Brownback's Chimerical Attempt to Curb Science
Outlawing human/animal chimeras will hurt serious research
Ronald Bailey
Last year, Sen. Sam Brownback (R-Kan) introduced the Human Chimera
Prohibition Act. The act is cosponsored by his fellow conservatives Sen.
John Ensign (R-Nev), Sen. James Inhofe (R-Okla) and Sen. Richard Santorum
(R-Penn). The aim of the act is to ban various types of research in which
human cells and genetic material are mixed with animal cells and genes. Why?
Because the act claims, "respect for human dignity and the integrity of the
human species may be threatened by chimeras." Violations of the Act would be
punishable by fines of $1 million or ten years in prison or both.
In his 2006 State of the Union message, President Bush, somewhat confusedly,
urged Congress to pass legislation that would ban "creating human-animal
hybrids." Why confusedly? Because interspecific hybrids are produced by
mating two individuals from different species such as donkeys and horses to
produce mules, but most people understood the President to be coming out
against human-animal chimeras and in support of Sen. Brownback's
legislation.
Before looking at the Act, what are chimeras anyway? In Greek mythology a
chimera was a fire-breathing monster that had the head of lion, body of a
goat, and tail of a serpent. In modern biotechnology chimeras are creatures
composed of cells from two or more species. An example would be the "geep"
that was created in 1984 by fusing goat and sheep embryos.
So what kind of heinous research does Sen. Brownback want to criminalize?
The Act would ban:
(A) a human embryo into which a non-human cell, or any component part of a
non-human cell, has been introduced;
(B) a human embryo that consists of cells derived from more than one human
embryo, fetus, or born individual;
(C) a human egg that has been fertilized by a non-human sperm;
(D) a non-human egg that has been fertilized by a human sperm;
(E) a human egg into which a non-human nucleus has been introduced;
(F) a non-human egg into which a human nucleus has been introduced;
(G) a human egg or a non-human egg that otherwise contains haploid sets of
chromosomes from both a human and a non-human life form;
(H) a non-human life form engineered such that human gametes develop within
the body of a non-human life form; or
(I) a non-human life form engineered such that it contains a human brain or
a brain derived wholly or predominantly from human neural tissues.
Let's consider how any of these proposed procedures might threaten respect
for human dignity and the integrity of the human species. The first
consideration, of course, is the endless argument over the moral status of
very early embryos. If one believes, for whatever reasons or revelations,
that an embryo consisting of a 100 or so cells has the same moral status as
a 30-year old mother that's the end of the matter for them. No experimenting
on human embryos, period. But please note, some of the procedures banned by
the Act arguably do not produce human embryos. And in any case, if one
doesn't believe that embryos are people, are there still good moral reasons
to ban some of the procedures listed in the Human Chimera Prohibition Act?
Let's turn provision A on its head-if it's wrong to introduce animals cells
into a human embryo, is it also wrong to introduce human cells into an
animal embryo? Well, actually researchers have already been doing something
similar to this. For example, University of Nevada-Reno researcher Esmail
Zanjani has been injecting sheep fetuses with human stem cells that then
incorporate themselves throughout their bodies to produce human liver,
heart, and other cells. Some of these chimeric sheep have livers that are
composed of 40 percent human cells. The hope is that this may become a way
to produce transplantable tissues.
In May, Chinese researchers reported that they had injected human cord blood
cells into goat fetuses which were then born with human cells spread
throughout their bodies. Evidently, waiting until fetal development has
already progressed significantly means that the injected human cells will
not proliferate to dominate the tissues and organs of the developing
chimeric animals which should allay any moral qualms that people may have.
Injecting human cells into fetal animals would probably not fall afoul of
the Act.
But what about a banning the creation of "a human embryo that consists of
cells derived from more than 1 human embryo, fetus, or born individual." One
clumsy interpretation of this language might find that it prohibits normal
sexual reproduction because after all today each embryo "consists of cells
derived from more than 1 . born individual"-namely eggs and sperm. This
language might well also be interpreted as outlawing both reproductive (to
produce a baby) and therapeutic cloning (to produce transplant tissues)
since cell nuclei could be taken from another embryo, fetus or person and
combined with an enucleated egg. In June, Harvard researchers announced that
they have begun a program to clone human embryos to create transplant
tissues. This provision would also outlaw an assisted reproduction technique
in which cytoplasm containing mitochondria from a donor egg is used to
rejuvenate another woman's egg so that she can bear healthy children.
Children born using this technique carry mitochondrial genomes from the
donor which means their genetic heritage derives from three people.
The next two prohibitions forbid creating embryonic chimeras by fertilizing
a human egg by a non-human sperm or fertilizing a non-human egg by a human
sperm. As far as I know this has only been done once in 1977 with a
researcher using human sperm in an attempt to fertilize a gibbon egg. The
sperm did penetrate the gibbon egg, but it turns out that human sperm
bounces off the eggs of non-hominoid monkeys, making it likely that it
wouldn't do much for the eggs of cows or pigs either. Of course, scientists
could force the matter by using intracytoplasmic sperm injection.
Normally, prolifers such as Brownback draw their line at protecting human
embryos. However, any embryos produced by combining human and animal gametes
are not human. So Brownback and his supporters must believe that human eggs
and sperm have a special moral status before they combine to produce
embryos. As Monty Python once suggested: Is every sperm sacred? Brownback
must also be taken aback by the recent finding that human ancestors and the
ancestors of chimpanzees practiced interspecific miscegenation a few million
years ago.
Presumably one goal of Brownback's ban on mixing human and animal gametes is
to prevent the birth of a creature that is in some sense a diminished human
being. Since combining human and non-hominoid animal gametes will most
likely not result in viable hybrids, banning that practice seems
superfluous. I don't think that any Institutional Review Board would approve
of an experiment that was designed to create a live hybrid by means of
fertilizing human eggs by chimpanzee sperm or vice versa. But if banning
such experiments would make Brownback happy, let's do it.
The next two provisions propose to ban cloning experiments. The second of
the two provisions would ban experiments that are already ongoing. For
instance researchers at Harvard are adding human cell nuclei to enucleated
rabbit eggs. They hope to use this cloning technique to produce
transplantable tissues. They are using rabbit eggs because they are much
more plentiful than human eggs. The first of these two provisions is
superfluous because human eggs are so hard to come by that it is unlikely
anyone would use them to produce transplantable tissues for rabbits. In any
case, such "embryos" would again not be human embryos. In fact, because such
embryos could not fully develop into living creatures, they would be very
much like the genetically impaired embryos that some members of the
President's Council on Bioethics believe could morally be used as sources of
stem cells.
The next provision would prohibit the creation of "a human egg or a
non-human egg that otherwise contains haploid sets of chromosomes from both
a human and a non-human life form." I'm not sure, but perhaps this provision
differs from the preceding ones that outlaw human/animal hybrid embryos by
forbidding the addition of individual chromosomes derived from animals or
humans to human and animal eggs.
The next to last provision bans the creation of "a non-human life form
engineered such that human gametes develop within the body of a non-human
life form." It could happen that injecting human stem cells into mice
fetuses could result in those stem cells migrating to the ovary or testes of
those fetuses where they develop into egg and sperm forming cells. One can
even imagine mating two such mice so that the embryo they produce would be a
human embryo. Given size differences, a mouse could never give birth to a
man. On the other hand, one can also imagine the same thing happening
between reproductively chimeric cows or sheep. Given safety issues and
concerns about the future well-being of any children that might be born of
domestic livestock, researchers must be careful to make sure that this kind
of mating between chimeric animals does not occur.
That being said, it has already been proposed that this technique might be
adapted to help some people who cannot produce gametes overcome their
infertility. For instance, a fertility specialist could inject bone marrow
stem cells from an infertile person into fetal mice in which those human
stem cells are transformed into cells that produce human gametes. Such fully
human gametes could be harvested from the chimeric mice and used to produce
genetically related children by means of conventional in vitro
fertilization.
Brownback's final prohibition would forbid the engineering of a non-human
life form such that it contains a human brain or a brain derived wholly or
predominantly from human neural tissues. Already, Stanford University
researcher Irving Weissman has injected human neurons into mouse fetuses
producing mice with brains composed of 1 percent human neurons. Weissman
next wants to create a strain of mice with brains made almost entirely of
human neurons. Such mice would be invaluable for studying human brain
diseases and testing medicines to cure those diseases. Mice with brains
composed entirely of human brain cells are unlikely to begin contemplating
the meaning of life. Why? Among other reasons, because mouse brains weigh
just 0.4 grams compared to around 1500 grams for human brains.
Still one can imagine that adding a substantial number of human neurons to
fetal primates might end up producing a creature that could be regarded as a
diminished human being. However, concerns of this sort should not be allowed
to outlaw experiments like that of Yale researcher Gene Redmond. Redmond is
trying to find a cure for Parkinson's disease using experiments in which he
injects human brain cells into the brains of green vervet monkeys.
This quick review shows that current experiments using chimeric animals and
embryos do not threaten our "respect for human dignity and the integrity of
the human species." Ultimately, the Human Chimera Prohibition Act is a
misbegotten legislative blunderbuss that would criminalize much valuable
research aimed at curing human diseases. We can afford to wait until we hear
that a Harvard or Stanford institutional review board has approved an
experiment to produce a humanzee before Congress needs to act.
Ronald Bailey is Reason's science correspondent.

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