WASHINGTON (AP) -- The human embryonic stem cells available for research are contaminated with nonhuman molecules from the culture medium used to grow the cells, researchers report. 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...