Children's Hospital Boston researchers create first stem cell line using fresh skin cells
New techniques pave way to developing lines from patients with a variety of diseases
December 23, 2007
Children's Hospital Boston's stem cell researchers have converted skin cells from an adult into cells that look and act like embryonic stem cells. The resulting cell lines, called induced pluripotent stem cells (iPS), can potentially form any cell type in the body. iPS cells allow a new way for scientists to model human diseases and may one day provide raw material for cell therapies to reverse leukemia, diabetes, Parkinson's disease, and paralysis, among other devastating conditions.
George Daley, MD, PhDThe study, led by first-author In Hyun Park, PhD, appears in the December 23 online Nature. It is similar to reports from laboratories in Japan and the University of Wisconsin that gained worldwide attention in November,* but the Children's study is the first to use tissue from a volunteer research subject rather than cells purchased commercially. "Ours is the only group to go from skin biopsy to cell line," says George Q. Daley, MD, PhD, associate director of Children's Stem Cell Program and the study's senior author. "We developed a strategy that integrates tissue procurement, culturing, and reprogramming the cells. We're now ready to apply this method to cells from patients with a variety of diseases."
Daley, one of the world's foremost experts on embryonic stem cells (ESC), is enthusiastic about the promise of reprogramming studies but far from ready to abandon experiments with embryonic stem cells. His is one of the few labs in the world pursuing both gene-based reprogramming and nuclear transfer, a technique that involves transferring the nucleus of a cell into an egg, which then allows isolation of ESCs that are genetically matched to specific patients.
Daley believes reprogramming and ESC research must advance in tandem to bring cell therapy to the clinic as quickly as possible. "Gene-based reprogramming is relatively easy and a boon to research into human disease, enabling researchers to create cell lines from patients with a specific disease and study them in the lab," he says. However, both the genes used to reprogram cells and the retroviruses that deliver them may pose a cancer risk, so significant hurdles must be overcome before iPS cells are viable for clinical applications.
Although ESCs are more difficult to produce by nuclear transfer, the cells are genetically pristine and may provide a faster and safer route to the clinic. In addition, ESC research may yield insights into reprogramming. "Understanding how to derive stem cells from embryos may teach us how to make the reprogramming process that much more efficient," says Daley.
Daley's research highlights the potential--and need--for more efficient reprogramming methods. His group reprogrammed six cell lines spanning development from embryo to adult. In their first experiment, they coaxed existing ESCs to become fibroblasts--cells responsible for wound healing--then converted them back to pluripotency. They then reprogrammed fibroblasts isolated from fetal lung, fetal skin, neonatal foreskin, and adult skin. They also reprogrammed mesenchymal stem cells, a distinct adult stem cell type isolated from bone marrow that is the precursor of fat, bone, and cartilage.
The researchers reprogrammed the cells by inserting four genes previously shown to work on mouse skin cells. They discovered that less mature fetal cells formed iPS cells far more readily than more mature adult cells. Indeed, the researchers had to add two additional genes to coax neonatal and adult cells to become iPS cells. Even at that, conversion rates were as much as 35 times lower than for the most malleable cells--the ESC-derived fibroblasts.
"The fact that embryonic and fetal cells convert more efficiently than adult cells was suggested in mouse studies but the pattern is quite apparent with human cells," says Daley. "This suggests that there are many aspects of the biology of reprogramming we still need to understand to make the process more efficient."
By continuing to study reprogramming where development happens naturally--in the egg and the embryo--Daley's team hopes to identify the key genes that must be activated to reverse the developmental clock. They are also generating disease-specific iPS lines for research, exploring ways to induce reprogramming without retroviruses, and continuing NT studies. Their aim is to exploit all potential avenues to the clinic, improving the odds that patients will one day become their own medicine cabinets, providing a plug of skin or dab of bone marrow to be cultured, reprogrammed, and turned into treatments.
This work was funded by the NIH Director's Pioneer Award of the NIH Roadmap for Research; direct reprogramming of somatic cells was a major goal articulated in Daley's proposal for the award. The work in Daley's laboratory was also made possible through the generosity and vision of Joshua and Anita Bekenstein, as well as through support from the Burroughs Wellcome Fund.
*Two papers showing that genes can reprogram human cells into iPS cells appeared while the Children's study was under review (Yu, et al., Science ; Takahashi, et al., Cell)
Children's Hospital Boston is home to the world's largest research enterprise based at a pediatric medical center, where its discoveries have benefited both children and adults since 1869. More than 500 scientists, including eight members of the National Academy of Sciences, 11 members of the Institute of Medicine and 10 members of the Howard Hughes Medical Institute comprise Children's research community. Founded as a 20-bed hospital for children, Children's Hospital Boston today is a 347-bed comprehensive center for pediatric and adolescent health care grounded in the values of excellence in patient care and sensitivity to the complex needs and diversity of children and families. Children's also is the primary pediatric teaching affiliate of Harvard Medical School. For more information about the hospital and its research visit: www.childrenshospital.org/newsroom.
George Daley, MD, PhD