Researchers of the Whitehead Institute have discovered a way to multiply an adult stem cell 30-fold, an expansion that offers tremendous promise for treatments such as bone marrow transplants and perhaps even gene therapy.

"A 30-fold increase is ten times higher than anyone's achieved before," says Lodish, senior author on the paper.

The study is published in Nature Medicine.

Unlike embryonic stem cells, adult stem cells are generally tissue-specific, each one destined to develop into several kinds of cells. Chengcheng Zhang, a researcher in the Lodish lab, was determined to develop a way to multiply adult stem cells once they've been isolated from tissue. Achieving this goal required some intricate laboratory sleuthing.

Zhang began by studying adult hematopoietic stem cells. Offspring of some of these cells develop into all of the red and white blood cells, while others form the immune system. Using fetal tissue from mice as the source of these cells, Zhang discovered a population of cells that were not stem cells, yet appeared to interact with stem cells, preserving and allowing them to multiply in the fetal environment. When he isolated the stem cells in the lab and cultured them in a dish by themselves, they died. When he mixed them with these newly discovered cells, they thrived.

Zhang used a microarray platform to search for genes that were active in these newly discovered cells, but not active in similar neighboring cells. Some such genes, he reasoned, might encode secreted proteins that sustained stem cells. Eventually, he located a number of such genes.

In the fall of 2003 and early 2005, Zhang reported in the journal Blood how one of these genes codes for a growth factor protein called IGF-2. When Zhang purified IGF-2 and added it in a solution to hematopoietic stem cells that he had isolated, the stem cells increased eight-fold in number.

Zhang then discovered that two more growth factor proteins, Angiopoietin-like 2 and –3, abbreviated as angpt12 and angpt13, were also abundantly expressed in these stem-cell supporting cells. When Zhang combined these two proteins with IGF-2 and added them to hematopoietic stem cells, the result was a 30-fold increase.

" People have been culturing and working with these cells for years, and never before have we seen such an increase," says Zhang.

Currently, patients with certain blood diseases are treated with stem cells. These stem cells can be acquired either from a donor's bone marrow, or even from cord blood. Still, in both these cases, the actual number of stem cells from a donor often falls short of the number needed to adequately treat the patient. This technique could directly address this problem.

Gene therapy is another area where these findings can be of immediate value, Lodish says.

With gene therapy, a genetic defect is corrected by administering a healthy version of the gene into a patient. For example, a physician isolates hematopoietic stem cells from a patient, introduces a harmless virus into them that expresses a correct version of the mutated gene, and then re-administers the stem cells back into the patients. While many clinical trials have succeeded, some ended tragically when the virus ended up activating a cancer-causing gene. Because of this, the Food and Drug Administration ( FDA ) is not currently approving any gene-therapy clinical trials.

" If, before the stem cells have been re-introduced into the patients, the physicians could first multiply them in the lab, they could then run assays determining if the virus has landed in any undesirable places," says Lodish. " They could then discard those bad cells, and only administer the good ones to the patients."

Source: Whitehead Institute for Biomedical Research, 2006


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