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Milking Animals for Drugs

by G S Mudur
A decade after biologists manipulated genes to create a "giant* mouse tn a laboratory, scientists are now attempting to turn farm animal* Into living factories for life-saving drugs.
Drawing upon an increasing knowledge about genetic mechanisms In mammals. re*car cher* backed by biotechnology companies, have launched programme* aimed at creating transgenic animal* that will synthesize chemical* used tn medicine.
And the results over the post year have been encourag ing. Research groups In the United States and the United Kingdom have reported the successful production of transgenic goats and sheep that produce pharmaceutically useful proteins In their milk
These gene transfer studies are part of the quest to create transgenic animals by Inserting foreign genes Into their exist Ing genomes to Invest them with unique traits that are commercially valuable
One alm of genetic engineer* storking on livestock mammal* has been to enhance the production of various animal product* like meat. milk, leather, or wool. The other alm ha* been to Introduce gene* into farm animals to make transgenic animals that will synthesize products that are not normally produced by them
Ten years ago. sciential* first demonstrated the potential of gene transfer tn mammals by using the growth hormone gene to create a transgenic mouse that grew to nearly twice the size of normal rate*. Experiments have since then been carried out on larger farm mammals like goat, sheep, and cattle. Although gene transfer has sown to be possible, scienlists say they don't get positive results everytime.
Studies aimed at turning animals Into biosynthesisers of various proteins have, how ever, shown success over the past few years. In 1990. scien lists reported the production of a protein called human alpha-1 ■antitrypsin In transgenic mice.
Now reports from Tufts University In the US and a group In Scotland in the UK have boosted prospects of producing large quantities of rncdically-useful products in the milk of transgenic livestock.
The Tufts group has produced the world's first transgenic goats that yield a chemical called human tissue plasminogen activator tn their milk. The tissue plasminogen activator Is a chemical that can dissolve deadly blood clots and ,1s given to heart attack patients.
A dose of the drug from the conventional route costs up to 2000 dollars, says Dr Mushtaq A Memon. Pakistan bom team member In the Tufts group. The cost might be brought down to between 50 and 200 dollars through the transgenic
animal*, he said at a recent International conference on goats held tn New Delhi
Dr. Me mon *aid the con
centrattons of the tissue plasminogen activator In the milk of transgenic goats suggest that economical viability Is within reach.
Reporting their work in the Journal Biotechnology, the Tufts University group said the atm of the programme was to produce a commercial prototype for the large-scale manufacture of high market-volume proteins in the transgenic mammary gland system using the dairy goat as a production animal
A transgenic mammary gland production system would have the potential advantages of not requiring an intensive capital expenditure In setting up a a manufacturing facility, and a providing a highly cost
cffleicnt system due to high expression levels and low ex pendable production costa.' the ten-member team said In
Its report In the journal.
Working on sheep, the Scottish mearch group at Edinburgh have create four transgenic female sheep that yield milk containing high levels of the protein human alpha-1-antitrypsin. This protein is usually present tn plasma, but a congenital disorder can lead to a deficiency In Its concentration in the body. The sufferers are at risk of developing life-threatening lung prob-Reporting their work tn the same issue of Biotechnology, the Edinburgh scientists said an analysis of expression of human alpha-1 -antitrypsin tn milk of three of the four female transgenic sheep has shown that all express the
chemical at levels greater than one gram per litre. In one case. the initial level* exceeded 60 grams per liter, bul stabilised at 35 grams per litre a* lactation progressed
The scientists said the protein purified from the milk of the transgenic sheep had biological activity Indistinguishable from human plasma-derived material.
The scien tlsta said this production route 1* "appealing" because of high production capabilities of the mammary gland, the relatively low operating costs, and the "potentially unlimited expansion of producer animals through established and emerging methods of animal husbandry.'
(Mr. G S Mudur Is a PTI Science Correspondent based In New Delhi)
— PT! Science Service