Gene therapy using recombinant adeno-associated virus (rAAV) is a common gene delivery tool for genetic diseases that is already used in clinic. rAAV vectors are non-pathogenic in humans, have no integrase activity and mediate long-term gene expression. It is known that different serotypes exhibit varying tropism, which is due to the various interaction with different receptors on the cell surface. AAV9 is known to successfully transduce cells of the CNS, such as neurons, and is also known to pass the blood-brain-barrier, making it a promising candidate for gene therapy in neurodegenerative disorders. Previous data from our lab showed widespread and high‐level retinal transduction after intravitreal injection for the newly engineered vectors AAV2.NN and AAV2.GL, which have a 7-mer peptide insertion.

In this work, we tested these novel vectors with the AAV9 capsid encoding eGFP under the control of different promoters in the mouse brain. In-vitro studies revealed that all capsid variants using the CMV promoter led to eGFP expression in neurons and astrocytes. When using the neuron-specific hSyn promoter eGFP expression was only observed in neurons. Based on these results, we injected the viral capsids into the thalami of WT mice by stereotaxic surgery. After three weeks, eGFP expression was quantified in different brain regions by qRT-PCR and Western Blot. All capsid variants were most prominent in the thalamus, but could also be detected in efferent brain regions. Overall, this characterisation of AAV9.NN and AAV9.GL elucidates that these vectors are promising candidates for use in gene therapy targeting neurodegenerative diseases.