Selectivity for full AAV capsids in affinity capture with camelid ligands

The industry standard for downstream processing of adeno-associated viral vectors (AAV) is purification by affinity capture and anion exchange polishing (AEX). Affinity capture is an attractive method for capturing AAVs as it can remove process-related impurities and selectively enrich AAVs. Full capsids are then separated on AEX-resin from product related impurities based on net surface charge. Enrichment of full capsids remains a big challenge, as biophysical properties of full and empty capsids are very similar. We present a novel approach to enrich full capsids during capture chromatography using affinity resins. We examined the impact of additives (NaCl, MgCl₂, Na₂SO₄), NaCl concentrations (0 - 1000 mM), temperature and different affinity ligands (POROS™ CaptureSelect™ AAVX, AAV8, AAV9; CaptoAVB and AVIPure AAV8). We tested our approach for the serotypes AAV8 wild type (WT), AAV9 WT and an rAAV2 derivative and demonstrated 2.5-fold full capsid enrichment in a robotic screening. Analyzing an elution peak in fine increments yielded in multiple fractions approaching 100% full capsids. While several affinity resins demonstrated full capsid selectivity, we report that AAVX achieved the highest resolution. The selectivity was then linked to the affinity ligands specific binding mechanism towards an AAV capsid. This novel capture method offers a trade-off between full capsid yield and purity without the need for additional unit operations while using an already established process. With enriched loading material for the subsequent anion exchange step, the polished elution pool has a higher full-to-total ratio (FTR) compared to a process based on standard affinity capture conditions.