L'utilisation d'hybrides, de chimères et d'hybrides cytoplasmiques dans la recherche sur les cellules souches
In stem cell research, creating and using human and non-human animal hybrids, chimeras and “cybrids” pose some of the most contentious ethical issues in stem cell science and policy. A chimera is an organism with a mixture of cells from two or more genetically distinct species. Hybrids are created by breeding across species and contain recombined genetic material through all their tissues. Cybrids, or cytoplasmic hybrids, are created by taking an egg from a non-human animal and removing the nuclear DNA. Human nuclear DNA is fused with the enucleated egg to create a cybrid embryo.
The main rationale behind the creation of cybrids, hybrids and chimeras in stem cell research is the creation of a non-human model system for studying diseases and potential therapies. Animal models are necessary because there are many experiments that are ethically and legally prohibited from being performed on humans. Arguments for the creation of human/non-human animal embryos in stem cell research include the practical and ethical difficulties in obtaining human ova. There is a scarcity of human ova due to the amount of time invested and physical discomfort that must be endured by a woman to produce enough eggs for retrieval from her body. In addition, the process of ova retrieval is onerous and risky. Animal ova are not scarce, however, where production and procurement of animal ova is involved, issues about proper treatment of animals arise.
Experiments that use animal-human chimeras and hybrids are subject to ethical and legal guidelines involving the use of animals in research activities. In addition to the animal welfare issues, public conversations about animal-human mixes have indicated an ethical unease that is reflected in policy. Arguments against mixing animal and human DNA range from arguments about whether humans ought to be creating living organisms not envisaged by God, to concerns about human dignity and moral confusion and also arguments that crossing the “species barrier” is morally repugnant and wrong. Still others find the alteration of natural physical characteristics the source of their unease or repugnance. Public acceptance of chimeric research is also swayed by the object of the research. In other words, if the goal of the unnatural process is immediate and life-saving therapy it might be more morally acceptable than research of some future indeterminate benefit.
The creation of animals with human genes is not novel, but chimeras and hybrids that involve transplantation of human neural tissue or use of human gametes are of particular ethical concern. In these cases it is important to be careful that animal chimeras not develop uniquely human characteristics such that some “degree of humanity” or human dignity has been conferred on them. This can lead to a sense of “moral confusion” and could create obligations toward these new entities that would require rethinking our categories of animals and humans.
The public, policy and regulatory discussions and limits placed on the use of chimeras, hybrids and cybrids in stem cell research reflect the ethical issues of using animals in research and of creating new life forms. These issues will not disappear, but only grow more complicated.