July 2006
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Stem cell milestone at Children's
Creating a worldwide buzz, Children's Hospital Boston and the Harvard Stem Cell Institute announced efforts on June 6 to create human embryonic stem cells, "master cells" that can give rise to any cell type in the body.
Work is already underway in the lab of George Daley, MD, PhD, associate director of Children's Stem Cell Program, to create embryonic stem cells that are customized to patients. As a hematologist, Daley wants to use these valuable cells to treat children with life-threatening blood diseases like sickle-cell anemia, immune deficiency disorders and leukemia. "We hope to become one of the first hospitals in the country to use stem cell therapy to cure childhood diseases," says Program Director Leonard Zon, MD.
The stem cells will be created from eggs and embryos donated by couples undergoing in vitro fertilization (IVF) at Brigham and Women's Hospital. In IVF, a couple's eggs and sperm are combined in the laboratory in hopes of achieving fertilization, and one or more resulting embryos are then implanted in the woman's uterus. However, some eggs do not fertilize, and some embryos are not transferred because their quality is too poor to produce a viable pregnancy. These eggs and embryos are normally discarded, but under a protocol approved by Institutional Review Boards and Embryonic Stem Cell Research Oversight Committees at both hospitals, couples will be offered the chance to anonymously donate them for research purposes.
"Healthy eggs and embryos are a precious and limited resource," Daley explains. "To get our work started, we will use eggs and embryos that, while not of clinical grade, are more readily available and will allow us to refine our techniques and answer important questions about how stem cells form and behave. Eventually, we will seek to generate stem cells using healthy eggs and embryos."
The embryonic stem cells will be created through nuclear transfer, a technique in which an egg's own nucleus is removed and replaced with a nucleus from a donor cell. The transferred nucleus contains the donor's DNA, and the process of transferring it to the empty egg cell "reprograms" it, giving it the ability to make all body tissues. The egg cell is then encouraged to develop for five days in a Petri dish, forming a tiny cluster of 50 to 200 cells, called a blastocyst. The inner cells are then removed and cultivated as embryonic stem cells.
Under stringent National Research Council guidelines, no embryo will be allowed to grow beyond the blastocyst stage. For now, the donor cells will come from donated embryos, but as the work advances to the clinic, patients themselves will supply the cells, most likely from their skin. Nuclei from these cells would then be transferred into fresh donor eggs (or, if the patient is female, her own eggs) to create embryonic stem cells that match the patient's tissue type.
"By using customized, genetically-matched cells—effectively patients' own cells—we hope to eliminate the need for tissue matching and avoid the rejection problems that currently plague transplants," Daley says.
Currently, the only hope for children with serious blood diseases is bone marrow transplantation, a risky and highly toxic treatment (see story on sickle cell disease). Often, a suitable marrow donor cannot be found, and unless the donor is an identical twin, transplants pose a serious risk of graft-versus-host disease, a potentially fatal complication in which donor cells begin attacking the recipient.
Ultimately, Daley hopes to combine embryonic stem cell creation with gene therapy. His team has already done this in mice with a genetic immune deficiency: after creating embryonic stem cells and replacing the defective gene, they generated healthy blood stem cells and injected them back into the mice, restoring the animals' immune function.
"Our long-term goal is to get healthy cells back into patients," Daley says. For more information, visit Children's online News Room: www.childrenshospital.org/newsroom.
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