A study (subscription required), just published in Nature by a group of researchers at UC-San Diego, suggests that the use of induced pluripotent stem cells, or iPS cells, for human therapy may be more problematic than previously thought. (iPS cells are cells reprogrammed from adult tissue to look and act like embryonic stem cells. The advantage of iPS cells lies in the fact that they aren't made from embryos, and they will be a genetic match for the person who provided the original cells - presumably reducing or eliminating the chances of rejection by the immune system.) The researchers showed in laboratory mice that the animals rejected even genetically identical iPS cells. The reason seems to be that the animals' immune systems were responding to at least one of the factors used to render the iPS cells pluripotent.
According to this just-posted New York Times article:
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.
I had the opportunity yesterday to ask radiologist and stem cell researcher Joseph Wu, MD, about the study prior to its publication. Wu, who has published interesting work exploring ways to reduce the body's immune response to embryonic stem cells, had this to say:
The overall significance of the finding is that more research needs to be done to examine whether or not iPS cells are immunoprivileged, or protected from an attack by the immune system. Are the findings in this study specific to the mouse iPSCs or will they also apply to human iPS cells? Will they also apply to differentiated iPS cells, which are more likely to be used in therapy? What is causing the rejection? Can we overcome it with advances in reprogramming techniques?
The research, and Wu's questions, are fascinating. Obviously we don't know all the answers yet. But it seems to validate the talking points of many stem cell researchers today, and that of the California Institute for Regenerative Medicine: It's important to continue research on both iPS cells and embryonic stem cells because each form may have advantages and disadvantages that we haven't yet identified.