Chimeric Neural Transplants

[ST88]

In the journal Science a few weeks back, there was an article about human neural transplants into non-human primates. Because neural transplant experimentation for humans is, at present, ethically dubious at the least, it has been suggested by many scientists that doing controlled experiments with neural transplants on non-human primates would be an acceptable compromise. But the thing that makes it such a good compromise also makes it an ethical quagmire.

Human neural transplants could be useful as therapies for brain injury and degeneration, such as with Alzheimer's disease and stroke sequelae. But we won't really know without experimentation. Using human stem cells, for example, to regrow brain tissue is certainly possible, but how? And would it really work or would it just create additional empty brain space where there once an injury? (Thereby leaving the injury intact despite the therapy.) Non-human primate studies may be the answer.

But what if the human neural transplants somehow made the non-human primates think differently? Implanting human neural tissue into the temporal lobes of gorillas, for example, may give them different abilities of thought closer to the human brain model than the primate model. Would this make them more human? And, if so, would this eliminate the acceptability of the ethics of doing the research in the first place?

The article suggests that this is a very real possibility, especially with possible experiments done on non-human primate fetuses given this type of therapy. We don't know if their brains would develop human properties inside a primate body. They use the word chimera to describe the concatenation of two species. Existing examples of chimeras include humans with porcine heart valves and skin grafts. But the brain is one of those areas we have yet to fully explain, and tinkering with it could produce undesirable results.

Should these experiments be allowed go forward? What types of objections are there, and are they too strong for scientific progress -- and the hope for a cure for many brain diseases -- to override them?