Induction of Durable Antitumor Response by a Novel Oncolytic Herpesvirus Expressing Multiple Immunomodulatory Transgenes

Oncolytic virotherapy stimulates anti‑tumor immune response and demonstrates activity in advanced sarcoma: Report of two cases

Sarcoma is derived from mesenchymal neoplasms and has numerous subtypes, accounting for 1% of all adult malignancies and 15% of childhood malignancies. The prognosis of metastatic or recurrent sarcoma remains poor. The current study presents two cases of sarcoma enrolled in a phase I dose escalation trial for solid tumor, who had previously failed all standard therapies. These patients were treated with VG161, an immune-stimulating herpes simplex virus type 1 oncolytic virus with payloads of IL-12, IL-15 and IL-15 receptor α unit, and a programmed cell death 1 (PD-1)/PD-1 ligand 1 blocking peptide. Both cases demonstrated stable disease as the best response, accompanied by a noteworthy prolongation of progression-free survival (11.8 months for chondrosarcoma and 11.9 months for soft tissue sarcoma, respectively) at a dose of 2.5×108 PFU/cycle. In addition, the treatment led to the activation of anti-cancer immunity, as evident from cytokine, lymphocyte subset and related pathway analyses of peripheral blood and/or tumor biopsy samples. These promising results suggest that VG161 monotherapy holds promise as an effective treatment for sarcoma and warrants further investigation through clinical trials. The two reported patients were part of a phase I clinical trial conducted and registered on the Australian New Zealand Clinical Trials Registry in Australia (registration no. ACTRN12620000244909; registration date, 26 February, 2020).

Improved antitumor effects elicited by an oncolytic HSV-1 expressing a novel B7H3nb/CD3 BsAb

Oncolytic viruses have emerged as a promising modality for cancer treatment due to their unique abilities to directly destroy tumor cells and modulate the tumor microenvironment. Bispecific T-cell engagers (BsAbs) have been developed to activate and redirect cytotoxic T lymphocytes, enhancing the antitumor response. To take advantage of the specific infection capacity and carrying ability of exogenous genes, we generated a recombinant herpes simplex virus type 1 (HSV-1), HSV-1dko-B7H3nb/CD3 or HSV-1dko-B7H3nb/mCD3, carrying a B7H3nb/CD3 or B7H3nb/mCD3 BsAb that replicates and expresses BsAb in tumor cells in vitro and in vivo. The new generation of oncolytic viruses has been genetically modified using CRISPR/Cas9 technology and the cre-loxp system to increase the efficiency of HSV genome editing. Additionally, we used two fully immunocompetent models (GL261 and MC38) to assess the antitumor effect of HSV-1dko-B7H3nb/mCD3. Compared with the HSV-1dko control virus, HSV-1dko-B7H3nb/mCD3 induced enhanced anti-tumor immune responses and T-cell infiltration in both GL261 and MC38 models, resulting in improved treatment efficacy in the latter. Furthermore, flow cytometry analysis of the tumor microenvironment confirmed an increase in NK cells and effector CD8+ T cells, and a decrease in immunosuppressive cells, including FOXP3+ regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), and CD206+ macrophages (M2). Overall, our study identified a novel camel B7H3 nanobody and described the genetic modification of the HSV-1 genome using CRISPR/Cas9 technology and the cre-loxp system. Our findings indicate that expressing B7H3nb/CD3 BsAb could improve the antitumor effects of HSV-1 based oncolytic virus.

New hopes for the breast cancer treatment: perspectives on the oncolytic virus therapy

Oncolytic virus (OV) therapy has emerged as a promising frontier in cancer treatment, especially for solid tumours. While immunotherapies like immune checkpoint inhibitors and CAR-T cells have demonstrated impressive results, their limitations in inducing complete tumour regression have spurred researchers to explore new approaches targeting tumours resistant to current immunotherapies. OVs, both natural and genetically engineered, selectively replicate within cancer cells, inducing their lysis while sparing normal tissues. Recent advancements in clinical research and genetic engineering have enabled the development of targeted viruses that modify the tumour microenvironment, triggering anti-tumour immune responses and exhibiting synergistic effects with other cancer therapies. Several OVs have been studied for breast cancer treatment, including adenovirus, protoparvovirus, vaccinia virus, reovirus, and herpes simplex virus type I (HSV-1). These viruses have been modified or engineered to enhance their tumour-selective replication, reduce toxicity, and improve oncolytic properties.Newer generations of OVs, such as Oncoviron and Delta-24-RGD adenovirus, exhibit heightened replication selectivity and enhanced anticancer effects, particularly in breast cancer models. Clinical trials have explored the efficacy and safety of various OVs in treating different cancers, including melanoma, nasopharyngeal carcinoma, head and neck cancer, and gynecologic malignancies. Notably, Talimogene laherparepvec (T-VEC) and Oncorine have. been approved for advanced melanoma and nasopharyngeal carcinoma, respectively. However, adverse effects have been reported in some cases, including flu-like symptoms and rare instances of severe complications such as fistula formation. Although no OV has been approved specifically for breast cancer treatment, ongoing preclinical clinical trials focus on four groups of viruses. While mild adverse effects like low-grade fever and nausea have been observed, the effectiveness of OV monotherapy in breast cancer remains insufficient. Combination strategies integrating OVs with chemotherapy, radiotherapy, or immunotherapy, show promise in improving therapeutic outcomes. Oncolytic virus therapy holds substantial potential in breast cancer treatment, demonstrating safety in trials. Multi-approach strategies combining OVs with conventional therapies exhibit more promising therapeutic effects than monotherapy, signalling a hopeful future for OV-based breast cancer treatments.

TS-2021, a third-generation oncolytic adenovirus that carried Ki67 promoter, TGF-β2 5'UTR, and IL-15 against experimental glioblastoma

Oncolytic virotherapy is a promising therapeutic approach for glioblastoma (GBM) treatment, although the outcomes are partially satisfactory. Hence, more effective strategies are needed urgently to modify therapeutic viruses to enhance their efficiency and safety in killing tumor cells and improve the survival rate of GBM patients. This study generated a new-generation oncolytic adenovirus Ad5 KT-E1A-IL-15 (TS-2021) and evaluated its antitumor efficacy. Ex vivo analyses revealed Ki67 and TGF-β2 co-localized in GBM cells. In addition, TS-2021 selectively replicated in GBM cells, which was dependent on the expression of Ki67 and TGF-β2. The immunocompetent mice model of GBM demonstrated the in vivo efficacy of TS-2021 by inhibiting tumor growth and improving survival proficiently. Notably, TS-2021 effectively reduced MMP3 expression by inactivating the MKK4/JNK pathway, thereby reducing tumor invasiveness. Altogether, the findings of the present study highlight that TS-2021 can effectively target GBM cells expressing high levels of Ki67 and TGF-β2, exerting potent antitumor effects. Additionally, it can improve efficacy and suppress tumor invasiveness by inhibiting the MKK4/JNK/MMP3 pathway. Thus our study demonstrates the efficiency of the novel TS-2021 in the mouse model and provides a potential therapeutic option for patients with GBM.

Prophylactic Vaccination and Intratumoral Boost with HER2-Expressing Oncolytic Herpes Simplex Virus Induces Robust and Persistent Immune Response against HER2-Positive Tumor Cells

The development of effective cancer vaccines remains a significant challenge due to immune tolerance and limited clinical benefits. Oncolytic herpes simplex virus type 1 (oHSV-1) has shown promise as a cancer therapy, but efficacy is often limited in advanced cancers. In this study, we constructed and characterized a novel oHSV-1 virus (VG22401) expressing the human epidermal growth factor receptor 2 (HER2), a transmembrane glycoprotein overexpressed in many carcinomas. VG22401 exhibited efficient replication and HER2 payload expression in both human and mouse colorectal cancer cells. Mice immunized with VG22401 showed significant binding of serum anti-HER2 antibodies to HER2-expressing tumor cells, inducing antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). Furthermore, mice primed with VG22401 and intratumorally boosted with the same virus showed enhanced antitumor efficacy in a bilateral syngeneic HER2(+) tumor model, compared to HER2-null backbone virus. This effect was accompanied by the induction of anti-HER2 T cell responses. Our findings suggest that peripheral priming with HER2-expressing oHSV-1 followed by an intratumoral boost with the same virus can significantly enhance antitumor immunity and efficacy, presenting a promising strategy for cancer immunotherapy.

Charting a killer course to the solid tumor: strategies to recruit and activate NK cells in the tumor microenvironment

The ability to expand and activate natural Killer (NK) cells ex vivo has dramatically changed the landscape in the development of novel adoptive cell therapies for treating cancer over the last decade. NK cells have become a key player for cancer immunotherapy due to their innate ability to kill malignant cells while not harming healthy cells, allowing their potential use as an "off-the-shelf" product. Furthermore, recent advancements in NK cell genetic engineering methods have enabled the efficient generation of chimeric antigen receptor (CAR)-expressing NK cells that can exert both CAR-dependent and antigen-independent killing. Clinically, CAR-NK cells have shown promising efficacy and safety for treating CD19-expressing hematologic malignancies. While the number of pre-clinical studies using CAR-NK cells continues to expand, it is evident that solid tumors pose a unique challenge to NK cell-based adoptive cell therapies. Major barriers for efficacy include low NK cell trafficking and infiltration into solid tumor sites, low persistence, and immunosuppression by the harsh solid tumor microenvironment (TME). In this review we discuss the barriers posed by the solid tumor that prevent immune cell trafficking and NK cell effector functions. We then discuss promising strategies to enhance NK cell infiltration into solid tumor sites and activation within the TME. This includes NK cell-intrinsic and -extrinsic mechanisms such as NK cell engineering to resist TME-mediated inhibition and use of tumor-targeted agents such as oncolytic viruses expressing chemoattracting and activating payloads. We then discuss opportunities and challenges for using combination therapies to extend NK cell therapies for the treatment of solid tumors.

Neoadjuvant use of oncolytic herpes virus G47Δ prevents local recurrence after insufficient resection in tongue cancer models

A complete resection of tongue cancer is often difficult. We investigate the usefulness of administering G47Δ (teserpaturev), a triple-mutated oncolytic herpes simplex virus type 1, prior to resection. G47Δ exhibits good cytopathic effects and replication capabilities in all head and neck cancer cell lines tested. In an orthotopic SCCVII tongue cancer model of C3H/He mice, an intratumoral inoculation with G47Δ significantly prolongs the survival. Further, mice with orthotopic tongue cancer received neoadjuvant G47Δ (or mock) therapy with or without "hemilateral" resection, the maximum extent avoiding surgical deaths. Neoadjuvant G47Δ and resection led to 10/10 survival (120 days), whereas the survivals for G47Δ alone and resection alone were 6/10 and 5/10, respectively: all control animals died by day 11. Furthermore, 100% survival was achieved with neoadjuvant G47Δ therapy even when the resection area was narrowed to "partial," providing insufficient resection margins, whereas hemilateral resection alone caused death by local recurrence in half of the animals. G47Δ therapy caused increased number of tumor-infiltrating CD8+ and CD4+ cells, increased F4/80+ cells within the residual tongues, and increased expression of immune-related genes in and around the tumor. These results imply that neoadjuvant use of G47Δ is useful for preventing local recurrence after tongue cancer surgery.

Immunostimulatory gene therapy targeting CD40, 4-1BB and IL-2R activates DCs and stimulates antigen-specific T-cell and NK-cell responses in melanoma models

BACKGROUND

The activation of dendritic cells (DCs) is pivotal for generating antigen-specific T-cell responses to eradicate tumor cells. Hence, immunotherapies targeting this interplay are especially intriguing. Moreover, it is of interest to modulate the tumor microenvironment (TME), as this harsh milieu often impairs adaptive immune responses. Oncolytic viral therapy presents an opportunity to overcome the immunosuppression in tumors by destroying tumor cells and thereby releasing antigens and immunostimulatory factors. These effects can be further amplified by the introduction of transgenes expressed by the virus.

METHODS

Lokon oncolytic adenoviruses (LOAd) belong to a platform of chimeric serotype Ad5/35 viruses that have their replication restricted to tumor cells, but the expression of transgenes is permitted in all infected cells. LOAd732 is a novel oncolytic adenovirus that expresses three essential immunostimulatory transgenes: trimerized membrane-bound CD40L, 4-1BBL and IL-2. Transgene expression was determined with flow cytometry and ELISA and the oncolytic function was evaluated with viability assays and xenograft models. The activation profiles of DCs were investigated in co-cultures with tumor cells or in an autologous antigen-specific T cell model by flow cytometry and multiplex proteomic analysis. Statistical differences were analyzed with Kruskal-Wallis test followed by Dunn's multiple comparison test.

RESULTS

All three transgenes were expressed in infected melanoma cells and DCs and transgene expression did not impair the oncolytic activity in tumor cells. DCs were matured post LOAd732 infection and expressed a multitude of co-stimulatory molecules and pro-inflammatory cytokines crucial for T-cell responses. Furthermore, these DCs were capable of expanding and stimulating antigen-specific T cells in addition to natural killer (NK) cells. Strikingly, the addition of immunosuppressive cytokines TGF-β1 and IL-10 did not affect the ability of LOAd732-matured DCs to expand antigen-specific T cells and these cells retained an enhanced activation profile.

CONCLUSIONS

LOAd732 is a novel immunostimulatory gene therapy based on an oncolytic adenovirus that expresses three transgenes, which are essential for mediating an anti-tumor immune response by activating DCs and stimulating T and NK cells even under imunosuppressive conditions commonly present in the TME. These qualities make LOAd732 an appealing new immunotherapy approach.

Development and application of oncolytic viruses as the nemesis of tumor cells

Viruses and tumors are two pathologies that negatively impact human health, but what occurs when a virus encounters a tumor? A global consensus among cancer patients suggests that surgical resection, chemotherapy, radiotherapy, and other methods are the primary means to combat cancer. However, with the innovation and development of biomedical technology, tumor biotherapy (immunotherapy, molecular targeted therapy, gene therapy, oncolytic virus therapy, etc.) has emerged as an alternative treatment for malignant tumors. Oncolytic viruses possess numerous anti-tumor properties, such as directly lysing tumor cells, activating anti-tumor immune responses, and improving the tumor microenvironment. Compared to traditional immunotherapy, oncolytic virus therapy offers advantages including high killing efficiency, precise targeting, and minimal side effects. Although oncolytic virus (OV) therapy was introduced as a novel approach to tumor treatment in the 19th century, its efficacy was suboptimal, limiting its widespread application. However, since the U.S. Food and Drug Administration (FDA) approved the first OV therapy drug, T-VEC, in 2015, interest in OV has grown significantly. In recent years, oncolytic virus therapy has shown increasingly promising application prospects and has become a major research focus in the field of cancer treatment. This article reviews the development, classification, and research progress of oncolytic viruses, as well as their mechanisms of action, therapeutic methods, and routes of administration.

Combination of novel oncolytic herpesvirus with paclitaxel as an efficient strategy for breast cancer therapy

BACKGROUND

New strategies are needed to improve the treatment of patients with breast cancer (BC). Oncolytic virotherapy is a promising new tool for cancer treatment but still has a limited overall durable antitumor response. A novel replicable recombinant oncolytic herpes simplex virus type 1 called VG161 has been developed and has demonstrated antitumor effects in several cancers. Here, we explored the efficacy and the antitumor immune response of VG161 cotreatment with paclitaxel (PTX) which as a novel oncolytic viral immunotherapy for BC.

METHODS

The antitumor effect of VG161 and PTX was confirmed in a BC xenograft mouse model. The immunostimulatory pathways were tested by RNA-seq and the remodeling of tumor microenvironment was detected by Flow cytometry analysis or Immunohistochemistry. Pulmonary lesions were analyzed by the EMT6-Luc BC model.

RESULTS

In this report, we demonstrate that VG161 can significantly represses BC growth and elicit a robust antitumor immune response in a mouse model. The effect is amplified when combined with PTX treatment. The antitumor effect is associated with the infiltration of lymphoid cells, including CD4⁺ T cells, CD8⁺ T cells, and NK cells (expressing TNF and IFN-γ), and myeloid cells, including macrophages, myeloid-derived suppressor cells, and dendritic cell cells. Additionally, VG161 cotreatment with PTX showed a significant reduction in BC lung metastasis, which may result from the enhanced CD4⁺ and CD8⁺ T cell-mediated responses.

CONCLUSIONS

The combination of PTX and VG161 is effective for repressing BC growth by inducing proinflammatory changes in the tumor microenvironment and reducing BC pulmonary metastasis. These data will provide a new strategy and valuable insight for oncolytic virus therapy applications in primary solid or metastatic BC tumors.

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.

Targeting carcinoembryonic antigen-expressing tumors using a novel transcriptional and translational dual-regulated oncolytic herpes simplex virus type 1

VG2025 is a recombinant oncolytic herpes simplex virus type 1 (HSV-1) that uses transcriptional and translational dual regulation (TTDR) of critical viral genes to enhance virus safety and promote tumor-specific virus replication without reducing virulence. The TTDR platform is based on transcriptional control of the essential HSV-1 immediate-early protein ICP27 using a tumor-specific carcinoembryonic antigen (CEA) promoter, coupled with translational control of the neurovirulence factor ICP34.5 using multiple microRNA (miR)-binding sites. VG2025 further incorporates IL-12 and the IL-15/IL-15 receptor alpha subunit complex to enhance the antitumor and immune stimulatory properties of oncolytic HSVs. The TTDR strategy was verified in vitro and shown to be highly selective. Strong in vivo antitumor efficacy was observed following both intratumoral and intravenous administration. Clear abscopal and immune memory effects were also evident, indicating a robust antitumor immune response. Gene expression profiling of treated tumors revealed increased immune cell infiltration and activation of multiple immune-signaling pathways when compared with the backbone virus. Absence of neurotoxicity was verified in mice and in rhesus monkeys. Taken together, the enhanced tumor clearance, excellent safety profile, and positive correlation between CEA levels and viral replication efficiency may provide an opportunity for using biomarker-based precision medicine in oncolytic virotherapy.

Development and Preliminary Application of a Droplet Digital PCR Assay for Quantifying the Oncolytic Herpes Simplex Virus Type 1 in the Clinical-Grade Production

Oncolytic herpes simplex virus (oHSV) is a type of virus that selectively targets and kills cancer cells, leaving normal cells unharmed. Accurate viral titer is of great importance for the production and application of oHSV products. Droplet digital PCR (ddPCR) is known for having good reproducibility, not requiring a standard curve, not being affected by inhibitors, and being precise even in the detection of low copies. In the present study, we developed a droplet digital PCR assay for the quantification of HSV-1 and applied it in the oHSV production. The established ddPCR showed good specificity, linearity, a low limit of quantification, great reproducibility, and accuracy. The quantification result was well-associated with that of plaque assay and CCID50. Amplification of the purified virus without DNA extraction by ddPCR presented similar results to that from the extracted DNA, confirming the good resistance against PCR inhibitors. With the ddPCR, viral titer could be monitored in real time during the production of oHSV; the optimal harvest time was determined for the best virus yield in each batch. The ddPCR can be used as a useful tool for the quantification of oHSV and greatly facilitate the manufacturing process of oHSV products.

VG161 activates systemic antitumor immunity in pancreatic cancer models as a novel oncolytic herpesvirus expressing multiple immunomodulatory transgenes

The VG161 represents the first recombinant oncolytic herpes simplex virus type 1 carrying multiple synergistic antitumor immuno-modulating factors. Here, we report its antitumor mechanisms and thus provide firm theoretical foundation for the upcoming clinical application in pancreatic cancer. Generally, the VG161-mediated antitumor outcomes were analyzed by a collaboration of techniques, namely the single-cell sequencing, airflow-assisted desorption electrospray ionization-mass spectrometry imaging (AFADSI-MSI) and nanostring techniques. In vitro, the efficacy of VG161 together with immune checkpoint inhibitors (ICIs) has been successfully shown to grant a long-term antitumor effect by altering tumor immunity and remodeling tumor microenvironment (TME) metabolisms. Cellular functional pathways and cell subtypes detected from patient samples before and after the treatment had undergone distinctive changes including upregulated CD8+ T and natural killer cells. More importantly, significant antitumor signals have emerged since the administration of VG161 injection. In conclusion, VG161 can systematically activate acquired and innate immunity in pancreatic models, as well as improve the tumor immune microenvironment, indicative of strong antitumor potential. The more robusting antitumor outcome for VG161 monotherapy or in combination with other therapies on pancreatic cancer is worth of being explored in further clinical trials.

Anti-cancer Virotherapy in Russia: Lessons from the Past, Current Challenges and Prospects for the Future

The idea of using the lytic power of viruses against malignant cells has been entertained for many decades. However, oncolytic viruses gained broad attention as an emerging anti-cancer therapy only recently with the successful implementation of several oncolytic viruses to treat advanced melanoma. Here we review the history of oncolytic viruses in the Russian Federation and recent biotechnological advances in connection with the perspectives of their practical use against aggressive tumors such as glioblastoma or pancreatic cancer. A particular emphasis is made on novel applications of safe non-lytic virus-derived vectors armed with prodrug-converting enzyme transgenes. Rational improvement of oncotropism by conjugation with biopolymers and nanoformulations is also discussed.

HSV: The scout and assault for digestive system tumors

More than 25% of all malignant tumors are digestive system tumors (DSTs), which mostly include esophageal cancer, gastric cancer, pancreatic cancer, liver cancer, gallbladder cancer and cholangiocarcinoma, and colorectal cancer. DSTs have emerged as one of the prominent reasons of morbidity and death in many nations and areas around the world, posing a serious threat to human life and health. General treatments such as radiotherapy, chemotherapy, and surgical resection can poorly cure the patients and have a bad prognosis. A type of immunotherapy known as oncolytic virus therapy, have recently shown extraordinary anti-tumor effectiveness. One of the viruses that has been the subject of the greatest research in this field, the herpes simplex virus (HSV), has shown excellent potential in DSTs. With a discussion of HSV-1 based on recent studies, we outline the therapeutic effects of HSV on a number of DSTs in this review. Additionally, the critical function of HSV in the detection of cancers is discussed, and some HSV future possibilities are shown.

Current landscape and perspective of oncolytic viruses and their combination therapies

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Oncolytic virotherapy has become an important branch of cancer immunotherapy in clinical practice.

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Multiple viruses can be engineered to be OVs and armed with anticancer genes to enhance their efficacy.

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OVs can reshape TME and produce synergistic anticancer efficacy when combined with other therapies.

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Safety and effectiveness are the main direction of future research and development of OVs.

Oncolytic virotherapy has become an important strategy in cancer immunotherapy. Oncolytic virus (OV) can reshape the tumor microenvironment (TME) through its replication-mediated oncolysis and transgene-produced anticancer effect, inducing an antitumor immune response and creating favorable conditions for the combination of other therapeutic measures. Extensive preclinical and clinical data have suggested that OV-based combination therapy has definite efficacy and promising prospects. Recently, several clinical trials of oncolytic virotherapy combined with immunotherapy have made breakthroughs. This review comprehensively elaborates the OV types and their targeting mechanisms, the selection of anticancer genes armed in OVs, and the therapeutic modes of action and strategies of OVs to provide a theoretical basis for the better design and construction of OVs and the optimization of OV-based therapeutic strategies.

Pre-Existing HSV-1 Immunity Enhances Anticancer Efficacy of a Novel Immune-Stimulating Oncolytic Virus

Oncolytic viruses (OVs) can specifically replicate in the host and cause cancer cell lysis while inducing an antitumor immune response. The aim of this study is to investigate the impact of either pre-existing immunity against herpes simplex virus type-1 (HSV-1) or multicycle treatment with OVs on anticancer efficacy of VG161, an HSV-1 OV in phase 2 clinical trial. VG161 efficacy was tested in CT26 mouse models by comparing the efficacy and immune response in naïve mice or in mice that were immunized with VG161. Moreover, VG161 efficacy in HLA-matched CD34+ humanized intrahepatic cholangiocarcinoma (ICC) patient-derived xenograft (PDX) models was also tested in multicycle treatment and was compared to standard chemotherapy for this type of cancer (gemcitabine). The HSV-1-immunized mice significantly inhibited tumor growth in VG161-treated mice compared to control naïve treated mice. RNA expression profiling and ELISPOT analyses indicated changes in the tumor's immune profile in the immunized and treated group compared to naïve and treated mice, as well as enhanced T cell function depicted by higher numbers of tumor specific lymphocytes, which was enhanced by immunization. In the ICC PDX model, repeated treatment of VG161 with 2 or 3 cycles seemed to increase the anticancer efficacy of VG161. In conclusion, the anticancer efficacy of VG161 can be enhanced by pre-immunization with HSV-1 and multicycle administration when the virus is given intratumorally, indicating that pre-existing antiviral immunity might enhance OV-induced antitumor immunity. Our results suggest potential clinical benefits of HSV-1-based OV therapy in HSV-1-seropositive patients and multicycle administration of VG161 for long-term maintenance treatment.

The In Vitro Replication, Spread, and Oncolytic Potential of Finnish Circulating Strains of Herpes Simplex Virus Type 1

Herpes simplex virus type 1 (HSV-1) is the only FDA- and EMA- approved oncolytic virus, and accordingly, many potential oncolytic HSVs (oHSV) are in clinical development. The utilized oHSV parental strains are, however, mostly based on laboratory reference strains, which may possess a compromised cytolytic capacity in contrast to circulating strains of HSV-1. Here, we assess the phenotype of thirty-six circulating HSV-1 strains from Finland to uncover their potential as oHSV backbones. First, we determined their capacity for cell-to-cell versus extracellular spread, to find strains with replication profiles favorable for each application. Second, to unfold the differences, we studied the genetic diversity of two relevant viral glycoproteins (gB/UL27, gI/US7). Third, we examined the oncolytic potential of the strains in cells representing glioma, lymphoma, and colorectal adenocarcinoma. Our results suggest that the phenotype of a circulating isolate, including the oncolytic potential, is highly related to the host cell type. Nevertheless, we identified isolates with increased oncolytic potential in comparison with the reference viruses across many or all of the studied cancer cell types. Our research emphasizes the need for careful selection of the backbone virus in early vector design, and it highlights the potential of clinical isolates as backbones in oHSV development.

Emerging Therapies for Hepatocellular Carcinoma (HCC)

Hepatocellular carcinoma (HCC) arises from hepatocytes and accounts for 90% of primary liver cancer. According to Global Cancer Incidence, Mortality and Prevalence (GLOBOCAN) 2020, globally HCC is the sixth most common cancer and the third most common cause of cancer-related deaths. Reasons for HCC prognosis remaining dismal are that HCC is asymptomatic in its early stages, leading to late diagnosis, and it is markedly resistant to conventional chemo- and radiotherapy. Liver transplantation is the treatment of choice in early stages, while surgical resection, radiofrequency ablation (RFA) and trans arterial chemoembolization (TACE) are Food and Drug Administration (FDA)-approved treatments for advanced HCC. Additional first line therapy for advanced HCC includes broad-spectrum tyrosine kinase inhibitors (TKIs), such as sorafenib and lenvatinib, as well as a combination of immunotherapy and anti-angiogenesis therapy, namely atezolizumab and bevacizumab. However, these strategies provide nominal extension in the survival curve, cause broad spectrum toxic side effects, and patients eventually develop therapy resistance. Some common mutations in HCC, such as in telomerase reverse transcriptase (TERT), catenin beta 1 (CTNNB1) and tumor protein p53 (TP53) genes, are still considered to be undruggable. In this context, identification of appropriate gene targets and specific gene delivery approaches create the potential of gene- and immune-based therapies for the safe and effective treatment of HCC. This review elaborates on the current status of HCC treatment by focusing on potential gene targets and advanced techniques, such as oncolytic viral vectors, nanoparticles, chimeric antigen receptor (CAR)-T cells, immunotherapy, and clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9), and describes future prospects in HCC treatment.

TNF blockade enhances the efficacy of myxoma virus-based oncolytic virotherapy

BACKGROUND

Oncolytic virotherapy (OV) represents a method to treat a variety of solid tumors by inducing antitumor immune responses. While this therapy has been extremely efficacious in preclinical models, translating these successes into human patients has proven challenging. One of the major reasons for these failures is the existence of immune-regulatory mechanisms, which dampen the efficacy of virally induced antitumor immunity. Unfortunately, the full extent of these immune-regulatory pathways remains unclear.

METHODS

To address this issue, we generated a doubly recombinant, oncolytic myxoma virus which expresses both a soluble fragment of programmed cell death protein 1 (PD1) and an interleukin 12 (IL-12) fusion protein (vPD1/IL-12 (virus-expressing PD1 and IL-12)). We then tested the molecular impact and therapeutic efficacy of this construct in multiple models of disseminated disease to identify novel pathways, which are associated with poor therapeutic outcomes.

RESULTS

Our results demonstrate that vPD1/IL-12 causes robust inflammation during therapy including inducing high levels of tumor necrosis factor (TNF). Surprisingly, although expression of TNF has generally been assumed to be beneficial to OV, the presence of this TNF appears to inhibit therapeutic efficacy by reducing intratumoral T-cell viability. Likely because of this, disruption of the TNF pathway, either through genetic knockout or antibody-based blockade, significantly enhances the overall outcomes of vPD1/IL-12-based therapy that allows for the generation of complete cures in normally non-responsive models.

CONCLUSIONS

These data suggest that some aspects of OV-induced inflammation might represent a double-edged sword during therapy and that specific blockade of TNF might enhance the efficacy of these treatments.

The use of oncolytic virotherapy in the neoadjuvant setting

Surgical removal of tumors remains a front-line therapy for many types of cancer. However, this treatment often fails to eradicate disease due to either recurrence of the original tumor or development of distant micrometastases. To address these challenges, patients are often given non-curative treatments presurgery with the intent of improving surgical outcomes. These treatments, collectively known as neoadjuvant therapies, have traditionally focused on the presurgical use of chemotherapeutics. Recently, however, a variety of immunotherapies have also been identified as potentially effective in the neoadjuvant setting. One of these immunotherapies is oncolytic virotherapy, whose clinical use has exploded with the Food and Drug Administration approval of Talimogene Laherparepvec. This review summarizes both the preclinical and clinical literature examining the use of oncolytic virotherapy in the neoadjuvant setting for different types of cancers and discusses some of the major questions that still need to be addressed in order for this unique use of immunotherapy to become clinically viable.

In Situ Cancer Vaccination and Immunovirotherapy Using Oncolytic HSV

Herpes simplex virus (HSV) can be genetically altered to acquire oncolytic properties so that oncolytic HSV (oHSV) preferentially replicates in and kills cancer cells, while sparing normal cells, and inducing anti-tumor immune responses. Over the last three decades, a better understanding of HSV genes and functions, and improved genetic-engineering techniques led to the development of oHSV as a novel immunovirotherapy. The concept of in situ cancer vaccination (ISCV) was first introduced when oHSV was found to induce a specific systemic anti-tumor immune response with an abscopal effect on non-injected tumors, in the process of directly killing tumor cells. Thus, the use of oHSV for tumor vaccination in situ is antigen-agnostic. The research and development of oHSVs have moved rapidly, with the field of oncolytic viruses invigorated by the FDA/EMA approval of oHSV talimogene laherparepvec in 2015 for the treatment of advanced melanoma. Immunovirotherapy can be enhanced by arming oHSV with immunomodulatory transgenes and/or using them in combination with other chemotherapeutic and immunotherapeutic agents. This review offers an overview of the development of oHSV as an agent for ISCV against solid tumors, describing the multitude of different oHSVs and their efficacy in immunocompetent mouse models and in clinical trials.

Strategies to Optimise Oncolytic Viral Therapies: The Role of Natural Killer Cells

Oncolytic viruses (OVs) are an emerging class of anti-cancer agents that replicate selectively within malignant cells and generate potent immune responses. Their potential efficacy has been shown in clinical trials, with talimogene laherparepvec (T-VEC or IMLYGIC®) now approved both in the United States and Europe. In healthy individuals, NK cells provide effective surveillance against cancer and viral infections. In oncolytic viral therapy, NK cells may render OV ineffective by rapid elimination of the propagating virus but could also improve therapeutic efficacy by preferential killing of OV-infected malignant cells. Existing evidence suggests that the overall effect of NK cells against OV is context dependent. In the past decade, the understanding of cancer and OV biology has improved significantly, which helped refine this class of treatments in early-phase clinical trials. In this review, we summarised different strategies that have been evaluated to modulate NK activities for improving OV therapeutic benefits. Further development of OVs will require a systematic approach to overcome the challenges of the production and delivery of complex gene and cell-based therapies in clinical settings.

Oncolytic HSV: Underpinnings of Tumor Susceptibility

Oncolytic herpes simplex virus (oHSV) is a therapeutic modality that has seen substantial success for the treatment of cancer, though much remains to be improved. Commonly attenuated through the deletion or alteration of the γ₁34.5 neurovirulence gene, the basis for the success of oHSV relies in part on the malignant silencing of cellular pathways critical for limiting these viruses in healthy host tissue. However, only recently have the molecular mechanisms underlying the success of these treatments begun to emerge. Further clarification of these mechanisms can strengthen rational design approaches to develop the next generation of oHSV. Herein, we review our current understanding of the molecular basis for tumor susceptibility to γ₁34.5-attenuated oHSV, with particular focus on the malignant suppression of nucleic acid sensing, along with strategies meant to improve the clinical efficacy of these therapeutic viruses.

Acquired Resistance to Immune Checkpoint Blockades: The Underlying Mechanisms and Potential Strategies

The immune checkpoint blockade therapy has completely transformed cancer treatment modalities because of its unprecedented and durable clinical responses in various cancers. With the increasing use of immune checkpoint blockades in clinical practice, a large number of patients develop acquired resistance. However, the knowledge about acquired resistance to immune checkpoint blockades is limited and poorly summarized. In this review, we clarify the principal elements of acquired resistance to immune checkpoint blockades. The definition of acquired resistance is heterogeneous among groups or societies, but the expert consensus of The Society for Immunotherapy of Cancer can be referred. Oligo-progression is the main pattern of acquired resistance. Acquired resistance can be derived from the selection of resistant cancer cell clones that exist in the tumor mass before therapeutic intervention or gradual acquisition in the sensitive cancer cells. Specifically, tumor intrinsic mechanisms include neoantigen depletion, defects in antigen presentation machinery, aberrations of interferon signaling, tumor-induced exclusion/immunosuppression, and tumor cell plasticity. Tumor extrinsic mechanisms include upregulation of other immune checkpoints. Presently, a set of treatment modalities is applied to patients with similar clinical characteristics or resistance mechanisms for overcoming acquired resistance, and hence, further research is required.