and produce trace compounds so that they might be tested 
clinically. It is also the only way to obtain species specific 
compounds such as peptide hormones. Human hormones such as 
insulin, which in the pas*’ could only be obtained with great 
difficulty, can now be produced on a commercial scale. 
Another potential application which holds exciting 
promise is the creation of synthetic vaccines. Most vaccines are 
produced from, attenuated viruses or bacteria, and though they are 
generally safe, are not without side effects due to the presence 
of multiple antigens. Many of these infectious agents have a 
single protein on their surface which can confer immunity upon 
the host. The gene for this protein can be cloned and a "single 
antigen" vaccine can be prepared which offers equal protection 
but reduced side effects. 
This last advance has been made in the veterinary fields 
as a vaccine against foot and mouth disease was produced using 
rDNA techniques. A further advantage of this technique is that 
only the genetic material of the virus needs to be screened. 
Dangerous viruses can be worked on in small quantities under 
carefully controlled conditions. This process leads to the 
cloning of the viral antigen gene away from the remainder of 
the viral genetic material. The antigen can be produced on a 
large scale from a completely safe organism, and the product 
antigen is completely free of viral genetic material and, 
therefore, is safe to use. 
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