Mouse embyronic stem cells
What's the News: Reprogrammed stem cells---cells taken from an adult and turned back into stem cells
---can be rejected by the body, at least in mice, suggests a new Nature study
. Donated tissues and organs are often attacked by a patient's immune system, since reprogrammed stem cells can be made from a patient's own skin, researchers had hoped these cells offered a way to avoid such rejection by letting patients, in essence, donate tissue to themselves. But the new finding may be a significant setback to what is a promising line of treatment. How the Heck:
Researchers took embryonic stem cells and reprogrammed stem cells---called induced pluripotent stem cells, or iPS cells---from two strains of mice. The mice in each strain were genetically identical to each other, so that mice within a strain would essentially recognize each other's cells as their own.
As expected, mice rejected embryonic stem cells from the other strain, but not from their own strain. Embryonic stem cells from their own strain grew and formed teratomas, clumps of differentiating tissues that are a sign the stem cells are doing well and able to form various adult tissues.
When the researchers injected mice with iPS cells from their own strain, few teratomas formed, and those that did were quickly rejected, much as though they'd been stem cells from the other strain.
What's the Context:
iPS cells were thought to have two primary advantages over embryonic stem cells: They didn't require the destruction of human embryos, thus circumventing those legal and ethical issues, and they could be genetically tailored to individual patients.
This was the first study to directly test whether the immune system would attack iPS cells.
It is not, however, the first problem with iPS cells that research has revealed. These stem cells sometimes retain epigentic traces of their past identities and are often riddled with errors in their genetic code, both of which could keep the cell from becoming a fully functional unit of a new tissue.
The fact that iPS cells can be rejected raises major questions about their treatment potential. "The path to the clinic just got a whole lot murkier," stem cell researcher Robert Lanzatold the New York Times.
Not So Fast:
Reference: Tongbiao Zhao, Zhen-Ning Zhang, Zhili Rong, & Yang Xu. "Immunogenicity of induced pluripotent stem cells." Nature, published online May 13, 2011. DOI: 10.1038/nature10135
Image: National Science Foundation