Building a Toolbox of Compact Enhancers for Cell Type-Specific Gene Expression from AAVs in the Primate Brain

Abstract

AAV gene therapy has tremendous potential to transform the treatment of brain diseases. Tissue and cell class-selective transgene expression could improve the safety and efficacy of AAV-based therapeutics for brain circuit-related disorders compared to ubiquitous transgene expression. Unfortunately, there are few known compact genetic regulatory elements that limit transgene expression to specific cell populations. We undertook a systematic screen to find enhancer elements capable of targeting AAV expression to all major neocortical cell populations. Our strategy leverages multi-modal transcriptomic and epigenetic analyses of brain cells from mouse and human, followed by brain-wide in vivo testing in mouse and ex vivo testing in NHP and human. These studies generated a diverse collection of enhancer-AAV vectors that specifically target neocortical neuronal and glial cell populations across species. Furthermore, we show endogenous enhancers can be rationally optimized to increase expression levels for preclinical lead optimization studies. These studies yield a growing toolbox of enhancer elements for cell type-specific targeting in the human brain that will enable more precise gene therapy.

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