Targeting an Oncolytic Influenza A Virus to Tumor Tissue by Elastase

Progression of oncolytic virus in liver cancer treatment

The liver plays a crucrial role in detoxification, metabolism, and nutrient storage. Because liver cancer ranks among the top three leading causes of death globally, there is an urgent need for developing treatment strategies for liver cancer. Although traditional approaches such as radiation, chemotherapy, surgical removal, and transplantation are widely practiced, the number of patients with liver cancer continues to increase rapidly each year. Some novel therapeutics for liver cancer have been studied for many years. In the past decade, oncolytic therapy has emerged, in which viruses selectively infect and destroy cancer cells while sparing normal cells. However, oncolytic virotherapy for liver cancer remains relatively obscure due to the aggressive nature of the disease and the limited effectiveness of treatment. To keep pace with the latest developments in oncolytic tumor therapy for liver cancer, this review summarizes basic science studies and clinical trials conducted within 5 years, focusing on the efficacy and safety profiles of the five most commonly used oncolytic viruses: herpes simplex virus, adenovirus, influenza virus, vaccinia virus, and coxsackievirus.

Tutorial: design, production and testing of oncolytic viruses for cancer immunotherapy

Oncolytic viruses (OVs) represent a novel class of cancer immunotherapy agents that preferentially infect and kill cancer cells and promote protective antitumor immunity. Furthermore, OVs can be used in combination with established or upcoming immunotherapeutic agents, especially immune checkpoint inhibitors, to efficiently target a wide range of malignancies. The development of OV-based therapy involves three major steps before clinical evaluation: design, production and preclinical testing. OVs can be designed as natural or engineered strains and subsequently selected for their ability to kill a broad spectrum of cancer cells rather than normal, healthy cells. OV selection is further influenced by multiple factors, such as the availability of a specific viral platform, cancer cell permissivity, the need for genetic engineering to render the virus non-pathogenic and/or more effective and logistical considerations around the use of OVs within the laboratory or clinical setting. Selected OVs are then produced and tested for their anticancer potential by using syngeneic, xenograft or humanized preclinical models wherein immunocompromised and immunocompetent setups are used to elucidate their direct oncolytic ability as well as indirect immunotherapeutic potential in vivo. Finally, OVs demonstrating the desired anticancer potential progress toward translation in patients with cancer. This tutorial provides guidelines for the design, production and preclinical testing of OVs, emphasizing considerations specific to OV technology that determine their clinical utility as cancer immunotherapy agents.

Combination Immunotherapy of Oncolytic Flu-Vectored Virus and Programmed Cell Death 1 Blockade Enhances Antitumor Activity in Hepatocellular Carcinoma

Oncolytic viruses (OVs) are appealing anti-tumor agents. But it is limited in its effectiveness. In this study, we used combination therapy with immune checkpoint inhibitor to enhance the antitumor efficacy of OVs. Using reverse genetics technology, we rescued an oncolytic influenza virus with the name delNS1-GM-CSF from the virus. After identifying the hemagglutination and 50% tissue culture infectivedose (TCID50) of delNS1-GM-CSF, it was purified, and the viral morphology was observed under electron microscopy. Reverse transcription quantitative-polymerase chain reaction (RT-qPCR) was used to identify the level of GM-CSF expression in delNS1-GM-CSF, and the GM-CSF expression level was determined after infection with delNS1-GM-CSF by enzyme linked immunosorbent assay (ELISA). To study the tumor-killing effect of delNS1-GM-CSF, we utilized the hepatocellular carcinoma (HCC) tumor-bearing mouse model. To examine signaling pathways, we performed transcriptome sequencing on mouse tumor tissue and applied western blotting to confirm the results. Changes in T-cell infiltration in HCC tumors following treatment were analyzed using flow cytometry and immunohistochemistry. DelNS1-GM-CSF can target and kill HCCs without damaging normal hepatocytes. DelNS1-GM-CSF combined with programmed cell death 1 blockade therapy enhanced anti-tumor effects and significantly improved mouse survival. Further, we found that combination therapy had an antitumor impact via the janus kinase-signal transducer and activator of transcription (JAK2-STAT3) pathway as well as activated CD4+ and CD8+T cells. Interestingly, combined therapy also showed promising efficacy in distant tumors. DelNS1-GM-CSF is well targeted. Mechanistic investigation revealed that it functions through the JAK2-STAT3 pathway. Combination immunotherapies expected to be a novel strategy for HCC immunotherapy.

Replication-competent influenza virus with a protein-responsive multiplication ability

Applications of influenza A viruses (IAV) for virotherapy and biotechnology have accelerated substantially with the development of reverse genetic technology and advances in the understanding of packaging signals. While the use of a replication-competent IAV is particularly promising, owing to its efficient transmission to organ depths with high infectivity, there is also a risk that its multiplication cannot be controlled in a cell-type-specific manner, causing an infectious disease. Therefore, here a simple and effective replication-competent IAV-based cell-targeting system has been developed. It was demonstrated that the activity of the ribonucleoprotein complex (RNP) of IAV could be regulated by the interaction between the endogenous protein and a nanobody fused to the subunit of RNA-dependent RNA polymerase (RdRp). To validate the feasibility of the method, it was demonstrated that RNP containing RdRp fused with Nb139, a nanobody against p53, is inactive in HEK293T cells expressing endogenous p53, but active in p53-defective Saos-2 cells. Finally, a replication-competent IAV was successfully generated that multiplies only in p53-defective tumor cells and an IAV vector was developed that can deliver a foreign gene in cell type-specific manner. The method is flexible because the nanobody can be easily altered to target a different cell type, offering a valuable platform for virotherapy and biotechnology.

Immune responses elicited by ssRNA(-) oncolytic viruses in the host and in the tumor microenvironment

Oncolytic viruses (OVs) are at the forefront of biologicals for cancer treatment. They represent a diverse landscape of naturally occurring viral strains and genetically modified viruses that, either as single agents or as part of combination therapies, are being evaluated in preclinical and clinical settings. As the field gains momentum, the research on OVs has been shifting efforts to expand our understanding of the complex interplay between the virus, the tumor and the immune system, with the aim of rationally designing more efficient therapeutic interventions. Nowadays, the potential of an OV platform is no longer defined exclusively by the targeted replication and cancer cell killing capacities of the virus, but by its contribution as an immunostimulator, triggering the transformation of the immunosuppressive tumor microenvironment (TME) into a place where innate and adaptive immunity players can efficiently engage and lead the development of tumor-specific long-term memory responses. Here we review the immune mechanisms and host responses induced by ssRNA(-) (negative-sense single-stranded RNA) viruses as OV platforms. We focus on two ssRNA(-) OV candidates: Newcastle disease virus (NDV), an avian paramyxovirus with one of the longest histories of utilization as an OV, and influenza A (IAV) virus, a well-characterized human pathogen with extraordinary immunostimulatory capacities that is steadily advancing as an OV candidate through the development of recombinant IAV attenuated platforms.

Oncolytic Activity of a Chimeric Influenza A Virus Carrying a Human CTLA4 Antibody in Hepatocellular Carcinoma

Oncolytic virotherapy belongs to a kind of active immunotherapy, which could trigger a potent antitumor immune response, showing great potential in clinical application. OVs could induce immune responses through the dual mechanisms of selective tumor killing without destroying normal tissues and induction of systemic antitumor immunity. In this study, we successfully rescued a chimeric oncolytic influenza virus carrying a human CTLA4 antibody in the background of the A/PR/8/34 (PR8) virus. The chimeric virus, called rFlu-huCTLA4, contained the heavy and light chains of the human CTLA4 antibody in the PB1 and PA segments of the PR8 virus, respectively. The first-generation hemagglutination (HA) titers of the rFlu-huCTLA4 virus ranged from 2⁷ to 2⁸, which could be passaged stably in specific pathogen-free (SPF) chicken embryos from P1 to P5. The morphology and size distribution of the chimeric virus were consistent with those of the wt influenza virus. The rFlu-huCTLA4 virus could effectively replicate in various cells in time- and dose-dependent manners. ELISA assay revealed that the secreted huCTLA4 antibody levels in chicken embryos increased gradually over time. Furthermore, MTS and crystal violet analysis showed that the selective cytotoxicity of the virus was higher in hepatocellular carcinoma cells (HepG2 and Huh7) than in normal liver cells (MIHA). In vivo experiments displayed that intratumoral injection with rFlu-huCTLA4 reduced tumor growth and increased the survival of mice compared with the PR8 group. More importantly, in the rFlu-huCTLA4 group, we found that CD4+ and CD8 +T cells were significantly increased in tumor-bearing BALB/c mice. Taken together, these findings demonstrated that the chimeric oncolytic virus rFlu-huCTLA4 could selectively destroy hepatocellular carcinoma cells in vitro and in vivo and may provide a promising clinical strategy for targeted immunotherapy of HCC with the oncolytic flu virus.

A recombinant influenza virus with a CTLA4-specific scFv inhibits tumor growth in a mouse model

Oncolytic viruses (OV) have shown excellent safety and efficacy in preclinical and clinical studies. Influenza A virus (IAV) is considered a promising oncolytic virus. In this report, we generated a recombinant influenza virus expressing an immune checkpoint blockade agent targeting CTLA4. Using reverse genetics, a recombinant influenza virus, termed rFlu-CTLA4, encoding the heavy chain of a CTLA4 antibody on the PB1 segment and the light chain of the CTLA4 antibody on the PA segment was produced. RFlu-CTLA4 could replicate to high titers, and antibodies were produced in the allantoic fluid of infected eggs. Furthermore, the selective cytotoxicity of the virus was higher in various hepatocellular carcinoma cancer cell lines than in the normal cell line L02 in vitro, as indicated by MTS assays. More importantly, in a subcutaneous H22 mouse hepatocarcinoma model, intratumoral injections of rFlu-CTLA4 inhibited the growth of treated tumors and increased the overall survival of mice compared with injections of the PR8 virus. Taken together, these results warrant further exploration of this novel recombinant influenza virus for its potential use as a single or combination agent for cancer immunotherapy.

Development and application of reverse genetic technology for the influenza virus

Influenza virus is a common virus in people's daily lives, and it has certain infectivity in humans and animals. Influenza viruses have the characteristics of a high mutation rate and wide distribution. Reverse genetic technology is primarily used to modify viruses at the DNA level through targeted modification of the virus cDNA. Genetically modified influenza viruses have a unique advantage when researching the transmission and pathogenicity of influenza. With the continuous development of oncolytic viruses in recent years, studies have found that influenza viruses also have certain oncolytic activity. Influenza viruses can specifically recognize tumor cells; activate cytotoxic T cells, NK cells, dendritic cells, etc.; and stimulate the body to produce an immune response, thereby killing tumor cells. This article will review the development and application of influenza virus reverse genetic technology.

From threat to cure: understanding of virus-induced cell death leads to highly immunogenic oncolytic influenza viruses

Oncolytic viruses constitute an emerging strategy in immunomodulatory cancer treatment. The first oncolytic virus, Talimogene laherparepvec (T-VEC), based on herpes simplex virus 1 (HSV-1), was approved by the Food and Drug Administration (FDA) and European Medicines Agency (EMA) in 2015. The field of oncolytic virotherapy is still in its beginnings, since many promising viruses remain only superficially explored. Influenza A virus causes a highly immunogenic acute infection but never leads to a chronic disease. While oncolytic influenza A viruses are in preclinical development, they have not made the transition into clinical practice yet. Recent insights into different types of cell death caused by influenza A virus infection illuminate novel possibilities of enhancing its therapeutic effect. Genetic engineering and experience in influenza A virus vaccine development allow safe application of the virus in patients. In this review we give a summary of efforts undertaken to develop oncolytic influenza A viruses. We discuss strategies for targeting viral replication to cancerous lesions and arming them with immunogenic transgenes. We furthermore describe which modes of cell death are induced by influenza A virus infection and how these insights may be utilized to optimize influenza A virus-based oncolytic virus design.

Recent advances in oncolytic virus-based cancer therapy

Administration of oncolytic viruses (OVs) is an emerging anticancer strategy that exploits the lytic nature of viral replication to enhance the killing of malignant cells. OVs can be used as tools to directly induce cancer cell death and to trigger local and/or systemic immune responses to metastatic cancer in vivo. The effectiveness of OV therapy was initially highlighted by the clinical use of the genetically modified herpes virus, talimogene laherparepvec, for melanoma therapy. A number of OVs are now being evaluated as potential treatments for cancer in clinical trials. In spite of being engineered to specifically target tumor cells, the safety and off-target effects of OV therapy are a concern. The potential safety concerns of OVs are highlighted by current clinical trial criteria, which exclude individuals harbouring other viral infections and people who are immunocompromised. Despite the potential for adverse effects, clinical trials to date revealed relatively minimal adverse immune-related effects, such as fever. With advances in our understanding of virus replication cycles, several novel OVs have emerged. Reverse genetic systems have facilitated the insertion of anticancer genes into a range of OVs to further enhance their tumor-killing capacity. In this review, we highlight the recent advances in OV therapy for a range of human cancers in in vitro and in in vivo animal studies. We further discuss the future of OVs as a therapeutic strategy for a range of life-threatening cancers.

Oncolytic Activity of a Novel Influenza A Virus Carrying Granulocyte-Macrophage Colony-Stimulating Factor in Hepatocellular Carcinoma

Oncolytic virotherapy is a promising strategy for the treatment of cancer. Influenza A virus has shown potential as an oncolytic agent. In this study, a recombinant PR8 influenza viral vector, called delNS1-GM-CSF, was generated with a partial deletion in NS and the granulocyte-macrophage colony-stimulating factor (GM-CSF) coding sequence inserted into the influenza nonstructural protein 1 gene. The morphological characteristics of delNS1-GM-CSF were examined. The delNS1-GM-CSF virus replicated well in various cell lines, including MDCK, A549, SMCC7721, and HepG2 cells. Moreover, selective cytotoxicity of the virus was observed in various hepatocellular carcinoma (HCC) cell lines, while no effect was demonstrated in the normal liver cell line LO2, as indicated by 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide and crystal violet assays. Importantly, using a model based on the growth of HepG2 cells as a xenograft in nude mice, it was found that a reassortant delNS1-GM-CSF virus inhibited tumor growth significantly following intratumoral injection in a dose-dependent manner. Ex vivo results showed that the tumor inhibition efficacy of delNS1-GM-CSF was observed in HCC clinical samples. Taken together, these results are the first to demonstrate that influenza A viruses may have potential as oncolytic virotherapeutic agents against HCC.

Trial Watch: Oncolytic viro-immunotherapy of hematologic and solid tumors

Oncolytic viruses selectively target and kill cancer cells in an immunogenic fashion, thus supporting the establishment of therapeutically relevant tumor-specific immune responses. In 2015, the US Food and Drug Administration (FDA) approved the oncolytic herpes simplex virus T-VEC for use in advanced melanoma patients. Since then, a plethora of trials has been initiated to assess the safety and efficacy of multiple oncolytic viruses in patients affected with various malignancies. Here, we summarize recent preclinical and clinical progress in the field of oncolytic virotherapy.