A number of important human diseases are caused by the inherited or acquired deficiency of a single serum protein. These include diabetes mellitus, pituitary dwarfism, hemophilias A an B and the erythropoietin (Epo) responsive anemias. Many of these diseases are currently treated by repeated intravenous or subcutaneous injections of purified or recombinant proteins. Such therapies although often life-saving are inconvenient and expensive. Moreover in some cases there is insufficient recombinant protein available to treat all patients prophylactically while in others intermittent administration of recombinant protein fails to ameliorate all of the side effects of the disease. These problems have stimulated interest in the development of novel gene transfer approaches that could be used for the treatment of acquired and inherited serum protein deficiencies. The long term goal of the studies described in this continuing application is the development of a muscle based somatic gene transfer approach that can be used to stably program physiologically regulated therapeutic levels of Epo in the circulation of patients with Epo responsive anemias. The method to be used is based on findings from the first three years of this grant which have demonstrated that genetically modified skeletal myocytes can be used to stably deliver physiological levels of Epo to the systemic circulation of mice and monkeys. In the studies described below the investigators propose to 1) develop novel adenoviral, adeno-associated viral and plasmid vectors for in vivo gene transfer of the Epo cDNA into skeletal muscle; 2) test the ability of these vectors to stably deliver physiological levels of Epo to the circulation of mice and monkeys following IM injection; 3) develop tetracycline-regulatable and skeletal muscle specific Epo expression vectors and test them in vitro and in vivo; and 4) test the hypothesis that hypoxia-inducible transcriptional regulatory elements from the Epo, LDH-A, and PGK genes can be used to construct hypoxia inducible Epo expression vectors that can be used to deliver physiologically regulated Epo to the circulation following IM injection. Taken together these studies should lay the foundation for successful human gene therapy trials for patients with Epo responsive anemias. They should also be relevant to the treatment of a number of other acquired and inherited serum protein deficiencies.
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