The breeding of mice as “model organisms” for research on human disorders by the introduction of disease-specific human genes into the mouse genome has been commonplace since as long ago as the 1980s. Researchers are now working on the transfer not only of genes but also of entire chromosomes. In addition, nerve precursor cells derived for instance from human stem cells have been transferred into the brains of experimental animals, including primates, for the investigation and possible eventual treatment of disorders such as Alzheimer’s and Parkinson’s disease. Such experiments increasingly call into question the biological species boundary between humans and animals. For this reason, the Ethics Council considers it necessary to identify the ethical challenges that may be presented by the creation of human-animal mixtures and to determine where it may be appropriate to set binding limits. With this in view the Ethics Council concentrates its attention on the transfer of human material to animals, which it examines on the basis of three examples: cytoplasmic hybrids (cybrids), formed by the insertion of a human cell nucleus into an enucleated animal egg; transgenic animals with human genetic material; and the transfer of human cells into the brains of fetal or adult animals (brain chimeras). The Ethics Council presents recommendations on these examples, chief among which are as follows.
The Ethics Council endorses the prohibition laid down in Section 7 of the Embryonenschutzgesetz [ESchG – Embryo Protection Act] on the transfer of human embryos into an animal or the creation of interspecific chimeras or hybrids using human embryos or human and animal gametes. These restrictions should be supplemented by a ban on the transfer of animal embryos into humans, a ban on the introduction of animal material into the human germline, and a ban on procedures that could result in the formation of human egg or sperm cells in an animal.
The members of the Ethics Council unanimously hold that human-animal cybrids must not be implanted into a human or animal uterus. An explicit prohibition of such implants should be incorporated in the Embryo Protection Act.
However, the positions of the Council members diverge on the issue of the cybrid creation. Some consider that the creation and use of cybrids is ethically acceptable, arguing, first, that the result is an artefact that can be classified neither as human nor as animal, but can on no account be regarded as a human embryo; and, second, that human embryos too may, subject to certain conditions, be used for research and, in the opinion of some members, even be created for that purpose.
The members of the Ethics Council who take the view that the creation and use of cybrids is ethically unacceptable because they possess all the characteristics of a fertilized human egg call for the inclusion of a statutory ban in the Embryo Protection Act.
On transgenic animals and brain chimeras, the Ethics Council makes different recommendations for primates, great apes and other mammals.
The Ethics Council considers that the common research practice of inserting human genes into the germline of mammals (other than primates) is ethically acceptable if the objective of the research is of overriding importance especially in terms of the expected benefit to humanity and provided that the generally applicable ethical requirements of animal welfare are satisfied.
On the other hand, owing to our provisional and limited knowledge of the possible effects on appearance, behaviour and capabilities, the insertion of human genetic material into the germline of primates should be permissible only after an interdisciplinary evaluation process involving the national committee stipulated in the European directive on the protection of animals used for scientific purposes. Such experiments should be carried out only if there is no alternative and if the expected medical benefit is of overriding importance.
The creation of transgenic human-animal mixtures involving great apes should be banned.
In the view of the Ethics Council, the creation of brain chimeras by the transfer of human cells to mammals other than primates is ethically acceptable if, first, the objective of the research is of overriding importance especially in terms of the expected medical benefit to humanity; second, the generally applicable ethical requirements of animal welfare are satisfied; and, third, chimerization does not take place prior to the formation of rudimentary organs. To ensure an appropriate level of concern for the animal, the degree of cell integration and the behaviour of the animal should preferably be monitored after birth.
In view of the possibly drastic repercussions of the implant of brain-specific human cells into primate brains, of the vital importance of the brain and nervous system for species-specific capabilities, and of our provisional and limited knowledge of the possible effects on physiognomy and cognitive capacity, the insertion of brain-specific human cells into primate brains should be permissible only after an interdisciplinary evaluation process involving the national committee.
The insertion of brain-specific human cells into the brains of great apes should be prohibited.
Council member Regine Kollek explains in a dissenting position statement why she is unable to agree with the version of the Opinion as presented. In her statement she also notes that she considers the creation of human-animal cybrids to be ethically acceptable because there are good reasons for assuming that such entities do not constitute viable human embryos.
The Opinion can be accessed (in German) at http://www.ethikrat.org.
An English translation will be available in due course.