Scientists explore possibilities of marrow stem cells

BOSTON -- Some surprisingly versatile bone marrow cells can transform themselves into building blocks of lungs, intestines, skin and probably most other parts of the body, raising the possibility of a rich and accessible source of spare parts, new animal research suggests.\nThe findings are the latest in the fast-moving field of stem cell research, which almost weekly produces fresh insights into the elusive cells the body uses to build and repair itself.\nThe blood, the brain and many other regions of the body have their own specialized stem cells that can make replacement cells when existing ones are damaged or die off. But the emerging research shows that some of these stem cells are amazingly adaptable, able to generate an assortment of seemingly unrelated types of cells.\nThe latest of these is a marrow stem cell that investigators say is the closest adult cell yet to the primordial stem cells found in embryos.\nDrs. Diane Krause of Yale and Neil Theise of New York University discovered that just one bone marrow stem cell, implanted in a mouse, eventually gives rise to new cells all through the creature\'s body. The researchers said they expect the same will prove true for humans.\n"This opens entirely new avenues of research and changes what we understood about stem cells," Krause said. The research is published in Friday\'s issue of the journal Cell.\nBone marrow stem cells were the first known adult stem cells. Until recently, experts believed they produced only new blood cells.\nBut experiments over the past two years have shown that marrow stem cells can make cells that are incorporated into the liver, heart, bones and muscle, among other things. Still, no one knew if a single kind of marrow stem cell could make all of these things, or whether the marrow hid stem cells that specialized in each body part. The new research suggests that indeed one basic stem cell is able to make all of these things.\nTo prove this, the researchers, working with Dr. Saul Sharkis of Johns Hopkins University, purified stem cells from the marrow of male mice. Then they took single copies of these cells and transplanted one apiece into 30 female mice whose marrow had been destroyed by radiation.\nEleven months later, the researchers scanned the five surviving females for tissue that grew from that one cell. It was easy to find, because each of the male-derived cells contained a Y chromosome -- something females lack.\nAs expected, the females had male-derived blood. But doctors were astonished to find that the females also had male-derived cells throughout their lungs, all along their gastrointestinal tracts and in their skin, Krause said.\nIf the marrow stem cells truly work as the latest research suggests, they could have many uses for making and repairing organs. For instance, if the liver lacks a particular protein because of an inherited disorder, the gene could be inserted into a marrow stem cell, which presumably would carry it there.\nKrause said giving people extra doses of the stem cells grown from their body\'s own supply might hasten the repair of damaged organs. Or it may be possible to trigger stem cells already in the marrow to do this.\nUntil now, the researchers said, the only known stem cells multitalented enough to produce such an array of tissue are those found in early embryos. Those cells give rise to the entire human body.\n"There is a resting stem cell in the bone marrow that has all the potential of an embryonic stem cell," Theise said.\nHowever, Dr. Evan Snyder, who studies brain stem cells at Boston's Children\'s Hospital, said this point is yet to be proven beyond doubt.\n"Whether these are really the adult version of embryonic cells we don\'t know," he said.\nThe issue is especially sensitive because experimentation with embryonic stem cells is so controversial. They are derived from leftover embryos destined to be discarded after test-tube fertilization, and abortion opponents say it is wrong to use them for research.\nSnyder and others cautioned that the latest discovery should not be used to argue against continuing research with the embryonic stem cells.\n"Everything that comes out raises new questions and questions previous answers," Snyder said. "To cut off any avenue of investigation would be unfortunate and shortsighted and premature"