Imaged Capillary Isoelectric Focusing (icIEF) Platform for Characterization of Charge Variants of Adeno-Associated Virus (AAV) Capsids and Impact on Their Transduction Efficiency.

Abstract

Objective: Adeno-Associated Virus (AAV) vectors are comprised of a capsid protein encapsulating a Deoxyribonucleic Acid (DNA) transgene that has been used in the gene therapy field showing potential to treat a range of genetic diseases. Methods in the field of gene therapy should be optimized or enhanced to deepen understanding of AAVs, specifically around charge heterogeneity of capsid species.

Methods: In this study, a versatile approach was presented for investigating the charge heterogeneity of Adeno-Associated Virus (AAV) capsid proteins of a variety of serotypes. This method employs Imaged Capillary Isoelectric Focusing (icIEF) coupled with native fluorescence imaging detection and has undergone exhaustive validation.

Results: Demonstrating its platform nature, this method analyzed seven different AAV serotypes from multiple manufacturing platforms. The distinctive profiles generated for each AAV serotype serve as valuable indicators for both identity confirmation and stability assessment. It was shown that thermal stress and pH conditions play a role in increasing acidic charged variants over time, affecting the charge heterogeneity of AAVs, which can be serotype-specific. Reverse phase LC-MS was used to identify and confirm the increased presence of Post-Translational Modifications (PTMs) that are linked to increasing acidic species variants relative to non-stressed AAVs.

Conclusion: These PTMs have biological consequences reflected in the diminished expression of the protein of interest in vitro. This cIEF method successfully analyzed a variety of AAV serotypes, and increasing trends of acidic variants led to reduced in vitro potency.