Researchers say stem cells contaminated

WASHINGTON – The human embryonic stem cells available for research are contaminated with nonhuman molecules from the culture medium used to grow the cells, researchers reported.

The nonhuman cell-surface sialic acid can compromise the potential uses of the stem cells in humans, say scientists at the University of California, San Diego. Their study was published Sunday in the online edition of Nature Medicine.

Stem cells form very early in an embryo’s development. They can develop into numerous types of cells to form organs and other parts of the body. Researchers hope to use these cells to repair damaged organs and cure diseases.

The work is controversial because the cells are taken from days-old embryos, which then die. President Bush has limited federal funding to cell lines already in use, but not to newly developed ones.

Currently available stem-cell lines have been grown in materials derived from animals. Such materials include connective tissue cells, called feeder layers, from mice and fetal calf serum.

That has raised concern about potential contamination. Last year, many senators urged easing limits on new cell lines, noting potential contamination could make available lines used for humans uncertain.