Strategies for Selection of AAV Vectors for Administration to Liver: Studies in Nonhuman Primates

Vectors based on adeno-associated virus (AAV) have demonstrated early promise in clinical trials, including published reports in patients with hemophilia B where therapeutic levels of factor IX have been achieved using AAV serotype 8, a member of the clade E family. With the success of these hemophilia B clinical trials utilizing AAV8, numerous alternative AAV capsid types that target the liver have begun to enter clinical testing across multiple disease indications. Specific properties of the various AAV capsids should be taken into account such as overall efficiency of hepatocyte gene transfer, differential gene transfer across the porto-central axis within the liver, durability of gene expression and the potential for vector re-administration. In this study, we evaluated these aspects of AAV-directed liver gene transfer in rhesus macaques across various capsid serotypes. Animals were injected with vectors expressing the secreted reporter gene rhesus bhCG and produced using different capsids [AAV5, AAV3b and two clade E vectors (AAVrh10 and AAV8)]. Nonhuman primates (NHPs) injected with clade E vectors expressing bhCG were administered 3 months later with AAV5 or AAV3b vectors expressing rhesus derived AFP. The key findings were: 1) in naïve animals, clade E vectors demonstrated the highest levels of periportal gene transfer with AAV5 vectors having the lowest levels of periportal gene transfer; 2) AAVrh10 and AAV5 elicited higher levels of neutralizing antibodies (NAb) than AAV8 and AAV3b; 3) significant animal-to-animal variation in transgene expression was noted with AAV3b in seronegative animals; and 4) within the short time frame tested NAb elicited from AAVrh10 appears to have inhibited subsequent in vivo transduction with the serologically distinct AAV3b serotype; prior exposure to AAV8 did not interfere with AAV3b transduction. These studies highlight the influence that capsids can play in efficiency and immunogenicity of AAV vectors for liver gene therapy.