Under the Microscope: Readers will be well familiar with the debate on human embryonic stem-cell research, writes Dr William Reville.
Whether it is ethical to use such cells for research hinges on the question of how much respect human embryos deserve. In my opinion they deserve enough respect to protect them from being killed in order to harvest stem cells. The potential of stem cells to alleviate human misery is great, but their potential is probably realisable through research on adult stem cells, whose use poses no ethical problems.
The unit of biological life is the cell. Most of the trillions of our body cells are differentiated tissue cells, e.g. muscle, liver, kidney, and so on, each performing functions unique to the tissue to which they belong. Stem cells, on the other hand, are undifferentiated cells that can give rise to specialised cells. There are three main sources of stem cells: a) embryonic stem cells (ES) derived from five- to seven-day-old embryos called blastocysts. b) stem cells isolated from aborted fetuses (FS). c) adult stem cells (AS) derived from adult tissue.
Apparently all adult tissues contain AScells. The function of these cells is to turn into differentiated cells peculiar to the particular tissue in the event of severe damage to the tissue, thereby repairing the damage.
Human development starts at conception when the father's sperm cell unites with the mother's egg cell to form a fertilised egg. Every cell in your adult body is descended through an unbroken line of cell divisions from that fertilised egg. The genetic information in every adult cell is a copy of the information in the fertilised egg. The term embryo applies to the developing organism from fertilisation until the end of the eight week of gestation, when it becomes known as a fetus.
The embryos from which ES cells are derived are typically four or five days old when the fertilised egg has undergone several cell divisions and has developed into a sphere (the blastocyst) of about 150 cells. The act of harvesting ES from the blastocyst kills the embryo.
Research on ES in the US and Europe refers to stem cells derived from "spare" embryos generated as by-products of in-vitro fertilisation (IVF) and held in frozen storage. Stem cells have the ability to continue to divide indefinitely and, so, stem cell lines that can be grown indefinitely in the laboratory have been prepared from ES harvested from spare IVF embryos.
Stem cells have uses in different areas of medical research. Studying stem cells will allow us to understand how they change into the large variety of specialised cells that constitute the great bulk of the body. Some grave medical problems, such as cancer and birth defects, are caused by problems that arise in this development process.
Secondly, if we knew how to trigger stem-cell development into a tissue of choice it should be possible to treat many diseases and problems, including Alzheimer's and Parkinson's disease, heart disease, diabetes, osteoarthritis, spinal cord injury, burns and strokes, by replacing the diseased/damaged cells with stem cells. Donated organs and tissues are used today to replace diseased or damaged tissues, but there is a severe shortage of organs available for transplantation.
Majority scientific opinion is that the ranking of potential usefulness of stem cells in human medicine is: ES are better than FS, which are better than AS, although some scientists believe that AS have the greatest potential. But, we are talking at this stage only of potential. Much research must be done before we will know for sure how useful stem cells can be in human medicine and it is unlikely that major advances will occur in the near future. The only type of stem cell commonly used in human therapy now is the blood-forming stem cell in bone marrow. Bone marrow transplants have been used for more than 40 years to treat leukaemia, lymphoma and some inherited blood disorders.
The argument is made by those in favour of using ES that "spare" embryos from IVF are destined to die anyway, so why not use them to alleviate human misery? This is a persuasive argument for those who do not believe that the embryo has the human right to its own life, but it cannot convince those who believe that the embryo has this right.
My personal position is as follows. The embryo is living, human and contains full human potential. The fertilised egg contains the full genetic information necessary to allow it to develop, under appropriate natural environmental conditions, into a unique human adult. Is the embryo fully human? In my opinion, yes. The embryo is a stage in human development. Some of the other stages are - fetus, baby, child, adult, old person. It is fully at its own stage of human development and, in that sense, is fully human.
Does the embryo have full human capacity? It has the full human capacity of its stage of development, just as the fetus, baby, child, adult or elderly person have the full human capacities of their stages. Does the embryo have full human rights? It has the rights appropriate to its developmental stage. The most basic human right is the right to life, without which other rights are meaningless. The embryo is entitled, at a minimum, to be given every chance to live when this entitlement does not threaten the life of the mother. The embryo is entitled not to be deliberately killed.
William Reville is associate professor of biochemistry and director of microscopy at UCC