James Thomson Interview

To start with, maybe you could explain exactly what a stem cell is and what it does.

James Thomson: It's actually pretty simple.

Get the Flash Player to see this video. A stem cell is something that can make more of itself, and it can give rise to something else. So in your skin, if you go out and get a sunburn today, part of your skin actually sloughs off, and it's the job of the stem cells in your skin to replace those cells. It lives at the bottom of your skin. And in the adult, cells either make one or just a few different cell types, these stem cells. But if you go back early enough in the embryo, there's a cell that can make everything. And in the intact embryo, it's actually not technically a stem cell, because when it goes off and makes everything, it goes away. And a stem cell is supposed to be something that will replace itself. So it's really a precursor cell. But if you take it out of the embryo and you put it in tissue cultures, conditions that are just right, it'll divide and replace itself, as far as we know, forever. And yet it maintains the form of everything in the whole body. And that's what an embryonic stem cell is.

What a powerful little thing.

James Thomson: Yeah, it's remarkable. It means we have access to the human body for the first time, because there's a lot of parts of your body that we can't culture, which means we can't study it in detail, which means we have to rely on mouse models. And as much as those models are different, it's wrong.

Before you succeeded in cultivating human embryonic stem cells -- ES cells -- you worked with primate stem cells, didn't you?

James Thomson: Yeah. We have to go back to the monkey one, 'cause that was actually more important biologically.

Get the Flash Player to see this video. We published primate embryonic stem cells in 1995. Mouse embryonic stem cells had been derived back in the early '80s. And a bunch of groups had attempted to do this in other species and failed. At the time we were starting to do this, it wasn't known whether it was just something funny about the biology of the mouse that allowed this or whether eventually it could be successful. So we really didn't know whether it would be successful or not. It turned out that the older conditions that were used for mouse ES cells allowed primate embryonic stem cells to be derived. But the specific factors -- we were just lucky we got it right, because they're all different than the specific factors for mouse cells. So you typically grow -- in the old days you'd grow mouse embryonic stem cells in feeder layers, and they'd make stuff that the cells like. But the stuff that the mouse ES cells like and the human embryonic stem cells like are entirely different. So it was just lucky the system worked. So we derived primate embryonic stem cells, and that showed that this could be done.

So cultivating the primate stem cells was the big breakthrough. What happened next?

Get the Flash Player to see this video. James Thomson: So we derived primate embryonic stem cells in 1995, and that showed that this could be done in a species other than the mouse. And given the evolutionary relatedness of humans and primates, we thought we could apply this to humans. So in 1995 I talked to some ethicists on our campus about how we would do this. And we were very fortunate to have two very good people on campus, one who's named Norm Fost, who is the head of our IRB (Institutional Review Board), which is the Human Subjects Committee you have to go through. And the other one is Alta Charo, who's a lawyer that had sat on some national panels dealing with ethical issues and human ES cell -- human embryo research, not human ES cell research -- and discussed how we would do this in an ethical way, and I did a lot of thought about whether I wanted to do it. And then finally we did the consent forms and we did it.

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