ZFN make unpredicted errors

[John2038]

"Nobody wants to have a zinc-finger nuclease loose in their cells that could make cancer-causing mutations."
The team found that on rare occasions, the enzyme breaks DNA near a gene linked to cancer. It is difficult to determine whether this poses a danger to patients, says Segal, because Liu's team tested the enzyme using leukaemia cell cultures, whereas the trial drug targets T-cells, a type of immune cell.
..
Philip Gregory, chief scientific officer at Sangamo Biosciences in Richmond, California, which makes the trial drug, also notes that Sangamo's nuclease has been further optimized for clinical use since the version in Liu and von Kalle's work was made.

Before embarking on clinical trials, Sangamo tested the safety of its enzyme by engrafting more than one billion genetically modified cells into over 150 animals and then looking for unwanted side effects.

Gregory thinks that von Kalle's method, which was developed with Sangamo, could be useful for screening future clinical candidates. But he believes that regulators at the US Food and Drug Administration (FDA) are unlikely to give up their requirement for safety testing in live animals. "The FDA is underwhelmed by fancy molecular techniques," he says. "They like the old-school, 'show me the modified cells and stick them into animals' approach."


http://www.nature.com/news/2011/110807/full/news.2011.461.html