Dose response to a single intramuscular injection of recombinant adeno-associated virus-erythropoietin in monkeys

Background, Anemia is a significant problem in many disease states. Erythro poietin (Epo) has been used in the treatment of anemia associated with nume rous chronic diseases. This study investigates the dose-response profiles o f a single intramuscular (im) injection of a recombinant adeno-associated v irus vector (rAAV) containing the Epo gene with the goal of achieving a sus tained elevation of hematocrit (Hct), Methods. Cynomolgus (cm) monkeys were given single injections of different doses of rAAV-cm-Epo, The biological effect of Epo gene expression was moni tored by determining the Hct levels and circulating hormone levels by ELISA . Antibody to the rAAV capsid protein was also measured over the 41-week pe riod of the experiment. Results. Epo expression was noted only when 2 x 10(11) or more particles we re injected. Epo was noted to be increased as soon as 1 week postinjection and was maximum in 6 to 8 weeks. This level of expression remained constant for nearly 20 weeks. Animals given the highest dose of rAAV developed a hi gher Hct over the first 8 weeks postinjection than those given an intermedi ate dose. However, the maximum levels of hemoglobin were the same. There wa s a weak correlation between amount of rAAV injected and capsid antibody re sponse. Conclusions. AAV vectors are able to transduce skeletal muscle and are capa ble of achieving sustained expression and systemic delivery of a therapeuti c protein following a single im administration. Dose responses to rAAV-Epo are achievable, although a threshold inoculum of virus is necessary to prod uce an effect and the therapeutic window is narrow. (C) 2000 Academic Press .