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Isolation and in vitro culture Embryonic stem cells were first derived from mouse embryos in 1981 by two independent research groups (Evans & Kaufman and Martin). A breakthrough in human embryonic stem cell research came in November 1998 when a group led by James Thomson at the University of Wisconsin-Madison first developed a technique to isolate and grow the cells when derived from human blastocysts. Production of male gametes Researchers at the Whitehead Institute announced in 2003 that they had successfully used embryonic stem cells to produce haploid, male gametes. They found embryonic stem cells that had begun to differentiate into embryonic germ cells and then further differentiated into the male haploid cells. When injected into oocytes, these haploid cells restored the somatic diploid complement of chromosomes and formed blastocysts in vitro. Contamination by reagents used in cell culture The online edition of Nature Medicine published a study on January 23, 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 media 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 was published in the online edition of Lancet Medical Journal on March 8, 2005 detailed information about a new stem cell line which 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 teratomas. These properties were also successfully maintained (for more than 30 passages) with the established stem-cell lines. Xenotransplantation of human ES cells Recently, in California, researchers have injected embryonic stem cells into mice as they developed in the womb. Upon maturing, it was found that some of the human ES cells had survived and two months after injection, the researchers found that the human ES cells had undertaken "the characteristics of mouse cells". Scientists in Australia have grown human prostate tissue in mice through the use of ES cells. The research involved combining human ES cells with mouse prostate cells, and then using a mouse as the host to grow the human prostate. The researchers were able to show the resulting tissue was also functional as a human prostate. This work may enable medical researchers to use a prostate derived in this manner as a model for studying prostate cancer and disease and analysis of future prostate-related drugs. Reducing donor-host rejection There is also ongoing research to reduce the potential for rejection of the differentiated cells derived from ES cells once researchers are capable of creating an approved therapy from ES cell research. One of the possibilities to prevent rejection is by creating embryonic stem cells that are genetically identical to the patient via therapeutic cloning. An alternative solution for rejection by the patient to therapies derived from non-cloned ES cells is to derive many well-characterized ES cell lines from different genetic backgrounds and use the cell line that is most similar to the patient; treatment can then be tailored to the patient, minimizing the risk of rejection. The Lanza technique On August 23, 2006, the online edition of ''Nature'' scientific journal published a letter by Dr Robert Lanza (medical director of Advanced Cell Technology in Worcester, MA) stating that his team had found a way to extract embryonic stem cells without destroying the actual embryo. This technical achievement would potentially enable scientists to work with new lines of embryonic stem cells derived using public funding. There are currently significant restrictions on federal funding of embryonic stem cell research that limit publicly-funded research to embryonic stem cell lines derived prior to August 2001. In the experiments, Lanza's team used a single-cell biopsy technique to pluck out a single cell when the embryo was at the 8-to-10 cell stage. This is the same stage used for preimplantation genetic diagnosis, which also requires the removal of a single cell from the blastocyst. As with times where preimplantation genetic diagnosis is used, excising a cell at this point doesn't interfere with the embryo's development and the excised cell can be used for both purposes at the same time. Using this method, Lanza and his team managed to get two stable human embryonic stem cell lines that behaved like conventional embryonic stem cell lines. More recently, this paper has come under some criticism as being "over-hyped". Examination of the paper reveals that the described process is highly inefficient, and in addition, no embryos survived the process. Nevertheless, Dr Lanza states that "he never intended to say more than that he had proved a principle, and that he is surprised by the reaction to the paper." | |||||||||
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