Possible problem with induced stem cells

High hopes for the ethically less controversial variety of pluripotent stem cell have been dimmed by research published this week in Nature. A team led by Yang Xu at the University of California, San Diego, demonstrated that induced pluripotent stem cells triggered immune reactions when they were implanted into mice. In some cases, the cells were completely destroyed by the animals' immune systems.

This was unexpected because the mouse and the stem cells had the same genetic blueprint. Theoretically there should have been no rejection.

Media reports suggested that this could cast a shadow over iPS research. "The assumption that cells derived from iPS cells are totally immune-tolerant has to be re-evaluated before considering human trials," Xu said.

However, there are other, more optimistic, interpretations of Xu’s experiment. One of the leading stem cell scientists in the US, Harvard’s George Daley, believes that these problems will be overcome. After iPS cells have differentiated, they may not express the problematic genes which appear to cause rejection. In principle, he told ScienceNow, “we should be able to make iPS cells that are the same as ES cells.”

As usual, both Xu and Daly emphasises that the ambiguous results once again underscore the need to continue to work with embryonic stem cells notwithstanding their ethical baggage. ~ Nature News, May 13

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