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?	On the Caribbean island of St. Kitts, researchers are implanting human neural stem cells into the brains of monkeys to study how to treat people afflicted with Parkinson's disease. Other scientists are working on creating a mouse with a brain made entirely of human cells to find ways to cure several neurological diseases, including brain cancer. Although scientists have been mixing animal species for more than a dozen years and mixing cells and organs in adult animals, the more recent blending of human stem cells with animals has generated a heated ethics debate. The National Academy of Sciences has released voluntary guidelines on stem cell research, including a section on chimeras. The chimeric guidelines say any animals with human embryonic stem cells should not be allowed to breed, and implanting human brain cells in animals should be carefully considered by an independent panel. The two lead scientists on the NAS' Committee on Guidelines for Stem Cell Research -- Dr. Richard Hynes, a professor of cancer research at the Massachusetts Institute of Technology, and Dr. Jonathan Moreno, a professor of biomedical ethics at the University of Virginia Health System -- answer your questions about the science and ethics surrounding chimeric research.