501. Radioiodinated Adeno-Associated Virus: A Promising New Approach for Monitoring Gene Therapy

Abstract

Late infantile neuronal ceroid lipofuscinosis (LINCL) is a form of Batten disease that is caused by mutations in the CLN2 gene. These defects cause widespread neurodegeneration resulting in death by the age of 10-12 years. One treatment for LINCL that has shown promise in animal and clinical studies is gene therapy using adeno-associated virus (AAV) as a vehicle to deliver the CLN2 gene throughout the brain. This is currently accomplished by direct infusion, but there is no way to measure the spatial distribution of administered vector. Iodine-124 labeling of the viral capsid may offer a means for non-invasive determination of spatial distribution using MicroPET imaging. The production of AAVrh.10CLN2 under GMP conditions met endotoxin, mycoplasma, sterility and transgene expression release criteria. Purified AAVrh.10CLN2 was concentrated to 1013 gene copies/ml. Labeling with Na124I was carried out at 2-5 0C under mild oxidizing conditions in pH 7.5 buffer. Following radiolabeling, the product mixture was purified using an anion exchange cartridge and centrifugal filtration. Purified I124-AAVrh.10CLN2 was formulated in a pH 7.4 PBS buffer. The sterile formulation was injected (2 ml at 2.5 μCi/ml) intraparenchymally to the striatum in the murine brain and imaged on a Siemens Inveon MicroPET scanner. Thirty minute PET scans were acquired for each mouse (n=3). For the control group, we performed the same procedure using free Na 124I alone (n=3). The radiolabeling efficiency of AAV was in the range of 12-14%. PET/CT imaging clearly demonstrated the spatial distribution of vector over a ten day period, with minimal 124I uptake in the unblocked thyroid. In contrast, free iodide was rapidly cleared from the brain within 2 days (Figure 1). In conclusion, adeno-associated virus was successfully labeled with 124I and its distribution in the mouse brain was observed. This radiolabeling approach has the potential for wide application in gene therapy trials. View Large Image | Download PowerPoint Slide