T-cell engager-armed oncolytic vaccinia virus significantly enhances antitumor therapy

Alliance between titans: combination strategies of CAR-T cell therapy and oncolytic virus for the treatment of hematological malignancies

There have been several clinical studies using chimeric antigen receptor (CAR)-T cell therapy for different hematological malignancies. It has transformed the therapy landscape for hematologic malignancies dramatically. Nonetheless, in acute myeloid leukemia (AML) and T cell malignancies, it still has a dismal prognosis. Even in the most promising locations, recurrence with CAR-T treatment remains a big concern. Oncolytic viruses (OVs) can directly lyse tumor cells or cause immune responses, and they can be manipulated to create therapeutic proteins, increasing anticancer efficacy. Oncolytic viruses have been proven in a rising number of studies to be beneficial in hematological malignancies. There are limitations that cannot be avoided by using either treatment alone, and the combination of CAR-T cell therapy and oncolytic virus therapy may complement the disadvantages of individual application, enhance the advantages of their respective treatment methods and improve the treatment effect. The alternatives for combining two therapies in hematological malignancies are discussed in this article.

Oncolytic virotherapy for hepatocellular carcinoma: A potent immunotherapeutic landscape

Hepatocellular carcinoma (HCC) is a systemic disease with augmented malignant degree, high mortality and poor prognosis. Since the establishment of the immune mechanism of tumor therapy, people have realized that immunotherapy is an effective means for improvement of HCC patient prognosis. Oncolytic virus is a novel immunotherapy drug, which kills tumor cells and exempts normal cells by directly lysing tumor and inducing anti-tumor immune response, and it has been extensively examined as an HCC therapy. This editorial discusses oncolytic viruses for the treatment of HCC, emphasizing viral immunotherapy strategies and clinical applications related to HCC.

The investigation of oncolytic viruses in the field of cancer therapy

Oncolytic viruses (OVs) have emerged as a potential strategy for tumor treatment due to their ability to selectively replicate in tumor cells, induce apoptosis, and stimulate immune responses. However, the therapeutic efficacy of single OVs is limited by the complexity and immunosuppressive nature of the tumor microenvironment (TME). To overcome these challenges, engineering OVs has become an important research direction. This review focuses on engineering methods and multi-modal combination therapies for OVs aimed at addressing delivery barriers, viral phagocytosis, and antiviral immunity in tumor therapy. The engineering approaches discussed include enhancing in vivo immune response, improving replication efficiency within the tumor cells, enhancing safety profiles, and improving targeting capabilities. In addition, this review describes the potential mechanisms of OVs combined with radiotherapy, chemotherapy, cell therapy and immune checkpoint inhibitors (ICIs), and summarizes the data of ongoing clinical trials. By continuously optimizing engineering strategies and combination therapy programs, we can achieve improved treatment outcomes and quality of life for cancer patients.

A review exploring the fusion of oncolytic viruses and cancer immunotherapy: An innovative strategy in the realm of cancer treatment

Oncolytic viruses (OVs) are increasingly recognized as potent tools in cancer therapy, effectively targeting and eradicating oncogenic conditions while sparing healthy cells. They enhance antitumor immunity by triggering various immune responses throughout the cancer cycle. Genetically engineered OVs swiftly destroy cancerous tissues and activate the immune system by releasing soluble antigens like danger signals and interferons. Their ability to stimulate both innate and adaptive immunity makes them particularly attractive in cancer immunotherapy. Recent advancements involve combining OVs with other immune therapies, yielding promising results. Transgenic OVs, designed to enhance immunostimulation and specifically target cancer cells, further improve immune responses. This review highlights the intrinsic mechanisms of OVs and underscores their synergistic potential with other immunotherapies. It also proposes strategies for optimizing armed OVs to bolster immunity against tumors.

The Role of Natural Killer Cells in Oncolytic Virotherapy: Friends or Foes?

Oncolytic virotherapy (OVT) has emerged as a promising cancer immunotherapy, and is capable of potentiating other immunotherapies due to its capacity to increase tumor immunogenicity and to boost host antitumor immunity. Natural killer (NK) cells are a critical cellular component for mediating the antitumor response, but hold a mixed reputation for their role in mediating the therapeutic efficacy of OVT. This review will discuss the pros and cons of how NK cells impact OVT, and how to harness this knowledge for the development of effective strategies that could modulate NK cells to improve OVT-based therapeutic outcomes.

Emerging role of immunogenic cell death in cancer immunotherapy: Advancing next-generation CAR-T cell immunotherapy by combination

Immunogenic cell death (ICD) is a stress-driven form of regulated cell death (RCD) in which dying tumor cells' specific signaling pathways are activated to release damage-associated molecular patterns (DAMPs), leading to the robust anti-tumor immune response as well as a reversal of the tumor immune microenvironment from "cold" to "hot". Chimeric antigen receptor (CAR)-T cell therapy, as a landmark in anti-tumor immunotherapy, plays a formidable role in hematologic malignancies but falls short in solid tumors. The Gordian knot of CAR-T cells for solid tumors includes but is not limited to, tumor antigen heterogeneity or absence, physical and immune barriers of tumors. The combination of ICD induction therapy and CAR-T cell immunotherapy is expected to promote the intensive use of CAR-T cell in solid tumors. In this review, we summarize the characteristics of ICD, stress-responsive mechanism, and the synergistic effect of various ICD-based therapies with CAR-T cells to effectively improve anti-tumor capacity.

Stepping forward: T-cell redirecting bispecific antibodies in cancer therapy

T cell-redirecting bispecific antibodies are specifically designed to bind to tumor-associated antigens, thereby engaging with CD3 on the T cell receptor. This linkage between tumor cells and T cells actively triggers T cell activation and initiates targeted killing of the identified tumor cells. These antibodies have emerged as one of the most promising avenues within tumor immunotherapy. However, despite success in treating hematological malignancies, significant advancements in solid tumors have yet to be explored. In this review, we aim to address the critical challenges associated with T cell-redirecting bispecific antibodies and explore novel strategies to overcome these obstacles, with the ultimate goal of expanding the application of this therapy to include solid tumors.

Immune landscape and response to oncolytic virus-based immunotherapy

Oncolytic virus (OV)-based immunotherapy has emerged as a promising strategy for cancer treatment, offering a unique potential to selectively target malignant cells while sparing normal tissues. However, the immunosuppressive nature of tumor microenvironment (TME) poses a substantial hurdle to the development of OVs as effective immunotherapeutic agents, as it restricts the activation and recruitment of immune cells. This review elucidates the potential of OV-based immunotherapy in modulating the immune landscape within the TME to overcome immune resistance and enhance antitumor immune responses. We examine the role of OVs in targeting specific immune cell populations, including dendritic cells, T cells, natural killer cells, and macrophages, and their ability to alter the TME by inhibiting angiogenesis and reducing tumor fibrosis. Additionally, we explore strategies to optimize OV-based drug delivery and improve the efficiency of OV-mediated immunotherapy. In conclusion, this review offers a concise and comprehensive synopsis of the current status and future prospects of OV-based immunotherapy, underscoring its remarkable potential as an effective immunotherapeutic agent for cancer treatment.

OV Modulators of the Paediatric Brain TIME: Current Status, Combination Strategies, Limitations and Future Directions

Oncolytic viruses (OVs) are characterised by their preference for infecting and replicating in tumour cells either naturally or after genetic modification, resulting in oncolysis. Furthermore, OVs can elicit both local and systemic anticancer immune responses while specifically infecting and lysing tumour cells. These characteristics render them a promising therapeutic approach for paediatric brain tumours (PBTs). PBTs are frequently marked by a cold tumour immune microenvironment (TIME), which suppresses immunotherapies. Recent preclinical and clinical studies have demonstrated the capability of OVs to induce a proinflammatory immune response, thereby modifying the TIME. In-depth insights into the effect of OVs on different cell types in the TIME may therefore provide a compelling basis for using OVs in combination with other immunotherapy modalities. However, certain limitations persist in our understanding of oncolytic viruses' ability to regulate the TIME to enhance anti-tumour activity. These limitations primarily stem from the translational limitations of model systems, the difficulties associated with tracking reliable markers of efficacy throughout the course of treatment and the role of pre-existing viral immunity. In this review, we describe the different alterations observed in the TIME in PBTs due to OV treatment, combination therapies of OVs with different immunotherapies and the hurdles limiting the development of effective OV therapies while suggesting future directions based on existing evidence.

ITPRIPL1 binds CD3ε to impede T cell activation and enable tumor immune evasion

Cancer immunotherapy has transformed treatment possibilities, but its effectiveness differs significantly among patients, indicating the presence of alternative pathways for immune evasion. Here, we show that ITPRIPL1 functions as an inhibitory ligand of CD3ε, and its expression inhibits T cells in the tumor microenvironment. The binding of ITPRIPL1 extracellular domain to CD3ε on T cells significantly decreased calcium influx and ZAP70 phosphorylation, impeding initial T cell activation. Treatment with a neutralizing antibody against ITPRIPL1 restrained tumor growth and promoted T cell infiltration in mouse models across various solid tumor types. The antibody targeting canine ITPRIPL1 exhibited notable therapeutic efficacy against naturally occurring tumors in pet clinics. These findings highlight the role of ITPRIPL1 (or CD3L1, CD3ε ligand 1) in impeding T cell activation during the critical "signal one" phase. This discovery positions ITPRIPL1 as a promising therapeutic target against multiple tumor types.

Advances in cell-based delivery of oncolytic viruses as therapy for lung cancer

Lung cancer's intractability is enhanced by its frequent resistance to (chemo)therapy and often high relapse rates that make it the leading cause of cancer death worldwide. Improvement of therapy efficacy is a crucial issue that might lead to a significant advance in the treatment of lung cancer. Oncolytic viruses are desirable combination partners in the developing field of cancer immunotherapy due to their direct cytotoxic effects and ability to elicit an immune response. Systemic oncolytic virus administration through intravenous injection should ideally lead to the highest efficacy in oncolytic activity. However, this is often hampered by the prevalence of host-specific, anti-viral immune responses. One way to achieve more efficient systemic oncolytic virus delivery is through better protection against neutralization by several components of the host immune system. Carrier cells, which can even have innate tumor tropism, have shown their appropriateness as effective vehicles for systemic oncolytic virus infection through circumventing restrictive features of the immune system and can warrant oncolytic virus delivery to tumors. In this overview, we summarize promising results from studies in which carrier cells have shown their usefulness for improved systemic oncolytic virus delivery and better oncolytic virus therapy against lung cancer.

Antiangiogenic Therapeutic mRNA Delivery Using Lung-Selective Polymeric Nanomedicine for Lung Cancer Treatment

Therapeutic antibodies that block vascular endothelial growth factor (VEGF) show clinical benefits in treating nonsmall cell lung cancers (NSCLCs) by inhibiting tumor angiogenesis. Nonetheless, the therapeutic effects of systemically administered anti-VEGF antibodies are often hindered in NSCLCs because of their limited distribution in the lungs and their adverse effects on normal tissues. These challenges can be overcome by delivering therapeutic antibodies in their mRNA form to lung endothelial cells, a primary target of VEGF-mediated pulmonary angiogenesis, to suppress the NSCLCs. In this study, we synthesized derivatives of poly(β-amino esters) (PBAEs) and prepared nanoparticles to encapsulate the synthetic mRNA encoding bevacizumab, an anti-VEGF antibody used in the clinic. Optimization of nanoparticle formulations resulted in a selective lung transfection after intravenous administration. Notably, the optimized PBAE nanoparticles were distributed in lung endothelial cells, resulting in the secretion of bevacizumab. We analyzed the protein corona on the lung- and spleen-targeting nanoparticles using proteomics and found distinctive features potentially contributing to their organ-selectivity. Lastly, bevacizumab mRNA delivered by the lung-targeting PBAE nanoparticles more significantly inhibited tumor proliferation and angiogenesis than recombinant bevacizumab protein in orthotopic NSCLC mouse models, supporting the therapeutic potential of bevacizumab mRNA therapy and its selective delivery through lung-targeting nanoparticles. Our proof-of-principle results highlight the clinical benefits of nanoparticle-mediated mRNA therapy in anticancer antibody treatment in preclinical models.

Recent progress in combination therapy of oncolytic vaccinia virus

In recent years, oncolytic viruses have emerged as promising agents for treating various cancers. An oncolytic virus is a non-pathogenic virus that, due to genetic manipulation, tends to replicate in and cause lysis of cancerous cells while leaving healthy cells unaffected. Among these viruses, vaccinia virus is an attractive platform for use as an oncolytic platform due to its 190 Kb genome with a high capacity for encoding therapeutic payloads. Combining oncolytic VV therapy with other conventional cancer treatments has been shown to be synergistic and more effective than monotherapies. Additionally, OVV can be used as a vector to deliver therapeutic payloads, alone or in combination with other treatments, to increase overall efficacy. Here, we present a comprehensive analysis of preclinical and clinical studies that have evaluated the efficacy of oncolytic vaccinia viruses in cancer immunotherapy. We discuss the outcomes of these studies, including tumor regression rates, overall survival benefits, and long-term responses. Moreover, we provide insights into the challenges and limitations associated with oncolytic vaccinia virus- based therapies, including immune evasion mechanisms, potential toxicities, and the development of resistance.

Expression of GPX4 by oncolytic vaccinia virus can significantly enhance CD8+T cell function and its impact against pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is currently difficult to treat, even when therapies are combined with immune checkpoint blockade (ICB). A novel strategy for immunotherapy would be to maximize the therapeutic potential of oncolytic viruses (OVs), which have been proven to engage the regulation of tumor microenvironment (TME) and cause-specific T-cell responses. To boost tumor sensitivity to ICB therapy, this study aimed to investigate how glutathione peroxide 4 (GPX4)-loaded OVs affect CD8+ T cells and repair the immunosuppressive environment. Here, we successfully constructed a novel recombinant oncolytic vaccinia virus (OVV) encoding the mouse GPX4 gene. We found the OVV-GPX4 effectively replicated in tumor cells and prompted the expression of GPX4 in T cells. Our research indicated that OVV-GPX4 could reshape the TME, rectify the depletion of CD8+T cells, and enhance the antitumor effects of ICB therapy.

Revolutionizing cancer treatment: the power of bi- and tri-specific T-cell engagers in oncolytic virotherapy

Bi- or tri-specific T cell engagers (BiTE or TriTE) are recombinant bispecific proteins designed to stimulate T-cell immunity directly, bypassing antigen presentation by antigen-presenting cells (APCs). However, these molecules suffer from limitations such as short biological half-life and poor residence time in the tumor microenvironment (TME). Fortunately, these challenges can be overcome when combined with OVs. Various strategies have been developed, such as encoding secretory BiTEs within OV vectors, resulting in improved targeting and activation of T cells, secretion of key cytokines, and bystander killing of tumor cells. Additionally, oncolytic viruses armed with BiTEs have shown promising outcomes in enhancing major histocompatibility complex I antigen (MHC-I) presentation, T-cell proliferation, activation, and cytotoxicity against tumor cells. These combined approaches address tumor heterogeneity, drug delivery, and T-cell infiltration, offering a comprehensive and effective solution. This review article aims to provide a comprehensive overview of Bi- or TriTEs and OVs as promising therapeutic approaches in the field of cancer treatment. We summarize the cutting-edge advancements in oncolytic virotherapy immune-related genetic engineering, focusing on the innovative combination of BiTE or TriTE with OVs.

Arming oncolytic viruses with bispecific T cell engagers: The evolution and current status

Oncolytic viruses (OVs) are emerging as therapeutically relevant anticancer agents as contemporary immunotherapy gains traction. Furthermore, OVs are an ideal platform for genetic modification to express therapeutic transgenes. Bispecific T cell engagers (BiTEs) can redirect T cells to tumor cells, resulting in targeted cytotoxicity. BiTEs have demonstrated success in hematological cancers but are rarely used in solid tumors. The drawbacks of BiTEs, including inadequate delivery and on-target-off-tumor activity have limited their efficacy. Combining OVs with BiTEs is a prospective area to investigate. This combined strategy can benefit from the best qualities of both therapies while overcoming the limitations.

Oncolytic viruses in lung cancer treatment: a review article

Lung cancer has a high morbidity rate worldwide due to its resistance to therapy. So new treatment options are needed to improve the outcomes of lung cancer treatment. This study aimed to evaluate the effectiveness of oncolytic viruses (OVs) as a new type of cancer treatment. In this study, 158 articles from PubMed and Scopus from 1994 to 2022 were reviewed on the effectiveness of OVs in the treatment of lung cancer. The oncolytic properties of eight categories of OVs and their interactions with treatment options were investigated. OVs can be applied as a promising immunotherapy option, as they are reproduced selectively in different types of cancer cells, cause tumor cell lysis and trigger efficient immune responses.

Oncolytic Virotherapy: A New Paradigm in Cancer Immunotherapy

Oncolytic viruses (OVs) are emerging as potential treatment options for cancer. Natural and genetically engineered viruses exhibit various antitumor mechanisms. OVs act by direct cytolysis, the potentiation of the immune system through antigen release, and the activation of inflammatory responses or indirectly by interference with different types of elements in the tumor microenvironment, modification of energy metabolism in tumor cells, and antiangiogenic action. The action of OVs is pleiotropic, and they show varied interactions with the host and tumor cells. An important impediment in oncolytic virotherapy is the journey of the virus into the tumor cells and the possibility of its binding to different biological and nonbiological vectors. OVs have been demonstrated to eliminate cancer cells that are resistant to standard treatments in many clinical trials for various cancers (melanoma, lung, and hepatic); however, there are several elements of resistance to the action of viruses per se. Therefore, it is necessary to evaluate the combination of OVs with other standard treatment modalities, such as chemotherapy, immunotherapy, targeted therapies, and cellular therapies, to increase the response rate. This review provides a comprehensive update on OVs, their use in oncolytic virotherapy, and the future prospects of this therapy alongside the standard therapies currently used in cancer treatment.

Oncolytic vaccinia virus and cancer immunotherapy

Oncolytic virotherapy (OVT) is a promising form of cancer treatment that uses genetically engineered viruses to replicate within cancer cells and trigger anti-tumor immune response. In addition to killing cancer cells, oncolytic viruses can also remodel the tumor microenvironment and stimulate a long-term anti-tumor immune response. Despite achieving positive results in cellular and organismal studies, there are currently only a few approved oncolytic viruses for clinical use. Vaccinia virus (VACV) has emerged as a potential candidate due to its ability to infect a wide range of cancer cells. This review discusses the mechanisms, benefits, and clinical trials of oncolytic VACVs. The safety and efficacy of different viral backbones are explored, as well as the effects of oncolytic VACVs on the tumor microenvironment. The potential combination of oncolytic VACVs with immunotherapy or traditional therapies is also highlighted. The review concludes by addressing prospects and challenges in the field of oncolytic VACVs, with the aim of promoting further research and application in cancer therapy.

Oncolytic virotherapy in cancer treatment: challenges and optimization prospects

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

[Oncolytic viruses: Actors and deliverers of therapeutic proteins against tumors]

The discovery of the unique ability of certain viruses to specifically target cancer cells has led to significant advancements in cancer immunotherapy research. In addition to inducing specific lysis of cancer cells, oncolytic viruses (OV) have been genetically modified to express molecules of interest within the tumor bed. The use of OV as vectors for therapeutic molecules has allowed to enhance antitumor responses while limiting the adverse effects associated with systemic administration of the molecule. Other studies are currently focused on delaying the neutralization and clearance of the virus by the host's immune system and improving its delivery insight tumors.

Claudin18.2 bispecific T cell engager armed oncolytic virus enhances antitumor effects against pancreatic cancer

Bispecific T cell engagers (BiTEs) represent a promising immunotherapy, but their efficacy against immunologically cold tumors such as pancreatic ductal adenocarcinoma remains unclear. Oncolytic viruses (OVs) can transform the immunosuppressive tumor microenvironment into the active state and also serve as transgene vectors to selectively express the desired genes in tumor cells. This study aimed to investigate whether the therapeutic benefits of tumor-targeting Claudin18.2 BiTE can be augmented by combining cancer selectively and immune-potentiating effects of OVs. Claudin18.2/CD3 BiTE was inserted into herpes simplex virus type 1 (HSV-1) to construct an OV-BiTE. Its expression and function were assessed using reporter cells and peripheral blood mononuclear cell (PBMC) co-culture assays. Intratumoral application of OV-BiTE restrained tumor growth and prolonged mouse survival compared with the unarmed OV in xenograft models and syngeneic mice bearing CLDN18.2-expressing KPC or Pan02 pancreatic cancer cells. Flow cytometry of tumor-infiltrating immune cells suggested both OV-BiTE and the unarmed OV remodeled the tumor microenvironment by increasing CD4+ T cell infiltration and decreasing regulatory T cells. OV-BiTE further reprogrammed macrophages to a more pro-inflammatory antitumor state, and OV-BiTE-induced macrophages exhibited greater cytotoxicity on the co-cultured tumor cell. This dual cytotoxic and immunomodulatory approach warrants further development for pancreatic cancer before clinical investigation.

Personalizing Oncolytic Virotherapy

The use of oncolytic viruses has become an attractive tool in the clinics for the treatment of various tumor types. Such viruses are genetically modified to conditionally replicate in malignant cells while unharming healthy cells. This platform offers a highly specific tumor killing with exceptional safety profiles. However, the use of oncolytic viruses as sole oncolytic platforms has not achieved full tumor clearance in murine models and in the clinics. In fact, the formation of anti-tumor immune responses is attributed to the effectiveness of oncolytic viruses. In this review, we will discuss the various strategies that scientists have employed to enhance the anti-tumor immune responses driven by oncolytic viruses. Moreover, focus will be drawn into personalizing such anti-tumor responses by the addition of tumor-associated peptides.

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

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

Preclinical and clinical trials of oncolytic vaccinia virus in cancer immunotherapy: a comprehensive review

Oncolytic virotherapy has emerged as a promising treatment for human cancers owing to an ability to elicit curative effects via systemic administration. Tumor cells often create an unfavorable immunosuppressive microenvironment that degrade viral structures and impede viral replication; however, recent studies have established that viruses altered via genetic modifications can serve as effective oncolytic agents to combat hostile tumor environments. Specifically, oncolytic vaccinia virus (OVV) has gained popularity owing to its safety, potential for systemic delivery, and large gene insertion capacity. This review highlights current research on the use of engineered mutated viruses and gene-armed OVVs to reverse the tumor microenvironment and enhance antitumor activity in vitro and in vivo, and provides an overview of ongoing clinical trials and combination therapies. In addition, we discuss the potential benefits and drawbacks of OVV as a cancer therapy, and explore different perspectives in this field.

Oncolytic Virus Engineering and Utilizations: Cancer Immunotherapy Perspective

Oncolytic viruses have positively impacted cancer immunotherapy over the past 20 years. Both natural and genetically modified viruses have shown promising results in treating various cancers. Various regulatory authorities worldwide have approved four commercial oncolytic viruses, and more are being developed to overcome this limitation and obtain better anti-tumor responses in clinical trials at various stages. Faster advancements in translating research into the commercialization of cancer immunotherapy and a comprehensive understanding of the modification strategies will widen the current knowledge of future technologies related to the development of oncolytic viruses. In this review, we discuss the strategies of virus engineering and the progress of clinical trials to achieve virotherapeutics.

Oncolytic virotherapy evolved into the fourth generation as tumor immunotherapy

BACKGROUND

Oncolytic virotherapy (OVT) is a promising anti-tumor modality that utilizes oncolytic viruses (OVs) to preferentially attack cancers rather than normal tissues. With the understanding particularly in the characteristics of viruses and tumor cells, numerous innovative OVs have been engineered to conquer cancers, such as Talimogene Laherparepvec (T-VEC) and tasadenoturev (DNX-2401). However, the therapeutic safety and efficacy must be further optimized and balanced to ensure the superior safe and efficient OVT in clinics, and reasonable combination therapy strategies are also important challenges worthy to be explored.

MAIN BODY

Here we provided a critical review of the development history and status of OVT, emphasizing the mechanisms of enhancing both safety and efficacy. We propose that oncolytic virotherapy has evolved into the fourth generation as tumor immunotherapy. Particularly, to arouse T cells by designing OVs expressing bi-specific T cell activator (BiTA) is a promising strategy of killing two birds with one stone. Amazing combination of therapeutic strategies of OVs and immune cells confers immense potential for managing cancers. Moreover, the attractive preclinical OVT addressed recently, and the OVT in clinical trials were systematically reviewed.

CONCLUSION

OVs, which are advancing into clinical trials, are being envisioned as the frontier clinical anti-tumor agents coming soon.

Recent advances in oncolytic virus therapy for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a highly refractory cancer and the fourth leading cause of cancer-related mortality worldwide. Despite the development of a detailed treatment strategy for HCC, the survival rate remains unsatisfactory. Oncolytic virus has been extensively researched as a new cancer therapeutic agent in the treatment of HCC. Researchers have designed a variety of recombinant viruses based on natural oncolytic diseases, which can increase the targeting of oncolytic viruses to HCC and their survival in tumors, as well as kill tumor cells and inhibit the growth of HCC through a variety of mechanisms. The overall efficacy of oncolytic virus therapy is known to be influenced by anti-tumor immunity, toxic killing effect and inhibition of tumor angiogenesis, etc. Therefore, a comprehensive review of the multiple oncolytic mechanisms of oncolytic viruses in HCC has been conducted. So far, a large number of relevant clinical trials are under way or have been completed, and some encouraging results have been obtained. Studies have shown that oncolytic virus combined with other HCC therapies may be a feasible method, including local therapy, chemotherapy, molecular targeted therapy and immunotherapy. In addition, different delivery routes for oncolytic viruses have been studied so far. These studies make oncolytic virus a new and attractive drug for the treatment of HCC.

Oncolytic virotherapy: basic principles, recent advances and future directions

Oncolytic viruses (OVs) have attracted growing awareness in the twenty-first century, as they are generally considered to have direct oncolysis and cancer immune effects. With the progress in genetic engineering technology, OVs have been adopted as versatile platforms for developing novel antitumor strategies, used alone or in combination with other therapies. Recent studies have yielded eye-catching results that delineate the promising clinical outcomes that OVs would bring about in the future. In this review, we summarized the basic principles of OVs in terms of their classifications, as well as the recent advances in OV-modification strategies based on their characteristics, biofunctions, and cancer hallmarks. Candidate OVs are expected to be designed as "qualified soldiers" first by improving target fidelity and safety, and then equipped with "cold weapons" for a proper cytocidal effect, "hot weapons" capable of activating cancer immunotherapy, or "auxiliary weapons" by harnessing tactics such as anti-angiogenesis, reversed metabolic reprogramming and decomposing extracellular matrix around tumors. Combinations with other cancer therapeutic agents have also been elaborated to show encouraging antitumor effects. Robust results from clinical trials using OV as a treatment congruously suggested its significance in future application directions and challenges in developing OVs as novel weapons for tactical decisions in cancer treatment.

Application of oncolytic virus in tumor therapy

Oncolytic viruses (OVs) can selectively kill tumor cells without affecting normal cells, as well as activate the innate and adaptive immune systems in patients. Thus, they have been considered as a promising measure for safe and effective cancer treatment. Recently, a few genetically engineered OVs have been developed to further improve the effect of tumor elimination by expressing specific immune regulatory factors and thus enhance the body's antitumor immunity. In addition, the combined therapies of OVs and other immunotherapies have been applied in clinical. Although there are many studies on this hot topic, a comprehensive review is missing on illustrating the mechanisms of tumor clearance by OVs and how to modify engineered OVs to further enhance their antitumor effects. In this study, we provided a review on the mechanisms of immune regulatory factors in OVs. In addition, we reviewed the combined therapies of OVs with other therapies including radiotherapy and CAR-T or TCR-T cell therapy. The review is useful in further generalize the usage of OV in cancer treatment.

Oncolytic adenovirus coding for bispecific T cell engager against human MUC-1 potentiates T cell response against solid tumors

Immunotherapy with bispecific T cell engagers has shown efficacy in patients with hematologic malignancies and uveal melanoma. Antitumor effects of bispecific T cell engagers in most solid tumors are limited due to their short serum half-life and insufficient tumor concentration. We designed a novel serotype 5/3 oncolytic adenovirus encoding a human mucin1 antibody and the human CD3 receptor, Ad5/3-E2F-d24-aMUC1aCD3 (TILT-321). TILT-321 is engineered to replicate only in cancer cells, leading to a high concentration of the aMUC1aCD3 molecule in the tumor microenvironment. Infection and cell viability assays were performed to determine the oncolytic potential of the novel construct. The functionality of the virus-derived aMUC1aCD3 was evaluated in vitro. When TILT-321 was combined with allogeneic T cells, rapid tumor cell lysis was observed. TILT-321-infected cells secreted functional aMUC1aCD3, as shown by increased T cell activity and its binding to MUC1 and CD3. In vivo, TILT-321 treatment led to effective antitumor efficacy mediated by increased intratumoral T cell activity in an A549 and patient-derived ovarian cancer xenograft mouse model humanized with peripheral blood mononuclear cells (PBMC). This study provides a proof of concept for an effective strategy to overcome the key limitations of recombinant bispecific T cell engager delivery for solid tumor treatment.

Cancer immunotherapies: A hope for the uncurable?

The use of cancer immunotherapies is not novel but has been used over the decades in the clinic. Only recently have we found the true potential of stimulating an anti-tumor response after the breakthrough of checkpoint inhibitors. Cancer immunotherapies have become the first line treatment for many malignancies at various stages. Nevertheless, the clinical results in terms of overall survival and progression free survival were not as anticipated. Majority of cancer patients do not respond to immunotherapies and the reasons differ. Hence, further improvements for cancer immunotherapies are crucially needed. In the review, we will discuss various forms of cancer immunotherapies that are being tested or already in the clinic. Moreover, we also highlight future directions to improve such therapies.

The emerging field of oncolytic virus-based cancer immunotherapy

Oncolytic viruses (OVs) provide novel and promising therapeutic options for patients with cancers resistant to traditional therapies. Natural or genetically modified OVs are multifaceted tumor killers. They directly lyse tumor cells while sparing normal cells, and indirectly potentiate antitumor immunity by releasing antigens and activating inflammatory responses in the tumor microenvironment. However, some limitations, such as limited penetration of OVs into tumors, short persistence, and the host antiviral immune response, are impeding the broad translation of oncolytic virotherapy into the clinic. If these challenges can be overcome, combination therapies, such as OVs plus immune checkpoint blockade (ICB), chimeric antigen receptor (CAR) T cells, or CAR natural killer (NK) cells, may provide powerful therapeutic platforms in the clinic.

Modifying oncolytic virotherapy to overcome the barrier of the hypoxic tumor microenvironment. Where do we stand?

Viruses are completely dependent on host cell machinery for their reproduction. As a result, factors that influence the state of cells, such as signaling pathways and gene expression, could determine the outcome of viral pathogenicity. One of the important factors influencing cells or the outcome of viral infection is the level of oxygen. Recently, oncolytic virotherapy has attracted attention as a promising approach to improving cancer treatment. However, it was shown that tumor cells are mostly less oxygenated compared with their normal counterparts, which might affect the outcome of oncolytic virotherapy. Therefore, knowing how oncolytic viruses could cope with stressful environments, particularly hypoxic environments, might be essential for improving oncolytic virotherapy.

Oncolytic vaccinia virus expressing a bispecific T-cell engager enhances immune responses in EpCAM positive solid tumors

Insufficient intratumoral T-cell infiltration and lack of tumor-specific immune surveillance in tumor microenvironment (TME) hinder the progression of cancer immunotherapy. In this study, we explored a recombinant vaccinia virus encoding an EpCAM BiTE (VV-EpCAM BiTE) to modulate the immune suppressive microenvironment to enhance antitumor immunity in several solid tumors. VV-EpCAM BiTE effectively infected, replicated and lysed malignant cells. The EpCAM BiTE secreted from infected malignants effectively mediated the binding of EpCAM-positive tumor cells and CD3ϵ on T cells, which led to activation of naive T-cell and the release of cytokines, such as IFN-γ and IL-2. Intratumoral administration of VV-EpCAM BiTE significantly enhanced antitumor activity in malignancies with high other than with low EpCAM expression level. In addition, immune cell infiltration was significantly increased in TME upon VV-EpCAM BiTE treatment, CD8+ T cell exhaustion was reduced and T-cell-mediated immune activation was markedly enhanced. Taken together, VV-EpCAM BiTE sophistically combines the antitumor advantages of bispecific antibodies and oncolytic viruses, which provides preclinical evidence for the therapeutic potential of VV-EpCAM BiTE.

Bispecific Antibodies: A Novel Approach for the Treatment of Solid Tumors

Advancement in sequencing technologies allows for the identification of molecular pathways involved in tumor progression and treatment resistance. Implementation of novel agents targeting these pathways, defined as targeted therapy, significantly improves the prognosis of cancer patients. Targeted therapy also includes the use of monoclonal antibodies (mAbs). These drugs recognize specific oncogenic proteins expressed in cancer cells. However, as with many other types of targeting agents, mAb-based therapy usually fails in the long-term control of cancer progression due to the development of resistance. In many cases, resistance is caused by the activation of alternative pathways involved in cancer progression and the development of immune evasion mechanisms. To overcome this off-target resistance, bispecific antibodies (bsAbs) were developed to simultaneously target differential oncogenic pathway components, tumor-associated antigens (TAA) and immune regulatory molecules. As a result, in the last few years, several bsAbs have been tested or are being tested in cancer patients. A few of them are currently approved for the treatment of some hematologic malignancies but no bsAbs are approved in solid tumors. In this review, we will provide an overview of the state-of-the-art of bsAbs for the treatment of solid malignancies outlining their classification, design, main technologies utilized for production, mechanisms of action, updated clinical evidence and potential limitations.

Oncolytic virus driven T-cell-based combination immunotherapy platform for colorectal cancer

Colorectal cancer is the third most diagnosed cancer and the second leading cause of cancer mortality worldwide, highlighting an urgent need for new therapeutic options and combination strategies for patients. The orchestration of potent T cell responses against human cancers is necessary for effective antitumour immunity. However, regression of a limited number of cancers has been induced by immune checkpoint inhibitors, T cell engagers (TCEs) and/or oncolytic viruses. Although one TCE has been FDA-approved for the treatment of hematological malignancies, many challenges exist for the treatment of solid cancers. Here, we show that TCEs targeting CEACAM5 and CD3 stimulate robust activation of CD4 and CD8-positive T cells in in vitro co-culture models with colorectal cancer cells, but in vivo efficacy is hindered by a lack of TCE retention in the tumour microenvironment and short TCE half-life, as demonstrated by HiBiT bioluminescent TCE-tagging technology. To overcome these limitations, we engineered Bispecific Engager Viruses, or BEVirs, a novel tumour-targeted vaccinia virus platform for intra-tumour delivery of these immunomodulatory molecules. We characterized virus-mediated TCE-secretion, TCE specificity and functionality from infected colorectal cancer cells and patient tumour samples, as well as TCE cytotoxicity in spheroid models, in the presence and absence of T cells. Importantly, we show regression of colorectal tumours in both syngeneic and xenograft mouse models. Our data suggest that a different profile of cytokines may contribute to the pro-inflammatory and immune effects driven by T cells in the tumour microenvironment to provide long-lasting immunity and abscopal effects. We establish combination regimens with immune checkpoint inhibitors for aggressive colorectal peritoneal metastases. We also observe a significant reduction in lung metastases of colorectal tumours through intravenous delivery of our oncolytic virus driven T-cell based combination immunotherapy to target colorectal tumours and FAP-positive stromal cells or CTLA4-positive Treg cells in the tumour microenvironment. In summary, we devised a novel combination strategy for the treatment of colorectal cancers using oncolytic vaccinia virus to enhance immune-payload delivery and boost T cell responses within tumours.

Dynamic impact of virome on colitis and colorectal cancer: Immunity, inflammation, prevention and treatment

The gut microbiome includes a series of microorganism genomes, such as bacteriome, virome, mycobiome, etc. The gut microbiota is critically involved in intestine immunity and diseases, including inflammatory bowel disease (IBD) and colorectal cancer (CRC); however, the underlying mechanism remains incompletely understood. Clarifying the relationship between microbiota and inflammation may profoundly improve our understanding of etiology, disease progression, patient management, and the development of prevention and treatment. In this review, we discuss the latest studies of the influence of enteric viruses (i.e., commensal viruses, pathogenic viruses, and bacteriophages) in the initiation, progression, and complication of colitis and colorectal cancer, and their potential for novel preventative approaches and therapeutic application. We explore the interplay between gut viruses and host immune systems for its effects on the severity of inflammatory diseases and cancer, including both direct and indirect interactions between enteric viruses with other microbes and microbial products. Furthermore, the underlying mechanisms of the virome's roles in gut inflammatory response have been explained to infer potential therapeutic targets with examples in specific clinical trials. Given that very limited literature has thus far discussed these various topics with the gut virome, we believe these extensive analyses may provide insight into the understanding of the molecular pathogenesis of IBD and CRC, which could help add the design of improved therapies for these important human diseases.

Improving cancer immunotherapy by rationally combining oncolytic virus with modulators targeting key signaling pathways

Oncolytic viruses (OVs) represent a new class of multi-modal immunotherapies for cancer, with OV-elicited antitumor immunity being key to their overall therapeutic efficacy. Currently, the clinical effectiveness of OV as monotherapy remains limited, and thus investigators have been exploring various combinations with other anti-cancer agents and demonstrated improved therapeutic efficacy. As cancer cells have evolved to alter key signaling pathways for enhanced cell proliferation, cancer progression and metastasis, these cellular and molecular changes offer promising targets for rational cancer therapy design. In this regard, key molecules in relevant signaling pathways for cancer cells or/and immune cells, such as EGFR-KRAS (e.g., KRAS^G12C), PI3K-AKT-mTOR, ERK-MEK, JAK-STAT, p53, PD-1-PD-L1, and epigenetic, or immune pathways (e.g., histone deacetylases, cGAS-STING) are currently under investigation and have the potential to synergize with OV to modulate the immune milieu of the tumor microenvironment (TME), thereby improving and sustaining antitumor immunity. As many small molecule modulators of these signaling pathways have been developed and have shown strong therapeutic potential, here we review key findings related to both OV-mediated immunotherapy and the utility of small molecule modulators of signaling pathways in immuno-oncology. Then, we focus on discussion of the rationales and potential strategies for combining OV with selected modulators targeting key cellular signaling pathways in cancer or/and immune cells to modulate the TME and enhance antitumor immunity and therapeutic efficacy. Finally, we provide perspectives and viewpoints on the application of novel experimental systems and technologies that can propel this exciting branch of medicine into a bright future.

Design Strategies and Precautions for Using Vaccinia Virus in Tumor Virotherapy

Oncolytic virotherapy has emerged as a novel form of cancer immunotherapy. Oncolytic viruses (OVs) can directly infect and lyse the tumor cells, and modulate the beneficial immune microenvironment. Vaccinia virus (VACV) is a promising oncolytic vector because of its high safety, easy gene editing, and tumor intrinsic selectivity. To further improve the safety, tumor-targeting ability, and OV-induced cancer-specific immune activation, various approaches have been used to modify OVs. The recombinant oncolytic VACVs with deleting viral virulence factors and/or arming various therapeutic genes have displayed better therapeutic effects in multiple tumor models. Moreover, the combination of OVs with other cancer immunotherapeutic approaches, such as immune checkpoint inhibitors and CAR-T cells, has the potential to improve the outcome in cancer patients. This will open up new possibilities for the application of OVs in cancer treatment, especially for personalized cancer therapies.

Bispecific Antibody Expressed by an Oncolytic Herpes Simplex Virus Type 2 Can Transform Heterologous T Cells Into Uniform Tumor Killer Cells

BsAb (bispecific antibody)-armed oncolytic viruses (OVs) are effective in regulating tumor microenvironment. However, oHSV2 (oncolytic herpes simplex virus type 2) expressing immune checkpoints targeting BsAb molecules are not reported. Here, we generated oHSV2-armed PD-L1/CD3 BsAb and established pharmacodynamic evaluation models, which suggested that our oHSV2-BsAb molecules have an improved oncolytic potency in vitro and in vivo. The oHSV2 viruses armed with BsAb molecules targeting programmed cell death ligand 1 (PD-L1)/CD3 or CD19/CD3 (oHSV2-PD-L1/CD3-BsAb or oHSV2-CD19/mCD3-BsAb) were constructed; besides inducing oncolysis in virus-infected tumor cells, the modified oncolytic virus oHSV2-PD-L1/CD3-BsAb can also activate peripheral blood mononuclear cells (PBMCs) by releasing PD-L1/CD3 BsAb and thereby induce PBMC-mediated killing of PD-L1-positive tumor cells, regardless of PD-L1 expression level. The expressed PD-L1/CD3 BsAb can upregulate the activation markers of T cells in PBMCs and induce different cytokine secretion. The activation of T cells and the enrichment of related immune regulatory pathways are further confirmed by proteomics. It also demonstrated that the OVs or PBMCs could upregulate PD-L1 expression on the surface of tumor cells through transforming "cold tumors" with low PD-L1 expression into "hot tumors" with high PD-L1 expression, which can facilitate the targeting of BsAb molecules and enhance the effect of oncolysis. oHSV2-PD-L1/CD3-BsAb or oHSV2-CD19/mCD3-BsAb showed an enhanced oncolytic effect in vitro and in vivo compared to backbone virus oHSV2-GFP. Our results showed that the newly designed oHSV2-BsAb had enhanced therapeutic effects against solid tumors and provided a new option of immunotherapy.

Remodeling the tumor microenvironment by oncolytic viruses: beyond oncolysis of tumor cells for cancer treatment

Tumor cells manipulate the local environment in which they grow, creating a tumor microenvironment (TME) that promotes tumor survival and metastasis. The TME is an extremely complex environment rich in immunosuppressive cells and cytokines. Various methods to therapeutically target the complicated TME are emerging as a potential approach for cancer treatment. Oncolytic viruses (OVs) are one of the most promising methods for remodeling the TME into an antitumor environment and can be used alone or in combination with other immunotherapy options. OVs replicate specifically in tumor cells and can be genetically engineered to target multiple elements of the TME simultaneously, thus representing a therapeutic with the potential to modify the TME to promote activation of antitumor immune cells and overcome tumor therapeutic resistance and recurrence. In this review, we analyze the tropism of OVs towards tumor cells and explore the interaction between OVs and immune cells, tumor stroma, vasculature and the metabolic environment in detail to help understand how OVs may be one of our most promising prospects for long-term curative therapies. We also discuss some of the challenges associated with TME therapies, and future perspectives in this evolving field.

Biological causes of immunogenic cancer cell death (ICD) and anti-tumor therapy; Combination of Oncolytic virus-based immunotherapy and CAR T-cell therapy for ICD induction

Chimeric antigen receptor (CAR) T-cell therapy is a promising and rapidly expanding therapeutic option for a wide range of human malignancies. Despite the ongoing progress of CAR T-cell therapy in hematologic malignancies, the application of this therapeutic strategy in solid tumors has encountered several challenges due to antigen heterogeneity, suboptimal CAR T-cell trafficking, and the immunosuppressive features of the tumor microenvironment (TME). Oncolytic virotherapy is a novel cancer therapy that employs competent or genetically modified oncolytic viruses (OVs) to preferentially proliferate in tumor cells. OVs in combination with CAR T-cells are promising candidates for overcoming the current drawbacks of CAR T-cell application in tumors through triggering immunogenic cell death (ICD) in cancer cells. ICD is a type of cellular death in which danger-associated molecular patterns (DAMPs) and tumor-specific antigens are released, leading to the stimulation of potent anti-cancer immunity. In the present review, we discuss the biological causes of ICD, different types of ICD, and the synergistic combination of OVs and CAR T-cells to reach potent tumor-specific immunity.

CD19-targeted BiTE expression by an oncolytic vaccinia virus significantly augments therapeutic efficacy against B-cell lymphoma

Immunotherapy with CD19-targeting bispecific T-cell engagers (CD19BiTEs) has demonstrated highly effective killing of cancer cells in patients with precursor acute lymphoblastic leukemia and non-Hodgkin's lymphomas. However, there are some drawbacks to this therapy, such as toxicity, short half-life in the serum, and immunosuppressive tumor microenvironment that could limit the use of CD19BiTEs in the clinic. Here, we generate an oncolytic vaccinia virus (OVV) encoding a CD19-specific BiTE (OVV-CD19BiTE). We demonstrate that OVV-CD19BiTE's ability to replicate and induce oncolysis was similar to that of its parental counterpart. Supernatants from OVV-CD19BiTE-infected cells could induce activation and proliferation of human T cells, and the bystander effect of the virus was also demonstrated. In vivo study showed that OVV-CD19BiTE selectively replicated within tumor tissue, and contributed to a more significantly increased percentage of CD3, CD8, and naïve CD8 T subpopulations within tumors in contrast to blinatumomab. More importantly, treatment with OVV-CD19BiTE both in vitro and in vivo resulted in potent antitumor activity in comparison with control OVV or blinatumomab, a first-in-class BiTE, thereby resulting in long-term tumor remissions without relapse. The study provides strong evidence for the therapeutic benefits of CD19-targeting BiTE expression by OVV, and suggests the feasibility of testing the approach in clinical trials.

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.

Poxvirus-driven human diseases and emerging therapeutics

Poxviridae have been successful pathogens throughout recorded history, infecting humans among a variety of other hosts. Although eradication of the notorious smallpox has been a globally successful healthcare phenomenon, the recent emergence of Monkeypox virus, also belonging to the Orthopoxvirus genus and causing human disease, albeit milder than smallpox, is a cause of significant public health concern. The ongoing outbreak of monkeypox, demonstrating human-human transmission, in previously nonendemic countries, calls for critical need into further research in the areas of viral biology, ecology, and epidemiology to better understand, prevent and treat human infections. In the wake of these recent events, it becomes important to revisit poxviral infections, their pathogenesis and ability to cause infection across multiple nonhuman hosts and leap to a human host. The poxviruses that cause human diseases include Monkeypox virus, Molluscum contagiosum virus, and Orf virus. In this review, we summarize the current understanding of various poxviruses causing human diseases, provide insights into their replication and pathogenicity, disease progression and symptoms, preventive and treatment options, and their importance in shaping modern medicine through application in gene therapy, oncolytic viral therapies for human cancers, or as poxvirus vectors for vaccines.

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

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

Recombinant adenovirus expressing the fusion protein PD1PVR improves CD8+ T cell-mediated antitumor efficacy with long-term tumor-specific immune surveillance in hepatocellular carcinoma

PURPOSE

Treatment-associated upregulation of suppressive checkpoints and a lack of costimulatory signals compromise the antitumor efficacy of oncolytic virus immunotherapy. Therefore, we aimed to identify highly effective therapeutic targets to provide a proof-of-principle for immune checkpoint together with oncolytic virus-mediated viro-immunotherapy for cancer.

METHODS

A fusion protein containing both the extracellular domain of programmed death-1 (PD-1) and the poliovirus receptor (PVR) was designed. Next, the corresponding expression fragment was inserted into the genome of a replication-competent adenovirus to generate Ad5sPD1PVR. The infection, expression, replication and oncolysis of Ad5sPD1PVR were investigated in hepatocellular carcinoma (HCC) cell lines. Immune activation and the antitumor efficacy of Ad5sPD1PVR were examined in HCC tumor models including a humanized immunocompetent mouse model.

RESULTS

Ad5sPD1PVR effectively infected and replicated in HCC cells and secreted sPD1PVR. In a H22 ascitic HCC mouse model, intraperitoneal injection of Ad5sPD1PVR markedly recruited lymphocytes and activated antitumor immune responses. Ad5sPD1PVR exerted a profound antitumor effect on ascitic HCC. Furthermore, we found that Ad5sPD1PVR-H expressing sPD1PVR of human origin exhibited potent antitumor effects in a HCC humanized mouse model. We also found that CD8+ T cells mediated the antitumor effects and long-term tumor-specific immune surveillance induced by Ad5sPD1PVR. Finally, when combined with fludarabine, the antitumor efficacy of Ad5sPD1PVR was found to be further improved in the ascitic HCC model.

CONCLUSIONS

From our data we conclude that the newly designed recombinant Ad5sPD1PVR virus significantly enhances CD8+ T cell-mediated antitumor efficacy with long-term tumor-specific immune surveillance in hepatocellular carcinoma, and that fludarabine is a promising therapeutic partner for Ad5sPD1PVR.

Viro-antibody therapy: engineering oncolytic viruses for genetic delivery of diverse antibody-based biotherapeutics

Cancer therapeutics approved for clinical application include oncolytic viruses and antibodies, which evolved by nature, but were improved by molecular engineering. Both facilitate outstanding tumor selectivity and pleiotropic activities, but also face challenges, such as tumor heterogeneity and limited tumor penetration. An innovative strategy to address these challenges combines both agents in a single, multitasking therapeutic, i.e., an oncolytic virus engineered to express therapeutic antibodies. Such viro-antibody therapies genetically deliver antibodies to tumors from amplified virus genomes, thereby complementing viral oncolysis with antibody-defined therapeutic action. Here, we review the strategies of viro-antibody therapy that have been pursued exploiting diverse virus platforms, antibody formats, and antibody-mediated modes of action. We provide a comprehensive overview of reported antibody-encoding oncolytic viruses and highlight the achievements of 13 years of viro-antibody research. It has been shown that functional therapeutic antibodies of different formats can be expressed in and released from cancer cells infected with different oncolytic viruses. Virus-encoded antibodies have implemented direct tumor cell killing, anti-angiogenesis, or activation of adaptive immune responses to kill tumor cells, tumor stroma cells or inhibitory immune cells. Importantly, numerous reports have shown therapeutic activity complementary to viral oncolysis for these modalities. Also, challenges for future research have been revealed. Established engineering technologies for both oncolytic viruses and antibodies will enable researchers to address these challenges, facilitating the development of effective viro-antibody therapeutics.