BioWorld Today
12 February 2010
By Anette Breindl,, Science Editor
Posted on the Yahoo board by worcester_rob
[What follows is the full text of the news story.]
Since their initial description, induced pluripotent stem cells, or iPS cells, have made an impressive splash, partly for scientific and partly for political reasons: They sometimes have been billed as embryonic stem cells without the ethical baggage.
But a paper in the Feb. 11, 2010, online edition of Stem Cells provided a sobering reminder of how much remains to be learned about iPS cells scientifically. Researchers directly compared cells derived from embryonic stem cells on the one hand and iPS cells on the other, and found that the iPS cells were less able to expand, and cells derived from them showed signs of premature aging.
Senior author Robert Lanza, as well as several co-authors, are at Worcester, Mass.-based Advanced Cell Technology, which is trying to get into the clinic with several embryonic stem cell-derived cell types. (See BioWorld Today, Jan. 11, 2010.)
But Lanza stressed that the paper is not the conflict-of-interest-ridden work of a company that is betting, for the time being, on embryonic stem cells.
"We had the most to lose by [iPS] cells not working," he told BioWorld Today, because Advanced Cell Technology hoped - and still hopes - to make type O blood that could be used as a universal donor from iPS cells.
But for the time being, he said, the results are "a show-stopper. . . . The last thing you want to do with a patient who has a disease of aging is give them these cells that will just die."
The authors, who are from Stem Cell and Regenerative Medicine International Inc., the University of Illinois and Harvard University, in addition to Advanced Cell Technology, used two different standard methods (though both involve the use of viral vectors) to generate eight iPS cell lines, and compared them to 25 embryonic stem cell lines.
The iPS cell lines, the authors wrote in their paper, "expressed the standard markers of pluripotency, and formed teratomas . . . and were all morphologically indistinguishable from hESCs." The cells also could be differentiated into embryoid bodies and blast cells.
But fewer blast cells developed from iPS cell lines than from embryonic cell lines. And many of those cells expressed proteins that are indicative of aging and programmed cell death processes. The blast cells from IPS cells also expanded much less over time than embryonic stem cell-derived blast cells.
The authors also compared the prowess of embryonic stem cells and iPS cells for making three particular cell types: retinal pigment epithelial cells, red blood cells and endothelial cells.
The authors were able to differentiate iPS cells into all three cell types. But over time, the iPS cell-derived cells simply could not keep up with their embryonic stem cell-derived counterparts.
With embryonic stem cell-derived RPE cells, "we could get 30 doublings," Lanza said. In contrast, the same cells derived from iPS cells showed signs of senescence "after their first division."
Red blood cells derived from both sources showed vast differences in their ability to expand, with embryonic stem cells producing red blood cells that were able to expand anywhere from 1,000- to 5,000-fold more than those from iPS cell sources. And as for vascular endothelial cells, made from iPS cells, "we couldn't even get them to fill the plate."
Lanza said that the new results do not mean the end for iPS cell dreams of the clinic - quite the contrary. Specifically, he said, recent advances that make it possible to create iPS cells without genetic manipulation are a step forward toward cells that are able not just to turn into different cell types, but to maintain their vigor as they do.
But for now, Lanza said he believes that embryonic stem cells are the best hope for those trying to move stem cells into clinical practice.
Solutions to medical problems "always seem to be right around the corner," he said, recounting his own experiences doing heart transplants 25 years ago, when surgeons were optimistic that any day now, there would be side effect-free drugs to prevent organ rejection.
Waiting a quarter century to bring the promise of pluripotent cells into the clinic is not an acceptable option: "I'm still very optimistic that this can be solved," Lanza said. "But in the meantime, you've got to move ahead with what you've got."
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