While President Obama recently lifted the ban on federal funding for embryonic stem cell research imposed by President Bush eight years ago, some people continue to oppose this move and call it unethical. So, while the scientific community is thrilled by the news and says the research will lead to medical breakthroughs, some communities consider the research as a "slippery slope". But, what exactly are stem cells and why are they so important as to generate hot debates among all sorts of circles - political, social, religious, and what not? Here's a look at some of those details.

The science behind stem cells
What sets stem cells 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 stem cells and non-embryonic stem cells. 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 are found in adult tissues.
Embryonic stem cells are pluripotent as opposed to adult stem cells that are multipotent. What this means is that embryonic stem cells 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 adult stem cells can only form a limited number of cell types (closely related family of cells).

Utility of stem cells
The importance of stem cell 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 possibly 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 (anaemia) through transfusions of stem cells.
Stem cell 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 embryonic stem cell 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, adult stem cells have been successfully used to treat leukemia (leukaemia) and related bone/blood cancers utilizing bone marrow transplants.

The controversy