In view of the current controversies surrounding stem cell research, it would be appropriate to try to present some information regarding stem cells. I will try to answer some common questions regarding embryonic stem cell research as well as other alternatives such as adult stem cells and induced pluripotent stem cells.
1) What are stem cells?
Stem cells are undifferentiated cells(ie. a cell that has not yet specialized into a particular type of cell like a liver cell or muscle cell or brain cell). They have the remarkable potential to develop into many different cell types in the body during early life and growth. In addition, in many tissues they serve as a sort of internal repair system, dividing essentially without limit to replenish other cells. A stem cell can divide into daughter cells identical with itself or it can become another type of cell with a more specialized function, such as a muscle cell, a red blood cell, or a brain cell.
2) Why are stem cells unique?
Stem cells are distinguished from other cell types by two important characteristics. First, they are unspecialized cells capable of renewing themselves through cell division, sometimes after long periods of inactivity. Second, under certain physiologic or experimental conditions, they can be induced to become tissue- or organ-specific cells with special functions. In some organs, such as the gut and bone marrow, stem cells regularly divide to repair and replace worn out or damaged tissues. In other organs, however, such as the pancreas and the heart, stem cells only divide under special conditions.
3) What is a stem cell’s potency?
Potency refers to its capacity to differentiate into particular type of human cells.
a) Totipotent stem cells: Totipotent stem cells can differentiate into every tissue in the human body including the extraembryonic support tissues like placenta, umbilical cord and amniotic sac, Such cells can construct a complete, viable, organism. A single celled embryo(also called a zygote) is totipotent These cells are produced from the fusion of an egg and sperm cell. Cells produced by the first few divisions of the fertilized egg are also totipotent.
b) Pluripotent stem cells: Pluripotent stem cells are the descendants of totipotent cells and can differentiate into nearly all cells, i.e. cells derived from any of the three germ layers but not the extra embryonic support tissues. Embryonic stem cells are pluripotent.
c) Multipotent stem cells: Multipotent stem cells can differentiate into a number of cells, but only those of a closely related family of cells e.g. blood cells.
d) Oligopotent stem cells: Oligopotent stem cells can differentiate into only a few cells, such as lymphoid or myeloid stem cells.
e) Unipotent stem cells: Unipotent cells can produce only one cell type, their own, but have the property of self-renewal which distinguishes them from non-stem cells (e.g. muscle stem cells).
4) What is the difference between embryonic stem cells and adult stem cells?
Embryonic stem cells are derived from the inner cell mass of an embryo usually during the blastocyst stage (around 5 days old). In the process of harvesting these cells, the embryo will be destroyed. Embryonic stem cells are undifferentiated, self renewing, pluripotent cells.
Adult stem cells too have the ability of self proliferation and differentiation. They are derived from adults cells but not from embryo. They are also found in newborn tissues e.g. the cord blood of new born babies. Although some adult stem cells have been found with the capacity for pluripotency, most are only capable of differentiating into the tissue type or related cell type of the tissue they were found.
5)What are the ethical concerns surrounding stem cell research?
The objective of stem cell research is indeed noble. It has the potential ability to treat a host of diseases such as Alzeimers / Parkinsons disease, spinal cord regeneration stroke, diabetes, heart failure, liver failure, inflammatory bowel disease, short bowel syndrome, GI motility disorders.
It is currently being used in haemopoietic stem cell replacement.
The nobility of such objectives should not justify the means. Is it justifiable to kill embryos to achieve such objectives? Those who judge human embryos to be human beings think that embryonic stem cell research is wrong. There are those who believe that embryos are “pre human entities” and that such research are justified. The Catholic church does not condone embryonic stem cell research. The Vatican and the United States Conference of Catholic Bishops have consistently supported stem cell research that does not exploit or destroy embryos. (Please refer to the following references: i)Pontifical Academy for Life, Declaration on the Production and the Scientific and Therapeutic Use of Human Embryonic Stem Cells (August 25, 2000); Catholic Online, "American Bishops Reaffirm Church Support for Adult Stem-Cell Research," www.catholic.org, June 26, 2006, www.catholic.org/national/national_story.php?id=20275. ii)Congregation for the Doctrine of the Faith, Instruction Dignitas Personae (On Certain Bioethical Questions) (2008), nos. 24, 31, 32.)
Adult stem cell research avoids this ethical problem by avoiding research on embryos altogether. Adult stem cell research has made remarkable progress in its ability to treat serious diseases. In contrast, embryonic stem cell research despite all the millions of dollars spent have produce nothing but failures.
6) What are induced pluripotent stem cells(IPSC)?
This latest research which was pioneered by researchers in late 2007 shows great promise as it avoids the ethical controversy surrounding embryonic stem cell altogether.
Here an adult somatic cells(usually a fibroblast) is induced to become like an embryonic stem cell through a process whereby certain genes are inserted into the somatic cell via the help of viral vectors. The resulting stem cell which is pluripotent will have similar properties to embryonic stem cells. These cells can then be allowed to develop into tissues to be used for transplantation and other therapeutic uses.
Source: Catholic Doctors Association of Malaysia 20 May 2009