Sir

Both proponents and opponents of embryonic stem-cell research should object to William Hurlbut's proposal for nuclear transfer embryos to be genetically engineered to block their capacity for development into human babies (“Altered embryos offered as solution to stem-cell rift” Nature 436, 309; 2005).

In describing such material as ‘embryo-like entities’, Hurlbut misses the point that that is what nuclear transfer embryos already are. Indeed, calling them ‘embryos’ seems somewhat tenuous, considering that they are not the products of a sexual process; nor are they clones. But, whatever they are called, it is inescapable that any potential for development to babies can only be realized by implantation into the wall of a uterus. Engineering then seems pointless: in order to block the capacity to develop into a baby, simply don't implant.

Deliberately altering genotype could have important consequences. Disablement of multitasking growth factors, for example, may interfere with cell-signalling mechanisms, thus affecting lab protocols for directed differentiation towards specialized cells in sufficient numbers for therapy.

From an ethical standpoint, intentionally downgrading the moral status of human embryos, in order to render them suitable for research that was otherwise deemed immoral, would be dissimulation.

We should be aiming to make this science more understandable and accessible to allow for proper informed debate. Instead, Hurlbut's complicating proposal is self-contradictory and detrimental to the progression of important human embryonic stem-cell research.