Prolonged susceptibility to antibody-mediated neutralization for adeno-associated vectors targeted to the liver

Adeno-associated virus (AAV) vectors demonstrate highly efficient gene transfer to hepatocytes in vivo. One of the remaining obstacles to the treatment of hemophilia B patients with AAV vectors is the sensitivity of these vectors to antibody-mediated neutralization following systemic delivery. Testing and implementation of strategies to circumvent pre-existing antibodies requires knowledge of the clearance kinetics of AAV from circulation. In this study, AAV clearance kinetics were established for serotypes 2 and 8 in cell culture and in mice. Administration of pooled neutralizing serum subsequent to administration of the vector was used to define the time period in which the vector is susceptible to antibody-mediated neutralization. These experiments defined the in vivo clearance rates for both AAV2 and AAV8 vectors to be between 2 and 4 hours. In mice, portal vein and tail vein administration of each vector was tested with similar results. Cell culture studies in W162 cells established that cellular attachment and internalization both contribute to the clearance kinetics of AAV vectors. These studies characterize the in vivo clearance rates of AAV vectors for the first time and guide the development of future strategies for the avoidance of antibody-mediated AAV vector neutralization.