunotherapy mechanism of the oHSV and provided a series of cases. We also pointed out that an in-depth study of the application of oHSV in cancer treatment will potentially benefits cancer patients more.

SOCS4 expressed by recombinant HSV protects against cytokine storm in a mouse model

Oncolytic viruses are genetically engineered viruses designed for the treatment of solid tumors, and are often coupled with the antitumor immunity of the host. The challenge of using oncolytic herpes simplex virus (oHSV) as an efficacious oncolytic agent is the potential host tissue damage caused by the production of a range of cytokines following intratumoral oHSV injection. An HSV-suppressor of cytokine signaling 4 (SOCS4) recombinant virus was created to investigate whether it inhibits cytokine storm. Recombinant HSV-SOCS4 and HSV-1(F) were used to infect mice, and levels of several representative cytokines, including monocyte chemoattractant protein-1, interleukin (IL)-1β, tumor necrosis factor-α, IL-6 and interferon γ, in serum and bronchoalveolar lavage fluid (BALF) of infected mice were determined, and immune cells in BALF and spleen were enumerated. Lung damage, virus titers in the lung, body weight and survival rates of infected mice were also determined and compared between the two groups. The cytokine concentration of HSV-SOCS4-infected mice was significantly decreased compared with that of HSV-1(F)-infected mice in BALF and serum, and a smaller number of cluster of differentiation (CD)11b⁺ cells of BALF, and CD8⁺CD62L⁺ T cells and CD4⁺CD62L⁺ T cells of the spleen were also identified in HSV-SOCS4-infected mice. HSV-SOCS4-infected mice exhibited slight lung damage, a decrease in body weight loss and a 100% survival rate. The results of the present study indicated that SOCS4 protein may be a useful regulator to inhibit cytokine overproduction, and that HSV-SOCS4 may provide a possible solution to control cytokine storm and its consequences following induction by oncolytic virus treatment.

Combinatorial Effects of VEGFR Kinase Inhibitor Axitinib and Oncolytic Virotherapy in Mouse and Human Glioblastoma Stem-Like Cell Models

Purpose: Glioblastoma (GBM), a fatal brain cancer, contains a subpopulation of GBM stem-like cells (GSCs) that contribute to resistance to current therapy. Angiogenesis also plays a key role in GBM progression. Therefore, we developed a strategy to target the complex GBM microenvironment, including GSCs and tumor vasculature.Experimental Design: We evaluated the cytotoxic effects of VEFGR tyrosine kinase inhibitor (TKI) axitinib in vitro and then tested antitumor efficacy of axitinib in combination with oncolytic herpes simplex virus (oHSV) expressing antiangiogenic cytokine murine IL12 (G47Δ-mIL12) in two orthotopic GSC-derived GBM models: patient-derived recurrent MGG123 GSCs, forming vascular xenografts in immunodeficient mice; and mouse 005 GSCs, forming syngeneic tumors in immunocompetent mice.Results: GSCs form endothelial-like tubes and were sensitive to axitinib. G47Δ-mIL12 significantly improved survival, as did axitinib, while dual combinations further extended survival significantly compared with single therapies alone in both models. In MGG123 tumors, axitinib was effective only at high doses (50 mg/kg), alone and in combination with G47Δ-mIL12, and this was associated with greatly decreased vascularity, increased macrophage infiltration, extensive tumor necrosis, and PDGFR/ERK pathway inhibition. In the mouse 005 model, antiglioma activity, after single and combination therapy, was only observed in immunocompetent mice and not the T-cell-deficient athymic mice. Interestingly, immune checkpoint inhibition did not improve efficacy.Conclusions: Systemic TKI (axitinib) beneficially combines with G47Δ-mIL12 to enhance antitumor efficacy in both immunodeficient and immunocompetent orthotopic GBM models. Our results support further investigation of TKIs in combination with oHSV for GBM treatment. Clin Cancer Res; 24(14); 3409-22. ©2018 AACR.

Targeting Poxvirus Decapping Enzymes and mRNA Decay to Generate an Effective Oncolytic Virus

Through the action of two virus-encoded decapping enzymes (D9 and D10) that remove protective caps from mRNA 5′-termini, Vaccinia virus (VACV) accelerates mRNA decay and limits activation of host defenses. D9- or D10-deficient VACV are markedly attenuated in mice and fail to counter cellular double-stranded RNA-responsive innate immune effectors, including PKR. Here, we capitalize upon this phenotype and demonstrate that VACV deficient in either decapping enzyme are effective oncolytic viruses. Significantly, D9- or D10-deficient VACV displayed anti-tumor activity against syngeneic mouse tumors of different genetic backgrounds and human hepatocellular carcinoma xenografts. Furthermore, D9- and D10-deficient VACV hyperactivated the host anti-viral enzyme PKR in non-tumorigenic cells compared to wild-type virus. This establishes a new genetic platform for oncolytic VACV development that is deficient for a major pathogenesis determinant while retaining viral genes that support robust productive replication like those required for nucleotide metabolism. It further demonstrates how VACV mutants unable to execute a fundamental step in virus-induced mRNA decay can be unexpectedly translated into a powerful anti-tumor therapy.

TGF-β Inhibition Improves Oncolytic Herpes Viroimmunotherapy in Murine Models of Rhabdomyosarcoma

Oncolytic viruses are an emerging class of cancer therapeutics that couple cytotoxicity with the induction of an anti-tumor immune response. Host-virus interactions are complex and modulated by a tumor microenvironment whose immunosuppressive activities can limit the effectiveness of cancer immunotherapies. In an effort to improve this aspect of oncolytic virotherapy, we combined the oncolytic herpes virus HSV1716 with the transforming growth factor beta receptor 1 (TGF-βR1) inhibitor A8301 to treat syngeneic models of murine rhabdomyosarcoma. Mice that received HSV1716 or A8301 alone showed little to no benefit in efficacy and survival over controls. Conversely, mice given combination therapy exhibited tumor stabilization throughout the treatment regimen, which was reflected in significantly prolonged survival times including some complete responses. In vitro cell viability and virus replication assays showed that the rhabdomyosarcoma cell lines were generally insensitive to HSV1716 and A8301. Likewise, in vivo virus replication assays showed that HSV1716 titers moderately decreased in the presence of A8301. The enhanced efficacy instead appears to be dependent on the generation of an improved anti-tumor T cell response as determined by its loss in athymic nude mice and following in vivo depletion of either CD4⁺ or CD8⁺ cells. These data suggest TGF-β inhibition can augment the immunotherapeutic efficacy of oncolytic herpes virotherapy.

Modulation of the Intratumoral Immune Landscape by Oncolytic Herpes Simplex Virus Virotherapy

Vaccines and immunotherapeutic approaches to cancers with the advent of immune checkpoint inhibitors and chimeric antigen receptor-modified T cells have recently demonstrated preclinical success and entered clinical trials. Despite advances in these approaches and combinatorial therapeutic regimens, depending on the nature of the cancer and the immune and metabolic landscape within the tumor microenvironment, current immunotherapeutic modalities remain inadequate. Recent clinical trials have demonstrated clear evidence of significant, and sometimes dramatic, antitumor activity, and long-term survival effects of a variety of oncolytic viruses (OVs), particularly oncolytic herpes simplex virus (oHSV). Acting as a multifaceted gene therapy vector and potential adjuvant-like regimens, oHSV can carry genes encoding immunostimulatory molecules in its genome. The oncolytic effect of oHSV and the inflammatory response that the virus stimulates provide a one-two punch at attacking tumors. However, mechanisms underlying oHSV-induced restoration of intratumoral immunosuppression demand extensive research in order to further improve its therapeutic efficacy. In this review, we discuss the current OV-based therapy, with a focus on the unique aspects of oHSV-initiated antiviral and antitumor immune responses, arising from virus-mediated immunological cell death to intratumoral innate and adaptive immunity.