Current strategies in engaging oncolytic viruses with antitumor immunity

Development of attenuated Orf virus as a safe oncolytic viral vector for nasopharyngeal carcinoma treatment

BACKGROUND

Orf virus (ORFV) is gaining attention as a promising viral vector for cancer therapy because of its unique properties. Recent studies have shown that ORFV could be effective against various cancers, particularly nasopharyngeal carcinoma. This research explores the ability of wild-type ORFV and recombinant ORFVs, which lack specific virulence factors, to kill NPC cells and modulate the immune response.

METHODS

Two NPC cell lines, HK1 (from Hong Kong) and TW02 (from Taiwan), were infected with wild-type ORFV and two recombinant ORFVs lacking either vascular endothelial growth factor (VEGF) or chemokine binding protein (CBP) virulence factors. The oncolytic effects were evaluated by assessing cell death pathways, particularly pyroptosis, which was monitored through the cleavage of gasdermin E (GSDME). The activation of survival pathways, such as focal adhesion kinase (FAK) and AKT, was also analyzed. In addition, the influence of ORFV infection on natural killer (NK) cell recruitment and cytotoxicity was investigated. In vivo experiments were conducted in a xenograft mouse model in which HK1 tumors were used to evaluate the antitumor activity of wild-type ORFV and two deletion-mutant ORFVs.

RESULTS

Wild-type ORFV effectively killed NPC cells, especially HK1 cells. The recombinant ORFVs, despite being attenuated by the loss of VEGF or CBP, retained the ability to infect and cause NPC cell death, with the CBP-deleted virus showing notable effectiveness in HK1 cells. Early ORFV infection led to pyroptosis via GSDME cleavage, causing cell detachment and a reduction in FAK and AKT activation. ORFV also enhanced NK cell recruitment and boosted NK cell-mediated cytotoxicity in infected NPC cells. In the HK1 xenograft model, CBP-deleted ORFV significantly inhibited tumor growth.

CONCLUSION

ORFV, particularly the wild-type and CBP-deleted variants, has significant potential as an oncolytic viral vector for NPC therapy. It induces cell death via pyroptosis and enhances immune-mediated tumor cell destruction through NK cells. The attenuated CBP-deleted ORFV offers a safer and effective option for cancer treatment, making it a promising candidate for future therapeutic applications.

Oncolytic virus encoding 4-1BBL and IL15 enhances the efficacy of tumor-infiltrating lymphocyte adoptive therapy in HCC

Previous studies have found that oncolytic virus (OVs) can improve the efficacy of TIL adoptive therapy in oral cancer, colon cancer, and pancreatic cancer. However, the curative effect in hepatocellular carcinoma (HCC) is still unclear. Therefore, this study aims to explore the therapeutic effect and mechanism of OVs encoding 4-1BBL and IL15 (OV-4-1BBL/IL15) combined with TIL adoptive therapy on HCC. In this study, the role and immunological mechanism of armed OVs combined with TILs were evaluated by flow cytometry and ELISA in patient-derived xenograft and syngeneic mouse tumor models. Co-culturing with TILs can up-regulate the expression of antigen-presenting cell (APC) markers on the surface of OV-infected primary HCC cells, and promote the specific activation ability and tumor-killing ability of TILs. OV-4-1BBL/IL15 combined with TIL adoptive therapy could induce tumor volume reduction and anti-tumor immune memory in patient-derived xenograft and syngeneic mouse tumor models. Furthermore, OV combined with TIL adoptive therapy can endow tumor cells with aAPC characteristics, activate T cells at the same time, and reprogram tumor macrophages into anti-tumor phenotype. OV-4-1BBL/IL15 can stimulate the anti-tumor potential of TIL therapy in HCC, and possess broad clinical application prospects.

4-1BBL-Armed Oncolytic Herpes Simplex Virus Exerts Antitumor Effects in Pancreatic Ductal Adenocarcinoma

Background: Pancreatic ductal adenocarcinoma (PDAC) is a highly malignant tumor with a notably poor response to therapy due to its immunosuppressive tumor microenvironment (TME) and intrinsic drug resistance. The oncolytic virus (OV) represents a promising therapeutic strategy capable of transforming the "cold" immunological profile of PDAC tumors to a "hot" one by reshaping the TME. 4-1BB (CD137), a crucial member of the tumor necrosis factor receptor superfamily, plays a significant role in T-cell activation and function. Methods: In this study, we constructed an oncolytic herpes simplex virus armed with 4-1BBL (oHSV-4-1BBL), the ligand for the 4-1BB receptor, and investigated its therapeutic effects in two mouse models of pancreatic cancer, Pan02_HVEM and KPC. Results: We found that oHSV-4-1BBL remarkably inhibited tumor growth and extended the median survival time in both models. To amplify the therapeutic effect, we further combined oHSV-4-1BBL with PD-1 antibody. This combination therapy not only further suppressed tumor growth but also extended the median survival time by an additional 11 days compared to oHSV (armed with GFP as a control) combined with PD-1 antibody treatment, with some mice achieving complete tumor regression. Conclusions: Our findings confirm the potential of combining oncolytic viral therapy with 4-1BB targeting in enhancing the treatment of pancreatic cancer.

Utilizing Adenovirus Knob Proteins as Carriers in Cancer Gene Therapy Amidst the Presence of Anti-Knob Antibodies

Numerous gene therapy drugs for cancer have received global approval, yet their efficacy against solid tumors remains inadequate. Our previous research indicated that the fiber protein, a component of the adenovirus capsid, can propagate from infected cells to neighboring cells that express the adenovirus receptor. We hypothesize that merging this fiber protein with an anti-cancer protein could enable the anti-cancer protein to disseminate around the transfected cells, presenting a novel approach to cancer gene therapy. In our study, we discovered that the knob region of the adenovirus type 5 fiber protein is the smallest unit capable of spreading to adjacent cells in a receptor-specific manner. We also showed that the recombinant knob protein infiltrates cells after dispersing to surrounding cells. To assess the potential of the knob protein to augment gene therapy for solid tumors in mice, we expressed a fusion gene of the A subunit of cytotoxic cholera toxin and the knob region in mouse tumors. We found that this fusion protein only inhibited tumor growth in receptor-expressing mouse melanomas, and this inhibitory effect persisted even in mice with anti-knob antibodies. Our study's findings propose a novel cancer gene therapy strategy that enhances therapeutic effects by specifically delivering therapeutic proteins, expressed from in vivo administered genes, to target molecules. This outcome offers a fresh perspective on gene therapy for solid cancers, and we anticipate that knob proteins will serve as a platform for this method.

Human umbilical cord mesenchymal stem cell exosomes deliver potent oncolytic reovirus to acute myeloid leukemia cells

In addition to chemotherapy, oncolytic viruses are an efficient treatment for acute myeloid leukemia (AML). Like other oncolytic viruses, the anti-tumor efficacy of reovirus when administered intravenously is reduced due to the presence of neutralizing antibodies. In this study, we evaluated the role of exosomes in human umbilical cord-derived mesenchymal stem cells (UC-MSCs) to deliver reovirus to AML cells. We show that UC-MSCs loaded with reovirus can deliver reovirus to tumor cells without cellular contact. We further demonstrate that the exosome inhibitor, GW4869, inhibits the release of exosomes as well as inhibited the transfer of reovirus from UC-MSCs to tumor cells. Mechanistically, we show that exosomes derived from reovirus-infected UC-MSCs (MSCREO-EXOs) have a tumor lysis effect and transmit reovirus to tumor cells mainly through clathrin-mediated endocytosis (CME) and macropinocytosis. In addition, we demonstrate the feasibility of using MSC-derived exosomes (MSC-EXOs) as a reovirus carrier to exert an anti-tumor effect on AML cells. Collectively, our data indicate that UC-MSCs transfer reovirus to AML cells via exosome release and prompt further study of MSC-EXOs as a potential reovirus carrier to treat AML.

Integrating system biology and intratumor gene therapy by trans-complementing the appropriate co-stimulatory molecule as payload in oncolytic herpes virus

Systems biology has been applied at the multi-scale level within the cancer field, improving cancer prevention, diagnosis and enabling precision medicine approaches. While systems biology can expand the knowledge and skills for oncological treatment, it also represents a challenging expedition due to cancer complexity, heterogeneity and diversity not only between different cancer indications, but also in its evolution process through space and time. Here, by characterizing the transcriptional perturbations of the tumor microenvironment induced by oncolytic, we aimed to rationally design a novel armed oncolytic herpes virus. We found that intratumor oncovirotherapy with HSV-1 induces T-cell activation signatures and transcriptionally activates several costimulatory molecules. We identified differentially expressed costimulatory receptors and binding partners, where inducible co-stimulators (ICOS) resulted in the potentially most beneficial targeted therapy. Through an ex-vivo transcriptomic analysis, we explored the potential of arming an oncolytic virus as a combination therapy strategy; in particular, we engineered a targeted herpes virus encoding ICOSL (THV_ICOSL), which resulted in a significant improvement in tumor size control compared to unarmed parental virus. Also, combination with a PD-1 inhibitor enhanced antitumor efficacy as predictable by upregulation of PD-1 and ligands pair (PD-L1/PD-L2) upon oncolytic virus injection. Generation of the human version of this virus encoding hICOSL orthologue effectively and specifically activated human T cells by triggering the ICOS pathway. Our data support the data-driven generation of armed oncolytic viruses as combination immunotherapeutic with checkpoint inhibitors.

Comparison of the oncolytic activity of a replication-competent and a replication-deficient herpes simplex virus 1

In 2015, the oncolytic herpes simplex virus 1 (HSV-1) T-VEC (talimogene laherparepvec) was approved for intratumoral injection in non-resectable malignant melanoma. To determine whether viral replication is required for oncolytic activity, we compared replication-deficient HSV-1 d106S with replication-competent T-VEC. High infectious doses of HSV-1 d106S killed melanoma (n = 10), head-and-neck squamous cell carcinoma (n = 11), and chondrosarcoma cell lines (n = 2) significantly faster than T-VEC as measured by MTT metabolic activity, while low doses of T-VEC were more effective over time. HSV-1 d106S and, to a lesser extent T-VEC, triggered caspase-dependent early apoptosis as shown by pan-caspase inhibition and specific induction of caspases 3/7, 8, and 9. HSV-1 d106S induced a higher ratio of apoptosis-inducing infected cell protein (ICP) 0 to apoptosis-blocking ICP6 than T-VEC. T-VEC was oncolytic for an extended period of time as viral replication continued, which could be partially blocked by the antiviral drug aciclovir. High doses of T-VEC, but not HSV-1 d106S, increased interferon-β mRNA as part of the intrinsic immune response. When markers of immunogenic cell death were assessed, ATP was released more efficiently in the context of T-VEC than HSV-1 d106S infection, whereas HMGB1 was induced comparatively well. Overall, the early oncolytic effect on three different tumour entities was stronger with the non-replicative strain, while the replication-competent virus elicited a stronger innate immune response and more pronounced immunogenic cell death.

Zika Virus: A Neurotropic Warrior against High-Grade Gliomas-Unveiling Its Potential for Oncolytic Virotherapy

Gliomas account for approximately 75-80% of all malignant primary tumors in the central nervous system (CNS), with glioblastoma multiforme (GBM) considered the deadliest. Despite aggressive treatment involving a combination of chemotherapy, radiotherapy, and surgical intervention, patients with GBM have limited survival rates of 2 to 5 years, accompanied by a significant decline in their quality of life. In recent years, novel management strategies have emerged, such as immunotherapy, which includes the development of vaccines or T cells with chimeric antigen receptors, and oncolytic virotherapy (OVT), wherein wild type (WT) or genetically modified viruses are utilized to selectively lyse tumor cells. In vitro and in vivo studies have shown that the Zika virus (ZIKV) can infect glioma cells and induce a robust oncolytic activity. Consequently, interest in exploring this virus as a potential oncolytic virus (OV) for high-grade gliomas has surged. Given that ZIKV actively circulates in Colombia, evaluating its neurotropic and oncolytic capabilities holds considerable national and international importance, as it may emerge as an alternative for treating highly complex gliomas. Therefore, this literature review outlines the generalities of GBM, the factors determining ZIKV's specific tropism for nervous tissue, and its oncolytic capacity. Additionally, we briefly present the progress in preclinical studies supporting the use of ZIKV as an OVT for gliomas.

A promising future in cancer immunotherapy: Oncolytic viruses

Alongside the conventional methods, attention has been drawn to the use of immunotherapy-based methods for cancer treatment. Immunotherapy has developed as a therapeutic option that can be more specific with better outcomes in tumor treatment. It can boost or regulate the immune system behind the targeted virotherapy. Virotherapy is a kind of oncolytic immunotherapy that investigated broadly in cancer treatment in recent decades, due to its several advantages. According to recent advance in the field of understanding cancer cell biology and its occurrence, as well as increasing the knowledge about conditionally replicating oncolytic viruses and their destructive function in the tumor cells, nowadays, it is possible to apply this strategy in the treatment of malignancies. Relying on achievements in clinical trials of oncolytic viruses, we can certainly expect that this therapeutic perception can play a more central role in cancer treatment. In cancer treatment, combination therapy using oncolytic viruses alongside standard cancer treatment methods and other immunotherapy-based treatments can expect more promising results in the future.

Harnessing the power of oncolytic virotherapy and tertiary lymphoid structures to amplify antitumor immune responses in cancer patients

Tertiary lymphoid structures (TLS) are ectopic aggregates of immune cells that develop in non-lymphoid tissues under persistent inflammation. Since their presence has been associated with a better prognosis in cancer patients, modulating TLS formation is being part of new challenges in immunotherapy. Although mechanisms underlying TLS genesis are still not fully understood, different strategies have been developed in preclinical models to induce their formation and ultimately enhance antitumor responses. Herein, we will discuss a new approach that would consist in using oncolytic viruses (OV). These viruses have the unique feature to preferentially infect, replicate in and kill cancer cells. Their immunoadjuvant property, their use as a vector of therapeutic molecules and their selectivity for cancer cells, make them an attractive strategy to induce TLS in the tumor microenvironment. This review will examine the current knowledge about TLS neogenesis, approaches for inducing them, and relevance of using OV for this purpose, especially in combination with immunotherapy such as immune checkpoint blockade.

Safety and dose escalation of the targeted oncolytic adenovirus OBP-301 for refractory advanced liver cancer: Phase I clinical trial

OBP-301 is an oncolytic adenovirus modified to replicate within cancer cells and lyse them. This open-label, non-comparative, phase I dose-escalation trial aimed to assess its safety and optimal dosage in 20 patients with advanced hepatocellular carcinoma. Good tolerance was shown with a maximum tolerated dose of 6 × 1012 viral particles. The most common treatment-emergent adverse events were influenza-like illness, pyrexia, fatigue, decreased platelet count, abdominal distension, and anemia. Cohorts 4 and 5 had approximately 50% higher levels of CD8+ T cells in the peripheral blood after injection. The best target response occurred in 14 patients, 4 of whom had progressive disease. Multiple intratumoral injections of OBP-301 were well tolerated in patients with advanced hepatocellular carcinoma. The stable disease rate for the injected tumors was greater than the overall response rate, even with no obvious tumor response. OBP-301 might have a greater impact on local response as histological examination revealed that the presence of OBP-301 was consistent with the necrotic area at the injection site. Increased infiltration of CD8+ T cells and <1% PD-L1 expression were observed in tumors after injection. Improved antitumor efficacy might be achieved in future studies via viral injection with volume adjustment and in combination with other immuno-therapeutics.

Nuclear Export Inhibitor Selinexor Enhances Oncolytic Myxoma Virus Therapy against Cancer

Oncolytic viruses exploited for cancer therapy have been developed to selectively infect, replicate, and kill cancer cells to inhibit tumor growth. However, in some cancer cells, oncolytic viruses are often limited in completing their full replication cycle, forming progeny virions, and/or spreading in the tumor bed because of the heterogeneous cell types within the tumor bed. Here, we report that the nuclear export pathway regulates oncolytic myxoma virus (MYXV) infection and cytoplasmic viral replication in a subclass of human cancer cell types where viral replication is restricted. Inhibition of the XPO-1 (exportin 1) nuclear export pathway with nuclear export inhibitors can overcome this restriction by trapping restriction factors in the nucleus and allow significantly enhanced viral replication and killing of cancer cells. Furthermore, knockdown of XPO-1 significantly enhanced MYXV replication in restrictive human cancer cells and reduced the formation of antiviral granules associated with RNA helicase DHX9. Both in vitro and in vivo, we demonstrated that the approved XPO1 inhibitor drug selinexor enhances the replication of MYXV and kills diverse human cancer cells. In a xenograft tumor model in NSG mice, combination therapy with selinexor plus MYXV significantly reduced the tumor burden and enhanced the survival of animals. In addition, we performed global-scale proteomic analysis of nuclear and cytosolic proteins in human cancer cells to identify the host and viral proteins that were upregulated or downregulated by different treatments. These results indicate, for the first time, that selinexor in combination with oncolytic MYXV can be used as a potential new therapy.

Significance

We demonstrated that a combination of nuclear export inhibitor selinexor and oncolytic MYXV significantly enhanced viral replication, reduced cancer cell proliferation, reduced tumor burden, and enhanced the overall survival of animals. Thus, selinexor and oncolytic MYXV can be used as potential new anticancer therapy.

Oncolytic Rodent Protoparvoviruses Evade a TLR- and RLR-Independent Antiviral Response in Transformed Cells

The oncolytic rodent protoparvoviruses (PVs) minute virus of mice (MVMp) and H-1 parvovirus (H-1PV) are promising cancer viro-immunotherapy candidates capable of both exhibiting direct oncolytic activities and inducing anticancer immune responses (AIRs). Type-I interferon (IFN) production is instrumental for the activation of an efficient AIR. The present study aims at characterizing the molecular mechanisms underlying PV modulation of IFN induction in host cells. MVMp and H-1PV triggered IFN production in semi-permissive normal mouse embryonic fibroblasts (MEFs) and human peripheral blood mononuclear cells (PBMCs), but not in permissive transformed/tumor cells. IFN production triggered by MVMp in primary MEFs required PV replication and was independent of the pattern recognition receptors (PRRs) Toll-like (TLR) and RIG-like (RLR) receptors. PV infection of (semi-)permissive cells, whether transformed or not, led to nuclear translocation of the transcription factors NFĸB and IRF3, hallmarks of PRR signaling activation. Further evidence showed that PV replication in (semi-)permissive cells resulted in nuclear accumulation of dsRNAs capable of activating mitochondrial antiviral signaling (MAVS)-dependent cytosolic RLR signaling upon transfection into naïve cells. This PRR signaling was aborted in PV-infected neoplastic cells, in which no IFN production was detected. Furthermore, MEF immortalization was sufficient to strongly reduce PV-induced IFN production. Pre-infection of transformed/tumor but not of normal cells with MVMp or H-1PV prevented IFN production by classical RLR ligands. Altogether, our data indicate that natural rodent PVs regulate the antiviral innate immune machinery in infected host cells through a complex mechanism. In particular, while rodent PV replication in (semi-)permissive cells engages a TLR-/RLR-independent PRR pathway, in transformed/tumor cells this process is arrested prior to IFN production. This virus-triggered evasion mechanism involves a viral factor(s), which exert(s) an inhibitory action on IFN production, particularly in transformed/tumor cells. These findings pave the way for the development of second-generation PVs that are defective in this evasion mechanism and therefore endowed with increased immunostimulatory potential through their ability to induce IFN production in infected tumor cells.

Oncolytic virus-based hepatocellular carcinoma treatment: Current status, intravenous delivery strategies, and emerging combination therapeutic solutions

Current treatments for advanced hepatocellular carcinoma (HCC) have limited success in improving patients' quality of life and prolonging life expectancy. The clinical need for more efficient and safe therapies has contributed to the exploration of emerging strategies. Recently, there has been increased interest in oncolytic viruses (OVs) as a therapeutic modality for HCC. OVs undergo selective replication in cancerous tissues and kill tumor cells. Strikingly, pexastimogene devacirepvec (Pexa-Vec) was granted an orphan drug status in HCC by the U.S. Food and Drug Administration (FDA) in 2013. Meanwhile, dozens of OVs are being tested in HCC-directed clinical and preclinical trials. In this review, the pathogenesis and current therapies of HCC are outlined. Next, we summarize multiple OVs as single therapeutic agents for the treatment of HCC, which have demonstrated certain efficacy and low toxicity. Emerging carrier cell-, bioengineered cell mimetic- or nonbiological vehicle-mediated OV intravenous delivery systems in HCC therapy are described. In addition, we highlight the combination treatments between oncolytic virotherapy and other modalities. Finally, the clinical challenges and prospects of OV-based biotherapy are discussed, with the aim of continuing to develop a fascinating approach in HCC patients.

Effects of pre-existing anti-adenovirus antibodies on transgene expression levels and therapeutic efficacies of arming oncolytic adenovirus

Oncolytic adenoviruses (OAds), most of which are based on species C human adenovirus serotype 5 (Ad5) (OAd5), have recently received much attention as potential anticancer agents. High seroprevalence of anti-Ad5 neutralizing antibodies is a major hurdle for Ad5-based gene therapy. However, the impacts of anti-Ad5 neutralizing antibodies on OAd5-mediated transgene expression in the tumor and antitumor effects remain to be fully elucidated. In this study, we examined the impact of anti-Ad5 neutralizing antibodies on the OAd5-mediated antitumor effects and OAd5-mediated transgene expression. The luciferase expression of OAd-tAIB-Luc, which contains the cytomegalovirus promoter-driven luciferase gene, was inhibited in human cultured cells in the presence of human serum. Although the inhibitory effects of human serum possessing the low anti-Ad5 neutralizing antibody titers were overcome by long-term infection, the in vitro tumor cell lysis activities of OAd-tAIB-Luc were entirely attenuated by human serum containing the high titers of anti-Ad5 neutralizing antibodies. OAd-tAIB-Luc-mediated luciferase expression in the subcutaneous tumors 3 days after administration and tumor growth suppression levels following intratumoral administration were significantly lower in mice possessing the high titers of anti-Ad5 neutralizing antibodies, compared to those in control mice. These results suggested that pre-existing anti-Ad5 antibodies attenuated both transgene expression and potential antitumor effects of OAd5 following intratumoral administration.

An armed oncolytic virus enhances the efficacy of tumor-infiltrating lymphocyte therapy by converting tumors to artificial antigen-presenting cells in situ

The full potential of tumor-infiltrating lymphocyte (TIL) therapy has been hampered by the inadequate activation and low persistence of TILs, as well as inefficient neoantigen presentation by tumors. We transformed tumor cells into artificial antigen-presenting cells (aAPCs) by infecting them with a herpes simplex virus 1 (HSV-1)-based oncolytic virus encoding OX40L and IL12 (OV-OX40L/IL12) to provide local signals for optimum T cell activation. The infected tumor cells displayed increased expression of antigen-presenting cell-related markers and induced enhanced T cell activation and killing in coculture with TILs. Combining OV-OX40L/IL12 and TIL therapy induced complete tumor regression in patient-derived xenograft and syngeneic mouse tumor models and elicited an antitumor immunological memory. In addition, the combination therapy produced aAPC properties in tumor cells, activated T cells, and reprogrammed macrophages to a more M1-like phenotype in the tumor microenvironment. This combination strategy unleashes the full potential of TIL therapy and warrants further evaluation in clinical studies.

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

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

Evolving role of seneca valley virus and its biomarker TEM8/ANTXR1 in cancer therapeutics

Oncolytic viruses have made a significant inroad in cancer drug development. Numerous clinical trials are currently investigating oncolytic viruses both as single agents or in combination with various immunomodulators. Oncolytic viruses (OV) are an integral pillar of immuno-oncology and hold potential for not only delivering durable anti-tumor responses but also converting “cold” tumors to “hot” tumors. In this review we will discuss one such promising oncolytic virus called Seneca Valley Virus (SVV-001) and its therapeutic implications. SVV development has seen seismic evolution over the past decade and now boasts of being the only OV with a practically applicable biomarker for viral tropism. We discuss relevant preclinical and clinical data involving SVV and how bio-selecting for TEM8/ANTXR1, a negative tumor prognosticator can lead to first of its kind biomarker driven oncolytic viral cancer therapy.

Immunotherapy by mesenchymal stromal cell delivery of oncolytic viruses for treating metastatic tumors

Oncolytic viruses (OVs) have emerged as a very promising anti-cancer therapeutic strategy in the past decades. However, despite their pre-clinical promise, many OV clinical evaluations for cancer therapy have highlighted the continued need for their improved delivery and targeting. Mesenchymal stromal cells (MSCs) have emerged as excellent candidate vehicles for the delivery of OVs due to their tumor-homing properties and low immunogenicity. MSCs can enhance OV delivery by protecting viruses from rapid clearance following administration and also by more efficiently targeting tumor sites, consequently augmenting the therapeutic potential of OVs. MSCs can function as “biological factories,” enabling OV amplification within these cells to promote tumor lysis following MSC-OV arrival at the tumor site. MSC-OVs can promote enhanced safety profiles and therapeutic effects relative to OVs alone. In this review we explore the general characteristics of MSCs as delivery tools for cancer therapeutic agents. Furthermore, we discuss the potential of OVs as immune therapeutics and highlight some of the promising applications stemming from combining MSCs to achieve enhanced delivery and anti-tumor effectiveness of OVs at different pre-clinical and clinical stages. We further provide potential pitfalls of the MSC-OV platform and the strategies under development for enhancing the efficacy of these emerging therapeutics.

Killers on the loose: Immunotherapeutic strategies to improve NK cell-based therapy for cancer treatment

Natural killer (NK) cells are innate lymphocytes that control tumor progression by not only directly killing cancer cells, but also by regulating other immune cells, helping to orchestrate a coordinated anti-tumor response. However, despite the tremendous potential that this cell type has, the clinical results obtained from diverse NK cell-based immunotherapeutic strategies have been, until recent years, rather modest. The intrinsic regulatory mechanisms that are involved in the control of their activation as well as the multiple mechanisms that tumor cells have developed to escape NK cell-mediated cytotoxicity likely account for the unsatisfactory clinical outcomes. The current approaches to improve long-term NK cell function are centered on modulating different molecules involved in both the activation and inhibition of NK cells, and the latest data seems to advocate for combining strategies that target multiple aspects of NK cell regulation. In this review, we summarize the different strategies (such as engineered NK cells, CAR-NK, NK cell immune engagers) that are currently being used to take advantage of this potent and complex immune cell.

Prostate Microbiota and Prostate Cancer: A New Trend in Treatment

Although the incidence and mortality of prostate cancer have gradually begun to decline in the past few years, it is still one of the leading causes of death from malignant tumors in the world. The occurrence and development of prostate cancer are affected by race, family history, microenvironment, and other factors. In recent decades, more and more studies have confirmed that prostate microflora in the tumor microenvironment may play an important role in the occurrence, development, and prognosis of prostate cancer. Microorganisms or their metabolites may affect the occurrence and metastasis of cancer cells or regulate anti-cancer immune surveillance. In addition, the use of tumor microenvironment bacteria in interventional targeting therapy of tumors also shows a unique advantage. In this review, we introduce the pathway of microbiota into prostate cancer, focusing on the mechanism of microorganisms in tumorigenesis and development, as well as the prospect and significance of microorganisms as tumor biomarkers and tumor prevention and treatment.

Oncolytic reovirus-mediated killing of mouse cancer-associated fibroblasts

Oncolytic viruses, which mediate tumor cell-specific infection, resulting in efficient tumor cell killing, have attracted much attention as a novel class of anti-cancer biopharmaceutical agents. Cancer-associated fibroblasts (CAFs) are an important component of the tumor microenvironment that strongly supports the growth, survival, and metastasis of tumor cells, suggesting that CAFs would have influence to the antitumor effects of oncolytic viruses; however, it remains to be fully evaluated whether oncolytic viruses affect the viabilities and properties of CAFs following treatment. Oncolytic reovirus, which is a non-enveloped virus that contains 10-segmented double-stranded RNA genome, shows efficient tumor cell lysis without apparent cytotoxicity to normal cells and has been tested worldwide in clinical trials against various types of tumors. In this study, we demonstrated that reovirus exhibited cytotoxicity against mouse primary CAFs isolated from subcutaneous tumors, but not against tail-tip fibroblasts. Infection with reovirus resulted in activation of caspase 3 and up-regulation of apoptosis-related gene expression, indicating that reovirus induced apoptosis of mouse primary CAFs. Intratumoral administration of reovirus induced apoptosis of mouse CAFs in the tumor. Taken together, these results indicate that reovirus has the potential to mediate antitumor effects by killing not only cancer cells but also CAFs.

Oncolytic Viruses: Newest Frontier for Cancer Immunotherapy

Cancer remains a leading cause of death worldwide. Despite many signs of progress, currently available cancer treatments often do not provide desired outcomes for too many cancers. Therefore, newer and more effective therapeutic approaches are needed. Oncolytic viruses (OVs) have emerged as a novel cancer treatment modality, which selectively targets and kills cancer cells while sparing normal ones. In the past several decades, many different OV candidates have been developed and tested in both laboratory settings as well as in cancer patient clinical trials. Many approaches have been taken to overcome the limitations of OVs, including engineering OVs to selectively activate anti-tumor immune responses. However, newer approaches like the combination of OVs with current immunotherapies to convert "immune-cold" tumors to "immune-hot" will almost certainly improve the potency of OVs. Here, we discuss strategies that are explored to further improve oncolytic virotherapy.