Scientists at Stemagen, a small biotechnology company in La Jolla, CA, reported yesterday that they have for the first time generated cloned human blastocysts--early-stage embryos--from adult skin cells. This is the first step in generating stem cell lines matched to individuals, which are crucial for creating new cellular models of disease and potentially important for future tissue replacement therapies. (See "Next Steps for Stem Cells" and "The Real Stem Cell Hope".) The new findings also confirm that access to fresh eggs from healthy young donors is a key part of successful cloning. Lack of access to human eggs has been the major barrier in the field. (See "Human Therapeutic Cloning at a Standstill".)

Cloned blastocysts have been generated before, but from embryonic stem cells rather than from adult cells. Scientists theorize that embryonic stem cells are easier to turn into blastocysts because of their earlier developmental stage.

Experts in the field have had a mixed reaction to the new work. "It's a nice achievement, but in my view, they haven't crossed the bar," says Evan Snyder, director of the Stem Cells and Regenerative Medicine Program at the Burnham Institute in La Jolla. "The real test will be, can you generate cell lines that are stable and self-renewing and normal?" Others applaud the confirmation of the feasibility of human cloning. "The fact that it can be done is important," says Jeanne Loring, a stem cell scientist at the Scripps Research Institute in La Jolla. "It wipes away that blot on our scientific integrity," she says, referring to a massive fraud unveiled in 2005 in which South Korean scientist Woo Suk Hwang claimed to have generated stem cell lines from cloned human embryos. (See "Stem Cells Reborn".)

To clone an embryo, a process also called nuclear transfer, scientists first strip an egg of its genetic material. Then they insert DNA from an adult cell, such as a skin cell, into the egg. Through an unknown process, the egg turns back the clock on the adult DNA and begins to develop as a normally fertilized egg would. From the embryo, researchers could theoretically collect a specialized ball of cells that can be coaxed to turn into stem cells. So far, however, no one has successfully performed this feat.

Stemagen, a relatively unknown player in the field, probably owes its success to access to human eggs through a close association with a local fertility clinic. (The company was founded by a fertility specialist at the Reproductive Sciences Center in La Jolla.) "We were able to get access to high-quality oocytes and have them in the incubator within one to two hours," says Andrew French, Stemagen's chief scientific officer.

Egg donors and the intended parents gave eggs in excess of those needed for in vitro fertilization to the Stemagen scientists for research. Regulations in many states prohibit compensation for donated eggs for ethical reasons, a requirement that has slowed other cloning efforts.