be reprogrammed to become pluripotent." In 2007, it was shown that pluripotent stem cells, highly similar to embryonic stem cells, can be induced by the delivery of four factors (Oct3/4, Sox2, c-Myc, and Klf4) to differentiated cells. Utilizing the four genes previously listed, the differentiated cells are "reprogrammed" into pluripotent stem cells, allowing for the generation of pluripotent/embryonic stem cells without the embryo. The morphology and growth factors of these lab induced pluripotent cells, are equivalent to embryonic stem cells, leading these cells to be known as induced pluripotent stem cells (iPS cells). This observation was observed in mouse pluripotent stem cells, originally, but now can be performed in human adult fibroblasts using the same four genes. Because ethical concerns regarding embryonic stem cells typically are about their derivation from terminated embryos, it is believed that reprogramming to these iPS cells may be less controversial. This may enable the generation of patient specific ES cell lines that could potentially be used for cell replacement therapies. In addition, this will allow the generation of ES cell lines from patients with a variety of genetic diseases and will provide invaluable models to study those diseases. However, as a first indication that the iPS cell technology can in rapid succession lead to new cures, it was used by a research team headed by Rudolf Jaenisch of the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, to cure mice of sickle cell anemia, as reported by Science journal's online edition on December 6, 2007. On January 16, 2008, a California-based company, Stemagen, announced that they had created the first mature cloned human embryos from single skin cells taken from adults. These embryos can be harvested for patient matching embryonic stem cells. Contamination by reagents used in cell culture The online edition of Nature Medicine published a study on January 24, 2005, which stated that the human embryonic stem cells available for federally funded research are contaminated with non-human molecules from the culture medium used to grow the cells. It is a common technique to use mouse cells and other animal cells to maintain the pluripotency of actively dividing stem cells. The problem was discovered when non-human sialic acid in the growth medium was found to compromise the potential uses of the embryonic stem cells in humans, according to scientists at the University of California, San Diego. However, a study published in the online edition