The science and implications of stem cell research

Stem cell biology represents a new scientific research frontier that may ultimately lead to a better quality of life for patients affected by a wide variety of medical conditions. Stem cell research has received widespread attention and the diversity of viewpoints in this area of research must include not only scientists, politicians and ethicists but also the patients themselves who, in the end, would be the most affected by the potential of such treatment.

Fertilisation occurs when the sperm fuses with the egg to form a zygote. The full complement of genetic material that results from this fusion will be later reproduced in nearly all types of cells found both in the embryo and the adult.

The fertilised egg has totipotent characteristics, meaning that it can develop in all types of cells found in the human body. Approximately four to eight days after fertilisation, a sphere of cells known as a blastocyst develops (containing around 50-100 cells - no bigger than the diameter of a human hair). The outside layer of the blastocyst will go on to form the placenta whereas the cells present inside will go on to form the embryo. Although the latter have the potential to form all types of cells that are found in the adult body, they cannot alone form an organism because they are unable to give rise to a placenta which is vital to embryonic development. Therefore, the cells present inside the blastocyst are known to be pluripotent, giving rise to many types of cells but not all the cells. If a cell from the inside of the blastocyst is placed inside a womb, it would never develop into an embryo. It is the cells that are present inside the blastocyst that are used to make embryonic stem cells.

After three or four weeks the cells start arranging themselves in definite layers, a process known as gastrulation, in which there is also the first evidence of nervous system formation. It is widely accepted that 14 days is the cut-off point for embryo research as gastrulation does not start until the third week following fertilisation. At 12 weeks of development, the embryo is recognisable as human and at this stage it starts to be called a foetus.

A fertilised egg gives rise to hundreds of different type of cells having different functions. This process of creating different types of cells is known as differentiation. Cells inside the blastocyst are not yet differentiated thus developing in mostly all types of adult cells. When cells reach a state where they cannot differentiate any more, they are referred to as terminally-differentiated cells. Many cells in the human body are of this type. However, in some tissues, the body will still need a supply of replacement cells, such as skin or blood cells. In order for this to occur, some cells inside the body will never become terminally differentiated. These cells are known as tissue stem cells. The latter are capable of producing one type or a subset of specialised cells (thus referred to as multipotent).

Embryonic stem cells, due to their ability to form most cells inside the body, have a huge therapeutic potential. However, several questions arise as these cells have to be collected from human embryos such as from "surplus" embryos obtained following in vitro (outside the body) fertilisation (IVF) procedures where more than one egg is created. On the other hand, tissue stems cells are not collected from embryos but their therapeutic potential is considerably limited as they only develop into one kind or a subset of cells.

As with all new areas of medical research, there are issues like efficacy, safety, risks, consent and confidentiality. But what makes this scientific field especially contentious is the source from which the cells are derived. Most people would feel uneasy at the idea of killing a human being, irrespective of its stage of development, to provide spare parts or cells to another. Yet, a good number of individuals are equally and deeply troubled that concerns about the status of a few cells in the very earliest stage of human development should be allowed to hold back the prospect of treating terminal disease or chronic human suffering. Others fall in between, seeing the human need but feeling that the human embryo is more than just a group of cells, even in its earlier stage.

At present, the main source of human embryonic stem cells is that of the existing so-called "surplus embryos", created for infertile couples in order to have a baby by IVF but which were never used. During this process, a number of embryos are created and a few of them are implanted. The others would normally be frozen for further attempts or eventually destroyed. Many would argue that since these embryos will be destroyed, there should be no objection to their use in producing embryonic stem cells. Tissue stem cells, on the other hand, do not offer any ethical or moral issues as these are naturally present inside the body.

So far, patients or patient groups have rarely been involved in discussions on stem cell research even though they would be the most affected by the potential of such therapies. Unfortunately, objective patient-orientated information is lacking. Policy makers must also understand the various issues involved so that appropriate policies can be tabled and seriously debated.

Dr Scerri is a lecturer at the Department of Pathology, Faculty of Medicine and Surgery, University of Malta.

charles.scerri@um.edu.mt