Prediction of adeno-associated virus neutralizing antibody activity for clinical application

Patients with neutralizing antibodies (Nabs) against adeno-associated virus (AAV) are usually excluded from the treatment with AAV vectors. To develop a standard assay for detecting Nab inhibition activity, we systematically studied current AAV Nab assays in vitro and in vivo. Several factors were found that influence the Nab titers based on the in vitro assay, including sera volume, AAV dose per cell, cell number and choice of transgenes. When the Nab titer assay was performed in vivo via intramuscular (IM) or systemic administration, a fourfold increase in sensitivity for measurement of Nab titers was observed compared with an identical in vitro test. To better mimic the clinical setting, after passively transferring human Nabs into mice, blood was collected before systemic injection of AAV vector and used for Nab titer analysis in vitro or via IM injection. The results showed that AAV delivered via IM injection had a similar inhibition pattern to systemic administration. These studies indicate critical parameters necessary for optimizing Nab sensitivity and that an in vivo Nab assay is more sensitive than an in vitro assay for inclusion/exclusion criteria. The variables identified by this study may explain some of the compounding clinical data seen to date with respect to efficiency of AAV transduction in various phase I clinical trials.