The promise of unprecedented benefits from stem cell therapy has excited the hopes of millions of patients with neurodegenerative diseases. Stem cells can be substituted for or programmed to replace damaged cells in the brain. In this way, they might be able to restore some of the functions that have been lost due to cell injury in conditions like multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Parkinson’s disease (PD), Alzheimer’s disease, and Huntington’s disease. Yet the journey toward making this treatment a clinical reality has been frustrating. Many patients continue to wonder why there hasn’t been more progress, since the positive aspects seem so obvious.

In part, progress has been delayed because questions about sources of stem cells have sparked heated political and ethical debates. Before the vision of stem cell therapy can become a reality, policy-makers and researchers alike need to agree on the best sources of such cells and exactly how to use them to improve patients’ lives.

Prior to the development of stem cell therapy, there was extensive experimentation, both animal and human, with fetal tissue transplantation for neurodegenerative diseases. The source of this tissue was aborted fetuses, and the tissue was used in research until 1988, when a moratorium on federal funding of research using fetal tissue was put in place by the Reagan administration after the National Institutes of Health (NIH), an agency that is part of the US Department of Health and Human Services that funds biomedical research, received a request to fund research that would involve transplanting fetal tissue into the brains of people with PD. The moratorium continued until 1993, when it was reversed by the Clinton administration, and later that year, Congress passed the National Institutes of Health Revitalization Act, allowing fetal tissue, including stem cells derived from human embryos, to be used in research and transplantation under certain conditions. These include strict anonymity for the donor, to ensure separation of the donation from the decision to terminate a pregnancy.

In 1994, an NIH panel provided recommendations on embryonic research, which included the recommendation that embryos created solely for research purposes should be used, based on the conclusion that this would not encourage abortions. The Clinton administration, however, banned federal funding of research that used such embryos but allowed federal funding of research on embryos that were left over from in vitro fertilization treatments. Congress then passed the Dickey Amendment (named so after Congressman Jay Dickey, who introduced the amendment) in 1995, which prohibits any federal funding of research that would involve the destruction of an embryo, regardless of the source. This amendment is still in effect.

The ban on federal funding, however, does not prevent research that uses embryos from being conducted. Such research can be conducted if it is funded by private sources. Indeed, because of privately funded research, the first human embryonic stem cell lines were created in 1998 by researchers at the University of Wisconsin and Johns Hopkins University, proving that stem cells taken from a human embryo could then be grown in a laboratory setting. The importance of the achievement, especially because of the potential it created for stem cells to be used in new treatments for many diseases and conditions, was quickly heralded by scientists, and President Bill Clinton allowed funding of research on embryonic stem cells that had been grown in a lab and were originally obtained by means supported by private funds (and, therefore, are not prohibited under the Dickey Amendment).

Three years later, President George W. Bush limited federal funding of embryonic stem cell research to a few cell lines that had existed prior to August 9, 2001, the date he announced this limitation. He later vetoed bills passed by Congress that would have allowed an expansion of the number of embryonic stem cell lines that could be used for research. The Bush administration did, however, authorize research into stem cell therapy using adult stem cells from bone marrow and stem cells from umbilical cord blood, which may also hold promise in treating several diseases and do not come from embryos.