Development of recombinant adeno-associated virus empty capsids as a reference standard for quality control of gene therapy products

INTRODUCTION. The development of adeno-associated virus (AAV)-based gene therapy products in Russia requires establishing reference standards, which are used throughout the pharmaceutical development cycle, and monitoring their stability during the storage period. A preparation of empty capsids of AAV serotype 9 (AAV9) is an appropriate material for a reference standard for empty AAV9 capsids (AAV9 RS).
AIM. This study aimed to develop analytical procedures to evaluate the AAV9 RS physicochemical quality parameters for its characterisation and to study its storage stability.
MATERIALS AND METHODS. Empty AAV9 capsids were produced in HEK293 suspension culture using serum-free medium and optimised transfection parameters. The next steps involved AAV9 clarification, concentration, and purification by affinity chromatography with AAVx resin and diafiltration. The analysis of AAV9 samples used electrophoresis, transmission electron microscopy, enzyme-linked immunosorbent assay (ELISA), size-exclusion chromatography, dynamic light scattering, spectrophotometry, and bio-layer interferometry. The concentration of capsids was measured by ELISA. Analytical procedures for physical titre determination were developed using an AAV9 standard with a known physical titre. The stability study of the AAV9 RS involved storage at –80 °C for 9 months.
RESULTS. Size-exclusion chromatography demonstrated the high purity of the established AAV9 RS, with at least 98% content of the viral capsid monomer. Dynamic light scattering, size-exclusion chromatography, and electron microscopy confirmed that the AAV9 RS was free of aggregates. The stability study showed that the AAV9 RS remained stable for 9 months. Dynamic light scattering and spectrophotometry were deemed optimal methods for routine quality analysis measuring the AAV9 RS physical titre, and bio-layer interferometry was recommended for regular analysis. The viral particle titres determined by these methods ranged from 1.48×10¹³ to 5.6×10¹³.
CONCLUSIONS. The AAV9 RS established in this study is suitable for quality control of AAV9-based gene therapy products.

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