Nov. 20, 2007 -- Working independently, scientists in the U.S. and in Japan have turned human skin cells back into embryo-like stem cells.
The reprogrammed adult cells become "truly pluripotent" stem cells -- that is, they can become any cell in the human body. Until now, only embryonic stem cells could do that trick. But unlike with embryonic stem cells, no embryo has to be destroyed to get these stem cell lines.
"Basically, what we are doing is trying to turn somatic cells from an adult body back into stem cells similar to embryonic stem cells," University of Wisconsin researcher Junying Yu, PhD, says in a podcast made available by the journal Science.
There is a catch. To reprogram the adult cells into what they call "induced pluripotent cells," both research teams had to use retroviruses as vectors to carry new genes into the cell nucleus. Once there, the retroviruses become part of the cell's genetic code. These retroviruses could cause deadly mutations or cancers in patients treated with the newly created stem cells.
"It is important to understand, however, that before the cells can be used in the clinic, additional work is required to avoid vectors that integrate into the genome, potentially introducing mutations at the insertion site," warn Yu and colleagues, in one of the two reports simultaneously announcing the results.
But both research teams are highly optimistic that science soon will leap this hurdle.
"Once the safety issue is overcome, human-induced pluripotent cells should be applicable in regenerative medicine," Kyoto University researcher Kazutoshi Takahashi and colleagues note in their report.
Until that breakthrough occurs, the stem cells will be of enormous value in drug development and in understanding human disease.
Not True Embryonic Stem Cells
Both research teams note that the induced pluripotent stem cells, or iPS cells, are not exactly the same as embryonic stem cells. Precisely how different they are remains a question. Regardless of the difference, the finding may represent a breakthrough in the ethical debate over the use of embryonic stem cells, says medical ethicist R. Alta Charo, JD, of the University of Wisconsin-Madison.
"This is a method for creating a stem cell line without ever having to work through, at any stage, an entity that is a viable embryo," Charo says in a news release. "Therefore, you manage to avoid many of those debates with the right-to-life community."
The two research teams used different techniques. Both used retroviruses to insert four genes into more mature cells, but only two of these genes were the same. The group working in Japan used skin cells from the face of a 36-year-old woman and from the connective tissue of a 69-year-old man. The group working in the U.S. used cells from a fetus and from a newborn child, although Yu says they are well on the way to using cells from human adults.
Both teams are building on mouse studies announced last year by the leader of the Japanese team, Shinya Yamanaka, MD, PhD, of Kyoto University. The leader of the U.S. team is James A. Thompson, DVM, PhD, of the University of Wisconsin-Madison.
Takahashi, Yamanaka, and colleagues report their findings in the Nov. 20 online edition of the journal Cell. Yu, Thompson, and colleagues report their findings in the Nov. 22 online edition of the journal Science Express.