There are also many legal and social questions that must be addressed before stem cell-based therapies become clinically available. Legal issues that will affect stem cell applications include how to address intellectual property concerns and how to apply and enforce diverse and sometimes conflicting state and national laws. Social issues include concerns about the destruction of embryos, the distribution of the benefits of the research, and the protection of both physical and privacy interests of egg and sperm donors and clinical research subjects. WHY STEM CELL RESEARCH IS BEING PURSUED 15 Parkinson’s disease is caused by the loss of a single type of nerve cell. These brain scans show the difference between a normal brain (left) and the brain of a Parkinson’s patient (right). Courtesy of Dr. David A. Rottenberg, Professor of Neurology and Radiology, University of Minnesota. 1956 First successful bone marrow transplant 1981 Embryonic stem cells are isolated from mouse blastocysts 1988 Hematopoietic (blood) stem cells from adult mice are purified and characterized 1992 Stem cells are identified in the adult human brain 1998 The first human embryonic stem cells are isolated Because Parkinson’s disease results from the loss of one specific type of nerve cell, stem cells offer a very tangible possibility for treatment. Researchers have recently learned how to differentiate embryonic stem cells into the specific type of brain cell that is lost in Parkinson’s disease. They have also successfully transplanted adult nerve stem cells into rat brains. When this technique is proven to be effective and safe, transplantation of stem cells into the brains of patients may one day allow doctors to reverse the burden of Parkinson’s disease and restore control of movement. Another strategy currently under study is the addition of chemicals or growth factors that aim to induce the patient’s own stem cells to repair the damaged nerves without needing to grow and transplant stem cells. Possible Fix for Diabetes? In people who suffer from type I diabetes, the beta cells of the pancreas that normally produce insulin are destroyed by the patient’s overactive immune system. Without insulin, the cells of the body cannot take up glucose and they starve. Patients with type I diabetes 16 WHY STEM CELL RESEARCH IS BEING PURSUED STEM CELL TIMELINE WHY STEM CELL RESEARCH IS BEING PURSUED require insulin injections several times a day for their entire lives. The only current cure is a pancreatic transplant from a recently deceased donor, but the demand for transplants far outweighs the supply. While adult stem cells have not yet been found in the pancreas, scientists have made progress transforming embryonic stem cells into insulin-producing cells. Combining beta-cell transplants with methods to “fix” the patient’s immune system—including chemotherapy to destroy malfunctioning immunesystem cells and blood transplants to replenish healthy white blood cells—could offer great hope for the many Americans suffering with type I diabetes. Cancer: Getting to the Root of the Problem Why are some cancers so hard to eliminate, even after many rounds of chemotherapy? The answer may lie in a few abnormal stem cells. Cancerous stem cells were first identified in 1997 when a research group from the University of Toronto transferred a few blood stem cells from human leukemia patients into mice and watched leukemia develop in the mice. Stem celllike cells have also recently been found in breast and brain tumors. Like normal stem cells, tumor stem cells exist in very low numbers, but they can replicate and give rise to a multitude of cells. Unlike normal stem cells, however, cancerous stem cells lack the controls that tell them when to stop dividing. Traditional chemotherapy kills off the majority of the tumor cells, but if any of the cancerous stem cells survive the treatment, the cancer may return. Research into the differences in gene expression between normal and tumor stem cells may lead to treatments where the root of the problem—the cancer stem cell—is targeted. Stem cell research continues to advance. Preliminary results from recent studies support the promise of stem cells for conducting basic research that may eventually lead to medical achievements. For example, in 2005, human embryonic stem cells were shown to differentiate into active functioning nerve cells when placed in mouse brains. Scientists also made significant progess in deriving pancreatic cells from adult stem cells. In 2006, scientists were able to derive embryonic stem cells from the morula of a mouse, and embryonic stem cells were first grown without animal products in the culture. Results of these and other recent experiments must be replicated and consistently demonstrated by other researchers before they become generally accepted by the scientific community. 2001 Mouse embryonic stem cells are created by nuclear transfer 2002 Pancreatic cells derived from mouse embryonic stem cells cure diabetes in mice 2004 The type of nerve cell lost in Parkinson’s disease is produced from human embryonic stem cells 17 Stem cells offer opportunities for scientific advances that go far beyond regenerative medicine. They offer a window for addressing many of biology’s most fundamental questions. Watching embryonic stem cells give rise to