An explanation of the difference between adult and embryonic stem cells, writing about the benefits of using stem cells to treat disease, and discuss concerns about their use.
Embryonic stem cells are cultures of cells taken from the inside of embryos (1). Embryonic stem cells can become any of over 200 different cell types found in the body (this is known as pluripotence). ES cells are easy to grow in cultures, and are generated by transferring cells from a preimplantation embryo into a petri dish filled with a culture medium (2).
Adult stem cells are found within an organ or tissue. The majority of the cells around them are differentiated, but an adult stem cell is not, though it is not pluripotent to the same degree as an embryonic stem cell, as it can only differentiate to the specialised cell types used within that particular organ or tissue. The primary role of adult stem cells is the maintenance and repair of the tissue which they are in. AS cells are harder to grow in culture than ES cells, because they are comparatively rare within mature tissue, which makes them difficult to isolate.
It is also believed that, if obtained, adult stem cells would be less likely to be rejected after transplant, because a patient’s own cells could be more easily forced to assume a specific type of cell, and they are recognised by the patient’s immune system (which therefore does not need to be suppressed with drugs).
The basis of using stem cells to treat diseases is that because they are undifferentiated, they are extremely malleable, which means that they can be developed into many different varieties of body cells. When the method of manipulating stem cells is mastered, it would theoretically be possible to artificially generate healthy body cells. The effect is that the treatment would help repair damaged tissue, which is often weaken by diseases such as Alzheimer’s, heart disease, diabetes, arthritis and osteoarthritis. The ultimate aim of stem cell research is the ability to completely regrow damaged tissue and organs, so that patients need no longer be left waiting for replacements to be donated. To the general public, stem cell research is often regarded as a way to stop the effects of ageing. This is to some extent true, as stem cell treatment would counteract the steady deterioration of old cells caused by the cumulative effects of poor cell division.
There are still numerous concerns surrounding the use of stem cell transplants, both scientific and ethical. Many of the scientific concerns are about the difficulty of getting the process exactly right, and thus the potential for complications.
One concern is that, in order to avoid the patient’s body rejecting the transplant, their immune system has to be deactivated. This makes them especially vulnerable to disease, and so any viruses present in the transplanted cells could easily overwhelm them. The chance of this is increased by the use of animal cell sources, which could contain diseases which we are not currently able to detect.
Another concern is that the fast growth of embryonic stem cells is difficult to control, and excessive growth of the wrong cell types could result in tumours, similar to the effects of cancer.
The ethical concerns about stem cell research are centred on where the cells are sourced. Originally, stem cells were taken from donated embryos (usually the by-products of assisted fertilisation attempts), but the UK law has recently been changed to allow scientists to create artificial human embryos for their research. Some have argued against this, on the basis that an embryo is a human life and should not be used as a mere scientific tool.
Controversies have since arisen as to the moral rights of the embryo. The Catholic Church, in particular, maintains that a foetus, or even a fertilised ovum, should hold all the human rights that a person does. Those of less absolute values are debating the exact point in its development at which a foetus becomes a person. The general consensus at present is that embryos can be used if they are less than two weeks old (which is essentially a small cluster of cells), though there will likely be many shifts in perspective throughout the years to come.
- Normally in the early stages of development
- Such as agar or gelatine