April 02, 2009
The stem cell issue-1: The science
The decision by the Obama administration to reverse the Bush-era policy of banning the use of federal funds for stem cell research has created some controversy. The earlier policy had led to some frustration in the scientific community.
Bush's policy was intended to be a compromise: it banned the use of federal funds for the creation of new embryonic stem-cell lines while allowing scientists to study 21 lines that had already been created. But researchers say those lines aren't diverse enough and they have been eager to study hundreds of other lines, some of which contain specific genetic mutations for diseases like Parkinson's. There have been practical challenges as well. The restrictions forced scientists to use different lab equipment for privately funded and government-funded research; some even built entirely separate lab space. One of the most disconcerting aspects, researchers say, has been the negative effect on collaboration, a hallmark of the scientific process. Researchers supported by private money haven't been able to team up with scientists funded by the government, potentially holding back new insights and advances.
Stem cells are those that have three properties. Unlike most cells like muscle or blood or nerve cells, 91) they are capable of replicating themselves for a long period (making them a valuable source to regenerate the body by replacing cells that die), (2) they are unspecialized, and (3) when they reproduce they can produce either more stem cells or become specialized cells like muscle or nerve or bone (a process known as differentiation). The National Institutes of health has an informative FAQ page on this topic.
The two main kinds of stem cells are the embryonic ones and the non-embryonic ones. The embryonic ones can proliferate for a year or more in the laboratory without differentiating while the non-embryonic ones cannot do so for very long, but the reasons for this difference are not known as yet. The embryonic stem cells are capable of eventually differentiating into any type of specialized cell, and are called pluripotent. Such pluripotent cells are valuable because they can be used to repair tissue in any part of the body as needed. But eventually they need to differentiate into specialized cells in order to perform the functions that those specialized cells carry out in the body. The process by which stem cells differentiate is still not fully understood, but part of it involves interaction with the external environment in which the stem cell finds itself.
Adult stem cells are one form of non-embryonic cells and are found amongst the differentiated cells that make up the tissues of the body, such as the brain and heart and bone marrow, and they are the cells that are used to maintain and repair those tissues by differentiating when needed to produce new tissues. Some adult stem cells seem to have the capacity to differentiate into more than one type of specialized cell though the range is limited, unlike in the case of embryonic stem cells. Such cells are called multipotent.
For example, some multipotent stem cells found in the bone marrow can generate bone, cartilage, fat, and connective tissue. Stem cells taken from umbilical cord blood and the placenta seem to also have multipotent properties and thus in the future it may become routine that a stock of umbilical or placental cells will be taken after every birth and preserved for possible future use. Adult stem cells have some uses but working with them is much more difficult since they are harder to obtain and are less flexible.
To understand the ethical issues involved in using embryonic stem cells, one should be aware that creating embryonic stem cell lines for research requires extraction of cells from the blastocyst. This is the stage reached by a fertilized egg after about three to five days when, after repeated cell division and duplication, there are about 70-100 identical cells in the shape of a hollow ball containing an inner clump of cells. The inner clump becomes the embryo and the outer hollow ball becomes the placenta. When this occurs in the uterus, this stage is reached before this collection of cells gets implanted in the uterus wall. Sometimes implantation does not occur, in which case the pregnancy is spontaneously terminated.
This video explains what stem cells are and how they work.
The embryos from which embryonic stem cells are taken are produced during treatment for infertility when a woman's egg is taken from her body and fertilized and grown to blastocyst stage in a culture outside the woman's body. In the very early days after the egg is fertilized and the cell starts splitting and reproducing itself, all the cells are identical. Embryonic stem cells are obtained from that inner clump of cells and thus the blastocyst has to be destroyed in the process. The cells from a single blastocyst can be used to generate millions of embryonic stem cells that can be divided among researchers, and these are the stem cell 'lines' that are referred to. The cells in a single line are all genetically identical.
While there are promising new ways of creating embryonic stem cells using adult skin cells (called induced pluripotent stem cells), they have their own ethical issues.
Since tissues created from a person's stem cells have the same genetic information as the host, the host body will not reject the implanted tissues as a foreign body, thus overcoming one of the biggest hurdles in organ transplants. While the possibility of growing tissues and entire organs for transplant purposes is often publicized as the biggest potential benefit of using stem cells, there are other more immediately realizable potential uses for embryonic stem cells.
One is that it enables the process by which cells differentiate into their specialized forms to be studied. Another is that by creating cells that have a particular disease, say Parkinson's or Lou Gehrig's, one can observe under a microscope even the earliest stages of the progression of the disease and thus hope to develop better treatments. Another use is to test the effects of drugs on cells before testing them on a real person. That would enable you to see if they are toxic to a particular individual, creating a level of personalized medicine that we do not currently have.
The potential benefits of embryonic stem cells in research are clear, even though it is very early days yet and there is still a long way to go before we can hope to even begin realizing those benefits. The key question is how to balance the ethical concerns involved in using such cells with the benefits.
This question will be examined in the next post.
POST SCRIPT: The Daily Show on stem cells
|The Daily Show With Jon Stewart||M - Th 11p / 10c|