Science breakthrough of the year: Cell reprogramming
The journal Science has named its 2008 Breakthrough of the Year: the ability to reprogram ordinary cells back to cells much like embryonic stem cells. Work by George Daley, MD, PhD and colleagues at Children's Hospital Boston is prominently featured. The science of induced pluripotent stem cells (iPS cells) and the contributions of the Daley Lab are highlighted below. Check here for further background on the Daley lab.
December 12, 2008
What are cell reprogramming and iPS cells?
Cell reprogramming involves taking a cell from the body (typically a cell extracted from skin called a dermal fibroblast) and genetically manipulating it to look and act like an embryonic stem cell. The resulting cell lines, called induced pluripotent stem cells (iPS), can potentially form any cell type in the body.
(Note: pluripotent cells, which include iPS cells and embryonic stem cells (ESCs), cannot make so-called "extra-embryonic" tissues such as the amnion, chorion, and other components of the placenta. Only the first few cells of the mammalian embryo are totipotent, capable of making all these tissues and forming an embryo.)
Thus far, reprogramming has been gene-based, using a retrovirus or adenovirus to carry the genes into a cell. The laboratories of George Q. Daley, MD, PhD, associate director of Children's Stem Cell Program, and others have shown that it requires only three to four genes to transform an adult skin cell into an iPS cell.
What has been the contribution of the Daley lab?
Within a few weeks of each other near the end of 2007, scientists in Japan and the University of Wisconsin, along with Daley’s laboratory, reported reprogramming human skin cells to create pluripotent stem cells. In the December 23 online edition of Nature, the Daley laboratory reported the first use of tissue from a volunteer research subject (rather than cells purchased commercially) to create iPS cells – going directly from skin biopsy to cell line.
In all, Daley’s group reprogrammed six cell lines. They first coaxed existing embryonic stem cells to become fibroblasts -- cells responsible for wound healing -- then converted them back to pluripotency. They also reprogrammed fibroblasts isolated from fetal lung, fetal skin, neonatal foreskin, and adult skin, as well as mesenchymal stem cells, an 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. The lab is now doing extensive research to improve the efficiency of reprogramming at the molecular level.
What work is planned or underway with iPS cells?
The Daley lab is focused on using iPS cells to understand human disease. In August, 2008, in the journal Cell , the lab reported creating a collection of 10 disease-specific stem cell lines using the new iPS technique. The diseases include Parkinson's Disease, Type I diabetes, Huntington's Disease, Down Syndrome, a form of combined immunodeficiency ("Bubble Boy's Disease"), Lesch-Nyhan syndrome, Gaucher's Disease, and two forms of Muscular Dystrophy, and others.
Researchers at Children’s and elsewhere are using these cell lines to study how diseases unfold during the earliest stages of development. The Harvard Stem Cell Institute, of which Daley is a member, has created an iPS Core, a repository for iPS cells, to make the cell lines available to scientists around the world.
Are there risks in using iPS cells in human patients?
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. The Daley lab is now exploring ways to induce reprogramming without retroviruses. One lab, at Massachusetts General Hospital, reported in September 2008 that it had used the same four genes to create iPS cells, carried not by retroviruses but by adenoviruses, which are thought to pose little risk of cancer.
Does the ability to reprogram cells to a pluripotent state mean we no longer need embryonic stem cell research?
Daley believes reprogramming and embryonic stem cell research must advance in tandem to bring cell therapy to the clinic as quickly as possible. His lab is one of the few in the world to simultaneously pursue a variety of strategies, each of which is informing the others.
- The Daley lab is continuing nuclear transfer experiments—transferring the nucleus of a patient's mature cell into an egg, inducing the egg to divide, and isolating embryonic stem cells that are exactly matched to the patient. This approach is more difficult than gene-based reprogramming but yields more genetically pristine cells and may provide a safer route to the clinic, Daley says.
- One nuclear transfer protocol, announced in June, 2006, uses donor eggs and embryos from women undergoing in vitro fertilization (IVF) treatment at Brigham and Women's Hospital's (BWH) Center for Reproductive Medicine. Top-quality eggs and embryos are difficult to obtain, but scientists are able to produce human embryonic stem cells for research purposes using eggs that do not fertilize and embryos of insufficient quality to produce a pregnancy, typically disposed of as medical waste. In January, 2008, the group reported the successful isolation of embryonic stem cells using flawed early-stage embryos in Nature Biotechnology.
- In December, 2006, in the journal Science, the group reported the use of unfertilized eggs alone to create embryonic stem cells that are genetically matched to the egg donor (and her close relatives) by tissue type.
- By continuing to study reprogramming where development happens naturally--in the egg and the embryo -- Daley's team hopes to insights into gene-based reprogramming, making it more efficient and safe.
Children's Hospital Boston
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 13 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 397-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.
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