Introduction Vascular gene transfer has been hampered by an efficient vector to deliver the gene of interest to endothelial (ECs) and smooth muscle cells (SMCs). Conventional approaches often require systemic administration of the viral vector, which lowers the concentration and hence transduction efficiency in target areas, such as particular regions within large vessels like aorta. Therefore, a more precise approach for vector delivery is required for clinical translation.

Purpose: Our study aims to develop a novel strategy to efficiently deliver vascular-specific adeno associated virus (AAV) vectors to the abdominal aorta by application of alginate hydrogels.

Methods: To transduce specifically endothelial and smooth muscle cells, we used AAV9 vectors with modified capsid (AAV9SLRSPPS) encoding enhanced green fluorescent protein (EGFP). AAVs were embeded into a solution containing 2% sodium alginate to a concentration of 10¹² viral genomes/mL. Calcium carbonate was used as a polymerizing reagent, leading to formation of gels with thickness of 2 mm. Biomaterials were next implanted infrarenally around the abdominal aorta. Two weeks after surgery, EGFP expression was proven in tissue sections by immunohistochemistry and quantitative PCR (qPCR). The levels of pro-inflammatory cytokines TNF-a and IL-6 were quantified using enzyme enzyme-linked immunosorbent assay (ELISA). Immunohistochemistry against Mac2 and CD4 was conducted to detect the presence of inflammatory cells after implantation. To determine transduction efficiency in human samples, aortic tissue isolated from patients subjected to cardiac surgery were embeded into AAV-containing hydrogel and successful transduction was determined by immunostaining, Western blot and qPCR after 3 days of culture.

Results: Infrarenal implantation of AAV9SLRSPPS-containing hydrogels led to an almost complete transduction of both aortic SMCs and ECs in mice in the area of the hydrogel. Notably, ELISA experiments revealed no significant changes in IL-6 and TNF-a concentrations in plasma. In addition, we could not detect the presence of pro-inflammatory macrophages and T cells in treated aortae. Importantly, our approach led to high transduction rates of human aortae ex vivo.

Conclusion: In summary, we describe for the first time a novel gene delivery approach to aortic tissue with an alginate hydrogel harbouring vascular-targeted AAV which will enable further studies with therapeutic gene overexpression in specific vascular diseases.