Stem Cells

Stem cells are the raw materials for other body cells. They are considered raw materials, because all other cells with specialised functions are generated from these cells.

In other words, stem cells are unspecialised cells which have not yet developed into mature, specialised cells. These cells have the ability to develop into different, specialised body cells.

 Stem cells have the following two important properties:

1. Ability of self-renewal: The ability of stem cells to go through numerous cycles of cell division while maintaining the undifferentiated state is called self-renewal. Under the right conditions in the body or a laboratory, stem cells divide to form more cells called daughter cells.

These daughter cells either become new stem cells (self-renewal) or become specialised cells (differentiation) with a more specific function. No other cell in the body has the natural ability to generate new cell types.

2. Ability to specialise: The stem cells have the capacity to differentiate into specialised cell types. They have the ability to specialise into various body cells types such as blood cells, brain cells, heart muscle or bone.

Sources of Stem Cells

Stem cells are obtained from the following various sources:

1. Embryonic stem cells: These stem cells come from embryos, three to five days after conception. At this stage, an embryo is called a blastocyst and has around 150 cells. These stem cells are pluripotent stem cells, meaning they can divide into more stem cells or can become any type of cell in the body. Thus, these stem cells can be used to regenerate or repair diseased tissues and organs.

2. Adult stem cells: These stem cells are found in small numbers in most adult tissues, such as bone marrow or fat. Compared to embryonic stem cells, adult stem cells have a limited ability to specialise into various cells of the body. For instance, bone marrow stem cells may be able to create bone or heart muscle cells, but not nerve cells. The research involving use of adult stem cells is undergoing clinical trials to test its usefulness and safety in people. For example, adult stem cells are currently being tested in people with neurological or heart disease.

Scientists have also successfully transformed regular adult cells into stem cells using genetic reprogramming. By altering the genes in the adult cells, researchers can reprogramme the cells to act similarly as embryonic stem cells. These stem cells are called induced pluripotent stem cells. However, researchers are yet to know if these reprogrammed cells will cause adverse effects in humans.

3. Perinatal stem cells: Perinatal means relating to time, usually a number of weeks, immediately before and after birth. Researchers have discovered stem cells in amniotic fluid in addition to umbilical cord blood stem cells. These stem cells also have the ability to change into specialised cells. Clinical trials are undertaken to understand the potential of amniotic fluid stem cells.

Totipotent, Pluripotent and Multipotent Cells

Totipotent cells can be specialised into all cell types in a body with the addition of extra-embryonic or placental cells. Embryonic cells within the first two cell divisions after fertilization are the only cells that are totipotent.

Pluripotent cells can be specialised into all the cell types that make up the body; embryonic stem cells are considered pluripotent.

Multipotent cells can be developed into more than one cell type, but their ability to specialise is more limited than pluripotent cells. Adult stem cells and umbilical cord blood stem cells are considered multipotent.

Uses of Stem Cells

Stem cells have the following applications:

1. Increased understanding of how diseases occur: By watching stem cells mature into cells in bones, heart muscles, nerves and other organs and tissue, researchers and doctors may better understand how diseases and conditions develop.

2. Generate healthy cells to replace diseased cells (regenerative medicine): Stem cells can be guided to become specific cells that can be used to regenerate and repair diseased or damaged tissues in people. People who might benefit from stem cell therapies include those with spinal cord injuries, Type 1 diabetes, Parkinson’s disease, Alzheimer’s disease, heart disease, burns, cancer and osteoarthritis.

3. Test new drugs for safety and effectiveness: Before using new drugs in people, some types of stem cells are useful to test the safety and quality of investigational drugs. For testing of new drugs, the cells are programmed to acquire properties of the type of cells to be tested. For instance, nerve cells could be generated to test a new drug for a nerve disease. Tests could show whether the new drug had any effect on the cells and whether the cells were harmed.

Ethical Issues in the Use of Stem Cells

Embryonic stem cells are obtained from early-stage embryos—a group of cells that forms when a woman’s egg is fertilised with a man’s sperm. Thus, the use of embryos to obtain stem cells is opposed by some religious bodies which believe that life begins immediately after fertilization.

Problems with the Use of Adult Stem Cells

Adult stem cells have limited ability to specialise, which limits how adult stem cells can be used to treat diseases.

Adult stem cells are also more likely to contain abnormalities such as toxins, or from errors acquired by the cells during replication.