Stem cells: what are they?

A promising area of science

Stem cells are one of the most fascinating areas of biology today. Research in the field has helped us understand how an organism develops from a single cell and how healthy cells replace damaged cells in adult organisms. 

This promising area of science is also leading researchers to investigate the possibility of cell-based therapies to treat diseases, which are often referred to as regenerative or reparative medicine. Stem cells are cells with the ability to divide for indefinite periods in culture and to give rise to specialised cells. They have two important characteristics that distinguish them from other types of cells. They are unspecialised cells that renew themselves for long periods through cell division.

In the three to five-day-old embryo, called a blastocyst, stem cells in developing tissue give rise to multiple specialised cell types that make up the heart, lung, skin, and other tissues.

Types of stem cells
Embryonic stem cells: Embryos from which human embryonic stem cells are derived are typically four or five days old and are a hollow microscopic ball of cells called the blastocyst.

Fetal stem cells: Primitive cell types found in fetuses. Fetal blood, placenta and umbilical cord are rich sources of fetal hematopoietic stem cells.

Umbilical cord stem cells: Umbilical cord blood contains circulating stem cells.
Adult stem cells: Their primary role in a living organism is to maintain and repair the tissue in which they are found. They are hidden deep within organs, surrounded by millions of ordinary cells, where they may remain quiescent (non-dividing) for many years until they are activated by disease or tissue injury. Adult tissues reported to contain stem cells include brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, skin and liver.

Stem cell culture
Growing stem cells in the laboratory is known as stem cell culture. Human embryonic stem cells are isolated by transferring the inner cell mass into a laboratory culture dish. The cells divide and spread over the surface of the dish. Over the course of several days, the cells of the inner cell mass proliferate and begin to crowd on the culture dish. When this occurs, they are removed and plated into several culture dishes.
The process of replating the cells is repeated many times and for many months, and is called subculturing. Embryonic stem cells that have proliferated in cell culture for months without differentiating, are pluripotent, and appear genetically normal are referred to as embryonic stem cell line.

Once cell lines are established, batches of them can be frozen and shipped to other laboratories for further culture.

Stability of the genome in embryonic stem cell lines may increase as they ‘age’. This means that embryonic stem cell banks would need to continually create new embryonic stem cell lines to maintain their stocks. Cancer development could be an inadvertent side effect of embryonic stem cell therapies.

Future of stem cells
Embryonic stem cell technology is already looking rather last-century, along with therapeutic cloning. By 2020 we may be able to produce a wide range of tissues using adult stem cells.

We will also see some exciting new pharmaceutical products in the pipeline, which promise to do some of the same tricks without having to remove a single stem cell from the body.

Using embryos as a source of spare-part cells will always be far more controversial than using adult tissue, or perhaps cells from umbilical cord after birth, and investors will wish to reduce unnecessary risk, both to the projects they fund, and to their own organisations by association.