Chimera and the Continuum of Humanity - Emory University School ...

348 EMORY LAW JOURNAL [Vol. 55
from independent embryos. 6 Under this biotechnological definition, any
particular cell in the chimera derives from one of the parent organisms but is
not a mix of the two parents as in sexual reproduction. 7 Thus, each cell in a
human-mouse chimera would be either completely human or completely
mouse. Chimera technology has rapidly left the realm of the hypothetical, and
this technology opens up a Pandora’s Box of legal and ethical questions by
intimately mixing human and animal.
As an example of the types of creatures being produced by chimera
technology, in early 2004 researchers at the Mayo Clinic produced chimera by
injecting human stem cells 8 into forty-day-old fetal pigs. 9 Because the human
cells were introduced well into fetal development, the organisms outwardly
look like pigs. 10 However, closer examination reveals that these creatures have
porcine cells and human cells mixed throughout their bodies. 11 Unlike a
human receiving a transplanted piece of animal tissue or an animal with a few
human genes inserted into its genome, these chimera represent a genetic and
structural mix of human and animal. 12
Presently, Irving Weissman, the director of Stanford University’s Institute
of Cancer/Stem Cell Biology and Medicine, is contemplating pushing the
envelope of chimera research even further by producing human-mouse chimera
whose brains would be composed of one hundred percent human cells. 13
6 Nicole E. Kopinski, Human-Nonhuman Chimeras: A Regulatory Proposal on the Blurring of Species
Lines, 45 B.C. L. REV. 619, 624–25 (2004). In accordance with most commentators, the term chimera will be
used as both the singular and plural in this Comment.
7 Id. at 625.
8 Stem cells are undifferentiated cells that have the potential to develop into specialized cells. Consuelo
G. Erwin, Embryonic Stem Cell Research: One Small Step for Science or One Giant Leap Back for Mankind?,
2003 U. ILL. L. REV. 211, 213.
9 Ogle et al., supra note 2, at 548–50.
10 See Gaia Vince, Pig-Human Chimeras Contain Cell Surprise, NEWSCIENTIST.COM, Jan. 13, 2004,
http://www.newscientist.com/news/news.jsp?id=ns99994558 (“The injections must be given after the body
plan of the fetus has developed, but before the immune system is active. The former ensures the animals look
like normal pigs and sheep. The latter prevents the human stem cells being rejected.”).
11 Id. Surprisingly, these chimera also contain hybrid cells with a mixture of human and porcine genetic
material. This was the first time researchers witnessed such hybrid cells in a chimera. Id.
12 Researchers discovered human cell lines integrated into the tissue structures in the thymus, kidney, and
skin of the chimeric animals. Ogle et al., supra note 2, at 548–50. These particular pig-human chimera are
much more pig than human because the total percentage of human cells present at one year and beyond was
approximately .1%. Id. As a result, it is difficult to imagine granting these particular chimera being viewed as
persons. However, there does not seem to be a scientific barrier to creating a human-animal chimera with a
much higher percentage of human cells by, for example, injecting the human stem cells at a much earlier time.
See Vince, supra note 10.
13 Weiss, supra note 1.