Today, Irving Weissman gave the Marian Koshland seminar here at Berkeley. Weissman is the Director of the Institute of Stem Cell Biology and Regenerative Medicine at Stanford. He was also recently featured in The New York Times (see also here). The title of his talk was "Stem cells: Units of regeneration, units in cancer and units of natural selection." He's a pioneer in the science of stem cells (having isolated and characterized the differentiation of the blood-forming cells); he also gives an awesome talk.

He started with an introduction to stem cells, then discussed how stem cells have been implicated in acute myeloid leukemias. His aim is to understand why 2-3% of tumor cells have properties similar to self-regenerating stem cells, and from all appearances, he is making progress. By regulating the expression profiles of hematopoeitic stem- and progenitor-cells, his lab is able to precisely control and induce cancers in a controlled way, including regulating the proliferation of monocytes from chronic myelomonocytic leukemia to acute myeloid leukemia (I hope I got that right!). This is a nice system because they can change exactly which expression program the cell is running at any given time, and observe the results in mice. It might not lead to immediate cures for cancer, but it will certainly help pinpoint how cells become neoplastic (cancerous), step-by-step. This could eventually lead to prophylactic treatments to destroy cells that are pre-cancerous.

But the highlight of his talk was his work on human neural stem cells. He injected human neural stem cells into mice, and they began to behave in certain ways just like mouse brain cells. They responded "correctly" to their microenvironment, differentiating into the proper cell forms and moving about in the mouse brain just as the mouse cells would have. These stem cells displayed plasticity and could repair spinal cord injuries. This is huge. It's easy to see that with some work, obtaining and culturing human neural stem cells could yield fantastic advances for victims of spinal cord injuries^(†).

Lastly, Weissman discussed a new model species—the protochordate Botryllus schlosseri—in which the somatic stem cells were under natural selection separately from the germline. He found a receptor in this species that may turn out to be an analog to a natural receptor for NK cells in vertebrates; he speculated that this putative NK receptor could help explain why transplant rejection occurs in some patients despite apparently good matches for the traditional cell surface antigens.

Stay tuned, there is still so much to be learned about human physiology at the cell level. We are just at the very beginning.

^(†) Weissman repeatedly noted that President Bush would call these experiments "abominations" because he is creating, after all, "human-animal hybrids." He was quick to point out that an individual's personal ethics could not possibly justify preventing research into life-saving treatments for others.