From bone to brain: transplanted male bone marrow makes nerve cells in women and girls.

An unusual study of the brains of women and girls who had received transplants of bone marrow from men indicates that marrow cells can transform into nerve cells. Researchers found that each female brain had nerve cells containing a Y chromosome, presumably derived from the transplanted bone marrow.

Over the past several years, numerous research groups have reported that bone marrow, the source of a person's blood cells, can transform into cells of the skin, muscle, heart, liver, and even brain. These lab and animal studies have raised hopes that bone marrow or cells derived from it could repair hearts, cure neurological disorders, and treat many other medical conditions.

Some investigators, however, have challenged the bone-marrow results. The stakes are high because of the politicized debate over whether adult stem cells, such as those in bone marrow, are as promising a therapeutic tool as stem cells derived from embryos are.

In an upcoming Proceedings of the National Academy of Sciences, Eva Mezey of the National Institute of Neurological Disorders and Stroke in Bethesda, Md., and her colleagues report their analysis of the brain tissue of two girls and two women. Each had received a bone-marrow transplant from a male donor in a futile attempt to treat her illness. Mezey's group exposed brain-tissue samples from the four females to a marker that attaches to a DNA sequence unique to a male's Y chromosome. The investigators also applied antibodies specific to nerve cells.

In each case, Mezey and her colleagues identified a small number of nerve cells with Y chromosomes. For example, one girl studied had received a bone-marrow transplant when she was 9 months old and died less than a year later. When researchers examined 182,000 of her brain cells, they found Y chromosomes in 519--and 19 of those male cells also displayed nerve cell markers.

Another research team's unpublished findings mirror Mezey's study. Last year, Martin Korbling of the University of Texas M.D. Anderson Cancer Center in Houston and his colleagues employed the same Y chromosome-based strategy to discover bone-marrow--derived skin, gut, and liver cells in a half-dozen women who had received marrow transplants before dying. Now, Korbling tells Science News, "we have data showing similar results in midbrain and cortex tissue."

Diane Krause of Yale University notes that her research team and many others are vigorously studying the mechanisms by which bone-marrow cells may transform into cells other than blood cells. Unless researchers can enhance the pace of this natural cellular makeover, the phenomenon is unlikely to be of much medical use, both she and Mezey caution.