— When is an embryo dead? Is it: A) When it is in an arrested form which no longer grows in the lab, but still contains revivable cells or; B) When it contains no living cells whatsoever?
The answer is important because it could decide whether a new source of human embryonic stem cells (hESCs) is deemed ethically acceptable.
Although hESCs may have huge potential for tissue repair, since they are able to differentiate into any type of the bodys cells, some people oppose their use because they must be derived from human embryos which perish after yielding their precious stem cells.
All this could change, however. Miodrag Stojkovic, at the Prince Felipe Investigation Centre in Valencia, Spain, and colleagues have successfully extracted human embryonic stem cells from early-stage embryos called blastocysts that Stojkovic classes as lifeless. A single line of hESCs was obtained from 13 arrested blastocysts which do not resume cell division and cannot be stated as live, according to the team who reported the breakthrough on Thursday.
Stojkovics team, including researchers from the University of Durham, UK, and at Sintocell, a company in Serbia, investigated 161 donated blastocysts in total, some of them normal and others in the so-called arrested form. Of the 119 blastocysts which arrested early having multiplied to no more than 10 cells none yielded viable embryonic stem cells.
The only successful line came from 13 late-arrested blastocysts, which had stalled after multiplying to between 16 and 24 cells.
The hESCs were retrieved and grown in the lab on a layer of human feeder cells and nutrients. In countries with a non-flexible policy, arrested blastocysts provide a more ethical source for research and hESC derivation, the team say. Our opinion is that all surplus and consented arrested and developing embryos, whether of poor or good quality, should be used for research or derivation of hESCs and not discarded.
The controversy continues, however. Not everyone thinks the blastocysts in question were indisputably dead. They are arrested, but still metabolically active, says Stephen Minger, a stem cell researcher at Kings College London, UK. So technically theyre still alive, and to spin it bio-politically as an ethical source of hESCs is completely misleading, he says.
Minger therefore doubts that they solve a moral dispute which he himself thinks is a non-issue because, he says, it is ethical anyway to obtain hESCs from spare but healthy blastocysts that would otherwise have been discarded.
Stojkovic says that the aim was less to solve the ethical dilemma, and more to make the best of all possible sources of hESCs, even those given up for dead.
One other worry, however, is that arrested blastocysts clearly faulty from the outset as evidenced by their stalled development may yield hESCs that are themselves faulty.
Proof of principle
The report is the second within the past month to propose an ethical source of hESCs. Bob Lanza and his colleagues at Advanced Cell Technology in Worcester, Massachusetts, successfully obtained two lines of hESCs from 16 human blastocysts by a technique that could theoretically allow the blastocysts to survive and be implanted into a uterus after extraction of a single cell which yields the ESCs.
Although he used every cell in all 16 blastocysts to ultimately obtain two viable lines of hESCs, Lanza said that the experiment had proved the principle that hESCs were obtainable from single cells of the blastocysts, called blastomeres.
Previously, he showed in mice both that ESCs could be obtained from a single blastomere, and that the remaining cells of the mouse blastocysts could produce a viable pregnancy and grow into baby mice.
Journal reference: Stem Cells (DOI: 10.1634/stemcells.2006-0377)