Whether or not West's prediction will be borne out depends on two major sets of factors, the scientific validity of the proposed method and the ethical and legal questions that related work has already raised. From discussions with scientists, ethicists and lawyers in the past few days, several concerns have emerged. Scientists are particularly critical of the lack of supporting evidence accompanying Advanced Cell Technology's announcement, saying in essence the claim could be true but there was no compelling reason yet to accept it. Even if the claim is valid, biologists note a serious uncertainty relating to an important part of the cells known as the mitochondria, components that produce the energy the cell needs and that are, in essence, the cell's batteries. If the bovine mitochondria should prove incompatible with their humanized environment the cells will not be viable.
Ethicists believe the mixing of species is likely to trouble the public severely, at least at first.
Lawyers who specialize in issues of human reproduction note that the moral and legal status of the human embryo is undecided in American law, a fact pointed up by the isolation of the human embryonic stem cells announced last week. The new entity adds further complexity. If Advanced Cell Technology can produce viable hybrid cells, those cells will offer a new route to grow tissue for transplant. This is the same goal held by the scientists who announced last week they had grown human embryonic stem cells in the laboratory. It is widely accepted in principle that embryonic stem cells can be directed to develop into any desired tissue, with enormous potential for medicine, even though this has yet to be achieved in practice.