From: Robert J. Bradbury (bradbury@www.aeiveos.com)
Date: Tue Nov 23 1999 - 04:03:59 MST
On Sun, 21 Nov 1999, Billy Brown wrote:
> Robert J. Bradbury wrote:
> > (b) Growing organs on dissolvable plastic frames from stem cells.
> > Requires a bit more work on getting growth factors correct
> > and being able to harvest appropriate stem cells from the
> > transplant recipient or other compatible donors. [But the
> > donor supply goes up significantly when you only a few stem
> > cells are needed and you don't have to be dead to give them.]
>
> I'd think that for most organs you'd also have to solve the problems
> involved in growing blood vessels and nerves in the proper configuration.
> How hard do these problems look?
>
Actually, for endothelial cells, for blood vessels, its probably just
about a done deal. The angiogenesis factors were isolated over the
last 2 years and the growth factors (e.g. fibroblast growth factors
of various types) have been known for many years. Lots of work
has been done trying to suppress endothelial cell growth after
angioplasty. If the Geron work is correct, endothelial cells
are quasi-replicative (like liver cells) so getting a supply
of them and inducing them to grow isn't difficult. You can
probably "3-D-implant" into the plastic the angiogenesis
factors and/or endothelial cell growth factors and have
no problems getting blood vessel growth where you want it.
Cells "naturally" have the ability to induce blood vessel
growth in hypooxygenation conditions, so even if you didn't
program the blood vessels, you could still get them if you
start out with stem cells in the right "stage".
I believe there is also work currently being done for smooth muscle
cells for artery growth (smooth muscle cells surround the endothelial
cells in larger vessels) and this is very close to going into
clinical trials (in bypass operations).
Nerves will be tougher in terms of "wiring" nerves into existing
connections, but given the spinal cord work I suspect this will
make rapid progress as well. There are probably multiple growth
factors and/or chemoattractants that remain to be isolated for
nerves however (but obviously big pharma wants them badly).
So, I'd be optimistic on the low end of Greg's time estimates.
Given the likely supply competition between the pig-engineered
and lab-engineered approaches these areas should advance rapidly.
Robert
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