# Mechanistic Insights into AAV Capsid–Stationary Phase Interactions Governing Native Stability and Chromatographic Separation Using AAV8 as a Model System

## TL;DR

This paper explores how adeno-associated virus (AAV) capsids interact with chromatography systems, offering new methods to separate different capsid types while preserving their stability.

## Contribution

The study introduces a novel weak anion exchange (AEX) separation strategy and a 2D buffer exchange setup to improve AAV8 capsid separation and stability.

## Key findings

- Operational regimes were identified that balance AAV8 capsid stability with effective chromatographic separation.
- A 2D in-line buffer exchange configuration enables separation of high-salt matrices without off-line desalting.

## Abstract

Background/Objectives: Adeno-associated viruses (AAVs) are widely used gene therapy vectors; yet their physicochemical stability and chromatographic behavior are highly sensitive to the solution conditions they are in. Effective separation of full (F), empty (E), and partially filled (P) capsids—most commonly achieved by anion exchange (AEX) chromatography—is essential for standard analytical characterization, process development, and product safety. However, conventional AEX methods rely on low-conductivity alkaline mobile phases with low salt, which promote capsid binding and therefore higher resolution, at the expense of structural stability. Conversely, formulations such as near-neutral buffers might preserve capsid integrity but often impair AEX retention and separation resolution. Methods: Here, we extend a mechanistic investigation using AAV8 capsids as a model system, focusing on detailed capsid interactions with strong AEX, and present novel AAV8 separation strategies on a weak AEX stationary phase. Results: By systematically varying buffer pH and ionic strength, we identify operational regimes that balance capsid stability with chromatographic separation efficiency. In parallel, we introduce an integrated two-dimensional (2D) in-line buffer exchange configuration that decouples AEX performance from sample formulation, enabling robust separation of stability-optimized, high-salt matrices without off-line desalting. Conclusions: By elucidating the roles of capsid charge modulation, ligand physicochemical properties, and local microenvironmental buffering, this study establishes practical design principles for stability-preserving chromatography. It lays a foundation for more reliable analytical and future preparative AAV workflows.