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Gene Cloning and DNA Analysis: An Introduction, Sixth Edition ...

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254<br />

Figure 14.8<br />

Part III The Applications of <strong>Gene</strong> <strong>Cloning</strong> <strong>and</strong> <strong>DNA</strong> <strong><strong>An</strong>alysis</strong> in Biotechnology<br />

The rationale behind the potential use<br />

of a recombinant vaccinia virus.<br />

Vaccinia<br />

promoter<br />

Recombinant<br />

vaccinia genome<br />

Hepatitis B major<br />

surface antigen gene<br />

Inject recombinant vaccinia<br />

particles into the bloodstream<br />

Hepatitis B<br />

protein<br />

Vaccinia<br />

virus<br />

Immune system synthesizes<br />

antibodies against both<br />

vaccinia <strong>and</strong> hepatitis B<br />

<strong>An</strong>ti-hepatitis B<br />

<strong>An</strong>ti-vaccinia<br />

against the much more dangerous smallpox virus. The term “vaccine” comes from<br />

vaccinia; its use resulted in the worldwide eradication of smallpox in 1980.<br />

A more recent idea is that recombinant vaccinia viruses could be used as live<br />

vaccines against other diseases. If a gene coding for a virus coat protein, for example<br />

HBsAg, is ligated into the vaccinia genome under control of a vaccinia promoter, then<br />

the gene will be expressed (Figure 14.8). After injection into the bloodstream, replication<br />

of the recombinant virus results not only in new vaccinia particles, but also in<br />

significant quantities of the major surface antigen. Immunity against both smallpox <strong>and</strong><br />

hepatitis B would result.<br />

This remarkable technique has considerable potential. Recombinant vaccinia viruses<br />

expressing a number of foreign genes have been constructed <strong>and</strong> shown to confer immunity<br />

against the relevant diseases in experimental animals (Table 14.2). The possibility<br />

of broad-spectrum vaccines is raised by the demonstration that a single recombinant<br />

vaccinia, expressing the genes for influenza virus hemagglutinin, HBsAg, <strong>and</strong> herpes<br />

simplex virus glycoprotein, confers immunity against each disease in monkeys. Studies<br />

of vaccinia viruses expressing the rabies glycoprotein have shown that deletion of the<br />

vaccinia gene for the enzyme thymidine kinase prevents the virus from replicating. This<br />

avoids the possibility that animals treated with the live vaccine will develop any form<br />

of cowpox, the disease caused by normal vaccinia. This particular live virus vaccine is<br />

now being used in rabies control in Europe <strong>and</strong> North America.

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