Embryonic stem cells (ES cells) are stem cells derived from the inner cell mass of an early stage embryo known as a blastocyst. Human embryos reach the blastocyst stage 4-5 days post fertilization, at which time they consist of 50-150 cells.
ES cells are pluripotent. This means they are able to differentiate into all derivatives of the three primary germ layers: ectoderm, endoderm, and mesoderm. These include each of the more than 220 cell types in the adult body. Pluripotency distinguishes ES cells from multipotent progenitor cells found in the adult; these only form a limited number of cell types. When given no stimuli for differentiation, (i.e. when grown in vitro), ES cells maintain pluripotency through multiple cell divisions
Lecture is presented by Sir John Bertrand Gurdon ,In 1962, Gurdon, then at Oxford University, announced that he had used the nucleus of fully differentiated adult intestinal cells to clone South African clawed frogs (Xenopus laevis).This was the first demonstration in animals that the nucleus of a differentiated somatic cell retains the potential to develop into all cell types (ie, is totipotent) and paved the way for future somatic cell nuclear transfer experiments, including the 1996 cloning of the sheep, Dolly.
Gurdon began cloning experiments using nonembryonic cells—specifically, cells from the intestinal lining of tadpoles. Gurdon believed that the tadpoles were old enough so that cells taken from them would be differentiated. Gurdon exposed a frog egg to ultraviolet light, which destroyed its nucleus. He then removed the nucleus from the tadpole intestinal cell and implanted it in the enucleated egg. The egg grew into a tadpole that was genetically identical to the DNA-donating tadpole. But the tadpoles cloned in Gurdon’s early experiments never survived to adulthood and scientists now believe that many of the cells used in these experiments may not have been differentiated cells after all. In later work, however, Gurdon successfully produced sexually mature adult frogs from eggs into which genetically marked nuclei had been transplanted from differentiated tadpole cells.
Gurdon’s experiments captured the attention of the scientific community and the tools and techniques he developed for nuclear transfer are still used today. The term clone (from the Greek word klōn, meaning “twig”) had already been in use since the beginning of the 20th century in reference to plants. In 1963 the British biologist J. B. S. Haldane, in describing Gurdon’s results, became one of the first to use the word clone in reference to animals.
In this Hitchcock lecture he explores the process of going from egg to organism.
Rudolf Jaenisch is one of the founders of transgenic science (gene transfer to create mouse models of human disease). His lab has produced mouse models leading to new understanding of cancers and various neurological diseases.
He received his doctorate in medicine from the University of Munich in 1967. He came to the Whitehead from the University of Hamburg in Germany, where he was head of the Department of Tumor Virology at the Heinrich Pette Institute.
Jaenisch received the 2002 Robert Koch Prize for Excellence in Scientific Achievement. In 2003, he was awarded the Charles Rodolphe Brupbacher Prize for basic research in oncology and was elected a member of the National Academy of Sciences.
Jaenisch is a fellow of the American Academy of Arts and Sciences and the American Academy of Microbiology, and a member of the American Association for the Advancement of Science
About Speaker
Robert A. Weinberg '64, PhD '69
Founding Member, MIT Center for Cancer Research
Member, Whitehead Institute Daniel K. Ludwig and American Cancer Society Professor for Cancer Research Department of Biology
Robert A. Weinberg has earned some of the top honors in his field. Most recently, he won the 2006 Landon-AACR Prize for Basic and Translational Cancer Research. He is also a 1997 National Medal of Science awardee.
Weinberg's laboratory discovered the first human oncogene and the first tumor suppressor gene. Today, much of his research focuses on new models of breast cancer development including the stages of tumor invasiveness and metastasis.
Part 2
He earned his Ph.D. in biology from MIT in 1969, and was one of the Founding Members of the MIT Center for Cancer Research in 1973. He was appointed a professor at MIT in 1982, the same year he joined the Whitehead Institute. Weinberg was named American Cancer Society Research Professor in 1985 and received the Daniel K. Ludwig Professorship for Cancer Research in 1997. He is a member of the National Academy of Sciences and the Institute of Medicine.
Genetics research is key to understanding the effects of aging and age-related diseases. How do stem cells change as we grow older, and can they be regulated to decrease cancer risk?
Dr. Benjamin Reubinoff explores the research his team at Hadassah University Hospital in Jerusalem has conducted with stem cells including the use of stem cells to treat rats with Parkinson's disease.
Stem cells are immature unspecialized cells that renew themselves for long periods through cell division. Under certain conditions, they can be induced to become mature cells with special functions such as the beating cells of the heart muscle or the insulin-producing cells of the pancreas.
Human embryonic stem cells (hESCs) are derived from early surplus human embryos (5-6 days after fertilization). The embryos used to derive these stem cells were created for infertility treatment purposes through in vitro fertilization (IVF) procedures and were donated to research when they were no longer needed for that purpose.
Human ES cells are unique in the universe since they can self-renew infinitely in culture yet still retain a normal genetic pattern, and also since they have a remarkable potential to develop into all cells and tissues of the human body.
The Potential of hESCs for Transplantation Therapy
Given their unique properties, hESCs are expected to have far- reaching applications in the study of early human development, the development of new drugs, and regenerative medicine. Human ES cell lines can serve as a renewable unlimited donor source of specialized human cells for transplantation therapy.
Human ES cell-derived mature cells could potentially be transplanted to restore tissue function in a wide range of human diseases that are associated with loss of cell function.
These conditions may include neurodegenerative disorders such as Parkinson’s and Alzheimer’s diseases, Multiple Sclerosis, cerebrovascular accidents, spinal cord injuries, as well as heart failure, diabetes mellitus, and others. The number of patients that potentially could benefit from transplantation of hESCs is overwhelming. For example there are over 16 million patients worldwide with neurodegenerative disorders, and over 120 million diabetic patients. Moreover, transplantation of genetically modified hESCs may allow the transfer and expression of foreign genes in target organs in the course of gene therapy.
While the promise of hESCs for cell and gene therapy is remarkable, further extensive research and development are required to exploit their potential for regenerative medicine.
James Alexander Thomson is an American developmental biologist who is best known for deriving the first human embryonic stem cell line. He serves as director of regenerative biology at the Morgridge Institute for Research in Madison, Wisconsin, and is a professor at the University of Wisconsin School of Medicine and Public Health.He is one of the leading scientific innovators in stem cell research.
In this lecture he explores current understanding how human embryonic cells can form any cell in the body and the implications for cancer research.
Dr. Irving Weissman, Professor of Pathology and Developmental Biology at Stanford University and Director of the Stanford Comprehensive Cancer Center discusses current research in stem cell biology and the effects of public policy on research.
Dr. Michael German, the clinical director of UC San Francisco's Diabetes Center, as he explores the steps human embryonic stem cells take to become insulin producing pancreatic islet cells, and the goal of clinicians to transplant these cells to treat diabetes
The discovery of methods to isolate and grow human embryonic stem cells in 1998 renewed the hopes of doctors, researchers, and diabetes patients and their families that a cure for type 1 diabetes, and perhaps type 2 diabetes as well, may be within striking distance. In theory, embryonic stem cells could be cultivated and coaxed into developing into the insulin-producing islet cells of the pancreas. With a ready supply of cultured stem cells at hand, the theory is that a line of embryonic stem cells could be grown up as needed for anyone requiring a transplant. The cells could be engineered to avoid immune rejection. Before transplantation, they could be placed into nonimmunogenic material so that they would not be rejected and the patient would avoid the devastating effects of immunosuppressant drugs. There is also some evidence that differentiated cells derived from embryonic stem cells might be less likely to cause immune rejection (see Chapter 10. Assessing Human Stem Cell Safety). Although having a replenishable supply of insulin-producing cells for transplant into humans may be a long way off, researchers have been making remarkable progress in their quest for it. While some researchers have pursued the research on embryonic stem cells, other researchers have focused on insulin-producing precursor cells that occur naturally in adult and fetal tissues.
Since their discovery three years ago, several teams of researchers have been investigating the possibility that human embryonic stem cells could be developed as a therapy for treating diabetes. Recent studies in mice show that embryonic stem cells can be coaxed into differentiating into insulin-producing beta cells, and new reports indicate that this strategy may be possible using human embryonic cells as well.
Last year, researchers in Spain reported using mouse embryonic stem cells that were engineered to allow researchers to select for cells that were differentiating into insulin-producing cells . Bernat Soria and his colleagues at the Universidad Miguel Hernandez in San Juan, Alicante, Spain, added DNA containing part of the insulin gene to embryonic cells from mice. The insulin gene was linked to another gene that rendered the mice resistant to an antibiotic drug. By growing the cells in the presence of an antibiotic, only those cells that were activating the insulin promoter were able to survive. The cells were cloned and then cultured under varying conditions. Cells cultured in the presence of low concentrations of glucose differentiated and were able to respond to changes in glucose concentration by increasing insulin secretion nearly sevenfold. The researchers then implanted the cells into the spleens of diabetic mice and found that symptoms of diabetes were reversed.
Manfred Ruediger of Cardion, Inc., in Erkrath, Germany, is using the approach developed by Soria and his colleagues to develop insulin-producing human cells derived from embryonic stem cells. By using this method, the non-insulin-producing cells will be killed off and only insulin-producing cells should survive. This is important in ensuring that undifferentiated cells are not implanted that could give rise to tumors. However, some researchers believe that it will be important to engineer systems in which all the components of a functioning pancreatic islet are allowed to develop.
Recently Ron McKay and his colleagues described a series of experiments in which they induced mouse embryonic cells to differentiate into insulin-secreting structures that resembled pancreatic islets . McKay and his colleagues started with embryonic stem cells and let them form embryoid bodies—an aggregate of cells containing all three embryonic germ layers. They then selected a population of cells from the embryoid bodies that expressed the neural marker nestin (see Appendix B. Mouse Embryonic Stem Cells). Using a sophisticated five-stage culturing technique, the researchers were able to induce the cells to form islet-like clusters that resembled those found in native pancreatic islets. The cells responded to normal glucose concentrations by secreting insulin, although insulin amounts were lower than those secreted by normal islet cells (see Figure 7.2. Development of Insulin-Secreting Pancreatic-Like Cells From Mouse Embryonic Stem Cells). When the cells were injected into diabetic mice, they survived, although they did not reverse the symptoms of diabetes.
According to McKay, this system is unique in that the embryonic cells form a functioning pancreatic islet, complete with all the major cell types. The cells assemble into islet-like structures that contain another layer, which contains neurons and is similar to intact islets from the pancreas . Several research groups are trying to apply McKay's results with mice to induce human embryonic stem cells to differentiate into insulin-producing islets.
Recent research has also provided more evidence that human embryonic cells can develop into cells that can and do produce insulin. Last year, Melton, Nissim Benvinisty of the Hebrew University in Jerusalem, and Josef Itskovitz-Eldor of the Technion in Haifa, Israel, reported that human embryonic stem cells could be manipulated in culture to express the PDX-1 gene, a gene that controls insulin transcription . In these experiments, researchers cultured human embryonic stem cells and allowed them to spontaneously form embryoid bodies (clumps of embryonic stem cells composed of many types of cells from all three germ layers). The embryoid bodies were then treated with various growth factors, including nerve growth factor. The researchers found that both untreated embryoid bodies and those treated with nerve growth factor expressed PDX-1. Embryonic stem cells prior to formation of the aggregated embryoid bodies did not express PDX-1. Because expression of the PDX-1 gene is associated with the formation of beta islet cells, these results suggest that beta islet cells may be one of the cell types that spontaneously differentiate in the embryoid bodies. The researchers now think that nerve growth factor may be one of the key signals for inducing the differentiation of beta islet cells and can be exploited to direct differentiation in the laboratory. Complementing these findings is work done by Jon Odorico of the University of Wisconsin in Madison using human embryonic cells of the same source. In preliminary findings, he has shown that human embryonic stem cells can differentiate and express the insulin gene .
More recently, Itskovitz-Eldor and his Technion colleagues further characterized insulin-producing cells in embryoid bodies . The researchers found that embryonic stem cells that were allowed to spontaneously form embryoid bodies contained a significant percentage of cells that express insulin. Based on the binding of antibodies to the insulin protein, Itskovitz-Eldor estimates that 1 to 3 percent of the cells in embryoid bodies are insulin-producing beta-islet cells. The researchers also found that cells in the embryoid bodies express glut-2 and islet-specific glucokinase, genes important for beta cell function and insulin secretion. Although the researchers did not measure a time-dependent response to glucose, they did find that cells cultured in the presence of glucose secrete insulin into the culture medium. The researchers concluded that embryoid bodies contain a subset of cells that appear to function as beta cells and that the refining of culture conditions may soon yield a viable method for inducing the differentiation of beta cells and, possibly, pancreatic islets.
Taken together, these results indicate that the development of a human embryonic stem cell system that can be coaxed into differentiating into functioning insulin-producing islets may soon be possible.
Future Directions
Ultimately, type 1 diabetes may prove to be especially difficult to cure, because the cells are destroyed when the body's own immune system attacks and destroys them. This autoimmunity must be overcome if researchers hope to use transplanted cells to replace the damaged ones. Many researchers believe that at least initially, immunosuppressive therapy similar to that used in the Edmonton protocol will be beneficial. A potential advantage of embryonic cells is that, in theory, they could be engineered to express the appropriate genes that would allow them to escape or reduce detection by the immune system. Others have suggested that a technology should be developed to encapsulate or embed islet cells derived from islet stem or progenitor cells in a material that would allow small molecules such as insulin to pass through freely, but would not allow interactions between the islet cells and cells of the immune system. Such encapsulated cells could secrete insulin into the blood stream, but remain inaccessible to the immune system.
Before any cell-based therapy to treat diabetes makes it to the clinic, many safety issues must be addressed (see Chapter 10. Assessing Human Stem Cell Safety). A major consideration is whether any precursor or stem-like cells transplanted into the body might revert to a more pluripotent state and induce the formation of tumors. These risks would seemingly be lessened if fully differentiated cells are used in transplantation.
But before any kind of human islet-precursor cells can be used therapeutically, a renewable source of human stem cells must be developed. Although many progenitor cells have been identified in adult tissue, few of these cells can be cultured for multiple generations. Embryonic stem cells show the greatest promise for generating cell lines that will be free of contaminants and that can self renew. However, most researchers agree that until a therapeutically useful source of human islet cells is developed, all avenues of research should be exhaustively investigated, including both adult and embryonic sources of tissue.
Page citation: 7. Stem Cells and Diabetes . In Stem Cell Information [World Wide Web site]. Bethesda, MD: National Institutes of Health, U.S. Department of Health and Human Services, 2006 [cited Monday, December 15, 2008] Available at <http://stemcells.nih.gov/info/scireport/chapter7>
