I received an e-mail from Eric Geislinger the other day containing some musings on a direction for embryonic stem cell research. You may recall the finding that embryonic stem cells from a growing fetus cross over into the mother's body, differentiate and become specialized cells - literally performing a form of stem cell therapy on the mother. Here is what Eric had to say:
Personally, I don't think this will affect the ethical arguments a whit, but it does bring up something I suggested years ago - large, periodic injections with genetically identical embryonic stem cells. Do you know of anyone trying out what seems to be a pretty obvious experiment? Or am I missing something? I wrote a similar question to [biogerontologist Aubrey de Grey] a while ago and received the following:
Aubrey wrote:As for large, periodic injections with genetically identical embryonic stem cells: well, the basic technical problem with stem cell therapy is not the amount of cell division, so "large" is probably not needed. The problem is getting them to differentiate along the desired pathway after injection. To *some* extent they respond to local cues from the tissue they're in, and just do what's needed, but by and large they need a bit more instruction than that. Some of this differentiation can be done in the lab, prior to injection. Basically stem cell work is at the point where we just need to do a lot of "fishing" -- trying lots of different things and seeing what works.
At this point he had to go off to some conferences and we haven't really gotten back to the conversation. While he didn't completely poo-hoo the idea, it didn't seem like he was very interested in it either. I don't get it. It *may* not be as difficult as folks are thinking. What we have here is a bunch of older women with some nice young cells incorporated into their bodies - not even the same sex, let alone genetically identical - and they're perking along doing their various (liver, thyroid, etc) little cell jobs. Seems important.
I think the differentiation problem is the wrong problem. For the last hundred years researchers have been more concerned with the diseases of aging rather than aging itself. I think a similar thing is happening with stem cells. Everybody has their own particular favorite organ or disease that they're working on and this wonderful new tool comes along (stem cells) so they're bashing their brains out trying to figure out how to use them to grow a new liver (or whatever). The Bianchi work indicates that this may not be necessary. The fact that the cells get enough clues from their surroundings to at least sometimes differentiate properly is all you need for a "proof of concept." And this was with cells that weren't even identical and were probably being attacked to some extent and were just the result of "leakage" in the first place.
Why not take an animal that can be cloned (like a rat), create a nice batch of ESCs, and just infuse the critter on a regular basis? It seems like, to at least some degree, you're going to create a chimera that's part young rat and part old rat. Unless someone like Michael West is working on this, everybody else seems too specialized to care.
What am I missing?
It seems like an experiment that should be performed in mice. There's certainly nothing to lose by trying! The current first generation of adult stem cell therapies have essentially come about through a educated trial and error process - finding out where injections of appropriately treated stem cells can assist the process of regeneration.