Retransforming diffrentiated fibroblasts into pluripotent stem cells

Takahashi et al.,
Induction of Pluripotent Stem Cells from Adult Human Fibroblasts by Defined Factors
Cell (2007), doi:10.1016/j.cell.2007.11.019
PDF file | Cell news report | NYtimes report | Wired report

What a surprise this morning. A glance at my NYtimes and Wired RSS feed and caught this amazing breakthrough. In the layman's language, this means that we could now get stem cells from skin cells, bypassing the messy ethical problems of obtaining stem cells from embryos. This also means that we could now generate stem cell that are compatible with any patient in need. And if you have been reading scientific related news for the past few years, I bed you already know all the therapeutic possibilities of stem cells. Yes, I mean regenerating backup organs and body parts for transplant; but no, not human cloning, which apparently is only of interest of science fiction stories.

Now, down into the details. If you can, I urge you to read the original pdf file of the paper it self. In a very Cell-unlike fashion, this paper is uncomplicated, straightforward and easy to read.

Here's how they did it. Takahashi et al. found 4 genes that could reverse differentiation in differentiated cells: Oct3/4, Sox2, c-Myc, and Klf4. A previous study showed that insertion of these 4 genes could reactivate pluripotency (the "stem cell" ability to develop into many forms of different cells) in mice skin cells. Now they repeated that in adult human dermal fibroblasts (HDF, a kind of skin cell). They used retroviruses as vectors (well, let's say it's a modified-unharmful version of HIV) to transfect the 4 genes into the fibroblasts, and after incubation, they induced the cells into stem cells, which they call "induced pluripotent stem cells" (iPS). Now, farther investigation showed that the iPS cells show several markers of embryonic stem cells (ES), and iPS cells could also be induced into all kinds of cells, including muscle, neural cells, adipose (fat storage), and others. And they could confirm via a genetic screen that the iPS cells were really fibroblasts with the four genes inserted, and not just ES cell contamination.

Of the 4 gene inserts, Oct3/4 & Sox2 are transcription factors that activate pluripotency; while they need the help of c-Myc & Klf4 which modifies chromatin structure (mostly via methylation & histone acetylation regulations) and thus allows Oct3/4 & Sox2 to access their target genes. Will, I'm not familiar with the other 3 genes, yet insertion of c-Myc, a well known oncogene, is downright scary. Also, the genes were inserted with retrovirus, which could insert it's genome into the cell genome randomly, which could also cause oncogenic mutations. Also stated in the discussions were that in the mice experiment, 20% of the induced stem cell generated mice progeny developed cancer due to c-Myc carrying retrovirus reactivation.

This is truly a breakthrough, yet as the author stated, it would be best if a non-gene-insert based method would be developed in the future. Only by eliminating the c-Myc and retrovirus risk factors could this became a safe method of producing transplant ready organs. I am also worried about how the iPS and ES cells differ genetically. If you could still tell apart them through a genetic screen, then would any genes that make up that difference be other risk factors?