RE: Ban on Human Cloning

Robert J. Bradbury (
Tue, 23 Nov 1999 03:03:59 -0800 (PST)

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.