— Jonathan M., Cebu City

Stem cells are cells that have the ability to divide and produce exact copies of themselves for an indefinite number of times and to transform to specialized cells. Where do stem cells come from and what can they do?

As I’m sure you know, humans arise from just a single cell, the fertilized ovum, which is the result of the union of the sperm cell of the male and the egg cell of the female. Soon after it is formed, the fertilized ovum multiplies many times over to produce cells called stem cells.

The stem cells that arise during the first few days of embryonic development are very versatile cells that have unlimited capability. They can transform to any type of specialized cell, but they remain so only during the first four days of embryonic development.

From that point on, they begin to specialize, which means they commit themselves to producing only certain cell types. In so doing, they loose their ability to transform to other cell types. Still, the stem cells of the embryo and the fetus are very versatile, they can replicate very fast and they can transform into numerous types of cell.

As the fetus matures, its stem cells become specialized further such that at birth, the capability of the existing stem cells has been very markedly reduced. They are no longer capable of producing new organs, but they are still able to replace those cells of the body that die due to physiologic reasons or injury.

Stem cells are the key elements in the body’s healing powers against disease and injury. They persist throughout life, but they gradually decrease in number as the person grows older. Likewise, they become more and more specialized and their capability to transform into other cell types becomes progressively limited. Consequently, as one gets older, wounds take longer to heal, infections become more difficult to fend-off, etc.

In adults, most organs contain enough stem cells that can be called upon to replace those cells that have been lost through disease and injury. For example, there are stem cells in the bone marrow that can continuously produce all types of blood cells (all blood cells have life spans), there are stem cells that can replace the cells lining the gastrointestinal tract that are normally shed off every few days, and there are stem cells that serve to replace those that have been destroyed by disease. But there are cell types, such as the nerve cell (the functional unit of the brain), for which there are no—or there are just very few—available stem cells. In adults, nerve cells that are lost are not replaced, the space they occupy is taken over by scar tissue.

Now, why is there so much ado about stem cells? Because it is possible to collect stem cells and coax them to multiply and develop into specific specialized cells in the laboratory. This is an idea that has an enormous potential in the field of medicine.

Theoretically, stem cells can be used to generate cells in the laboratory which can then be introduced to the body to replace damaged, injured or dead cells in any tissue or organ. For example, heart muscle cells can be grown in the laboratory from stem cells and then transplanted into a person’s ailing heart. Stem cells can be induced to become pancreatic cells, then transplanted into the pancreas to cure diabetes.

Likewise, stem cells can serve as sources of replacement cells that can treat many diseases that affect the brain and the spinal cord such as stroke, spinal cord injury, Alzheimer’s disease and Parkinson’s disease. Stem cells can also be made to multiply rapidly and transform into skin cells that can cover burned areas. Indeed, stem cells can be used to form new cells to replace damaged or dead ones in any organ of the body like the kidney, liver and lung.

However, before we can fully realize the potential medical benefits of stem cells, we need to know more about them. We need to find out the factors that prompt stem cells to divide and proliferate.

More importantly, we need to find out the factors that induce stem cells to transform into particular cell types. For example, we need to know what makes a bone marrow stem cell transform into a red blood cell instead of a white blood cell and vice-versa.

Likewise, we need to find solutions to a lot of related problems that can hamper the medical use of stem cells such as the phenomenon of immune rejection of transplanted cells.

A tremendous amount of research needs to be done to uncover the secrets of stem cells and this is the reason why thousands of scientific laboratories all over the world are currently agog on them.