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PubMed1983

Rescue of adeno-associated virus from recombinant plasmids: gene correction within the terminal repeats of AAV.

We have isolated three types of pBR322-AAV recombinant plasmids that contain deletions within the 145 bp AAV terminal repeats. When the plasmids were transfected into human cells, mutants that contained deletions within the left (type I) or right (type II) terminal repeat were viable. Of four mutants examined that contained deletions in both termini (type III), only one was viable. All of the viable mutants produced AAV virions that contained wild-type AAV DNA. Furthermore, the viable type III deletion could be converted to a nonviable mutant by deleting all copies of an 11 bp sequence from its termini. We conclude that there is an efficient mechanism for correcting deletions within the AAV termini. A model that could account for these observations is also discussed.

Chromosome Deletion↗
PubMed1990

In vitro resolution of covalently joined AAV chromosome ends.

We have developed an assay for a key step in the replication of adeno-associated virus (AAV) DNA. We demonstrate the covalently joined ends of linear AAV DNA can be resolved in vitro to the open duplex configuration. Only extracts prepared from human cells that have been infected with both adenovirus and AAV are capable of carrying out the reaction. The reaction is initiated by a site-specific and strand-specific endonucleolytic cut at a terminal resolution site near the end of the AAV terminal palindrome. During resolution the orientation of the terminal palindrome is inverted, and the 3' viral strand is extended by DNA synthesis. The size of the newly synthesized 3' strand is nearly identical to that found in viral particles. These observations provide direct biochemical evidence for an essential step in the model for AAV DNA replication.

Base Sequence↗
PubMed2004

Potent inhibition of arterial intimal hyperplasia by TIMP1 gene transfer using AAV vectors.

Seminal to the process of arterial restenosis after balloon angioplasty is extracellular matrix degradation by metalloproteinases (MMPs); activity of these proteins is strongly inhibited by the tissue inhibitors of MMPs (TIMPs). Here we exploit gene transfer using an adeno-associated virus (AAV) for TIMP1 gene delivery in a rat model of intimal hyperplasia. High-titer AAV-Timp1 efficiently transduced human coronary artery smooth muscle cells (SMCs) in vitro and inhibited the capacity of these cells to migrate through a Matrigel barrier. In injured rat carotid arteries, AAV vectors were found to transduce SMCs efficiently and to maintain transgene expression for several weeks in vivo. In AAV-Timp1-transduced animals, the intima:media ratio of injured carotids was significantly reduced by 70.5% after 2 weeks, by 58.5% after 1 month, and by 52.4% after 2 months from treatment. The decrease in intimal hyperplasia was paralleled by a significant inhibition of collagen accumulation and by increased elastin deposition in the neointima, two findings that relate to the inhibition of MMP activity. These results indicate that AAV vectors are efficient tools for delivering genes to the arterial wall and emphasize the importance of MMPs for the generation of intimal hyperplasia. Local TIMP1 gene transfer might thus represent an efficient strategy to prevent restenosis.

Angioplasty, Balloon↗
PubMed2005

AAV transcytosis through barrier epithelia and endothelium.

To transduce efficiently barrier epithelia such as the lung is the goal of several gene therapy applications. However, experiments with AAV-2 suggest that transduction is limited in this type of barrier epithelia. In contrast, other serotypes of AAV transduce barrier epithelia and exhibit broad dissemination throughout the tissue. Transcytosis is a process by which proteins and pathogens overcome barrier layers to reach the opposite cell surface. To understand better the entry pathway of AAV particles and their ability to penetrate barrier epithelia, we tested the hypothesis that the limited transduction of some barrier epithelia in vitro or the spread of some AAV serotypes through tissue in vivo is due to transcytosis. Our experiments demonstrate that dependoviruses can penetrate barrier cells by transcytosis. The process is rapid as well as serotype and cell-type specific and can be blocked by neutralizing antibodies, temperature, or chemical inhibitors of transcytosis. The particles isolated following apical-to-basolateral transport are still encapsulated and they can transduce permissive cell lines in vitro. Furthermore, the entry pathway used by AAV-5 for transcytosis appears to be independent of the one used for transduction. Importantly, inhibition of virus transcytosis results in a dramatic increase in intracellular vector and transduction.

Biological Transport↗
PubMed1999

Efficient CFTR expression from AAV vectors packaged with promoters--the second generation.

Gene therapy studies of cystic fibrosis (CF) have shown that AAV-based vector was efficient in transferring but not in expressing the CFTR cDNA in the target cells. The levels of CFTR gene expression were limited by the small packaging capacity of AAV because it had been difficult to package the CFTR cDNA with an efficient promoter. In the present study we have developed a new generation of AAV/CFTR vectors which contain efficient short promoters to express the CFTR gene in target cells. To do so, we reduced the size of the CFTR cDNA by determining the minimal untranslated regions required for expression of CFTR cDNA. We also identified short and efficient promoters that could be packaged with the down-sized CFTR cDNA into a novel AAV vector that had a maximal packaging capacity. Functional analyses showed that the new vectors were packaged efficiently and expressed higher levels of CFTR than a vector in which the CFTR gene was driven by the ITR sequence of AAV. Transduction of airway epithelial cells containing [symbol: see text] 508 mutation with the new vectors demonstrated efficient expression of the wild-type CFTR and correction of the CF phenotype. In contrast, no significant CFTR expression was detected in cells infected with the vector that express the CFTR gene from the ITR. These findings support the notion that the AAV can be developed into an efficient vector to transduce the CFTR gene and vectors expressing higher levels of CFTR from an efficient promoter should provide better efficacy for gene therapy of cystic fibrosis.

Cystic Fibrosis↗
PubMed2006

AAV serotype-1 mediates early onset of gene expression in mouse hearts and results in better therapeutic effect.

Adeno-associated viral vectors (AAV) are attractive tool for gene therapy for coronary artery disease. However, gene expression in myocardium mediated by AAV serotype 2 (AAV2) does not peak until 4-6 weeks after gene transfer. This delayed gene expression may reduce its therapeutic potential for acute cardiac infarction. To determine whether earlier gene expression and better therapeutic effect could be achieved using a different serotype, CMV promoter driving the EPO gene (AAV-EPO) was packaged into AAV serotypes 1-5 capsids and injected into mouse myocardium. EPO expression was studied by measuring the hematocrits and EPO mRNA. After we found that AAV1 mediates the highest gene expression after 4 days of gene transduction, AAV-LacZ (CMV promoter driving LacZ gene expression) and MLCVEGF (hypoxia-inducible and cardiac-specific VEGF expression) were packaged into AAV1 and 2 capsids. LacZ expression was detected in AAV1-LacZ but not in AAV2-LacZ-injected hearts 1 day after vector injection. Compared to AAV2-MLCVEGF that mediated no significant VEGF expression, AAV1-MLCVEGF mediated 13.7-fold induction of VEGF expression in ischemic hearts 4 days after gene transduction and resulted in more neovasculatures, better cardiac function and less myocardial fibrosis. Thus, AAV1 mediates earlier and higher transgene expression in myocardium and better therapeutic effects.

Animals↗
PubMed2003

A single adeno-associated virus (AAV)-murine factor VIII vector partially corrects the hemophilia A phenotype.

A major obstacle for delivery of factor (F)VIII using adeno-associated virus (AAV) vectors is the large size of FVIII cDNA, which is well above the 5 kb packaging limit for AAV. Here we construct a < 5 kb FVIII-AAV vector using murine FVIII cDNA and a strong liver-specific albumin promoter. We assessed the efficacy of this vector using three different routes of administration, intraportal, intrasplenic and tail vein injection, in FVIII knockout (FVIII KO) mice. The peak level of FVIII observed was about 8% of normal mouse FVIII activity. Even at 9 months, post vector injection, 14 of 19 mice receiving FVIII-AAV demonstrated phenotypic correction and roughly 2% FVIII activity. The transgene copy number ranged from 0.001 to 0.1 copies per cell, depending upon the somatic tissue. The potential for germline transmission of AAV was assayed in 34 pups obtained from five pairs of treated, phenotypically corrected adult hemophilic mice. Although the parents harbored the transgene in liver, spleen, and gonads, none of the 34 offspring was positive for the transgene, suggesting that the risk of inadvertent germline transmission is low.

Animals↗
PubMed2004

Preclinical gene therapy studies for hemophilia using adeno-associated virus (AAV) vectors.

Gene therapy offers a potential cure for hemophilia and several gene transfer vectors have been evaluated for their ability to treat this disease. This article reviews the studies that have been performed to evaluate the ability of recombinant adeno-associated virus (AAV) vectors to achieve safely the sustained expression of clotting factors following intramuscular, intravenous, and intrahepatic delivery to several animal models. These routes of administration are all effective in providing sustained and therapeutic levels of factor IX (FIX), although the levels vary. Intrahepatic delivery is more efficacious than intravenous administration, which is superior to intramuscular delivery. The recent development of efficient factor VIII (FVIII) expression cassettes has made AAV-based gene therapy for hemophilia A also within reach. Although no acute toxicity has been observed with any route of administration, an increased risk of antibody formation against FIX has been noted following intramuscular delivery. Biodistribution studies concluded that the vector disseminates to most tissues in a dose-dependent and time-dependent manner, but the majority of the vector resides in the targeted tissue. In addition, the risk of germline transmission has been shown to be low or absent. The relatively recent isolation of new AAV serotypes has resulted in the identification of vectors that have enhanced tropism for certain tissues. This combined with the potential of these new vectors to evade the immune response to AAV2, makes them attractive candidates for gene therapy. Although much progress has been made using AAV to treat hemophilia, there are several outstanding issues that need to be addressed. Delivery of AAV to large animals has not been reproducible, which could be due to nonoptimized delivery and/or immune responses to the vector or transgene product. In addition, a complete understanding of the biology of these vectors is required to assess their long-term safety. Solving these issues will lead to the development of a successful gene therapy product.

Animals↗
PubMed1996

A novel adenovirus-adeno-associated virus hybrid vector that displays efficient rescue and delivery of the AAV genome.

Adenovirus and adeno-associated virus (AAV) are eukaryotic DNA viruses being developed as vectors for human gene therapy. The strengths of each system have been exploited in a novel vector that is based on an adenovirus-AAV hybrid virus incorporated into a plasmid-based molecular conjugate. Efficient rescue and replication of the recombinant AAV genome in this hybrid required transient expression of rep. This feature was incorporated into the transducing particle by conjugating a rep expression plasmid to the hybrid virus through a polylysine bridge. The resulting particle is an attractive vehicle for gene therapy because it is easily manufactured and capable of efficiently transducing cells with the end result being rescue and replication of the recombinant AAV genome. This particle is also useful in the production of recombinant AAV resulting in yields 10-fold greater than that achieved with transfection-based protocols.

Adenoviruses, Human↗
PubMed1977

Complementation of adeno-associated satellite virus (AAV) by temperature-sensitive mutants of adenovirus type 31.

Temperature-sensitive (ts) matants of human adenovirus type 31 were able to complement adeno-associated satellite virus (AAV) antigen production in both HEK and KB cells at both permissive and non-permissive temperatures. However, mutant ts 94, an adenovirus 31 mutant which produces apparently normal amounts of structural protein and DNA but is defective in maturation, was significantly inhibited in its ability to potentiate AAV infectivity at the non-permissive temperature. Normal AAV DNA and adenovirus DNA were isolated from co-infections with AAV and mutant ts 94 at the non-permissive temperature. We suggest that an adenovirus-coded maturation function common to both adenovirus and AAV maturation is defective in the ts 94 system.

Adenoviruses, Human↗
PubMed2001

AAV-mediated gene transfer for hemophilia.

Hemophilia is a particularly attractive model for developing a gene transfer approach for the treatment of disease. The protein is very well characterized, the genes are cloned and available, and there are large and small animal models of the disease. Moreover, in contrast to many diseases, there is no requirement for a specific target tissue for gene delivery, and the gene product itself does not require precise regulation of expression. Earlier efforts to establish a gene transfer approach to the treatment of hemophilia had failed to achieve the twin goals of long-term expression at levels that were adequate to result in phenotypic improvement of the disease. We have exploited advances in vector development that occurred in the mid-1990s to establish an experimental basis for an AAV (adeno-associated viral vector)-mediated gene transfer approach to the treatment of hemophilia B. Based on the observation that introduction of an AAV vector into skeletal muscle could result in sustained expression of beta-galactosidase, we engineered an AAV vector expressing human factor IX and demonstrated in immunodeficient mice that intramuscular injection of the vector resulted in long-term expression of the secreted transgene product factor IX. Subsequently, we generated an AAV vector expressing canine factor IX; intramuscular injection into dogs with severe hemophilia B resulted in a dose-dependent increase in circulating levels of factor IX. The animal treated at the highest dose showed prolonged expression (>3 years and still under observation) at a level (70 ng/ml, 1.4% of normal circulating levels of factor IX) likely to result in phenotypic improvement in humans. Detailed studies in tissue culture using human myotubes have shown that muscle cells are capable of executing the posttranslational modifications required for activity of factor IX, and that the specific activity of myotube-synthesized factor IX is similar to that of hepatocyte-synthesized material, although some details of posttranslational processing differ. Based on these and other safety and efficacy studies, a clinical trial of AAV-mediated, muscle-directed gene transfer for hemophilia B has been initiated. The study has a dose-escalation design, with three subjects to be enrolled in three dose cohorts beginning with a dose of 2 x 10(11) vg/kg. Results in the initial dose cohort showed no evidence of toxicity associated with vector administration or transgene expression. Analysis of muscle biopsies done on injected tissue showed clear evidence of gene transfer by PCR and Southern blot and of gene expression by immunocytochemistry. The general characteristics of muscle transduction appear similar in humans and in other animal models. The goal of dose escalation is to find a dose that is nontoxic but that results in circulating levels of factor IX >1% in all patients.

Animals↗
PubMed2001

Expression of AAV Rep proteins in SV40-transformed and untransformed cells: reciprocal interaction with host DNA synthesis.

Adeno-associated virus (AAV) inhibits the induction of host DNA synthesis by simian virus 40 (SV40) large-tumour (T) antigen, mediated through AAV-encoded 'Rep' regulatory proteins. Rep proteins are normally synthesized by AAV-infected cells only in the presence of adenovirus. However, we observed a low level of Rep protein expression in SV40 transformed cells even in the absence of helper virus. In an effort to understand the functional interaction between SV40 T antigen and regulators of AAV rep expression, we evaluated Rep protein production by cell lines transformed with various T antigen mutants known to vary in their induction of host DNA synthesis. We observed Rep protein expression proportional to SV40-induced host DNA synthesis, as measured previously for these T antigen mutants in the absence of AAV, suggesting that rep gene expression - although it opposes the oncogenic stimulation of cell cycling by SV40 - may itself be elicited by host DNA synthesis. To test this, we employed two inhibitors of DNA synthesis: hydroxyurea, which acts by depleting deoxyribose nucleotide triphosphate pools, and aphidicolin, a specific inhibitor of DNA polymerases alpha and delta. Each inhibitor markedly and significantly reduced Rep protein levels, both in immortal cells transformed by wild-type T antigen and in normal human fibroblasts, confirming the dependence of Rep protein expression on host DNA synthesis.

Antigens, Viral, Tumor↗
PubMed2026

CD8+ T cell activation occurs 24 hours after AAV administration and is driven by muscle promoter specificity.

Immune responses against transgene products can compromise adeno-associated virus-mediated (AAV-mediated) gene transfer. Although several factors influencing this immunogenicity have been described, the early in vivo events driving CD8+ T cell activation remain poorly defined. Here, we examined antigen presentation kinetics following intramuscular AAV administration in mice. Strikingly, viral genomes were detected in draining lymph nodes as early as 1 hour after injection, and transgene-derived peptides were presented to CD8+ T cells from day 1, resulting in progressive activation and first cell divisions detected at day 4. Removal of the injection site demonstrated that AAV particles reaching draining lymph nodes within the first hour were sufficient to induce cytotoxic transgene-specific CD8+ T cells. Finally, AAV vectors incorporating different muscle-specific promoters and regulatory sequences were evaluated. Although muscle specific, all promoters exhibited variable transgene expression in dendritic cells in vitro, correlating with early T cell activation in vivo; notably, those associated with higher early antigen presentation induced robust T cell response, whereas reduced presentation correlated with absence of CD8+ T cells. These findings reveal an unexpectedly early onset of transgene-derived epitope presentation, modulated by promoter specificity, which critically shapes CD8+ T cell response. This provides a rationale for evaluating and mitigating AAV immunogenicity in gene therapy design.

Animals↗
PubMed2004

AAV-mediated gene transfer to the liver.

The liver is a frequent target of gene-transfer experiments, because of its central role in many metabolic and synthetic pathways. For applications where prolonged expression of genes in the liver is required, adeno-associated virus (AAV) has proven to be an effective tool for in vivo gene transfer. High-level, persistent hepatic expression has been achieved in a number of experimental systems following a single treatment with AAV in murine and larger animal models. This prolonged expression is particularly useful for the treatment of genetic diseases such as the inborn errors of metabolism, where lifelong expression of the deficient enzyme may be required. Therapeutic benefits using AAV vectors have been demonstrated in animal models of amino acid disorders, lysosomal storage diseases, and coagulopathies (3-5), and Phase I clinical trials are proposed for the treatment of hemophilia B (6). Gene transfer to the murine liver using AAV is achieved by intravenous (iv) injection of recombinant virus, either via a peripheral or portal vein. The liver is the primary organ transduced following intravenous injection of AAV, although other tissues such as heart and lung may also take up virus to a lesser extent when peripheral injection sites are used (7). Portal-vein injection can reduce the amount of extra-hepatic transduction, and allows a larger dose of virus to be delivered to the liver. However, this technique requires surgical expertise, and can only be performed on adult mice.

Animals↗
PubMed1998

[Gene delivery using adeno-associated (AAV) vectors].

Gene transfer vectors based on the replication-defective adeno-associated virus (AAV) are emerging as promising vehicles for gene therapeutic approaches for the neurologic disease, cystic fibrosis and cancers. AAV vectors have been used to efficiently transduce genes into cells in vitro and in vivo. However, transduced recombinant AAV vectors are integrated into human chromosomes. Thus we have discussed that the review about the AAV vectors and transduction, and reported the results used AAV vectors for expression of ribozyme.

Animals↗
PubMed2025

Identification of a robust promoter in mouse and human hepatocytes by in vivo biopanning of a barcoded AAV library.

Recombinant adeno-associated viruses (AAVs) are leading vectors for in vivo human gene therapy. An integral vector element is promoters, which control transgene expression in either a ubiquitous or cell-type-selective manner. Identifying optimal capsid-promoter combinations is challenging, especially when considering on- versus off-target expression. Here, we report a pipeline for in vivo promoter biopanning in AAV building on our AAV capsid barcoding technology and illustrate its potential by screening 53 promoters in 16 murine tissues using an AAV9 vector. Surprisingly, the 2.2-kb human glial fibrillary acidic protein (GFAP) promoter was the top hit in the liver, where it outperformed robust benchmarks such as the human &#x3b1;-1-antitrypsin promoter or the clinically used liver-specific promoter 1 (LP1). Analysis of hepatic cell populations revealed preferred GFAP promoter activity in hepatocytes. Notably, the GFAP promoter also surpassed the LP1 and cytomegalovirus promoters in human hepatocytes engrafted in an immune-deficient mouse. These findings establish the GFAP promoter as an exciting alternative for research and clinical applications requiring efficient and specific transgene expression in hepatocytes. Our pipeline expands the arsenal of technologies for high-throughput in vivo screening of viral vector components and is compatible with capsid barcoding, facilitating the combinatorial interrogation of complex AAV libraries.

Dependovirus↗
PubMed2025

Long-Term Correction of Murine Glycogen Storage Disease Type III by AAV-Mediated Gene Therapy Using an Immunotolerizing Dual Promoter to Express Bacterial Pullulanase.

BACKGROUND: We recently reported an innovative gene therapy approach for GSD III using a recombinant adeno-associated virus serotype 9 vector (AAV9-Dual-Pull) expressing a bacterial debranching enzyme (pullulanase) driven by a tandem dual promoter that consists of an immunotolerizing liver-specific promoter (LSP) and the ubiquitous CMV enhance/chicken &#x3b2;-actin (CB) promoter. In this follow-up study, we evaluated the long-term efficacy of this gene therapy in GSD IIIa mice. METHODS: Three-month-old GSD IIIa mice were intravenously injected with AAV9-LSP-Pull or AAV9-Dual-Pull at the same dose (2.5 &#xd7; 1013 vg/kg). Tissues were collected after 9 months for AAV genome quantification, pullulanase expression determination, and glycogen content measurement. Liver and muscle enzymes in plasma and disease biomarker in urine were analyzed at multiple time points to examine the correction of liver and muscle damage. Behavioral tests were performed during the course of AAV treatment to evaluate the improvement of muscle function. RESULTS: The AAV-Dual-Pull treatment led to persistent pullulanase expression and effective glycogen reduction in the liver, heart, and skeletal muscle, accompanied by the reversal of liver fibrosis, decrease of plasma enzyme activities, and long-term improvement of muscle function. The AAV-LSP-Pull treatment showed a better therapeutic efficacy in the liver but had no effect on the cardiac and skeletal muscles. CONCLUSION: Our results demonstrated the long-term efficacy and safety of systemic AAV9-Dual-Pull delivery in GSD IIIa mice. Future studies will test this gene therapy approach in GSD IIIa dogs prior to the clinical translation to GSD III patients.

AAV gene therapy↗
PubMed2026

Decoding Nonlinearities in AAV-Based Gene Therapy Using PBPK Modelling.

The objective of this research was to develop a physiologically based pharmacokinetic (PBPK) model for AAV-based gene therapy, which can capture the nonlinearity observed in both viral vector and transgene product pharmacokinetics (PK) across a wide range of doses, while accounting for the effect of immunogenicity. To develop the PBPK model, previously published PK data generated in mice using AAV8 vector containing the transgene for a non-binding monoclonal antibody was used. Immunocompetent mice were administered with AAV at a wide range of doses (1E8, 1E9, 5E9, 1E10, 2E10, 1E11, 2E11, 1E12, and 1E13vg per mouse), and the PK of transgene and transgene product (i.e., antibody) in plasma and/or tissue was collected. The nonlinearity in transgene product concentrations was characterized using a saturable production process and a concentration-dependent antibody elimination rate was used to characterize the effect of anti-drug antibody (ADA) on transgene product. The model successfully described the PK of both the vector and the transgene product across all dose levels and accurately captured the sigmoidal dose-exposure-response relationship for AAV. Notably, the model described a dose-dependent ADA response, with the high dose group exhibiting an earlier onset and faster rate of transgene product elimination. Lower dose group showed delayed onset and minimal ADA-mediated elimination of transgene product. Overall, the PBPK model presented here effectively characterizes vector and transgene product kinetics in mice and demonstrates utility in preclinical-to-clinical translation and dose optimization of AAV-based gene therapies.

Animals↗