Limitations of an idea
The cell sorting technique, however, has limits, observes Douglas Smith, an oncologist and leukemia expert at Johns Hopkins University's Sidney Kimmel Comprehensive Cancer Center. He explains that "there have been many different attempts to find drugs or antibodies to 'purge' the leukemia from a patient's own bone marrow or blood cells so that they can be used in transplants. However, these approaches are not always effective. Most of the time, the patients own leukemia returns following the transplant."
According to Majeti, "we do not fully understand why the bone marrow starts making these abnormal cells in the first place"; predicting the return of leukemia is difficult. And Smith notes that "introducing stem cells from a donor for such a transplant avoids the risk of reintroducing the patient's own leukemia and is one reason transplants from donors have a better outcome for most leukemias."
Still, given the current poor understanding and prognosis of the disease, Smith goes on to say that the technique is an advance in how we study leukemia and normal blood cells. David Ritchie and Mark Smyth, both at the Peter MacCallum Cancer Center in Australia, are also optimistic about the implications of these papers. In a preview published in Cell, they wrote that these results will "ultimately lead to improved outcomes of leukemia."
The Stanford group believes that their findings will have implications regarding other cancers, as well. Irving Weissman, the senior author on the studies, suspects that CD47-based stealth might also play a role in other cancers. "I believe this will be a general mechanism for cancer to evade macrophages," he says, noting a 1992 study led by Ian Campbell that showed 90 percent of ovarian cancer cells express CD47 on the cell surface. The Stanford team is investigating the possibility that many cancerous cells use the CD47 protein as a shield. And if they're right, new weapons can be developed that may target a wide range of cancers.