Jane Gitschier, with the UCSF Departments of Medicine and Pediatrics, interviewed U Wisc stem cell researcher Jamie Thomson for PLoS Genetics. Thomson was the first person to derive a human embryonic stem cell line and has other firsts to his credit. The whole interview is worth a read. But the most interesting point to me related to how Thomson's lab first figured out how to create human pluripotent stem cells (capable of becoming all cell types) without using embryonic cells as a starting point. Thomson could have made the induced pluripotent stem cell breakthrough 5 years sooner but the problem seemed it must be really hard to solve and so he didn't immediately try the easiest ways to make this happen.
Gitschier: And now, you've developed a new technology that may obviate some of these political and funding issues: Induced pluripotent stem [IPS] cells. Set the stage for that for me.
Thomson: The stage was Dolly really—that changed the mindset of developmental biologists in a big way, including mine. About 5 years ago, I hired the post-doc [Junying Yu] who was the first author on our paper [published in 2007]. My conversation with her at the time was that we have to try this, even though it probably isn't going to work. And it's probably like a 20-year problem, because the thought back then was that it has just got to be really complicated. All those little factors, and how can you manipulate all of those? It didn't really seem sensible.
I thought by doing such a combinatorial screen, we might get PARTIAL reprogramming in some way.
Gitschier: Describe what you mean by combinatorial screen.
Thomson: I'll tell you what we did, and it was very similar to what Yamanaka did in the mouse. We were doing it at the same time, but he got ahead of us because mouse work is actually much faster than human work, although we actually had a partially defined system with a more complicated set of factors prior to publication of his mouse work.
Back in the '70s, it was found that if you fuse blood cells with embryonic carcinoma [EC] cells—ES cells hadn't been derived yet—that within that heterokaryon, the dominant phenotype could either be the blood cell or the EC cell, but it was often the EC cell. So that was early evidence for reprogramming.
We started to do similar experiments several years ago, in which we took ES cell–derived blood cells. We had a well-defined, cloned, expandable hematopoietic cell type that we used in cell fusions for a model for reprogramming, and we showed that the dominant phenotype was the ES cell.
We did gene expression analysis of both those cell types and started to clone genes that were specifically enriched in ES cells. So Junying cloned between 100 and 200 genes, and she started taking pools of them to test for reprogramming ability and we used a knock-in human ES cell line that turns green and gets drug resistant when it reprograms to an ES cell state. Last summer, Junying kept paring it down until there were four factors, and we repeated it in different cell types.
It was kind of a dumb thing to do—it worked and that is nice. If you look at the factors we found, OCT4, SOX2, and NANOG—they're everybody's favorite genes already—these are key pluripotency genes. But we had this mindset, which was so strong, that it HAD to be complicated, we just never tested them! It would have been a lot easier to just test them 5 years ago and gotten it done in a month or two!
Gitschier: These IPS cells won't be restricted in terms of federal funding?
Thomson: No. That changes everything.
This breakthrough speeds up progress toward the development of useful stem cell therapies because it opens up the funding floodgates for working with human pluripotent stem cells by producing them in a way that doesn't involve use of a human fetus. But the gene twiddling involved in this technique might not produce cells safe enough for injection into humans. More refined ways to manipulate adult cells to revert them into an embryonic state might be necessary to produce cells that won't go cancerous.
|Share |||Randall Parker, 2008 September 08 02:36 PM Biotech Stem Cells|