Most of the cells in our bodies have a short life span and a specific job to do. Stem cells, found in many organs from skin to bone marrow, are different. The “ancestors” of ordinary cells, they can replenish themselves indefinitely. Given the right biochemical signals, these cells can divide and transform themselves into a range of different cell types as and when the need arises.
Such versatility means that stem cells have the potential to regenerate damaged organ tissues and provide amazing new treatments for a range of now devastating diseases. Indeed, stem cells may perhaps make it possible for humans to “grow new organs” to replace diseased ones, thereby providing for the possibility of new forms of cell-based therapies.
On the basis of research with comparable cells from mice, scientists envision that stem cells could be used to replace bone marrow in patients suffering from cancer, produce pancreatic cells for alleviating diabetes, or neuronal cells for treating Parkinson's disease, Alzheimer's disease, and various brain and spinal cord disorders.
Stem cells used in this research are best derived from very early stage embryos created by in vitro fertilization, but this leads to ethical dilemmas. The idea that human embryos could be created with the express purpose of “harvesting” them for medical purposes incites fear of a “brave new world” revisited. Even if that extreme is unlikely, the possibility of abuse of any sort generates strong opposition.
Most of those who oppose stem cell research do not question its scientific and medical value, but object to the use of human embryos. These critics, especially in Germany, where stem cell research evokes nightmares of Nazi era eugenics, argue that research with stem cells derived from embryos is unnecessary because multi-potential stem cells occur naturally in adult tissues as well. While guardedly encouraged by recent reports of the remarkable plasticity of stem cells obtained from adult tissues, scientists know little about their potential for prolonged maintenance outside the body, their capacity for differentiation, and whether they can be obtained in the quantities needed to explore their utility for clinical use.
If embryonic stem cell research were to be halted based on that hope, it is possible that years may pass before scientists could determine if adult-derived stem cells are equivalent to embryonic stem cells in their potential to treat disease. We cannot afford the luxury of proceeding with these promising technologies sequentially. We owe it to those who are in need to explore all possible avenues that could lead to medical cures. While research on adult-derived stem cells should be pursued aggressively, it should not be at the expense of an aggressive program to explore the full potential of stem cells for use in human therapies.
Another restriction has been recently adopted in the United States, where the issue was explored by the National Biomedical Ethics Advisory Commission in extensive hearings and discussions with ethicists, religious leaders, scientists and physicians. They concluded that it is ethically permissible to prepare stem cell lines from frozen embryos, but only from those obtained in the course of in vitro fertilization procedures and deemed by donors and their physician to be in excess of clinical requirements. (More eggs are usually fertilized than are actually implanted in women who want to become pregnant.)
Following these discussions, the US National Institute of Health (NIH) promulgated guidelines that allow the use of government funds for stem-cell research but, in their present form, prohibit federally-funded investigators from creating new stem cell lines. That restriction requires that stem cell lines must be obtained only from privately-funded or commercial sources that follow the protocols mandated by the guidelines.
I believe that restricting the use of government funds for the creation of stem cells, although politically prudent, imposes substantial scientific handicaps. We know that a variety of poorly understood factors cause embryonic stem cells to lose their capacity to differentiate into all possible cell types. This loss of capacity to differentiate may be caused by the particular mode in which the stem cells are derived, the conditions surrounding their growth, and other variables of handling.
Enabling individual government-funded investigators to derive stem cell lines using a variety of conditions in their own laboratories, as permitted recently in Britain and France, is the best route to determining what conditions are critical for generating cells for specific therapeutic purposes. Embryonic stem cells prepared in a scientist’s own laboratory are most likely to have been derived, stored and maintained in ways that maximize their potency for particular uses. Cells obtained from commercial sources are likely to be of unknown genetic background and history and therefore be less useful for some important studies.
While various remote contingencies are sometimes invoked, the fundamental ethical choice posed by stem cell research is more circumscribed: whether human embryos, which will ultimately be legally discarded, should be used to create potentially life-saving therapies for those in need. Those who oppose abortion irrespective of its purpose argue that sacrificing a human embryo to obtain stem cells is akin to abortion and therefore immoral. But harvesting stem cells from very early stage embryos that will in the end be discarded is, in my view, ethically distinct from abortion. For we must also consider the moral consequences of failing to pursue this line of research if it has the potential to save and improve human lives. What greater morality exists than doing all we can do to help individuals whose lives are blighted by disease and disability?