Encapsulation of recombinant adenovirus into alginate microspheres circumvents vector-specific immune response

An intranasal combination vaccine induces systemic and mucosal immunity against COVID-19 and influenza

Despite prolonged surveillance and interventions, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza viruses continue to pose a severe global health burden. Thus, we developed a chimpanzee adenovirus-based combination vaccine, AdC68-HATRBD, with dual specificity against SARS-CoV-2 and influenza virus. When used as a standalone vaccine, intranasal immunization with AdC68-HATRBD induced comprehensive and potent immune responses consisting of immunoglobin (Ig) G, mucosal IgA, neutralizing antibodies, and memory T cells, which protected the mice from BA.5.2 and pandemic H1N1 infections. When used as a heterologous booster, AdC68-HATRBD markedly improved the protective immune response of the licensed SARS-CoV-2 or influenza vaccine. Therefore, whether administered intranasally as a standalone or booster vaccine, this combination vaccine is a valuable strategy to enhance the overall vaccine efficacy by inducing robust systemic and mucosal immune responses, thereby conferring dual lines of immunological defenses for these two viruses.

Alginate microbeads and hydrogels delivering meropenem and bacteriophages to treat Pseudomonas aeruginosa fracture-related infections

Bacteriophage (phage) therapy has shown promise in treating fracture-related infection (FRI); however, questions remain regarding phage efficacy against biofilms, phage-antibiotic interaction, administration routes and dosing, and the development of phage resistance. The goal of this study was to develop a dual antibiotic-phage delivery system containing hydrogel and alginate microbeads loaded with a phage cocktail plus meropenem and evaluate efficacy against muti-drug resistant Pseudomonas aeruginosa. Two phages (FJK.R9-30 and MK.R3-15) displayed enhanced antibiotic activity against P. aeruginosa biofilms when tested in combination with meropenem. The antimicrobial activity of both antibiotic and phage was retained for eight days at 37 °C in dual phage and antibiotic loaded hydrogel with microbeads (PA-HM). In a mouse FRI model, phages were recovered from all tissues within all treatment groups receiving dual PA-HM. Moreover, animals that received the dual PA-HM either with or without systemic antibiotics had less incidence of phage resistance and less serum neutralization compared to phages in saline. The dual PA-HM could reduce bacterial load in soft tissue when combined with systemic antibiotics, although the infection was not eradicated. The use of alginate microbeads and injectable hydrogel for controlled release of phages and antibiotics, leads to the reduced development of phage resistance and lower exposure to the adaptive immune system, which highlights the translational potential of the dual PA-HM. However, further optimization of phage therapy and its delivery system is necessary to achieve higher bacterial killing activity in vivo in the future.

Manganese Mineralization of Pathogenic Viruses as a Universal Vaccine Platform

Biomimetic viral mineralization improves viral vaccine stability and immunogenicity using inorganic metals such as Ca, Al, or Fe. Mn is a metal found in high concentrations in mammalian tissues; however, under natural or laboratory conditions, Mn mineralization by medical viruses has yet to be established. Herein, a single IAV particle is successfully encapsulated with manganese phosphate (MnP) under specific conditions using the human influenza A virus (IAV). MnP-mineralized IAVs (IAV@Mn) exhibited physiochemical and in vitro properties similar to Ca-mineralized IAVs. In animal models, IAV@Mn shows limited replication in immune-competent cells and a significant attenuation compared to naïve cells. Moreover, a single-dose vaccination with IAV@Mn induced robust humoral and cellular immune responses and conferred significant protection against a wild-type IAV challenge in mice. Thus, Mn mineralization in pathogenic viruses provides a rapid and universal strategy for generating an emergency vaccine in response to emerging viruses.

Adenoviral Vector-Based Vaccine Platform for COVID-19: Current Status

The coronavirus disease (COVID-19) breakout had an unimaginable worldwide effect in the 21st century, claiming millions of lives and putting a huge burden on the global economy. The potential developments in vaccine technologies following the determination of the genetic sequence of SARS-CoV-2 and the increasing global efforts to bring potential vaccines and therapeutics into the market for emergency use have provided a small bright spot to this tragic event. Several intriguing vaccine candidates have been developed using recombinant technology, genetic engineering, and other vaccine development technologies. In the last decade, a vast amount of the vaccine development process has diversified towards the usage of viral vector-based vaccines. The immune response elicited by such vaccines is comparatively higher than other approved vaccine candidates that require a booster dose to provide sufficient immune protection. The non-replicating adenoviral vectors are promising vaccine carriers for infectious diseases due to better yield, cGMP-friendly manufacturing processes, safety, better efficacy, manageable shipping, and storage procedures. As of April 2022, the WHO has approved a total of 10 vaccines around the world for COVID-19 (33 vaccines approved by at least one country), among which three candidates are adenoviral vector-based vaccines. This review sheds light on the developmental summary of all the adenoviral vector-based vaccines that are under emergency use authorization (EUA) or in the different stages of development for COVID-19 management.

Significance of Preexisting Vector Immunity and Activation of Innate Responses for Adenoviral Vector-Based Therapy

An adenoviral (AdV)-based vector system is a promising platform for vaccine development and gene therapy applications. Administration of an AdV vector elicits robust innate immunity, leading to the development of humoral and cellular immune responses against the vector and the transgene antigen, if applicable. The use of high doses (10¹¹-10¹³ virus particles) of an AdV vector, especially for gene therapy applications, could lead to vector toxicity due to excessive levels of innate immune responses, vector interactions with blood factors, or high levels of vector transduction in the liver and spleen. Additionally, the high prevalence of AdV infections in humans or the first inoculation with the AdV vector result in the development of vector-specific immune responses, popularly known as preexisting vector immunity. It significantly reduces the vector efficiency following the use of an AdV vector that is prone to preexisting vector immunity. Several approaches have been developed to overcome this problem. The utilization of rare human AdV types or nonhuman AdVs is the primary strategy to evade preexisting vector immunity. The use of heterologous viral vectors, capsid modification, and vector encapsulation are alternative methods to evade vector immunity. The vectors can be optimized for clinical applications with comprehensive knowledge of AdV vector immunity, toxicity, and circumvention strategies.

The use of adenoviral vectors in gene therapy and vaccine approaches

Adenovirus was first identified in the 1950s and since then this pathogenic group of viruses has been explored and transformed into a genetic transfer vehicle. Modification or deletion of few genes are necessary to transform it into a conditionally or non-replicative vector, creating a versatile tool capable of transducing different tissues and inducing high levels of transgene expression. In the early years of vector development, the application in monogenic diseases faced several hurdles, including short-term gene expression and even a fatality. On the other hand, an adenoviral delivery strategy for treatment of cancer was the first approved gene therapy product. There is an increasing interest in expressing transgenes with therapeutic potential targeting the cancer hallmarks, inhibiting metastasis, inducing cancer cell death or modulating the immune system to attack the tumor cells. Replicative adenovirus as vaccines may be even older and date to a few years of its discovery, application of non-replicative adenovirus for vaccination against different microorganisms has been investigated, but only recently, it demonstrated its full potential being one of the leading vaccination tools for COVID-19. This is not a new vector nor a new technology, but the result of decades of careful and intense work in this field.

rAAV expressing recombinant neutralizing antibody for the botulinum neurotoxin type A prophylaxis

Botulinum neurotoxin (BoNT) is one of the most dangerous bacterial toxins and a potential biological weapon component. BoNT mechanism of pathological action is based on inhibiting the release of neurotransmitters from nerve endings. To date, anti-BoNT therapy is reduced to the use of horse hyperimmune serum, which causes many side effects, as well as FDA-approved drug BabyBig which consists of human-derived anti-BoNT antibodies (IgG) for infant botulinum treatment. Therapeutics for botulism treatment based on safer monoclonal antibodies are undergoing clinical trials. In addition, agents have been developed for the specific prevention of botulism, but their effectiveness has not been proved. In this work, we have obtained a recombinant adeno-associated virus (rAAV-B11-Fc) expressing a single-domain antibody fused to the human IgG Fc-fragment (B11-Fc) and specific to botulinum toxin type A (BoNT/A). We have demonstrated that B11-Fc antibody, expressed via rAAV-B11-Fc treatment, can protect animals from lethal doses of botulinum toxin type A, starting from day 3 and at least 120 days after administration. Thus, our results showed that rAAV-B11-Fc can provide long-term expression of B11-Fc-neutralizing antibody in vivo and provide long-term protection against BoNT/A intoxication. Consequently, our study demonstrates the applicability of rAAV expressing protective antibodies for the prevention of intoxication caused by botulinum toxins.

Prolongation of Fate of Bacteriophages In Vivo by Polylactic-Co-Glycolic-Acid/Alginate-Composite Encapsulation

With concern growing over antibiotics resistance, the use of bacteriophages to combat resistant bacteria has been suggested as an alternative strategy with which to enable the selective control of targeted pathogens. One major challenge that restrains the therapeutic application of bacteriophages as antibacterial agents is their short lifespan, which limits their antibacterial effect in vivo. Here, we developed a polylactic-co-glycolic acid (PLGA)/alginate-composite microsphere for increasing the lifespan of bacteriophages in vivo. The alginate matrix in PLGA microspheres encapsulated the bacteriophages and protected them against destabilization by an organic solvent. Encapsulated bacteriophages were detected in the tissue for 28 days post-administration, while the bacteriophages administered without advanced encapsulation survived in vivo for only 3–5 days. The bacteriophages with extended fate showed prophylaxis against the bacterial pathogens for 28 days post-administration. This enhanced prophylaxis is presumed to have originated from the diminished immune response against these encapsulated bacteriophages because of their controlled release. Collectively, composite encapsulation has prophylactic potential against bacterial pathogens that threaten food safety and public health.

Microencapsulated Multifunctionalized Graphene Oxide Equipped with Chloroquine for Efficient and Sustained siRNA Delivery

A multifunctionalized graphene oxide (GO)-based carrier with conjugation of aminated-polyethylene glycol (PEG-diamine), octaarginine (R8), and folic acid (FA), which also contains chloroquine (CQ), a lysosomotropic agent, is introduced. The cellular uptake mechanisms and intracellular targeting of FA-functionalized nanocarriers are examined. The localized releases of CQ and siRNA intracellular delivery are evaluated. Microencapsulation of the nanocarrier complexed with genes in layer-by-layer coating of alginate microbeads is also investigated. The covalently coconjugated FA with PEG and R8 provides a stable formulation with increased cellular uptake compared to FA-free carrier. The CQ-equipped nanocarrier shows a 95% release of CQ at lysosomal pH. The localized release of the drug inside the lysosomes is verified which accelerates the cargo discharge into cytoplasm.

COVID-19 Vaccines: An Overview of Different Platforms

Vaccination is one of the key strategies to stop the COVID-19 pandemic. This review aims to evaluate the current state of vaccine development and to determine the issues that merit additional research. We conducted a literature review of the development of COVID-19 vaccines, their effectiveness, and their use in special patient groups. To date, 140 vaccines are in clinical development. Vector, RNA, subunit, and inactivated vaccines, as well as DNA vaccines, have been approved for human use. Vector vaccines have been well studied prior to the COVID-19 pandemic; however, their long-term efficacy and approaches to scaling up their production remain questionable. The main challenge for RNA vaccines is to improve their stability during production, storage, and transportation. For inactivated vaccines, the key issue is to improve their immunogenicity and effectiveness. To date, it has been shown that the immunogenicity of COVID-19 vaccines directly correlates with their clinical efficacy. In view of the constant mutation, the emerging new SARS-CoV-2 variants have been shown to be able to partially escape post-vaccination immune response; however, most vaccines remain sufficiently effective regardless of the variant of the virus. One of the promising strategies to improve the effectiveness of vaccination, which is being studied, is the use of different platforms within a single vaccination course. Despite significant progress in the development and study of COVID-19 vaccines, there are many issues that require further research.

Human Adenovirus Serotype 3 Infection Modulates the Biogenesis and Composition of Lung Cell-Derived Extracellular Vesicles

Adenovirus (Ad) is a major causal agent of acute respiratory infections. However, they are a powerful delivery system for gene therapy and vaccines. Some Ad serotypes antagonize the immune system leading to meningitis, conjunctivitis, gastroenteritis, and/or acute hemorrhagic cystitis. Studies have shown that the release of small, membrane-derived extracellular vesicles (EVs) may offer a mechanism by which viruses can enter cells via receptor-independent entry and how they influence disease pathogenesis and/or host protection considering their existence in almost all bodily fluids. We proposed that Ad3 could alter EV biogenesis, composition, and trafficking and may stimulate various immune responses in vitro. In the present study, we evaluated the impact of in vitro infection with Ad3 vector on EV biogenesis and composition in the human adenocarcinoma lung epithelial cell line A549. Cells were infected in an exosome-free media at different multiplicity of infections (MOIs) and time points. The cell viability was determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and fluorometric calcein-AM. EVs were isolated via ultracentrifugation. Isolated EV proteins were quantified and evaluated via nanoparticle tracking, transmission electron microscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and immunoblotting assays. The cell viability significantly decreased with an increase in MOI and incubation time. A significant increase in particle mean sizes, concentrations, and total EV protein content was detected at higher MOIs when compared to uninfected cells (control group). A549 cell-derived EVs revealed the presence of TSG101, tetraspanins CD9 and CD63, and heat shock proteins 70 and 100 with significantly elevated levels of Rab5, 7, and 35 at higher MOIs (300, 750, and 1500) when compared to the controls. Our findings suggested Ad3 could modulate EV biogenesis, composition, and trafficking which could impact infection pathogenesis and disease progression. This study might suggest EVs could be diagnostic and therapeutic advancement to Ad infections and other related viral infections. However, further investigation is warranted to explore the underlying mechanism(s).

Polymeric membranes for biomedical applications

The rapid development of nanotechnology paved the way for further expansion of polymer chemistry and the fabrication of advanced polymeric membranes. Such modifications allowed enhancing or adding some unique properties, including mechanical strength, excellent biocompatibility, easily controlled degradability, and biological activity. This chapter discusses various applications of polymeric membranes in three significant areas of biomedicine, including tissue engineering, drug delivery systems, and diagnostics. It is intended to highlight here possible ways of improvement the properties of polymeric membranes, by modifying with other polymers, functional groups, compounds, drugs, bioactive components, and nanomaterials.

Humoral immune responses to AAV gene therapy in the ocular compartment

Viral vectors can be utilised to deliver therapeutic genes to diseased cells. Adeno-associated virus (AAV) is a commonly used viral vector that is favoured for its ability to infect a wide range of tissues whilst displaying limited toxicity and immunogenicity. Most humans harbour anti-AAV neutralising antibodies (NAbs) due to subclinical infections by wild-type virus during infancy and these pre-existing NAbs can limit the efficiency of gene transfer depending on the target cell type, route of administration and choice of serotype. Vector administration can also result in de novo NAb synthesis that could limit the opportunity for repeated gene transfer to diseased sites. A number of strategies have been described in preclinical models that could circumvent NAb responses in humans, however, the successful translation of these innovations into the clinical arena has been limited. Here, we provide a comprehensive review of the humoral immune response to AAV gene therapy in the ocular compartment. We cover basic AAV biology and clinical application, the role of pre-existing and induced NAbs, and possible approaches to overcoming antibody responses. We conclude with a framework for a comprehensive strategy for circumventing humoral immune responses to AAV in the future.

Is Viral Vector Gene Delivery More Effective Using Biomaterials?

Gene delivery has been extensively investigated for introducing foreign genetic material into cells to promote expression of therapeutic proteins or to silence relevant genes. This approach can regulate genetic or epigenetic disorders, offering an attractive alternative to pharmacological therapy or invasive protein delivery options. However, the exciting potential of viral gene therapy has yet to be fully realized, with a number of clinical trials failing to deliver optimal therapeutic outcomes. Reasons for this include difficulty in achieving localized delivery, and subsequently lower efficacy at the target site, as well as poor or inconsistent transduction efficiency. Thus, ongoing efforts are focused on improving local viral delivery and enhancing its efficiency. Recently, biomaterials have been exploited as an option for more controlled, targeted and programmable gene delivery. There is a growing body of literature demonstrating the efficacy of biomaterials and their potential advantages over other delivery strategies. This review explores current limitations of gene delivery and the progress of biomaterial-mediated gene delivery. The combination of biomaterials and gene vectors holds the potential to surmount major challenges, including the uncontrolled release of viral vectors with random delivery duration, poorly localized viral delivery with associated off-target effects, limited viral tropism, and immune safety concerns.

Materials promoting viral gene delivery

Therapeutic viral gene delivery is an emerging technology which aims to correct genetic mutations by introducing new genetic information to cells either to correct a faulty gene or to initiate cell death in oncolytic treatments. In recent years, significant scientific progress has led to several clinical trials resulting in the approval of gene therapies for human treatment. However, successful therapies remain limited due to a number of challenges such as inefficient cell uptake, low transduction efficiency (TE), limited tropism, liver toxicity and immune response. To adress these issues and increase the number of available therapies, additives from a broad range of materials like polymers, peptides, lipids, nanoparticles, and small molecules have been applied so far. The scope of this review is to highlight these selected delivery systems from a materials perspective.

Adenoviral Vector-Based Vaccine Platforms for Developing the Next Generation of Influenza Vaccines

Ever since the discovery of vaccines, many deadly diseases have been contained worldwide, ultimately culminating in the eradication of smallpox and polio, which represented significant medical achievements in human health. However, this does not account for the threat influenza poses on public health. The currently licensed seasonal influenza vaccines primarily confer excellent strain-specific protection. In addition to the seasonal influenza viruses, the emergence and spread of avian influenza pandemic viruses such as H5N1, H7N9, H7N7, and H9N2 to humans have highlighted the urgent need to adopt a new global preparedness for an influenza pandemic. It is vital to explore new strategies for the development of effective vaccines for pandemic and seasonal influenza viruses. The new vaccine approaches should provide durable and broad protection with the capability of large-scale vaccine production within a short time. The adenoviral (Ad) vector-based vaccine platform offers a robust egg-independent production system for manufacturing large numbers of influenza vaccines inexpensively in a short timeframe. In this review, we discuss the progress in the development of Ad vector-based influenza vaccines and their potential in designing a universal influenza vaccine.

MnCaCs-Biomineralized Oncolytic Virus for Bimodal Imaging-Guided and Synergistically Enhanced Anticancer Therapy

Oncolytic adenovirus (OA) is an ideal candidate for clinical anticancer treatment, because it can specifically replicate in tumor cells with high titer. However, its systemic administration is still hindered, because of severely compromised antitumor efficacy. Herein, an engineered OA was innovatively developed by enwrapping OA with calcium and manganese carbonates (MnCaCs) biomineral shell, which could protect the virus from removal of the host immune system and prolong its in vivo circulation. Upon accumulating in tumor sites, MnCaCs readily dissolved under the acidic microenvironment, releasing Mn²⁺ that could convert endogenous H₂O₂ into oxygen (O₂) and then enhance the duplication ability of OA, thus significantly increased the antitumor efficacy. Meanwhile, Mn²⁺ and the increased O₂ individually endowed the T1 modal magnetic resonance imaging (MRI) and photoacoustic imaging (PAI) feasibility, providing real-time monitoring information for the therapy. This versatile engineered OA demonstrated its promise for visible and efficient oncolytic virotherapy by systemic administration.

Applications of alginate microspheres in therapeutics delivery and cell culture: Past, present and future

Polymers are the backbone of pharmaceutical drug delivery. There are several polymers with varying properties available today for use in different pharmaceutical applications. Alginate is widely used in biomedical research due to its attractive features such as biocompatibility, biodegradability, inertness, low cost, and ease of production and formulation. Encapsulation of therapeutic agents in alginate/alginate complex microspheres protects them from environmental stresses, including the acidic environment in the gastro-intestinal tract (GIT) and enzymatic degradation, and allows targeted and sustained delivery of the agents. Microencapsulation is playing an increasingly important role in drug delivery as evidenced by the recent surge in research articles on the use of alginate in the delivery of small molecules, cells, bacteria, proteins, vaccines, and for tissue engineering applications. Formulation of these alginate microspheres (AMS) are commonly achieved by conventional external gelation method using various instrumental manipulation such as vortexing, homogenization, ultrasonication or spray drying, and each method affects the overall particle characteristics. In this review, an inclusive summary of the currently available methods for the formulation of AMS, its recent use in the encapsulation and delivery of therapeutics, and future outlook will be discussed.

Characterizing the encapsulation and release of lentivectors and adeno-associated vectors from degradable alginate hydrogels

Gene therapy using viral vectors has been licensed for clinical use both in the European Union and the United States. Lentivectors (LV) and adeno-associated vectors (AAV) are two promising and FDA approved gene-therapy viral vectors. Many future applications of these vectors will benefit from targeting specific regions of interest within the body. Therefore, building on the early success of these vectors may depend on finding effective delivery systems to localize therapeutic administration. Degradable alginate hydrogels have been tested as appealing delivery vehicles for the controlled delivery of vector payloads. In this study, we compare the ability of two different degradable alginate hydrogel formulations to efficiently deliver LV and AAV. We propose that release rates of viral vectors are dependent on the physical properties of both the hydrogels and vectors. Here, we demonstrate that the initial strength and degradation rate of alginate hydrogels provides levers of control for tuning LV release but do not provide control in the release of AAV. While both alginate formulations used showed sustained release of both LV and AAV, LV release was shown to be dependent on alginate hydrogel degradation, while AAV release was largely governed by diffusive mechanisms. Altogether, this study demonstrates alginate's use as a possible delivery platform for LV and, for the first time, AAV - highlighting the potential of injectable degradable alginate hydrogels to be used as a versatile delivery tool in gene therapy applications.

Matrix Mediated Viral Gene Delivery: A Review

Polymeric matrices inherently protect viral vectors from pre-existing immune conditions, limit dissemination to off-target sites, and can sustain vector release. Advancing methodologies in development of particulate based vehicles have led to improved encapsulation of viral vectors. Polymeric delivery systems have contributed to increasing cellular transduction, responsive release mechanisms, cellular infiltration, and cellular signaling. Synthetic polymers are easily customizable, and are capable of balancing matrix retention with cellular infiltration. Natural polymers contain inherent biorecognizable motifs adding therapeutic efficacy to the incorporated viral vector. Recombinant polymers use highly conserved motifs to carefully engineer matrices, allowing for precise design including elements of vector retention and responsive release mechanisms. Composite polymer systems provide opportunities to create matrices with unique properties. Carefully designed matrices can control spatiotemporal release patterns that synergize with approaches in regenerative medicine and antitumor therapies.

A hydrogel matrix prolongs persistence and promotes specific localization of an oncolytic adenovirus in a tumor by restricting nonspecific shedding and an antiviral immune response

Currently, intratumoral injection of an oncolytic adenovirus (Ad) is the conventional administration route in clinical trials. Nonetheless, the locally administered Ad disseminates to the surrounding nontarget tissues and has short biological activity due to immunogenicity of Ad, thus necessitating multiple injections to achieve a sufficient therapeutic index. In the present study, a tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-expressing oncolytic Ad (oAd-TRAIL) was encapsulated in a gelatin hydrogel (oAd-TRAIL/gel) to enhance and prolong antitumor efficacy of the virus after a single intratumoral injection. oAd-TRAIL/gel showed greater antitumor efficacy than naked oAd-TRAIL did due to enhanced and prolonged intratumoral accumulation of Ad up to a 20-day period, showing potent induction of apoptosis and inhibition of tumor cell proliferation. Furthermore, the gel system effectively prevented shedding of oncolytic Ad from the injection site to hepatic and other healthy tissues. oAd-TRAIL/gel treatment resulted in a markedly weaker antiviral immune response against Ad relative to naked oAd-TRAIL, further contributing to prolonged persistence of the oncolytic Ad in tumor tissue. Moreover, the hydrogel matrix preserved oAd-TRAIL's ability to induce an antitumor immune response, resulting in higher intratumoral infiltration by CD4⁺/CD8⁺ T cells. Taken together, these findings show that single intratumoral administration of the Ad/hydrogel modality may prolong and potentiate the therapeutic efficacy of Ad, modulate the immune reaction in favor of the virotherapy, and enhance intratumoral localization of the virus, ultimately overcoming limitations of oncolytic virotherapy revealed in recent clinical trials.

Biomaterial-Guided Gene Delivery for Musculoskeletal Tissue Repair

Gene therapy is a promising strategy for musculoskeletal tissue repair and regeneration where local and sustained expression of proteins and/or therapeutic nucleic acids can be achieved. However, the musculoskeletal tissues present unique engineering and biological challenges as recipients of genetic vectors. Targeting specific cell populations, regulating expression in vivo, and overcoming the harsh environment of damaged tissue accompany the general concerns of safety and efficacy common to all applications of gene therapy. In this review, we will first summarize these challenges and then discuss how biomaterial carriers for genetic vectors can address these issues. Second, we will review how limitations specific to given vectors further motivate the utility of biomaterial carriers. Finally, we will discuss how these concepts have been combined with tissue engineering strategies and approaches to improve the delivery of these vectors for musculoskeletal tissue regeneration.

Evolving lessons on nanomaterial-coated viral vectors for local and systemic gene therapy

Viral vectors are promising gene carriers for cancer therapy. However, virus-mediated gene therapies have demonstrated insufficient therapeutic efficacy in clinical trials due to rapid dissemination to nontarget tissues and to the immunogenicity of viral vectors, resulting in poor retention at the disease locus and induction of adverse inflammatory responses in patients. Further, the limited tropism of viral vectors prevents efficient gene delivery to target tissues. In this regard, modification of the viral surface with nanomaterials is a promising strategy to augment vector accumulation at the target tissue, circumvent the host immune response, and avoid nonspecific interactions with the reticuloendothelial system or serum complement. In the present review, we discuss various chemical modification strategies to enhance the therapeutic efficacy of viral vectors delivered either locally or systemically. We conclude by highlighting the salient features of various nanomaterial-coated viral vectors and their prospects and directions for future research.

Viruses, Artificial Viruses and Virus-Based Structures for Biomedical Applications

Nanobiomaterials such as virus particles and artificial virus particles offer tremendous opportunities to develop new biomedical applications such as drug- or gene-delivery, imaging and sensing but also improve understanding of biological mechanisms. Recent advances within the field of virus-based systems give insights in how to mimic viral structures and virus assembly processes as well as understanding biodistribution, cell/tissue targeting, controlled and triggered disassembly or release and circulation times. All these factors are of high importance for virus-based functional systems. This review illustrates advances in mimicking and enhancing or controlling these aspects to a high degree toward delivery and imaging applications.

Vaccine Engineering with Dual-Functional Mineral Shell: A Promising Strategy to Overcome Preexisting Immunity

Dual-functional biomineral-vaccine core-shell nanohybrids are obtained using recombinant adenovirus serotype 5 (rAd5) as templates, which efficiently masks the neutralizing epitope of vaccines and preserve their original immunogenicity. The versatile vaccine hybrid can evade the preexisting anti-Ad5 immunity, leading to boosted multifunctional antigen-specific cytokine-secreting T cell responses and presenting promising applications of vaccine-material hybrid for the rational design of vaccines.

Adenoviral Vector Vaccines Antigen Transgene

In the past decade adenovirus-based vaccines have progressed from preclinical studies, which universally showed the vectors’ high immunogenicity, to testing in humans. Clinical trials showed that adenovirus vectors are well tolerated by humans. They induce robust immune responses that can be expanded by booster immunization. The effect of preexisting neutralizing antibodies on vectors’ immunogenicity appears to be less severe than was observed in experimental animals and can readily be circumvented by using vectors to which most humans lack neutralizing antibodies. Additional clinical studies are needed to firmly establish the efficacy of adenoviral vector vaccines.

Microfluidic generation of alginate microgels for the controlled delivery of lentivectors

Microgels fabricated through distinct microfluidic procedures encapsulate and release functioning lentivectors in a controlled manner.

Strategies to circumvent humoral immunity to adeno-associated viral vectors

INTRODUCTION

Recent success in gene therapy of certain monogenic diseases in the clinic has infused enthusiasm into the continued development of recombinant adeno-associated viral (AAV) vectors as next-generation biologics. However, progress in clinical trials has also highlighted the challenges posed by the host humoral immune response to AAV vectors. Specifically, while pre-existing neutralizing antibodies (NAbs) limit the cohort of eligible patients, NAb generation following treatment prevents vector re-dosing.

AREAS COVERED

In this review, we discuss a spectrum of complementary strategies that can help circumvent the host humoral immune response to AAV.

EXPERT OPINION

Specifically, we present a dual perspective, that is, vector versus host, and highlight the clinical attributes, potential caveats and limitations as well as complementarity associated with the various approaches.

MicroRNA delivery for regenerative medicine

MicroRNA (miRNA) directs post-transcriptional regulation of a network of genes by targeting mRNA. Although relatively recent in development, many miRNAs direct differentiation of various stem cells including induced pluripotent stem cells (iPSCs), a major player in regenerative medicine. An effective and safe delivery of miRNA holds the key to translating miRNA technologies. Both viral and nonviral delivery systems have seen success in miRNA delivery, and each approach possesses advantages and disadvantages. A number of studies have demonstrated success in augmenting osteogenesis, improving cardiogenesis, and reducing fibrosis among many other tissue engineering applications. A scaffold-based approach with the possibility of local and sustained delivery of miRNA is particularly attractive since the physical cues provided by the scaffold may synergize with the biochemical cues induced by miRNA therapy. Herein, we first briefly cover the application of miRNA to direct stem cell fate via replacement and inhibition therapies, followed by the discussion of the promising viral and nonviral delivery systems. Next we present the unique advantages of a scaffold-based delivery in achieving lineage-specific differentiation and tissue development.

Gene delivery from polymer scaffolds for tissue engineering

The combination of gene therapy with tissue engineering offers the potential to direct progenitor cell proliferation and differentiation into functional tissue replacements. Many approaches to engineering tissue replacements feature a polymer scaffold to create and maintain a space, support cell adhesion, and organize tissue formation. Polymer scaffolds, either natural, synthetic, or a combination of the two, have also been adapted to serve as delivery vehicles for viral and nonviral vectors, which can induce the expression of tissue inductive factors. Gene delivery is a versatile approach, capable of targeting any cellular process through localized expression of tissue inductive factors. The design and application of tissue engineering scaffolds for localized gene transfer are reviewed. Scaffolds are designed either to release the vector into the local tissue environment or maintain the vector at the polymer surface, which is regulated by the effective affinity of the vector for the polymer. Polymeric delivery can enhance gene transfer locally, promote and extend transgene expression, avoid vector distribution to distant tissues, and reduce the immune response to the vector. Scaffolds capable of controlled DNA delivery can provide a fundamental tool for directing progenitor cell function, which has applications with the engineering of numerous types of tissue. The utility of this approach will increase with the development of design parameters that correlate release and transgene expression, and with continued research into the biology of tissue formation.

Synthesis and enhanced thermal stability of albumins@alumina: towards injectable sol-gel materials

A major obstacle to the introduction of bioactively-doped sol-gel based materials for medical applications has been the fact that silica - the most widely studied sol-gel material - despite being a GRAS material, which is widely used as an additive in foods and drug formulations, is still not approved by regulatory agencies for intramuscular injections. Here we point to a potential solution to this problem by shifting the weight to alumina, which is approved for injections as the most common immunization adjuvant. Towards the achievement of this goal we describe the development of protein entrapment methods tailored to alumina, and show high thermal stability of protein-dopants, using a newly developed DSC methodology for this purpose.

Hydrogels for lentiviral gene delivery

INTRODUCTION

Gene delivery from hydrogel biomaterials provides a fundamental tool for a variety of clinical applications including regenerative medicine, gene therapy for inherited disorders and drug delivery. The high water content and mild gelation conditions of hydrogels support their use for gene delivery by preserving activity of lentiviral vectors and acting to shield vectors from any host immune response.

AREAS COVERED

Strategies to control lentiviral entrapment within and retention/release from hydrogels are reviewed. The authors discuss the ability of hydrogel design parameters to control the transgene expression profile and the capacity of hydrogels to protect vectors from (and even modulate) the host immune response.

EXPERT OPINION

Delivery of genetic vectors from scaffolds provides a unique opportunity to capitalize on the potential synergy between the biomaterial design for cell processes and gene delivery. Hydrogel properties can be tuned to directly control the events that determine the tissue response to controlled gene delivery, which include the extent of cell infiltration, preservation of vector activity and vector retention. While some design parameters have been identified, numerous opportunities for investigation are available in order to develop a complete model relating the biomaterial properties and host response to gene delivery.

Circumventing antivector immunity by using adenovirus-infected blood cells for repeated application of adenovirus-vectored vaccines: proof of concept in rhesus macaques

Adenovirus has been extensively exploited as a vector platform for delivering vaccines. However, preexisting antiadenovirus immunity is the major stumbling block for application of adenovirus-vectored vaccines. In this study, we found that freshly isolated peripheral blood mononuclear cells (PBMCs), mostly CD14(+) cells, from adenovirus serotype 5 (Ad5)-seropositive primates (humans and rhesus macaques) can be efficiently infected with Ad5 in vitro. On the basis of this observation, a novel strategy based on adenoviral vector-infected PBMC (AVIP) immunization was explored to circumvent antivector immunity. Autologous infusion of Ad5-SIVgag-infected PBMCs elicited a strong Gag-specific cellular immune response but induced weaker Ad5-neutralizing antibody (NAb) in Ad5-seronegative macaques than in macaques intramuscularly injected with Ad5-SIVgag. Moreover, Ad5-seropositive macaques receiving multiple AVIP immunizations with Ad5-SIVenv, Ad5-SIVgag, and Ad5-SIVpol vaccines elicited escalated Env-, Gag-, and Pol-specific immune responses after each immunization that were significantly greater than those in macaques intramuscularly injected with these Ad5-SIV vaccines. After challenged intravenously with a highly pathogenic SIVmac239 virus, macaques receiving AVIP immunization demonstrated a significant reduction in viral load at both the peak time and set-point period compared with macaques without Ad5-SIV vaccines. Our study warranted further research and development of the AVIP immunization as a platform for repeated applications of adenovirus-vectored vaccines.

Adenovirus-triggered innate signalling pathways

Adenoviruses are important infectious agents and also emerging vectors in different biomedical applications. These viruses elicit a strong innate and adaptive immune response, which influences both the course of disease and the success of the applied vectors. Several Toll-like Receptor (TLR)-dependent and -independent mechanisms contribute to these responses. Understanding of the involved viral and cellular factors is crucial for the treatment of various adenovirus diseases and the optimal design of adenovirus vector applications. Here we summarize our current understanding of the complex nature of adenovirus-induced innate immune mechanisms.

Enhancing the therapeutic efficacy of adenovirus in combination with biomaterials

With the reason that systemically administered adenovirus (Ad) is rapidly extinguished by innate/adaptive immune responses and accumulation in liver, in vivo application of the Ad vector is strictly restricted. For achieving to develop successful Ad vector systems for cancer therapy, the chemical or physical modification of Ad vectors with polymers has been generally used as a promising strategy to overcome the obstacles. With polyethylene glycol (PEG) first in order, a variety of polymers have been developed to shield the surface of therapeutic Ad vectors and well accomplished to extend circulation time in blood and reduce liver toxicity. However, although polymer-coated Ads can successfully evacuate from a series of guarding systems in vivo and locate within tumors by enhanced permeability and retention (EPR) effect, the possibility to entering into the target cell is few and far between. To endow targeting moiety to polymer-coated Ad vectors, a diversity of ligands such as tumor-homing peptides, growth factors or antibodies, have been introduced with avoiding unwanted transduction and enhancing therapeutic efficacy. Here, we will describe and classify the characteristics of the published polymers with respect to Ad vectors. Furthermore, we will also compare the properties of variable targeting ligands, which are being utilized for addressing polymer-coated Ad vectors actively.

Electrospun nanofibrous scaffolds for controlled release of adeno-associated viral vectors

The integration of viral gene delivery with key features of biomaterial scaffolds that modulate viral delivery in a controlled manner offers a promising strategy for numerous tissue engineering applications. In this study adeno-associated virus (AAV), which is widely utilized in human gene therapy as a gene carrier due to its safety and efficient gene delivery capability, was encapsulated within electrospun nanofibrous scaffolds composed of blended mixtures of elastin-like polypeptides (ELP) and poly (ε-caprolactone) (PCL) and was employed to transduce fibroblasts adherent on the scaffolds. Combinatorial interactions between ELP and PCL chains upon physical blending significantly altered the mechanical properties (i.e. wettability, elastic modulus, strain, etc.) of the ELP/PCL composites, thus providing key tools to mediate controlled release of AAV vectors and robust cellular transduction on the fibrous scaffolds. The ability of ELP/PCL composites to manipulate the controlled release of AAV-mediated gene delivery for subsequent high-efficiency cellular transduction will provide tremendous opportunities for a variety of tissue engineering applications.

Enhancing the Clinical Potential of AAV Vectors by Capsid Engineering to Evade Pre-Existing Immunity

Vectors based on adeno-associated viruses (AAV) have shown considerable promise in both preclinical models and increasingly in clinical trials. However, one formidable challenge is pre-existing immunity due to widespread exposure to numerous AAV variants and serotypes within the human population, which affect efficacy of clinical trials due to the accompanying high levels of anti-capsid neutralizing antibodies. Transient immunosuppression has promise in mitigating cellular and humoral responses induced by vector application in naïve hosts, but cannot overcome the problem that pre-existing neutralizing antibodies pose toward the goal of safe and efficient gene delivery. Shielding of AAV from antibodies, however, may be possible by covalent attachment of polymers to the viral capsid or by encapsulation of vectors inside biomaterials. In addition, there has been considerable progress in using rational mutagenesis, combinatorial libraries, and directed evolution approaches to engineer capsid variants that are not recognized by anti-AAV antibodies generally present in the human population. While additional progress must be made, such strategies, alone or in combination with immunosuppression to avoid de novo induction of antibodies, have strong potential to significantly enhance the clinical efficacy of AAV vectors.

Future of local bone regeneration - Protein versus gene therapy

The most promising attempts to achieve bone regeneration artificially are based on the application of mediators such as bone morphogenetic proteins (BMPs) directly to the deficient tissue site. BMPs, as promoters of the regenerative process, have the ability to induce de novo bone formation in various tissues, and many animal models have demonstrated their high potential for ectopic and orthotopic bone formation. However, the biological activity of the soluble factors that promote bone formation in vivo is limited by diffusion and degradation, leading to a short half-life. Local delivery remains a problem in clinical applications. Several materials, including hydroxyapatite, tricalcium phosphate, demineralised bone matrices, poly-lactic acid homo- and heterodimers, and collagen have been tested as carriers and delivery systems for these factors in a sustained and appropriate manner. Unfortunately these delivery vehicles often have limitations in terms of biodegradability, inflammatory and immunological rejection, disease transmission, and most importantly, an inability to provide a sustained, continuous release of these factors at the region of interest. In coping with these problems, new approaches have been established: genes encoding these growth factor proteins can be delivered to the target cells. In this way the transfected cells serve as local "bioreactors", as they express the exogenous genes and secrete the synthesised proteins into their vicinity. The purpose of this review is to present the different methods of gene versus growth factor delivery in tissue engineering. Our review focuses on these promising and innovative methods that are defined as regional gene therapy and provide an alternative to the direct application of growth factors. Various advantages and disadvantages of non-viral and viral vectors are discussed. This review identifies potential candidate genes and target cells, and in vivo as well as ex vivo approaches for cell transduction and transfection. In explaining the biological basis, this paper also refers to current experimental and clinical applications.

Engineering biomaterial systems to enhance viral vector gene delivery

Integrating viral gene delivery with engineered biomaterials is a promising strategy to overcome a number of challenges associated with virus-mediated gene delivery, including inefficient delivery to specific cell types, limited tropism, spread of vectors to distant sites, and immune responses. Viral vectors can be combined with biomaterials either through encapsulation within the material or immobilization onto a material surface. Subsequent biomaterial-based delivery can increase the vector's residence time within the target site, thereby potentially providing localized delivery, enhancing transduction, and extending the duration of gene expression. Alternatively, physical or chemical modification of viral vectors with biomaterials can be employed to modulate the tropism of viruses or reduce inflammatory and immune responses, both of which may benefit transduction. This review describes strategies to promote viral gene delivery technologies using biomaterials, potentially providing opportunities for numerous applications of gene therapy to inherited or acquired disorders, infectious disease, and regenerative medicine.

Production of adenovirus vectors and their use as a delivery system for influenza vaccines

IMPORTANCE OF THE FIELD

With the emergence of highly pathogenic avian influenza H5N1 viruses that have crossed species barriers and are responsible for lethal infections in humans in many countries, there is an urgent need for the development of effective vaccines which can be produced in large quantities at a short notice and confer broad protection against these H5N1 variants. In order to meet the potential global vaccine demand in a pandemic scenario, new vaccine-production strategies must be explored in addition to the currently used egg-based technology for seasonal influenza.

AREAS COVERED IN THIS REVIEW

Adenovirus (Ad) based influenza vaccines represent an attractive alternative/supplement to the currently licensed egg-based influenza vaccines. Ad-based vaccines are relatively inexpensive to manufacture, and their production process does not require either chicken eggs or labor-intensive and time-consuming processes necessitating enhanced biosafety facilities. Most importantly, in a pandemic situation, this vaccine strategy could offer a stockpiling option to reduce the response time before a strain-matched vaccine could be developed.

WHAT THE READER WILL GAIN

This review discusses Ad-vector technology and the current progress in the development of Ad-based influenza vaccines.

TAKE HOME MESSAGE

Ad vector-based influenza vaccines for pandemic preparedness are under development to meet global vaccine demand.

Potentiating cancer immunotherapy using an oncolytic virus

Oncolytic viruses (OVs) are highly immunogenic and this limits their use in immune-competent hosts. Although immunosuppression may improve viral oncolysis, this gain is likely achieved at the cost of antitumoral immunity. We have developed a strategy wherein the immune response against the OV leads to enhanced therapeutic outcomes. We demonstrate that immunization with an adenoviral (Ad) vaccine before treatment with an oncolytic vesicular stomatitis virus (VSV) expressing the same tumor antigen (Ag) leads to significantly enhanced antitumoral immunity. Intratumoral replication of VSV was minimally attenuated in Ad-immunized hosts but extending the interval between treatments reduced the attenuating effect and further increased antitumoral immunity. More importantly, our combination approach shifted the immune response from viral Ags to tumor Ags and further reduced OV replication in normal tissues, leading to enhancements in both efficacy and safety. These studies also highlight the benefits of using a replicating, OV to boost a pre-existing antitumoral immune response as this approach generated larger responses versus tumor Ag in tumor-bearing hosts than could be achieved in tumor-free hosts. This strategy should be applicable to other vector combinations, tumor Ags, and tumor targets.

Engineered adenovirus serotypes for overcoming anti-vector immunity

Adenovirus (Ad)-based gene transfer has been successfully utilised in gene therapy and vaccine applications. To date, an increasing number of human clinical trials utilise recombinant Ad-based vectors as a gene transfer platform. In particular, progress has been made recently in utilising Ad-based vectors as a vaccine platform in HIV, cancer immunotherapy approaches and in vaccination for other infections. Despite these successes, the scientific and bio-industrial communities have recently recognised that innate and pre-existing immunity against Ad vectors can constitute a serious obstacle to the development and application of this technology. It is essential to overcome vector-mediated immune responses, such as production of inflammatory cytokines and pre-existing immunity to Ad, because the induction of these responses not only shortens the period of gene expression but also leads to serious side effects. This review focuses on the biology of Ad infection and the approaches that are being adopted to overcome immunity against the Ad-based vectors.

Using viral vectors as gene transfer tools (Cell Biology and Toxicology Special Issue: ETCS-UK 1 day meeting on genetic manipulation of cells)

In recent years, the development of powerful viral gene transfer techniques has greatly facilitated the study of gene function. This review summarises some of the viral delivery systems routinely used to mediate gene transfer into cell lines, primary cell cultures and in whole animal models. The systems described were originally discussed at a 1-day European Tissue Culture Society (ETCS-UK) workshop that was held at University College London on 1st April 2009. Recombinant-deficient viral vectors (viruses that are no longer able to replicate) are used to transduce dividing and post-mitotic cells, and they have been optimised to mediate regulatable, powerful, long-term and cell-specific expression. Hence, viral systems have become very widely used, especially in the field of neurobiology. This review introduces the main categories of viral vectors, focusing on their initial development and highlighting modifications and improvements made since their introduction. In particular, the use of specific promoters to restrict expression, translational enhancers and regulatory elements to boost expression from a single virion and the development of regulatable systems is described.

Adenoviral vector-based strategies for cancer therapy

Definitive treatment of cancer has eluded scientists for decades. Current therapeutic modalities like surgery, chemotherapy, radiotherapy and receptor-targeted antibodies have varied degree of success and generally have moderate to severe side effects. Gene therapy is one of the novel and promising approaches for therapeutic intervention of cancer. Viral vectors in general and adenoviral (Ad) vectors in particular are efficient natural gene delivery systems and are one of the obvious choices for cancer gene therapy. Clinical and preclinical findings with a wide variety of approaches like tumor suppressor and suicide gene therapy, oncolysis, immunotherapy, anti-angiogenesis and RNA interference using Ad vectors have been quite promising, but there are still many hurdles to overcome. Shortcomings like increased immunogenicity, prevalence of preexisting anti-Ad immunity in human population and lack of specific targeting limit the clinical usefulness of Ad vectors. In recent years, extensive research efforts have been made to overcome these limitations through a variety of approaches including the use of conditionally-replicating Ad and specific targeting of tumor cells. In this review, we discuss the potential strengths and limitations of Ad vectors for cancer therapy.

Adenovirus receptors and their implications in gene delivery

Adenoviruses (Ads) have gained popularity as gene delivery vectors for therapeutic and prophylactic applications. Ad entry into host cells involves specific interactions between cell surface receptors and viral capsid proteins. Several cell surface molecules have been identified as receptors for Ad attachment and entry. Tissue tropism of Ad vectors is greatly influenced by their receptor usage. A variety of strategies have been investigated to modify Ad vector tropism by manipulating the receptor-interacting moieties. Many such strategies are aimed at targeting and/or detargeting of Ad vectors. In this review, we discuss the various cell surface molecules that are implicated as receptors for virus attachment and internalization. Special emphasis is given to Ad types that are utilized as gene delivery vectors. Various strategies to modify Ad tropism using the knowledge of Ad receptors are also discussed.

A novel chimpanzee serotype-based adenoviral vector as delivery tool for cancer vaccines

The use of adenovirus (Ad) as vaccine vectors is hindered by pre-existing immunity to human Ads in most of the human population. In order to overcome this limitation, uncommon alternative Ad serotypes need to be utilized. In this study, an E1-E3 deleted recombinant Ad based on the chimpanzee serotype 3 (ChAd3) was engineered to express human carcinoembryonic antigen (CEA) protein or rat neu extracellular/transmembrane domains (ECD.TM). ChAd3 vectors were tested in CEA transgenic (CEA.Tg) and BALB/NeuT mice, which show immunologic tolerance to these antigens. ChAd3 is capable of inducing an immune response comparable to that of hAd5 serotype-based vectors, thus breaking tolerance to tumor associated antigens (TAAs) and achieving anti-tumor effects. Of importance is that ChAd3 can overcome hAd5 pre-existing immunity and work in conjunction with DNA electroporation (DNA-EP) and other Ad vaccines based on common human serotypes.