July 28, 2008

Genetic engineering: DNA scissors go open source

A consortium of eight labs led by molecular biologist J. Keith Joung at Massachusetts General Hospital in Boston has come up with what they call an "open-source" method of making efficient zinc finger nucleases. The group created an archive of 66 "pools," or sets, of individual zinc fingers that have been selected to bind different DNA sequences. Zinc finger nucleases fashioned with these finger pools made specific edits in a plant gene and three human genes at relatively high efficiencies--1% to 50% of treated cells had the desired changes, according to a report today in Molecular Cell. That's comparable to efficiencies reported by Sangamo and by researchers using traditional gene therapy methods.

The consortium has stored the 66 pools of zinc fingers in a freezer, and any lab will be able to order them from a nonprofit distributor at a low cost of perhaps $200 per pool, says Joung. (Researchers will need at least six pools to modify a single gene.) The group also plans to make more pools--192 are needed to target all possible sites in the human genome. "I think it's a game changer. It gives academics the ability to make these proteins without going to Sangamo," says Joung. Although Sangamo has patents on using zinc finger nucleases, the company so far has not exerted any intellectual property claims against academic researchers, he says.

Using "traditional" gene therapy, you'd infect the patient with a virus containing a good copy of the gene, hoping the DNA inserts into the person's genome in a spot that doesn't trigger cancer.

"There's got to be a better way," you tell yourself--and there is. About a decade ago, researchers began developing a new strategy that relies on proteins called zinc finger nucleases that bind to a very specific place on a chromosome. The nucleases work like scissors, cutting the DNA at this precise location--say, the site of your defective gene--so that the gene can be repaired. The technique has worked in fruit fly, plant, and even human cells. But there's a hitch: The best zinc finger nucleases come from a company called Sangamo BioSciences, which until now has shared them only through chosen academic collaborations (Science, 23 December 2005, p. 1894).

Sangamo plans to begin selling custom-made zinc fingers nucleases this fall through the chemical supplier Sigma-Aldrich. But Wolfe says that the $25,000 per set that Sigma-Aldrich expects to charge is "a lot of money." The new open-source method "is an important step forward," he says.

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