To finish my three-week tribute to the Nobel Prize winners in the sciences, I get to end on a subject that is as controversial as it is miraculously life-saving: stem cells. Now before you burn my skin off with those disapproving glares, let me finish my article. I’m not talking about the embryonic stem cells that get everyone so worked up. I’m talking about induced stem cells, the kind ripped from your own body and infected until they lose their identity so scientists can give them a new one.
Last year’s winners for the Nobel Prize in Physiology or Medicine were Sir John B. Gurdon and Shinya Yamanaka for discovering “that mature cells can be reprogrammed to become pluripotent.” What that means is that they discovered a way to take mature cells and turn the cells into any other kind of cell they want. Not only does this avoid the controversy brought up by embryonic stem cells, but also avoids many of the medical problems they carry, like the need to suppress the receiver’s immune system from rejecting the new cells.
In 1962, Gurdon opened the door to cell reprogramming with a couple of frogs. At the time, researchers had an idea of how to transplant DNA from one cell to another, but they hadn’t done it with fully-differentiated cells. Gurdon, who worked on the original transplanting technique two years before, took cells from the lining of a tadpole’s intestines and transplanted the DNA into a prepared, DNA-less egg cell. The egg cell then accepted the new DNA and continued normal development into a squirming little tadpole. The egg cell could use the DNA because every cell in the body contains the full DNA sequence of the organism even though it only expresses a few genes according to the type of cell it is.
Forty-four years later, Yamanaka took Gurdon’s idea a few steps further by taking the DNA from mature cells and reprogramming them back into a stem cell-like state. These kinds of cells are called induced pluripotent stem (iPS) cells, pluripotent meaning that the cells can be influenced to differentiate and develop into many kinds of cells. Yamanaka created iPS cells by taking fibroblasts — a type of structural cell — and using a retrovirus — a virus that only carries its RNA — to insert transcription factors into the DNA sequence. Transcription factors influence the expression of genes. In this case, Yamanaka turned on Oct 3/4, Sox2, c-Myc, and Klf4. These four genes reverted the cells back to a pluripotent state, at which point Yamanaka cultured them, injected them back into the mice, and watched them grow into fibroblasts, nerve cells and gut cells.
Gurdon and Yamanaka’s experiments are considered breakthroughs in gene therapy. As stated before, using stem cells derived from a person’s own body negates any chance of immune reaction, and taking cells from a living person is a lot less likely to inspire people to pick up their picket signs. Scientists are further looking into iPS cells as the future standard treatment, but the technique still has a long way to go.