Recombinant vesicular stomatitis virus targeted to Her2/neu combined with anti-CTLA4 antibody eliminates implanted mammary tumors

Vesicular Stomatitis Virus (VSV) G Glycoprotein Can Be Modified to Create a Her2/Neu-Targeted VSV That Eliminates Large Implanted Mammary Tumors

Viral oncolytic immunotherapy is a nascent field that is developing tools to direct the immune system to find and eliminate cancer cells. Safety is improved by using cancer-targeted viruses that infect or grow poorly on normal cells. The recent discovery of the low-density lipoprotein (LDL) receptor as the major vesicular stomatitis virus (VSV) binding site allowed for the creation of a Her2/neu-targeted replicating recombinant VSV (rrVSV-G) by eliminating the LDL receptor binding site in the VSV-G glycoprotein (gp) and adding a sequence coding for a single chain antibody (SCA) to the Her2/neu receptor. The virus was adapted by serial passage on Her2/neu-expressing cancer cells resulting in a virus that yielded a 15- to 25-fold higher titer following in vitro infection of Her2/neu+-expressing cell lines than that of Her2/neu-negative cells (~1 × 108/mL versus 4 × 106 to 8 × 106/mL). An essential mutation resulting in a higher titer virus was a threonine-to-arginine change that produced an N-glycosylation site in the SCA. Infection of Her2/neu+ subcutaneous tumors yielded >10-fold more virus on days 1 and 2 than Her2/neu- tumors, and virus production continued for 5 days in Her2/neu+ tumors compared with 3 days that of 3 days in Her2/neu- tumors. rrVSV-G cured 70% of large 5-day peritoneal tumors compared with a 10% cure by a previously targeted rrVSV with a modified Sindbis gp. rrVSV-G also cured 33% of very large 7-day tumors. rrVSV-G is a new targeted oncolytic virus that has potent antitumor capabilities and allows for heterologous combination with other targeted oncolytic viruses. IMPORTANCE A new form of vesicular stomatitis virus (VSV) was created that specifically targets and destroys cancer cells that express the Her2/neu receptor. This receptor is commonly found in human breast cancer and is associated with a poor prognosis. In laboratory tests using mouse models, the virus was highly effective at eliminating implanted tumors and creating a strong immune response against cancer. VSV has many advantages as a cancer treatment, including high levels of safety and efficacy and the ability to be combined with other oncolytic viruses to enhance treatment results or to create an effective cancer vaccine. This new virus can also be easily modified to target other cancer cell surface molecules and to add immune-modifying genes. Overall, this new VSV is a promising candidate for further development as an immune-based cancer therapy.

Anti-tumor memory CD4 and CD8 T-cells quantified by bulk T-cell receptor (TCR) clonal analysis

Simple, reliable methods to detect anti-tumor memory T-cells are necessary to develop a clinical tumor vaccination program. A mouse model of curative viral onco-immunotherapy found that peritoneal tumor challenge following cure identified an oligoclonal anti-tumor memory CD4 and CD8 T-cell response. Clonotypes differed among the challenged animals but were congruent in blood, spleen and peritoneal cells (PC) of the same animal. Adoptive transfer demonstrated that the high-frequency responding T-cells were tumor specific. Tetramer analysis confirmed that clonotype frequency determined by T-cell receptor (TCR)- chain (TRB) analysis closely approximated cell clone frequency. The mean frequency of resting anti-tumor memory CD4 T-cells in unchallenged spleen was 0.028% and of memory CD8 T-cells was 0.11% which was not high enough to distinguish them from background. Stimulation produced a mean ~10-fold increase in splenic and 100-fold increase in peritoneal anti-tumor memory T-cell clonotypes. This methodology can be developed to use blood and tissue sampling to rapidly quantify the effectiveness of a tumor vaccine or any vaccine generating therapeutic T-cells.

Immunotherapy for HER-2 positive breast cancer

Immunotherapy is a developing treatment for advanced breast cancer. Immunotherapy has clinical significance for the treatment of triple-negative breast cancers and human epidermal growth factor receptor-2 positive (HER2+) breast cancers. As a proved effective passive immunotherapy, clinical application of the monoclonal antibodies trastuzumab, pertuzumab and T-DM1 (ado-trastuzumab emtansine) has significantly improved the survival of patients with HER2+ breast cancers. Immune checkpoint inhibitors that block programmed death receptor-1 and its ligand (PD-1/PD-L1) have also shown benefits for breast cancer in various clinical trials. Adoptive T-cell immunotherapies and tumor vaccines are emerging as novel approaches to treating breast cancer, but require further study. This article reviews recent advances in immunotherapy for HER2+ breast cancers.

Virotherapy, gene transfer and immunostimulatory monoclonal antibodies

Malignant cells are susceptible to viral infection and consequent cell death. Virus-induced cell death is endowed with features that are known to stimulate innate and adaptive immune responses. Thus danger signals emitted by cells succumbing to viral infection as well as viral nucleic acids are detected by specific receptors, and tumor cell antigens can be routed to professional antigen-presenting cells. The anticancer immune response triggered by viral infection is frequently insufficient to eradicate malignancy but may be further amplified. For this purpose, transgenes encoding cytokines as co-stimulatory molecules can be genetically engineered into viral vectors. Alternatively, or in addition, it is possible to use monoclonal antibodies that either block inhibitory receptors of immune effector cells, or act as agonists for co-stimulatory receptors. Combined strategies are based on the ignition of a local immune response at the malignant site plus systemic immune boosting. We have recently reported examples of this approach involving the Vaccinia virus or Semliki Forest virus, interleukin-12 and anti-CD137 monoclonal antibodies.

Lassa-VSV chimeric virus targets and destroys human and mouse ovarian cancer by direct oncolytic action and by initiating an anti-tumor response

Ovarian cancer is the third most common female cancer, with poor survival in later stages of metastatic spread. We test a chimeric virus consisting of genes from Lassa and vesicular stomatitis viruses, LASV-VSV; the native VSV glycoprotein is replaced by the Lassa glycoprotein, greatly reducing neurotropism. Human ovarian cancer cells in immunocompromised nude mice were lethal in controls. Chemotherapeutic paclitaxel and cisplatin showed modest cancer inhibition and survival extension. In contrast, a single intraperitoneal injection of LASV-VSV selectively infected and killed ovarian cancer cells, generating long-term survival. Mice with human ovarian cancer cells in brain showed rapid deterioration; LASV-VSV microinjection into brain blocked cancer growth, and generated long-term survival. Treatment of immunocompetent mice with infected mouse ovarian cancer cells blocked growth of non-infected ovarian cancer cells peritoneally and in brain. These results suggest LASV-VSV is a viable candidate for further study and may be of use in the treatment of ovarian cancer.

Oncolytic Viruses: Priming Time for Cancer Immunotherapy

New immuno-oncology therapies are improving cancer treatments beyond the former standard of care, as evidenced by the recent and continuing clinical approvals for immunotherapies in a broad range of indications. However, a majority of patients (particularly those with immunologically cold tumors) still do not benefit, highlighting the need for rational combination approaches. Oncolytic viruses (OV) both directly kill tumor cells and inflame the tumor microenvironment. While OV spread can be limited by the generation of antiviral immune responses, the initial local tumor cell killing can reverse the immunosuppressive tumor microenvironment, resulting in more effective release of tumor-associated antigens (TAAs), cross-presentation, and antitumoral effector T cell recruitment. Moreover, many OVs can be engineered to express immunomodulatory genes. Rational combination approaches to cancer immunotherapy include the use of OVs in combination with immune checkpoint inhibitors (ICIs) or adoptive T cell therapy (ACT) to promote sustained antitumoral immune responses. OV combinations have additive or synergistic efficacy in preclinical tumor models with ICIs or ACT. Several preclinical studies have confirmed systemic reactivation and proliferation of adoptively transferred antitumoral T cells in conjunction with oncolytic OVs (expressing cytokines or TAAs) resulting from the specific tumor cell killing and immunostimulation of the tumor microenvironment which leads to increased tumor trafficking, activity, and survival. Recent clinical trials combining OVs with ICIs have shown additive effects in melanoma. Additional clinical data in an expanded range of patient indications are eagerly awaited. The relative timings of OV and ICI combination remains under-studied and is an area for continued exploration. Studies systematically exploring the effects of systemic ICIs prior to, concomitantly with, or following OV therapy will aid in the future design of clinical trials to enhance efficacy and increase patient response rates.

HER2-Positive Breast Cancer Immunotherapy: A Focus on Vaccine Development

Clinical progress in the field of HER2-positive breast cancer therapy has been dramatically improved by understanding of the immune regulatory mechanisms of tumor microenvironment. Passive immunotherapy utilizing recombinant monoclonal antibodies (mAbs), particularly trastuzumab and pertuzumab has proved to be an effective strategy in HER2-positive breast cancer treatment. However, resistance to mAb therapy and relapse of disease are still considered important challenges in clinical practice. There are increasing reports on the induction of cellular and humoral immune responses in HER2-positive breast cancer patients. More recently, increasing efforts are focused on using HER2-derived peptide vaccines for active immunotherapy. Here, we discuss the development of various HER2-derived vaccines tested in animal models and human clinical trials. Different formulations and strategies to improve immunogenicity of the antigens in animal studies are also discussed. Furthermore, other immunotherapeutic approaches to HER2 breast cancer including, CTLA-4 inhibitors, immune checkpoint inhibitors, anti PD-1/PD-L1 antibodies are presented.

Enhanced Therapeutic Efficacy of a Novel Oncolytic Herpes Simplex Virus Type 2 Encoding an Antibody Against Programmed Cell Death 1

The efficacy of immune checkpoint blockade therapy against immunologically “cold” tumors can be enhanced by applying the checkpoint inhibitors in combination with oncolytic viruses. Alternatively, the oncolytic virus construct has been modified to express factors that boost oncolytic virus function. We engineered a novel oncolytic herpes simplex virus 2 (HSV2) encoding an anti-human programmed cell death 1 (PD-1) monoclonal antibody (oHSV2-aPD1). This virus resulted in the detectable expression of a functional monoclonal antibody against human PD-1 by infecting eukaryotic cells. Therapeutic efficacy of oHSV2-aPD1 proved superior to unmodified oncolytic HSV2 treatment or PD-1 blockade alone and as effective as their combination in the poorly immunogenic melanoma models. Additionally, local oHSV2-aPD1 treatment induced a durable antitumor response and activated many immune effector cells and molecules both in the tumor microenvironment and in the systemic immune system. This provides support for combinatorial strategies involving local administration of an oncolytic HSV2 expressing a PD-1 inhibitor.

Cancer DNA vaccines: current preclinical and clinical developments and future perspectives

The recent developments in immuno-oncology have opened an unprecedented avenue for the emergence of vaccine strategies. Therapeutic DNA cancer vaccines are now considered a very promising strategy to activate the immune system against cancer. In the past, several clinical trials using plasmid DNA vaccines demonstrated a good safety profile and the activation of a broad and specific immune response. However, these vaccines often demonstrated only modest therapeutic effects in clinical trials due to the immunosuppressive mechanisms developed by the tumor. To enhance the vaccine-induced immune response and the treatment efficacy, DNA vaccines could be improved by using two different strategies. The first is to increase their immunogenicity by selecting and optimizing the best antigen(s) to be inserted into the plasmid DNA. The second strategy is to combine DNA vaccines with other complementary therapies that could improve their activity by attenuating immunosuppression in the tumor microenvironment or by increasing the activity/number of immune cells. A growing number of preclinical and clinical studies are adopting these two strategies to better exploit the potential of DNA vaccination. In this review, we analyze the last 5-year preclinical studies and 10-year clinical trials using plasmid DNA vaccines for cancer therapy. We also investigate the strategies that are being developed to overcome the limitations in cancer DNA vaccination, revisiting the rationale for different combinations of therapy and the different possibilities in antigen choice. Finally, we highlight the most promising developments and critical points that need to be addressed to move towards the approval of therapeutic cancer DNA vaccines as part of the standard of cancer care in the future.

Oncolytic viruses and checkpoint inhibitors: combination therapy in clinical trials

Advances in the understanding of cancer immunotherapy and the development of multiple checkpoint inhibitors have dramatically changed the current landscape of cancer treatment. Recent large-scale phase III trials (e.g. PHOCUS, OPTiM) are establishing use of oncolytic viruses as another tool in the cancer therapeutics armamentarium. These viruses do not simply lyse cells to achieve their cancer-killing effects, but also cause dramatic changes in the tumor immune microenvironment. This review will highlight the major vector platforms that are currently in development (including adenoviruses, reoviruses, vaccinia viruses, herpesviruses, and coxsackieviruses) and how they are combined with checkpoint inhibitors. These vectors employ a variety of engineered capsid modifications to enhance infectivity, genome deletions or promoter elements to confer selective replication, and encode a variety of transgenes to enhance anti-tumor or immunogenic effects. Pre-clinical and clinical data have shown that oncolytic vectors can induce anti-tumor immunity and markedly increase immune cell infiltration (including cytotoxic CD8⁺ T cells) into the local tumor microenvironment. This "priming" by the viral infection can change a 'cold' tumor microenvironment into a 'hot' one with the influx of a multitude of immune cells and cytokines. This alteration sets the stage for subsequent checkpoint inhibitor delivery, as they are most effective in an environment with a large lymphocytic infiltrate. There are multiple ongoing clinical trials that are currently combining oncolytic viruses with checkpoint inhibitors (e.g. CAPTIVE, CAPRA, and Masterkey-265), and the initial results are encouraging. It is clear that oncolytic viruses and checkpoint inhibitors will continue to evolve together as a combination therapy for multiple types of cancers.

Therapeutic potency of oncolytic virotherapy in breast cancer targeting, current status and perspective

Breast cancer is the most common cause of cancer death in women and presents a serious therapeutic challenge worldwide. Traditional treatments are less successful at targeting cancer tumors, leading to recurrent treatment-resistant secondary malignancies. Oncolytic virotherapy (OV) is a novel anticancer strategy with therapeutic implications at targeting cancer cells by using mechanisms that differ from conventional therapies. Administration of OVs either alone or in combination with standard therapies provide new insights regarding the effectiveness and improvement of treatment responses for breast cancer patients. This review summarizes cellular, animal and clinical studies investigating therapeutic potency of oncolytic virotherapy in breast cancer treatment for a better understanding and hence a better management of this disease.

Emerging functional markers for cancer stem cell-based therapies: Understanding signaling networks for targeting metastasis

Metastasis is one of the most challenging issues in cancer patient management, and effective therapies to specifically target disease progression are missing, emphasizing the urgent need for developing novel anti-metastatic therapeutics. Cancer stem cells (CSCs) gained fast attention as a minor population of highly malignant cells within liquid and solid tumors that are responsible for tumor onset, self-renewal, resistance to radio- and chemotherapies, and evasion of immune surveillance accelerating recurrence and metastasis. Recent progress in the identification of their phenotypic and molecular characteristics and interactions with the tumor microenvironment provides great potential for the development of CSC-based targeted therapies and radical improvement in metastasis prevention and cancer patient prognosis. Here, we report on newly uncovered signaling mechanisms controlling CSC's aggressiveness and treatment resistance, and CSC-specific agents and molecular therapeutics, some of which are currently under investigation in clinical trials, gearing towards decisive functional CSC intrinsic or surface markers. One special research focus rests upon subverted regulatory pathways such as insulin-like growth factor 1 receptor signaling and its interactors in metastasis-initiating cell populations directly related to the gain of stem cell- and EMT-associated properties, as well as key components of the E2F transcription factor network regulating metastatic progression, microenvironmental changes, and chemoresistance. In addition, the study provides insight into systems biology tools to establish complex molecular relationships behind the emergence of aggressive phenotypes from high-throughput data that rely on network-based analysis and their use to investigate immune escape mechanisms or predict clinical outcome-relevant CSC receptor signaling signatures. We further propose that customized vector technologies could drastically enhance systemic drug delivery to target sites, and summarize recent progress and remaining challenges. This review integrates available knowledge on CSC biology, computational modeling approaches, molecular targeting strategies, and delivery techniques to envision future clinical therapies designed to conquer metastasis-initiating cells.

Armed oncolytic viruses: A kick-start for anti-tumor immunity

Oncolytic viruses (OVs), viruses that specifically result in killing tumor cells, represent a promising class of cancer therapy. Recently, the focus in the OV therapy field has shifted from their direct oncolytic effect to their immune stimulatory effect. OV therapy can function as a "kick start" for the antitumor immune response by releasing tumor associated antigens and release of inflammatory signals. Combining OVs with immune modulators could enhance the efficacy of both immune and OV therapies. Additionally, genetic engineering of OVs allows local expression of immune therapeutics, thereby reducing related toxicities. Different options to modify the tumor microenvironment in combination with OV therapy have been explored. The possibilities and obstacles of these combinations will be discussed in this review.

Tune Up In Situ Autovaccination against Solid Tumors with Oncolytic Viruses

With the progress of immunotherapy in cancer, oncolytic viruses (OVs) have attracted more and more attention during the past decade. Due to their cancer-selective and immunogenic properties, OVs are considered ideal candidates to be combined with immunotherapy to increase both specificity and efficacy in cancer treatment. OVs preferentially replicate in and lyse cancer cells, resulting in in situ autovaccination leading to adaptive anti-virus and anti-tumor immunity. The main challenge in OV approaches is how to redirect the host immunity from anti-virus to anti-tumor and optimize the clinical outcome of cancer patients. Here, we summarize the conceptual updates on oncolytic virotherapy and immunotherapy in cancer, and the development of strategies to enhance the virus-mediated anti-tumor immune response, including: (1) arm OVs with cytokines to modulate innate and adaptive immunity; (2) combining OVs with immune checkpoint inhibitors to release T cell inhibition; (3) combining OVs with immune co-stimulators to enhance T cell activation. Future studies need to be enforced on developing strategies to augment the systemic effect on metastasized tumors.

Recombinant viruses with other anti-cancer therapeutics: a step towards advancement of oncolytic virotherapy

Cancer as a disease is a multifaceted foe which sometimes succumbs to the prescribed treatment and sometimes develops resistance against various therapies. Conventional cancer therapies suffer from many limitations, the least of which is their specificity and systemic side effects. In a majority of cases, acquired mutations render the cancer cells resistant to therapy and lower the prognostic outcome. In the constant effort to devise a therapeutic moiety which can comprehensively eliminate cancer cells, oncolytic viruses provide an attractive avenue as they selectively infect and lyse cancer cells sparing normal cells from their effects. Viruses can be engineered for their host specificity and toxicity as a promising anti-cancer tool. As it is essential to devise a strategy to address all targets involved in cancer development and progression, the idea of using oncolytic viruses with enhanced anti-cancer activity through arming with foreign genes gained merit and is showing promising advent in clinical studies. The use of oncolytic viruses as an agent of combination therapy for cancer treatment also gained much attention in the recent past. This review focuses on the emerging role of oncolytic viruses as vital components of anti-cancer regimen presenting a new dimension in an ever-changing cancer therapy scenario.

Lighting a Fire in the Tumor Microenvironment Using Oncolytic Immunotherapy

Oncolytic virus (OV) therapy is potentially a game-changing cancer treatment that has garnered significant interest due to its versatility and multi-modal approaches towards tumor eradication. In the field of cancer immunotherapy, the immunological phenotype of the tumor microenvironment (TME) is an important determinant of disease prognosis and therapeutic success. There is accumulating data that OVs are capable of dramatically altering the TME immune landscape, leading to improved antitumor activity alone or in combination with assorted immune modulators. Herein, we review how OVs disrupt the immunosuppressive TME and can be used strategically to create a "pro-immune" microenvironment that enables and promotes potent, long-lasting host antitumor immune responses.

Oncolytic Viruses as Antigen-Agnostic Cancer Vaccines

Selective destruction of neoplastic tissues by oncolytic viruses (OVs) leads to antigen-agnostic boosting of neoantigen-specific cytotoxic T lymphocyte (CTL) responses, making OVs ideal companions for checkpoint blockade therapy. Here we discuss the mechanisms whereby OVs modulate both adjuvanticity and antigenicity of tumor cells. Suppression of antitumor immunity after OV therapy has not been observed, possibly because viral antigen expression diminishes as the antiviral response matures, thereby progressively honing the CTL response to tumor neoantigens. By combining direct in situ tumor destruction with the ability to boost antitumor immunity, OVs also have the potential to be powerful standalone cancer therapies.

Oncotargeting by Vesicular Stomatitis Virus (VSV): Advances in Cancer Therapy

Modern oncotherapy approaches are based on inducing controlled apoptosis in tumor cells. Although a number of apoptosis-induction approaches are available, site-specific delivery of therapeutic agents still remain the biggest hurdle in achieving the desired cancer treatment benefit. Additionally, systemic treatment-induced toxicity remains a major limiting factor in chemotherapy. To specifically address drug-accessibility and chemotherapy side effects, oncolytic virotherapy (OV) has emerged as a novel cancer treatment alternative. In OV, recombinant viruses with higher replication capacity and stronger lytic properties are being considered for tumor cell-targeting and subsequent cell lysing. Successful application of OVs lies in achieving strict tumor-specific tropism called oncotropism, which is contingent upon the biophysical interactions of tumor cell surface receptors with viral receptors and subsequent replication of oncolytic viruses in cancer cells. In this direction, few viral vector platforms have been developed and some of these have entered pre-clinical/clinical trials. Among these, the Vesicular stomatitis virus (VSV)-based platform shows high promise, as it is not pathogenic to humans. Further, modern molecular biology techniques such as reverse genetics tools have favorably advanced this field by creating efficient recombinant VSVs for OV; some have entered into clinical trials. In this review, we discuss the current status of VSV based oncotherapy, challenges, and future perspectives regarding its therapeutic applications in the cancer treatment.

Targeting Melanoma with Cancer-Killing Viruses

Melanoma is the deadliest skin cancer with ever-increasing incidence. Despite the development in diagnostics and therapies, metastatic melanoma is still associated with significant morbidity and mortality. Oncolytic viruses (OVs) represent a class of novel therapeutic agents for cancer by possessing two closely related properties for tumor reduction: virus-induced lysis of tumor cells and induction of host anti-tumor immune responses. A variety of viruses, either in "natural" or in genetically modified forms, have exhibited a remarkable therapeutic efficacy in regressing melanoma in experimental and/or clinical studies. This review provides a comprehensive summary of the molecular and cellular mechanisms of action of these viruses, which involve manipulating and targeting the abnormalities of melanoma, and can be categorized as enhancing viral tropism, targeting the tumor microenvironment and increasing the innate and adaptive antitumor responses. Additionally, this review describes the "biomarkers" and deregulated pathways of melanoma that are responsible for melanoma initiation, progression and metastasis. Advances in understanding these abnormalities of melanoma have resulted in effective targeted and immuno-therapies, and could potentially be applied for engineering OVs with enhanced oncolytic activity in future.

Viroimmunotherapy for Colorectal Cancer: Clinical Studies

Colorectal cancer is a leading cause of cancer incidence and death. Therapies for those with unresectable or recurrent disease are not considered curative at present. More effective and less toxic therapies are desperately needed. Historically, the immune system was thought to be an enemy to oncolytic viral therapy. Thinking that oncolysis would be the only mechanism for cell death, oncolytic virologists theorized that immune clearance was a detriment to oncolysis. Recent advances in our understanding of the tumor microenvironment, and the interplay of tumor survival and a patient's immune system have called into question our understanding of both arenas. It remains unclear what combination of restrictions or enhancements of innate and/or cell-mediated immunity can yield the highest likelihood of viral efficacy. This article reviews the variety of mechanisms explored for viruses such as immunotherapy for colorectal cancer.

Murine Tumor Models for Oncolytic Rhabdo-Virotherapy

The preclinical optimization and validation of novel treatments for cancer therapy requires the use of laboratory animals. Although in vitro experiments using tumor cell lines and ex vivo treatment of patient tumor samples provide a remarkable first-line tool for the initial study of tumoricidal potential, tumor-bearing animals remain the primary option to study delivery, efficacy, and safety of therapies in the context of a complete tumor microenvironment and functional immune system. In this review, we will describe the use of murine tumor models for oncolytic virotherapy using vesicular stomatitis virus. We will discuss studies using immunocompetent and immunodeficient models with respect to toxicity and therapeutic treatments, as well as the various techniques and tools available to study cancer therapy with Rhabdoviruses.

Checkpoint Blockade for the Treatment of Advanced Melanoma

Immunotherapy with immune checkpoint inhibition has been improving the outcomes of patients with many different types of malignancies. Immune checkpoint inhibition has been most extensively studied in patients with advanced melanoma and there are three FDA approved antibodies already widely used in clinical practice (ipilimumab, nivolumab, and pembrolizumab). In this chapter, we review the mechanistic basis behind the development of immune checkpoint blocking antibodies. We then discuss specifics regarding each agent, unique clinical considerations in treating patients with this approach, and future directions, including combination strategies. This chapter is focused on melanoma, but the principles related to this immunotherapy approach are applicable to patients with many types of malignancies.

Overcoming Barriers in Oncolytic Virotherapy with HDAC Inhibitors and Immune Checkpoint Blockade

Oncolytic viruses (OVs) target and destroy cancer cells while sparing their normal counterparts. These viruses have been evaluated in numerous studies at both pre-clinical and clinical levels and the recent Food and Drug Administration (FDA) approval of an oncolytic herpesvirus-based treatment raises optimism that OVs will become a therapeutic option for cancer patients. However, to improve clinical outcome, there is a need to increase OV efficacy. In addition to killing cancer cells directly through lysis, OVs can stimulate the induction of anti-tumour immune responses. The host immune system thus represents a "double-edged sword" for oncolytic virotherapy: on the one hand, a robust anti-viral response will limit OV replication and spread; on the other hand, the immune-mediated component of OV therapy may be its most important anti-cancer mechanism. Although the relative contribution of direct viral oncolysis and indirect, immune-mediated oncosuppression to overall OV efficacy is unclear, it is likely that an initial period of vigorous OV multiplication and lytic activity will most optimally set the stage for subsequent adaptive anti-tumour immunity. In this review, we consider the use of histone deacetylase (HDAC) inhibitors as a means of boosting virus replication and lessening the negative impact of innate immunity on the direct oncolytic effect. We also discuss an alternative approach, aimed at potentiating OV-elicited anti-tumour immunity through the blockade of immune checkpoints. We conclude by proposing a two-phase combinatorial strategy in which initial OV replication and spread is maximised through transient HDAC inhibition, with anti-tumour immune responses subsequently enhanced by immune checkpoint blockade.

Oncolytic Immunotherapy for Treatment of Cancer

Immunotherapy entails the treatment of disease by modulation of the immune system. As detailed in the previous chapters, the different modes of achieving immune modulation are many, including the use of small/large molecules, cellular therapy, and radiation. Oncolytic viruses that can specifically attack, replicate within, and destroy tumors represent one of the most promising classes of agents for cancer immunotherapy (recently termed as oncolytic immunotherapy). The notion of oncolytic immunotherapy is considered as the way in which virus-induced tumor cell death (known as immunogenic cancer cell death (ICD)) allows the immune system to recognize tumor cells and provide long-lasting antitumor immunity. Both immune responses toward the virus and ICD together contribute toward successful antitumor efficacy. What is now becoming increasingly clear is that monotherapies, through any of the modalities detailed in this book, are neither sufficient in eradicating tumors nor in providing long-lasting antitumor immune responses and that combination therapies may deliver enhanced efficacy. After the rise of the genetic engineering era, it has been possible to engineer viruses to harbor combination-like characteristics to enhance their potency in cancer immunotherapy. This chapter provides a historical background on oncolytic virotherapy and its future application in cancer immunotherapy, especially as a combination therapy with other treatment modalities.

Immunovirotherapy with vesicular stomatitis virus and PD-L1 blockade enhances therapeutic outcome in murine acute myeloid leukemia

Patients with relapsed acute myeloid leukemia (AML) have limited therapeutic options. Vesicular stomatitis virus (VSV)-interferon β (IFNβ)-sodium iodide symporter (NIS) is an oncolytic VSV encoding IFNβ and the NIS reporter. Syngeneic AML C1498 tumors responded to IV therapy with VSV-murine IFNβ (mIFNβ)-NIS in a dose-dependent manner. Imaging for NIS expression showed robust virus infection within the tumors. Virus infection did not increase programmed death ligand 1 (PD-L1) on tumor cells. Combining VSV-mIFNβ-NIS with anti-PD-L1 antibody (Ab) therapy enhanced antitumor activity compared with treatment with virus alone or Ab alone; this enhancement was not significant at higher VSV-mIFNβ-NIS doses. Systemic VSV therapy reduced systemic C1498-green fluorescent protein (GFP) tumor burden in the blood, bone marrow, spleen, and liver of mice with AML. Combination VSV-mIFNβ-NIS and anti-PD-L1 Ab therapy significantly enhanced the survival of these mice with no evidence of toxicity, compared with isotype control, anti-PD-L1, or virus alone. There was an increase in tumor-infiltrating CD4 and CD8 cells. Single-agent VSV-mIFNβ-NIS virotherapy induced both VSV-specific and GFP-specific CD8 T cells as determined by IFN-γ enzyme-linked immunospot, pentamer, and intracellular IFN-γ staining assays. Both of these responses were further enhanced by addition of anti-PD-L1 Ab. Depletion of CD8 or natural killer cells, but not CD4 cells, resulted in loss of antitumor activity in the VSV/anti-PD-L1 group. Clinical samples from chronic myelomonocytic leukemia and acute myelomonocytic leukemia appear to be especially susceptible to VSV. Overall, our studies show that oncolytic virotherapy combined with immune checkpoint blockade is a promising approach to AML therapy.

Harnessing the Power of Onco-Immunotherapy with Checkpoint Inhibitors

Oncolytic viruses represent a diverse class of replication competent viruses that curtail tumor growth. These viruses, through their natural ability or through genetic modifications, can selectively replicate within tumor cells and induce cell death while leaving normal cells intact. Apart from the direct oncolytic activity, these viruses mediate tumor cell death via the induction of innate and adaptive immune responses. The field of oncolytic viruses has seen substantial advancement with the progression of numerous oncolytic viruses in various phases of clinical trials. Tumors employ a plethora of mechanisms to establish growth and subsequently metastasize. These include evasion of immune surveillance by inducing up-regulation of checkpoint proteins which function to abrogate T cell effector functions. Currently, antibodies blocking checkpoint proteins such as anti-cytotoxic T-lymphocyte antigen-4 (CTLA-4) and anti-programmed cell death-1 (PD-1) have been approved to treat cancer and shown to impart durable clinical responses. These antibodies typically need pre-existing active immune tumor microenvironment to establish durable clinical outcomes and not every patient responds to these therapies. This review provides an overview of published pre-clinical studies demonstrating superior therapeutic efficacy of combining oncolytic viruses with checkpoint blockade compared to monotherapies. These studies provide compelling evidence that oncolytic therapy can be potentiated by coupling it with checkpoint therapies.

Mechanistic insights into the oncolytic activity of vesicular stomatitis virus in cancer immunotherapy

Immunotherapy and oncolytic virotherapy have both shown anticancer efficacy in the clinic as monotherapies but the greatest promise lies in therapies that combine these approaches. Vesicular stomatitis virus is a prominent oncolytic virus with several features that promise synergy between oncolytic virotherapy and immunotherapy. This review will address the cytotoxicity of vesicular stomatitis virus in transformed cells and what this means for antitumor immunity and the virus’ immunogenicity, as well as how it facilitates the breaking of tolerance within the tumor, and finally, we will outline how these features can be incorporated into the rational design of new treatment strategies in combination with immunotherapy.

Releasing the Brake on Oncolytic Viral Therapy

Oncolytic virus that selectively targets and eradicates tumor cells and immune checkpoint blockade that unleashes host antitumor immune responses show synergistic effects against cancer. This combination holds great promise for future treatment of a broad range of cancers in patients. Clin Cancer Res; 21(24); 5417-9. ©2015 AACR.See related article by Rojas et al., p. 5543.

Oncolytic potency of HER-2 retargeted VSV-FH hybrid viruses: the role of receptor ligand affinity

The hybrid oncolytic vesicular stomatitis virus (VSV-FH) deleted for its G glycoprotein and displaying the measles virus (MV) envelope glycoproteins (hemagglutinin H and fusion F) is fusogenic, infects cells via any of the three MV receptors and has potent oncolytic activity against subcutaneous and disseminated myeloma tumors. To tailor VSV-FH as an oncolytic virus for ovarian cancer, we ablated its natural tropism and retargeted the virus by display of a single-chain antibody (scFv) with specificity to the HER-2/neu receptor. A panel of six VSVFH-αHER2 viruses displaying anti-HER2 scFv that bind to the same HER2 epitope but with different K_d (10⁻⁶ to 10⁻¹¹ M, VSVFH-αHER2#6 to #11, respectively) were rescued and characterized. A K_d of at least 10⁻⁸ M is required for infection of HER-2 positive SKOV3ip.1 cells. The higher affinity viruses (>10⁻⁸ M) were able to infect and fuse SKOV3ip.1 cells more efficiently, inducing more extensive cytopathic effects. We next compared the antitumor potency of the viruses against SKOV3ip.1 tumor xenografts. In contrast to the saline-treated animals, one intratumoral injection of VSVFH-αHER2#9, #10, or #11 resulted in efficient tumor control. There was no significant difference between viruses with an affinity higher than 10⁻⁹ M in terms of oncolytic potency. VSVFH-αHER2 virus may be a promising agent for the treatment of HER-2 positive malignancies.

Potentiation of immunomodulatory antibody therapy with oncolytic viruses for treatment of cancer

Identification of the immune suppressive mechanisms active within the tumor microenvironment led to development of immunotherapeutic strategies aiming to reverse the immunosuppression and to enhance the function of tumor-infiltrating lymphocytes. Of those, cancer therapy with antibodies targeting the immune costimulatory and coinhibitory receptors has demonstrated significant promise in the recent years, with multiple antibodies entering clinical testing. The responses to these agents, however, have not been universal and have not been observed in all cancer types, calling for identification of appropriate predictive biomarkers and development of combinatorial strategies. Pre-existing immune infiltration in tumors has been demonstrated to have a strong association with response to immunotherapies, with the type I interferon (IFN) pathway emerging as a key player in tumor innate immune recognition and activation of adaptive immunity. These findings provide a rationale for evaluation of strategies targeting the type I IFN pathway as a means to enhance tumor immune recognition and infiltration, which could potentially make them susceptible to therapeutics targeting the cosignaling receptors. To this end in particular, oncolytic viruses (OVs) have been demonstrated to enhance tumor recognition by the immune system through multiple mechanisms, which include upregulation of major histocompatibility complex and costimulatory molecules on cancer cells, immunogenic cell death and antigen release, and activation of the type I IFN pathway. Evidence is now emerging that combination therapies using OVs and agents targeting immune cosignaling receptors such as 4-1BB, PD-1, and CTLA-4 may work in concert to enhance antitumor immunity and therapeutic efficacy. Our evolving understanding of the interplay between OVs and the immune system demonstrates that the virus-induced antitumor immune responses can be harnessed to drive the efficacy of the agents targeting cosignaling receptors and provides a strong rationale for integration of such therapies in clinic.

NK cells in the tumor microenvironment

The presence of natural killer (NK) cells in the tumor microenvironment correlates with outcome in a variety of cancers. However, the role of intratumoral NK cells is unclear. Preclinical studies have shown that, while NK cells efficiently kill circulating tumor cells of almost any origin, they seem to have very little effect against the same type of tumor cells when these have extravasated. The ability to kill extravasated tumor cells is, however, is dependent of the level of activation of the NK cells, as more recent published and unpublished studies, discussed below, have demonstrated that interleukin-2-activated NK cells are able to attack well-established solid tumors.

Changing faces in virology: the dutch shift from oncogenic to oncolytic viruses

Viruses have two opposing faces. On the one hand, they can cause harm and disease. A virus may manifest directly as a contagious disease with a clinical pathology of varying significance. A viral infection can also have delayed consequences, and in rare cases may cause cellular transformation and cancer. On the other hand, viruses may provide hope: hope for an efficacious treatment of serious disease. Examples of the latter are the use of viruses as a vaccine, as transfer vector for therapeutic genes in a gene therapy setting, or, more directly, as therapeutic anticancer agent in an oncolytic-virus therapy setting. Already there is evidence for antitumor activity of oncolytic viruses. The antitumor efficacy seems linked to their capacity to induce a tumor-directed immune response. Here, we will provide an overview on the development of oncolytic viruses and their clinical evaluation from the Dutch perspective.

Viral infection of implanted meningeal tumors induces antitumor memory T-cells to travel to the brain and eliminate established tumors

BACKGROUND

Leptomeningeal metastases occur in 2%-5% of patients with breast cancer and have an exceptionally poor prognosis. The blood-brain and blood-meningeal barriers severely inhibit successful chemotherapy. We have developed a straightforward method to induce antitumor memory T-cells using a Her2/neu targeted vesicular stomatitis virus. We sought to determine whether viral infection of meningeal tumor could attract antitumor memory T-cells to eradicate the tumors.

METHODS

Meningeal implants in mice were studied using treatment trials and analyses of immune cells in the tumors.

RESULTS

This paper demonstrates that there is a blood-meningeal barrier to bringing therapeutic memory T-cells to meningeal tumors. The barrier can be overcome by viral infection of the tumor. Viral infection of the meningeal tumors followed by memory T-cell transfer resulted in 89% cure of meningeal tumor in 2 different mouse strains. Viral infection produced increased infiltration and proliferation of transferred memory T-cells in the meningeal tumors. Following viral infection, the leukocyte infiltration in meninges and tumor shifted from predominantly macrophages to predominantly T-cells. Finally, this paper shows that successful viral therapy of peritoneal tumors generates memory CD8 T-cells that prevent establishment of tumor in the meninges of these same animals.

CONCLUSIONS

These results support the hypothesis that a virally based immunization strategy can be used to both prevent and treat meningeal metastases. The meningeal barriers to cancer therapy may be much more permeable to treatment based on cells than treatment based on drugs or molecules.

Oncolytic viruses as anticancer vaccines

Oncolytic virotherapy has shown impressive results in preclinical studies and first promising therapeutic outcomes in clinical trials as well. Since viruses are known for a long time as excellent vaccination agents, oncolytic viruses are now designed as novel anticancer agents combining the aspect of lysis-dependent cytoreductive activity with concomitant induction of antitumoral immune responses. Antitumoral immune activation by oncolytic virus infection of tumor tissue comprises both, immediate effects of innate immunity and also adaptive responses for long lasting antitumoral activity, which is regarded as the most prominent challenge in clinical oncology. To date, the complex effects of a viral tumor infection on the tumor microenvironment and the consequences for the tumor-infiltrating immune cell compartment are poorly understood. However, there is more and more evidence that a tumor infection by an oncolytic virus opens up a number of options for further immunomodulating interventions such as systemic chemotherapy, generic immunostimulating strategies, dendritic cell-based vaccines, and antigenic libraries to further support clinical efficacy of oncolytic virotherapy.

Armed therapeutic viruses - a disruptive therapy on the horizon of cancer immunotherapy

For the past 150 years cancer immunotherapy has been largely a theoretical hope that recently has begun to show potential as a highly impactful treatment for various cancers. In particular, the identification and targeting of immune checkpoints have given rise to exciting data suggesting that this strategy has the potential to activate sustained antitumor immunity. It is likely that this approach, like other anti-cancer strategies before it, will benefit from co-administration with an additional therapeutic and that it is this combination therapy that may generate the greatest clinical outcome for the patient. In this regard, oncolytic viruses are a therapeutic moiety that is well suited to deliver and augment these immune-modulating therapies in a highly targeted and economically advantageous way over current treatment. In this review, we discuss the blockade of immune checkpoints, how oncolytic viruses complement and extend these therapies, and speculate on how this combination will uniquely impact the future of cancer immunotherapy.

Immunomodulatory therapy for melanoma: ipilimumab and beyond

In 2011, the U.S. Food and Drug Administration approved the first new therapy for melanoma in more than a decade, ipilimumab (Yervoy). Ipilimumab is a novel antibody that blocks cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), a regulatory molecule expressed on activated T cells. Blockade of this important immune checkpoint can lead to durable tumor regression, and phase III studies show an overall survival benefit for patients with advanced melanoma. During the clinical development of ipilimumab, several unique features of this immunotherapy were identified, including the remarkable durability of responses and a distinct side-effects profile. We review the preclinical and clinical development of CTLA-4-blocking antibodies and describe current practices using ipilimumab for the treatment of advanced melanoma. Unique clinical issues related to ipilimumab will be summarized. Lastly, we will briefly preview combination therapies that incorporate ipilimumab and new checkpoint-targeting antibodies currently in clinical development.

Immunomodulatory therapy for melanoma: ipilimumab and beyond

In 2011, the U.S. Food and Drug Administration approved the first new therapy for melanoma in more than a decade, ipilimumab (Yervoy). Ipilimumab is a novel antibody that blocks cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), a regulatory molecule expressed on activated T cells. Blockade of this important immune checkpoint can lead to durable tumor regression, and phase III studies show an overall survival benefit for patients with advanced melanoma. During the clinical development of ipilimumab, several unique features of this immunotherapy were identified, including the remarkable durability of responses and a distinct side-effects profile. We review the preclinical and clinical development of CTLA-4-blocking antibodies and describe current practices using ipilimumab for the treatment of advanced melanoma. Unique clinical issues related to ipilimumab will be summarized. Lastly, we will briefly preview combination therapies that incorporate ipilimumab and new checkpoint-targeting antibodies currently in clinical development.

Highly attenuated recombinant vesicular stomatitis virus VSV-12'GFP displays immunogenic and oncolytic activity

Vesicular stomatitis virus (VSV) has shown considerable promise both as an immunization vector and as an oncolytic virus. In both applications, an important concern is the safety profile of the virus. To generate a highly attenuated virus, we added two reporter genes to the 3' end of the VSV genome, thereby shifting the NPMGL genes from positions 1 to 5 to positions 3 to 7. The resulting virus (VSV-12'GFP) was highly attenuated, generating smaller plaques than four other attenuated VSVs. In one-step growth curves, VSV-12'GFP displayed the slowest growth kinetics. The mechanism of attenuation appears to be due to reduced expression of VSV genes downstream of the reporter genes, as suggested by a 10.4-fold reduction in L-protein RNA transcript. Although attenuated, VSV-12'GFP was highly effective at generating an immune response, indicated by a high-titer antibody response against the green fluorescent protein (GFP) expressed by the virus. Although VSV-12'GFP was more attenuated than other VSVs on both normal and cancer cells, it nonetheless showed a greater level of infection of human cancer cells (glioma and melanoma) than of normal cells, and this effect was magnified in glioma by interferon application, indicating selective oncolysis. Intravenous VSV-12'GFP selectively infected human gliomas implanted into SCID mice subcutaneously or intracranially. All postnatal day 16 mice given intranasal VSV-12'GFP survived, whereas only 10% of those given VSV-G/GFP survived, indicating reduced neurotoxicity. Intratumoral injection of tumors with VSV-12'GFP dramatically suppressed tumor growth and enhanced survival. Together these data suggest this recombinant virus merits further study for its oncolytic and vaccine potential.

AMP-activated protein kinase is required for the macropinocytic internalization of ebolavirus

Identification of host factors that are needed for Zaire Ebolavirus (EBOV) entry provides insights into the mechanism(s) of filovirus uptake, and these factors may serve as potential antiviral targets. In order to identify novel host genes and pathways involved in EBOV entry, gene array findings in the National Cancer Institute's NCI-60 panel of human tumor cell lines were correlated with permissivity for EBOV glycoprotein (GP)-mediated entry. We found that the gene encoding the γ2 subunit of AMP-activated protein kinase (AMPK) strongly correlated with EBOV transduction in the tumor panel. The AMPK inhibitor compound C inhibited infectious EBOV replication in Vero cells and diminished EBOV GP-dependent, but not Lassa fever virus GPC-dependent, entry into a variety of cell lines in a dose-dependent manner. Compound C also prevented EBOV GP-mediated infection of primary human macrophages, a major target of filoviral replication in vivo. Consistent with a role for AMPK in filovirus entry, time-of-addition studies demonstrated that compound C abrogated infection when it was added at early time points but became progressively less effective when added later. Compound C prevented EBOV pseudovirion internalization at 37°C as cell-bound particles remained susceptible to trypsin digestion in the presence of the inhibitor but not in its absence. Mouse embryonic fibroblasts lacking the AMPKα1 and AMPKα2 catalytic subunits were significantly less permissive to EBOV GP-mediated infection than their wild-type counterparts, likely due to decreased macropinocytic uptake. In total, these findings implicate AMPK in macropinocytic events needed for EBOV GP-dependent entry and identify a novel cellular target for new filoviral antivirals.

Relationship between lymphocytopenia and circulating tumor cells as prognostic factors for overall survival in metastatic breast cancer

INTRODUCTION

Lymphocytopenia and circulating tumor cells (CTCs) have been reported as independent prognostic factors for overall survival (OS) in metastatic breast cancer (MBC), and both have been associated with bone metastases. Our objective was to compare the prognostic significance of lymphocytopenia, CTC count, and extensive bone metastases (> 2 lesions) assessed by fluorine-18 ((18)F) fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) in patients with MBC.

PATIENTS AND METHODS

This is a retrospective study that included patients with MBC who were starting a new line of systemic therapy. The study population consisted of patients treated at the University of Texas MD Anderson Cancer Center between 2004 and 2008 for whom baseline CTC count, lymphocyte counts, and FDG-PET/CT scans were available. Patients were stratified according to estrogen receptor status (positive vs. negative), human epidermal growth factor receptor 2 (HER2) status (amplified vs. constitutive), baseline CTC counts per 7.5 mL of blood (< 5 CTCs/7.5 mL of blood vs. ≥ 5 CTCs/7.5 mL of blood), lymphocytopenia (< 1000 vs. ≥ 1000/μL), and extensive bone metastases (> 2 vs. ≤ 2 lesions).

RESULTS

In 195 assessable patients, the median OS was 27 months (range, 1 to > 45 months). In multivariate analysis, lymphocytopenia, ≥ 5 CTCs/7.5 mL of blood, estrogen receptor status, and line of therapy were the only predictive factors for progression-free survival (PFS) (2P = .001, 2P = .032, 2P = .029, and 2P = .002, respectively) and OS (2P = .001, 2P = .009, 2P = .004, and 2P = .024, respectively).

CONCLUSION

CTC measurement and lymphocytopenia are independent prognostic factors for PFS and OS in patients with MBC.

Replication-competent herpes simplex virus retargeted to HER2 as therapy for high-grade glioma

Oncolytic herpes simplex viruses (HSVs) represent a novel frontier against tumors resistant to standard therapies, like glioblastoma (GBM). The oncolytic HSVs that entered clinical trials so far showed encouraging results; however, they are marred by the fact that they are highly attenuated. We engineered HSVs that maintain unimpaired lytic efficacy and specifically target cells that express tumor-specific receptors, thus limiting the cytotoxicity only to cancer cells, and leaving unharmed the neighboring tissues. We report on the safety and efficacy in a high-grade glioma (HGG) model of R-LM113, an HSV recombinant retargeted to human epidermal growth factor receptor 2 (HER2), frequently expressed in GBMs. We demonstrated that R-LM113 is safe in vivo as it does not cause encephalitis when intracranially injected in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice, extremely sensitive to wild-type HSV. The efficacy of R-LM113 was assessed in a platelet-derived growth factor (PDGF)-induced infiltrative glioma model engineered to express HER2 and transplanted intracranially in adult NOD/SCID mice. Mice injected with HER2-engineered glioma cells infected with R-LM113 showed a doubled survival time compared with mice injected with uninfected cells. A doubling in survival time from the beginning of treatment was obtained also when R-LM113 was administered into already established tumors. These data demonstrate the efficacy of R-LM113 in thwarting tumor growth.

Treatment with targeted vesicular stomatitis virus generates therapeutic multifunctional anti-tumor memory CD4 T cells

A generally applicable, easy-to-use method of focusing a patient's immune system to eradicate or prevent cancer has been elusive. We are attempting to develop a targeted virus to accomplish these aims. We previously created a recombinant replicating Vesicular Stomatitis Virus that preferentially infected Her2/neu expressing breast cancer cells and showed therapeutic efficacy in an implanted Balb/c mouse tumor model. The current work shows that this therapy generated therapeutic anti-tumor CD4 T-cells against multiple tumor antigens. CD4 T-cells transferred directly from cured donor mice could eradicate established tumors in host mice. T-cells were transferred directly from donor mice and were not stimulated ex vivo. Both tumors that expressed Her2/neu and those that did not were cured by transferred T-cells. Analysis of cytokines secreted by anti-tumor memory CD4 T-cells displayed a multifunctional pattern with high levels of IFNγ, IL-4 and IL-17. Anti-tumor memory CD4 T-cells traveled to the mesenteric lymph nodes and were activated there. Treatment with targeted rrVSV is a potent immune adjuvant that generates therapeutic, multifunctional anti-tumor memory CD4 T-cells that recognize multiple tumor antigens. Immunity elicited by viral therapy is independent of host major histocompatibility complex (MHC) or knowledge of tumor antigens. Virus-induced tumor immunity could have great benefit in the prevention and treatment of tumor metastases.

Dendritic cells transfected with PD-L1 recombinant adenovirus induces T cell suppression and long-term acceptance of allograft transplantation

The purpose of this study is to assess the potential of dendritic cells transfected with PD-L1 recombinant adenovirus induces CD8+ T cell suppression and kidney allograft tolerance. To prove it, DCs transfected with PD-L1 recombinant adenovirus (DC/Ad-PD-L1) were transferred into the MHC-mismatched rat kidney transplants. After kidney transplantation, the mixed lymphocyte reaction (MLR) assay and kidney function were analyzed. The results demonstrated that after administration of DC/Ad-PD-L1, the proliferation, cytokines secretion and activation marker expression of CD8+ T cells were suppressed. In addition, DC/Ad-PD-L1 could improve kidney function and survival of transplants. The findings suggested that DC/Ad-PD-L1 could induce CD8+ T cell tolerance and lead to kidney allograft tolerance, which provided a promising finding for clinical application.

Vesicular stomatitis virus modified with single chain IL-23 exhibits oncolytic activity against tumor cells in vitro and in vivo

Viruses are potentially attractive agents for development as novel oncolytic agents. Reverse genetic approaches allow for the attenuation of candidate viruses and can enhance their ability to exploit inherent cellular and molecular properties of tumors, including deficiencies in interferon (IFN) signaling. Vesicular stomatitis virus (VSV) is a promising oncolytic agent for exactly these reasons. VSV infection of immunocompetent mice is usually rapidly cleared due to the virus' sensitivity to type I IFN responses. However, in tumors that are unable to activate the IFN response, VSV is able to replicate without inhibition, resulting in cell destruction. Unfortunately, when VSV is introduced into mice intranasally or systemically via therapeutic doses into tumor-bearing rodents, hosts may develop fatal encephalitis. We have previously found that a recombinant VSV expressing the pro-inflammatory cytokine interleukin-23 (IL-23) is significantly attenuated in the central nervous system (CNS). As a result of this, we hypothesized that attenuation in the CNS is partially a result of enhanced NO response as a result of IL-23 signaling. Infection of the CNS with this virus (designated VSV23) is characterized by decreased viral replication, morbidity, and mortality. We have now extended those studies which reveal that VSV23 maintains oncolytic capacity in vitro in multiple cell lines including NB41A3 neuroblastomas, L929 adipose-derived cells, immortalized BHK-21 cells, and the murine mammary derived JC cells. Additionally, in vivo VSV23 infection results in JC tumor destruction and induces enhanced memory responses against tumor cells.

Modulation of CTLA-4 and GITR for cancer immunotherapy

The rational manipulation of antigen-specific T cells to reignite a tumor-specific immune response in cancer patients is a challenge for cancer immunotherapy. Targeting coinhibitory and costimulatory T cell receptors with specific antibodies in cancer patients is an emerging approach to T cell manipulation, namely "immune modulation." Cytotoxic T-lymphocyte antigen-4 (CTLA-4) and glucocorticoid-induced tumor necrosis factor family receptor (GITR) are potential targets for immune modulation through anti-CTLA-4 blocking antibodies and anti-GITR agonistic antibodies, respectively. In this review, we first discuss preclinical findings key to the understanding of the mechanisms of action of these immunomodulatory antibodies and the preclinical evidence of antitumor activity which preceded translation into the clinic. We next describe the outcomes and immune related adverse effects associated with anti-CTLA-4 based clinical trials with particular emphasis on specific biomarkers used to elucidate the mechanisms of tumor immunity in patients. The experience with anti-CTLA-4 therapy and the durable clinical benefit observed provide proof of principle to effective antitumor immune modulation and the promise of future clinical immune modulatory antibodies.

Cytokine-modified VSV is attenuated for neural pathology, but is both highly immunogenic and oncolytic

Vesicular stomatitis virus (VSV), an enveloped, nonsegmented, negative-stranded RNA virus, is being tested by several laboratories as an antitumor agent. Unfortunately, viral infection of the central nervous system (CNS) has been observed by many groups following administration to tumor-bearing animals. In rodents, VSV encephalitis is characterized by weight-loss, paralysis, and high mortality. In order to provide protection from VSV infection of the CNS after therapeutic administration, we have attenuated VSV by the introduction of the gene encoding the proinflammatory cytokine interleukin (IL)-23, and designated the new virus VSV23. We hypothesize that while VSV23 is replicating within tumors, resulting in tumor destruction, the expression of IL-23 will enhance host antitumor and antiviral immune responses. In the event that the virus escapes from the tumor, the host's immune system will be activated and the virus will be rapidly cleared from healthy tissue. Experimental VSV23 infection of the CNS is characterized by decreased viral replication, morbidity, and mortality. VSV23 is capable of stimulating the enhanced production of nitric oxide in the CNS, which is critical for elimination of VSV from infected neurons. Intraperitoneal administration of VSV23 stimulates both nonspecific natural killer cell, virus-specific cytolytic T lymphocyte and memory virus-specific proliferative T cell responses against wild-type VSV in splenocytes. Furthermore, VSV23 is able to replicate in, and induce apoptosis of tumor cells in vitro. These data indicate that VSV23 is immunogenic, attenuated and suitable for testing as an efficacious and safe oncolytic agent.

The case of oncolytic viruses versus the immune system: waiting on the judgment of Solomon

The three-way interaction between oncolytic viruses, the tumor microenvironment, and the immune system is critical to the outcome of antitumor therapy. Classically, the immune system is thought to limit the efficacy of therapy, leading to viral clearance. However, preclinical and clinical data suggest that in some cases virotherapy may in fact act as cancer immunotherapy. In this review we discuss the ability of oncolytic viruses to alter the immunogenic milieu of the tumor microenvironment, and the role of innate and adaptive immunity in both restricting and augmenting therapy. Strategies to improve virotherapy by immunomodulation, including suppression or enhancement of the innate and adaptive responses, are discussed.

Inhibition of human tumor growth in mice by an oncolytic herpes simplex virus designed to target solely HER-2-positive cells

Oncolytic virotherapy exploits the ability of viruses to infect, replicate into, and kill tumor cells. Among the viruses that entered clinical trials are HSVs. HSVs can be engineered to become tumor-specific by deletion of selected genes or retargeting to tumor-specific receptors. A clinically relevant surface molecule is HER-2, hyperexpressed in one fourth of mammary and ovary carcinomas, and associated with high metastatic ability. As a previously undescribed strategy to generate HSV recombinants retargeted to HER-2 and detargeted from natural receptors, we replaced the Ig-folded core in the receptor-binding virion glycoprotein gD with anti-HER-2 single-chain antibody. The recombinant entered cells solely via HER-2 and lysed HER-2-positive cancer cells. Because of the high specificity, its safety profile in i.p. injected mice was very high, with a LD(50) >5 x 10(8) pfu, a figure at least 10,000-fold higher than that of corresponding WT-gD carrying virus (LD(50) approximately 5 x 10(4) pfu). When administered intratumorally to nude mice bearing HER-2-hyperexpressing human tumors, it strongly inhibited progressive tumor growth. The results provide a generally applicable strategy to engineer HSV recombinants retargeted to a wide range of receptors for which a single-chain antibody is available, and show the potential for retargeted HSV to exert target-specific inhibition of human tumor growth. Therapy with HER-2-retargeted oncolytic HSV could be effective in combined or sequential protocols with monoclonal antibodies and small inhibitors, particularly in patients resistant to HER-2-targeted therapy because of alterations in HER-2 signaling pathway, or against brain metastases inaccessible to anti-HER-2 antibodies.