Blood Stem Cell May Help Repair Bone

A single type of primitive stem cell, transplanted from donor mice, gave rise to both blood-forming and bone-forming cells in recipient mice, suggesting that it may someday be the basis of new medical treatments to replace or repair bone lost to disease or injury.

Researchers used a technique called retroviral insertion site analysis to determine which type of bone marrow cell from mice could give rise to bone-producing cells when transplanted into recipient mice. In this technique, researchers add a piece of DNA marked with a green fluorescent protein to bone marrow cells taken from donor mice. The added DNA inserts itself randomly into one of the chromosomes and is duplicated each time the cell replicates. The daughter cells of the originally marked cell were identified by locating the marker in the same site of the chromosome in each succeeding generation.

Using this technique, the researchers at St. Jude Children's Research Hospital (Memphis, TN, USA) followed the fates of the cells removed from donor mice and transplanted into recipient mice whose own marrow cells had been destroyed by radiation. The cells identified in this study seem to be better able to engraft in bone than other bone marrow cells called mesenchymal cells. However, the osteoblasts that arose from donor cells were detectable for only several months in recipient mice, as occurs in human bone marrow transplant patients.

This suggests that repair and regeneration during the first few months after transplantation is driven by the transplanted donor cells that engraft in bones of the recipient. However, long-term maintenance of bone strength may be primarily controlled by other cells already present in the recipient's bone. The results of the research were reported in the August 10, 2004, issue of the Proceedings of the [U.S.] National Academy of Sciences.

"Our findings in mice coupled with previous experience with bone marrow transplantation in humans suggest that we have identified primitive cells in mice that are responsible for bone repair and regeneration,” said senior author Edwin Horwitz, M.D., Ph.D., associate member of the department of hematology/oncology at St. Jude.




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