In terms of developing replacement cell therapies from iPS cells, the finding may be a boon. “It’s a double-edged sword,” says Daley. “It’s been very challenging to make and direct differentiation of iPS cells into specific tissues.” Starting off with the tissue of interest may make that easier, he says. To grow new bone cells, for example, scientists would be better off taking a bone biopsy from the patient as starting material, rather than beginning with blood or skin cells.
A second study released online today in Nature Biotechnology shows that these cellular memories fade after the cells have been grown for successive generations. “When the cells undergo hundreds of thousands of cell divisions, this memory seems to disappear,” says Harvard stem cell biologist Konrad Hochedlinger, who led the second study. “The cells become indistinguishable from each other, and the differences we observe early on seem to vanish.” But because extensive culturing can also introduce genetic mutations in the cells, this may not be a viable solution to wiping cellular memory.
Collectively, the studies make clear that researchers still have a lot to understand about iPS cells. “If for no other reason, we should still be studying nuclear transfer in order to study how nature does its own programming,” says Evan Snyder, who directs the stem cell and regenerative biology program at the Sanford-Burnham Medical Research Institute in La Jolla, CA. Snyder was not involved with the research. Nuclear transfer is a tricky process, never successfully performed in human cells and not a likely candidate for therapeutic use. But even as a research tool, it’s largely disappeared, and few labs continue to study it now that they can create their own iPS cells.