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Yeast-made vaccine nearing market.

While much recombinant DNA research has used bacteria as the "factory," the first human vaccine made by genetic engineering is expected to be a product of yeast. Initial human trials of a hepatitis B vaccine made by yeast have been encouraging, researchers told SCIENCE NEWS this week, and a spokesperson for the manufacturer says Food and Drug Administration approval is expected in 1986.

Saul Krugman and Morton Davidson of New York University have used the new yeast vaccine on about 250 people. "It's going extremely well," says Krugman. "ninety-six to 98 percent of the recipients have had an antibody response, and the only occasional complaint is local soreness."

Pearl Toy of San Francisco General Hospital is studying the yeast-made vaccine in infants born to hepatitis B carriers. The vaccine has worked well in the first 30 infants, but it is still too early to tell if it is effective, she says.

After University of California at San Francisco researchers were able to get yeast saddled with hepatitis B virus DNA to synthesize a hepatitis B protein (SN: 8/8/81, p. 84), some of them started Chiron Corp., an Emeryville, Calif., genetic engineering firm whose first project was to produce a yeast-derived hepatitis B vaccine.

They licensed the technology to Merck Sharp & Dohme of West Point, Pa., a drug company that already produces a hepatitis B vaccine purified from the blood of chronic carriers. There is no treatment for hepatitis B infection, which attacks the liver and can lead to death from cancer or cirrhosis. The blood-derived vaccine takes a year to manufacture and costs about $100 for the three-shot regimen--a price that puts it beyond the means of Third World countries, where in some areas as much as 20 percent of the population carries the virus.

The recipe for yeast-engineered products is similar to the bacterial process. Enzymes are used to snip out the DNA that produces the product in question. "Cut-and-paste" enzymes insert the DNA into circular pieces of yeast chromosomes that are then put into yeast. There they float about and produce the desired product, which is harvested by breaking open the yeast.

The advantages of yeast, says Pablo Valenzuela, one of the San Francisco researchers now at Chiron, are that unlike bacteria it doesn't produce toxins; the technology for growing it is well developed; and the species being used -- baker's yeast and brewer's yeast -- don't infect humans.

Chiron is now testing yeast-made products for osteoarthritis and feline leukemia, and doing toxicology studies on several other yeast-produced agents, says Valenzuela. Researchers at Genentech, Inc., in South San Francisco have gotten yeast to produce interferon (SN: 2/26/83, p. 138), and other companies are working on the process as well.
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Title Annotation:first human vaccine made by genetic engineering
Author:Silberner, Joanne
Publication:Science News
Date:Jul 27, 1985
Words:453
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