Poly (lactic-glycolic) acid copolymer encapsulation of recombinant adenovirus reduces immunogenicity in vivo

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.

Clinical applications of the CRISPR/Cas9 genome-editing system: Delivery options and challenges in precision medicine

CRISPR/Cas9 is an effective gene editing tool with broad applications for the prevention or treatment of numerous diseases. It depends on CRISPR (clustered regularly interspaced short palindromic repeats) as a bacterial immune system and plays as a gene editing tool. Due to the higher specificity and efficiency of CRISPR/Cas9 compared to other editing approaches, it has been broadly investigated to treat numerous hereditary and acquired illnesses, including cancers, hemolytic diseases, immunodeficiency disorders, cardiovascular diseases, visual maladies, neurodegenerative conditions, and a few X-linked disorders. CRISPR/Cas9 system has been used to treat cancers through a variety of approaches, with stable gene editing techniques. Here, the applications and clinical trials of CRISPR/Cas9 in various illnesses are described. Due to its high precision and efficiency, CRISPR/Cas9 strategies may treat gene-related illnesses by deleting, inserting, modifying, or blocking the expression of specific genes. The most challenging barrier to the in vivo use of CRISPR/Cas9 like off-target effects will be discussed. The use of transfection vehicles for CRISPR/Cas9, including viral vectors (such as an Adeno-associated virus (AAV)), and the development of non-viral vectors is also considered.

Current applications and future perspective of CRISPR/Cas9 gene editing in cancer

Clustered regularly interspaced short palindromic repeats (CRISPR) system provides adaptive immunity against plasmids and phages in prokaryotes. This system inspires the development of a powerful genome engineering tool, the CRISPR/CRISPR-associated nuclease 9 (CRISPR/Cas9) genome editing system. Due to its high efficiency and precision, the CRISPR/Cas9 technique has been employed to explore the functions of cancer-related genes, establish tumor-bearing animal models and probe drug targets, vastly increasing our understanding of cancer genomics. Here, we review current status of CRISPR/Cas9 gene editing technology in oncological research. We first explain the basic principles of CRISPR/Cas9 gene editing and introduce several new CRISPR-based gene editing modes. We next detail the rapid progress of CRISPR screening in revealing tumorigenesis, metastasis, and drug resistance mechanisms. In addition, we introduce CRISPR/Cas9 system delivery vectors and finally demonstrate the potential of CRISPR/Cas9 engineering to enhance the effect of adoptive T cell therapy (ACT) and reduce adverse reactions.

Delivery of CRISPR-Cas9 system for screening and editing RNA binding proteins in cancer

RNA-binding proteins (RBPs) play an important role in RNA metabolism, regulating the stability, localization, and functional dynamics of RNAs. Alternation in the RBP-RNA network has profound implications in cellular physiology, and is related to the development and spread of cancer in certain cases. To regulate the expression of specific genes and their biological activities, various strategies have been applied to target RBPs for cancer treatments, including small-molecule inhibitors, small-interfering RNA, peptides, and aptamers. Recently, the deployment of the CRISPR-Cas9 technology has provided a new platform for RBP screening and regulation. This review summarizes the delivery systems of the CRISPR-Cas9 system and their role in RBP-based cancer therapeutics, including identification of novel RBPs and regulation of cancer-associated RBPs. The efficient delivery of the CRISPR-Cas9 system is important to the profound understanding and clinical transition of RBPs as cancer therapeutic targets.

Integrative approaches to enhance adeno-associated viral gene delivery

To meet the present and future challenges in achieving therapeutic in vivo gene delivery using adeno-associated virus (AAV), new innovations are required that integrate knowledge from disciplines ranging from biomaterials science, drug delivery, immunobiology, to tissue engineering. One of the foremost challenges remaining is in addressing pre-existing and therapy induced immune responses to AAV which significantly limit its therapeutic effect. In addition, functional correction of diseased tissues will depend on the ability of AAVs to retain activity after local or systemic administration and broadly distribute in target tissues. In this contribution to the Orations - New Horizons of the Journal of Controlled Release, I will introduce new concepts and potential strategies pursued by our lab and others to better understand and overcome these hurdles to effective AAV gene therapy. These multi-disciplinary approaches may open the door to the creation of precision gene therapies to treat heavily burdensome and often deadly diseases.

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.

Delivery systems for enhancing oncolytic adenoviruses efficacy

Oncolytic adenovirus (OAds) has long been considered a promising biotherapeutic agent against various types of cancer owing to selectively replicate in and lyse cancer cells, while remaining dormant in healthy cells. In the last years, multiple (pre)clinical studies using genetic engineering technologies enhanced OAds anti-tumor effects in a broad range of cancers. However, poor targeting delivery, tropism toward healthy tissues, low-level expression of Ad receptors on tumor cells, and pre-existing neutralizing antibodies are major hurdles for systemic administration of OAds. Different vehicles have been developed for addressing these obstacles, such as stem cells, nanoparticles (NPs) and shielding polymers, extracellular vesicles (EVs), hydrogels, and microparticles (MPs). These carriers can enhance the therapeutic efficacy of OVs through enhancing transfection, circulatory longevity, cellular interactions, specific targeting, and immune responses against cancer. In this paper, we reviewed adenovirus structure and biology, different types of OAds, and the efficacy of different carriers in systemic administration of OAds.

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.

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.

Heterologous prime-boost vaccination with adenoviral vector and protein nanoparticles induces both Th1 and Th2 responses against Middle East respiratory syndrome coronavirus

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Immunization with MERS spike protein nanoparticles induced only Th2-biased response.

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Heterologous prime-boost immunization induced both Th1 and Th2-biased responses.

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Our vaccination strategy showed the protective effect against MERS-CoV.

The Middle East respiratory syndrome coronavirus (MERS-CoV) is a highly pathogenic and zoonotic virus with a fatality rate in humans of over 35%. Although several vaccine candidates have been developed, there is still no clinically available vaccine for MERS-CoV. In this study, we developed two types of MERS-CoV vaccines: a recombinant adenovirus serotype 5 encoding the MERS-CoV spike gene (Ad5/MERS) and spike protein nanoparticles formulated with aluminum (alum) adjuvant. Next, we tested a heterologous prime–boost vaccine strategy, which compared priming with Ad5/MERS and boosting with spike protein nanoparticles and vice versa, with homologous prime–boost vaccination comprising priming and boosting with either spike protein nanoparticles or Ad5/MERS. Although both types of vaccine could induce specific immunoglobulin G against MERS-CoV, neutralizing antibodies against MERS-CoV were induced only by heterologous prime–boost immunization and homologous immunization with spike protein nanoparticles. Interestingly, Th1 cell activation was induced by immunization schedules including Ad5/MERS, but not by those including only spike protein nanoparticles. Heterologous prime–boost vaccination regimens including Ad5/MERS elicited simultaneous Th1 and Th2 responses, but homologous prime–boost regimens did not. Thus, heterologous prime–boost may induce longer-lasting immune responses against MERS-CoV because of an appropriate balance of Th1/Th2 responses. However, both heterologous prime–boost and homologous spike protein nanoparticles vaccinations could provide protection from MERS-CoV challenge in mice. Our results demonstrate that heterologous immunization by priming with Ad5/MERS and boosting with spike protein nanoparticles could be an efficient prophylactic strategy against MERS-CoV infection.

Neutralizing antibodies against adenovirus type 2 in normal and HIV-1-infected subjects: Implications for use of Ad2 vectors in vaccines

Pre-existing neutralizing antibodies (NAbs) directed against vaccine vectors have attracted considerable research attention. Therefore, our aim was to establish a high-throughput economical neutralization assay to investigate the epidemiology of adenovirus type 2 (Ad2)-specific immunity in China and developed countries, including in a Chinese Human immunodeficiency virus (HIV)-1-infected population, and to guide the application of Ad2-vectored vaccines. We established a FluoroSpot-based anti-Ad2-virus neutralization assay using a recombinant replication-deficient Ad2 that expresses enhanced green fluorescent protein and standardized the critical parameters, including the choice of cell line, cell concentration, viral infective dose, and incubation time. The sera of 561 healthy individuals from China and developed countries and from 230 HIV-1-infected Chinese individuals were screened with this assay for Nabs against Ad2. The prevalence of anti-Ad2 NAbs was high in both China (92.2%) and developed countries (86.9%). Of the Ad2-seropositive individuals, 64.6% in China and 77.4% in developed countries had high NAb titers (> 810). The frequency of anti-Ad2 NAbs was higher in Anhui (97.5%) than in Beijing (88.7%). Their prevalence differed significantly according to age in Beijing, but not in Anhui Province, but by sex in neither province. Ad2 seroprevalence was as high among HIV-1-infected individuals (88.7%) as among healthy individuals (92.2%) in China. In conclusion, a simple, intuitive, high-throughput, economical fluorescence-based neutralization assay was developed to determine anti-Ad2 NAbs titers. Ad2 exposure was high in both healthy and HIV-1-infected populations in China, so vectors based on Ad2 may be inappropriate for human vaccines.

A bacterial-biofilm-induced oral osteolytic infection can be successfully treated by immuno-targeting an extracellular nucleoid-associated protein

Periodontal disease exemplifies a chronic and recurrent infection with a necessary biofilm component. Mucosal inflammation is a hallmark response of the host seen in chronic diseases, such as colitis, gingivitis, and periodontitis (and the related disorder peri-implantitis). We have taken advantage of our recently developed rat model of human peri-implantitis that recapitulates osteolysis, the requirement of biofilm formation, and the perpetuation of the bona fide disease state, to test a new therapeutic modality with two novel components. First we used hyperimmune antiserum directed against the DNABII family of proteins, now known to be a critical component of the extracellular matrix of bacterial biofilms. Second we delivered the antiserum as cargo in biodegradable microspheres to the site of the biofilm infection. We demonstrated that delivery of a single dose of anti-DNABII in poly(lactic-co-glycolic acid) (PLGA) microspheres induced significant resolution of experimental peri-implantitis, including marked reduction of inflammation. These data support the continued development of a DNABII protein-targeted therapeutic for peri-implantitis and other chronic inflammatory pathologies of the oral cavity in animals and humans.

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.

Drug encapsulated polymeric microspheres for intracranial tumor therapy: A review of the literature

Despite intensive surgical excision, radiation therapy, and chemotherapy, the current life expectancy for patients diagnosed with glioblastoma multiforme is only 12 to 15months. One of the approaches being explored to increase chemotherapeutic efficacy is to locally deliver chemotherapeutics encapsulated within degradable, polymeric microspheres. This review describes the techniques used to formulate drug encapsulated microspheres targeted for intracranial tumor therapy and how microsphere characteristics such as drug loading and encapsulation efficiency can be tuned based on formulation parameters. Further, the results of in vitro studies are discussed, detailing the varied drug release profiles obtained and validation of drug efficacy. Finally, in vivo results are summarized, highlighting the study design and the effectiveness of the drug encapsulated microspheres applied intracranially.

Preparation of microspheres encapsulating a recombinant TIMP-1 adenovirus and their inhibition of proliferation of hepatocellular carcinoma cells

OBJECTIVE

The study aim was to prepare poly-DL-lactide-poly (PELA) microspheres encapsulating recombinant tissue inhibitors of metalloproteinase-1 (TIMP-1) in an adenovirus to investigate its inhibition on the proliferation of hepatocellular carcinoma cells HepG2.

METHODS

Microspheres were prepared by encapsulating the recombinant TIMP-1 adenovirus into biodegradable PELA. The particle size, viral load, encapsulation efficiency and in-vitro release were measured. Microspheres were used to infect HepG2 cells, then infection efficiency was examined under a fluorescent microscope and ultrastructural changes assessed by TEM. Expression of TIMP-1 mRNA in HepG2 cells was examined by semi-quantitative RT-PCR and proliferation by MTT and cell growth curve assays.

RESULTS

We successfully prepared microspheres encapsulating recombinant TIMP-1 adenovirus with a diameter of 1.965μm, an encapsulation efficiency of 60.0%, a viral load of 10.5?108/mg and approximate 60% of virus release within 120 h, the total releasing time of which was longer than 240 h. The microspheres were confirmed to be non-toxic with blank microspheres. Infected HepG2 cells could stably maintain in-vitro expression of TIMP-1, with significantly effects on biological behaviour.

CONCLUSION

PELA microspheres encapsulating a recombinant TIMP-1 adenovirus can markedly inhibit the proliferation of HepG2 cells, which provides an experimental basis for polymer/chemistry-based gene therapy of hepatocellular carcinomas.

Encapsulation of adenovirus serotype 5 in anionic lecithin liposomes using a bead-based immunoprecipitation technique enhances transfection efficiency

Oncolytic viruses (OVs) constitute a promising class of cancer therapeutics which exploit validated genetic pathways known to be deregulated in many cancers. To overcome an immune response and to enhance its potential use to treat primary and metastatic tumors, a method for liposomal encapsulation of adenovirus has been developed. The encapsulation of adenovirus in non-toxic anionic lecithin-cholesterol-PEG liposomes ranging from 140 to 180 nm in diameter have been prepared by self-assembly around the viral capsid. The encapsulated viruses retain their ability to infect cancer cells. Furthermore, an immunoprecipitation (IP) technique has shown to be a fast and effective method to extract non-encapsulated viruses and homogenize the liposomes remaining in solution. 78% of adenovirus plaque forming units were encapsulated and retained infectivity after IP processing. Additionally, encapsulated viruses have shown enhanced transfection efficiency up to 4 × higher compared to non-encapsulated Ads. Extracting non-encapsulated viruses from solution may prevent an adverse in vivo immune response and may enhance treatment for multiple administrations.

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.

Double-deleted vaccinia virus in virotherapy for refractory and metastatic pediatric solid tumors

BACKGROUND

Previous studies have shown successful antitumor effects of systemically delivered double-deleted vaccinia virus (vvDD) against a number of adult tumor models, including glioma, colon and ovarian cancers. The purpose of this study was to investigate the oncolytic potential of vvDD against a panel of cell lines representative of pediatric solid tumors that are currently difficult to cure.

METHODS

Cell lines derived from central nervous system atypical teratoid rhabdoid tumor (AT/RT) (BT12, BT16 and KCCF1), sarcoma (143B, HOS, RD and RH30), and neuroblastoma (SKNAS, SKNBE2, IMR-5 and IMR-32) were examined for vvDD mediated cytotoxicity defined by virus expansion followed by loss of tumor cell viability. The normal human fibroblast cell line HS68 was used as a control. Next, relevant orthotopic, subcutaneous and lung metastasis xenograft models were treated with intravenous doses of live vvDD or killed virus controls (DV). Tumor growth inhibition and viral replication were quantified and survival outcomes of these animals were assessed.

RESULTS

vvDD was able to infect and kill nine of eleven of the pediatric tumor cells (81.8%) in vitro. In xenograft models, intravenous administration of a single dose of vvDD significantly inhibited the growth of tumors and prolonged the survival of intracranial and metastatic tumors.

CONCLUSIONS

Oncolytic vvDD administered i.v. shows activity in preclinical models of pediatric malignancies that are resistant to many currently available treatments. Our data support further evaluation of vvDD virotherapy for refractory pediatric solid tumors.

Site-specific gene delivery to stented arteries using magnetically guided zinc oleate-based nanoparticles loaded with adenoviral vectors

Gene therapeutic strategies have shown promise in treating vascular disease. However, their translation into clinical use requires pharmaceutical carriers enabling effective, site-specific delivery as well as providing sustained transgene expression in blood vessels. While replication-deficient adenovirus (Ad) offers several important advantages as a vector for vascular gene therapy, its clinical applicability is limited by rapid inactivation, suboptimal transduction efficiency in vascular cells, and serious systemic adverse effects. We hypothesized that novel zinc oleate-based magnetic nanoparticles (MNPs) loaded with Ad would enable effective arterial cell transduction by shifting vector processing to an alternative pathway, protect Ad from inactivation by neutralizing factors, and allow site-specific gene transfer to arteries treated with stent angioplasty using a 2-source magnetic guidance strategy. Ad-loaded MNPs effectively transduced cultured endothelial and smooth muscle cells under magnetic conditions compared to controls and retained capacity for gene transfer after exposure to neutralizing antibodies and lithium iodide, a lytic agent causing disruption of free Ad. Localized arterial gene expression significantly stronger than in control animal groups was demonstrated after magnetically guided MNP delivery in a rat stenting model 2 and 9 d post-treatment, confirming feasibility of using Ad-loaded MNPs to achieve site-specific transduction in stented blood vessels. In conclusion, Ad-loaded MNPs formed by controlled precipitation of zinc oleate represent a novel delivery system, well-suited for efficient, magnetically targeted vascular gene transfer.

Passive immunization with a recombinant adenovirus expressing an HA (H5)-specific single-domain antibody protects mice from lethal influenza infection

One effective method for the prevention and treatment of influenza infection is passive immunization. In our study, we examined the feasibility of creating an antibody-based preparation with a prolonged protective effect against influenza virus. Single-domain antibodies (sdAbs) specific for influenza virus hemagglutinin were generated. Experiments in mouse models showed 100% survivability for both intranasal sdAbs administration 24h prior to influenza challenge and 24h after infection. sdAb-gene delivery by an adenoviral vector led to gene expression for up to 14days. Protection by a recombinant adenovirus containing the sdAb gene was observed in cases of administration prior to influenza infection (14d-24h). We also demonstrated that the single administration of a combined preparation containing sdAb DNA and protein expanded the protection time window from 14d prior to 48h after influenza infection. This approach and the application of a broad-spectrum sdAbs will allow the development of efficient drugs for the prevention and treatment of viral infections produced by pandemic virus variants and other infections.

Tissue engineering tools for modulation of the immune response

Tissue engineering scaffolds have emerged as a powerful tool within regenerative medicine. These materials are being designed to create environments that promote regeneration through a combination of: (i) scaffold architecture, (ii) the use of scaffolds as vehicles for transplanting progenitor cells, and/or (iii) localized delivery of inductive factors or genes encoding for these inductive factors. This review describes the techniques associated with each of these components. Additionally, the immune response is increasingly recognized as a factor influencing regeneration. The immune reaction to an implant begins with an acute response to the injury and innate recognition of foreign materials, with the subsequent chronic immune response involving specific recognition of antigens (e.g., transplanted cells) by the adaptive immune response, which can eventually lead to rejection of the implant. Thus, we also describe the impact of each component on the immune response, and strategies (e.g., material design, anti-inflammatory cytokine delivery, and immune cell recruitment/transplantation) to modulate, yet not eliminate, the local immune response in order to promote regeneration, which represents another important tool for regenerative medicine.

Chapter six--Adenovirus-based immunotherapy of cancer: promises to keep

Progress in vector design and an increased knowledge of mechanisms underlying tumor-induced immune suppression have led to a new and promising generation of Adenovirus (Ad)-based immunotherapies, which are discussed in this review. As vaccine vehicles Ad vectors (AdVs) have been clinically evaluated and proven safe, but a major limitation of the commonly used Ad5 serotype is neutralization by preexistent or rapidly induced immune responses. Genetic modifications in the Ad capsid can reduce intrinsic immunogenicity and facilitate escape from antibody-mediated neutralization. Further modification of the Ad hexon and fiber allows for liver and scavenger detargeting and selective targeting of, for example, dendritic cells. These next-generation Ad vaccines with enhanced efficacy are now becoming available for testing as tumor vaccines. In addition, AdVs encoding immune-modulating products may be used to convert the tumor microenvironment from immune-suppressive and proinvasive to proinflammatory, thus facilitating cell-mediated effector functions that can keep tumor growth and invasion in check. Oncolytic AdVs, that selectively replicate in tumor cells and induce an immunogenic form of cell death, can also be armed with immune-activating transgenes to amplify primed antitumor immune responses. These novel immunotherapy strategies, employing highly efficacious AdVs in optimized configurations, show great promise and warrant clinical exploration.

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.

Elastin-like polypeptide matrices for enhancing adeno-associated virus-mediated gene delivery to human neural stem cells

The successful development of efficient and safe gene delivery vectors continues to be a major obstacle to gene delivery in stem cells. In this study, we have developed an elastin-like polypeptide (ELP)-mediated adeno-associated virus (AAV) delivery system for transducing fibroblasts and human neural stem cells (hNSCs). AAVs have significant promise as therapeutic vectors because of their safety and potential for use in gene targeting in stem cell research. ELP has been recently employed as a biologically inspired 'smart' biomaterial that exhibits an inverse temperature phase transition, thereby demonstrating promise as a novel drug carrier. The ELP that was investigated in this study was composed of a repetitive penta-peptide with [Val-Pro-Gly-Val-Gly]. A novel AAV variant, AAV r3.45, which was previously engineered by directed evolution to enhance transduction in rat NSCs, was nonspecifically immobilized onto ELPs that were adsorbed beforehand on a tissue culture polystyrene surface (TCPS). The presence of different ELP quantities on the TCPS led to variations in surface morphology, roughness and wettability, which were ultimately key factors in the modulation of cellular transduction. Importantly, with substantially reduced viral quantities compared with bolus delivery, ELP-mediated AAV delivery significantly enhanced delivery efficiency in fibroblasts and hNSCs, which have great potential for use in tissue engineering applications and neurodegenerative disorder treatments, respectively. The enhancement of cellular transduction in stem cells, as well as the feasibility of ELPs for utilization in three-dimensional scaffolds, will contribute to the advancement of gene therapy for stem cell research and tissue regenerative medicine.

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.

Development of adenoviral vector-based mucosal vaccine against influenza

The recent pandemic threat of the influenza virus makes the increased safety and efficiency of vaccination against the pathogen a most important issue. It has been well established that for maximum protective effect, the vaccination should mimic natural infection. Therefore, recent efforts to develop a new influenza vaccine have focused on intranasal immunization strategies. Intranasal immunization is capable of inducing secretory IgA and serum IgG responses to provide a double defense against mucosal pathogens. On the other hand, it is desirable that a live pathogen is not present in the vaccine. In addition, for optimal induction of the immune responses via the nasal route, efficient and safe mucosal adjuvants are also required. This is possible to attain using an adenoviral vector for vaccine development. Adenoviral vectors are capable of delivering and protecting the antigen encoding sequence. They also possess a natural mechanism for penetrating into the nasal mucous membrane and are capable of activating the innate immune response. This review describes the basic prerequisites for the involvement of recombinant adenoviruses for mucosal (nasal) vaccine development against the influenza virus.

Silk-elastinlike protein polymers improve the efficacy of adenovirus thymidine kinase enzyme prodrug therapy of head and neck tumors

BACKGROUND

Adenoviral-directed enzyme prodrug therapy is a promising approach for head and neck cancer gene therapy. The challenges faced by this approach, however, comprise transient gene expression and dissemination of viruses to distant organs.

METHODS

We used recombinant silk-elastinlike protein polymer (SELP) matrices for intratumoral delivery of adenoviruses containing both thymidine kinase-1 and luciferase genes in a nude mouse model of JHU-022 head and neck tumor. Hydrogels made from two SELP analogues (47K and 815K), with similar silk to elastinlike block ratios but different block lengths, were studied for intratumoral viral delivery. Tumor-bearing mice were followed up for tumor progression and luciferase gene expression concomitantly for 5 weeks. Polymer safety was evaluated through body weight change, blood count, and liver and kidney functions, in addition to gross and microscopic histological examination.

RESULTS

SELP-815K analogues efficiently controlled the duration and extent of transfection in tumors for up to 5 weeks with no detectable spread to the liver. An approximately five-fold greater reduction in tumor volume was obtained with matrix-mediated delivery compared to intra-tumoral injection of adenoviruses in saline. SELP matrix proved safe in all injected mice compared to the control group.

CONCLUSIONS

The SELP-controlled gene delivery approach could potentially improve the anticancer activity of virus-mediated gene therapy at the same time as limiting viral spread to normal organs.

The effect of surface modification of adenovirus with an arginine-grafted bioreducible polymer on transduction efficiency and immunogenicity in cancer gene therapy

Adenoviral vectors offer many advantages for cancer gene therapy, including high transduction efficiency, but safety concerns related to severe immunogenicity and other side effects have led to careful reconsideration of their use in human clinical trials. To overcome these issues, a strategy of generating hybrid vectors that combine viral and non-viral elements as more intelligent gene carriers has been employed. Here, we coated adenovirus (Ad) with an arginine-grafted bioreducible polymer (ABP) via electrostatic interaction. We examined the effect of ABP-coated Ad complex at various ABP molecules/Ad particle ratios. Enhanced transduction efficiency was observed in cells treated with cationic ABP polymer-coated Ad complex compared to naked Ad. We also examined the coating of Ad with ABP polymers at the optimal polymer ratio using dynamic light scattering and transmission electron microscopy. In both high and low coxsackie virus and adenovirus receptor (CAR)-expressing cells, ABP-coated Ad complex produced higher levels of transgene expression than cationic polymer 25K PEI. Notably, high cytotoxicity was observed with 25K PEI-coated Ad complex treatment, but not with ABP-coated Ad complex treatment. In addition, ABP-coated Ad complex was not significantly inhibited by serum, in contrast to naked Ad. Moreover, ABP-coated Ad complex significantly reduced the innate immune response relative to naked Ad, as assessed by interleukin-6 (IL-6) cytokine release from macrophage cells. Overall, our studies demonstrate that Ad complex formed with ABP cationic polymer may improve the efficiency of Ad and be a promising tool for cancer gene therapy.

Sustained viral gene delivery through core-shell fibers

Although viral gene transfer is efficient in achieving transgene expression for tissue engineering, drawbacks of virus dissemination, toxicity and transient gene expression due to immune response have hindered its widespread application. Many tissue engineering studies thus opt to genetically engineer cells in vitro prior to their introduction in vivo. However, it would be attractive to obviate the need for in vitro manipulation by transducing the infiltrating progenitor cells in situ. This study introduces the fabrication of a virus-encapsulated electrospun fibrous scaffold to achieve sustained and localized transduction. Adenovirus encoding the gene for green fluorescent protein was efficiently encapsulated into the core of poly(epsilon-caprolactone) fibers through co-axial electrospinning and was subsequently released via a porogen-mediated process. HEK 293 cells seeded on the scaffolds expressed high level of transgene expression over a month, while cells inoculated by scaffold supernatant showed only transient expression for a week. RAW 264.7 cells cultured on the virus-encapsulated fibers produced a lower level of IL-1 beta, TNF-alpha and IFN-alpha, suggesting that the activation of macrophage cells by the viral vector was reduced when encapsulated in the core-shell PCL fibers. In demonstrating sustained and localized cell transduction, this study presents an attractive alternative mode of applying viral gene transfer for regenerative medicine.

Development of adenovirus immobilization strategies for in situ gene therapy

BACKGROUND

Regenerative gene therapy using viral vectors enables transduced cells to express bioactive factors in vivo. Viral delivery with spatial control can enhance transduction efficiency and may limit systemic infection. Consequently, we tethered biotinylated adenovirus via interactions with avidin on chitosan surfaces to gain robust control for in situ transduction.

METHODS

Avidin was either directly conjugated to chitosan (virus-biotin-avidin-material; VBAM) or indirectly docked on biotinylated chitosan surfaces (virus-biotin-avidin-biotin-material; VBABM) to tether biotinylated adenovirus. Enzyme-linked immunosorbent assay (ELISA) and spectroscopic analysis were performed to demonstrate the binding profiles. Biotin-alkaline phosphatase and biotinylated adenovirus were used as different sized particles to evaluate binding efficiencies and were compared by the Sips isotherm adsorption method. Scanning electron microscopy (SEM) examination illustrated virus distribution, and the transduction efficiency was determined by in vitro cell transduction.

RESULTS

ELISA and spectroscopic analysis both demonstrated that the VBAM system led to multilayer avidin formation on biomaterial surfaces, whereas VBABM formed a monolayer of avidin. Sips isotherm adsorption indicated that the VBAM method increased heterogeneity and steric hindrance of binding sites. By contrast, the VBABM method docked avidin on chitosan surfaces and orientated the binding sites to facilitate ligand binding. In addition, SEM images illustrated that the VBABM method led to more even viral distribution. In vitro cell infection experiments also demonstrated that the VBABM system enhanced virus immobilization and thus improved cell transduction efficiency over the VBAM system.

CONCLUSIONS

The VBABM strategy is a superior method for in situ transduction from biomaterials. This strategy could be adapted for use with a variety of biomaterials as well as viral vectors, and thus may be an alternative method for in vivo regenerative gene therapy.

Treatment of hepatocellular carcinoma in mice with PE38KDEL type I mutant-loaded poly(lactic-co-glycolic acid) nanoparticles conjugated with humanized SM5-1 F(ab') fragments

We reported previously the development of SMFv-PE38KDEL type I mutant (PE38KDEL-I; Mut-I), a recombinant immunotoxin in which a single-chain antibody derived from mouse SM5-1 monoclonal antibody is genetically fused to PE38KDEL-I. In comparison with the SMFv-PE38KDEL wild-type, Mut-I showed improved therapeutic efficacy and reduced toxicity. To overcome the problems associated with the immune response to the Pseudomonas exotoxin A (PE) component of Mut-I, we have constructed PE38KDEL-I-loaded poly(lactic-co-glycolic acid) nanoparticles conjugated with F(ab') fragments of a humanized SM5-1 monoclonal antibody (PE-NP-S). PE-NP-S specifically bound to SM5-1 binding protein-expressing hepatocellular carcinoma cell lines and was then internalized by these cells, resulting in significant cytotoxic effect. In SM5-1 binding protein-overexpressing tumor xenograft model, administration of PE-NP-S significantly inhibited tumor development and induced tumor regression. Moreover, PE-NP-S was shown to be much weaker in inducing vascular leakage syndrome in mice than Mut-I. The LD(50) of PE-NP-S was about 4-fold higher than that of Mut-I. Remarkably, PE-NP-S was of low immunogenicity in development of anti-PE neutralizing antibodies in vivo and was less susceptible to inactivation by anti-PE neutralizing antibodies compared with Mut-I. In conclusion, the resultant PE-NP-S possessed increased cancer therapeutic efficacy and had reduced nonspecific toxicity and immunogenicity, suggesting that it is a potential candidate in cancer therapy.

Nasal delivery of an adenovirus-based vaccine bypasses pre-existing immunity to the vaccine carrier and improves the immune response in mice

Pre-existing immunity to human adenovirus serotype 5 (Ad5) is common in the general population. Bypassing pre-existing immunity could maximize Ad5 vaccine efficacy. Vaccination by the intramuscular (I.M.), nasal (I.N.) or oral (P.O.) route with Ad5 expressing Ebola Zaire glycoprotein (Ad5-ZGP) fully protected naïve mice against lethal challenge with Ebola. In the presence of pre-existing immunity, only mice vaccinated I.N. survived. The frequency of IFN-γ+ CD8+ T cells was reduced by 80% and by 15% in animals vaccinated by the I.M. and P.O. routes respectively. Neutralizing antibodies could not be detected in serum from either treatment group. Pre-existing immunity did not compromise the frequency of IFN-γ+ CD8+ T cells (3.9±1% naïve vs. 3.6±1% pre-existing immunity, PEI) nor anti-Ebola neutralizing antibody (NAB, 40±10 reciprocal dilution, both groups). The number of INF-γ+ CD8+ cells detected in bronchioalveolar lavage fluid (BAL) after I.N. immunization was not compromised by pre-existing immunity to Ad5 (146±14, naïve vs. 120±16 SFC/million MNCs, PEI). However, pre-existing immunity reduced NAB levels in BAL by ∼25% in this group. To improve the immune response after oral vaccination, the Ad5-based vaccine was PEGylated. Mice given the modified vaccine did not survive challenge and had reduced levels of IFN-γ+ CD8+ T cells 10 days after administration (0.3±0.3% PEG vs. 1.7±0.5% unmodified). PEGylation did increase NAB levels 2-fold. These results provide some insight about the degree of T and B cell mediated immunity necessary for protection against Ebola virus and suggest that modification of the virus capsid can influence the type of immune response elicited by an Ad5-based vaccine.

Characterization and real-time imaging of gene expression of adenovirus embedded silk-elastinlike protein polymer hydrogels

Transient expression levels, vector dissemination and toxicities associated with adenoviral vectors have prompted the usage of matrices for localized and controlled gene delivery. Two recombinant silk-elastinlike protein polymer analogues, SELP-47K and SELP-415K, consisting of different lengths and ratios of silk and elastin units, were previously shown to be injectable hydrogels capable of matrix-mediated controlled adenoviral gene delivery. Reported here is a study of spatiotemporal control over adenoviral gene expression with these SELP analogues in a human tumor xenograft model of head and neck cancer using whole animal imaging. Real-time images of viral expression levels indicate that polymer concentration and polymer structure are predominant factors that affect viral release and, thus, viral transfection. Decrease in polymer concentration and increase in polymer elastin content results in greater release, probably due to changes in the network structure of the hydrogel. To better understand this relationship, macro- and microstructural properties of the hydrogels were analyzed using dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM). The results confirm that the concentration and the elastin content of the protein polymer affect the pore size of the hydrogel by changing the physical constraints of the SELP fibril network and the degree of hydration of the SELP fibrils. The potential to modulate viral release using SELP hydrogel delivery vehicles that can be injected intratumorally by minimally invasive techniques holds significant promise for the delivery of therapeutic viruses.

Oral adenoviral-based vaccines: historical perspective and future opportunity

Adenoviral vaccines delivered orally have been used for decades to prevent respiratory illness, but are now being seriously explored again as a platform technology to make vaccines against a variety of pathogens. Years of use in military populations as a preventative measure for adenoviral infection have demonstrated the safety of oral administration of adenovirus. The advantages of using this approach as a platform technology for vaccines include rapid development and distribution, as well as ease of administration. Recent discoveries may allow this platform approach to reach the clinic within a few years.

PE38KDEL-loaded anti-HER2 nanoparticles inhibit breast tumor progression with reduced toxicity and immunogenicity

The clinical use of Pseudomonas exotoxin A (PE)-based immunotoxins is limited by the toxicity and immunogenicity of PE. To overcome the limitations, we have developed PE38KDEL-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles conjugated with Fab' fragments of a humanized anti-HER2 monoclonal antibody (rhuMAbHER2). The PE38KDEL-loaded nanoparticles-anti-HER2 Fab' bioconjugates (PE-NP-HER) were constructed modularly with Fab' fragments of rhuMAbHER2 covalently linked to PLGA nanoparticles containing PE38KDEL. Compared with nontargeted nanoparticles that lack anti-HER2 Fab', PE-NP-HER specifically bound to and were sequentially internalized into HER2 overexpressing breast cancer cells, which result in significant cytotoxicity in vitro. In HER2 overexpressing tumor xenograft model system, administration of PE-NP-HER showed a superior efficacy in inhibiting tumor growth compared with PE-HER referring to PE38KDEL conjugated directly to rhuMAbHER2. Moreover, PE-NP-HER was well tolerated in mice with a higher LD(50) (LD(50) of 6.86 +/- 0.47 mg/kg vs. 2.21 +/- 0.32 mg/kg for PE-NP-HER vs. PE-HER (mean +/- SD); n = 3), and had no influence on the plasma level of plasma alanine aminotransferase (ALT) of animals when injected at a dose of 1 mg/kg where PE-HER caused significant increase of serum ALT in the treated mice. Notably, PE-NP-HER was of low immunogenicity in development of anti-PE38KDEL neutralizing antibodies and was less susceptible to inactivation by anti-PE38KDEL antibodies compared with PE-HER. This novel bioconjugate, PE-NP-HER, may represent a useful strategy for cancer treatment.

Characterization of Structurally Related Adenovirus-laden Silk-elastinlike Hydrogels

Genetically engineered silk-elastinlike protein polymer (SELP) analogs, SELP-47 K and -415 K, consisting of varying ratio(s) and length(s) of silk and elastin in their monomer repeats and capable of spontaneous hydrogel formation were evaluated as matrices for controlled adenoviral release in vitro. The degree of swelling (q) and the amount of soluble fraction of SELP hydrogel analogs were evaluated with and without the incorporation of adenoviruses. The results indicate that polymer concentration and structure and not the incorporated adenoviruses are the predominant factors that influence q and the soluble fraction in these hydrogels over a 28-day period. The release of adenoviruses was a function of polymer concentration and structure. The higher cumulative percentage release observed in SELP-415 K compared to SELP-47 K can be attributed to the longer elastin sequence in the polymer backbone. These results indicate the potential of customizing the network properties and release from SELPs by manipulating the macromolecular architecture using recombinant synthesis.

Exploring DNA damage responses in human cells with recombinant adenoviral vectors

Recombinant adenoviral vectors provide efficient means for gene transduction in mammalian cells in vitro and in vivo. We are currently using these vectors to transduce DNA repair genes into repair deficient cells, derived from xeroderma pigmentosum (XP) patients. XP is an autosomal syndrome characterized by a high frequency of skin tumors, especially in areas exposed to sunlight, and, occasionally, developmental and neurological abnormalities. XP cells are deficient in nucleotide excision repair (affecting one of the seven known XP genes, xpa to xpg) or in DNA replication of DNA lesions (affecting DNA polymerase eta, xpv). The adenovirus approach allows the investigation of different consequences of DNA lesions in cell genomes. Adenoviral vectors carrying several xp and photolyases genes have been constructed and successfully tested in cell culture systems and in vivo directly in the skin of knockout model mice. This review summarizes these recent data and proposes the use of recombinant adenoviruses as tools to investigate the mechanisms that provide protection against DNA damage in human cells, as well as to better understand the higher predisposition of XP patients to cancer.

Biomaterial-mediated retroviral gene transfer using self-assembled monolayers

Biomaterial-mediated gene delivery has recently emerged as a promising alternative to conventional gene transfer technologies that focus on direct delivery of viral vectors or DNA-polymer/matrix complexes. However, biomaterial-based strategies have primarily targeted transient gene expression vehicles, including plasmid DNA and adenovirus particles. This study expands on this work by characterizing biomaterial properties conducive to the surface immobilization of retroviral particles and subsequent transduction of mammalian cells at the cell-material interface. Self-assembled monolayers (SAMs) of functionally-terminated alkanethiols on gold were used to establish biomaterial surfaces of defined chemical composition. Gene transfer was observed to be greater than 90% on NH(2)-terminated surfaces, approximately 50% on COOH-functionalized surfaces, and undetectable on CH(3)-terminated SAMs, similar to controls of tissue culture-treated polystyrene. Gene delivery via the NH(2)-SAM was further characterized as a function of retrovirus coating time, virus concentration, and cell seeding density. Finally, SAM-mediated gene delivery was comparable to fibronectin- and poly-l-lysine-based methods for gene transfer. This work is significant to establishing safe and effective gene therapy strategies, developing efficient methods for gene delivery, and supporting recent progress in the field of biomaterial-mediated gene transfer.

Encapsulation of adenoviral vectors into chitosan–bile salt microparticles for mucosal vaccination

The objective of this study is the incorporation of adenoviral vectors into a microparticulate system adequate for mucosal delivery. Microencapsulation of the vectors was accomplished by ionotropic coacervation of chitosan, using bile salts as counter-anion. The process was optimized in order to promote high encapsulation efficiency, with a minimal loss of viral infectivity. The maintenance of sterility during all the encapsulation procedure was also taken into account. The principle relies on the simple addition of a solution containing adenoviral vectors to a solution of neutralized chitosan, under stirring. Some surfactants were added to the chitosan solution, to improve the efficiency of this process, such as Tween 80, and Pluronic F68 at 1% (w/v). Encapsulation efficiency higher than 84% was achieved with formulations containing sodium deoxycholate as counter-anion and Pluronic F68 as dispersant agent. The infectivity of the adenoviral vectors incorporated into microparticles was assessed by release assays in PBS and by direct inoculation in 293 and Caco-2 cells. The release in aqueous media was negligible but, when in contact with monolayers of the cells, an effective release of bioactive adenovirus was obtained. Our work shows that encapsulation in microparticles, not only appear to protect the adenovirus from the external medium, namely from low pH, but can also delay their release that is fully dependent on cell contact, an advantage for mucosal vaccination purposes. The formulations developed are able to maintain AdV infectivity and permit a delayed release of the bioactives that is promoted by digestion in situ of the microparticles by the cell monolayers. The onset of delivery is, that way, host-controlled. In view of these results, these formulations showed good properties for mucosal adenovirus delivery.

Gene-modified tissue-engineered skin: the next generation of skin substitutes

Tissue engineering combines the principles of cell biology, engineering and materials science to develop three-dimensional tissues to replace or restore tissue function. Tissue engineered skin is one of most advanced tissue constructs, yet it lacks several important functions including those provided by hair follicles, sebaceous glands, sweat glands and dendritic cells. Although the complexity of skin may be difficult to recapitulate entirely, new or improved functions can be provided by genetic modification of the cells that make up the tissues. Gene therapy can also be used in wound healing to promote tissue regeneration or prevent healing abnormalities such as formation of scars and keloids. Finally, gene-enhanced skin substitutes have great potential as cell-based devices to deliver therapeutics locally or systemically. Although significant progress has been made in the development of gene transfer technologies, several challenges have to be met before clinical application of genetically modified skin tissue. Engineering challenges include methods for improved efficiency and targeted gene delivery; efficient gene transfer to the stem cells that constantly regenerate the dynamic epidermal tissue; and development of novel biomaterials for controlled gene delivery. In addition, advances in regulatable vectors to achieve spatially and temporally controlled gene expression by physiological or exogenous signals may facilitate pharmacological administration of therapeutics through genetically engineered skin. Gene modified skin substitutes are also employed as biological models to understand tissue development or disease progression in a realistic three-dimensional context. In summary, gene therapy has the potential to generate the next generation of skin substitutes with enhanced capacity for treatment of burns, chronic wounds and even systemic diseases.

Polymers for gene delivery across length scales

A number of human diseases stem from defective genes. One approach to treating such diseases is to replace, or override, the defective genes with normal genes, an approach called 'gene therapy'. However, the introduction of correctly functioning DNA into cells is a non-trivial matter, and cells must be coaxed to internalize, and then use, the DNA in the desired manner. A number of polymer-based synthetic systems, or 'vectors', have been developed to entice cells to use exogenous DNA. These systems work across the nano, micro and macro length scales, and have been under continuous development for two decades, with varying degrees of success. The design criteria for the construction of more-effective delivery vectors at each length scale are continually evolving. This review focuses on the most recent developments in polymer-based vector design at each length scale.

Biomimetic approaches to protein and gene delivery for tissue regeneration

Novel therapeutic strategies that promote wound healing seek to mimic the response of the body to wounding, to regenerate rather than repair injured tissues. Many synthetic or natural biomaterials have been developed for this purpose and are used to deliver wound therapeutics in a controlled manner that prevents unwanted and potentially harmful side-effects. Here, we review the natural and synthetic biomaterials that have been developed for protein and gene delivery to enhance tissue regeneration. Particular emphasis is placed on novel biomimetic materials that respond to environmental stimuli or release their cargo according to cellular demand. Engineering biomaterials to release therapeutic agents in response to physiologic signals mimics the natural healing process and can promote faster tissue regeneration and reduce scarring in severe acute or chronic wounds.

Polyethylene Glycol (Molecular Weight 400 DA) Vehicle Improves Gene Expression of Adenovirus Mediated Gene Therapy

PURPOSE

A significant limitation of adenoviral mediated suicide gene therapy is poor gene distribution in vivo. The choice of vehicle has been demonstrated to affect the level of adenoviral delivered gene transduction. We examined the hypotheses that 1) adenovirus suspended in PEG400 improves gene expression in the naïve canine prostate model, 2) improved transgene expression with PEG400 results in improved tumor control and 3) vehicle affects the initial adenoviral spread from a single intratumor injection.

MATERIALS AND METHODS

The magnitude and volume of gene expression were measured 24 hours following intraprostatic injection of adenovirus suspended in PEG400 (12.5% weight per volume) or saline as vehicle. Tumor growth delay was measured in mice bearing human tumor xenografts following the injection of adenovirus in PEG400 and saline. The initial spread of adenovirus was measured by confocal microscopy following a single injection of fluorescently labeled adenoviral particles in human tumor xenografts using each vehicle.

RESULTS

Adenovirus suspended in PEG400 provided an average of twice the level of gene expression in the canine prostate and significantly better tumor control relative to saline in preclinical tumor models (p = 0.046 and 0.036, respectively). The initial spread of adenovirus with PEG400 was superior to that of adenovirus in saline and the latter was largely limited to the needle tract.

CONCLUSIONS

Adenoviral gene therapy vectors suspended in PEG400 results in improved tumor control because of greater initial adenoviral spread, and the increased volume and magnitude of gene expression in vivo.

Nanoparticulate System for Efficient Gene Transfer into Refractory Cell Targets

A biocompatible, nanoparticulate formulation has been designed to retain, protect, and deliver adenoviral gene constructs over an extended time course. Such devices can be administered locally or systemically with low toxicity. A multipolymeric nanoparticulate system, featuring very high stability in physiologic media, was designed to allow efficient in vitro gene transfer. The efficacy of nanoparticulate delivery is effective in cell systems that are normally refractory to gene transfer, such as pancreatic islets and antigen-presenting cells. The findings suggest a nonspecific uptake system that permits adenoviral particle release within the transfected cells. A comparison with literature data revealed that our system is efficient at much lower levels (at least three orders of magnitude) of infectious viral particles.