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