Two methods that create embryonic stem (ES) cells without destroying viable embryos can work--at least in mice. But neither method resolves all the ethical questions, scientists and ethicists warn.
A common objection to some stem cell research is that it creates embryos only to destroy them. In a paper published on 16 October online in Nature, developmental biologists Rudolf Jaenisch and Alexander Meissner of the Massachusetts Institute of Technology in Cambridge demonstrated a new technique that derives ES cells through nuclear transfer without creating any viable embryos. By knocking out a gene called Cdx2 in a skin cell and then fusing that with an oocyte, Jaenisch and Meissner created cells that could give rise to ES cells, but could not implant in a uterus and therefore had no chance to develop into a full organism.
"It is a technically beautiful experiment," says stem cell researcher George Daley of Children's Hospital in Boston. However, he cautions, "the embryo that is established in the first few days is substantially normal. ... It is not clear this will answer all the critics."
In a second paper also published 16 October in Nature, Robert Lanza and his colleagues at Advanced Cell Technology (ACT), a biotech company in Worcester, Massachusetts, demonstrated a different technique. They removed one cell from a very early mouse embryo and grew it into a stem cell line, allowing the remaining embryo cells to develop into a live-born pup. The method is similar to a well-known technique used by fertility clinics to test one or two cells from early human embryos for genetic markers of disease. Lanza says fertility clinics could use similar techniques to derive new human ES cell lines under existing regulations and safety guidelines.
But the ACT method has ethical problems as well. A cell taken from an early embryo might still be able to form a complete organism--a genetic twin of the original embryo--in which case, some argue, the technique would still destroy a potential life. The procedure also carries "a small but known risk," says fertility and stem cell expert John Gearhart of Johns Hopkins University in Baltimore, Maryland. The risk is not only to the embryo but also to the potential mother, who might have to go through additional in vitro fertilization cycles if the embryo fails to develop.