“Countless” attempts have been made to edit human stem cells. Yet according to Linzhao Cheng, Ph.D., an associate professor of gynecology and obstetrics and member of the Johns Hopkins Institute of Cell Engineering, “To date, only about six genes have been successfully targeted or edited in human stem cells. That’s just not efficient enough if we want to move disease research and therapy forward.”
Moving disease research forward is precisely what researchers at the Johns Hopkins School of Medicine have done. As reported in Cell Stem Cell, the team of scientists has successfully edited the “genome of human-induced pluripotent stem cells (iPS), making it possible for the future development of patient-specific stem cell therapies.” The researchers modified a gene known to cause a rare blood disease called paroxysmal nocturnal hemoglobinuria (PNH). Their work has – for the first time – brought about a useful system to learn more about the disease. “We’ve been able to improve gene targeting and editing in human embryonic stem cells more than 200 fold,” says Dr. Cheng.
The system they developed involved the use of human embryonic stem cells, which can be expanded without limitation in the laboratory setting. They also were required to create a mutation as found in patients with PNH, an acquired disease that occurs only in adults. As Dr. Cheng explains, “It’s a tough condition to study because we need to study it in blood stem cells and they’re difficult to grow in the lab. So for years we’ve been trying to develop another cell system to better understand and perhaps fix what’s going on in PNH.”
In order to target and remove the function of the one specific gene responsible for causing the disease, the researchers successfully improved upon the standard approach of gene targeting. Their enhancements included the use of custom designed DNA cutting enzymes called molecular scissors, which are made by collaborators at Harvard University and University of Texas Southwestern Medical Center. As the study reports, the scissors were used to make a precise break in the gene that causes PNH. The researchers 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 iPS cells.” (iPS cells are like embryonic stem cells in terms of biological properties, but generated by using adult tissues such as skin.)
Eight iPS cells lines were grown for further study. Closer examination showed that the cells contained the right number of chromosomes. There was also no trace of the molecular scissors found. And the cells had characteristics as cells from PNH patients that lack a group of cell surface molecules. “We are 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,” says Dr. Cheng, who says he and his team will continue to improve the techniques and start to apply them to iPS cells from patients.
News Release: Genes edited in human stem cells www.sciencedaily.com June 19, 2009
