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Targeted infection of HIV-1 Env expressing cells by HIV(CD4/CXCR4) vectors reveals a potential new rationale for HIV-1 mediated down-modulation of CD4.

BACKGROUND: Efficient targeted gene transfer and cell type specific transgene expression are important for the safe and effective expression of transgenes in vivo. Enveloped viral vectors allow insertion of exogenous membrane proteins into their envelopes, which could potentially aid in the targeted transduction of specific cell types. Our goal was to specifically target cells that express the T cell tropic HIV-1 envelope protein (Env) using the highly specific interaction of Env with its cellular receptor (CD4) inserted into the envelope of an HIV-1-based viral vector. RESULTS: To generate HIV-1-based vectors carrying the CD4 molecule in their envelope, the CD4 ectodomain was fused to diverse membrane anchors and inserted together with the HIV-1 coreceptor CXCR4 into the envelopes of HIV-1 vector particles. Independent of the type of CD4 anchor, all chimeric CD4 proteins inserted into HIV-1 vector envelopes and the resultant HIV(CD4/CXCR4) particles were able to selectively confer neomycin resistance to cells expressing the fusogenic T cell tropic HIV-1 Env protein. Unexpectedly, in the absence of Env on the target cells, all vector particles carrying the CD4 ectodomain anchored in their envelope adhered to various cell types without infecting these cells. This cell adhesion was very avid. It was independent of the presence of Env on the target cell, the type of CD4 anchor or the presence of CXCR4 on the particle. In mixed cell populations with defined ratios of Env+/Env- cells, the targeted transduction of Env+ cells by HIV(CD4/CXCR4) particles was diminished in proportion to the number of Env- cells. CONCLUSION: Vector diversion caused by a strong, non-selective cell binding of CD4+-vector particles effectively prevents the targeted transduction of HIV-1 Env expressing cells in mixed cell populations. This Env-independent cell adhesion severely limits the effective use of targeted HIV(CD4/CXCR4) vectors designed to interfere with HIV-1 replication in vivo. Importantly, the existence of this newly described and remarkably strong CD4-dependent cell adhesion suggests that the multiple viral efforts to reduce CD4 cell surface expression may, in part, be to prevent cell adhesion to non-target cells and thereby to increase the infectivity of viral progeny. Preventing CD4 down-modulation by HIV-1 might be an effective component of a multi-faceted antiviral strategy.

Animals↗

Recombinant E1-deleted adenoviral vectors induce apoptosis in a rat airway epithelial mucous goblet cell line.

Replication-defective adenoviruses (Ad) are used as vectors for delivering therapeutic genes to human airway cells. We examined whether E1-deleted Ad vectors (Ad5-CMV-LacZ) had effects on cell kinetics in SPOC1 cells, which is a rat airway epithelial mucous goblet cell line. There was a vector multiplicity of infection (moi)-dependent increase of the transduction efficiency of the LacZ reporter gene in SPOC cells. Cell proliferation was inhibited in the vector-infected cells compared with that in vehicle-exposed cells. However, increased cell death was observed in the vector-infected cells with a higher moi. The morphology of vector-exposed cells revealed apoptotic features including nuclear condensation and a fragmented nucleus. These results indicate that higher moi of vectors allows the cells to achieve higher gene transfer, but also induce apoptosis of infected cells. Minimizing the induction of apoptosis of vector-infected cells may be an important strategy for the prolongation of transduction efficiency of Ad vectors in airway epithelial mucous goblet cells.

Adenoviridae↗

Fifty-one kilobase HSV-1 plasmid vector can be packaged using a helper virus-free system and supports expression in the rat brain.

Herpes simplex virus type 1 (HSV-1) plasmid vectors have a number of attractive features for gene transfer into neurons. In particular, the large size of the HSV-1 genome suggests that HSV-1 vectors might be designed to accommodate large inserts. We now report the construction and characterization of a 51 kb HSV-1 plasmid vector. This vector was efficiently packaged into HSV-1 particles using a helper virus-free packaging system. The structure of the packaged vector DNA was verified by both Southern blot and PCR analyses. A vector stock was microinjected into the rat striatum, the rats were sacrificed at 4 days after gene transfer, and numerous X-gal positive striatal cells were observed. This 51 kb vector was constructed using general principles that may support the routine construction of large vectors. Potential applications of such HSV-1 vectors include characterizing large promoter fragments or genomic clones and co-expressing multiple genes.

Animals↗

Lentivirus vector purification using anion exchange HPLC leads to improved gene transfer.

Recombinant lentiviral vectors stably transduce both dividing and nondividing cells. Virus pseudotyping with vesicular stomatitis virus envelope G (VSV-G) protein broadens the host range of lentiviral vector and enables vector concentration by ultra-centrifugation. However, as a result of virus vector concentration, contaminating protein debris derived from vector-producing cell culture media is toxic to target cells and reduces the transduction efficiency. Here we report a new and rapid technique for purifying lentivirus vector using the strong anion exchange column that significantly improves gene transfer rates. We purified VSV-G pseudotyped self-inactivating lentivirus vector and obtained two protein elution peaks (Peak 1 and Peak 2) corresponding to transducing activity. Peak 1 viral particles were 4-8 times more effective in transducing target cells than Peak 2 or non-purified (pre-HPLC) viral particles. We used purified lentivirus vector expressing the human Fanconi anemia group A (FANCA) gene to transduce murine hematopoietic stem/progenitor cells. We observed a consistent 2- to 3-fold increase in gene transfer rates using Peak 1 purified virus compared with non-purified virus. We conclude that the purification method using the HPLC system provides the highly purified virus vector that reduces cell toxicity and significantly improves gene transfer in primary cells.

Animals↗

SV40 pseudovirions as highly efficient vectors for gene transfer and their potential application in cancer therapy.

Among viral and non-viral gene delivery systems, SV40-based vectors show great promise in the cancer gene therapy field. SV40 vectors very efficiently deliver genes such as anti-viral agents, DNA vaccine, genes for chemoprotection (such as ABC transporters genes), suicide genes and antiangiogenic genes. The recombinant SV40 vectors can infect a wide variety of cells-dividing cells as well as non-cycling ones. Most of the SV40-based vectors can incorporate larger transgenes than the capacity of the SV40 wild-type, which is 5.2 kb; Moreover, in vitro packaged vectors demonstrate efficient delivery of plasmids with a molecular weight of up to 17.7 kb. SV40-based vectors carry some SV40 viral sequences, but the SV40 in vitro-packaged vectors are free of any SV40 wild-type viral DNA sequences. These vectors are prepared with nuclear extracts of SF9 insect cells containing the main viral capsid protein of the SV40 wild-type virus, VP1. This review summarizes different strategies in which SV40 vectors are used to deliver genes in vitro, to living mice, and to tumors growing in nude mice.

Antineoplastic Agents↗

Alphavirus vectors for gene therapy applications.

High-titer alphavirus vectors have been generated for efficient gene delivery both in vitro and in vivo. Studies on CNS infection via intranasal and peripheral injections with virulent and avirulent replication-competent Semliki Forest virus (SFV) strains has demonstrated the potential of gene delivery. Replication-deficient alphavirus particles have shown high local transgene expression of a transient nature in rodent brain. Alphavirus vectors have been demonstrated to induce apoptosis in infected human tumor cell lines and SFV vectors expressing interleukin-12 resulted in tumor regression in a B16 murine melanoma model. Repeated SFV injections led to stronger anti-tumor effects without immunogenic response detected against SFV. It has also been shown that intra-tumoral SFV-injections into nude mice with implanted human lung carcinomas led to tumor regression. Likewise, injection of replicative SFV-LacZ RNA resulted in tumor response as well as prophylactic protection against tumor formation. Alphaviruses have also showed potential in vaccine production. Additionally, modifications in the envelope structure of Sindbis virus resulted in substantial change in host range and demonstrated the feasibility of targeting alphavirus vectors. Moreover, SFV has been used as an expression vector for the generation of high-titer retrovirus-like particles. Recent alphavirus vector development has introduced novel non-cytopathogenic vectors, tightly temperature-regulated vectors as well as replication-persistent forms that should prolong the duration of expression. Alphavirus vectors can therefore be considered as highly potential gene delivery vehicles for future gene therapy applications, especially where only short-term expression is required, or even preferred.

Alphavirus↗

Polycistronic viral vectors.

Traditionally, vectors for gene transfer/therapy experiments were mono- or bicistronic. In the latter case, vectors express the gene of interest coupled with a marker gene. An increasing demand for more complex polycistronic vectors has arisen in recent years to obtain complex gene transfer/therapy effects. In particular, this demand is stimulated by the hope of a more powerful effect from combined gene therapy than from single gene therapy in a process whose parallels lie in the multi-drug combined therapies for cancer or AIDS. In the 1980's we had only splicing signals and internal promoters to construct such vectors: now a new set of biotechnological tools enables us to design new and more reliable bicistronic and polycistronic vectors. This article focuses on the description and comparison of the strategies for co-expression of two genes in bicistronic vectors, from the oldest to the more recently described: internal promoters, splicing, reinitiation, IRES, self-processing peptides (e.g. foot-and-mouth disease virus 2A), proteolytic cleavable sites (e.g. fusagen) and fusion of genes. I propose a classification of these strategies based upon either the use of multiple transcripts (with transcriptional mechanisms), or single transcripts (using translational/post-translational mechanisms). I also examine the different attempts to utilize these strategies in the construction of polycistronic vectors and the main problems encountered. Several potential uses of these polycistronic vectors, both in basic research and in therapy-focused applications, are discussed. The importance of the study of viral gene expression strategies and the need to transfer this knowledge to vector design is highlighted.

Artificial Gene Fusion↗

Improvement of nonviral gene therapy by Epstein-Barr virus (EBV)-based plasmid vectors.

The nonviral gene transfer technologies include naked DNA administration, electrical or particle-mediated transfer of naked DNA, and administration of DNA-synthetic macromolecule complex vectors. Each method has its advantage, such as low immunogenicity, inexpensiveness, ease in handling, etc., but the common disadvantage is that the transfection efficiency has been relatively poor as far as conventional plasmid vectors are involved. To improve the nonviral gene transfer systems, Epstein-Barr virus (EBV)-based plasmid vectors (also referred to EBV-based episomal vectors) have been employed. These vectors contain the EBNA1 gene and oriP element that enable high transfer efficiency, strong transgene expression and long term maintenance of the expression. In the current article, I review recent preclinical gene therapy studies with the EBV plasmid vectors conducted against various diseases. For gene therapy against malignancies, drastic tumor suppression was achieved by gancyclovir administrations following an intratumoral injection with an EBV plasmid vector encoding the HSV1-TK suicide gene. Equiping the plasmid with carcinoembryonic antigen (CEA) promoter sequences enabled targeted killing of CEA-positive tumor cells, which was not accomplished by conventional plasmid vectors without the EBV genetic elements. Transfection with an apoptosis-inducing gene was also effective in inhibiting tumors. Interleukin (IL)-12 and IL-18 gene transfer, either local or systemic, induced therapeutic antitumoral immune responses including augmentation of the cytotoxic T lymphocyte (CTL) and natural killer (NK) activities, while an autologous tumor vaccine engineered to secrete Th1 cytokines via the EBV system also induced growth retardation of tumors. Non-EBV conventional plasmids were much less effective in eliciting these therapeutic outcomes. Intracardiomuscular transfer of the beta-adrenergic receptor gene induced a significant elevation in cardiac output in cardiomyopathic animals, suggesting the usefulness of the EBV system in treating heart failure. The EBV-based nonviral delivery also worked as genetic vaccine that triggered prophylactic cellular and humoral immunity against acute lethal viral infection. All the nonviral delivery vehicles so far tested showed an improved transfection rate when combined with the EBV-plasmids. Collectively, the EBV-based plasmid vectors may greatly contribute to nonviral gene therapy against a variety of disorders, including malignant, congenital, chronic and infectious diseases.

Animals↗

Tissue-specific targeting for cardiovascular gene transfer. Potential vectors and future challenges.

The introduction of genes to cardiovascular cells in vivo remains the major challenge for current gene therapy modalities. However, recent developments in retargeting adenoviral vectors are promising to improve transduction efficiency in the cardiovascular cells. After systemic application, most adenoviral vectors are trapped by the liver, hampering delivery to target cardiovascular tissues. Furthermore, a majority of vectors for vascular gene transfer utilizes strong heterologous viral promoters, such as CMV. A potential side effect related to the use of such vectors is the systemic organ toxicity resulting from unrestricted transgene expression. These vectors have the additional problem of being frequently shut-down in vivo. Therefore, both retargeting adenoviral vectors and the use of tissue-specific promoter-driven vectors offer an enhanced safety profile by reducing ectopic expression in vital organs including the liver and lung. However, the limiting factor for the use of tissue-specific promoters is the low-level of expression compared with their viral counterparts. Both the development of efficient and strong vectors using cell-specific regulatory elements and the production of therapeutic proteins at sufficient levels is urgently needed to inhibit vasculoproliferative disorders. This review will focus on some of the recent achievements in vector development relevant to the delivery of vascular gene therapies targeted to the vascular endothelium, smooth muscle cells and macrophages during arterial remodelling.

Adenoviridae↗

Beyond oncolytic virotherapy: replication-competent retrovirus vectors for selective and stable transduction of tumors.

As cancer gene therapy employing replication-defective vectors has met with limited clinical success, there is renewed interest in using replication-competent viruses for oncolytic virotherapy. In preclinical and clinical studies, various attenuated vaccine strains and engineered virus vectors are currently being tested for their ability to achieve tumor-selective cell killing. However, significant improvements are still required in tumor selectivity, cytolytic potency, and modulating immune responses to achieve anti-tumor effects without prematurely terminating virus spread. Recently, we have developed murine leukemia virus (MLV)-based replication-competent retrovirus (RCR) vectors for highly efficient, selective, and persistent gene transfer to cancer cells, and found that such vectors may offer significant advantages as oncolytic agents. In a variety of preclinical models, RCR vectors can achieve efficient and persistent gene delivery as the virus replicates throughout an entire tumor mass after inoculation with initial multiplicities of infection as low as 0.001. When engineered to deliver suicide genes, RCR vectors achieve highly efficient and synchronized cell killing triggered by pro-drug administration, both in culture and in tumor models in vivo. Further strategies are being explored to enhance the packaging capacity, efficiency, and specificity of this vector system through the development of semi-replicative RCR vectors, adenovirus-RCR hybrids, and incorporation of tumor targeting mechanisms via modification of binding tropism and transcriptional regulation. In addition, the ability of these vectors to achieve stable transgene expression in infected tumor cells may allow therapeutic applications that move beyond oncolysis per se.

Drug Design↗

Amplicons as vaccine vectors.

HSV-1 amplicon vectors efficiently transduce cultured antigen-presenting cells (APC), including both human and murine dendritic cells as well as primary human chronic lymphocytic leukemia (CLL) B cells. Helper-free amplicons have been shown to be especially well-suited for this purpose, since they do not impair the antigen-presenting functions of these target cells. In vivo, amplicon vectors have been used in preclinical studies aimed at the development of therapeutic cancer vaccines, as well as vaccines for Alzheimer's disease, and selected microbial pathogens. Studies in small animal model systems have shown that ex vivo transduction of irradiated tumor cells with amplicon vectors encoding immunomodulatory cytokines such as IL-2 or GM-CSF can elicit protective responses against a tumor challenge. In an experimental model for cancer immunotherapy, direct transduction of preformed tumors with vectors encoding CD40L resulted in slowed tumor growth or tumor eradication. Other studies have examined the ability of amplicons to elicit immune responses against encoded antigens, and have shown that strong cellular immune responses can be generated against amplicon encoded HIV-1 antigens in mice. Thus, amplicon vectors have shown significant promise as vaccine vectors in a range of settings. These promising initial findings highlight the need to perform additional studies, including experiments to evaluate the immunogenicity of amplicon vectors in additional animal models, possibly including nonhuman primates. Overall, amplicon vectors offer compelling advantages when compared to other vaccine-delivery platforms, which include the capacity to incorporate a very large transgene payload and the potential to efficiently transduce mucosal surfaces. It will be important to design future studies to directly test and exploit these features of the amplicon system. The next few years therefore promise to be an exciting and important period in the development of amplicons as vaccine vectors.

Animals↗

Live recombinant vectors for AIDS vaccine development.

Live recombinant vectors entered the AIDS vaccine field with the realization that live attenuated HIV vaccines posed too great a safety risk, and that subunit vaccines elicited antibodies which lacked the breadth or potency needed to induce sterilizing immunity. Vectored vaccines provided a means to bring the cellular arm of the immune system into play by mimicking natural viral infection. By delivering antigens within host cells, processing and presentation could occur for induction of cellular immune responses. This recombinant vector approach, either alone or combined with other strategies, has produced impressive results. Recombinants have been generated from DNA and RNA viruses and bacteria. With few exceptions, each vector poses some risk, yet each possesses unique features that make it attractive. In addition to safety, key considerations in vector selection have included previous success as a vaccine against the wild-type agent or other pathogens; ability to induce potent, persistent immune responses; ability to target mucosal inductive sites and antigen presenting cells; lack of integration into the host genome; presence of pre-existing immunity in people; ease of mucosal administration; cloning capacity; ease of engineering and production; and stability of the final product. Here we up-date the status of several live recombinant vectors that have shown good potential in pre-clinical studies. Some have progressed to human clinical trials, and others will shortly. The abundance of vectors, coupled with the complexity arising from use of combination regimens with other vaccine types and heterologous vectors, will necessitate selection of the most promising candidates for large-scale efficacy trials in people. The sooner comparative studies can be designed and implemented in which live recombinant vectors containing the same inserted genes are evaluated head-to-head, the closer we will be to an eventual vaccine.

AIDS Vaccines↗

Expression of erythropoietin in cats treated with a recombinant adeno-associated viral vector.

OBJECTIVE: To characterize the biological effects of IM administration of a recombinant adeno-associated virus serotype 2 (rAAV2) vector containing feline erythropoietin (fEPO) cDNA and determine whether readministration of the vector or removal of muscle tissue at the injection sites alters those effects. ANIMALS: 10 healthy 7-week-old specific pathogen-free cats. PROCEDURE: Cats received 1 X 10(7) infective units (iU; n = 3), 1 X 10(8) iU (3), or 1 X 10(9) iU (2) of rAAV2-fEPO vector IM (day 0). Two control cats received an rAAV2 vector containing the LacZ gene (1 X 10(9) iU, IM). In all cats, hematologic variables and serum fEPO concentration were measured at intervals; anti-rAAV2 antibody titer was measured on day 227. In cats that did not respond to treatment, the rAAV2-fEPO vector was readministered. Injection sites were subsequently surgically removed. RESULTS: Compared with control cats, cats treated with 1 X 10(9) iU of rAAV2-fEPO vector had increased Hct and serum fEPO concentrations. One of these cats developed pure RBC aplasia; its Hct normalized following injection site excision. Cats receiving lower doses of vector had no response; on retreatment, 1 of those cats developed sustained erythrocytosis that persisted despite injection site removal and the others did not respond or responded transiently. Antibodies against rAAV2 were detected in all vector-treated cats. CONCLUSIONS AND CLINICAL RELEVANCE: Gene therapy may be an effective treatment for cats with hypoproliferative anemia. However, rAAV2-fEPO vector administration may result in pure RBC aplasia or pathologic erythrocytosis, and injection site removal does not consistently abolish the biological response.

Actins↗

Adenovirus vectors deleted for genes essential for viral DNA replication.

Adenovirus (Ad) gene therapy vectors made replication defective by deletion of the E1 region (first-generation vectors) induce high-level inflammation that leads to loss of both transduced gene expression and transduced cells. First-generation vectors were initially considered to be incapable of viral DNA replication, but it is necessary to delete one or more of the genes, all in the E2 transcription unit, that encode proteins essential for Ad DNA replication to completely eliminate viral DNA replication. Vectors deleted for one or more of the E2 genes (second-generation vectors) induce reduced levels of inflammation in certain animal models and offer promise for understanding the mechanisms by which adenovirus vectors induce inflammation and how inflammation can be inhibited. While first-generation vectors dominated the initial human gene therapy trials using adenovirus vectors, second-generation vectors may offer greater promise and greater safety for clinical studies.

Adenoviridae↗

Dendritic cell maturation, but not CD8+ T cell induction, is dependent on type I IFN signaling during vaccination with adenovirus vectors.

To understand how vaccines initiate adaptive immune responses, it is necessary to study how they interact with APCs such as dendritic cells (DCs). In this study, we analyzed interactions between recombinant adenovirus (Ad) vectors and mouse DCs. Mouse bone marrow-derived DCs transduced with Ad vectors produced type I IFN, which promoted the maturation of both transduced and bystander DCs. DCs transduced with a vector derived from a chimpanzee Ad serotype (AdC68) produced more type I IFN and matured more efficiently compared with DCs transduced with a vector derived from a human Ad serotype (AdHu5). Both vectors stimulated type I IFN production independently of viral transcription, replication, and TLR signaling. However, each vector induced type I IFN through distinct pathways; whereas AdHu5 vectors required phosphoinositide-3-OH kinase for type I IFN induction, AdC68 vectors did not. Both vectors induced strong transgene product-specific CD8+ T cell responses in wild-type mice. DCs isolated from mice that have a defect in type I IFN signaling failed to undergo full maturation after Ad vaccination, but surprisingly, these mice mounted strong transgene product-specific CD8+ T cell responses. In these mice, we were able to detect a small number of transduced DCs that expressed high levels of costimulatory molecules, and these DCs were able to stimulate transgene product-specific CD8+ T cells. Thus, type I IFN signaling is an important component of Ad-mediated DC maturation but is dispensable during the generation of transgene product-specific CD8+ T cell responses.

Adenoviridae↗

Vector-mediated cancer gene therapy: an overview.

In recent years there has been a dramatic increase in developing gene therapy approaches for the treatment of cancer. The two events that have permitted the formulation of concept of cancer gene therapy are the new understanding of the molecular mechanisms underlying oncogenesis, and the development of the DNA-delivery vehicles or vectors. Many approaches to cancer gene therapy have been proposed, and several viral and non-viral vectors have been utilized. The purpose of this review article is to describe the various strategies of cancer gene therapy (transfer of tumor suppressor genes, suicide genes-enzyme/pro-drug approach, inhibition of dominant oncogenes, immunomodulation approaches, expression of molecules that affect angiogenesis, tumor invasion and metastasis, chemosensitization and radiosensitization approaches, and chemoprotection of stem cells). The chapter also reviews the commonly used vectors (retroviral vectors, adenoviral vectors, adeno-associated viral vectors, pox viruses, herpes simplex viruses, HIV- vectors, non-viral vectors and targetable vectors) for cancer gene therapy. Some of the important issues in cancer gene therapy, and the potential future directions are also being discussed.

Forecasting↗

Confirmation of Anopheles varuna in vietnam, previously misidentified and mistargeted as the malaria vector Anopheles minimus.

Malaria control programs in Southeast Asia are faced with several questions concerning vector behavior and species identification, which need to be answered to consolidate and further improve the results of control practices. The vector system in Southeast Asia is complex because of the number of species potentially involved in malaria transmission. Additionally, the follow-up and evaluation of preventive control measures are hampered by the misidentification of vectors due to overlapping morphological characters of the female mosquitoes. In central Vietnam, control practices are aimed at 2 main species, Anopheles dirus s.l. and Anopheles minimus s.l. These reputed vectors were studied in an area of Binh Thuan Province of south-central Vietnam. Different collection methods were used to capture mosquitoes quarterly during a 1-year period. Mosquitoes were identified in the field and later subjected to detailed morphological examination and polymerase chain reaction-restriction fragment length polymorphism analysis. What was thought to be an unusual morphotype of An. minimus was shown to be Anopheles varuna, and most specimens identified as the former species in the field proved to be the latter species. Very few An. minimus individuals were found during the study period. The population of An. varuna was found to be highly zoophilic, and based on this behavior, it cannot be considered a vector in Vietnam. Because this species was previously being misidentified as An. minimus, a nonvector was mistargeted as a malaria vector in Binh Thuan Province. Anopheles dirus, which was found positive for Plasmodium falciparum circumsporozoite via enzyme-linked immunosorbent assay, is clearly the main vector in this area. Despite the fact that several potential secondary vectors were found during the study, the primary target for vector control in the region should be An. dirus.

Animals↗

Adenoviral vectors for liver-directed gene therapy.

Adenoviral vectors currently represent one of the most efficient means of in vivo hepatocyte gene delivery. Consequently, liver-directed gene transfer has been increasingly explored as a promising approach for the treatment of a diverse range of genetic and acquired diseases. Numerous demonstrations of efficacious adenoviral vector-mediated delivery of a wide array of transgenes in several animal species and humans have been reported. In general, transgene expression was efficient, but transient, in many cases lasting < 1 month. Currently, efforts in the field are focused on the development of highly attenuated adenoviral vectors designed to prolong transgene expression by reducing vector immunogenicity and hepatoxicity. Vector optimization strategies include the development of vectors devoid of all viral coding regions, the generation of chimeric vectors engineered to capitalize on favorable aspects of the component viral systems, the development of tissue-specific regulated gene expression, and the development of strategies to circumvent the host immune system. The use of adenoviral vectors for gene therapy of hereditary, malignant and infectious diseases of the liver, and the vector optimization strategies outlined above are discussed in this work.

Adenoviridae↗