Stanford Leading Matters (the end): Lecture on Stem Cells

Stanford Leading Matters (the end): Lecture on Stem Cells

Please read the Preamble of the previous post to understand the context of this article. As always, I encourage comments and responses. Remember that you can find and listen to the actual lecture on Stanford on iTunes.

"Stem Cells and the Promise of New Cancer Therapies" by Dr. Henry Weissman

A stem cell has a unique property, which is that when it divides, one of the two resulting cells is also a stem cell. Dr. Weissman took pains, at this point and several times later in his lecture, to debunk the myth that a stem cell can produce any tissue. He said that there are several types of stem cells (blood-forming, bone-forming, muscle-forming, etc.) and that they are not interchangeable at all.

Blood-forming stem cells can be obtained in three ways:

• from the bone marrow
• from "mobilized blood": you can give someone a drug that flushes stem cells into the bloodstream for just a few hours; during that time you can collect as many stem cells as you would normally get from as many as 100 bone marrow taps.
• from umbilical cord blood — but again, people who propose "cures" derived from this source for all sorts of ailments are charlatans.

California has a law (Prop. 71, adopted in 2005) that allows a university to perform clinical trials of treatments that a company might not want to fund. This is what the Stem Cell Research Center at Stanford does.

The speaker described the potential to help fight blood-related and brain-related diseases with stem cells. However, there is a complex interaction between graft rejection mechanisms and stem-cell transplants. You need to circumvent the rejection mechanism to successfully implant foreign stem cells into a person.

Moving to the importance of this research for cancer, Weissman said that when a chemotherapy drug kills ordinary tumor cells but not the tumor stem cells (TSCs), the cancer will regenerate. Leukemia cells carry a CD47 protein that serves as a "don't eat me" signal to macrophages that would otherwise eliminate them. Therefore, antibodies targeted at CD47 seem promising, but so far experiments have only been conducted in the form of xenografts from humans to mice. In those experiments, the antibodies have arrested the development of the cancer cells transplanted into the mice.

In conclusion, Dr. Weissman pointed out that this research has a lot of implications because of the passionate opinions for or against the use of fetal stem cells. He did not shy from the controversy.

An audience member asked about potential solutions that could come from transplants from mice to humans. Dr. Weissman said that unfortunately, mice have about 150 viruses they live with, but which could potentially cause leukemia in humans. There are current efforts to raise virus-free pigs, because their hearts are about the same size as human hearts, so they would be suitable for transplants.

In answer to another question, the speaker said that his research center is performing clinical trials in the UK because patients are covered by a single national health insurance system. In the U.S., he would have to negotiate about the coverage with a number of private insurance companies, and after some of them deny coverage, the remaining sample population for the trials would be small.

Feel free to comment on these last three posts — either about the subject matter or about the usefulness of these notes.