Recombinant adeno-associated virus (rAAV) are promising vehicles for in vivo gene delivery for liver and retinal diseases. However, clinical trials have shown that high doses of vectors are needed to achieve efficacy causing inflammatory responses and raising safety concerns. There is a need to develop new generation of AAV-based vector with improved efficiency.

We designed a new strategy to chemically modify the tyrosine on the AAV capsid. We hypothesized that this chemical modification with molecules of interest would have benefits (increase therapeutic index, reduce proteasome degradation …). The bioconjugation of the AAV capsid is achieved using synthetic molecules composed of a ligand for selective targeting of the tissue of interest (GalNAc for liver and mannose (Man) for retina), and a reactive function specific to tyrosine.

After validation of the chemical coupling using analytical assays, we evaluated in vivo efficiency of these new vectors. Mice were injected either intravenously or subretinally for liver and retina targeting respectively. Unmodified AAV2 vectors were compared to chemically (GalNAc- or Man-) modified AAV2 vectors, both carrying an eGFP reporter gene. One month post injection, ratios between eGFP mRNA levels (RQ) and vector copy numbers (vg/dg) in liver showed that one copy of GalNAc-AAV2 vector expressed up to 90 times more eGFP mRNA than one copy of unmodified AAV2. In the retina, eye fundus imaging one month post-injection also showed higher levels of GFP expression with Man-AAV2 compared to AAV2.

All together, these encouraging results reveal the potential of chemically modified AAV to improve in vivo AAV-mediated gene therapy.