|Alan Trounson, CIRM President|
The full report this month includes a couple important advances in understanding the underlying nature of stem cells that result from reprogramming adult cells to become like embryonic stem cells, induced pluripotent stem cells (iPS). Although the science that revealed that this feat could be accomplished won the Nobel prize this year, much remains unknown about the resulting cells.
You can read that full report here, but I want to focus this blog on another paper that appeared in November, one that I frankly never expected to read. A team at Stanford placed embryonic stem cells directly into animal patients and they did not see wide spread formation of tumors. The very hallmark of pluripotent stem cells, whether embryonic or iPS cells, is that when they are transplanted directly they uniformly form a type of multi-tissue tumor called a teratoma. That is why the conventional wisdom is that pluripotent cells would always be matured at least part way to the desired final adult cell before ever being transplanted into patients.
The Stanford team only saw tumors in two out of 42 mice that received the transplants. In taking the leap to try this experiment, the researchers were building on knowledge built up in recent years about the key roll of the environment around stem cells in determining their fate; that is determining what type of adult cell they mature into. In this case they wanted the cells to become bone to replace a hole they had created in the animals’ skulls. They placed the cells on a synthetic scaffold to make the cells array as in bone and laced the scaffold with a protein known to enhance bone formation. The team attributed an additional push to form bone to signals the stem cells received from the neighboring bone at the graft site.
Two tumors out of 42 is still two too many for any regulatory approval of the process. But the team wrote that they hope to enhance the technique to yield completely tumor-free recipients. One thing they are suggesting is adding other cell types to the scaffold to act as “chaperones” for the stem cells.
My full report is available online, along with links to my reports from previous months.