The benefits of stem cell research

Submitted by Anon on 12 January, 2005 - 5:59

Hardly a day goes by without news of research involving stem cells. It is also a subject of hot political debate: the Swiss recently voted 2 to 1 in favour of allowing it, while the US forbids the use of government money in some stem cell research.

Proponents include medical scientists and supporters of people with conditions such as spinal injury (such as the late Christopher Reeve) and Alzheimer’s disease (such as the family of Ronald Reagan).

Opponents range from the religious Right to some Green Parties (as in the Swiss referendum). To be precise, the political opposition is directed at embryonic stem cell research. So what’s the deal here? Les Hearn examines the issues

Most cells in the body are specialised for particular jobs, such as nerve, blood and muscle cells, and no longer divide. If they die or are damaged, they must be replaced, and that is the role of the stem cells. In adults, stem cells in the skin, gut and bone marrow continually divide, producing cells that replace dead skin, gut and blood cells.

In treating the disease leukaemia, the cancerous cells are destroyed, together with the stem cells needed for new blood. The latter can be replaced by a bone marrow transplant, effectively a stem cell transplant, from a compatible donor, something that has been possible for some 30 years.

Unfortunately, some tissues have few or no stem cells left in adulthood. These include heart muscle, pancreas, brain and spinal cord. Thus, people with heart failure, spinal injury, diabetes or Parkinson’s disease are unable to regenerate dead cells. This is where embryonic stem cells may come in.

What are embryonic stem cells?

In the first few days after fertilisation, the egg divides many times to make a hollow ball of cells, called the blastocyst. At the 100 cell stage, the 70 outer cells are destined to become the placenta, if implantation in the uterus succeeds; the 30 or so cells in the inner cell mass are destined to become the embryo and its amniotic sac.

Each of these is actually a stem cell, with the difference that they can each become any of the cells in the mature adult: they are totipotent, as opposed to adult stem cells which are unipotent (but can be induced to become pluripotent).

If the inner cell mass is cultured (supplied with oxygen and nutrients) in a dish, it spreads out and forms colonies of stem cells. These can then be induced to differentiate, or become specific cell types, by adding certain biochemicals or by grafting them into parts of the body.

Experiments are mainly at the stage of using mouse embryonic stem cells with mouse recipients, but stem cells have already been induced to become nerve cells similar to those lost in Parkinson’s disease.

Human embryonic stem cells were first grown in culture six years ago, but were soon shown to be capable of forming many types of body cells when transplanted into mice.

What are the advantages and disadvantages of each type of stem cell?

Adult stem cells could be extracted from the patient and, when transplanted back, would not trigger rejection, which often causes failure of transplants to “take”. However, they are difficult to find and to grow in large enough numbers for transplanting.

The problem of inducing one type of stem cell to differentiate into another type of cell needs to be solved also, though progress has been made.

Embryonic stem cells can easily be obtained and grown in large numbers. Substantial progress has been made in inducing differentiation. However, there remains the problem of rejection, since the embryonic cells would be as unrelated as any other donor to the recipient.

A way round this might be to clone the patient’s DNA into a fertilised egg. Much fuss has been made about this proposal as being a step on a “slippery slope” to human cloning.

There are very good reasons why humans should not be cloned, to do with the very many defects that seem to be present in all animals cloned so far. However, if it could be done without danger to the clone, there would be no logical objection… apart from it’s being a colossal waste of time and money.

In any case, the cloning people are talking about at the moment would be for the purpose of growing a dish of cells, not an embryo.

With the same DNA as the recipient, there should be no problem of rejection.

In fact, not all the DNA would be identical: cells contain tiny energy-producing organelles, called mitochondria, that have their own DNA. It is not clear if this would trigger an immune response but, even if it did, it would be less of a problem than transplants from other people.

There are some people who oppose any use of embryonic material, since even a 100-cell blastocyst could develop into a foetus if it were introduced into a uterus and became implanted (a surprisingly rare occurrence).

These embryos are surplus ones created during IVF treatment, though, and would be destroyed otherwise. The process of removing the outer layer of the blastocyst to get at the inner cell mass removes all possibility of further embryonic development — a dish of cells is not even a potential human being.

The future of stem cell research

Stem cell research is still in its infancy. To be useful for transplants, stem cells must be able to:

1. divide to produce sufficient cells;
2. differentiate into the cell types needed;
3. survive after transplant;
4. mesh into the surrounding tissues;
5. function properly for long enough to extend the recipient’s life or to improve it significantly; and
6. avoid harming the recipient.

The best donor of cells or organs is your identical twin (assuming they don’t have the same problem as you). If you are unlucky enough not to have one, stem cells could help instead.

And the list of diseases for which stem cells may provide cures includes Parkinson’s disease (which affects about 1 in 50 of over-65s), Alzheimer’s disease (there are some 700,000 sufferers in UK), Duchenne muscular dystrophy, and other degenerative nerve diseases, stroke, burns, osteo- and rheumatoid arthritis, diabetes (which affects well over one million Britons), spinal cord injury, heart disease, vision and hearing loss, as well as the problem of transplant rejection — it is well worth exploring all avenues of stem cell research.

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