Structural characterization and epitope mapping of the AAVX affinity purification ligand.

The application of adeno-associated virus (AAV) vectors in human gene therapies requires reproducible and homogeneous preparations for clinical efficacy and safety. For the AAV production process, often scalable affinity chromatography columns are utilized, such as the POROS CaptureSelect AAVX affinity resin, during downstream processing to ensure highly purified AAV vectors. The AAVX ligand is based on a camelid single-domain antibody capturing a wide range of recombinant AAV capsids. Described here is the identification of the AAV8 capsid epitope to AAVX at 2.3 Å resolution using cryo-electron microscopy. The ligand binds near the 5-fold axis of the capsid in a similar manner to the previously characterized AVB affinity ligand but does not conform to the capsid's icosahedral symmetry. The cross-reactivity of AAVX to other AAV capsids is achieved by primarily interacting with the peptide backbone of the AAV capsid's structurally conserved DE and HI loops. These observations will guide AAV capsid engineering efforts to retain the ability of future recombinant capsid designs to be purified using antibody-based affinity ligands.