A California biotech announced at the Stem Cell Summit in New York City on Tuesday that they have successfully reprogrammed human skin, kidney, and retina cells to a stem-cell-like state without using potentially cancer-causing retroviruses. But experts say their claims are impossible to evaluate since the work has not been peer-reviewed. The company researchers did not say these new cells produced teratomas -- the sign that cells are truly pluripotent.

The company, PrimeGen Biotech based in Irvine, Ca., said it used carbon-based particles coated with DNA coding for the four transcription factors Oct3/4, SOX2, c-Myc, and Klf4, the New Scientist reported. These are the same factors Shinya Yamanaka used with retroviruses to reprogram skin cells into stem cell-like cells last November. In a statement regarding Yamanaka's paper, Douglas Melton, stem cell researcher at Harvard University, said that "retroviruses are a real limitation to stem cell reprogramming" because they can disrupt other genes required for normal cell function.

PrimeGen said in an accompanying press release that they are looking for sponsorship and help in developing their cell lines. But some researchers are skeptical about the company's findings. Until the results go through the peer review process they will be hard to evaluate, James Thomson, at the University of Wisconsin, Madison, whose group also reported reprogrammed stem cells last November, told Forbes. One independent researcher who has tested the new cells, Denis Clegg at the University of California, Santa Barbra, told Forbes they behave like embryonic stem cells, but expressed surprise at the company's early announcement.