Classification and quantification of full vs. empty adeno-associated virus reference capsids via infrared attenuated total reflection spectroscopy

Gene therapy is based on the introduction of nucleic acids into cells using vectors to enable therapeutic benefits. Hereby, adeno-associated virus (AAV) vectors are preferred for in vivo gene delivery to target cells due to their stability, their ability to transduce a broad range of cell types, and the long-term expression of vector-encoded therapeutic genes in slowly or non-replicating cells. However, large-scale production and quality control during and after manufacturing represent significant challenges. Currently, methods for the analysis of AAVs are rather complex, laborious, expensive, and poorly standardized. Most analyses have to be performed off-line and are not suitable for adaptation toward real-time monitoring during the manufacturing process. Optical analytical methods such as infrared attenuated total reflection (IR-ATR) spectroscopy offer a promising alternative serving as a rapid, cost-efficient, and non-destructive analytical technique with potential on-line monitoring capabilities. The present study fundamentally demonstrates the feasibility of IR-ATR spectroscopy to classify and quantify reference standard materials of full vs. empty AAV type 2 virus capsids. Chemometric methods enable rapid and automated processing of the obtained spectra using specifically partial least squares regression (PLS-R) models. Excellent classification results were achieved, unambiguously identifying samples with predominantly empty capsids vs. those containing predominantly full capsids. The obtained results confirm that IR-ATR spectroscopy in combination with multivariate data evaluation strategies is indeed capable of providing information on the presence of genome-containing virus particles along with the corresponding genomic titer. This analytical strategy may potentially translate into a real-world on-line bioreactor process analytical monitoring technology (PAT) augmenting viral vector production scenarios.