Stem Cells - The Science, the Benefits, the Debate

The science behind stem cells

What sets stem cells (SCs) apart from other cells is their ability to turn into any other type of tissue in the body. A stem cell from the bone marrow, for example, can be transformed into a neuron or nerve cell in the brain.

Types of stem cells: Embryonic stem cells versus Adult stem cells

Broadly, there are two types of stem cells in humans - embryonic and non-embryonic. Embryonic stem cells (ESC), as the name suggests, are isolated from the inner cell mass of an early-stage embryo (4-5 days post fertilization, and consisting of 50-150 cells). On the other hand, non-embryonic stem cells which are also known as adult stem cells (ASCs) are found in adult tissues.

ESCs are pluripotent as opposed to ASCs which are multipotent. What this means is that ESCs can differentiate into any of the more than 220 cell types in the adult body (to be able to give rise to any mature cell type) while ASCs can only form a limited number of cell types (closely related family of cells).

Utility of stem cells

The importance of stem cells lies in the fact that they can be converted into any type of other cells or tissues in the body - neurons, pancreatic tissue, heart muscle cells, etc.

So, for example, stem cells harvested from your bone marrow can be used to repair the damage in your heart muscle caused during a heart attack or to correct blood disorders such as sickle cell anemia (anemia) through transfusions of stem cells.

SC therapy is believed to have the potential to dramatically change the treatment of human disease. Embryonic stem (ES) cell therapies have been proposed for regenerative medicine and tissue replacement after injury or disease.

But, it should be noted at this point that ESC therapies are not in use yet. They are still only in the stage where medical researchers are testing them on animals.

On the other hand, ASCs have been successfully used to treat leukemia (leukemia) and related bone/blood cancers utilizing bone marrow transplants.

The controversy

The controversy behind SC research pertains only to human ESC research and not all stem cell research. What is controversial is the fact that the source of the research material, human embryos, is destroyed in the process of harvesting the SCs. Pro-life activists oppose the research arguing that a human embryo is a human life that is entitled to protection.

Another area of controversy is that ESC technologies are a slippery slope that may lead to reproductive cloning which may devalue human life.

The production of ASCs, on the other hand, does not require the destruction of an embryo and therefore, ASC research and therapy are not as controversial. Though, ASC treatment does carry a risk of rejection by the body's immune system.

The present state of stem cell research

Some countries offer treatments using SCs (read about medical tourism) but in such therapies, only ASCs derived from the patient's body are used (autograft). When possible, autografts are preferred as they remove the risk of rejection by the recipient's body.

There is promising research ongoing in the field of SCs to derive treatments for a wider variety of diseases including cancer, Parkinson's disease, spinal cord injuries, diabetes, heart disease, Alzheimer's disease, Amyotrophic lateral sclerosis or ALS (Lou Gehrig's disease), multiple sclerosis, lung disease, arthritis, organ failure, and muscle damage, amongst several other impairments and conditions.

The future

The ultimate question on the minds of many is - "Why can't we simply use adult stem cells instead of harvesting embryonic stem cells?"

Theoretically, ESCs are considered better because they work as a biological blank slate and are the most versatile of all SCs whereas ASCs are sort of semi-specialized cells and are not as versatile as ESCs.

Though the field of ASCs is not marred by controversies, the problem with them is also that they are often present only in minute quantities, are difficult to isolate and purify, and their numbers may decrease with age, according to a primer by the National Institutes of Health (NIH).