We’ve heard it all by now. “Stem cells will cure everything.” “Stem cells kill embryos.” “Stem cells are overrated.” We hear much less about the science of it all. (Oh, no! Not science!) And that’s too bad, because it can tell us a lot about the rest of what we hear. Let’s get to it.
Think of stem cells like tiny organ transplants, and you’ll be pretty close to grasping the essentials. If you could grow a new heart from your own tissues, there wouldn’t be any need to worry about transplant rejection. That’s how adult stem cells work when used in the adult they came from. Used in another person, they’re like a transplant. Anti-rejection drugs need to be taken for the duration.
So, conceptually, stem cells are simple. Politically, it’s another matter. I’m going to try to give the Cliff Notes version of both the science and my take on the ethics, as well as what we can realistically expect in the way of cures in the near term.
Intro … at warp speed
Adult stem cells are a very rare cell type, are hard to grow, and are hard to turn into useful tissues. Embryonic stem cells are easier to find because they’re present in much higher proportions relative to the total number of cells in the embryo. The earlier the embryonic stage, the more stem cells, until at the very earliest stages (zygote, blastula) it’s pretty much all stem cells. Embryonic stem cells are easier to grow and mature. They can generally be coaxed to mature into a wider variety of tissues.
Also, the earlier the stage, the less developed the immune system is, so the less chance there is of rejection even when the tiny cell transplant is given to an unrelated person. However, due to research restrictions in the US, there hasn’t been enough work done here to know whether rejection will be an issue or not. Research is being carried forward elsewhere (Britain, South Korea, Australia, Singapore, China, Brazil, and other countries), but I haven’t heard about definitive results on this question yet.
The downside of stem cells is that they can have a nasty tendency to turn cancerous. There’s some evidence (eg here, and here) that at least some cancers get their start as stem cells that lose the fine-grained regulation necessary to grow and differentiate into something useful. Instead, they just grow. However, it’s still not clear whether so-called cancer stem cells start as normal stem cells or just look like them in some ways.
There are also other down sides. One is that more research really does need to be done. We’re just taking the first baby steps in this field.
Some results are being obtained now, and those are therapies for conditions due to malfunction of a single cell type. Things like macular degeneration blindness (retinal cells), replacing insulin-producing cells, and regrowing damaged nerve cells, such as in Parkinson’s (simpler, here), and brain or spine damage. But we’re years away from growing new organs.
[update, Sept. 4. The hardest thing about writing this post is that the field overtakes me before I have the paragraphs finished. The scuttlebutt is that Israeli researchers have grown a whole heart from embryonic stem cells. So we're obviously not years away from growing new organs. We're not even days away, if that report is right.]
Getting a stem cell to mature into one cell type is just a matter of figuring out how to trigger it and then keep the cells alive while they grow. An organ is dozens (hundreds?) of cell types, all of which have to be perfectly placed together in order to function. At this point, we’re miles (but not light years) away from understanding cell growth regulation well enough to know how to do that. Figuring out how far away we are from growing new hearts or limbs is an unknown itself. It’s like trying to figure out how far away a mountain peak is when you’re hiking. If you’re seeing the whole mountain, it’s on the horizon and maybe fifty miles away. If you’re only seeing the tip, then the base is around the curve of the Earth somewhere and it could be 500 miles away. We don’t know enough about growth regulation to know how far we have to go, but we can see the peaks in the distance.
And then there’s the huge downside that people get hung up on stem cells, especially when they’re from an embryo. So let’s just dive right into that issue, since it has to be addressed before anything else can be done.
[Fair warning: this is a long post...] Read more »
Print This Post