What is a stem cell?
A stem cell is essentially a “blank” [unspecialized] cell, capable of becoming another more differentiated cell type in the body, such as a skin cell, a muscle cell, or a nerve cell.
Why are stem cells important?
Stem cells can be used to replace or heal damaged tissues or cells in the body.
What are the two broad classes of stem cells?
The two broad classes of stem cells are embryonic type and adult type. The embryonic type are: embryonic stem cells and embryonic germ cells. The adult type are: umbilical cord stem cells, placental stem cells and adult stem cells.
Where do adult stem cells come from?
• Umbilical cords, placentas and amniotic fluid – Adult type stem cells can be derived from various pregnancy-related tissues.
• Adult Tissues – In adults, stem cells are present within various tissues and organ systems. These include the bone marrow, liver, epidermis, retina, skeletal muscle, intestine, brain, dental pulp, and elsewhere. Even fat obtained from liposuction has been shown to contain significant numbers of adult type stem cells.
• Cadavers – Neural stem cells have been removed from specific areas in post-mortem human brains as late as 20 hours following death.
How do embryonic and adult stem cells compare?
Embryonic stem cell advantages:
1.Flexible – appear to have the potential to make any cell.
2. “Immortal” – one embryonic stem cell line can potentially provide an endless supply of cells with defined characteristics.
3.Availability – embryos from in vitro fertilization clinics.
Embryonic stem cell disadvantages:
1.Destruction of human life.
2.Difficult to differentiate uniformly and homogeneously into a target tissue.
3.Immunogenic – embryonic stem cells from a random embryo donor are likely to be rejected after transplant.
4.Tumorigenic – capable of forming tumors or promoting tumor formation.
Adult stem cell advantages:
1.Special adult type stem cells from bone marrow and from umbilical cords have been isolated recently which appear to be as flexible as the embryonic type.
2.Already somewhat specialized – inducement may be simpler.
3.Not immunogenic – recipients who receive the products of their own stem cells will not experience immune rejection.
4.Relative ease of procurement – some adult stem cells are easy to harvest (skin, muscle, marrow, fat), while others may be more difficult to obtain (brain stem cells). Umbilical and placental stem cells are likely to be readily available.
5.Non-tumorigenic – tend not to form tumors.
6.No harm done to donor.
Adult stem cell disadvantages:
1.Limited quantity – can sometimes be difficult to obtain in large numbers.
2.Finite – may not live as long as embryonic stem cells in culture.
3.Less flexible (with the exception of #1 under “Adult stem cell advantages”) – may be more difficult to reprogram to form other tissue types.
Why are adult stem cells preferable to embryonic stem cells?
Adult stem cells are a “natural” solution. They naturally exist in our bodies, and they provide a natural repair mechanism for many tissues of our bodies. They belong in the microenvironment of an adult body, while embryonic stem cells belong in the microenvironment of the early embryo, not in an adult body where they tend to cause tumors and immune system reactions. Most importantly, adult stem cells have already been successfully used in human therapies for many years. As of the date of this publication, NO therapies in humans have been successfully carried out using embryonic stem cells. New therapies using adult stem cells, on the other hand, are being developed all the time. There are many examples of success stories using adult stem cells.
Presented here with permission of Reverend Tadeusz Pacholczyk, PhD of the National Catholic Bioethics Center
Read the Pennsylvania Bishops’ statement on stem cell research
