Ever wonder how come mother's immune system never reject her own children who have different genetic make-up? Or fertilized egg from similar species can develop naturally in the womb if artificial implanted. There must be some signature protein or whatever that the antibodies are looking for to identify foreign object. Maybe we can modify a line of stem cells that don't have that signature or have the flexiblity to be added that signature in order to adopt the host's body.

Now, spare human parts can be mass produced. A gross thing if you want to imagine it. But people will be able to live lot longer because of it.
-- bing, Apr 17 2002

They currently can (and do) grow (i.e. clone) pigs with human organs (sort of -- they have genetically mutated them so their organs grow without a particular gene that makes the human body reject it -- it effectively sees the organ as a human one). This is very successful so far and it seems to me the most promising area of research in this area.

Of course, it's still risky (nasty pig viruses not the least of the problems), but the point is, I think they'll work all that out soon, and then you can drink like a pig all you want and when your liver gives up on you, you can just get a new liver from a pig clone -- and have a nice pork roast that same night. And a beer.
-- globaltourniquet, Apr 17 2002


/ … mother's immune system never reject her own children … /

Don't quickly jump to this conclusion. You're only partly correct about the ability of a fully functioning immune system to defeat an overwhelmingly huge and well insulated internal *symbiant*. Initially, mom's body is programmed to be tolerant to the deposit of 'different genetic' material in the same way that exposure to sunlight radiation reduces an immune response. As the cell surface area of an organism increases, antigenic immune signature markers increase in number and in density, but this is not random as in the wild. At some point in the life of an fœtus there will be sufficient signature proteins lost to and aquired by the parent's immune system to allow a defense to form (the case of an Rh¯ child in an Rh+ parent) and an attack to follow on the fœtus.

Most of a developing organism consists of internal cell constituents (esp. fluids and mitochondria) and relatively inert lipid layers of the cell membrane that are wholly of the mother. One must acknowledge the genetic advantage of the mother in carrying her embryo, and imagine the consequences of the same embryonic material implanted into its father. Surface proteins are shared, yes, but are essentially processed and packaged in a form approved by the internal cellular constituents -- do you get the sense of a much lower propensity for triggering an immune response? Must be something like this, or a virus would collapse a cell that it entered and we know that doesn't necessarily occur.

What can be done with stem cells? The very thing you suggest, certainly. That it is not yet a finished task is a testimony to the variability of our species and to our resistance to modification -- and to the fact that failures thusfar preclude any fast forward attempt to produce an entire organ. I'd like some butt cheeks that look like a single-slice popup toaster. Call when they're ready.
-- reensure, Apr 17 2002



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