The announcement last year by scientists in Japan, at the Harvard Stem Cell Institute (HSCI), and at the Whitehead Institute that they had each — independently — coaxed adult cells into reverting to an embryonic stem cell-like state was arguably the biggest news in developmental biology since the cloning of Dolly the ewe.

This creation of what are being called induced pluripotent (iPS) cells was hailed by opponents of embryonic stem cell scrutiny as the end of the need for research using embryonic stem cells, and was seen by those who do stem cell careful search as potentially providing them with another important tool with which to study normal development and the progression of disease.

But for all their excitement, scientists noted that attempts to reprogram adult cells were only succeeding about .1 percent of the time, which left them with the question, “Could any cell be reprogrammed, or was it only possible to reprogram adult stem cells that were present at a rate of about .1 percent in the cell populations on which the experiments were being conducted?”

Now Konrad Hochedlinger and colleagues Matthias Stadtfeld and Kristen Brennand of HSCI and the Massachusetts General Hospital (MGH) have answered that question, advancing the understanding of iPS cells by demonstrating that fully differentiated, i.e., adult, catch mice cells can be reprogrammed to produce iPS cells.

In a paper in the latest issue of Current Biology, Hochedlinger, one assistant professor in Harvard’s new Department of Stem Cell and Regenerative Biology, reports genetically marking pancreatic beta cells — the cells that produce insulin — before successfully reprogramming them into iPS cells.

Harvard Stem Cell Institute Co-Director Doug Melton described Hochedlinger’s latest work as “a well-designed experiment that proves the projection of reprogramming works on fully differentiated cells, not a rare undifferentiated cell in the starting population. It also opens the door to making reprogrammed cells from other adult tissues, not just skin.”

While scientists — including Hochedlinger — had previously reported reprogramming adult cells, the cells they reprogrammed were not genetically marked, so if, for pattern, they were reprogramming adult skin cells, they had no scheme of knowing if the percentage of cells that did re-create to iPS state had started as fully differentiated cells, or if they were skin stem cells.

“This success shows that a fully specialized cell can still give rise to an iPS cell,” Hochedlinger explained during an conference. “This means that adult stem cells are not imperfectly cooked cells giving rise to iPS cells, which in form of expression means that the reason reprogramming is so inefficient must be due to some other explanation.”

Which also means that this is a good news/ complicated news story. The fact that fully differentiated cells can be reprogrammed is good news, because it property that researchers theoretically be able to reprogram any cell type in the body. But it’s a complicated advice story for the cause that it also means that there is an extremely important part of the reprogramming process that researchers still do not understand. Why does the process fail approximately 99.9 percent of the time?