Key Findings
Long binding times on affinity resins lead to serotype-specific yield losses and changes in capsid protein composition, though they improve the clearance of impurities. On CaptureSelect AAVX resin, washing for eight hours or longer reduced elution yields for AAV9 (from 9.89 x 10^12 to 7.08 x 10^12 capsids per milliliter, a 28% loss) and rAAV2 (from 7.59 x 10^12 to 4.96 x 10^12 capsids per milliliter, a 35% loss). In contrast, AAV8 yield remained constant at roughly 7.60 x 10^12 capsids per milliliter. Temperature is a critical factor for AAV9; a 24-hour wash at 10 degrees Celsius caused a 95% viral genome yield reduction, dropping the full-to-total ratio from 21.9% to below 2%.
Technical Details
Researchers from Roche Diagnostics GmbH and the Karlsruhe Institute of Technology tested three constructs (rAAV2, wild-type AAV8, and wild-type AAV9) carrying a 4.7 kilobase mGreenLantern transgene. The study utilized three VHH fragment-based ligands: POROS CaptureSelect AAVX, POROS CaptureSelect AAV9, and Capto AVB. To simulate long loading phases, material was bound to resin and washed for up to 24 hours at either room temperature or 10 degrees Celsius.
- Capsid Composition: Extended hold times increased the relative abundance of VP3. AAV9 showed the largest enrichment (approximately 1.9% above control after 24 hours at 10 degrees Celsius).
- Impurity Clearance: Host-cell protein log removal factors improved with longer washing, rising from 3.34 to 4.71 for AAV8, 3.34 to 4.87 for rAAV2, and 2.77 to 4.91 for AAV9.
Background & Context
Recombinant AAV vectors are captured from cell culture harvests using affinity chromatography. Because upstream titers are often low, manufacturers frequently employ long loading phases lasting several hours. This study sought to characterize the consequences of extended capsid-ligand contact, which had previously remained largely uncharacterized.
Significance & Outlook
The data indicates that capsids washing off over time are selectively enriched in VP1 and VP2. While the loss of yield is a drawback, the substantial improvement in impurity clearance offers a process benefit. The authors suggest that for AAV9, cooling alters the conformational flexibility of the DE loop, destabilizing binding.
Source: https://bioengineer.org/long-contact-times-on-aav-affinity-resins-reshape-yield-and-purity/
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