Editing Embryonic stem cell (section)

===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.<ref name=ebert>{{cite journal |last=Ebert |first=Jessica |date=24 January 2005 |title=Human stem cells trigger immune attack |journal=Nature News |publisher=[[Nature Publishing Group]] |location=London |url=http://cmbi.bjmu.edu.cn/news/0501/124.htm |doi=10.1038/news050124-1 |access-date=2009-02-27 |url-status=dead |archive-url=https://web.archive.org/web/20100924071349/http://cmbi.bjmu.edu.cn/news/0501/124.htm |archive-date=2010-09-24 |url-access=subscription }}</ref> 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]].<ref>{{cite journal |vauthors=Martin MJ, Muotri A, Gage F, Varki A |title=Human embryonic stem cells express an immunogenic nonhuman sialic acid |journal=Nat. Med. |volume=11 |issue=2 |pages=228–232 |year=2005 |pmid=15685172 |doi=10.1038/nm1181|s2cid=13739919 }}</ref>

However, a study published in the online edition of ''Lancet Medical Journal'' on March 8, 2005, detailed information about a new stem cell line that was derived from human embryos under completely cell- and serum-free conditions. After more than 6 months of undifferentiated proliferation, these cells demonstrated the potential to form derivatives of all three embryonic germ layers both ''in vitro'' and in [[teratoma]]s. These properties were also successfully maintained (for more than 30 passages) with the established stem cell lines.<ref>{{cite journal |vauthors=Klimanskaya I, Chung Y, Meisner L, Johnson J, West MD, Lanza R |title=Human embryonic stem cells derived without feeder cells |journal=Lancet |volume=365 |issue=9471 |pages=1636–1641 |year=2005 |pmid=15885296 |doi=10.1016/S0140-6736(05)66473-2|s2cid=17139951 }}</ref>