Last week, Nature reported a new study which found that a promising new type of stem cell might be rejected by a patient's immune system. Back in 2006, researchers managed to create induced pluripotent stem (iPS) cells using adult cells. As the New York Times explains:
The initial creation of human iPS cells in 2007 electrified scientists because the cells seemed to have two big advantages over embryonic stem cells. They were not controversial, because their creation did not entail the destruction of human embryos. And since the stem cells could be made from a particular patient's skin cells, they could be used to make tissues that presumably would not be rejected by that patient's immune system.
But that latter assumption was never really tested, until now. When Yang Xu, a biologist at the University of California, San Diego, and colleagues did so, they found that iPS cells made from mouse skin cells were nonetheless rejected by genetically identical mice.
The new research tried installing iPS cells in mice where they were rejected. The researchers speculate that the process of switching adult cells into iPS cells abnormally activates some genes producing proteins that the immune system interprets as being foreign. Will this failure lead back to the process of producing cloned embryos from which patient-specific therapeutic stem cells suitable for transplant can be derived? Earlier studies showed that tissues made from such cloned embryonic stem cells are not rejected.
Perhaps not. Researchers have been developed a new method using microRNA to transform adult cells into stem cells far more efficiently. It is yet unknown if these cells would be deemed abnormal by a patient's immune system. In addition, last week the New England Journal of Medicine published work in which researchers identified adult stem cells in the lungs. These cells have the power to differentiate into various tissues and might be used to repair a patient's damaged lungs without being rejected.