CHIMERAS: ANIMAL-HUMAN HYBRIDS

August 2005
		Researchers are implanting human cells in animals in order to make more human-like models for medical research, prompting heated ethics debates inside and outside of the scientific community. A scientist and an ethicist answer your questions about this so-called "chimeric" research. Special Report: Chimeras: Animal-Human Hybrids

Forum Introduction Is an animal with a human stem cell brain more intelligent than one with a normal brain? Is the President's Council on Bioethics germane to chimeric research? Is there evidence that chimeras occurs naturally in pregnancy? Are test monkeys usually injured in the experiments? Will scientists one day be able to turn off genes that control many of debilitative diseases?	Larry of Allentown, Pa. asks: Are test monkeys usually injured in the experiments? Also, wouldn't mixing human stem cells with cells of these animals make them partially human? Dr. Richard Hynes responds: To the first question: As in all animal experiments, there are stringent regulations concerning the handling of animals to minimize pain and discomfort and to monitor the animals for any ill-effects. All such experiments must be reviewed by a panel including veterinarians, members of the public as well as scientists and, if approved, the experiments are monitored by the veterinary staff not involved in the experiments and they ensure appropriate care of the animals To the second question: Yes it would -- that is what a chimera means -- an animal with cells from two different species. The question is to what degree and when does this become a concern. In general, apart from the overall issues of proper treatment of experimental animals, people are not especially concerned when some component such as blood cells or skin cells of two species coexist in a chimera. We experience similar chimerism in anyone who has a blood transfusion or an organ transplant -- usually between individuals, not between species. However, in the case of heart valve transplants from pigs into people, they are then interspecies chimeras and we do not view that as inappropriate. For most people, the concerns arise when they think about the possibility that a chimera might acquire some specifically "human" properties and that most commonly refers to brain function. We do not yet know to what degree human cells can contribute to brain function in chimeras. The expert opinion is that their contribution in a mouse would be very small but that in a primate might be larger. Because we do not know for certain, scientists believe that such experiments should proceed with caution, in a gradual phased way with appropriate analysis of each experiment before proceeding to the next -- see further discussion in the answer to the previous question. Dr. Jonathan Moreno responds: There are strict federal rules about using animals in experiments. All experiments must be reviewed by an Animal Care and Use Committee. Harms to animals and the number of animals used must be kept justified and kept to a minimum. One could say that mixing cells from human sources in animals would make them "partially human," but it would be more accurate to say that they are still lower animals with a few human cells. It must be remembered that animal cells are used to make vaccines and have been used, for example, in heart valves (from pigs); does that make those of us with these things in them partially lower animal?   Bob Fry of Bermuda Dunes, Calif. asks: On a recent edition of Charlie Rose's talk show, a guest said within the next 10 to 15 years scientists will be able to turn off genes that control many of the debilitative diseases we currently suffer from. The basis for this ability, he said, was [advances in how] computers map the genes that control many of those diseases. Do you have similar feelings? Dr. Richard Hynes responds: I did not see the program. But, I think it is actually unclear as a general statement how rapidly we will be able to "turn off genes" -- I suspect that within 10-15 years we will be able to block the effects of some genes that contribute to some debilitating diseases -- others will be harder and when the genetic modification we wish to fix is caused by a loss of a gene or its function, it will be harder still (although not impossible) to find ways of replacing the gene or its effects. I am not sure what the guest meant about computers but it is true that application of computation to analysis of biology is increasing greatly and will contribute to improvements in diagnosis and amelioration of disease. Dr. Jonathan Moreno responds: It's always dangerous to make predictions about how rapidly science will advance, and for those who are suffering from serious diseases it can create false hope. However, there are some very interesting studies going on to learn how genetic expression occurs. This is part of what many believe will be the next revolution in medicine: going beyond drugs that are often poorly targeted and have side effects and using the bodies own processes to heal it. The stem cell area is an important part of this field, known as regenerative medicine, as is genetics.