![]() ![]() ![]() Rather, a range of different types of pluripotent stem cells have been generated in mice and humans using different techniques. However, since 2007 it has been clear that there is not one type of pluripotent stem cell. Indeed, cellular therapeutics derived from human pluripotent stem cells are already in clinical trials for spinal cord injury, diabetes and macular degeneration. Many researchers have now shown they can make functional human tissues of medical significance from human pluripotent cells, such as nerve, heart, liver and kidney cells. Human pluripotent stem cells can be grown indefinitely in the laboratory, and like their mouse counterparts, they can form all the tissues of the body. More recently, researchers have become interested in investigating the ability of human pluripotent stem cells – “master cells” – obtained from human embryos or created in the laboratory from body cells, to contribute to the tissues of chimeric animals. The pioneers of this technology are Oliver Smithies, Mario Cappechi and Martin Evans, who received a Nobel Prize in Physiology or Medicine in 2007 for their work. Along with the ability to use those cells in the development of chimeras, this has enabled researchers to produce animals that can be used to study how genes influence health and disease. This has been made possible by advances in gene targeting in mouse embryonic stem cells, allowing scientists to alter the cells to express or silence certain genes. The creation of chimeric mice has been essential for research in developmental biology, genetics, physiology and pathology. Following a successful bone marrow transplantation to treat leukaemia, patients have cells in their bone marrow from the donor as well as themselves.Ĭhimeras can be generated artificially in the laboratory through combining the cells from early embryos of the same or different species. Marmoset monkeys often display chimerism in their blood and other tissues as a result of transfer of cells between twins while still in the womb. But it also raises serious ethical concerns.Ī chimera is an organism containing cells from two or more individuals and they do occur in nature, albeit rarely. Even so, the study represents a first step in a new avenue of stem cell research which has great promise. The actual proportion of human cells in the chimeras was quite low and their presence appeared to interfere with development. The chimeric pig foetuses produced by Juan Izpisua Belmonte, Jun Wu and their team at the Salk Institute were not allowed to develop to term, and contained human cells in multiple tissues. Jun Wu (front) and Juan Carlos Izpisua Belmonte, who led the team that developed the human-animal chimeras.
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