Stem cells are the cellular putty from which all tissues of the body are made. Ever since human embryonic stem cells were first grown in the lab, researchers have dreamed of using them to repair damaged tissue or create new organs, but such medical uses have also attracted controversy. Yesterday, the potential of stem cells to revolutionise medicine got a huge boost with news of an ultra-versatile kind of stem cell from adult mouse cells using a remarkably simple method. This timeline takes you through the ups and downs of the stem cell rollercoaster.
1997, Dolly the sheep
Ian Wilmut and his colleagues at the Roslin Institute, Edinburgh unveil Dolly the sheep, the first artificial animal clone. The process involves fusing a sheep egg with an udder cell and implanting the resulting hybrids into a surrogate mother sheep. Researchers speculate that similar hybrids made by fusing human embryonic stem cells with adult cells from a particular person could be used to create genetically matched tissue and organs.
1998, Stem cells go human
James Thomson of the University of Wisconsin in Madison and John Gearhart of Johns Hopkins University in Baltimore, respectively, isolate human embryonic stem cells and grow them in the lab.
2001, Bush controversy
US president George W. Bush limits federal funding of research on human embryonic stem cells because a human embryo is destroyed in the process. But Bush does allow continued research on human embryonic stem cells lines that were created before the restrictions were announced.
2005, Fraudulent clones
Woo Suk Hwang of Seoul National University in South Korea reports that his team has used therapeutic cloning – a technique inspired by the one used to create Dolly – to create human embryonic stem cells genetically matched to specific people. Later that year, his claims turn out to be false.
2006, Cells reprogrammed
Shinya Yamanaka of Kyoto University in Japan reveals a way of making embryonic-like cells from adult cells – avoiding the need to destroy an embryo. His team reprograms ordinary adult cells by inserting four key genes – forming "induced pluripotent stem cells".
2007, Nobel prize
Evans shares the Nobel prize for medicine with Mario Capecchi and Oliver Smithies for work on genetics and embryonic stem cells.
President Barack Obama lifts 2001 restrictions on federal funding for human embryonic stem cell research.
2010, Spinal injury
A person with spinal injury becomes the first to receive a medical treatment derived from human embryonic stem cells as part of a trial by Geron of Menlo Park, California, a pioneering company for human embryonic stem cell therapies.
2012, Blindness treated
Human embryonic stem cells show medical promise in a treatment that eases blindness.
2012, Another Nobel
Yamanaka wins a Nobel prize for creating induced pluripotent stem cells, which he shares with John Gurdon of the University of Cambridge.
2013, Therapeutic cloning
Shoukhrat Mitalipov at the Oregon National Primate Research Center in Beaverton and his colleagues produce human embryonic stem cells from fetal cells using therapeutic cloning – the breakthrough falsely claimed in 2005.
2014, Pre-embryonic state
Charles Vacanti of Harvard Medical School together with Haruko Obokata at the Riken Center for Developmental Biology in Kobe, Japan, and colleagues announced a revolutionary discovery that any cell can potentially be rewound to a pre-embryonic state – using a simple, 30-minute technique.
2014, Therapeutic cloning – with adult cells
Teams led by Dieter Egli of the New York Stem Cell Foundation and Young Gie Chung from CHA University in Seoul, South Korea, independently produce human embryonic stem cells from adult cells, using therapeutic cloning. Egli's team use skin cells from a woman with diabetes and demonstrate that the resulting stem cells can be turned into insulin-producing beta cells. In theory, the cells could be used to replace those lost to the disease.
2014, Human trials
Masayo Takahashi at the same Riken centre is due to select patients for what promises to be the world's first trial of a therapy based on induced pluripotent stem cells, to treat a form of age-related blindness.
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