Gene transfer to subdermal tissues via a new gene gun design

Although particle-mediated gene transfer technology (gene gun) has been applied for gene transfer to external tissues, the application of this technology to other tissues has met with limited success. Here we report the development of a new design of a gene gun that uses helium discharge to propel DNA-coated gold beads that are suspended in liquid. Higher discharge pressures allow for the delivery of DNA to deeper tissues. Using the new gene gun to deliver a luciferase expression plasmid resulted in higher levels of gene expression in the skin than observed with conventional guns, as well as in subdermal tissues, including subcutaneous tumors. Even when using as little as 125 ng of DNA, gene expression in skin and muscle reached its peak level at 24 hr postbombardment and remained for at least 1 week. The use of a LacZ expression plasmid showed that gene expression was distributed throughout the skin with no observable pathology. The new gene gun was used to deliver a model tumor rejection antigen (a modified human papilloma virus [HPV] E7 gene) to mice. All of the treated animals developed protective immunity against HPV-positive tumors. These results demonstrate that our new design can be used in standard gene gun applications and extends the reach of gene gun technology to tissues that were previously unavailable.