Rejuvenated Skin Cells Make Stem Cells
Adult Cells Turned Back Into Embryo-Like Stem Cells
Nov. 20, 2007 -- Working independently, scientists in the U.S. and in Japan
have turned human skin cells back into embryo-like
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
But both research teams are highly optimistic that science soon will leap
"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
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