Researchers at Children's Hospital Boston have begun attempts to create human embryonic stem cells using nuclear transfer with human eggs and embryos, after receiving approval from the Institutional Review Boards and ESCRO (Embryonic Stem Cell Research Oversight) committees of Children's Hospital Boston and Partners HealthCare.
The work is underway in the Children's Hospital laboratory of George Daley, MD, PhD, Associate Director of the Children's Hospital Stem Cell Program and a member of the Executive Committee of the Harvard Stem Cell Institute.
Because of Federal funding restrictions on human embryonic stem cell research, these studies are being funded through private philanthropy donated to Children's Hospital Boston and the Harvard Stem Cell Institute (HSCI).
Two other HSCI scientists at Harvard University, Doug Melton, PhD, and Kevin Eggan, PhD, have likewise received approval to begin similar experiments aimed at producing disease-specific embryonic stem cells.
The first goal of Daley and his Children's colleagues is to gain proficiency in creating stem cell lines; ultimately, they intend to create patient-specific stem cell lines to treat patients using their own cells.
The work in the Daley laboratory is utilizing donor eggs and embryos from women undergoing in vitro fertilization (IVF) treatment at Brigham and Women's Hospital's (BWH) Center for Reproductive Medicine.
During IVF treatment, a subset of retrieved eggs do not fertilize, and some embryos are not of sufficient quality to successfully produce a pregnancy.
These eggs and embryos are typically disposed of as medical waste. However, these materials are capable of providing human embryonic stem cells (hESCs). They offer invaluable study opportunities for medical researchers.
"The availability of top quality eggs and embryos is extremely limited and this can slow the research," explains Daley, an HSCI senior investigator.
"The eggs and embryos described in our initial protocol-since they are regularly available as a byproduct of IVF-will give us a ready supply of material for research."
"This will allow us to immediately investigate some basic questions of biology, such as how stem cells form and how they behave."
In the future, Daley's team will also seek approval to derive hESCs from healthy eggs and embryos, and from patient tissues such as skin cells, and eventually to begin treating patients at Children's Hospital Boston with stem-cell-based therapies.
In this initial protocol, Daley and colleagues hope to obtain failed-to-fertilize eggs and poor-quality embryos. They will then use two methods to create hESCs:
1) Nuclear transfer: This technique involves using a microscopic needle to remove the nucleus from an egg, and replacing this nucleus with a donor nucleus, containing the donor's genetic material, or DNA.
The process of transferring the donor nucleus into the egg "reprograms" it, reactivating the full set of genes for making all the tissues of the body.
The resulting "reprogrammed" cell is encouraged to develop and divide, and by about day 5, forms a blastocyst-a ball of 50-200 cells.
The blastocyst's outer cells are destined to become the placenta, while the inner cells have the potential to form all of the tissues of the body. At this point, development is halted and the inner cells are isolated to derive hESCs.
Because the nucleus implanted into the egg contained the patient's DNA, the hESCs derived by this method are genetically matched to the patient.
In the future, under separately approved protocols, Daley and colleagues hope to obtain donor cells from actual patients, and to transfer the donor nucleus into a fresh egg from a donor or from the patient herself, if female. The donor cell would be of a type easy to obtain, such as a skin cell.
For now, under the approved study protocol, Daley and colleagues will obtain the donor nucleus from a blastomere, a single cell from a poor-quality embryo of less than 8 days' gestation.
They will then transfer this nucleus into a failed-to-fertilize egg, wait for a blastocyst to develop, and isolate hESCs from its inner cell mass.
"Our long-term goal is to create embryonic stem cells from a patient's tissues, correct the genetic defects, and get the repaired cells back into the patients," Daley says.
"In the meantime, however, using an embryonic cell rather than a skin cell will increase the chances that nuclear transfer will be successful, because the nucleus of an embryonic cell is much easier to reprogram than the nucleus of a skin cell."
"This will allow us to answer some basic questions of stem cell biology while becoming technically proficient in creating stem cell lines."
2) In a second technique, hESCs will be created directly from poor-quality embryos, and eventually from frozen, good-quality embryos, without nuclear transfer.
The researchers will add feeder cells, chemicals and growth factors to encourage the embryo to grow to the blastocyst stage. They will then stop development and derive hESCs from the blastocyst's inner cell mass.
This procedure will generate "generic" hESC lines - not customized to an individual - that can be used to study how stem cells behave and differentiate.
Leonard Zon, MD, director of Children's Stem Cell Program, Chair of HSCI's Executive Committee, and Chair of the State Biomedical Research Advisory Committee, was responsible for orchestrating the institutional and administrative oversight and review structures that have allowed the work to be done at Children's.
"The work, if successful, will have a major impact on our understanding of human development and tissue formation, and will provide a scaffold for the treatment of many diseases of children and adults," Zon says.
"There will be no transfer of cloned embryos to a womb, and no embryo will be allowed to grow beyond the blastocyst stage."