Shimmering Chimeras

Moving sheepishly toward the biotech future


Possibly transplantable human tissues and organs are being grown in sheep and pigs, reports The New Scientist. Esmail Zanjani, a professor of medicine at the University of Nevada at Reno, and his colleagues have created animal/human chimeras by injecting human stem cells into fetal sheep about halfway through their gestation.

"Chimera" has come to mean, in modern biotech, a creature made by injecting embryonic or stem cells from one species into the developing embryo or fetus of the member of another species. The term is derived from the beast from Greek mythology that was part goat, part lion, and part dragon. Zanjani found that about halfway through fetal development, sheep fetuses' immune systems couldn't recognize foreign cells. Thus, the fetuses happily accept human cells and incorporate them into various organs where they develop and multiply. Guided by the sheep's own growth signals, the human stem cells develop into liver, heart, skin, or other types of cells. Zanjani reports that in some cases between 7 and 15 percent of the cells in a sheep's liver are human.

Zanjani's results indicate the promise for a potentially powerful therapy for humans with damaged organs. A physician could take bone-marrow stem cells from a patient whose liver is failing and inject them in a sheep or pig fetus. After the lamb or piglet is born, the physician could then harvest human liver cells that would be perfectly compatible with the patient's immune system (after all, they are the patient's own cells) and install them to repair the damaged liver. This technique might also repair hearts after heart attacks or cure diabetes by restoring islet cells in pancreases. Further down the line, it might be possible to inject human stem cells at just the right stage of development in the sheep or pig fetus so that essentially whole human organs are created.

Researchers will have to evaluate the dangers of possibly transmitting animal viruses when organs from animal/human chimeras are transplanted. Already several hundred patients from around the world have undergone either cellular, whole organ, or extracorporeal xenotransplantation (transplantation between species) without significant transmissions of either infectious viruses or endogenous retroviruses (viruses incorporated into the genomes of animals), according to a 2003 report to the European Commission on xenotransplantation.

For example, in 1997, 17-year-old Robert Pennington went into a coma from liver failure and needed a transplant. To gain time to obtain a usable organ, his physicians cleansed his blood by passing it through a genetically modified pig's liver outside his body. Pennington received a transplant and there is no sign that he picked up any diseases from the pig's liver.

Growing human tissues and organs in human/animal chimeras avoids the contentious ethical debate over creating transplantable stem cells using human embryos. Of course, animal rights activists will object, but surely if one can kill a sheep for lamb chops or a pig for a ham, such animals can be sacrificed to obtain organs that could keep a human being healthy and alive.

One would think, then, that only radical animal-rights ideologues could object to research into chimera organs. Alas, the frontiers of biotech research are never so peaceful. Back in 1997, anti-biotech activists Jeremy Rifkin from the Foundation on Economic Trends and his collaborator, Stuart Newman, a professor of cell biology at New York Medical College in Valhalla, New York, filed a patent application for "chimeric embryos and animals containing human cells."

The patent the men seek claims the rights to every possible mammal-human combination, both in embryonic form and as viable animals. They want the patent so that they can block any such chimera research. If they get their patent, they intend to refuse to license anyone to conduct any such research, out of a larger objection to any corporate development of biotechnology.

In a semi-hysterical article in the January/February issue of Mother Jones, Mark Dowie outlines the gruesome possibility of these new biotech methods creating chimeric half human/half primate slaves. "Could one animal cell make a being suitable for ownership, forced labor, and medical experimentation, just as 'one drop' of black blood once did?" he breathlessly asks. That's over-the-top rhetoric. Just as a gene for human insulin in an E. coli bacterium does not make it human, so too an animal cell or animal gene for insulin in a human being would not make that human an animal.

"Using human embryonic cells and stem cells" for chimera research, Dowie asserts, is "likely to raise the ire of anyone who believes life begins at conception or that human cells are more sacred than those of other creatures." That's not at all clear. First, as noted before, injecting adult stem cells into animal embryos to produce human tissues and organs should in fact make right-to-lifers happy, since it eliminates the need to use human stem cells from embryos for the same purpose. Second, who in the world believes that "human cells are more sacred than those of other creatures?" Human beings are more sacred than other creatures, but I neither worship my skin cells nor venerate my gall bladder.

So far the U.S. Patent Office has refused to issue Rifkin and Newman their desired patent on the somewhat tenuous grounds that "[s]ince applicant's claimed invention embraces a human being it is not considered to be patentable subject matter." It is far from clear what "embraces a human being" means. A human gene is not a human being; a human chromosome is not a human being; a human cell is not a human being; a human organ is not a human being (except, perhaps, for a human brain). Rifkin and Newman are challenging the Patent Office's refusal, pointing out that several patents involving human genes and cells have already been issued. As much as it pains me to say it, they may have a good legal point here.

Please keep in mind that Zanjani's chimeric sheep don't look like sheepmen or mensheep; they look like sheep. They bleat just like sheep and they chew their cud just like sheep. They are just sheep, but sheep that could offer hope to thousands who need organ transplants. The bottom line is that if Rifkin and Newman had already been awarded the patent they seek, it is likely that Professor Zanjani's hopeful research could not have gone forward. What is more immoral—working to provide transplants for sick people, or blocking the development of such transplants?