Albumin-binding adenoviruses circumvent pre-existing neutralizing antibodies upon systemic delivery

The Immune System-A Double-Edged Sword for Adenovirus-Based Therapies

Pathogenic adenovirus (Ad) infections are widespread but typically mild and transient, except in the immunocompromised. As vectors for gene therapy, vaccine, and oncology applications, Ad-based platforms offer advantages, including ease of genetic manipulation, scale of production, and well-established safety profiles, making them attractive tools for therapeutic development. However, the immune system often poses a significant challenge that must be overcome for adenovirus-based therapies to be truly efficacious. Both pre-existing anti-Ad immunity in the population as well as the rapid development of an immune response against engineered adenoviral vectors can have detrimental effects on the downstream impact of an adenovirus-based therapeutic. This review focuses on the different challenges posed, including pre-existing natural immunity and anti-vector immunity induced by a therapeutic, in the context of innate and adaptive immune responses. We summarise different approaches developed with the aim of tackling these problems, as well as their outcomes and potential future applications.

Nanotechnology and nano-sized tools: Newer approaches to circumvent oncolytic adenovirus limitations

Oncolytic adenoviruses (OAds), engineered Ads preferentially infect and lyse tumor cells, have attracted remarkable attention as immunotherapy weapons for the treatment of various malignancies. Despite hopeful successes in preclinical investigations and translation into clinical phases, they face some challenges that thwart their therapeutic effectiveness, including low infectivity of cancer cells, liver sequestration, pre-existing neutralizing antibodies, physical barriers to the spread of Ads, and immunosuppressive TME. Nanotechnology and nano-sized tools provide several advantages to overcome these limitations of OAds. Nano-sized tools could improve the therapeutic efficacy of OAds by enhancing infectivity and cellular uptake, targeting and protecting from pre-existing immune responses, masking and preventing liver tropism, and co-delivery with other therapeutic agents. Herein, we reviewed the constructs of various OAds and their application in clinical trials, as well as the limitations they have faced. Furthermore, we emphasized the potential applications of nanotechnology to solve the constraints of OAds to improve their anti-tumor activities.

Oncolytic Virotherapy: A New Paradigm in Cancer Immunotherapy

Oncolytic viruses (OVs) are emerging as potential treatment options for cancer. Natural and genetically engineered viruses exhibit various antitumor mechanisms. OVs act by direct cytolysis, the potentiation of the immune system through antigen release, and the activation of inflammatory responses or indirectly by interference with different types of elements in the tumor microenvironment, modification of energy metabolism in tumor cells, and antiangiogenic action. The action of OVs is pleiotropic, and they show varied interactions with the host and tumor cells. An important impediment in oncolytic virotherapy is the journey of the virus into the tumor cells and the possibility of its binding to different biological and nonbiological vectors. OVs have been demonstrated to eliminate cancer cells that are resistant to standard treatments in many clinical trials for various cancers (melanoma, lung, and hepatic); however, there are several elements of resistance to the action of viruses per se. Therefore, it is necessary to evaluate the combination of OVs with other standard treatment modalities, such as chemotherapy, immunotherapy, targeted therapies, and cellular therapies, to increase the response rate. This review provides a comprehensive update on OVs, their use in oncolytic virotherapy, and the future prospects of this therapy alongside the standard therapies currently used in cancer treatment.

Oncolytic Virus Engineering and Utilizations: Cancer Immunotherapy Perspective

Oncolytic viruses have positively impacted cancer immunotherapy over the past 20 years. Both natural and genetically modified viruses have shown promising results in treating various cancers. Various regulatory authorities worldwide have approved four commercial oncolytic viruses, and more are being developed to overcome this limitation and obtain better anti-tumor responses in clinical trials at various stages. Faster advancements in translating research into the commercialization of cancer immunotherapy and a comprehensive understanding of the modification strategies will widen the current knowledge of future technologies related to the development of oncolytic viruses. In this review, we discuss the strategies of virus engineering and the progress of clinical trials to achieve virotherapeutics.

Oncolytic viruses in hematological malignancies: hijacking disease biology and fostering new promises for immune and cell-based therapies

The increased tropism for malignant cells of some viruses has been highlighted in recent studies, prompting their use as a strategy to modify the transcriptional profile of those cells, while sparing the healthy ones. Likewise, they have been recognized as players modulating microenvironmental immunity, namely through an increase in antigen-presenting, natural-killer, and T CD8+ cytotoxic cells by a cross-priming mechanism elicited by tumor-associated antigens. The immunomodulatory role of the oncolytic virus seems relevant in hematological malignancies, which may relapse as a result of a proliferative burst elicited by an external stimulus in progenitor or neoplastic stem cells. By reprogramming the host cells and the surrounding environment, the potential of virotherapy ranges from the promise to eradicate the minimal measurable disease (in acute leukemia, for example), to the ex vivo purging of malignant progenitor cells in the setting of autologous bone marrow transplantation. In this review, we analyze the recent advances in virotherapy in hematological malignancies, either when administered alone or together with chemotherapeutic agents or other immunomodulators.

Oncolytic Virus-Driven Biotherapies from Bench to Bedside

With advances in cancer biology and an ever-deepening understanding of molecular virology, oncolytic virus (OV)-driven therapies have developed rapidly and become a promising alternative to traditional cancer therapies. In recent years, satisfactory results for oncolytic virus therapy (OVT) are achieved at both the cellular and organismal levels, and efforts are being increasingly directed toward clinical trials. Unfortunately, OVT remains ineffective in these trials, especially when performed using only a single OV reagent. In contrast, integrated approaches, such as using immunotherapy, chemotherapy, or radiotherapy, alongside OVT have demonstrated considerable efficacy. The challenges of OVT in clinical efficacy include the restricted scope of intratumoral injections and poor targeting of intravenous administration. Further optimization of OVT delivery is needed before OVs become a viable therapy for tumor treatment. In this review, the development process and antitumor mechanisms of OVs are introduced. The advances in OVT delivery routes to provide perspectives and directions for the improvement of OVT delivery are highlighted. This review also discusses the advantages and limitations of OVT monotherapy and combination therapy through the lens of recent clinical trials and aims to chart a course toward safer and more effective OVT strategies.

Preexisting immunity: Barrier or bridge to effective oncolytic virus therapy?

Oncolytic viruses (OVs) represent a highly promising treatment strategy for a wide range of cancers, by mediating both the direct killing of tumor cells as well as mobilization of antitumor immune responses. As many OVs circulate in the human population, preexisting OV-specific immune responses are prevalent. Indeed, neutralizing antibodies (NAbs) are abundantly present in the human population for commonly used OVs, such as Adenovirus type 5 (Ad5), Herpes Simplex Virus-1 (HSV-1), Vaccinia virus, Measles virus, and Reovirus. This review discusses (pre)clinical evidence regarding the effect of preexisting immunity against OVs on two distinct aspects of OV therapy; OV infection and spread, as well as the immune response induced upon OV therapy. Combined, this review provides evidence that consideration of preexisting immunity is crucial in realizing the full potential of the highly promising therapeutic implementation of OVs. Future investigation of current gaps in knowledge highlighted in this review should yield a more complete understanding of this topic, ultimately allowing for better and more personalized OV therapies.

A versatile toolkit for overcoming AAV immunity

Recombinant adeno-associated virus (AAV) is a promising delivery vehicle for in vivo gene therapy and has been widely used in >200 clinical trials globally. There are already several approved gene therapy products, e.g., Luxturna and Zolgensma, highlighting the remarkable potential of AAV delivery. In the past, AAV has been seen as a relatively non-immunogenic vector associated with low risk of toxicity. However, an increasing number of recent studies indicate that immune responses against AAV and transgene products could be the bottleneck of AAV gene therapy. In clinical studies, pre-existing antibodies against AAV capsids exclude many patients from receiving the treatment as there is high prevalence of antibodies among humans. Moreover, immune response could lead to loss of efficacy over time and severe toxicity, manifested as liver enzyme elevations, kidney injury, and thrombocytopenia, resulting in deaths of non-human primates and patients. Therefore, extensive efforts have been attempted to address these issues, including capsid engineering, plasmapheresis, IgG proteases, CpG depletion, empty capsid decoy, exosome encapsulation, capsid variant switch, induction of regulatory T cells, and immunosuppressants. This review will discuss these methods in detail and highlight important milestones along the way.

An Optimized CRISPR/Cas9 Adenovirus Vector (AdZ-CRISPR) for High-Throughput Cloning of sgRNA, Using Enhanced sgRNA and Cas9 Variants

Recombinant adenovirus vectors enable highly efficient gene delivery in vitro and in vivo. As a result, they are widely used in gene therapy, vaccination, and anticancer applications. We have previously developed the AdZ vector system, which uses recombineering to permit high-throughput cloning of transgenes into Adenovirus vectors, simplifies alteration of the vector backbone, and enables rapid recovery of infectious virus, even if a transgene is incompatible with vector replication. In this study, we adapt this vector system to enable high-throughput cloning of sequences for CRISPR/Cas9 editing. Vectors were optimized to ensure efficient cloning, and high editing efficiency using spCas9 and single guide RNA (sgRNA) sequences in a single vector. Using a multiplicity of infection of 50, knockout efficiencies of up to 80% could be achieved with a single sgRNA. Vectors were further enhanced by altering the spCas9 sequence to match that of SniperCas9, which has reduced off-target activity, but maintains on-target efficiency, and by applying modifications to the sgRNA sequence that significantly enhance editing efficiency. Thus, the AdZ-CRISPR vectors offer highly efficient knockout, even in hard to transfect cells, and enables large-scale CRISPR/Cas9 projects to be undertaken easily and quickly.

Emerging systemic delivery strategies of oncolytic viruses: A key step toward cancer immunotherapy

Oncolytic virotherapy (OVT) is a novel type of immunotherapy that induces anti-tumor responses through selective self-replication within cancer cells and oncolytic virus (OV)-mediated immunostimulation. Notably, talimogene laherparepvec (T-Vec) developed by the Amgen company in 2015, is the first FDA-approved OV product to be administered via intratumoral injection and has been the most successful OVT treatment. However, the systemic administration of OVs still faces huge challenges, including in vivo pre-existing neutralizing antibodies and poor targeting delivery efficacy. Recently, state-of-the-art progress has been made in the development of systemic delivery of OVs, which demonstrates a promising step toward broadening the scope of cancer immunotherapy and improving the clinical efficacy of OV delivery. Herein, this review describes the general characteristics of OVs, focusing on the action mechanisms of OVs as well as the advantages and disadvantages of OVT. The emerging multiple systemic administration approaches of OVs are summarized in the past five years. In addition, the combination treatments between OVT and traditional therapies (chemotherapy, thermotherapy, immunotherapy, and radiotherapy, etc.) are highlighted. Last but not least, the future prospects and challenges of OVT are also discussed, with the aim of facilitating medical researchers to extensively apply the OVT in the cancer therapy.

Coating an adenovirus with functionalized gold nanoparticles favors uptake, intracellular trafficking and anti-cancer therapeutic efficacy

Adenoviral (Ad) vectors have proven to be important tools for gene and cell therapy, although some issues still need to be addressed, such as undesired interactions with blood components and off-target sequestration that ultimately hamper efficacy. In the past years, several organic and inorganic materials have been developed to reduce immunogenicity and improve biodistribution of Ad vectors. Here we investigated the influence of the functionalization of 14 nm PEGylated gold nanoparticles (AuNPs) with quaternary ammonium groups and an arginine-glycine-aspartic acid (RGD)-motif on the uptake and biodistribution of Ad vectors. We report the formation of Ad@AuNPs complexes that promote cell attachment and uptake, independently of the presence of the coxsackievirus and adenovirus receptor (CAR) and α_vβ₃ and α_vβ₅ integrins, significantly improving transduction without limiting Ad bioactivity. Besides, the presence of the RGD peptide favors tumor targeting and decreases Ad sequestration in the liver. Additionally, tumor delivery of a coated Ad vector expressing the human sodium iodide symporter (hNIS) by mesenchymal stem cells induces increased accumulation of radioactive iodine (¹³¹I) and tumor volume reduction compared to naked Ad-hNIS, highlighting the promising potential of our coating formulation in cancer gene therapy. STATEMENT OF SIGNIFICANCE: Modification of adenoviral vectors with lipids and polymers can reduce interactions with blood components and increase tumor accumulation; however, increased toxicity and reduced transduction efficiency were indicated. Coating with gold nanoparticles has proven to be a successful strategy for increasing the efficiency of transduction of receptor-defective cell lines. Here we explore the contribution of cell surface receptors on the mechanisms of entry of Ad vectors coated with gold nanoparticles in cell lines with varying degrees of resistance to infection. The enhancement of the anti-tumoral effect shown in this work provides new evidence for the potential of our formulation.

Synthetic Biology Approaches for Engineering Next-Generation Adenoviral Gene Therapies

Synthetic biology centers on the design and modular assembly of biological parts so as to construct artificial biological systems. Over the past decade, synthetic biology has blossomed into a highly productive field, yielding advances in diverse areas such as neuroscience, cell-based therapies, and chemical manufacturing. Similarly, the field of gene therapy has made enormous strides both in proof-of-concept studies and in the clinical setting. One viral vector of increasing interest for gene therapy is the adenovirus (Ad). A major part of the Ad's increasing momentum comes from synthetic biology approaches to Ad engineering. Convergence of gene therapy and synthetic biology has enhanced Ad vectors by mitigating Ad toxicity in vivo, providing precise Ad tropisms, and incorporating genetic circuits to make smart therapies which adapt to environmental stimuli. Synthetic biology engineering of Ad vectors may lead to superior gene delivery and editing platforms which could find applications in a wide range of therapeutic contexts.

An Albumin-Binding Domain Peptide Confers Enhanced Immunoprotection Against Viral Myocarditis by CVB3 VP1 Vaccine

Coxsackievirus B3 (CVB3)-induced viral myocarditis is a common clinical cardiovascular disease without effective available vaccine. In this study, we tried to potentiate the immunoprotection efficacy of our previous CVB3-specific VP1 protein vaccine by introducing a streptococcal protein G-derived, draining lymph nodes (dLNs)-targeting albumin-binding domain (ABD) peptide. We found that compared with the original VP1 vaccine, ABD-fused VP1 (ABD-VP1) vaccine gained the new ability to efficiently bind murine albumin both in vitro and in vivo, possessed a much longer serum half-life in serum and exhibited more abundance in the dLNs after immunization. Accordingly, ABD-VP1 immunization not only significantly facilitated the enrichment and maturation of dendritic cells (DCs), induced higher percentages of IFN-γ+ CD8 + cells in the dLNs, but also robustly promoted VP1-induced T cell proliferation and cytotoxic T lymphocyte (CTL) responses in the spleens. More importantly, ABD-VP1 also elicited higher percentages of protective CD44hi CD62Lhi memory T cells in dLNs and spleens. Consequently, obvious protective effect against viral myocarditis was conferred by ABD-VP1 vaccine compared to the VP1 vaccine, reflected by the less body weight loss, improved cardiac function, alleviated cardiac histomorphological changes and an increased 28-day survival rate. Our results indicated that the ABD might be a promising immune-enhancing regime for vaccine design and development.

Adenoviral vector vaccine platforms in the SARS-CoV-2 pandemic

Adenoviral vectors have been explored as vaccine agents for a range of infectious diseases, and their ability to induce a potent and balanced immune response made them logical candidates to apply to the COVID-19 pandemic. The unique molecular characteristics of these vectors enabled the rapid development of vaccines with advanced designs capable of overcoming the biological challenges faced by early adenoviral vector systems. These successes and the urgency of the COVID-19 situation have resulted in a flurry of candidate adenoviral vector vaccines for COVID-19 from both academia and industry. These vaccines represent some of the lead candidates currently supported by Operation Warp Speed and other government agencies for rapid translational development. This review details adenoviral vector COVID-19 vaccines currently in human clinical trials and provides an overview of the new technologies employed in their design. As these vaccines have formed a cornerstone of the COVID-19 global vaccination campaign, this review provides a full consideration of the impact and development of this emerging platform.

Genetic and Chemical Capsid Modifications of Adenovirus Vectors to Modulate Vector-Host Interactions

Adenovirus-based vectors are playing an important role as efficacious genetic vaccines to fight the current COVID-19 pandemic. Furthermore, they have an enormous potential as oncolytic vectors for virotherapy and as vectors for classic gene therapy. However, numerous vector-host interactions on a cellular and noncellular level, including specific components of the immune system, must be modulated in order to generate safe and efficacious vectors for virotherapy or classic gene therapy. Importantly, the current widespread use of Ad vectors as vaccines against COVID-19 will induce antivector immunity in many humans. This requires the development of strategies and techniques to enable Ad-based vectors to evade pre-existing immunity. In this review article, we discuss the current status of genetic and chemical capsid modifications as means to modulate the vector-host interactions of Ad-based vectors.

Polymer stealthing and mucin-1 retargeting for enhanced pharmacokinetics of an oncolytic vaccinia virus

Vaccinia virus (VV) is a powerful tool for cancer treatment with the potential for tumor tropism, efficient cell-to-cell spread, rapid replication in cancer cells, and stimulation of anti-tumor immunity. It has a well-defined safety profile and is being assessed in late-stage clinical trials. However, VV clinical utility is limited by rapid bloodstream neutralization and poor penetration into tumors. These factors have often restricted its route of delivery to intratumoral or intrahepatic artery injection and may impede repeat dosing. Chemical stealthing improves the pharmacokinetics of non-enveloped viruses, but it has not yet been applied to enveloped viruses such as VV. In the present study, amphiphilic polymer was used to coat VV, leading to reduced binding of a neutralizing anti-VV antibody (81.8% of polymer-coated VV [PCVV] staining positive versus 97.1% of VV [p = 0.0038]). Attachment of anti-mucin-1 (aMUC1) targeting antibody, to give aMUC1-PCVV, enabled binding of the construct to MUC1. In high MUC1 expressing CAPAN-2 cells, infection with PCVV was reduced compared to VV, while infection was restored with aMUC1-PCVV. Pharmacokinetics of aMUC1-PCVV, PCVV, and VV were evaluated. After intravenous (i.v.) injection of 1 × 108 viral genomes (VG) or 5 × 108 VG, circulation time for PCVV and aMUC1-PCVV was increased, with ~5-fold higher circulating dose at 5 min versus VV.

Evolving Status of Clinical Immunotherapy with Oncolytic Adenovirus

Cancer immunotherapy targeting immune checkpoint inhibitors shows efficacy in several human cancers, but "cold tumors" that lack immune cells are typically unresponsive. Among the potential therapeutic approaches that could "heat" or promote lymphocyte infiltration of cold tumors, oncolytic viruses have attracted interest for their lytic and immunogenic mechanisms of action. In this article, we review the use of oncolytic adenoviruses in cancer immunotherapy, with a particular focus on preclinical and clinical data of oncolytic adenovirus-triggered immune responses against tumor antigens. We also discuss parameters to consider in clinical trial design and the combination of oncolytic adenoviruses with conventional treatments or other immunotherapies.

Oncolytic adenovirus with hyaluronidase activity that evades neutralizing antibodies: VCN-11

Tumor targeting and intratumoral virus spreading are key features for successful oncolytic virotherapy. VCN-11 is a novel oncolytic adenovirus, genetically modified to express hyaluronidase (PH20) and display an albumin-binding domain (ABD) on the hexon. ABD allows the virus to self-coat with albumin when entering the bloodstream and evade neutralizing antibodies (NAbs). Here, we validate VCN-11 mechanism of action and characterize its toxicity. VCN-11 replication, hyaluronidase activity and binding to human albumin to evade NAbs was evaluated. Toxicity and efficacy of VCN-11 were assessed in mice and hamsters. Tumor targeting, and antitumor activity was analyzed in the presence of NAbs in several tumor models. VCN-11 induced 450 times more cytotoxicity in tumor cells than in normal cells. VCN-11 hyaluronidase production was confirmed by measuring PH20 activity in vitro and in virus-infected tumor areas in vivo. VCN-11 evaded NAbs from different sources and tumor targeting was demonstrated in the presence of high levels of NAbs in vivo, whereas the control virus without ABD was neutralized. VCN-11 showed a low toxicity profile in athymic nude mice and Syrian hamsters, allowing treatments with high doses and fractionated administrations without major toxicities (up to 1.2x10¹¹vp/mouse and 7.5x10¹¹vp/hamster). Fractionated intravenous administrations improved circulation kinetics and tumor targeting. VCN-11 antitumor efficacy was demonstrated in the presence of NAbs against Ad5 and itself. Oncolytic adenovirus VCN-11 disrupts tumor matrix and displays antitumor effects even in the presence of NAbs. These features make VCN-11 a safe promising candidate to test re-administration in clinical trials.

Structure-Based Modeling of Complement C4 Mediated Neutralization of Adenovirus

Adenovirus (AdV) infection elicits a strong immune response with the production of neutralizing antibodies and opsonization by complement and coagulation factors. One anti-hexon neutralizing antibody, called 9C12, is known to activate the complement cascade, resulting in the deposition of complement component C4b on the capsid, and the neutralization of the virus. The mechanism of AdV neutralization by C4b is independent of downstream complement proteins and involves the blockage of the release of protein VI, which is required for viral escape from the endosome. To investigate the structural basis underlying how C4b blocks the uncoating of AdV, we built a model for the complex of human adenovirus type-5 (HAdV5) with 9C12, together with complement components C1 and C4b. This model positions C4b near the Arg-Gly-Asp (RGD) loops of the penton base. There are multiple amino acids in the RGD loop that might serve as covalent binding sites for the reactive thioester of C4b. Molecular dynamics simulations with a multimeric penton base and C4b indicated that stabilizing interactions may form between C4b and multiple RGD loops. We propose that C4b deposition on one RGD loop leads to the entanglement of C4b with additional RGD loops on the same penton base multimer and that this entanglement blocks AdV uncoating.

Adenoviral vectors for in vivo delivery of CRISPR-Cas gene editors

Harnessing the bacterial clustered regularly interspaced short palindromic repeats (CRISPR) system for genome editing in eukaryotes has revolutionized basic biomedical research and translational sciences. The ability to create targeted alterations of the genome through this easy to design system has presented unprecedented opportunities to treat inherited disorders and other diseases such as cancer through gene therapy. A major hurdle is the lack of an efficient and safe in vivo delivery system, limiting most of the current gene therapy efforts to ex vivo editing of extracted cells. Here we discuss the unique features of adenoviral vectors that enable tissue specific and efficient delivery of the CRISPR-Cas machinery for in vivo genome editing.

Retargeting adenoviruses for therapeutic applications and vaccines

Adenoviruses (Ads) are robust vectors for therapeutic applications and vaccines, but their use can be limited by differences in their in vitro and in vivo pharmacologies. This review emphasizes that there is not just one Ad, but a whole virome of diverse viruses that can be used as therapeutics. It discusses that true vector targeting involves not only retargeting viruses, but importantly also detargeting the viruses from off-target cells.

Oligopeptide-modified poly(beta-amino ester)s-coated AdNuPARmE1A: Boosting the efficacy of intravenously administered therapeutic adenoviruses

Oncolytic adenoviruses are used as agents for the treatment of cancer. However, their potential is limited due to the high seroprevalence of anti-adenovirus neutralizing antibodies (nAbs) within the population and the rapid liver sequestration when systemically administered. To overcome these challenges, we explored using nanoparticle formulation to boost the efficacy of systemic oncolytic adenovirus administration.

Methods: Adenovirus were conjugated with PEGylated oligopeptide-modified poly(β-amino ester)s (OM-pBAEs). The resulting coated viral formulation was characterized in terms of surface charge, size, aggregation state and morphology and tested for anti-adenovirus nAbs evasion and activity in cancer cells. In vivo pharmacokinetics, biodistribution, tumor targeting, and immunogenicity studies were performed. The antitumor efficacy of the oncolytic adenovirus AdNuPARmE1A coated with OM-pBAEs (SAG101) in the presence of nAbs was evaluated in pancreatic ductal adenocarcinoma (PDAC) mouse models. Toxicity of the coated formulation was analyzed in vivo in immunocompetent mice.

Results: OM-pBAEs conjugated to adenovirus and generated discrete nanoparticles with a neutral charge and an optimal size. The polymeric coating with the reporter AdGFPLuc (CPEG) showed enhanced transduction and evasion of antibody neutralization in vitro. Moreover, systemic intravenous administration of the formulation showed improved blood circulation and reduced liver sequestration, substantially avoiding activation of nAb production. OM-pBAEs coating of the oncolytic adenovirus AdNuPARmE1A (SAG101) improved its oncolytic activity in vitro and enhanced antitumor efficacy in PDAC mouse models. The coated formulation protected virions from neutralization by nAbs, as antitumor efficacy was preserved in their presence but was completely lost in mice that received the non-formulated AdNuPARmE1A. Finally, coated-AdNuPARmE1A showed reduced toxicity when high doses of the formulation were administered.

Conclusions: The developed technology represents a promising improvement for future clinical cancer therapy using oncolytic adenoviruses.

Artificially cloaked viral nanovaccine for cancer immunotherapy

Virus-based cancer vaccines are nowadays considered an interesting approach in the field of cancer immunotherapy, despite the observation that the majority of the immune responses they elicit are against the virus and not against the tumor. In contrast, targeting tumor associated antigens is effective, however the identification of these antigens remains challenging. Here, we describe ExtraCRAd, a multi-vaccination strategy focused on an oncolytic virus artificially wrapped with tumor cancer membranes carrying tumor antigens. We demonstrate that ExtraCRAd displays increased infectivity and oncolytic effect in vitro and in vivo. We show that this nanoparticle platform controls the growth of aggressive melanoma and lung tumors in vivo both in preventive and therapeutic setting, creating a highly specific anti-cancer immune response. In conclusion, ExtraCRAd might serve as the next generation of personalized cancer vaccines with enhanced features over standard vaccination regimens, representing an alternative way to target cancer.

Cancer therapy using oncolytic virus has shown pre-clinical and clinical efficacy. Here, the authors report ExtraCRAd, an oncolytic virus cloaked with tumour cell membrane and report its therapeutic effects in vitro and in vivo in multiple mouse tumour models.

Innate immunity to adenovirus: lessons from mice

Adenovirus is a highly evolutionary successful pathogen, as it is widely prevalent across the animal kingdom, infecting hosts ranging from lizards and frogs to dolphins, birds, and humans. Although natural adenovirus infections in humans rarely cause severe pathology, intravenous injection of high doses of adenovirus-based vectors triggers rapid activation of the innate immune system, leading to cytokine storm syndrome, disseminated intravascular coagulation, thrombocytopenia, and hepatotoxicity, which individually or in combination may cause morbidity and mortality. Much of the information on exactly how adenovirus activates the innate immune system has been gathered from mouse experimental systems. Intravenous administration of adenovirus to mice revealed mechanistic insights into cellular and molecular components of the innate immunity that detect adenovirus particles, activate pro-inflammatory signaling pathways and cytokine production, sequester adenovirus particles from the bloodstream, and eliminate adenovirus-infected cells. Collectively, this information greatly improved our understanding of mechanisms of activation of innate immunity to adenovirus and may pave the way for designing safer adenovirus-based vectors for therapy of genetic and acquired human diseases.

Targeting the tumor stroma with an oncolytic adenovirus secreting a fibroblast activation protein-targeted bispecific T-cell engager

BACKGROUND

Oncolytic virus (OV)-based therapies have an emerging role in the treatment of solid tumors, involving both direct cell lysis and immunogenic cell death. Nonetheless, tumor-associated stroma limits the efficacy of oncolytic viruses by forming a barrier that blocks efficient viral penetration and spread. The stroma also plays a critical role in progression, immunosuppression and invasiveness of cancer. Fibroblast activation protein-α (FAP) is highly overexpressed in cancer-associated fibroblasts (CAFs), the main cellular component of tumor stroma, and in this study we assessed whether arming oncolytic adenovirus (OAd) with a FAP-targeting Bispecific T-cell Engager (FBiTE) could retarget infiltrated lymphocytes towards CAFs, enhancing viral spread and T cell-mediated cytotoxicity against the tumor stroma to improve therapeutic activity.

METHODS

The bispecific T-cell Engager against FAP was constructed using an anti-human CD3 single-chain variable fragment (scFv) linked to an anti-murine and human FAP scFv. This FBiTE was inserted in the oncolytic adenovirus ICOVIR15K under the control of the major late promoter, generating the ICO15K-FBiTE. ICO15K-FBiTE replication and potency were assessed in HT1080 and A549 tumor cell lines. The expression of the FBiTE and the activation and proliferation of T cells that induced along with the T cell-mediated cytotoxicity of CAFs were evaluated by flow cytometry in vitro. In vivo, T-cell biodistribution and antitumor efficacy studies were conducted in NOD/scid/IL2rg^-/^- (NSG) mice.

RESULTS

FBiTE expression did not decrease the infectivity and replication potency of the armed virus. FBiTE-mediated binding of CD3⁺ effector T cells and FAP⁺ target cells led to T-cell activation, proliferation, and cytotoxicity of FAP-positive cells in vitro. In vivo, FBiTE expression increased intratumoral accumulation of T cells and decreased the level of FAP, a marker of CAFs, in tumors. The antitumor activity of the FBiTE-armed adenovirus was superior to the parental virus.

CONCLUSIONS

Combination of viral oncolysis of cancer cells and FBiTE-mediated cytotoxicity of FAP-expressing CAFs might be an effective strategy to overcome a key limitation of oncolytic virotherapy, encouraging its further clinical development.

Capsid-Incorporation Strategy To Display Antigens for an Alternative Adenoviral Vector Vaccine Approach

The adenovirus (Ad) is widely used as a vaccine because of its ability to induce a cellular and humoral immune response. In addition, human clinical trials have validated the safety and efficacy of Ad as a vaccine vector. The traditional approach for employing the adenovirus as vaccine is to configure the antigen genes into the expression cassette of the Ad genome. An alternative method for inducing an immune response is the "capsid-incorporation" strategy. This strategy is based upon the incorporation of proteins or peptides into the capsid proteins. This review will focus on the established uses of this approach as well as highlighting the new developments regarding the capsid-incorporation strategy.

Display of the Albumin-Binding Domain in the Envelope Improves Lentiviral Vector Bioavailability

Vesicular stomatitis virus G glycoprotein (VSVg) is extensively used for retroviral and lentiviral vector (LV) pseudotyping. However, VSVg pseudotyped vectors are serum inactivated, blocking the in vivo gene delivery. Several strategies have been employed to prevent complement inactivation, including chemical and genetic envelope modifications. This study employed the streptococcal albumin-binding domain (ABD) to generate a construct to express ABD as a glycosylphosphatidylinositol-anchored protein. LV particles bearing ABD are able to bind bovine and human serum albumin in vitro. Neither the lentiviral vector production titer nor the in vitro transduction was affected by the ABD display. The study demonstrated that ABD-bearing LVs are protected from human complement inactivation. More importantly, intravenous administration demonstrated that the presence of ABD significantly reduces lentivector sequestration in liver and bone-marrow cells. Therefore, the use of ABD represents an improvement for in vivo gene therapy applications. The results strongly point to ABD display as a universal strategy to increase the in vivo efficacy of different viral vectors.

Advances in oncolytic adenovirus therapy for pancreatic cancer

Survival rates for pancreatic cancer patients have remained unchanged for the last four decades. The most aggressive, and most common, type of pancreatic cancer is pancreatic ductal adenocarcinoma (PDAC), which has the lowest 5-year survival rate of all cancers globally. The poor prognosis is typically due to late presentation of often non-specific symptoms and rapid development of resistance to all current therapeutics, including the standard-of-care cytotoxic drug gemcitabine. While early surgical intervention can significantly prolong patient survival, there are few treatment options for late-stage non-resectable metastatic disease, resulting in mostly palliative care. In addition, a defining feature of pancreatic cancer is the immunosuppressive and impenetrable desmoplastic stroma that blocks access to tumour cells by therapeutic drugs. The limited effectiveness of conventional chemotherapeutics reveals an urgent need to develop novel therapies with different mechanisms of action for this malignancy. An emerging alternative to current therapeutics is oncolytic adenoviruses; these engineered biological agents have proven efficacy and tumour-selectivity in preclinical pancreatic cancer models, including models of drug-resistant cancer. Safety of oncolytic adenoviral mutants has been extensively assessed in clinical trials with only limited toxicity to normal healthy tissue being reported. Promising efficacy in combination with gemcitabine was demonstrated in preclinical and clinical studies. A recent surge in novel adenoviral mutants entering clinical trials for pancreatic cancer indicates improved efficacy through activation of the host anti-tumour responses. The potential for adenoviruses to synergise with chemotherapeutics, activate anti-tumour immune responses, and contribute to stromal dissemination render these mutants highly attractive candidates for improved patient outcomes. Currently, momentum is gathering towards the development of systemically-deliverable mutants that are able to overcome anti-viral host immune responses, erythrocyte binding and hepatic uptake, to promote elimination of primary and metastatic lesions. This review will cover the key components of pancreatic cancer oncogenesis; novel oncolytic adenoviruses; clinical trials; and the current progress in overcoming the challenges of systemic delivery.

Modulation of serum albumin protein corona for exploring cellular behaviors of fattigation-platform nanoparticles

Albumin is the most abundant protein in blood, and is the most frequently identified protein in the protein corona of nanoparticles (NPs). Thus, albumin plays an important role in modulating NPs' physicochemical properties and bioavailability. In this study, the effect of bovine serum albumin (BSA) on gelatin-oleic nanoparticles' (GONs) physicochemical properties and cellular uptake were evaluated. Coumarin-6 was used as indicator to track the cellular uptake of GONs. The binding of BSA onto the GON surface increased the size, slightly reduced the negative net charge of the GON, and improved GON stability. The presence of BSA in cell culture media reduced the cellular uptake of BSA-uncoated GONs on human embryonic kidney cells 293 (HEK 293) and human adenocarcinoma alveolar basal epithelial cells (A549) in the media without FBS addition. Pre-coated BSA corona decreased cellular uptake of GONs in A549 cells in the media, with and without supplemented with 10% fetal bovine serum (FBS) but drastically increased cellular uptake on HEK 293 cells. BSA could be used to modulate protein corona as an endogenous ligand in NP design simply by mixing or incubating BSA with NPs before in vivo administration to inhibit or induce cellular uptake in specific cell types.

Adaptation of vectors and drug-inducible systems for controlled expression of transgenes in the tumor microenvironment

Biological therapies based on recombinant proteins such as antibodies or cytokines are continuously improving the repertoire of treatments against cancer. However, safety and efficacy of this approach is often limited by inappropriate biodistribution and pharmacokinetics of the proteins when they are administered systemically. Local administration of gene therapy vectors encoding these proteins would be a feasible alternative if they could mediate long-term and controlled expression of the transgene after a single intratumoral administration. We describe a new vector platform specially designed for this purpose. Different combinations of transactivators and promoters were evaluated to obtain a fully humanized inducible system responsive to the well-characterized drug mifepristone. The optimal transactivator conformation was based on DNA binding domains from the chimeric protein ZFHD1 fused to the progesterone receptor ligand binding domain and the NFkb p65 activation domain. The expression of this hybrid transactivator under the control of the elongation factor 1α (EF1α) or the chimeric CAG promoters ensured functionality of the system in a variety of cancer types. Expression cassettes with luciferase as a reporter gene were incorporated into High-Capacity adenoviral vectors (HC-Ad) for in vivo evaluation. Systemic administration of the vectors into C57BL/6 mice revealed that the vector based on the EF1α promoter (HCA-EF-ZP) allows tight control of transgene expression and remains stable for at least two months, whereas the CAG promoter suffers a progressive inactivation. Using an orthotopic pancreatic cancer model in syngeneic C57BL/6 mice we show that the local administration of HCA-EF-ZP achieves better tumor/liver ratio of luciferase production than the intravenous route. However, regional spread of the vector led to substantial transgene expression in peritoneal organs. We reduced this leakage through genetic modification of the vector capsid to display RGD and poly-lysine motifs in the fiber knob. Safety and antitumor effect of this gene therapy platform was demonstrated using interleukin-12 as a therapeutic gene. In conclusion, we have developed a new tool that allows local, sustained and controlled production of therapeutic proteins in tumors.

Oncolytic Viruses-Interaction of Virus and Tumor Cells in the Battle to Eliminate Cancer

Oncolytic viruses (OVs) are an emerging treatment option for many cancer types and have recently been the focus of extensive research aiming to develop their therapeutic potential. The ultimate aim is to design a virus which can effectively replicate within the host, specifically target and lyse tumor cells and induce robust, long lasting tumor-specific immunity. There are a number of viruses which are either naturally tumor-selective or can be modified to specifically target and eliminate tumor cells. This means they are able to infect only tumor cells and healthy tissue remains unharmed. This specificity is imperative in order to reduce the side effects of oncolytic virotherapy. These viruses can also be modified by various methods including insertion and deletion of specific genes with the aim of improving their efficacy and safety profiles. In this review, we have provided an overview of the various virus species currently being investigated for their oncolytic potential and the positive and negative effects of a multitude of modifications used to increase their infectivity, anti-tumor immunity, and treatment safety, in particular focusing on the interaction of tumor cells and OVs.

Strategies for Preparing Albumin-based Nanoparticles for Multifunctional Bioimaging and Drug Delivery

Biosafety is the primary concern in clinical translation of nanomedicine. As an intrinsic ingredient of human blood without immunogenicity and encouraged by its successful clinical application in Abraxane, albumin has been regarded as a promising material to produce nanoparticles for bioimaging and drug delivery. The strategies for synthesizing albumin-based nanoparticles could be generally categorized into five classes: template, nanocarrier, scaffold, stabilizer and albumin-polymer conjugate. This review introduces approaches utilizing albumin in the preparation of nanoparticles and thereby provides scientists with knowledge of goal-driven design on albumin-based nanomedicine.

Turbocharging vaccines: emerging adjuvants for dendritic cell based therapeutic cancer vaccines

Development of therapeutic cancer vaccines has been hindered by the many pro-tumorigenic mechanisms at play in cancer patients that serve to suppress both antigen presenting cells and T cells. In face of these obstacles, cancer vaccines are most likely to promote anti-tumorigenic immune responses only when formulated with strong adjuvants, and in combination with new immune interventions designed to reverse immune suppression and exhaustion of T cells in the tumor microenvironment. Dendritic cells (DCs) are often termed 'nature's adjuvant' due to their exceptional capacity for initiating both innate and adaptive immune responses. Hence, the past decade has witnessed a flurry of activity in testing DC based immunotherapies for cancer intervention. In this review we will discuss advances in conventional adjuvants and provide insight into new adjuvants as they pertain to DC cancer therapy.

Human Menstrual Blood-Derived Mesenchymal Stem Cells as Potential Cell Carriers for Oncolytic Adenovirus

Antitumor efficacy of systemically administered oncolytic adenoviruses (OAdv) is limited due to diverse factors such as liver sequestration, neutralizing interactions in blood, elimination by the immune system, and physical barriers in tumors. It is therefore of clinical relevance to improve OAdv bioavailability and tumor delivery. Among the variety of tumor-targeting strategies, the use of stem cells and specifically bone marrow-derived mesenchymal stem cells (BM-MSCs) is of particular interest due to their tumor tropism and immunomodulatory properties. Nonetheless, the invasive methods to obtain these cells, the low number of MSCs present in the bone marrow, and their restricted in vitro expansion represent major obstacles for their use in cancer treatments, pointing out the necessity to identify an alternative source of MSCs. Here, we have evaluated the use of menstrual blood-derived mesenchymal stem cells (MenSCs) as cell carriers for regional delivery of an OAdv in the tumor. Our results indicate that MenSCs can be isolated without invasive methods, they have an increased proliferation rate compared to BM-MSCs, and they can be efficiently infected with different serotype 5-based capsid-modified adenoviruses, leading to viral replication and release. In addition, our in vivo studies confirmed the tumor-homing properties of MenSCs after regional administration.

Protein corona: a new approach for nanomedicine design

After administration of nanoparticle (NP) into biological fluids, an NP-protein complex is formed, which represents the "true identity" of NP in our body. Hence, protein-NP interaction should be carefully investigated to predict and control the fate of NPs or drug-loaded NPs, including systemic circulation, biodistribution, and bioavailability. In this review, we mainly focus on the formation of protein corona and its potential applications in pharmaceutical sciences such as prediction modeling based on NP-adsorbed proteins, usage of active proteins for modifying NP to achieve toxicity reduction, circulation time enhancement, and targeting effect. Validated correlative models for NP biological responses mainly based on protein corona fingerprints of NPs are more highly accurate than the models solely set up from NP properties. Based on these models, effectiveness as well as the toxicity of NPs can be predicted without in vivo tests, while novel cell receptors could be identified from prominent proteins which play important key roles in the models. The ungoverned protein adsorption onto NPs may have generally negative effects such as rapid clearance from the bloodstream, hindrance of targeting capacity, and induction of toxicity. In contrast, controlling protein adsorption by modifying NPs with diverse functional proteins or tailoring appropriate NPs which favor selective endogenous peptides and proteins will bring promising therapeutic benefits in drug delivery and targeted cancer treatment.