Spatial and longitudinal tracking of enhancer-AAV vectors that target transgene expression to injured mouse myocardium

Tissue regeneration enhancer elements (TREEs) direct expression of target genes in injured and regenerating tissues. Additionally, TREEs of zebrafish origin were shown to direct expression of transgenes in border zone regions after cardiac injury when packaged into recombinant adeno-associated viral (AAV) vectors and introduced into mice. Future implementation of TREEs into AAV-based vectors as research tools and potential gene therapy modalities requires a deeper understanding of expression dynamics and potential off-target effects. Here, we applied in vivo bioluminescent imaging to mice systemically injected with AAV vectors containing different combinations of capsids, enhancers, and timing of delivery. Longitudinal tracking of expression directed by different TREEs revealed distinct amplitudes and durations of reporter gene expression in the injured heart. The liver-de-targeted AAV capsid, AAV.cc84, could deliver TREEs either pre- or post-cardiac injury to negate off-target expression in the liver while maintaining transduction in the heart. By screening AAV9-based capsid libraries dosed systemically in mice post-cardiac injury, we discovered a new capsid variant, AAV.IR41, with enhanced transduction in cardiac injuries and with elevated transduction of TREE-driven transgenes versus conventional AAV9 vectors. In vivo bioluminescence imaging offers insights into how enhancers and engineered capsids can be implemented to modulate spatiotemporal transgene expression for targeted therapies.