Cloning stem cells - change on the horizon
Dr Ames Dhai
Research into stem cells from human embryos raises a number of ethical and
legal issues. On the one hand, the medical profession and the public grapple
with the promise that important knowledge could benefit society at large. On the
other hand, the moral complexities require consideration - not only the why and
how, but also whether there are compelling reasons to limit or prohibit research
in this field entirely.
The ethical debate - an overview
There have been mixed reactions to the prospect of cloning for biomedical
research. Supported by some for its medical promise, it is opposed by others who
view it as intentional exploitation and destruction of nascent human life
created specifically for research purposes. Human dignity would in this way be
undermined. Debated also is the issue of proceeding with research that is
considered fraught with moral uncertainty. Other anxieties: the possibility that
women (as donors of eggs) would be exploited; the slippery slope towards
reproductive cloning; and promises made too early creating false hope among sick
patients.
Chronic debilitating degenerative diseases including those of the brain
(Parkinson's and Alzheimer's Disease), pancreas (diabetes), liver (hepatitis),
joints (rheumatoid arthritis) heart, lungs and kidneys and spinal cord injuries
cause immense suffering to patients, their families and society. Embryonic stem
cell research may offer unique ways of investigating and possibly treating many
of these diseases.
Moreover, embryonic stem cells could benefit patients requiring transplants.
Organs and tissues created from nuclear transfer utilising recipient nuclei (for
example, a patient with kidney disease could grow his or her own replacement
organ) hypothetically would survive the expected normal immune rejection, in
which the patient's body rejects the new organ as a foreign object. The possible
medical gains of embryonic stem cell research are immense.
Cloning and the law
The laws governing genetic manipulation are - in South Africa, at any rate -
about to change. In South Africa, neither reproductive nor therapeutic cloning
is allowed but the National Health Bill is due to be passed before parliament
closes at the end of 2003, and many things will change when this bill becomes
law.
Embryo stem cell research and therapeutic cloning will not be legislated
against. Reproductive cloning remains off limits. Very strict regulatory
criteria will have to be fulfilled for therapeutic cloning, including
authorization by the Minister of Health for work in this field. Section 62(4)
affirms that the Minister may permit research on stem cells and zygotes that are
not more than 14 days old. Public participation in this process has been in
effect since August 2002 when the bill appeared in the Government Gazette and
there were advertisements in national print media soliciting presentations for
the discussions at the parliamentary portfolio committee of health.
The Medical Research Council in South Africa recommends that for the present,
fetal tissue from cadavers and embryos remaining after completion of infertility
treatments should be the only source of embryonic stem cells for the purposes of
research. But these recommendations are too restrictive and may stifle
scientific progress whose objective is to benefit patients with irreversible and
debilitating disease.
What are Stem Cells?
Stem cells are tissue precursor cells that have the ability to self-renew and
differentiate into more specific cell types. They are important because they can
replace dying, old or damaged cells. These cells are found in human embryos,
fetuses, children and adults, i.e. at all stages of development and in most
tissues but it is the embryonic cells which have raised the most controversy.
Early human embryos (5 - 6 day old blastocysts) have an outer cell layer from
which the placenta develops, and an inner cell mass, in the region of 200 cells,
which gives rise to the fetus. This inner cell mass is the source of embryonic
stem cells.
Deriving embryonic stem cells
We need to distinguish between two fundamental types of embryonic stem
cells. Totipotent stem cells are found in the 16-cell stage embryo. These
cells have the ability to form an entirely independent human being if placed
in the uterus. Because of the potential of totipotent cells and the resultant
ethical dilemmas, scientists have, in the main, avoided research on this type of
stem cells.
On the other hand, the inner cell mass of the late blastocyst stage of the
embryo comprise pluripotent stem cells which have a limited ability to give rise
to any type of specialised cell. Pluripotent stem cells are being considered for
therapeutic work, combating debilitating diseases and finding new drug
treatments for diseases. (In addition, in the adult, somatic stem cells are more
committed or multipotent. This means that their differentiation is restricted to
only one or a few tissue lineages. There is still much research being done on
these cells.)
Potential sources of stem cells are:
- fetal tissue that becomes available after an abortion
- excess embryos from assisted reproductive technologies such as commonly
used in fertility clinics
- embryos created through in vitro fertilization specifically for research
purpose, and
- embryos created asexually as a result of the transfer of a human somatic
cell nucleus to an egg with its own nucleus removed.
Other sources of stem cells are those from umbilical cord blood, and bone
marrow. In addition, neural stem cells, haematopoetic stem cells and mesenchymal
stem cells can be harvested from fetal blood and fetal tissue.
Cloning
Strictly speaking, "clone" means a precise genetic copy of a life
form. The proposed National Health Bill of the Republic of South Africa defines
therapeutic cloning as the manipulation of genetic material from either adult,
zygote or embryonic cells in order to alter the function of cells or tissues.
Cloning at a molecular level involves the copying of DNA fragments containing
genes and amplifying these in a host cell. The copying of somatic cells through
growing in culture results in cellular cloning. This type of cloning could be
used for the testing and production of new drugs. For example, if high
cholesterol is found to have a specific gene defect, we can with therapeutic
cloning allowed then clone the cell and test drugs on the defective gene.
What's your say? Send us your feedback.
Glossary
Stem cells: A cell that can replicate indefinitely and which can
differentiate into other cells; stem cells serve as a continuous source of new
cells. Specifically, this refers to the self-regenerating cells in bone marrow
and the testis.
Totipotent stem cells: Stem cells which are capable of forming every
type of body cell. Each totipotent cell could replicate and differentiate and
become a human being. All cells within the early embryo are totipotent up until
the 16 cell stage or so.
Pluripotent stem cells: Pluripotent stem cells can eventually
specialize in any bodily tissue, but they cannot themselves develop into a human
being.
Somatic Cells: Cells from the body that compose the tissues, organs,
and parts of that individual other than the germ (sex) cells. Each somatic cell
contains a full set of chromosomes, whereas sex cells only contain half.
Zygote: An egg cell that comes from fertilization. It contains the
complete set of chromosomes received from the union of the male (sperm) and
female (egg) sex cells. The zygote develops into the organisms adult body.
More information
1. The President's Council on Bioethics. Human Cloning and Human Dignity: An
Ethical Inquiry. Washington DC July 2002; 80-110. www.bioethics.gov
2. The Advisory Committee on Health Research. Genomics and World Health. World
Health Organisation Geneva 2002; 107-173.
3. Fisk NM, Braude P. Stem Cells. The Obstetrician and Gynaecologist 2001: 3
:211-212.
4. Holm S. Going to the Roots of the Stem Cell Controversy. Bioethics 2002;
16:493-507.
5. Lochner JdeV. The Ethics of Research on Stem Cells of Human Origion. SAMJ
2002; 8:54-57.
6. Office of News and Public Affairs, UW Madison. Stem Cell Pres Kit, 1998. http://www.news.wisc.edu/emediakit/fact.html
7. Varmus H. Statement of Harold Varmus, Director, National Institutes of
Health, before the Senate Appropriations Subcommittee on Labor, Health and Human
Services, Education and Related Agencies, 26 January, 1999. http://www.hhs.gov/progorg/asl/testify/t990126a.html
8. National Bioethics Advisory Commission. Ethical Issues in Human Stem Cell
Research - Executive Summary, September1999.
9. Campagnoli C, Fisk N, Overton T, Bennet P, Watts T, Roberts I. Circulating
haematopoetic progenitor cells in the first trimester fetal blood. Blood 2000:
95 : 1967-72.
10. Medical Research Council South Africa. Reproductive Biology and Genetic
Research. Guidelines on Ethics for Medical Research;2:36-50.
11. National Bioethics Advisory Commission. Cloning Human Beings - Report and
Recommendations of t he National Bioethics Advisory Commission, 1997.
12. The National Health Bill, Republic of South Africa. Government Gazette No.
23696 of 8 August 2002. [B 32- 2003]. Section 62
13. Solter D, Gearhart J. Putting stem cells to work. Science 1999: 283:
1468-70.
The Human Tissue Act No. 65 of 1983. Section 39A.
Public Understanding of Biotechnology website www.pub.ac.za
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