Stem cells: A factfile

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PARIS: Embryonic stem cells have crossed a threshold with the announcement Monday that this novel but also contested treatment has moved out of the lab and into a clinical trial.

Stem cells are primitive cells that diversify into the roughly 200 types of cell that comprise the body's tissues.

The dream is to use these cells to replenish tissue damaged by disease, accident, war or normal wear-and-tear. Heart disease, cancer, Alzheimer's and diabetes are among the many disorders that could be targeted, according to champions of this research.

EMBRYONIC STEM CELLS are by far the most versatile stem cells, as they are "totipotent," or able to differentiate into any cell type.

They come from fertilised eggs that typically are allowed to grow for three to five days. The harvested cells are then kept in self-replicating "lines" for study.

But their use has come under fire from religious conservatives who contend that a human life begins at conception and destroying the embryo is thus tantamount to murder.

Their clout in the United States led to a seven-year ban on federal research funding for new cell lines that was overturned in 2009 by President Barack Obama. His decision has been legally challenged.

The first trial of embryonic stem cells is being conducted by the US biotech company, the Geron Corporation, on a patient enrolled at a spinal cord and brain injury rehabilitation hospital in Atlanta, Georgia.

In its first phase, the treatment will be assessed for safety and tolerance, Geron said.

The other source of stem cells are ADULT STEM CELLS, which while still immature are genetically programmed to differentiate into specific cell types.

Adult stem cells have traditionally attracted far less publicity than embryonic stem cells.

But in recent years they have been found to be more versatile than thought and to exist in a wider range of tissues, including the brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, skin and liver.

Researchers in 2007 said they had found a way to make pluripotent stem cells by "reprogramming" adult stem cells taken from skin. And in January 2008, a team led by Robert Lanza at Advanced Cell Technology (ACT), a Massachusetts biotech company, announced they had created the first human
embryonic stem cells without destruction of the embryo.

Biomedical experts caution that several big questions remain to be answered before stem cells fully deliver on their great promise.

Still unclear is exactly how a stem cell "differentiates" into a specialized cells and ensuring that transplanted stem cells are not attacked as alien by the immune system.

One area of work is to clone stem cells so that they carry the DNA signature of the patient and thus are not treated as foreign.