Multi-step engineered adeno-associated virus enables whole-brain mRNA delivery

Abstract Adeno-associated viruses (AAVs) are commonly used vectors for DNA delivery in gene therapy. Here we developed a system that enables the AAV shell to package mRNAs by multi-step introduction of RNA-packaging components and modification of AAV Rep proteins. The resultant mRNA-carrying AAVs (RAAVs) retained most properties of conventional AAVs, including capsid composition, virus morphology, and tissue tropism. These RAAVs could mediate mRNA transfer into target cells and tissues, leading to transient expression of the functional protein. Importantly, intravenously injected RAAVs efficiently crossed the blood-brain barrier (BBB) and infected the whole mouse brain. Thus, the DNA viral vector could be modified for RNA delivery, and our RAAV represents the first highly efficient BBB-crossing mRNA delivery system that could be used for therapeutic purposes via whole-brain infection.