A facile chemical strategy to synthesize precise AAV-protein conjugates for targeted gene delivery

The efficacy of current gene therapy approaches using adeno associated virus (AAV) vectors is limited by the poor control over their tissue tropism. Untargeted AAV vectors require high doses to achieve therapeutic efficacy, which is associated with toxic off-target impacts and increased therapeutic costs. The ability to reprogram existing AAV vectors to selectively transduce target tissues is essential to develop next-generation human gene therapies that are safer, more efficacious, and less expensive. Using selective and high-affinity antibodies and antibody-like proteins to retarget existing AAV vectors to bind novel cell-surface receptors offers an attractive and modular approach to reprogram their tropism. However, attaching these proteins onto the complex and delicate AAV capsids remains challenging. Here, we report a versatile chemical strategy to covalently attach recombinant proteins onto the capsid of AAV, using a combination of genetic code expansion and bioorthogonal conjugation chemistry. This method is efficient, and allows precise control over the site and stoichiometry of protein attachment onto the AAV capsid, enabling systematic optimization of the resulting conjugate. Using this approach, we generated conjugates of AAV2 with an anti-HER2 nanobody and a full-length anti-HER2 IgG, which show highly efficient and selective gene delivery into HER2+ cancer cells. Remarkably, the optimized AAV2-nanobody conjugate facilitated efficient transduction of HER2+ tumor xenograft in mice with little off-target gene expression, including in the liver. Programmable synthesis of AAV-protein conjugates using this method offers a promising new strategy to rationally engineer next-generation gene therapy vectors.