The team's technological improvement includes the use of custom-designed molecular scissors that are made by collaborators at Harvard University and University of Texas Southwestern Medical Center. These engineered DNA cutting enzymes make a precise break at specific locations in a cell's DNA-in this case in the gene that causes PNH. They added the molecular scissors and a fragment of DNA containing a gene that confers selection of rare targeted clones in both human embryonic stem cells and induced pluripotent stem cells. The latter, also known as iPS cells, are very similar to embryonic stem cells in biological properties, but generated by using adult tissues such as skin.

Of all the cells surviving selection, they picked and grew eight iPS cell lines to study further, and five of those contained a targeted insertion at the gene site. Further examination showed that the cells contained the correct number of chromosomes, no longer contained any trace of the molecular scissors and had characteristics as cells from PNH patients that lack a group of cell surface molecules.

"I commend my team especially Dr. Jizhong Zou who spent three years with the help of many collaborators on this challenging project," says Cheng. "We're very excited about this accomplishment; it will enable better studies for other blood diseases. But there's still much to do before we can really use human iPS cells in clinical therapies."

Cheng's team will continue to improve on techniques and begin applying these techniques to iPS cells from patients.

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