Production of high-titer recombinant adeno-associated virus vectors in the absence of helper adenovirus

Current and future strategies for the treatment of malignant brain tumors

Glioblastoma (GB) is the most common subtype of primary brain tumor in adults. These tumors are highly invasive, very aggressive, and often infiltrate critical neurological areas within the brain. The mean survival time after diagnosis of GB has remained unchanged during the last few decades, in spite of advances in surgical techniques, radiotherapy, and also chemotherapy; patients' survival ranges from 9 to 12 months after initial diagnosis. In the same time frame, with our increasing understanding and knowledge of the physiopathology of several cancers, meaningful advances have been made in the treatment and control of several cancers, such as breast, prostate, and hematopoietic malignancies. Although a number of the genetic lesions present in GB have been elucidated and our understanding of the progressions of this cancer has increased dramatically over the last few years, it has not yet been possible to harness this information towards developing effective cures. In this review, we will focus on the classical ways in which GB is currently being treated, and will introduce a novel therapeutic modality, i.e., gene therapy, which we believe will be used in combination with classical treatment strategies to prolong the life-span of patients and to ultimately be able to control and/or cure these brain tumors. We will discuss the use of several vector systems that are needed to introduce the therapeutic genes within either the tumor mass, if these are not resectable, or the tumor bed, after successful tumor resection. We also discuss different therapeutic modalities that could be exploited using gene therapy, i.e., conditional cytotoxic approach, direct cytotoxicity, immunotherapy, inhibition of angiogenesis, and the use of pro-apoptotic genes. The advantages and disadvantages of each of the current vector systems available to transfer genes into the CNS are also discussed. With the advances in molecular techniques, both towards the elucidation of the physiopathology of GB and the development of novel, more efficient and less toxic vectors to deliver putative therapeutic genes into the CNS, it should be possible to develop new rationale and effective therapeutic approaches to treat this devastating cancer.

Pseudotyped AAV vectors for constitutive and regulated gene expression in the eye

Since the first reports describing the injection of recombinant adeno-associated viral (AAV) vectors in the murine eye, the advancement of the field has been enormous resulting in the correction of several animal models of retinal diseases. The recent development of "pseudotyped" AAV vectors with transduction characteristics that best fit the correction of specific retinal disease phenotypes and of sophisticated systems for tight regulation of gene expression expands on the potentiality of this delivery system for the eye.

Packaging of an AAV vector encoding human acid alpha-glucosidase for gene therapy in glycogen storage disease type II with a modified hybrid adenovirus-AAV vector

We have developed an improved method for packaging adeno-associated virus (AAV) vectors with a replication-defective adenovirus-AAV (Ad-AAV) hybrid virus. The AAV vector encoding human acid alpha-glucosidase (hGAA) was cloned into an E1, polymerase/preterminal protein-deleted adenovirus, such that it is packaged as an Ad vector. Importantly, the Ad-AAV hybrid cannot replicate during AAV vector packaging in 293 cells, because of deletion of polymerase/preterminal protein. The residual Ad-AAV in the AAV vector stock was reduced to <1 infectious particle per 10(10) AAV vector particles. These modifications resulted in approximately 30-fold increased packaging of the AAV vector for the hybrid Ad-AAV vector method as compared with standard transfection-only methods. Similarly improved packaging was demonstrated for pseudotyping the AAV vector as AAV6, and for AAV vector packaging with a second Ad-AAV vector encoding canine glucose-6-phosphatase. Liver-targeted delivery of either the Ad-AAV hybrid or AAV vector particles in acid alpha-glucosidase-knockout (GAA-KO) mice revealed secretion of hGAA with the Ad-AAV vector, and sustained secretion of hGAA with an AAV vector in hGAA-tolerant GAA-KO mice. Further development of hybrid Ad-AAV vectors could offer distinct advantages for gene therapy in glycogen storage diseases.

Consequences of DNA-dependent protein kinase catalytic subunit deficiency on recombinant adeno-associated virus genome circularization and heterodimerization in muscle tissue

Circular concatemerization of the recombinant adeno-associated virus (rAAV) genome has been suggested as the predominant process facilitating long-term rAAV transduction in muscle. A recent study (S. Song, P. J. Laipis, K. I. Berns, and T. R. Flotte, Proc. Natl. Acad. Sci. USA 98:4084-4088, 2001) with SCID mice, which are defective in the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), has suggested that DNA-PKcs regulates the removal of free rAAV vector ends in muscle tissue. In the present study, we have sought to evaluate whether a lack of DNA-PKcs activity reduces circularization of rAAV genomes in SCID muscle and whether such a reduction alters the directivity of heterodimerization. Consistent with the previous report, linear rAAV genomes and free vector ends were detected only in DNA-PKcs-deficient muscle by Southern blotting. Appreciable amounts of circular rAAV genomes were detected in both DNA-PKcs-deficient and wild-type muscle samples by Southern blotting and bacterial trapping experiments. The existence of double-D inverted terminal repeat circular intermediates in SCID and wild-type muscles was also supported by their sensitivity to T7 endonuclease I digestion. However, DNA-PKcs-deficient muscle did demonstrate a approximately 50% reduction in the abundance of rescued circular genomes, despite equivalent levels of single rAAV transduction seen in wild-type animals. Dual trans-splicing lacZ vectors were used to functionally evaluate directional head-to-tail intermolecular viral genome concatamerization in vivo. Although AAV genomes are processed differently in SCID and wild-type muscles, a comparable level of trans-splicing-mediated beta-galactosidase expression was observed in both strains, suggesting that both circular and linear AAV concatemers may have contributed to the trans-splicing-mediated transgene expression. In summary, we have shown that SCID skeletal muscle retains a fairly high capacity to form circular genomes, despite a significant increase in linear vector genomes. Furthermore, the alteration in equilibrium between circular and linear concatemer genomes caused by the lack of DNA-PKcs activity does not appear to significantly affect the efficiency of dual-vector gene expression from head-to-tail linear and/or circular heterodimers.

Genetic editing of dysfunctional myocardium

Ongoing advances in vector technology, cardiac gene delivery, and, most importantly, our understanding of HF pathogenesis, encourage consideration of gene therapy for HF at this time. At the present time, strategies that enhance sarcoplasmic calcium transport are supported by substantial evidence in both cardiomyocytes derived from patients with HF and in animal models. In addition, efforts to promote cardiomyocyte survival and function through modulation of antiapoptotic signaling appear quite promising. In ongoing efforts to target cardiac dysfunction, gene transfer provides an important tool to improve our understanding of the relative contribution of specific pathways. Through such experiments, molecular targets can be validated for therapeutic intervention, whether pharmacologic or genetic. Translating these basic investigations into clinical gene therapy for HF, however, remains a formidable challenge. Further development of concepts established in rodent models will be required in large animal models with clinical grade vectors and delivery systems to evaluate both efficacy and safety of these approaches. Nevertheless, practical advances and our growing understanding of the molecular pathogenesis of HF provide reason for cautious optimism.

Gene therapy and tissue engineering in repair of the musculoskeletal system

Historically, surgeons have sought and used different procedures in order to augment the repair of various skeletal tissues. Now, with the completion of the Human Genome Project, many researchers have turned to gene therapy as a means to aid various ailments. In the orthopedic field, many strides have been made toward using gene therapy and tissue engineering in a clinical setting. In this review, several studies are outlined in different areas that gene therapy has or will influence orthopedic surgery. Gene therapy and tissue engineering can aid in fracture healing and spinal fusions by inducing bone formation, ligamentous repairs by increasing the production of connective tissue fibers, intervertebral disc disease by creating potential replacements, and articular cartilage repairs by providing means to improve cartilage. As we continue to see great contributions, such as the few mentioned here, this field will continue to mature and develop.

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.

Evidence for packaging of rep-cap sequences into adeno-associated virus (AAV) type 2 capsids in the absence of inverted terminal repeats: a model for generation of rep-positive AAV particles

We previously reported that a 350-bp region of the adeno-associated virus (AAV) type 2 rep gene contains a cis-acting element responsible for the Rep-dependent replication of a transiently transfected rep-cap plasmid. In this study, we further report that replicated rep-cap sequences can be packaged into AAV capsids in the absence of the inverted terminal repeats.

Marker rescue of adeno-associated virus (AAV) capsid mutants: a novel approach for chimeric AAV production

Marker rescue, the restoration of gene function by replacement of a defective gene with a normal one by recombination, has been utilized to produce novel adeno-associated virus (AAV) vectors. AAV serotype 2 (AAV2) clones containing wild-type terminal repeats, an intact rep gene, and a mutated cap gene, served as the template for marker rescue. When transfected alone in 293 cells, these AAV2 mutant plasmids produced noninfectious AAV virions that could not bind heparin sulfate after infection with adenovirus dl309 helper virus. However, the mutation in the cap gene was corrected after cotransfection with AAV serotype 3 (AAV3) capsid DNA fragments, resulting in the production of AAV2/AAV3 chimeric viruses. The cap genes from several independent marker rescue experiments were PCR amplified, cloned, and then sequenced. Sequencing results confirmed not only that homologous recombination occurred but, more importantly, that a mixed population of AAV chimeras carrying 16 to 2,200 bp throughout different regions of the type 3 cap gene were generated in a single marker rescue experiment. A 100% correlation was observed between infectivity and the ability of the chimeric virus to bind heparin sulfate. In addition, many of the AAV2/AAV3 chimeras examined exhibited differences at both the nucleotide and amino acid levels, suggesting that these chimeras may also exhibit unique infectious properties. Furthermore, AAV helper plasmids containing these chimeric cap genes were able to function in the triple transfection method to generate recombinant AAV. Together, the results suggest that DNA from other AAV serotypes can rescue AAV capsid mutants and that marker rescue may be a powerful, yet simple, technique to map, as well as develop, chimeric AAV capsids that display different serotype-specific properties.

Gene transfer to subdermal tissues via a new gene gun design

Although particle-mediated gene transfer technology (gene gun) has been applied for gene transfer to external tissues, the application of this technology to other tissues has met with limited success. Here we report the development of a new design of a gene gun that uses helium discharge to propel DNA-coated gold beads that are suspended in liquid. Higher discharge pressures allow for the delivery of DNA to deeper tissues. Using the new gene gun to deliver a luciferase expression plasmid resulted in higher levels of gene expression in the skin than observed with conventional guns, as well as in subdermal tissues, including subcutaneous tumors. Even when using as little as 125 ng of DNA, gene expression in skin and muscle reached its peak level at 24 hr postbombardment and remained for at least 1 week. The use of a LacZ expression plasmid showed that gene expression was distributed throughout the skin with no observable pathology. The new gene gun was used to deliver a model tumor rejection antigen (a modified human papilloma virus [HPV] E7 gene) to mice. All of the treated animals developed protective immunity against HPV-positive tumors. These results demonstrate that our new design can be used in standard gene gun applications and extends the reach of gene gun technology to tissues that were previously unavailable.

Adeno-associated virus vector-mediated gene transfer into dystrophin-deficient skeletal muscles evokes enhanced immune response against the transgene product

Duchenne muscular dystrophy (DMD) is an X-linked, lethal muscular disorder caused by a defect in the DMD gene. AAV vector-mediated micro-dystrophin cDNA transfer is an attractive approach to treatment of DMD. To establish effective gene transfer into skeletal muscle, we examined the transduction efficiency of an AAV vector in skeletal muscles of dystrophin-deficient mdx mice. When an AAV vector encoding the LacZ gene driven by a CMV promoter (AAV-CMVLacZ) was introduced, beta-galactosidase expression markedly decreased in mdx muscle 4 weeks after injection due to immune responses against the transgene product. We also injected AAV-CMVLacZ into skeletal muscles of mini-dystrophin-transgenic mdx mice (CVBA3'), which show ameliorated phenotypes without overt signs of muscle degeneration. AAV vector administration, however, evoked substantial immune responses in CVBA3' muscle. Importantly, AAV vector using muscle-specific MCK promoter also elicited responses in mdx muscle, but at a considerably later period. These results suggested that neo-antigens introduced by AAV vectors could evoke immune reactions in mdx muscle, since increased permeability allowed a leakage of neo-antigens from the dystrophin-deficient sarcolemma of muscle fibers. However, resident antigen-presenting cells, such as myoblasts, myotubes and regenerating immature myofibers, might also play a role in the immune response.

A novel gene expression control system and its use in stable, high-titer 293 cell-based adeno-associated virus packaging cell lines

Previous attempts to establish 293cell-based stable and high-titer adeno-associated virus (AAV) packaging cell lines were unsuccessful, primarily due to adenovirus E1-activated Rep gene expression, which exerts cytostatic and cytotoxic effects on the host cells. Control of the two large AAV Rep proteins (Rep78/68) was insufficient to eliminate the adverse effects, because of the leaky expression of the two small Rep proteins (Rep52/40). However, it was unsuccessful to control Rep52/40 gene expression since its promoter is located within the coding sequence of Rep78/68. To tightly regulate all four Rep proteins by using their own promoters, we have developed a novel gene control paradigm termed "dual splicing switch," which disrupts all four Rep genes by inserting into their shared coding region an intron that harbors transcription termination sequences flanked the LoxP sites. As a result, the structure and activities of the Rep gene promoters, both p5 and p19, are not affected; however, all of the Rep transcripts are prematurely terminated and the genes were inactivated. Removal of the terminator by Cre protein reactivates the transcription of all four Rep proteins derived from their own promoters. This switch system was initially tested in the lacZ gene and a 600-fold induction of beta-galactosidase activity was observed. Using the dual splicing switch strategy, we have subsequently established a number of AAV packaging cell lines from 293 cells, which showed a normal growth rate, high stability, and more importantly, high yields of AAV vectors. Such a gene control paradigm is also useful for other viruses, e.g., autonomous parvoviruses. Finally, the high-titer 293-based AAV packaging cell lines should greatly reduce the risk of wild-type adenovirus contamination and provide a scalable AAV vector production method for both preclinical and clinical studies.

A versatile and scalable two-step ion-exchange chromatography process for the purification of recombinant adeno-associated virus serotypes-2 and -5

Here we describe the development of a two-step chromatography process based on the use of ion-exchange resins for the purification of recombinant adeno-associated virus (rAAV) serotypes-2 and-5. In vitro and in vivo results demonstrate that this method, which does not require any prepurification step of the cell lysate, can be applied to obtain highly pure rAAV2 and rAAV5 stocks. As such,this procedure can be easily transferred in vector cores and also scaled up, allowing the direct comparison of these two, and potentially other, AAV serotypes in large animal models.

Insect cells as a factory to produce adeno-associated virus type 2 vectors

Recombinant adeno-associated viruses (rAAV) are produced transiently in mammalian cells usually by cotransfecting two or three plasmids containing AAV genes, adenovirus helper genes, and a vector genome. Expansion and transfection of adherent cells limit the scale of rAAV production. Efficient transfection is performed with cells on solid support media such as tissue culture plates. A large animal study or a human clinical trial may require 10(15) particles of vector, depending on dose. To generate this quantity of rAAV by transfection, more than 10(11) HEK293 cells may be needed, which would require about 5000 x 175 cm(2) flasks. The ability to scale up rAAV production by these methods severely restricts the commercialization and use of AAV vectors. A recombinant baculovirus derived from the Autographa californica nuclear polyhedrosis virus is widely employed for large-scale production of heterologous proteins in cultured insect cells and may provide an attractive alternative. Toward this goal, we have explored the production of rAAV in invertebrate cells. Sf9 cells may be coinfected in suspension cultures with three recombinant baculoviruses (a Rep-baculovirus, a VP-baculovirus, and an AAV ITR vector genome baculovirus) and, 3 days later, rAAV is recovered. The particles produced are indistinguishable from 293 cell-produced rAAV, as determined on the basis of physical properties and biologic activities. Particles produced by either method were composed of similar proteins and nucleic acid. The yield of genome-containing particles produced per Sf9 cell approached 5 x 10(4), thus, 1000 ml of cultured Sf9 cells produced the equivalent of between 500 to 1000 x 175 cm(2) flasks of 293 cells. This robust system provides a simple, cost-effective method for AAV vector production.

Adeno-associated viral vectors as agents for gene delivery: application in disorders and trauma of the central nervous system

The use of viral vectors as agents for gene delivery provides a direct approach to manipulate gene expression in the mammalian central nervous system (CNS). The present article describes in detail the methodology for the injection of viral vectors, in particular adeno-associated virus (AAV) vectors, into the adult rat brain and spinal cord to obtain reproducible and successful transduction of neural tissue. Surgical and injection procedures are based on the extensive experience of our laboratory to deliver viral vectors to the adult rat CNS and have been optimized over the years. First, a brief overview is presented on the use and potential of viral vectors to treat neurological disorders or trauma of the CNS. Next, methods to deliver AAV vectors to the rat brain and spinal cord are described in great detail with the intent of providing a practical guide to potential users. Finally, some data on the experimental outcomes following AAV vector-mediated gene transfer to the adult rat CNS are presented as is a brief discussion on both the advantages and limitations of AAV vectors as tools for somatic gene transfer.

Gene therapy for treatment of cerebral ischemia using defective recombinant adeno-associated virus vectors

In this review we present our results and experiences in performing gene therapy of cerebral stroke using recombinant adeno-associated virus (rAAV) vectors in a rat model. The methodologies involving the production of AAV vectors, gene transfer to the brain, and a trivessel ligation model of focal ischemic cerebral stroke in rats are described. Furthermore, a brief description of other viral vectors and candidates of therapeutic transgenes used for gene therapy of cerebral stroke are presented. The potential advantages and limitations of stroke gene therapy are also discussed with the intention of outlining the design of more appropriate experiments.

Production and purification of serotype 1, 2, and 5 recombinant adeno-associated viral vectors

Recombinant adeno-associated viral (rAAV) vectors based on serotype 2 are currently being evaluated most extensively in animals and human clinical trials. rAAV vectors constructed from other AAV serotypes (serotypes 1, 3, 4, 5, and 6) can transduce certain tissues more efficiently and with different specificity than rAAV2 vectors in animal models. Here, we describe reagents and methods for the production and purification of AAV2 inverted terminal repeat-containing vectors pseudotyped with AAV1 or AAV5 capsids. To facilitate pseudotyping, AAV2rep/AAV1cap and AAV2rep/AAV5cap helper plasmids were constructed in an adenoviral plasmid backbone. The resultant plasmids, pXYZ1 and pXYZ5, were used to produce rAAV1 and rAAV5 vectors, respectively, by transient transfection. Since neither AAV5 nor AAV1 binds to the heparin affinity chromatography resin used to purify rAAV2 vectors, purification protocols were developed based on anion-exchange chromatography. The purified vector stocks are 99% pure with titers of 1 x 10(12) to 1 x 10(13)vector genomes/ml.

Production methods for gene transfer vectors based on adeno-associated virus serotypes

Vectors derived from adeno-associated virus serotype 2 (AAV-2) represent a most promising tool for human gene transfer because these vectors are neither pathogenic nor toxic to the target cell, and allow long-term gene expression in a large variety of tissues. However, they are rather inefficient at infecting a number of clinically relevant cell types, and transduction by these vectors is likely hampered by neutralizing antibodies that are highly prevalent in the human population. Therefore, an increasing number of researchers are currently turning their attention to the five other serotypes of AAV, to try and develop these as novel vectors for human gene transfer, hoping to overcome the problems associated with AAV-2 vectors. Here I describe and discuss the methodology to produce these alternative AAV vectors in tissue culture. In detail, two strategies are compared that rely on transfection of cells in culture with either two or three plasmids, containing the AAV vector genome and encoding AAV and adenoviral helper functions. Either of these protocols can be used to package a recombinant AAV genome into capsids of its own serotype (generation of "real" serotypes) or to "cross-package" this vector DNA into capsids derived from another AAV serotype ("pseudotyping"). As these approaches are still in their early stages, the existing limitations of current technology are discussed, and possible further improvements proposed.

Recombinant adeno-associated virus vector design and gene expression in the mammalian brain

Efficiency and stability of recombinant adeno-associated virus (rAAV)-mediated gene expression within the mammalian brain are determined by several factors. These include the dose of infectious particles, the purity of the vector stock, the serotype of rAAV, the route of administration, and the intrinsic properties, most notably the rAAV receptor density, of the targeted area. Furthermore, the choice of appropriate regulatory elements in rAAV vector design is of fundamental importance to achieve high-level sustained in vivo transcription and translation. This review summarizes the characteristics of various transcriptional and posttranscriptional regulatory elements, and highlights their influence on the expression performance of rAAV vectors in the mammalian brain.

Efficient gene transfer of CD40 ligand into primary B-CLL cells using recombinant adeno-associated virus (rAAV) vectors

B cells of chronic lymphocytic leukemia (B-CLL) are resistant to transduction with most currently available vector systems. Using an optimized adenovirus-free packaging system, recombinant adeno-associated virus (rAAV) vectors coding for the enhanced green fluorescent protein (AAV/EGFP) and CD40 ligand (AAV/CD40L) were packaged and highly purified resulting in genomic titers up to 3 × 1011/mL. Cells obtained from 24 patients with B-CLL were infected with AAV/EGFP or AAV/CD40L at a multiplicity of infection (MOI) of 100 resulting in transgene expression in up to 97% of cells as detected by flow cytometry 48 hours after infection. Viral transduction could be specifically blocked by heparin. Transduction with AAV/CD40L resulted in up-regulation of the costimulatory molecule CD80 not only on infected CLL cells but also on noninfected bystander leukemia B cells, whereas this effect induced specific proliferation of HLA-matched allogeneic T cells. Vaccination strategies for patients with B-CLL using leukemia cells infected ex vivo by rAAV vectors now seems possible in the near future.

Sustained high-level expression of human factor IX (hFIX) after liver-targeted delivery of recombinant adeno-associated virus encoding the hFIX gene in rhesus macaques

The feasibility, safety, and efficacy of liver-directed gene transfer was evaluated in 5 male macaques (aged 2.5 to 6.5 years) by using a recombinant adeno-associated viral (rAAV) vector (rAAV-2 CAGG-hFIX) that had previously mediated persistent therapeutic expression of human factor IX (hFIX; 6%-10% of physiologic levels) in murine models. A dose of 4 x 10(12) vector genomes (vgs)/kg of body weight was administered through the hepatic artery or portal vein. Persistence of the rAAV vgs as circular monomers and dimers and high-molecular-weight concatamers was documented in liver tissue by Southern blot analysis for periods of up to 1 year. Vector particles were present in plasma, urine, or saliva for several days after infusion (as shown by polymerase chain reaction analysis), and the vgs were detected in spleen tissue at low copy numbers. An enzyme-linked immunosorption assay capable of detecting between 1% and 25% of normal levels of hFIX in rhesus plasma was developed by using hyperimmune serum from a rhesus monkey that had received an adenoviral vector encoding hFIX. Two macaques having 3 and 40 rAAV genome equivalents/cell, respectively, in liver tissue had 4% and 8% of normal physiologic plasma levels of hFIX, respectively. A level of hFIX that was 3% of normal levels was transiently detected in one other macaque, which had a genome copy number of 25 before abrogation by a neutralizing antibody (inhibitor) to hFIX. This nonhuman-primate model will be useful in further evaluation and development of rAAV vectors for gene therapy of hemophilia B.

Adeno-associated virus-mediated osteoprotegerin gene transfer protects against particulate polyethylene-induced osteolysis in a murine model

OBJECTIVE

Osteoprotegerin (OPG), a natural negative regulator of osteoclastogenesis and bone resorption, may be a potential therapeutic agent for treatment of osteolysis-associated prosthetic joint loosening. Using an in vivo adeno-associated virus (AAV)-mediated gene transfer technique, this study was designed to evaluate the protective effects of OPG transgene against orthopedic wear debris-induced bone loss in a murine model of osteolysis.

METHODS

Bone tissue was implanted into established pouches on BALB/c mice, followed by the introduction of ultra-high-molecular-weight polyethylene (UHMWPE) particles to provoke inflammation and osteolysis. The viruses encoding human OPG gene (rAAV-hOPG) or beta-galactosidase marker gene (rAAV-LacZ) were injected into the air pouches, and the tissue was harvested 7 days after viral infection for histologic and molecular analyses.

RESULTS

Successful transgene expression was confirmed by the detection of OPG by enzyme-linked immunosorbent assay and positive X-Gal staining of pouch tissue (LacZ). Real-time polymerase chain reaction indicated significant diminishment of messenger RNA expression of osteoclast markers in OPG-transduced pouches compared with rAAV-LacZ-transduced pouches. The transduction and expression of OPG also markedly decreased the gene copies of the biologic receptor activator of nuclear factor kappaB. The expression of OPG in the bone-implanted pouch reduced bone calcium release by a mean of 39% compared with the calcium release in the other 2 groups. Computerized image analysis revealed that expression of OPG significantly protected against bone collagen loss.

CONCLUSION

OPG gene transfer mediated by rAAV effectively protects against particulate polyethylene-induced bone resorption in this experimental model. Data suggest that gene transfer using rAAV-OPG may be a feasible and effective therapeutic candidate to treat or prevent wear debris-associated osteolysis and aseptic loosening.

Delivery of alpha- and beta-sarcoglycan by recombinant adeno-associated virus: efficient rescue of muscle, but differential toxicity

The sarcoglycanopathies are a group of four autosomal recessive limb girdle muscular dystrophies (LGMD 2D, 2E, 2C, and 2F), caused by mutations of the alpha-, beta-, gamma-, or delta-sarcoglycan genes, respectively. The delta-sarcoglycan-deficient hamster has been the most utilized model for gene delivery to muscle by recombinant adeno-associated virus (AAV) vectors; however, human patients with delta-sarcoglycan deficiency are exceedingly rare, with only two patients described in the United States. Here, we report construction and use of AAV vectors expressing either alpha- or beta-sarcoglycan, the genes responsible for the most common forms of the human sarcoglycanopathies. Both vectors showed successful short-term genetic, biochemical, and histological rescue of both alpha- and beta-sarcoglycan-deficient mouse muscle. However, comparison of persistence of expression in 51 injected mice showed substantial differences between AAV alpha-sarcoglycan (alpha-SG) and beta-sarcoglycan (beta-SG) vectors. AAV-beta-SG showed long-term expression with no decrease in expression for more than 21 months after injection, whereas AAV-alpha-SG showed a dramatic loss of positive fibers between 28 and 41 days post-injection (p = 0.006). Loss of immunopositive myofibers was correlated with significant inflammatory cell infiltrate, primarily macrophages. To determine whether the loss of alpha-sarcoglycan-positive fibers was due to an immune response or cytotoxic effect of alpha-sarcoglycan overexpression, severe combined immunodeficient (SCID) mouse muscle was assayed for cytotoxicity after injection with AAV-alpha-SG, AAV-beta-SG, or phosphate-buffered saline. The results were consistent with overexpression of alpha-sarcoglycan causing significant cytotoxicity. The cytotoxicity of alpha-sarcoglycan, and not beta- or delta-sarcoglycan overexpression, was consistent with biochemical studies of the hierarchical order of assembly of the sarcoglycan complex. Our data suggest that even closely related proteins might require different levels of expression to avoid toxicity and achieve long-term tissue rescue.

Adeno-associated virus vector-mediated minidystrophin gene therapy improves dystrophic muscle contractile function in mdx mice

Duchenne muscular dystrophy (DMD) is the most common disabling and lethal genetic muscle disorder, afflicting 1 of every 3500 males. Patients with DMD experience progressive muscle degeneration and weakness and succumb to respiratory or cardiac failure by their early twenties. No treatment is currently available for DMD. Mutations in the dystrophin gene result in lack of a functional dystrophin protein in striated muscle, which induces instability in the muscle cell membrane leading to persistent muscle injury after contraction. We have previously created novel minidystrophin genes and demonstrated that adeno-associated virus (AAV)-mediated intramuscular delivery of the minigenes effectively ameliorated mdx dystrophic histopathology and led to normal cell membrane integrity for more than 1 year. In this paper, we investigated whether AAV-minidystrophin could also improve mdx muscle contractile function. Two-month-old adult male mdx mice, with established muscular dystrophy, were given a single-dose injection of an AAV-minidystrophin vector in the tibialis anterior (TA) muscle of one leg, with the untreated contralateral leg used as a control. The treated TA muscle showed both (1) a significant increase in isometric force generation and (2) a significant increase in resistance to lengthening activation-induced muscle force decrements. We conclude that AAV-minidystrophin gene treatment is effective in improving mdx muscle contractile function.

Structural changes in the forefoot of individuals with diabetes and a prior plantar ulcer

BACKGROUND

Plantar ulcers produced by diabetic foot disease are devastating and costly. Better understanding of the ulcer-producing process is important to improve detection of feet that are at risk and to improve intervention. We identified and quantified soft-tissue and osseous structural changes in the forefoot of diabetic patients with a prior plantar ulcer.

METHODS

Thirty-two individuals with a mean age (and standard deviation) of 57 +/- 11 years were studied; sixteen had diabetes (of a mean of 20 +/- 11 years' duration), peripheral neuropathy, and a prior plantar ulcer, and sixteen were matched controls. Computed tomography was used to evaluate forefoot structure, including the plantar soft-tissue (muscle) density, soft-tissue thickness beneath the metatarsal heads, metatarsophalangeal joint angle, metatarsal bone density, and metatarsophalangeal joint arthropathy.

RESULTS

Plantar soft-tissue (muscle) density was lower in the individuals with diabetes (mean, 1 HU [Hounsfield unit]) than it was in the controls (mean, 18 HU). There was no difference in the soft-tissue thickness beneath the metatarsal heads (mean, 10 mm) between the individuals with diabetes and the controls, but the soft-tissue thickness decreased with age. The individuals with diabetes had greater extension deformity of the first, second, and third metatarsophalangeal joints and greater arthropathy of the second, third, and fourth metatarsophalangeal joints. There were no significant differences in metatarsal bone density between the groups.

CONCLUSIONS

There were significant differences between the forefeet of individuals with diabetes and a previous plantar ulcer and those of controls: plantar muscle density was decreased, and metatarsophalangeal joint extension and arthropathy were increased. Interestingly, the soft-tissue thickness under the metatarsal heads in the controls was not greater than that in the diabetic patients.

CLINICAL RELEVANCE

This study demonstrated structural differences between the forefeet of patients with diabetes and a previous ulcer and those of normal age-matched controls. The information can serve to guide new interventions to prevent or treat foot ulcerations in this patient population.

Development and optimization of a real-time quantitative PCR-based method for the titration of AAV-2 vector stocks

Despite the clinical application of adeno-associated virus (AAV) gene therapy, the titration of viral stocks has not yet been standardized. This complicates the comparison of viral stocks between laboratories. Functional titering of AAV is time-consuming, requires the manipulation of hazardous material, and often has a high degree of variability. We established an optimized real-time quantitative polymerase chain reaction (RQ-PCR) titration assay to determine viral titers and compared it with a functional green fluorescent protein (GFP)-based titration method. With a combination of improved lysis procedures and RQ-PCR protocols we could decrease the intraexperimental coefficient of variation (CV) from 0.24 +/- 0.03 to 0.042 +/- 0.004 and the interexperimental CV from 0.34 +/- 0.06 to 0.093 +/- 0.028 following functional and RQPCR-based titration, respectively. This low variability conforms to even the strictest quality standards required, for example, in clinical laboratories. The highly standardized titration by RQPCR described here will be especially advantageous for groups working on AAV-based gene therapy in a good manufacturing practice setting.

Light-activated gene transduction enhances adeno-associated virus vector-mediated gene expression in human articular chondrocytes

OBJECTIVE

To evaluate the effects of ultraviolet (UV) light as an adjuvant for recombinant adeno-associated virus (rAAV) transduction in human articular chondrocytes.

METHODS

Primary articular chondrocytes and immortalized chondrocytes (tsT/AC62) were exposed to various doses of UV light (0-1,000 J/m(2)) and infected at various multiplicities of infection (MOIs) with rAAV containing the enhanced green fluorescent protein (EGFP) gene. Cells were analyzed for viability and EGFP expression by fluorescence-activated cell sorting on days 2, 4, and 8 following infection. To evaluate the transduction efficiency in intact articular cartilage, full-thickness explants were exposed to UV light (0-200 J/m(2)), infected with rAAV-eGFP, and analyzed for transduction via immunohistochemistry.

RESULTS

Toxicity from UV exposure was observed at doses > or =500 J/m(2) and > or =200 J/m(2) in primary and immortalized chondrocyte cultures, respectively. Transduction efficiency was dependent on the UV dose, MOI, and time. In the cell line, the adjuvant effect of UV on the percentage of cells transduced was modest, but 100 J/m(2) increased the mean fluorescence intensity (MFI) of the transduced cells 4-fold. In contrast, UV treatment had a profound effect on the transduction efficiency of primary chondrocytes, which reached approximately 100% after exposure to 100 J/m(2) of UV light and 10(3) MOIs for 8 days. Under the same conditions, 200 J/m(2) of UV light enhanced the MFI 7-fold. In cartilage explants, there was no difference in the number of transduced chondrocytes at the edge of the explants in the superficial, intermediate, or basal zones; however, 200 J/m(2) of UV light increased the transduction efficiency 2-fold at a low MOI. In the center of the explants, the superficial chondrocytes were efficiently transduced; those in the intermediate and basal zones could not be efficiently transduced under any condition. In the superficial chondrocytes, a low MOI and 200 J/m(2) of UV light increased the transduction efficiency 3-fold (to 100%).

CONCLUSION

UV light at doses of up to 200 J/m(2) (which do not significantly affect cell viability) significantly enhances the transduction efficiency and expression of the transduced gene in cultures of rAAV-infected primary chondrocytes and in chondrocytes in the superficial zone of intact articular cartilage. These findings support the concept that UV-activated gene transduction could be used as an adjuvant for in vivo rAAV articular cartilage gene therapy with low viral titers to prevent and/or treat arthritis.

Chronic suppression of heart-failure progression by a pseudophosphorylated mutant of phospholamban via in vivo cardiac rAAV gene delivery

The feasibility of gene therapy for cardiomyopathy, heart failure and other chronic cardiac muscle diseases is so far unproven. Here, we developed an in vivo recombinant adeno-associated virus (rAAV) transcoronary delivery system that allows stable, high efficiency and relatively cardiac-selective gene expression. We used rAAV to express a pseudophosphorylated mutant of human phospholamban (PLN), a key regulator of cardiac sarcoplasmic reticulum (SR) Ca(2+) cycling in BIO14.6 cardiomyopathic hamsters. The rAAV/S16EPLN treatment enhanced myocardial SR Ca(2+) uptake and suppressed progressive impairment of left ventricular (LV) systolic function and contractility for 28-30 weeks, thereby protecting cardiac myocytes from cytopathic plasma-membrane disruption. Low LV systolic pressure and deterioration in LV relaxation were also largely prevented by rAAV/S16EPLN treatment. Thus, transcoronary gene transfer of S16EPLN via rAAV vector is a potential therapy for progressive dilated cardiomyopathy and associated heart failure.

Clinical protocol. Gene therapy of Canavan disease: AAV-2 vector for neurosurgical delivery of aspartoacylase gene (ASPA) to the human brain

This clinical protocol describes virus-based gene transfer for Canavan disease, a childhood leukodystrophy. Canavan disease, also known as Van Bogaert-Bertrand disease, is a monogeneic, autosomal recessive disease in which the gene coding for the enzyme aspartoacylase (ASPA) is defective. The lack of functional enzyme leads to an increase in the central nervous system of the substrate molecule, N-acetyl-aspartate (NAA), which impairs normal myelination and results in spongiform degeneration of the brain. No effective treatment currently exists; however, virus-based gene transfer has the potential to arrest or reverse the course of this otherwise fatal condition. This procedure involves neurosurgical administration of approximately 900 billion genomic particles (approximately 10 billion infectious particles) of recombinant adeno-associated virus (AAV) containing the aspartoacylase gene (ASPA) directly to affected regions of the brain in each of 21 patients with Canavan disease. Pre- and post-delivery assessments include a battery of noninvasive biochemical, radiological, and neurological tests. This gene transfer study represents the first clinical use of AAV in the human brain and the first instance of viral gene transfer for a neurodegenerative disease.

Adenoviral and adeno-associated viral vector mediated gene transfer in the guinea pig cochlea

Peripheral sensorineural hearing loss is a very common inner ear disorder affecting nearly 10% of the population. At present there is no cure for this disorder but gene therapy has been suggested as a potentially effective method for clinical treatment in the future. Thus we investigated the effectiveness of adenoviral (Ad) and adeno-associated viral (AAV) vectors to transduce the cochlea of guinea pigs. After direct injection into the basal turn of the cochlea, we found that both Ad and AAV vectors coding for the reporter genes lacZ or GFP readily transduced spiral ganglion cells. In addition, some transgene expression was detected in the stria vascularis after AAV-GFP injection. Gene expression persisted at least 8 weeks after viral vector injection. Present findings will help to develop future gene therapy protocols in the inner ear by using Ad and AAV coding for neurotrophins such as NT-3, BDNF, GDNF and VEGF.

Adenovirus mediated gene transfer to skeletal muscle

Transfer of therapeutic genes into muscle tissue has promise for the treatment of a variety of muscular dystrophies. Various vectors have been used to deliver genes to skeletal muscle but their application has faced several major limitations including: (1) the lack of transgene persistence caused by the immune rejection of transduced myofibers and/or vector toxicity, and (2) the maturation dependence of viral transduction. While the immunorejection and/or cytotoxic problems are being overcome with the development of new vectors, maturation-dependent viral transduction is still a major hurdle in gene transfer to skeletal muscle. Poor adenoviral transduction in mature myofibers has been attributed to: (1) the extracellular matrix of mature myofibers may form a physical barrier and prevent the passage of large viral particles; (2) viral receptors are down-regulated with muscle maturation; and (3) loss of myoblasts with muscle maturation, which serve as intermediaries in the viral transduction. In this review, we will focus on recent developments in overcoming those hurdles of gene therapy in skeletal muscle, especially to adenovirus (Ad), including: (1) new mutant vectors lacking all viral genes to decrease immunogenicity, and hence, improve persistence of transgene expression in muscle in vivo; (2) using tissue specific promoters to evade immunorejection; (3) permeabilization of the extracellular matrix; (4) modifying the viral receptors in mature myofibers; and (5) myoblast or muscle stem cell mediated ex vivo gene transfer.

Targeted transgene insertion into human chromosomes by adeno-associated virus vectors

Efficient methods are needed for the precise genetic manipulation of diploid human cells, in which cellular senescence and low conventional gene targeting rates limit experimental and therapeutic options. We have shown previously that linear, single-stranded DNA vectors based on adeno-associated virus (AAV) could accurately introduce small (<20 bp) genetic modifications into homologous human chromosomal sequences. Here we have used AAV vectors to introduce large (>1 kb) functional transgene cassettes into the hypoxanthine phosphoribosyl transferase (HPRT) and Type I collagen (COL1A1) loci in normal human fibroblasts. The transgene cassettes are inserted at high frequencies (1% of the total cell population under optimal conditions) and without secondary mutations. Selection for the inserted transgene cassette can be used to enrich for targeting events, such that >70% of surviving cells have undergone gene targeting with an appropriately designed vector. This approach should prove useful both for functional genomic analysis in diploid human cells and for therapeutic gene targeting.

Expression of human factor VIII by splicing between dimerized AAV vectors

Adeno-associated virus (AAV) is a useful vector for hemophilia gene therapy, but the limited effective packaging capacity of AAV (5 kb) appears to be incompatible with factor VIII (gene symbol F8) cDNA (7 kb). Although we previously demonstrated efficient packaging and expression of B-domain-deleted human F8 (BDD-F8) using a single AAV vector, the packaging limit still excludes the use of large/strong regulatory elements. Here we exploited the split AAV vector technology that expands the packaging capacity of AAV through head-to-tail dimerization. To test the feasibility of AAV heterodimerization for F8 expression, we generated a 5' vector that includes a large enhancer/promoter cassette linked with exons 1-12 of the F8 cDNA and a half-intron-carrying splice donor site. A complementing 3' vector contains another half-intron-carrying splice acceptor site linked with the remaining F8 cDNA and a polyadenylation signal. Following coinfection of 293 and HepG2 cells, the 5' and 3' vectors together produced functional human factor VIII protein at a level of 120 mU/ml (24 ng/ml). No factor VIII protein was detected if only one of the vectors was used. Correct head-to-tail vector dimerization as well as spliced BDD-F8 mRNA was detected by DNA PCR and RT-PCR, respectively. Furthermore, intraportal injection of two rAAV/F8 vectors in immunodeficient mice produced 2% of the normal level of factor VIII for four months. Our results demonstrate the potential use of AAV dimerization for F8 expression.

Safety of adeno-associated virus gene therapy vectors: a current evaluation

An increasing number of strategies for molecular treatment of disease rely on the adeno-associated virus (AAV) as a therapeutic gene delivery vector. One of the most attractive features of this viral DNA vector is the perceived safety of AAV gene delivery. Recent applications in human clinical trials support the safety record established in preclinical trials, with evidence of gene transfer in the absence of cellular immune responses or tissue disturbance. Nevertheless, many aspects of the biology of the wild type AAV and its derivatives are still being explored. While the therapeutic potential of novel recombinant AAV therapeutics appears promising, recent insights suggest aspects of their pharmacokinetics, biodistribution and toxicity that require consideration to achieve the safest application of these molecular medicines.

Adeno-associated virus-mediated transfer of human acid maltase gene results in a transient reduction of glycogen accumulation in muscle of Japanese quail with acid maltase deficiency

Glycogen storage disease type II (GSD II), Pompe's disease, is caused by the deficiency of acid alpha-D-glucosidase (GAA) in lysosome and is the most common form of GSD in Taiwan. Most cases are the infantile form. The disease is relentless and most patients die of cardiac failure and respiratory tract infection in the first year of life. At present, no treatment has been proved effective for this fatal disease. The applicability of enzyme replacement therapy is under investigation. However, high price and transient efficiency are the major problems to be solved. Accordingly, gene therapy by viral method has been conducted. In this study we constructed a plasmid that contained 5'-shortened BglII-NotI fragment human GAA cDNA, downstream of CMV promoter and bovine growth hormone polyadenylation signal, as well as AAV ITR region. When fibroblasts obtained from GSD II patients were cultured and infected with rAAV-GAA, the GAA activity of the fibroblasts increased four- to five-fold. Using acid maltase deficient (AMD) Japanese quail as the animal model, rcAAV-GAA 0.1 ml per site (1 x 10(9)-10) particles), totally 10 different sites to make 1 ml (1 x 10(1)0-11) particles), was injected into unilateral deep pectoral muscle of AMD quails. Medium (hepes) was only injected in the same way into the contralateral deep pectoral muscle to serve as control. Four days after injection, PAS staining showed disappearance of the glycogenosomes with regeneration of myocytes surrounding the intramuscular injected area as compared with the contralateral muscle of the same birds. Using anti-GAA monoclonal antibody, GAA was demonstrated on the regenerated myocytes by immunohistochemical staining and absent on the contralateral muscle of the same birds. Nevertheless, T lymphocytes infiltration was noted in both the rcAAV-GAA and hepes (medium) injected muscles and more prominent in the rcAAV-GAA-injected site. Functional evaluation demonstrated that wing flapping movement improved with wide flapping in the rAAV-GAA injected side, but not in the counterpart. Unfortunately, these histochemical and functional improvements faded away in 14 days, probably due to destruction of rcAAV by cell-mediated immunity of infiltrated T cells. Taken together, the present study suggests that rAAV can enter either human or quail cells and express and effectively reduce the glycogen accumulation in the skeletal muscle of AMD quails. These preliminary results are similar to these of low-dose rGAA replacement therapy. The mechanisms underlying the induction of cell-mediated immunity are unknown. How to elevate the number of packaged AAV, enhance the infectivity of AAV and reduce cell-mediated immunity must be solved in the future.

Correction of the enzymatic and functional deficits in a model of Pompe disease using adeno-associated virus vectors

Pompe disease is a lysosomal storage disease caused by the absence of acid alpha-1,4 glucosidase (GAA). The pathophysiology of Pompe disease includes generalized myopathy of both cardiac and skeletal muscle. We sought to use recombinant adeno-associated virus (rAAV) vectors to deliver functional GAA genes in vitro and in vivo. Myotubes and fibroblasts from Pompe patients were transduced in vitro with rAAV2-GAA. At 14 days postinfection, GAA activities were at least fourfold higher than in their respective untransduced controls, with a 10-fold increase observed in GAA-deficient myotubes. BALB/c and Gaa(-/-) mice were also treated with rAAV vectors. Persistent expression of vector-derived human GAA was observed in BALB/c mice up to 6 months after treatment. In Gaa(-/-) mice, intramuscular and intramyocardial delivery of rAAV2-Gaa (carrying the mouse Gaa cDNA) resulted in near-normal enzyme activities. Skeletal muscle contractility was partially restored in the soleus muscles of treated Gaa(-/-) mice, indicating the potential for vector-mediated restoration of both enzymatic activity and muscle function. Furthermore, intramuscular treatment with a recombinant AAV serotype 1 vector (rAAV1-Gaa) led to nearly eight times normal enzymatic activity in Gaa(-/-) mice, with concomitant glycogen clearance as assessed in vitro and by proton magnetic resonance spectroscopy.

Adeno-associated virus capsids displaying immunoglobulin-binding domains permit antibody-mediated vector retargeting to specific cell surface receptors

Recombinant adeno-associated virus type 2 (rAAV2) is a promising vector for human somatic gene therapy. However, its broad host range is a disadvantage for some applications, because it reduces the specificity of the gene transfer. To overcome this limitation, we sought to create a versatile rAAV vector targeting system which would allow us to redirect rAAV binding to specific cell surface receptors by simple coupling of different ligands to its capsid. For this purpose, an immunoglobulin G (IgG) binding domain of protein A, Z34C, was inserted into the AAV2 capsid at amino acid position 587. The resulting AAV2-Z34C mutants could be packaged and purified to high titers and bound to IgG molecules. rAAV2-Z34C vectors coupled to antibodies against CD29 (beta(1)-integrin), CD117 (c-kit receptor), and CXCR4 specifically transduced distinct human hematopoietic cell lines. In marked contrast, no transduction was seen in the absence of antibodies or in the presence of specific blocking reagents. These results demonstrate for the first time that an immunoglobulin binding domain can be inserted into the AAV2 capsid and coupled to various antibodies, which mediate the retargeting of rAAV vectors to specific cell surface receptors.

Models of repair mechanisms for future treatment modalities of Parkinson's disease

Parkinson's disease is one of the most likely neurological disorders to be fully treatable by drugs and new therapeutic modalities. The age-dependent and multifactorial nature of its pathogenesis allows for many strategies of intervention and repair. Most data indicate that the selectively vulnerable dopaminergic neurons in the substantia nigra of patients that have developed Parkinson's disease can be modified by protective and reparative therapies. First, the oxidative stress, protein abnormalities, and cellular inclusions typically seen could be dealt with by anti-oxidants, trophic factors, and proteolytic enhancements. Secondly, if the delay of degeneration is not sufficient, then immature dopamine neurons can be placed in the parkinsonian brain by transplantation. Such neurons can be derived from stem cell sources or even stimulated to repair from endogenous stem cells. Novel molecular and cellular treatments provide new tools to prevent and alleviate Parkinson's disease.

Recombinant adeno-associated virus serotypes 2- and 5-mediated gene transfer in the mammalian brain: quantitative analysis of heparin co-infusion

Recombinant adeno-associated viruses (rAAVs) are among the most promising vectors for gene delivery into the CNS. However, a major hurdle for gene transfer to the mammalian brain is to achieve high transduction levels in target cells beyond the immediate injection site. Therefore, building upon the optimization of injection parameters on which we have recently reported, it is important to define additional methods to increase the volume of distribution. Here, we establish an optimal heparin concentration, and show that co-injection of heparin together with rAAV2 leads to a significantly higher and more homogeneous distribution of transduced cells. In contrast, the diffusion pattern of rAAV serotype 5 differs from that of rAAV2, in that its distribution is less homogeneous, more variable, and patchy. Furthermore, this study illustrates the influence of receptor binding on the expression pattern following injection of rAAV in the CNS. In addition to improvements in expression cassettes and viral titers and the use of very slow infusion rates, gene transfer studies in the CNS where the goal is to obtain widespread transduction should consider co-injecting the viral vector rAAV2 with heparin to maximize transduction efficiency and viral spread.

Ubiquitination of both adeno-associated virus type 2 and 5 capsid proteins affects the transduction efficiency of recombinant vectors

In the presence of complementing adeno-associated virus type 2 (AAV-2) Rep proteins, AAV-2 genomes can be pseudotyped with the AAV-5 capsid to assemble infectious virions. Using this pseudotyping strategy, the involvement of the ubiquitin-proteasome system in AAV-5 and AAV-2 capsid-mediated infections was compared. A recombinant AAV-2 (rAAV-2) proviral luciferase construct was packaged into both AAV-2 and AAV-5 capsid particles, and transduction efficiencies in a number of cell lines were compared. Using luciferase expression as the end point, we demonstrated that coadministration of the viruses with proteasome inhibitors not only increased the transduction efficiency of rAAV-2, as previously reported, but also augmented rAAV-5-mediated gene transfer. Increased transgene expression was independent of viral genome stability, since there was no significant difference in the amounts of internalized viral DNA in the presence or absence of proteasome inhibitors. Western blot assays of immunoprecipitated viral capsid proteins from infected HeLa cell lysates and in vitro reconstitution experiments revealed evidence for ubiquitin conjugation of both AAV-2 and AAV-5 capsids. Interestingly, heat-denatured virus particles were preferential substrates for in vitro ubiquitination, suggesting that endosomal processing of the viral capsid proteins is a prelude to ubiquitination. Furthermore, ubiquitination may be a signal for processing of the capsid at the time of virion disassembly. These studies suggest that the previously reported influences of the ubiquitin-proteasome system on rAAV-2 transduction are also active for rAAV-5 and provide a clearer mechanistic framework for understanding the functional significance of ubiquitination.

Modular flexibility of dystrophin: implications for gene therapy of Duchenne muscular dystrophy

Attempts to develop gene therapy for Duchenne muscular dystrophy (DMD) have been complicated by the enormous size of the dystrophin gene. We have performed a detailed functional analysis of dystrophin structural domains and show that multiple regions of the protein can be deleted in various combinations to generate highly functional mini- and micro-dystrophins. Studies in transgenic mdx mice, a model for DMD, reveal that a wide variety of functional characteristics of dystrophy are prevented by some of these truncated dystrophins. Muscles expressing the smallest dystrophins are fully protected against damage caused by muscle activity and are not morphologically different from normal muscle. Moreover, injection of adeno-associated viruses carrying micro-dystrophins into dystrophic muscles of immunocompetent mdx mice results in a striking reversal of histopathological features of this disease. These results demonstrate that the dystrophic pathology can be both prevented and reversed by gene therapy using micro-dystrophins.

Adeno-associated virus effectively mediates conditional gene modification in the brain

The Cre/loxP system is increasingly showing promise for investigating genes involved in neural function. Here, we demonstrate that in vivo modification of genes in the mouse brain can be accomplished in a spatial- and temporal-specific manner by targeted delivery of an adeno-associated virus (AAV) encoding a green fluorescent protein/Cre recombinase (GFP/Cre) fusion protein. By using a reporter mouse, in which Cre recombinase activates beta-galactosidase expression, we demonstrate long-term recombination of neurons in the hippocampus, striatum, and septum as early as 7 days after stereotaxic injection of virus. Recombined cells were observed for at least 6 months postinjection without evidence of cell loss or neural damage. AAV-mediated delivery of GFP/Cre provides a valuable approach to alter the mouse genome, as AAV delivers genes efficiently to neurons with low toxicity. This approach will greatly facilitate the study of genetic modifications in the mouse brain.

Gene therapy for Parkinson's disease

Significant progress has been made in the field of gene therapy for Parkinson's disease (PD). Successful vehicles for gene transfer into the central nervous system have been developed and clinical efficacy and safety have both been shown in various animal models of PD. Further optimisation of dosing, timing and location of gene therapy delivery as well as the ability to regulate and prolong gene expression will be important for the commencement of human trials. Current gene therapy models for PD have focused on two treatment strategies. One is the replacement of biosynthetic enzymes for dopamine synthesis and the second strategy is the addition of neurotrophic factors for protection and restoration of dopaminergic neurones. Concepts of neuroprotection and restoration of the nigrostriatal pathway will become important themes for future genetic treatment strategies for PD and may include, in addition to neurotrophic factors, genes to prevent apoptosis or detoxify free radical species. This review will highlight the recent literature on gene therapy for PD and summarise general approaches to gene therapy.

Feasibility of generating adeno-associated virus packaging cell lines containing inducible adenovirus helper genes

The adeno-associated virus (AAV) vector system is based on nonpathogenic and helper-virus-dependent parvoviruses. The vector system offers safe, efficient, and long-term in vivo gene transfer in numerous tissues. Clinical trials using AAV vectors have demonstrated vector safety as well as efficiency. The increasing interest in the use of AAV for clinical studies demands large quantities of vectors and hence a need for improvement in vector production. The commonly used transient-transfection method, although versatile and free of adenovirus (Ad), is not cost-effective for large-scale production. While the wild-type-Ad-dependent AAV producer cell lines seem to be cost-effective, this method faces the problem of wild-type Ad contamination. To overcome these shortcomings, we have explored the feasibility of creating inducible AAV packaging cell lines that require neither transfection nor helper virus infection. As a first step toward that goal, we have created a cell line containing highly inducible Ad E1A and E1B genes, which are essential for AAV production. Subsequently, the AAV Rep and Cap genes and an AAV vector containing a green fluorescent protein (GFP) reporter gene were stably introduced into the E1A-E1B cell line, generating inducible AAV-GFP packaging cell lines. Upon induction of E1A and E1B genes and infection with replication-defective Ad with E1A, E1B, and E3 deleted, the packaging cells yielded high-titer AAV-GFP vectors. Finally, the E2, E4, and VA genes of Ad, under the control of their endogenous promoters, were also introduced into these cells. A few producer cell lines were obtained, which could produce AAV-GFP vectors upon simple drug induction. Although future improvement is necessary to increase the stability and vector yield of the cells, our study has nonetheless demonstrated the feasibility of generating helper-virus-free inducible AAV producer cell lines.

Transduction of human neural progenitor cells using recombinant adeno-associated viral vectors

Human neural progenitor cells (hNPCs) represent an attractive source for cell therapy of neurological disorders. Genetic modification of hNPCs may allow a controlled release of therapeutic proteins, suppress immune rejection, or produce essential neurotransmitters. In search of an effective gene delivery vehicle, we evaluated the efficiency of a recombinant adeno-associated viral (rAAV) vector expressing enhanced green fluorescent protein (CAGegfp). Our study demonstrated that CAGegfp efficiently transduced both proliferating and differentiated hNPCs in vitro. EGFP expression was detected as early as 1 day after exposure to CAGegfp and was detectable for up to 4 months. Following transduction, the growth rate of hNPCs slowed down, but they were still able to differentiate into neurons and glia. Furthermore, CAGegfp-modified hNPCs survived, differentiated and expressed EGFP after transplanting into spinal cord of adult rats. Our results indicated that rAAV vectors might be a useful tool in hNPC-based cell and gene therapy for neurological disorders.

Recombinant adeno-associated virus serotype 2 vectors mediate stable interleukin 10 secretion from salivary glands into the bloodstream

We have constructed a recombinant adeno-associated virus serotype 2 vector encoding human interleukin 10 (rAAVhIL10). IL-10 is a potent antiinflammatory/immune cytokine, which has received growing attention for its therapeutic potential. Human IL-10 (hIL-10) production was virus dose dependent after in vitro infection of HSG cells, a human submandibular gland cell line. The vector-derived hIL-10 produced was biologically active, as the medium from rAAVhIL10-infected HSG cells caused a dose-dependent blockade of IL-12 secretion from spleen cells of IL-10 knockout mice challenged with heat-killed Brucella abortus. Administration of rAAVhIL10 (10(10) genomes per gland) to both mouse submandibular glands led to hIL-10 secretion into the bloodstream (approximately 1-5 pg/ml), that is, in an endocrine manner, which was stable for approximately 2 months. Salivary gland administration of rAAVhIL10 under experimental conditions was more efficacious than intravenous administration (approximately 0.5-0.7 pg/ml). Also, hIL-10 was readily secreted in vitro from organ cultures of minced submandibular glands infected with rAAVhIL10, 6 or 8 weeks earlier. Consistent with these results, hIL-10 mRNA was detected by reverse transcription-polymerase chain reaction in submandibular glands of mice infected with rAAVhIL10 but not from control mice. At these doses, little to no hIL-10 was detected in mouse saliva. Using a rAAV serotype 2 vector encoding beta-galactosidase, we observed that the primary parenchymal target cells were ductal. These findings represent the first report of rAAV use to target exocrine glands for systemic secretion of a therapeutic protein, and support the notion that rAAV serotype 2 vectors may be useful in salivary glands for local (periglandular) and systemic gene-based protein therapeutics.

Nucleic acid biotechnology

Driven by advances in the acquisition of genetic sequence information and the ability to manipulate small quantities of nucleic acid, a number of technologies are emerging that exploit nucleic acids for research, diagnostic, and therapeutic utility. In this review, we cover three technologies based on nucleic acids--DNA microarrays, antisense technology, and gene therapy--that are especially promising and may make a substantial impact in the laboratory and in the clinic during the coming years. For each of these areas, an overview of the current status and applications is provided, followed by a discussion of critical issues and challenges to be faced for further advancement of the technology; an emphasis is placed on quantitative and engineering aspects.

Gene therapy: promises and problems

Gene therapy can be broadly defined as the transfer of genetic material to cure a disease or at least to improve the clinical status of a patient. One of the basic concepts of gene therapy is to transform viruses into genetic shuttles, which will deliver the gene of interest into the target cells. Based on the nature of the viral genome, these gene therapy vectors can be divided into RNA and DNA viral vectors. The majority of RNA virus-based vectors have been derived from simple retroviruses like murine leukemia virus. A major shortcoming of these vectors is that they are not able to transduce nondividing cells. This problem may be overcome by the use of novel retroviral vectors derived from lentiviruses, such as human immunodeficiency virus (HIV). The most commonly used DNA virus vectors are based on adenoviruses and adeno-associated viruses. Although the available vector systems are able to deliver genes in vivo into cells, the ideal delivery vehicle has not been found. Thus, the present viral vectors should be used only with great caution in human beings and further progress in vector development is necessary.