In the primate CNS, the proposed studies aim to test and compare possible vectors for gene therapy derived from three groups of viruses: recombinant herpes simplex virus (HSV), adenovirus (Ad) and adenoassociated virus (AAV). Although these vectors have been studied in the rodent CNS, few studies have addressed the issue of safety, optimal delivery, vector expression in specific cell populations, persistence of transgene expression, and function of putative therapeutic genes in a systematic fashion in the primate CNS. HSV, Ad and AAV vectors have been shown to be capable of packaging and delivering gene sequences to the rodent CNS, and advantages, disadvantages and selectivity inherent to each have been identified. Viral stocks harboring the cellular marker gene, nuclear localized lacZ (lacZnl) or human glial cell line derived neurotrophic factor (GDNF), will be produced and quality controlled. Initial studies will address methods of delivery, transduction efficiency, spread from the site of injection including retrograde transport, cellular tropism, vector persistence, stability and level of transgene expression, neuropathology and host cellular responses. Systemic challenge with related viruses also will be studied to address safety and immune responses. One vector will be selected to deliver GDNF or an inactive mutant GDNF to assess function. GDNF has well documented morphological, biochemical and functional effects on dopamine neurons, which are associated with many higher brain functions and with motor control. We will assess cognitive and motor effects of vector-delivered GDNF in two brain areas, the prefrontal cortex and the caudate nucleus, after MPTP-induced dopamine depletions in monkeys. Measures of efficacy will include behavioral parameters, molecular assays of transgene expression using ELISA for protein, RT-PCR for mRNA and PCR for vector DNA, biochemical assays of DA and its metabolites, neuroanatomical and morphometric analyses, neuropathology, and autoradiography. These studies aim to provide fundamental information on viral vectors in the primate CNS through an integrated, comparative experimental design. The choice of cognitive and motor effects of dopamine depletion and the GDNF gene to test functional outcomes of gene therapy in the primate brain are based on the well characterized nature of these effects in primates and the reported effects of GDNF in rodents and primates, including GDNF gene therapy in rodent dopamine depletion models. However, the major aim of these studies is to contribute to the development of effective and safe gene delivery systems for future application to the human CNS for a wide range of conditions.
