Light touch.
A single cell taken from an 8-stage human embryo (left) can be coaxed to grow into an embryonic stem cell line, while the rest of the embryo can develop to the blastocyst stage (right) and beyond.

The Power of a Single Cell

In an advance touted as a way around current political logjams, scientists have said they can derive human embryonic stem (ES) cell lines without destroying an embryo. Although not yet very efficient, the technique, reported online in Nature this week, could in theory allow scientists to derive new human ES cell lines that might be eligible for federal funding under current rules.

In the past few years, scientists have proposed several alternatives to deriving human ES cells that would not require destruction of a human embryo (Science, 24 December 2004, p. 2174). One idea is to grow a cell line from a single cell removed from an early embryo, leaving the rest of the embryo intact. Doctors do such biopsies when they perform pre-implantation genetic diagnosis (PGD), which allows a couple undergoing in-vitro fertilization (IVF) to screen out embryos carrying genetic diseases.

Last year, Robert Lanza of Advanced Cell Technology (ACT) in Worcester, Massachusetts, and his colleagues reported that they had found a way to culture a single cell from an early mouse embryo so that it grew into a line of ES cells (ScienceNOW, 17 October 2005). Now, they have refined their technique to apply to human cells.

The team thawed 16 frozen embryos donated by couples who had undergone IVF treatments and no longer needed the embryos. The ACT scientists allowed the embryos to develop to the morula stage, when the embryo contains 8 to 16 cells, also called blastomeres. They used a pipette to separate the blastomeres and then cultured each one separately to see if it would grow into an ES cell line. More than half of the 91 blastomeres divided at least once, and 28 formed clumps that grew in culture. The scientists transferred the clumps to cultures where other human ES cells, marked with green fluorescent protein, were already growing. In two cases, the transferred cells grew into cultures that behaved like human ES cells.

Lanza says researchers could use the technique to derive ES cells from embryos undergoing PGD. Researchers could allow the removed blastomere to grow overnight, giving it time to divide. One cell could then be used for the genetic diagnosis, and the other could be cultured into an ES cell line. The embryo could be implanted and go on to develop into a full-term pregnancy.

James Battey, chair of the Stem Cell Task Force at the National Institutes of Health in Bethesda, Maryland, says the paper is an interesting proof of principle but doesn't solve all outstanding ethical and legal questions. Federal law prohibits funding for work which "endangers" human embryos, he notes. Because the PGD biopsy does carry some risk to the embryo, he says, government lawyers would have to weigh in on whether cells derived with the new technique could be eligible for NIH funds.

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