Gene Delivery Using Physical Methods - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 96

3.5 Particle Bombardment Using Gene Gun
The particle bombardment system (i.e., the gene gun), established in late 1987
[143,144] , is one of the best methods for physical delivery of the gene to target tis-
sues, and it works on the principle of high pressure. In addition, the gene gun is a
fast, simple, and flexible method for gene delivery in small amounts and confers
desirable transcription results with a poor toxicity profile [145,146] . The gene gun
was first used in plants for gene transformation [143,144] and later was applied for
in vivo transformation experiments in mammalian species as well as for in vivo and
in vitro gene relocation [145,147] .
Efficient gene gun delivery of macromolecules, like DNA, RNA, proteins, or
peptides, to the target cells involves coating macromolecules onto microcarrier par-
ticles such as gold and tungsten, which are then introduced into the target cells with
a high-velocity stream, using an electric discharge or a pressurized helium pulse
[148,149] . The coated microcarrier particles can be transported into numerous cells
in a single delivery, as they easily pierce the cell cytoplasm of the target cells. A gene
gun carries multiple genes by coating them onto the microcarriers, inert, nontoxic,
and subcellular-sized (0.5-5 M) spheres with enough density to enter the target tis-
sues. Based on a similar idea, two principal helium-driven gene gun devices were
developed and marketed, the Accell gene gun by Agracetus, Inc. [149-152] and the
Helios gene gun by Bio-Rad �aboratories. Factors such as amount of macromole-
cules; ratio, dimension, and material of carrier particles; method of covering carrier
particles with macromolecules; bombardment force; kind of gene gun; circulation of
carrier particles at target site; kind of targeted cells and tissues [152] ; and density of
carrier particles and macromolecules [153] markedly affect the competence of the
gene transfer by the particle bombardment system. Thus, the control of these factors
is most important for efficient gene delivery [152] .
The gene gun system has a number of advantages in relation to the more common
needle injection system. It facilitates direct transfer of the gene in various tissues,
overcoming barriers such as the cell wall, and this gene transfer is not affected by the
kinds of cell, receptors, and molecules at the cell surface. Furthermore, degradation
of the gene is reduced, as they are forced to enter the cytoplasm of target cells and
bypass the enzymes in endosomes and lysosomes, and nuclear hurdles. In addition,
the gene gun allows delivery of several genes simultaneously to the same target tis-
sues, which enables studying the interaction among the gene products. Because the
gene gun delivers a small amount of DNA efficiently, it is a promising approach for
DNA vaccination. Various studies reported in the literature reveal that DNA deliv-
ered in very small amounts by a gene gun elevates immune responses in animals like
mice [150,154-157] , rabbits [156-158] , nonhuman primates [159-161] , and guinea
pigs [162] . Thus, particle bombardment is widely applicable for in vivo and in vitro
gene delivery to mammalian cells [145,163,164] for gene therapy [165-169] . Particle
bombardment is shown in Figure 3.2 .
Besides all these advantages, the gene gun system has some disadvantages: it
requires costly devices and reagents such as a gene gun and gold particles. In addition,
gene guns elicit high humoral immune responses [161,170,171] . Minimal surgery is