Biodistribution and safety assessment of AAV2‐GAD following intrasubthalamic injection in the rat

Abstract

The steps necessary to translate promising new biological therapies to the clinic are poorly documented. For gene therapy, there are unique aspects that need to be addressed in biodistribution studies. Notably, the spread of the vector beyond the intended target cells or tissue may result in persistent unwanted biological activity or unpredictable biological events; thus, it is critical to evaluate the risks associated with viral vector-mediated gene transfer prior to embarking on human clinical trials. In the present study, we conducted a comprehensive assessment of vector biodistribution throughout the brain, blood and major organs of rats that had been injected via the subthalamic nucleus with recombinant adeno-associated virus (AAV) expressing glutamic acid decarboxylase (GAD). In addition, behavioral and histological analyses were also performed. AAV genomes were not detected in blood or cerebrospinal fluid, and did not disseminate to organs outside of the brain in the majority of animals. In the brain, an average of 97.3% of AAV2-GAD genomes were restricted to the area of the ipsilateral subthalamic nucleus (STN). There were no discernable effects of AAV2-GAD on general health, and a behavioral assessment of the animals did not reveal any alteration in general behavior, exploration, locomotion or motor symmetry. The present study met Food and Drug Administration requirements, in addition to efficacy and toxicity studies in rodents and nonhuman primates, to support and supplement a Phase II clinical trial invloving the gene transfer of AAV2-GAD to the human STN for the potential therapy of Parkinson's disease.