Ballistic DNA Injection

Ballistic DNA injection, also known as particle bombardment, microprojectile gene transfer, or the gene-gun, was first developed for gene transfer into plants. Since its initial introduction, it has been modified to transfer genes into mammalian cells both in vitro and in vivo. Below is a diagram of the nuts and bolts of the gene-gun. (Wolff, JA. Gene Therapeutics, 1994. p. 195.).

Plasmid DNA encoding the gene of interest is coated onto microbeads, and these particles are then accelerated by motive force to penetrate cell membranes. Specifically, the plasmid DNA is precipitated onto 1-3 micron sized gold or tungsten particles. These particles are then placed onto a carrier sheet which is inserted above a discharge chamber. At discharge, the carrier sheet accelerates toward a retaining screen which stops the carrier sheet, yet allows the particles to continue toward the target surface. The force can be generated by a variety of means; the most common include high-voltage electronic discharge, spark discharge, or helium pressure discharge.

Applications. Ballistic DNA injection has been successfully used to transfer genes to a wide variety of cell lines and also to the epidermis, muscle and liver. In vivo applications have predominantly focused on the liver, skin, muscle or other organs which can easily be exposed surgically. Ballistic DNA injection also offers the capacity to deliver precise DNA dosages. Unfortunately, genes delivered by this method are expressed transiently and there is considerable cell damage occurring at the center of the discharge site.

DNA-based immunization. Currently the most exciting application of intramuscular and ballistic plasmid DNA injection is in DNA-based immunization protocols. DNA-based vaccinations are being developed to prevent infectious diseases and cancer. Cells which express a foreign protein and subsequently present that protein on their surface are more likely to result in a cell-mediated immune response. Such a response may be more important in fighting lateral viral infections such as those caused by HIV, HSV, CMV, or RSV. Techniques which inject a foreign antigen usually only yield an antibody-mediated immunity. Both the gene gun and direct intramuscular plasmid DNA injection are being used in protocols to immunize against HIV, hepatitis B and C, HSV, influenza, papilloma, tuberculosis, RSV, CMV, Lyme disease, Helicobacter pylori, malaria and Mycoplasma pulmonis. Because of their simplicity, intramuscular or ballistic plasmid DNA injection techniques may offer advantages over viral vectors for development of DNA-based immunizations.

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