"The study is proof of principle that therapeutic cloning can be used to create tissues without the threat of rejection," says Anthony Atala, M.D., director of Tissue Engineering at Children's Hospital Boston and the senior author on the paper. "While more work needs to be done, this demonstrates the potential use of this technology."
As many as 3,000 Americans die every day from diseases that may someday be treatable with tissues created through stem cells, according to the Centers for Disease Control. Somatic cell nuclear transfer ("therapeutic cloning"), which is one way to derive stem cells, shows potential in generating functional replacement cells such as insulin-producing cells associated with diabetes. It also shows promise in reconstituting more complex tissues and organs, such as blood vessels, myocardial "patches," kidneys, and even entire hearts. Additionally, it has the potential to eliminate the rejection responses associated with transplantation of "non-self" tissues, and thus the need for immunosuppressive drugs, which carry the risk of serious and potentially life-threatening complications and enormous cost to the United States health care system.
In the study, researchers obtained cow oocytes (donor eggs from cow ovaries) and removed and discarded the nuclei, which contain the cells' genetic material, leaving behind just the shell. A skin cells from the cow's ears was placed inside the egg shell and burst with electrical energy to expand the cells. That induces the one skin cell to become several cells. The resulting blastocysts (4-day old embryonic cell masses) were transferred into surrogate-mother cows for a 5- to 6-week incubation period.
Cow embryonic stem cells that can be induced to differentiate into specified tissues in vitro have not yet been isolated. Therefore, for the study it was necessary to generate an early stage cow embryo. Fortunately, the same is not true for humans, where stem cells have been successfully differentiated into different cells, including beating cardiac muscle cells, smooth muscle, and insulin-producing cells, among others. However, there is an ethical consensus in the United States not to allow preimplantation human embryos to develop beyond 80 to 100 cells, about the size of a pinhead. For humans, stem cells generated through nuclear transfer could be harvested and used as a source of genetically matched cells for transplantation.
Bioengineered tissues were created from heart, skeletal muscle and kidney cells cloned from adult cow skin cells. The cloned cells were harvested, expanded in culture and transferred to three-dimensional molds. The molds were placed in incubators to allow the cells to attach and form tissue. The cell-mold structures were implanted back into the cows from which the initial skin cells were harvested. Miniature kidneys, skeletal and heart muscle tissues were cloned. The miniature kidneys were able to excrete metabolic waste products through a urinelike fluid. There was no rejection response to the cloned tissues.
Currently, approximately 100,000 individuals in the US are awaiting an organ for transplantation and approximately 250,000 are on kidney dialysis. Atala and other regenerative medicine experts view nuclear transfer as one promising avenue to create tissues and organs that could be used for patients with various diseases.
The researchers of the paper from Children's Hospital Boston and Harvard Medical School collaborated with scientists from Advanced Cell Technology, Worcester, Massachusetts; the Mayo Clinic, Rochester, Minnesota; and the University of Miami School of Medicine, Miami, Florida. The papers other authors are Ho Yun Chung, James Yoo, Gunter Schuch, and Shay Soker of Children's Hospital; Robert P. Lanza, Michael D. West and Catherine Blackwell of ACT; Peter J. Wettstein, Nancy Borson, and Erik Hofmeister of the Mayo Clinic; and Carlos T. Moraes of the University of Miami School of Medicine.
Children's Hospital Boston is the nation's premier pediatric medical center. Children's Hospital is the primary pediatric teaching affiliate of Harvard Medical School, home to the world's leading pediatric research enterprise, and the largest provider of health care to the children of Massachusetts. For more information about the hospital visit: www.childrenshospital.org.