D. Blicq dblicq@rrc.mb.ca
Nov. 2006 (update 01/04/2010) DIRECTORY I BIO I NOTICE BOARD
Embryonic stem cells offer an enormous potential for medical sciences - the remarkable potential for cellular, tissue and perhaps even organ regeneration. At the same time, any research or medical therapies involving fetal / embryonic cells is certain to raise some level of
controversy.
The technical aspects begin with the fertilization of an oocyte / egg. Once a sperm has fertilized an egg it creates a zygote with the potential to develop into an embryo. During the first hours following fertilization, any one of these cells has unlimited division and differentiation capacity.
Embryonic stem cells are derived from cells of the inner cell mass of the blastocyst which forms about four to five days following fertilization. The blastocyst is an early (less that five days) embryonic cell mass which typically has less than 160 cells in total. Embryonic stem cells have two core characteristics which set them apart from other related cells:
- an unlimited capacity to self-replicate
- the capability (potency) of differentiating into any one of the more than two hundred identified tissue types found in the human body.
http://www.csa.com/discoveryguides/stemcell/images/pluri.jpg
A core distinction between embryonic stem cells and somatic / adult stem cells is found not only in their source, but also in their overall capacity for differentiation. Many of the adult stem cells may be more accurately described as progenitor cells, since they may have some limitations on self replication and may be pluripotent or unipotent (forming several different cells types or a single differentiated cell). A more detailed schematic diagram of the relationship between the different types of stem cell is presented below. At the apex of the chart is the totipotent embryonic stem cell.
http://www.molbio.princeton.edu/courses/mb427/2001/projects/09/differentiationtutorial.htm
A great deal of research effort is committed to examining techniques for growing / culturing embryonic stem cells in the laboratory (in vitro). This technique could be employed to establish a library of totipotent stem cells with unlimited applications in medical therapies. In addition, it may provide a source of totipotent cells without the controversy of fetal tissues being directly involved.
Currently there are four main sources for embryonic stem cells: existing stem cell lines (post 2001 in the US), aborted or miscarried embryos, unused in-vitro fertilized embryos, and cloned embryos. In the US, each of these sources may have significantly different legislative restrictions depending on the state. The use embryonic stem cells (regardless of source) is an issue that has generated significant controversy at all levels.
In the Fall of 2004, voters in California voters approved a $3 billion fund to support embryonic stem cell research. New Jersey, Wisconsin and Massachusetts legislators are also following a similar strategy of localized support for stem cell research and development. In contrast, embryonic stem cell research is prohibited in Arkansas, Iowa, North and South Dakota and Michigan. The US federal government is currently adhering to the following policy:
"No federal funds will be used for:
(1) the derivation or use of stem cell lines derived from newly destroyed embryos;
(2) the creation of any human embryos for research purposes; or
(3) the cloning of human embryos for any purpose."Interestingly, public opinion in the US is slowing changing as indicated by a CNN/USA Today/Gallup Poll (May 20-22, 2005. 1,006 adults. MoE ± 3) which asked:
"How closely have you followed the debate about government funding of stem cell research: very closely, somewhat closely, not too closely, or not closely at all?"
|
Very Closely |
Somewhat Closely |
Not Too Closely |
Not At All | Unsure | |
| % | % | % | % | % | |
|
May 2005 |
12 | 46 | 27 | 15 | - |
|
August 2001 |
18 | 37 | 22 | 23 | - |
Additional information on the issues and positions on embryonic stem research and therapeutics is found in the section "Controversy".
Umbilical Cord Blood
The use of umbilical cord blood (post
delivery) as a source of stem cells has allay
ed the concerns of some critics of the embryonic stem cell process but for some still remains a
controversial procedure.
Currently, more than 45 disorders can be treated
with with therapies that involve the use of stem cells from umbilical
cord blood. It is interesting to note that a number of independent
companies now offer to "bank" a baby's umbilical cord blood as a
potential source of stem cells which could one day combat currently
untreatable disorders.
Once a consistent source of pluripotent stem cells is achieved through alternative means, much of the controversy regarding embryonic sources may well dissipate. Some groups even offer "blood banking" of umbilical cord cells in the event of future disease that could be treated by future stem cell techniques.
For more detailed information on the ethics and issues involving stem cells refer to the section "Controversy" above.
