THE moral maze surrounding embryonic stem cell research just got more complicated.
Two new techniques published this week offer ways to create embryonic stem cells without harming any embryos that could in theory develop into babies. But no one, from opponents of embryonic stem cell (ESC) research, including representatives of the Vatican, to advisors to the Bush administration, to supporters 鈥� including scientists 鈥� has yet come to any conclusions on the techniques鈥� moral, political or philosophical ramifications.
ESCs could potentially be used to grow therapeutic tissues and repair damaged organs. Today almost all ESCs are harvested from early-stage human embryos called blastocysts 鈥� balls of about 100 cells. But the embryo perishes once the cells have been removed, which is the critics鈥� principal objection.
Advertisement
Now Bob Lanza and colleagues at Advanced Cell Technology in Worcester, Massachusetts, say they have devised a way to avoid harming the embryo. They took a mouse embryo that had reached the eight-cell stage, and removed one cell. This was then placed alongside other ESCs. These produce signalling chemicals that instruct the lone cell to itself become an ESC, which can then be cultured into a potentially inexhaustible supply (Nature, DOI: 10.1038/nature04277).
Crucially, the remaining seven-cell embryos developed normally when implanted into the wombs of female mice. In 47 attempts, 23 grew into healthy baby mice, the same success rate as is achieved when implanting normal eight-cell embryos. And the ESCs that Lanza鈥檚 team used to trigger the change in the embryo cell could be replaced by teratocarcinoma cells harvested from tumours, removing any need to harm an embryo. Researchers now plan to find out if the method works in people. If it does, says Lanza, 鈥渋t means we overcome the key pro-life objection, that you must destroy life to save life鈥�.
The second technique, called altered nuclear transfer, was devised by Rudolf Jaenisch and Alexander Meissner at the Massachusetts Institute of Technology鈥檚 Whitehead Institute in Boston. ANT overcomes ethical objections to extracting ESCs from 鈥渢ransient cloned鈥� embryos. These are created by removing the nucleus from an egg, and replacing it with the nucleus of a donor cell, such as a skin cell. An electric current then prompts the altered cell to develop into an embryo, which is destroyed when its ESCs are harvested. By using a patient鈥檚 own skin cell, ESCs created this way could be used to make matched tissues for that person.
Jaenisch and Meissner took a mouse skin cell and infected it with a virus that blocks the action of Cdx2, a gene essential for formation of the placenta (see Diagram). The cell鈥檚 nucleus was then placed in a mouse egg to create a modified embryo that, in theory, is not viable as it cannot implant in the womb (Nature, DOI: 10.1038/nature04257).
Jacques Suaudeau of the Vatican鈥檚 Pontifical Academy for Life told New 杏吧原创 that the Catholic Church will not officially respond to the new work for some time. But he indicated that Lanza鈥檚 technique is the more acceptable of the two. It 鈥渄oes solve part of the problem of ESCs from an ethical standpoint鈥�, he says, because the embryo created is able to develop normally. 鈥淭he procedure does respect early human life.鈥� But Suaudeau is less convinced about Jaenisch鈥檚 ANT technique. 鈥淚t seems difficult to accept the idea of deliberately creating a defective embryo for the sake of using it.鈥�
Yet neuroscientist William Hurlbut at Stanford University, a member of President Bush鈥檚 Council on Bioethics, draws the opposite conclusion, despite holding the view that life begins at conception. Hurlbut himself proposed ANT as a morally acceptable form of cloning, and thinks Jaenisch and Meissner鈥檚 technique overcomes objections. 鈥淚f it doesn鈥檛 have a human potential, it鈥檚 not the same moral entity,鈥� says Hurlbut. 鈥淭he key is that you obtain fully functional ESCs from an entity that is not a fully constituted embryo,鈥� he says.
Critically, the defect is introduced before, rather than after, the embryo is created, he argues. 鈥淭iming is everything. It鈥檚 a pre-emptive intervention, so you are not interfering with something that鈥檚 en route.鈥�
Hurlbut is more critical of Lanza鈥檚 technique. US law prevents federal research that endangers or destroys a human embryo. And he thinks that will happen if one of the eight cells is removed. 鈥淚t鈥檚 reasonable to think you might get a slightly different person鈥�. Lanza disagrees, pointing out that during IVF a single cell is sometimes removed from an embryo before it is implanted to screen it for genetic defects that might kill it in the womb. 鈥淭his procedure has been done hundreds of thousands of times, so we know it has a minimal or negligible effect on the embryo.鈥�
鈥淚t seems difficult to accept the idea of deliberately creating a defective embryo for the sake of using it鈥�
Whether either technique will influence the US government鈥檚 stance on ESC research is unclear. Private companies are allowed to create new embryonic stem cells, but federal researchers can only experiment on ESCs drawn from 22 lines approved by President Bush in 2001, a restriction that has hindered stem cell research at public labs such as those run by the National Institutes of Health. Lanza, Jaenisch and Meissner say their alternative techniques should supplement rather than replace today鈥檚 research into ESCs, which they agree must continue.
But Arthur Caplan of the Center for Bioethics at the University of Pennsylvania in Philadelphia warns they must be careful how they present their work, which has only been done in rodents. If people believe there are straightforward ways to create ESCs without harming embryos then they may seek even wider restrictions on existing ESC research.
鈥淚t鈥檚 politically naive to talk about alternatives. It undermines the moral stance of scientists pursuing the other techniques,鈥� Caplan says. 鈥淚f you hint that it might solve the moral dispute, you鈥檙e providing ammunition for opponents. It鈥檚 essential to back the original stance.鈥�
