Stress test for zinc finger nucleases reveals rare cases of imprecision
Heidelberg/Milan – Zinc finger nucleases are designed for genome editing at high precision, but in rare cases even these potential gene therapy tools miss the bull’s-eye. The first genome-wide survey to reveal off-target action of zinc finger nucleases (ZFNs) shows that the enzymes occasionally cut and modify a different, nearly identical DNA sequence.
Several off-target cuts
An international team lead by Christof von Kalle at the German Cancer Research Center in Heidelberg looked at leukemia cells in which a ZFN cuts the CCR-5 receptor (Nature Biotechnology, DOI:10.1038/nbt.1948 ). To track down cutting errors made by the enzymes, they transfected cells with tagged virus particles that bound to the broken ends of the DNA – by and large, the ZFN bound to the target CCR-5 DNA. About 1 in 20,000 times, however, the molecular scalpels cleaved a second receptor gene nearly identical in sequence. These off-target breaks were spotted in locations that were not predicted by conventional methods. In summing up their “molecular stress test”, the researchers underlined that ZFNs still proved extremely specific in comparison to other tools such as viruses. A similar test might be used in future in early drug development to pick the zinc finger nuclease candidates with the best efficacy.