Adeno-associated virus (AAV) is the leading vector in emerging treatments of inherited diseases. Higher transduction efficiencies and cellular specificity are required for broader clinical application, motivating investigations of virus-host molecular interactions during cell entry. High-throughput methods are identifying host proteins more comprehensively, with subsequent molecular studies revealing unanticipated complexity and serotype specificity. Cryogenic electron microscopy (cryo-EM) provides a path towards structural details of these sometimes heterogeneous virus-host complexes, and is poised to illuminate more fully the steps in entry. Here presented, is progress in understanding the distinct steps of glycan attachment, and receptor-mediated entry/trafficking. Comparison with structures of antibody complexes provides new insights on immune neutralization with implications for the design of improved gene therapy vectors.Virus-host interactions: a foundation for improved gene therapy vectors AAV (see Glossary) is a small, single-stranded DNA virus of the family Parvoviridae whose three viral capsid proteins (VP1, VP2, and VP3) comprise a non-enveloped shell of icosahedral symmetry [1]. Since wild-type (wt) AAVs possess wide tissue tropism and low pathogenicity (as replication-deficient dependoparvoviruses), recombinantly produced AAV vectors (rAAVs) are now pre-eminent vehicles for therapeutic gene delivery, with clinical payloads replacing the ~4.7 kb native genome. The past 3 years have seen FDA approval of two AAV therapeutics, LUXTURNA™ (rAAV2 for RPE65-related retinal dystrophy) and ZOLGENSMA® (rAAV9 for spinal muscular atrophy). Despite successes, target-specific vector optimization and higher transduction efficiency remain crucial for wider clinical application [2]. We find that each AAV capsid variant discovered, engineered, or derived, can reveal, through its unique sequence-encoded phenotype, clues to improving targeting, transduction, and immune evasion. AAV capsid interactions with host cell entry factors, in particular, have been a focus of recent research, with exciting results.Advances in high-throughput screening and structure determination are being employed by the AAV community to identify and visualize AAV-host molecule interactions critical to cell transduction. Increasingly high-resolution cryo-EM structures help to elucidate the molecular determinants of receptor, antibody, and cell-surface glycan interactions. Here we summarize the current understanding of AAV entry factors and their identification, and the potential for high-resolution structures to inform future vector design. A recent review by Riyad and Weber [3] presents an excellent perspective on the cellular processes of AAV entry and trafficking, while, here, emphasis is on the biophysical chemistry and detailed characterization of molecular interactions.
AAV cell entry: sequence of eventsPromiscuous attachment of AAVs to glycans on the cell surface is thought to increase the likelihood of internalization through increased en...