Boston researchers find stem cells "remember" origins

By Carolyn Y. Johnson, Globe Staff

Two teams of Boston researchers have demonstrated that a technique used to transform adult cells into stem cells has a limitation: the stem cells retain a "memory" of their original cell type.

Since 2006, researchers have been excited by the possibility of using cocktails of genes or chemicals to reprogram adult skin cells into induced pluripotent stem cells, or iPS cells, that behave like embryonic stem cells and are capable of developing into any cell in the body. But increasingly, researchers have been trying to understand any differences that could hinder the use of such cells both in research and for therapy.

In separate papers published online today, both teams showed that these stem cells continue to harbor genetic signatures of the original cell from which they were derived.

Led by Dr. George Q. Daley at Children's Hospital Boston and the Harvard Stem Cell Institute, researchers made iPS cells from older mice and compared them with stem cells made with cloning, the same method used to create Dolly the sheep. They reported in the journal Nature that the iPS cells were more limited in their ability to turn into blood and bone cells, compared with the cells made by cloning.

A second team, led by Konrad Hochedlinger at Massachusetts General Hospital, found that iPS cells also retained a memory of their original cell type. In their research, published in Nature Biotechnology, found that over many generations, those memories would fade, making them more similar to embryonic stem cells.

"So many people have talked about the similarity of iPS and embryonic stem cells, and I think now the time is ripe to ask the question: what are the differences in iPS and embryonic stem cells and how do they influence utility and therapeutic potential of cells,"Hochedlinger said. "That's an important question that needs to be addressed."