Last week in San Francisco, California, at the annual meeting of the International Society for Stem Cell Research, Andrew Baker, from the University of Glasgow, reported an astounding finding. When Baker and his colleague Nicole Kane set up their lab to study induced pluripotent stem cells (iPSCs), they decided to test their HIV-based vector that they had designed to introduce genes into adult skin cells. To this end, they designed an experiment that introduced marker genes into the skin cells without transforming them into a different cell type. However, when they used high concentrations of this virus, it changed the cultured skin cells into iPSCs. Therefore Baker and Kane were able to make iPSCs without introducing a single new gene into the adult cells!!
Baker was very cautious about these results. He said, “There needs to be a note of caution and respect for the way the virus works.” He continued, “There are a lot of people routinely using the viruses as tools without really understanding them.”
At first, Nicole Kane thought that she had contaminated her experiment with iPSCs from a different source. To determine if this was the case, she sent the samples to an independent forensics lab at the local police department, where a DNA fingerprinting expert confirmed that the iPSCs matched the original skin cells.
Once it was clear that the skin cells had been converted into iPSCs, were they really pluripotent cells. The answer was yes. When Baker and Kane put these cells through various tests to determine if they were, in fact, pluripotent, their virus-induced iPSCs, they past every single test. Therefore, they are clearly pluripotent. However, the efficiency of their conversion was very inefficient – less than one cell in a million became an iPSC. Also, chromosomal abnormalities were commonly found in these cells. However, Baker and Kane have used skin cells from several different patients, and all of them were transformed into iPSCs when exposed to high levels of their HIV-based gene vector. Therefore, the experiment was not a fluke. There is something about this vector that can push adult cells into becoming iPSCs.
Nicole Kane noted, “If you push the system a little with a virus, you breach the threshold of toxicity.” She continued, “That makes the cell unstable, and if you provide the right environment, such as adding the necessary culture media, it can induce a cell that satisfies all the criteria for an iPS cell.” If we study where these viruses integrate into the genome, we might be able to identify those genes whose manipulation might make reprogramming more efficient. In fact, several genes have been identified that are involved in cell cycling, microRNA regulation and other processes implicated in the developmental transition that gives the cell stem-cell characteristics, as well as several genes that are activated during cellular reprogramming.
There are folks who are not so convinced by these results. Ernst Wolvetang, at the Australian Institute for Bioengineering and Nanotechnology in Brisbane, was not convinced that the proposed iPS cells were not just skin cells that had become cancerous. To be sure that the cells truly were pluripotent, this experiment should be repeated in mice and shown to make sperm and eggs, which is the hallmark of pluripotency. Wolvetang added that if this experiment was done, he would buy the results that their interpretation.
Wolvetang’s concerns are, in my view, spot on. The chromosomal abnormalities are troubling, and if this last experiment can be done, then I think it is the real deal. If not, then it seems to be a case of slow transformation.