The year 2006 ended with something of a stampede of genetically manipulated cow news.
In the Dec. 31, 2006 online issue of Nature Biotechnology, scientists from the USDA, the University of Texas Medical Branch in Galveston and biotechnology companies Kirin Pharmaceuticals, of Tokyo; Hematech Inc., of Sioux Falls, S.D.; and Gemini Science Inc., of La Jolla, Calif., reported on a knockout cow that lacks prion protein. The paper was published three days after the FDA issued draft documents on the safety of animal clones for the food supply.
The Nature Biotechnology paper presents histological and clinical data on a dozen prion protein knockouts. The researchers have followed the cows for 20 months to date. "The bottom line is that they have been amazingly healthy," Hematech President and Chief Scientific Officer James Robl told BioWorld Today.
Robl said that the function of normal prion protein is actually still unclear. In the mouse, "there have been many studies, but none of them has been conclusive."
But misfolded prion protein is widely believed to be the infectious agent behind spongiform encephalopathies - degenerative brain disorders that include mad cow disease in cows, scrapie in sheep and Creutzfeldt-Jacob disease (CJD) in humans. That makes the brain one obvious place to look for the effects of knocking out prion protein. The researchers looked at the brains histologically, and for abnormal motor responses such as tremors or an abnormal gait. They found that "The nervous system evaluation revealed little change other than a mild increased reaction to external stimulation (menace and sounds)" in some of the knockouts.
The other focus of the Hematech team was on possible immune system effects, since their ultimate goal is to produce polyclonal antibodies in cows. "We want to make human antibodies, so clearly we need cows with a normal immune system," Robl said. The scientists tested the knockouts' immune systems in several ways, paying special attention to T cells, which proliferated less in some mouse studies.
The cows, though, showed no such effects. When they were challenged with an antigen that required a T-cell response, "the antibody response was exactly the same in controls and in knockouts," Robl said.
The prion protein knockouts are the extension of a gene-targeting method published by Hematech scientists in 2004. Technically, Robl said, the gene targeting work "represents an enormous leap forward" for cloning technology. While knockout mice are commonplace these days, in large animals there are "very few papers" describing gene targeting or knockout work - and in those, usually only one copy is knocked out, leaving the animal with half of its protein.
The commercial relevance of the work is less clear. Robl said he sees the most immediate applications in the production of prion-free sera and enzymes for cell culture studies.
Hematech itself seeks to produce polyclonal antibodies for the treatment of autoimmune diseases, but the decision on whether to use prion knockout cows for such production has not yet been made. Robl said that when the work began in 1999, concern about bovine spongiform encephalopathy (BSE) was much higher than it is now, but prion protein contamination in antibodies is easy to avoid through tight control of the cattle food supply and exposure, and easy to purify out of antibodies. "Essentially, we have eliminated the risk in our particular product," Robl said.
One thing Hematech is not planning on is the sale of guaranteed BSE-free burgers. "We have no intention of putting any of our animals into the food chain," Robl said. Recent developments do make that at least a theoretical possibility, though. A draft risk assessment published by the FDA last week declared meat and milk from cloned animals safe, though the agency also is asking food producers to not introduce milk or meat from clones or their offspring into the food supply just yet.
The draft document, which is now open for review and comment by the public, is a hefty 678 pages, but the executive summary was clear enough. While cloning poses health risks for the clones themselves, "extensive evaluation of the available data has not identified any food consumption risks or subtle hazards in healthy clones of cattle, swine or goats. Thus, edible products from healthy clones that meet existing requirements for meat and milk in commerce pose no increased food consumption risk(s) relative to comparable products from sexually-derived animals." (According to the document, there was insufficient data to draw any conclusions about sheep.)
Robl said that Hematech would be open to licensing agreements that would enable prion protein knockouts to be used for food production, but anyone interested "would have to take a good long look" at the commercial possibilities of such a move. That could be a risky venture at best, given that large swaths of the population appear to find the idea of eating cloned meat nearly as distasteful as contracting BSE from a burger. According to a December 2006 poll by the Pew Initiative on Food and Biotechnology, 22% of respondents felt foods from animal clones are safe, while 43% believed they are unsafe.