Molecular Circuits of Immune Sensing and Response to Oncolytic Virotherapy.

Oncolytic virotherapy is a promising immunotherapy approach for cancer treatment that utilizes viruses to preferentially infect and eliminate cancer cells while stimulating the immune response. In this review, we synthesize the current literature on the molecular circuits of immune sensing and response to oncolytic virotherapy, focusing on viral DNA or RNA sensing by infected cells, cytokine and danger-associated-signal sensing by neighboring cells, and the subsequent downstream activation of immune pathways. These sequential sense-and-response mechanisms involve the triggering of molecular sensors by viruses or infected cells to activate transcription factors and related genes for a breadth of immune responses. We describe how the molecular signals induced in the tumor upon virotherapy can trigger diverse immune signaling pathways, activating both antigen-presenting-cell-based innate and T cell-based adaptive immune responses. Insights into these complex mechanisms provide valuable knowledge for enhancing oncolytic virotherapy strategies.

Combination therapy with oncolytic virus and T cells or mRNA vaccine amplifies antitumor effects.

Antitumor therapies based on adoptively transferred T cells or oncolytic viruses have made significant progress in recent years, but the limited efficiency of their infiltration into solid tumors makes it difficult to achieve desired antitumor effects when used alone. In this study, an oncolytic virus (rVSV-LCMVG) that is not prone to induce virus-neutralizing antibodies was designed and combined with adoptively transferred T cells. By transforming the immunosuppressive tumor microenvironment into an immunosensitive one, in B16 tumor-bearing mice, combination therapy showed superior antitumor effects than monotherapy. This occurred whether the OV was administered intratumorally or intravenously. Combination therapy significantly increased cytokine and chemokine levels within tumors and recruited CD8+ T cells to the TME to trigger antitumor immune responses. Pretreatment with adoptively transferred T cells and subsequent oncolytic virotherapy sensitizes refractory tumors by boosting T-cell recruitment, down-regulating the expression of PD-1, and restoring effector T-cell function. To offer a combination therapy with greater translational value, mRNA vaccines were introduced to induce tumor-specific T cells instead of adoptively transferred T cells. The combination of OVs and mRNA vaccine also displays a significant reduction in tumor burden and prolonged survival. This study proposed a rational combination therapy of OVs with adoptive T-cell transfer or mRNA vaccines encoding tumor-associated antigens, in terms of synergistic efficacy and mechanism.

Patient-derived tumoroids and proteomic signatures: tools for early drug discovery.

Onco-virotherapy is an emergent treatment for cancer based on viral vectors. The therapeutic activity is based on two different mechanisms including tumor-specific oncolysis and immunostimulatory properties. In this study, we evaluated onco-virotherapy in vitro responses on immunocompetent non-small cell lung cancer (NSCLC) patient-derived tumoroids (PDTs) and healthy organoids. PDTs are accurate tools to predict patient's clinical responses at the in vitro stage. We showed that onco-virotherapy could exert specific antitumoral effects by producing a higher number of viral particles in PDTs than in healthy organoids. In the present work, we used multiplex protein screening, based on proximity extension assay to highlight different response profiles. Our results pointed to the increase of proteins implied in T cell activation, such as IFN-γ following onco-virotherapy treatment. Based on our observation, oncolytic viruses-based therapy responders are dependent on several factors: a high PD-L1 expression, which is a biomarker of greater immune response under immunotherapies, and the number of viral particles present in tumor tissue, which is dependent to the metabolic state of tumoral cells. Herein, we highlight the use of PDTs as an alternative in vitro model to assess patient-specific responses to onco-virotherapy at the early stage of the preclinical phases.

Fn-OMV potentiates ZBP1-mediated PANoptosis triggered by oncolytic HSV-1 to fuel antitumor immunity.

Oncolytic viruses (OVs) show promise as a cancer treatment by selectively replicating in tumor cells and promoting antitumor immunity. However, the current immunogenicity induced by OVs for tumor treatment is relatively weak, necessitating a thorough investigation of the mechanisms underlying its induction of antitumor immunity. Here, we show that HSV-1-based OVs (oHSVs) trigger ZBP1-mediated PANoptosis (a unique innate immune inflammatory cell death modality), resulting in augmented antitumor immune effects. Mechanistically, oHSV enhances the expression of interferon-stimulated genes, leading to the accumulation of endogenous Z-RNA and subsequent activation of ZBP1. To further enhance the antitumor potential of oHSV, we conduct a screening and identify Fusobacterium nucleatum outer membrane vesicle (Fn-OMV) that can increase the expression of PANoptosis execution proteins. The combination of Fn-OMV and oHSV demonstrates potent antitumor immunogenicity. Taken together, our study provides a deeper understanding of oHSV-induced antitumor immunity, and demonstrates a promising strategy that combines oHSV with Fn-OMV.

Molecular insights and promise of oncolytic virus based immunotherapy.

Discovering a therapeutic that can counteract the aggressiveness of this disease's mechanism is crucial for improving survival rates for cancer patients and for better understanding the most different types of cancer. In recent years, using these viruses as an anticancer therapy has been thought to be successful. They mostly work by directly destroying cancer cells, activating the immune system to fight cancer, and expressing exogenous effector genes. For the treatment of tumors, oncolytic viruses (OVs), which can be modified to reproduce only in tumor tissues and lyse them while preserving the healthy non-neoplastic host cells and reinstating antitumor immunity which present a novel immunotherapeutic strategy. OVs can exist naturally or be created in a lab by altering existing viruses. These changes heralded the beginning of a new era of less harmful virus-based cancer therapy. We discuss three different types of oncolytic viruses that have already received regulatory approval to treat cancer as well as clinical research using oncolytic adenoviruses. The primary therapeutic applications, mechanism of action of oncolytic virus updates, future views of this therapy will be covered in this chapter.

Fusogenic vesicular stomatitis virus combined with natural killer T cell immunotherapy controls metastatic breast cancer.

BACKGROUND: Metastatic breast cancer is a leading cause of cancer death in woman. Current treatment options are often associated with adverse side effects and poor outcomes, demonstrating the need for effective new treatments. Immunotherapies can provide durable outcomes in many cancers; however, limited success has been achieved in metastatic triple negative breast cancer. We tested whether combining different immunotherapies can target metastatic triple negative breast cancer in pre-clinical models. METHODS: Using primary and metastatic 4T1 triple negative mammary carcinoma models, we examined the therapeutic effects of oncolytic vesicular stomatitis virus (VSVΔM51) engineered to express reovirus-derived fusion associated small transmembrane proteins p14 (VSV-p14) or p15 (VSV-p15). These viruses were delivered alone or in combination with natural killer T (NKT) cell activation therapy mediated by adoptive transfer of α-galactosylceramide-loaded dendritic cells. RESULTS: Treatment of primary 4T1 tumors with VSV-p14 or VSV-p15 alone increased immunogenic tumor cell death, attenuated tumor growth, and enhanced immune cell infiltration and activation compared to control oncolytic virus (VSV-GFP) treatments and untreated mice. When combined with NKT cell activation therapy, oncolytic VSV-p14 and VSV-p15 reduced metastatic lung burden to undetectable levels in all mice and generated immune memory as evidenced by enhanced in vitro recall responses (tumor killing and cytokine production) and impaired tumor growth upon rechallenge. CONCLUSION: Combining NKT cell immunotherapy with enhanced oncolytic virotherapy increased anti-tumor immune targeting of lung metastasis and presents a promising treatment strategy for metastatic breast cancer.

Clinical trial links oncolytic immunoactivation to survival in glioblastoma.

Immunotherapy failures can result from the highly suppressive tumour microenvironment that characterizes aggressive forms of cancer such as recurrent glioblastoma (rGBM)1,2. Here we report the results of a first-in-human phase I trial in 41 patients with rGBM who were injected with CAN-3110-an oncolytic herpes virus (oHSV)3. In contrast to other clinical oHSVs, CAN-3110 retains the viral neurovirulence ICP34.5 gene transcribed by a nestin promoter; nestin is overexpressed in GBM and other invasive tumours, but not in the adult brain or healthy differentiated tissue4. These modifications confer CAN-3110 with preferential tumour replication. No dose-limiting toxicities were encountered. Positive HSV1 serology was significantly associated with both improved survival and clearance of CAN-3110 from injected tumours. Survival after treatment, particularly in individuals seropositive for HSV1, was significantly associated with (1) changes in tumour/PBMC T cell counts and clonal diversity, (2) peripheral expansion/contraction of specific T cell clonotypes; and (3) tumour transcriptomic signatures of immune activation. These results provide human validation that intralesional oHSV treatment enhances anticancer immune responses even in immunosuppressive tumour microenvironments, particularly in individuals with cognate serology to the injected virus. This provides a biological rationale for use of this oncolytic modality in cancers that are otherwise unresponsive to immunotherapy (ClinicalTrials.gov: NCT03152318 ).

Oncolytic virotherapy as promising immunotherapy against cancer: mechanisms of resistance to oncolytic viruses.

Oncolytic virotherapy has currently emerged as a powerful therapeutic approach in cancer treatment. Although the history of using viruses goes back to the early 20th century, the approval of talimogene laherparepvec (T-VEC) in 2015 increased interest in oncolytic viruses (OVs). OVs are multifaceted biotherapeutic agents because they replicate in and kill tumor cells and augment immune responses by releasing immunostimulatory molecules from lysed cells. Despite promising results, some limitations hinder the efficacy of oncolytic virotherapy. The delivery challenges and the upregulation of checkpoints following oncolytic virotherapy also mediate resistance to OVs by diminishing immune responses. Furthermore, the localization of receptors of viruses in the tight junctions, interferon responses, and the aberrant expression of genes involved in the cell cycle of the virus, including their infection and replication, reduce the efficacy of OVs. In this review, we present different mechanisms of resistance to OVs and strategies to overcome them.

Lay abstract Using viruses in the treatment of cancer goes back to the early 20th century. One of the promising fields in cancer virotherapy is viruses' ability to preferentially lysis tumor cells, either naturally or genetically engineered cells; these viruses are termed 'oncolytic viruses.' As with other therapeutic strategies, resistance to the oncolytic viruses is the main challenge in their application in clinical trials. This review summarizes the mechanisms of resistance to oncolytic viruses and the strategies that have been used to overcome these challenges.

Antiviral Responses in Cancer: Boosting Antitumor Immunity Through Activation of Interferon Pathway in the Tumor Microenvironment.

In recent years, it became apparent that cancers either associated with viral infections or aberrantly expressing endogenous retroviral elements (EREs) are more immunogenic, exhibiting an intense intra-tumor immune cell infiltration characterized by a robust cytolytic apparatus. On the other hand, epigenetic regulation of EREs is crucial to maintain steady-state conditions and cell homeostasis. In line with this, epigenetic disruptions within steady-state cells can lead to cancer development and trigger the release of EREs into the cytoplasmic compartment. As such, detection of viral molecules by intracellular innate immune sensors leads to the production of type I and type III interferons that act to induce an antiviral state, thus restraining viral replication. This knowledge has recently gained momentum due to the possibility of triggering intratumoral activation of interferon responses, which could be used as an adjuvant to elicit strong anti-tumor immune responses that ultimately lead to a cascade of cytokine production. Accordingly, several therapeutic approaches are currently being tested using this rationale to improve responses to cancer immunotherapies. In this review, we discuss the immune mechanisms operating in viral infections, show evidence that exogenous viruses and endogenous retroviruses in cancer may enhance tumor immunogenicity, dissect the epigenetic control of EREs, and point to interferon pathway activation in the tumor milieu as a promising molecular predictive marker and immunotherapy target. Finally, we briefly discuss current strategies to modulate these responses within tumor tissues, including the clinical use of innate immune receptor agonists and DNA demethylating agents.

Oncolytic virotherapy as immunotherapy.

Recognizing immune responses to oncolytic virotherapy opens the way for new combinations.

Arenavirus Therapy in Combination with Checkpoint Blockade as an Effective Way for Better Tumour Clearance.

Viruses have been widely used to treat cancer for many years and they achieved tremendous success in clinical trials with outstanding results, which has led to the foundation of companies that develop recombinant viruses for a better tumor treatment. Even though there has been a great progress in the field of viral tumor immunotherapy, until now only one virus, the oncolytic virus talimogene laherparepvec (TVEC), a genetically modified herpes simplex virus type 1 (T-VEC), has been approved by the FDA for cancer treatment. Although oncolytic viruses showed progress in certain cancer types and patient populations but they have yet shown limited efficacy when it comes to solid tumors. Only recently it was demonstrated that the immune stimulatory aspect of oncolytic viruses can strongly contribute to their anti-tumoral activity. One specific example in this context are arenaviruses, which have been shown to be non-cytopathic in nature lead to the massive immune activation within the tumor resulting in strong anti-tumoral activity. This strong immune activation might be also linked to their noncytopathic features, as their immune stimulatory potential is not self-limiting as is the case for oncolytic viruses due to their fast eradication by anti-viral immune effects. Because of this strong immune activation, arenaviruses appear superior to oncolytic viruses when it comes to potent and long-lasting anti-tumor effects in a broad variety of tumor types. Currently one of the most promising therapeutics which has turned to be very much beneficial for the treatment of different cancer types is represented by antibodies targeting checkpoint inhibitors such as PD-1/PD-L-1. In this review, we will summarize anti-tumoral effects of arenaviruses, and will discuss their potential to be combined with checkpoint inhibitors for a more efficient tumor treatment, which further emphasizes that arenavirus therapy as a viroimmunotherapy can be an efficient tool for the better clearance of tumors.

Neoadjuvant talimogene laherparepvec plus surgery versus surgery alone for resectable stage IIIB-IVM1a melanoma: a randomized, open-label, phase 2 trial.

Talimogene laherparepvec (T-VEC) is a herpes simplex virus type 1-based intralesional oncolytic immunotherapy approved for the treatment of unresectable melanoma. The present, ongoing study aimed to estimate the treatment effect of neoadjuvant T-VEC on recurrence-free survival (RFS) of patients with advanced resectable melanoma. An open-label, phase 2 trial (NCT02211131) was conducted in 150 patients with resectable stage IIIB-IVM1a melanoma who were randomized to receive T-VEC followed by surgery (arm 1, n = 76) or surgery alone (arm 2, n = 74). The primary endpoint was a 2-year RFS in the intention-to-treat population. Secondary and exploratory endpoints included overall survival (OS), pathological complete response (pCR), safety and biomarker analyses. The 2-year RFS was 29.5% in arm 1 and 16.5% in arm 2 (overall hazard ratio (HR) = 0.75, 80% confidence interval (CI) = 0.58-0.96). The 2-year OS was 88.9% for arm 1 and 77.4% for arm 2 (overall HR = 0.49, 80% CI = 0.30-0.79). The RFS and OS differences between arms persisted at 3 years. In arm 1, 17.1% achieved a pCR. Increased CD8+ density correlated with clinical outcomes in an exploratory analysis. Arm 1 adverse events were consistent with previous reports for T-VEC. The present study met its primary endpoint and estimated a 25% reduction in the risk of disease recurrence for neoadjuvant T-VEC plus surgery versus upfront surgery for patients with resectable stage IIIB-IVM1a melanoma.

An oncolytic virus expressing a full-length antibody enhances antitumor innate immune response to glioblastoma.

Oncolytic herpes simplex virus-1 is capable of lysing tumor cells while alerting the immune system. CD47, in collaboration with SIRPα, represents an important immune checkpoint to inhibit phagocytosis by innate immune cells. Here we show locoregional control of glioblastoma by an oncolytic herpes virus expressing a full-length anti(α)-human CD47 IgG1 or IgG4 antibody. The antibodies secreted by the virus-infected glioblastoma cells block the CD47 'don't eat me' signal irrespective of the subclass; however, αCD47-IgG1 has a stronger tumor killing effect than αCD47-IgG4 due to additional antibody-dependent cellular phagocytosis by macrophages and antibody-dependent cellular cytotoxicity by NK cells. Intracranially injected αCD47-IgG1-producing virus continuously releases the respective antibody in the tumor microenvironment but not into systemic circulation; additionally, αCD47-IgG1-producing virus also improves the survival of tumor-bearing mice better than control oncolytic herpes virus combined with topical αCD47-IgG1. Results from immunocompetent mouse tumor models further confirm that macrophages, and to a lesser extent NK cells, mediate the anti-tumor cytotoxicity of antibody-producing oncolytic herpesviruses. Collectively, oncolytic herpes simplex virus-1 encoding full-length antibodies could improve immune-virotherapy for glioblastoma.

Concepts in Oncolytic Adenovirus Therapy.

Oncolytic adenovirus therapy is gaining importance as a novel treatment option for the management of various cancers. Different concepts of modification within the adenovirus vector have been identified that define the mode of action against and the interaction with the tumour. Adenoviral vectors allow for genetic manipulations that restrict tumour specificity and also the expression of specific transgenes in order to support the anti-tumour effect. Additionally, replication of the virus and reinfection of neighbouring tumour cells amplify the therapeutic effect. Another important aspect in oncolytic adenovirus therapy is the virus induced cell death which is a process that activates the immune system against the tumour. This review describes which elements in adenovirus vectors have been identified for modification not only to utilize oncolytic adenovirus vectors into conditionally replicating adenoviruses (CRAds) that allow replication specifically in tumour cells but also to confer specific characteristics to these viruses. These advances in development resulted in clinical trials that are summarized based on the conceptual design.

A phase 1b study of intraperitoneal oncolytic viral immunotherapy in platinum-resistant or refractory ovarian cancer.

OBJECTIVE: Our objective was to assess safety and adverse events associated with intraperitoneal Olvi-Vec virotherapy in patients with platinum-resistant or refractory ovarian cancer (PRROC). Secondary objectives included objective response rate (ORR) per RECIST 1.1 and progression-free survival (PFS). METHODS: Olvi-Vec is a modified vaccinia virus that causes oncolysis and immune activation. An open-label phase 1b trial using a 3 + 3 dose escalation was conducted. Intraperitoneal Olvi-Vec was given as monotherapy in two consecutive daily doses. Translational analyses included anti-virus antibody levels, viral shedding, circulating tumor cells (CTCs) and T cells. RESULTS: Twelve patients (median age: 69 years, range: 45-77) with median 5 prior therapies (range: 2-10) and 2 prior platinum lines (range: 1-5) were enrolled. There were three dose level cohorts: 3 × 109 (n = 6), 1 × 1010 (n = 5), and 2.5 × 1010 (n = 1) plaque forming units (PFU)/day on two consecutive days. Treatment-related adverse events (TRAEs) included G1/G2 nausea (n = 6), fever (n = 6), abdominal distention (n = 5), and abdominal pain (n = 4). There were no Grade 4 TRAEs, no dose relationship to TRAEs, and no deaths attributed to Olvi-Vec. The ORR was 9% (1/11). Stable disease (SD) was 64% (7/11), and SD ≥15 weeks was 46% (5/11). Median PFS was 15.7 weeks (95%CI: 5.7-34.5), including extended PFS in four patients (23.2, 34.5, 59.4+ and 70.8 weeks). Three patients had extended overall survival (deceased 33.6 months, and alive with disease at 54 and 59 months). CTCs diminished in 6/8 (75%) baseline-positive patients. Immune activation was demonstrated from virus-enhanced tumor infiltration of CD8+ T-cells and activation of tumor-specific T-cells in peripheral blood. CONCLUSIONS: Oncolytic viral therapy with intraperitoneal Olvi-Vec showed promising safety, clinical activities, and immune activation in patients with PRROC, warranting further clinical investigation.

Genotype of Immunologically Hot or Cold Tumors Determines the Antitumor Immune Response and Efficacy by Fully Virulent Retargeted oHSV.

We report on the efficacy of the non-attenuated HER2-retargeted oHSV named R-337 against the immunologically hot CT26-HER2 tumor, and an insight into the basis of the immune protection. Preliminarily, we conducted an RNA immune profiling and immune cell content characterization of CT26-HER2 tumor in comparison to the immunologically cold LLC1-HER2 tumor. CT26-HER2 tumor was implanted into HER2-transgenic BALB/c mice. Hallmarks of R-337 effects were the protection from primary tumor, long-term adaptive vaccination directed to both HER2 and CT26-wt cell neoantigens. The latter effect differentiated R-337 from OncoVEXGM-CSF. As to the basis of the immune protection, R-337 orchestrated several changes to the tumor immune profile, which cumulatively reversed the immunosuppression typical of this tumor (graphical abstract). Thus, Ido1 (inhibitor of T cell anticancer immunity) levels and T regulatory cell infiltration were decreased; Cd40 and Cd27 co-immunostimulatory markers were increased; the IFNγ cascade was activated. Of note was the dampening of IFN-I response, which we attribute to the fact that R-337 is fully equipped with genes that contrast the host innate response. The IFN-I shut-down likely favored viral replication and the expression of the mIL-12 payload, which, in turn, boosted the antitumor response. The results call for a characterization of tumor immune markers to employ oncolytic herpesviruses more precisely.

Current strategies for intratumoural immunotherapy - Beyond immune checkpoint inhibition.

Immunotherapy has revolutionised cancer treatment through restoration of host antitumour immune response. Immune checkpoint inhibitors (ICIs) confer durable responses in only a subset of patients. Mechanisms of ICI resistance to improve durable response rates and overall survival are an area of intense clinical research. Robust clinical development is ongoing to evaluate novel combination therapies to overcome ICI resistance, including targeting immunoregulatory pathways in the tumour microenvironment. Intratumoural (IT) immunotherapies such as toll-like receptor agonists, stimulator of interferon-induced gene agonists, retinoic-inducible gene I-like receptor agonists and oncolytic viruses may represent potential combination treatment options to overcome ICI resistance. Use of IT immunotherapies in combination with ICIs may alter the tumour microenvironment to address resistance mechanisms and improve antitumour response. Optimisation of IT immunotherapy clinical trials will elucidate resistance mechanisms, facilitate clinical trial design, define pharmacodynamic predictors that identify patients who may most benefit and inform clinical development of combination immunotherapy regimens. Here we provide an overview of IT immunotherapy principles, mechanisms of action, categories of IT immunotherapeutics, emerging data, clinical development strategies, response assessment, dose and schedule determination, clinical trial design and translational study design.

A modular self-adjuvanting cancer vaccine combined with an oncolytic vaccine induces potent antitumor immunity.

Functional tumor-specific cytotoxic T cells elicited by therapeutic cancer vaccination in combination with oncolytic viruses offer opportunities to address resistance to checkpoint blockade therapy. Two cancer vaccines, the self-adjuvanting protein vaccine KISIMA, and the recombinant oncolytic vesicular stomatitis virus pseudotyped with LCMV-GP expressing tumor-associated antigens, termed VSV-GP-TAA, both show promise as a single agent. Here we find that, when given in a heterologous prime-boost regimen with an optimized schedule and route of administration, combining KISIMA and VSV-GP-TAA vaccinations induces better cancer immunity than individually. Using several mouse tumor models with varying degrees of susceptibility for viral replication, we find that priming with KISIMA-TAA followed by VSV-GP-TAA boost causes profound changes in the tumor microenvironment, and induces a large pool of poly-functional and persistent antigen-specific cytotoxic T cells in the periphery. Combining this heterologous vaccination with checkpoint blockade further improves therapeutic efficacy with long-term survival in the spectrum. Overall, heterologous vaccination with KISIMA and VSV-GP-TAA could sensitize non-inflamed tumors to checkpoint blockade therapy.

Novel oncolytic adenovirus expressing enhanced cross-hybrid IgGA Fc PD-L1 inhibitor activates multiple immune effector populations leading to enhanced tumor killing in vitro, in vivo and with patient-derived tumor organoids.

BACKGROUND: Despite the success of immune checkpoint inhibitors against PD-L1 in the clinic, only a fraction of patients benefit from such therapy. A theoretical strategy to increase efficacy would be to arm such antibodies with Fc-mediated effector mechanisms. However, these effector mechanisms are inhibited or reduced due to toxicity issues since PD-L1 is not confined to the tumor and also expressed on healthy cells. To increase efficacy while minimizing toxicity, we designed an oncolytic adenovirus that secretes a cross-hybrid Fc-fusion peptide against PD-L1 able to elicit effector mechanisms of an IgG1 and also IgA1 consequently activating neutrophils, a population neglected by IgG1, in order to combine multiple effector mechanisms. METHODS: The cross-hybrid Fc-fusion peptide comprises of an Fc with the constant domains of an IgA1 and IgG1 which is connected to a PD-1 ectodomain via a GGGS linker and was cloned into an oncolytic adenovirus. We demonstrated that the oncolytic adenovirus was able to secrete the cross-hybrid Fc-fusion peptide able to bind to PD-L1 and activate multiple immune components enhancing tumor cytotoxicity in various cancer cell lines, in vivo and ex vivo renal-cell carcinoma patient-derived organoids. RESULTS: Using various techniques to measure cytotoxicity, the cross-hybrid Fc-fusion peptide expressed by the oncolytic adenovirus was shown to activate Fc-effector mechanisms of an IgA1 (neutrophil activation) as well as of an IgG1 (natural killer and complement activation). The activation of multiple effector mechanism simultaneously led to significantly increased tumor killing compared with FDA-approved PD-L1 checkpoint inhibitor (Atezolizumab), IgG1-PDL1 and IgA-PDL1 in various in vitro cell lines, in vivo models and ex vivo renal cell carcinoma organoids. Moreover, in vivo data demonstrated that Ad-Cab did not require CD8+ T cells, unlike conventional checkpoint inhibitors, since it was able to activate other effector populations. CONCLUSION: Arming PD-L1 checkpoint inhibitors with Fc-effector mechanisms of both an IgA1 and an IgG1 can increase efficacy while maintaining safety by limiting expression to the tumor using oncolytic adenovirus. The increase in tumor killing is mostly attributed to the activation of multiple effector populations rather than activating a single effector population leading to significantly higher tumor killing.

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.