Limitation of Assay Sensitivity Revealed by the Improvement of Cell-Based Assay Against Various Adeno-Associated Virus Serotypes

Gene therapy using adeno-associated virus (AAV) vectors is currently expanding to broad clinical applications. As the presence of a neutralizing antibody (NAb) against AAV capsids significantly restrains their efficacy, an accurate evaluation of NAb status is crucial for selecting appropriate candidates for gene therapy. Notably, cell-based NAb assays may not be sufficiently sensitive for detecting low-titer NAb, and few assays can evaluate multiple AAV serotypes using a commonly available cell. In this study, we developed a sensitive NAb assay against various AAV serotypes using commonly available HEK293 and Huh-7 cells. We found that adding glucose efficiently enhanced transgene expression across various AAV serotypes without causing cell damage. In addition, by combining a highly sensitive reporter gene, NanoLuc, the necessary dose of AAV vector was significantly reduced. The reduction of AAV dose resulted in the increased sensitivity of NAb detection as low as 100 vector genomes/cell. At the lower vector doses, sensitivity improvement was not observed regardless of serotypes, suggesting the limit of assay sensitivity of the cell-based NAb assay. These findings provide a highly sensitive methodology for assessing NAb titers and offer insights into conditions to attain maximal sensitivity in the cell-based NAb assay.