Combined biolistic and cell penetrating delivery for an effective and scalable intradermal DNA vaccine 

Physical-based gene delivery via biolistic methods involves precipitation of nucleic acids onto microparticles and direct transfection through cell membrane by high velocity acceleration. The glycosaminoglycan (GAG)-binding enhanced transduction (GET) system exploits novel fusion peptides consisting of cell-binding, nucleic acid-condensing, and cell-penetrating domains, which enable enhanced transfection across multiple cell types. In this study, we combined chemical (GET) and physical (gene gun) DNA delivery systems and hypothesized the combination would generate enhanced distribution and effective uptake in cells.

Initial transfection studies explored formulations to determine the optimal GET-gold-DNA ratio, followed by incorporation into fireable gene gun bullets. Subsequent experiments explored physicochemical characterization, optimisation of bullets and transfection experiments in vitro (monolayers, engineered tissue) and in vivo. 

Transfection experiments in cell monolayers and engineered tissue demonstrated these formulations transfected efficiently, including in DC2.4 dendritic cells. We incorporated these formulations into a biolistic format for gene gun by forming fireable dry bullets obtained via lyophilization. Extracted GET bullet contents retained their ability to mediate transfection significantly higher than standard bullet contents. Fired GET bullets in cells, collagen gels and mice showed increased reporter gene transfection compared to untreated controls, whilst maintaining cell viability. Lastly, a SARS-CoV-2 DNA vaccine with spike protein-receptor binding domain was delivered by gene gun using GET bullets. Specific T cell and antibody responses comparable to the conventional system were generated. 

The non-physical and physical combination of GET-gold-DNA carriers using gene gun showed potential as an alternative DNA delivery method that is scalable for mass deployed vaccination and intradermal gene delivery.