Stem cells: Embryonic and adult stem cells

The rapidly developing scientific frontier of the study of stem cells, has been voted as one of the top ten medical news in the last 25 years. Indeed it had raised many hopes and controversies. It was probably in 1996 when the first mammal, the sheep Dolly, was cloned, that it received most media and therefore worldwide attention.

So what are stem cells? They are a remarkable versatile class of cells that can in principle be transformed into a variety of body tissues. This potential offers great promise in the treatment of diseases that results from death or dysfunction of specific cell types like Parkinson’s or diabetes. Stem cells can be developed from embryos (embryonic stem cells) or from adult tissues (adult stem cells). The potential for the two types of stem cells differs in that embryonic stem cells are far more versatile in the types of tissues they can form. Embryonic stem cells derived from very early embryos (four and half days old!) are capable of becoming any type of tissue, (including a new baby!). If cultured (grown) properly in perfect conditions, one of these cells could implant into the uterine walls of a hormonally receptive woman, developing into a full term infant. If on the other hand embryonic stem cells are derived from older embryos, the cells are called pluripotent. These cells are capable of forming into tissues but not into a complete body, nor can it get implanted into the uterine wall to develop into a foetus. Adult stem cells are till now believed to have more restrictions.

In the early 1900s, scientists realized that all blood cells came from a mother cell called "stem cell." These adult stem cells are those residing in bone marrow, which are involved in blood formation and in the development of the immune system. In 1968, the first bone marrow transplant (adult stem cells) was successfully used. Since the 1970’s, bone marrow transplants have been used for treatment of immunodeficiencies and leukaemia. In the year 1953, a young scientist Leroy Stevens, at the Jackson Laboratory in Bar Harbour, Maine was investigating the effects of cigarette papers as distinct from tobacco in laboratory mice. One day he noticed that one of the mice had an enlarged scrotum, which was completely unrelated to smoking trials. He found that the scrotum tissue contained teratoma (a form of cancer) containing various tissues, in this case – teeth and hair growing in the testicles! After many years of further detailed investigation, he found that by injecting cells taken from the inner mass of early embryos directly into the testicles of adult mice, he could induce teratoma! In 1970, Stevens named these cells as "pluripotent embryonic stem cells". In 1975, two scientists Beatrice Mintz and Karl Illmensee showed that embryonic stem cells could give rise to whole organisms. Gail Martin et al., showed in 1981 that the inner cell mass of embryo could support development.

In 1998, James Thompson of the University of Wisconsin and John Gearhart of Johns Hopkins University first isolated embryonic stem cells in independent experiments. Embryonic stem cells have been used to generate various types of tissue. Thompson used such cells to form heart tissue. Ronald McKay of the National Institute of Neurological Disorders and Strokes was able to use nerve tissue produced from embryonic stem cells to partially reverse the effects of Parkinson's disease in rats. In 2000 Margaret Goodell of Baylor University Texas, turned skeletal muscle stem cells into blood cells.
There has been early success with the study of adult stem cells. Human stem cells have been shown to turn on genes found in bone, cartilage, adipose, muscle, blood forming, endothelial, and neuronal cells. Multipotent adult stem cells have been shown to differentiate into functional, liver cell-like cells. It has been found that human neural stem cells can migrate extensively in the brain after injection. Adult stem cells have been isolated from amniotic fluid, peripheral blood, umbilical cord blood, umbilical cord, brain tissue, muscle, liver, pancreas, cornea, salivary gland, skin, tendon, heart, cartilage, thymus, dental pulp, and adipose tissue. Progress has been made in the area of human cloning as well. In 2001, the first ever cloned human embryos were produced (only to six cell stage) created by Advanced Cell Technology (USA). Last year (2004), the first human cloned blastocyst created and the scientists in Korea have established a cell line.

Possible advantages of stem cell research are immense. The technology can help replace tissues or organs, repair defective cell types and deliver genetic therapies. At present, no cure exists in the treatment of spinal cord injuries, Parkinson’s and Alzheimer’s diseases, diabetes, and multiple sclerosis. Human pluripotent stem cells may be used in the future to generate normal tissues that could be used to replace those that have been damaged in the above medical conditions, as well as in other debilitating diseases and conditions (kidney or liver failure, heart failure, stroke, burns, arthritis, etc.). Such technology may also eliminate the need for organ transplants (which are difficult in that they require recipient-donor antigenic matching and immune suppression to prevent rejection) in the treatment of certain conditions.

Stem cells research has a long way to go. It has raised many doubts on ethical grounds. Should human cloning be allowed? Should research on embryonic stem cells be funded?

Celebrities have been calling for expansion of stem cell research to help in the treatment for juvenile diabetes, Alzheimer’s disease and others.

Superman actor and activist Christopher Reeve had a personal interest in the federal funding of embryonic stem cell research. He was paralysed from the neck down when he was thrown from a horse back in 1995. Former first lady of the US, Mrs Nancy Reagan champions the cause of forwarding embryonic stem cell research. Her husband, former President Ronald Reagan, was afflicted with Alzheimer's disease and she believes stem cells, which are considered the building blocks of the human body, might someday provide a cure.

The point is – yes, stem cells have potential. A lot needs to be done before we get the results we want.