Sir

Your Opinion article “The meaning of life” (Nature 412, 255; 2001) implied that the suggestion made by Advanced Cell Technology's ethics advisory board, to substitute the term 'ovumsum' for 'embryo' in the case of eggs activated following nuclear transfer, is an attempt to sidestep the moral issue associated with deriving stem cells from human embryos. This implication is not correct.

I am the board member who derived the term 'ovasome' (not 'ovumsum') for reasons of accuracy of language, not out of a desire to sidestep controversial issues. Much of the current confusion in the US Congress stems from describing new methodologies with existing language.

The heart of the matter rests with the wondrous properties of eggs. Because, as you point out in your article, neither eggs nor sperm are dead before fertilization, a compelling argument has been made that fertilization is not the beginning of life, but a continuum of life in a new form. The real issue is, therefore, the perceived threat to the sanctity of the union of egg and sperm to create a new individual.

Unfortunately, the union of human eggs and sperm fails far more often than it succeeds in producing a new being. It is this high failure rate, and the inability to prevent it, that has led to the horrifying stores of frozen human embryos worldwide. Rather than asking if these frozen embryos can be used to derive stem cells, we should be asking why so many were created. And should more be created for the sole purpose of deriving stem cells, as was done recently in a Virginia clinic?

The answer is no. Other technologies can be developed to produce stem cells with greater medical advantage. Stem-cell therapy holds the promise of replacing defective cells in adult organs, and the optimal way to attempt this medically is with cells from the affected individual. Eggs are capable, by an as-yet unknown mechanism, of remodelling the nucleus of an adult cell into the much larger, more open format of a 'pronucleus', the first nucleus formed by an activated egg. This yields a new cell with vastly expanded potential to develop into a variety of cell types: this is the power to be harnessed.

An alternative approach is to activate the egg with its own genetic material intact (parthenogenesis). Stem cells derived from parthenotes will have half as many problems of tissue rejection as stem cells derived from eggs fertilized by sperm, which will have the same tissue compatibility problems as transplanted organs.

The early stages of developing these procedures may be similar to those used to clone individuals, but as time goes on the efficiency of creating genetically matched stem cells from activated eggs will increase, and the potential for development to an offspring will decrease. It follows that if creating an offspring is not the goal, the term 'embryo' is not accurate. 'Cloning' is more accurate, but is broadly used to describe a variety of experimental procedures. Hence my suggestion of 'ovasomagenesis' to describe the process and 'ovasome' to describe the product of activating an egg to become a somatic cell.