(421a) Food, Pharmaceutical and Bioengineering Division Award in Chemical Engineering: Directed Evolution of New Viruses for Therapeutic Gene Delivery

Gene therapy – the delivery of genetic material to a patient for therapeutic benefit – has experienced an increasing number of successful human clinical trials, particularly ones using delivery vehicles or vectors based on adeno-associated viruses (AAV). These include trials for hemophilia B, Leber’s congenital amaurosis (LCA2), spinal muscular atrophy, and lipoprotein lipase deficiency (LPLD). As a result, AAV is the basis for a clinically approved gene therapy product to treat LPLD in the European Union, and an AAV-based gene therapy will likely receive FDA approval this year for LCA2. AAV is thus capable of safe and therapeutic gene delivery to some cell targets. However, vectors in general face a number of challenges that limit their efficacy, not surprisingly since the parent viruses upon which these vectors are based were not evolved by nature for our convenience to use as human therapeutics. For most applications, there is unfortunately insufficient mechanistic knowledge of underlying virus structure-function relationships to empower rational design to improve such vectors.

As an alternative approach, we were the first to develop and have since been implementing directed evolution – involving the iterative genetic diversification of a viral genome and functional selection for desired properties – to address a number of problems with AAV. Genetic diversification has included the random diversification of peptide sequences at defined locations in the capsid, random point mutagenesis of the cap gene, and recombination of cap genes from a number of parental serotypes to create random chimeras. Using a range of in vitro and in vivo strategies to select the resulting large (~108) libraries for improved function, we have evolved AAVs for evasion of neutralizing antibodies, enhanced biodistribution and spread within a target tissue, greatly improved delivery efficiency, and targeted delivery in vitro and in vivo, thereby substantially improving the vectors’ capacity to meet human therapeutic needs.