The technique used by Drs. Mitalipov, Paula Amato, M.D., and their colleagues in OHSU's Division of Reproductive Endocrinology and Infertility, Department of Obstetrics & Gynecology, is a variation of a commonly used method called somatic cell nuclear transfer, or SCNT. It involves transplanting the nucleus of one cell, containing an individual's DNA, into an egg cell that has had its genetic material removed. The unfertilized egg cell then develops and eventually produces stem cells.
"A thorough examination of the stem cells derived through this technique demonstrated their ability to convert just like normal embryonic stem cells, into several different cell types, including nerve cells, liver cells and heart cells. Furthermore, because these reprogrammed cells can be generated with nuclear genetic material from a patient, there is no concern of transplant rejection," explained Dr. Mitalipov. "While there is much work to be done in developing safe and effective stem cell treatments, we believe this is a significant step forward in developing the cells that could be used in regenerative medicine."
Another noteworthy aspect of this research is that it does not involve the use of fertilized embryos, a topic that has been the source of a significant ethical debate.
The Mitalipov team's success in reprogramming human skin cells came through a series of studies in both human and monkey cells. Previous unsuccessful attempts by several labs showed that human egg cells appear to be more fragile than eggs from other species. Therefore, known reprogramming methods stalled before stem cells were produced.
To solve this problem, the OHSU group studied various alternative approaches first developed in monkey cells and then applied to human cells. Through moving findings between monkey cells and human cells, the researchers were able to develop a successful method.
The key to this success was finding a way to prompt egg cells to stay in a state called "metaphase" during the nuclear transfer process. Metaphase is a stage in the cell's natural division process (meiosis) when genetic material aligns in the middle of the cell before the cell divides. The research team found that chemically maintaining metaphase throughout the transfer process prevented the process from stalling and allowed the cells to develop and produce stem cells.
"This is a remarkable accomplishment by the Mitalipov lab that will fuel the development of stem cell therapies to combat several diseases and conditions for which there are currently no treatments or cures," said Dr. Dan Dorsa, Ph.D., OHSU Vice President for Research. "The achievement also highlights OHSU's deep reproductive expertise across our campuses. A key component to this success was the translation of basic science findings at the OHSU primate center paired with privately funded human cell studies."
One important distinction is that while the method might be considered a technique for cloning stem cells, commonly called therapeutic cloning, the same method would not likely be successful in producing human clones otherwise known as reproductive cloning. Several years of monkey studies that utilize somatic cell nuclear transfer have never successfully produced monkey clones. It is expected that this is also the case with humans. Furthermore, the comparative fragility of human cells as noted during this study, is a significant factor that would likely prevent the development of clones.
"Our research is directed toward generating stem cells for use in future treatments to combat disease," added Dr. Mitalipov. "While nuclear transfer breakthroughs often lead to a public discussion about the ethics of human cloning, this is not our focus, nor do we believe our findings might be used by others to advance the possibility of human reproductive cloning."
Skin Cells Turned Directly Into the Cells That Insulate Neurons
Apr. 15, 2013 — Researchers at the Stanford University School of Medicine have succeeded in transforming skin cells directly into oligodendrocyte precursor cells, the cells that wrap nerve cells in the insulating myelin sheaths that help nerve signals propagate.
The current research was done in mice and rats. If the approach also works with human cells, it could eventually lead to cell therapies for diseases like inherited leukodystrophies -- disorders of the brain's white matter -- and multiple sclerosis, as well as spinal cord injuries. The study will be published online April 14 in Nature Biotechnology.
Without myelin to insulate neurons, signals sent down nerve cell axons quickly lose power. Diseases that attack myelin, such as multiple sclerosis, result in nerve signals that are not as efficient and cannot travel as far as they should. Myelin disorders can affect nerve signal transmission in the brain and spinal cord, leading to cognitive, motor and sensory problems.
Previous research in rodent disease models has shown that transplanted oligodendrocyte precursor cells derived from embryonic stem cells and from human fetal brain tissue can successfully create myelin sheaths around nerve cells, sometimes leading to dramatic improvements in symptoms. "Unfortunately, the availability of human fetal tissue is extremely limited, and the creation of OPCs from embryonic stem cells is slow and tedious," said the study's senior author, Marius Wernig, MD, assistant professor of pathology and a member of Stanford's Institute for Stem Cell Biology and Regenerative Medicine. "It appeared we wouldn't be able to create enough human OPCs for widespread therapeutic use, so we began to wonder if we could create them directly from skin cells."
Nan Yang, PhD, a postdoctoral scholar in the Wernig laboratory and lead author of the study, pointed out that there is another advantage to using this technique. "By using the patient's own skin cells, we should be able to generate transplantable OPCs that are genetically identical to the patient's natural OPCs," Yang said. "This allows us to avoid the problem of immune rejection, which is a major complication in transplantation medicine."
Last year, Wernig's team successfully created human nerve cells out of skin cells. Other researchers had successfully used a similar process to turn skin cells into embryonic-like cells called induced pluripotent stem cells, and then grow those iPS cells into nerve cells, but Wernig's lab was the first to convert skin cells directly into nerve cells without the intermediate iPS cell step.
The team's current research project also involved directly converting skin cells into OPCs without having to create iPS cells. The researchers showed that mouse and rat skin cells could be directly converted into OPCs, and that these cells would successfully myelinate nerve cells when transplanted into the brains of mice with a myelin disorder.
Next, the team plans to reproduce the research in human cells; if successful, the approach could lay the groundwork for therapies for a wide array of myelin disorders and spinal cord injury.
"Dr. Young may be on the threshold of a new biology, whose principle—if proven—could revolutionize the biology and medicine worlds." Neil Solomon, M.D., Ph.D.
