Gene Delivery Using Physical Methods - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 97

Figure 3.2 Particle
bombardment for DNA
delivery to cells .

Firing piston

Macroprojectile

Microparticles

Stopping plate

Target tissue

required for efficient gene transfer to the target organ, as gene guns deliver macromol-
ecules to a narrow region at a very small depth when delivered from the surface [146] .
As well, target tissue damage also occurred due to solid particle bombardment with
high speed.
Pure gold particles of appropriate size are most commonly used in gene gun deliv-
ery. The gold particles are then coated with pure macromolecules, for example, DNA,
to form the complex. After that the gold-DNA complex so formed is layered uni-
formly on the internal face of the Teflon tubing. Generally, the tubing size is 3.17 mm
outer diameter and 2.32 mm inner diameter, which will offer the desired surface area
for uniform coating. The coated Teflon tubing is then cut into cartridges of required
size (generally 12.5 mm). The cartridges are loaded into the gene gun and the coated
particles are fired by a high-pressure helium blast or electric discharge into target
cells [147,172] . The particles should load into the gene gun immediately before use
or bombardment, and the loaded particles should be used within 60 min of loading
[157] . Gene gun delivery must be optimized every time, with consideration given to
such factors as animal species used, target tissue thickness, bombardment force, and
size of gold carriers for effective penetration into target tissues [147] .
Because the gene gun is fast, simple, flexible, and provides easy physical accessi-
bility, it is widely applicable for introducing DNA in various biological systems like
skin and muscles. The gene gun is also helpful for recognizing promoter genes, like
cornea-specific keratin 12 promoter gene, and for understanding its mechanism of
expression in the cells [173,174] . In addition, it is also useful in judging the impact
of opioid growth factor in corneal epithelium [175] . This technique is also applicable
for determining the duration of graft survival by CT�A-4 or IL-4 encoding plasmids
[176,177] . Genetic vaccination, a significant application of gene gun delivery, con-
sists in delivering DNA to the target tissues to bring out immune response. Currently,
dermal DNA vaccination is most useful because of dense network of �angerhans