of hiding. As they differentiate, human ES cells express increased levels of immune system proteins.
Human embryonic stem (ES) cells receive no free pass of the immune system, unlike the early hopes of researchers. As the cells grow, they express increased levels of markers revealing the body uses to distinguish between native and foreign cells. This means that scientists hope to use the cells to treat Parkinson's disease, diabetes and other diseases have to worry about transplant rejection.
earlier evidence from human embryos raised the slim but tantalizing possibility that ES cells can be "immune privileged," unrecognizable by the body's defenses against foreign cells. One study reported that embryonic cells that give rise to ES cells express the so-called MHC proteins that help the immune system identify an invader; another produced inconclusive results.
Hoping a clear response, a team led by cell biologist Nissim Benvenisty of the Hebrew University of Jerusalem has sought MHC molecules in human ES cell lines. Researchers measured MHC molecules during three stages of development of ES cells using a fluorescent labeled antibody. As a control, they also tested a non-human ES cell line called HeLa. They found very low but constant expression of MHC class 1 molecules on ES cells undifferentiated, as they describe in a paper published online the week of July 8 by Proceedings of the National Academy science . However, as the differentiated cells, they stepped MHC protein production, but not as high as in HeLa cells.
The new findings lay to rest the hope that ES cells can stay under the radar of the immune system, said Hugh Auchincloss, a transplant surgeon at Harvard Medical School in Boston. But the news is not all bad, says Andrew Bradley, a transplant surgeon at the University of Cambridge, UK The relatively low levels of MHC expression could at least say that the tissues derived from ES cells would be less prone to rejection than whole organs transplants today.
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