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 ...