AAV2-mediated gene delivery to monkey putamen: evaluation of an infusion device and delivery parameters

In this study, a modified infusion procedure and a novel infusion device designed for use in humans (Clinical Device B) were evaluated for delivery of recombinant adeno-associated virus (AAV2) to brain. The device is composed of 1.2 m of fused silica inserted through a 24.6-cm surgical steel cannula designed to fit a standard Leksell clinical stereotaxic frame and micro-infusion syringe pump. AAV2 encoding the human aromatic l-amino acid decarboxylase gene (AAV-hAADC-2) was infused into the putamen of 4 normal rhesus monkeys as a supportive study for a clinical trial in Parkinson's disease (PD) patients. Two infusion protocols were tested: a ramped procedure (slow stepwise increases in rate from 0.2 muL/min to 1 muL/min), thought to be essential for convection-enhanced delivery (CED), and a non-ramped infusion at a constant rate of 1 muL/min. The primary endpoints were safety evaluation of the infusion procedures and assessment of transgene expression at 5.5 weeks post-infusion. Clinical observations after vector infusions revealed no behavioral abnormalities during the study period. No differences in gross pathology with either the ramped or non-ramped infusion procedure were observed. Histopathology of the putamen was comparable with both procedures, and revealed only minimal localized inflammatory tissue reaction along the needle track in response to cannula placement and vector infusion. AADC immunohistochemistry demonstrated that vector was distributed throughout the putamen, with no significant difference in volume of immunostaining with either infusion procedure. Serum antibody levels against AAV2 vector exhibited a minor increase after infusion. These results validate the clinical utility of this new infusion device and non-ramped infusion conditions for intraputamenal gene therapy, and have the potential to impact a number of human diseases in which delivery of therapeutics to brain is indicated.