Just curious. If a person (an identical twin ) had worked in the sun all his life and terminal melanoma cancer, and his less sun loving, non-cancerous twin was recently in an accident that left him brain dead with this otherwise healthy body on life support, could you transplant the sick twins brain to the healthy body of the brain dead twin without fear of immune response complications or rejection?
Lets assume the twins previously signed a document that said the other twin could have their organs (if needed) if they were brain dead.
You could theoretically do the tranplant without fear of rejection.
However at the very best the brain would be alive but without sensation or function. We simply have no technology that would allow us to connect the brian up to the nerves of the new body. So there would be no sight, no smell, no hearing, no sensation of touch from any part of the body and of course no ability to move or speak. Absolute and total sensory deprivation. The prson wouldbe a tital vegetable. although an EEG woul d show signs of life. For the person involved I would imagine the best result would be total insanity within a few days.
Somewhat more plauisble would be a head transplant. Once again we’d have no technology to reconnect the spinal cord so the person would be totally paralysed from the neck down, but at least they could hear and speak. Of course the life expectancy for such a level of parlaysis is less than 10 years anyway, so it’s probably not a great option.
To address this point specifically, you can generally do organ transplants between identical twins without problems with an immune response because their immune systems are the same. But As has already been noted, the problem with a brain transplant is hooking it up with the rest of the nervous system, which we don’t know how to do yet.
It seems to me that in addition to the brain, the entire spinal cord with major nerves intact would need to be transplanted also. Otherwise I would think that the person would be paralized from the head down because you can’t even nick they spinal cord without some consequence.
To elaborate a bit; there shouldn’t be a tissue rejection problem with identical twins (or at least I don’t think so), but the reason we can’t reconnect a severed spine is (at least) twofold:
-Physically reconnecting severed neurons is really difficult, perhaps practically impossible.
-Even if we did have the technology to physically reconnect them, the task of mapping the severed ends in their correct pairs within the spinal cord would be almost impossibly complex; connecting the severed ends of person A’s spinal neurons with the appropriate severed end of person B’s spinal neurons is even more complex, because the way they are laid out in the bundle is not guaranteed to be identical for both individuals. Furthermore, if the layout is different, then there’s twisting/crossing over that would need to be done to make the meaningful reconnections.
If, as others have suggested, you transplant the nervous system more or less entirely, then some of these problems are avoided somewhat, but at the expense of creating brand new, equally difficult problems to deal with.
I was under the impression that in victims of brain damage, different parts of the brain can be ‘retrained’ to perform functions formerly carried out by the damaged parts. If the brain/spine transplant was possible and the neurons roughly reconnected, could they not potentially relearn their new function?
Possibly, but I’m not at all sure; for a start, you have to make sure that motor neurons are connected to motor neurons and likewise with the sensory ones; not to mention the reflex arcs; it is reasonable that the brain might be able to relearn the connections if just a few of them got disturbed or switched over, but not all of them at once; the retraining burden would be too great, I think.
In any case, what does ‘roughly’ mean - how are the neurons in the spinal cord organised? Are they even grouped in relation to the area of the body for which they are responsible? If so, is this grouping identical, or even broadly similar for everyone?
To be honest, when I said ‘roughly’ I was picturing the surgeon knitting together the neurons in a slapdash fashion and hoping for the best…this is why I generally fail to rewire something as straightforward as a bedside lamp.
I think there is a semantic problem here. If you could attach the central nervous system of person A to the body of person B, what would the identity of the resulting person be if they regained consciousness? The most likely thing is that they would identify themself as person A, and find that their old body had gone and they had a new body. So I don’t think it makes any sense to talk about a “brain transplant”: what you really have is a body transplant.
Oddly enough, from what I remember of the head/brain transplant experiments performed by Dr. Robert White in the 60s, the brain itself is “immunologically privilaged”—it can be transplanted (or grafted onto) another body without fear of rejection. (I don’t know if this also applies to the other tissues surrounding the brain—blood vessels, the dura, etc.)
The good doctor (who calls it a “body transplant,” himself) was able to swap the head of one non-identical monkey with that of another, and he’s claimed that something similar could probably be done on a human. (With, of course, the problem of totally paralyzing the transplanted head from the chop-mark down.)
“Immunologically priveleged” refers to parts of the body that are normally sequestered from the immune system - the immune system doesn’t normally go there. They include the brain and spinal cord (due to the blood-brain barrier), the interior of the eyeball, and, oddly enough, the cheek pouches of the Syrian hamster, which has been used quite a bit in studying immune responses.
