Hemophilia B is a severe X-linked bleeding diathesis caused by the absence of functional blood coagulation factor IX, and is an excellent candidate for treatment of a genetic disease by gene therapy. Using an adeno-associated viral vector, we demonstrate sustained expression (>17 months) of factor IX in a large-animal model at levels that would have a therapeutic effect in humans (up to 70 ng/ml, adequate to achieve phenotypic correction, in an animal injected with 8.5 × 10 12 vector particles/kg). The five hemophilia B dogs treated showed stable, vector dose-dependent partial correction of the whole blood clotting time and, at higher doses, of the activated partial thromboplastin time. In contrast to other viral gene delivery systems, this minimally invasive procedure, consisting of a series of percutaneous intramuscular injections at a single timepoint, was not associated with local or systemic toxicity. Efficient gene transfer to muscle was shown by immunofluorescence staining and DNA analysis of biopsied tissue. Immune responses against factor IX were either absent or transient. These data provide strong support for the feasibility of the approach for therapy of human subjects.

Somatic gene therapy has been proposed as a means to achieve systemic delivery of therapeutic proteins. However, there is limited evidence that current methods of gene delivery can practically achieve this goal. In this study, we demonstrate that, following a single intramuscular administration of a recombinant adeno-associated virus (rAAV) vector containing the ␤-galactosidase (AAV-lacZ) gene into adult BALB͞c mice, protein expression was detected in myofibers for at least 32 weeks. A single intramuscular administration of an AAV vector containing a gene for human erythropoietin (AAV-Epo) into mice resulted in dosedependent secretion of erythropoietin and corresponding increases in red blood cell production that persisted for up to 40 weeks. Primary human myotubes transduced in vitro with the AAV-Epo vector also showed dose-dependent production of Epo. These results demonstrate that rAAV vectors are able to transduce skeletal muscle and are capable of achieving sustained expression and systemic delivery of a therapeutic protein following a single intramuscular administration. Gene therapy using AAV vectors may provide a practical strategy for the treatment of inherited and acquired protein deficiencies.

The purpose of this work was to develop an efficient Therefore the minimum set of genes required to produce method for the production of adeno-associated virus (AAV) AAV helper activity equivalent to that provided by adenvectors in the absence of helper virus. The adenovirus ovirus infection consists of, or is a subset of, the following regions that mediate AAV vector replication were identified genes: the E4orf6 gene, the 72-M r , E2A protein gene, the and assembled into a helper plasmid. These included the VA RNA genes and the E1 region. AAV vector preparations VA, E2A and E4 regions. When this helper plasmid was made with adenovirus and by the helper virus-free method cotransfected into 293 cells, along with plasmids encoding were essentially indistinguishable with respect to particle the AAV vector, and rep and cap genes, AAV vector was density, particle to infectivity ratio, capsimer ratio and produced as efficiently as when using adenovirus infection efficiency of muscle transduction in vivo. Only AAV vector as a source of help. CMV-driven constructs expressing the preparations made by the helper virus-free method were E4orf6 and the 72-M r , E2A proteins were able to funcnot reactive with anti-adenovirus sera. tionally replace the E4 and E2A regions, respectively.

Adeno-associated virus (AAV) vectors delivered through the systemic circulation successfully transduce various target tissues in animal models. However, similar attempts in humans have been hampered by the high prevalence of neutralizing antibodies to AAV, which completely block vector transduction. We show in both mouse and nonhuman primate models that addition of empty capsid to the final vector formulation can, in a dose-dependent manner, adsorb these antibodies, even at high titers, thus overcoming their inhibitory effect. To further enhance the safety of the approach, we mutated the receptor binding site of AAV2 to generate an empty capsid mutant that can adsorb antibodies but cannot enter a target cell. Our work suggests that optimizing the ratio of full/empty capsids in the final formulation of vector, based on a patient's anti-AAV titers, will maximize the efficacy of gene transfer after systemic vector delivery.