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Scientists have discovered a compound that allows the immune system to attack bladder, brain, breast, colon, liver, ovary, and prostate cancers--when the cancers are transplanted to mice. Development of a version of the drug for humans is underway.

Honest oncologists tell their patients that it's never really the treatment that gets rid of cancer for good, it's the immune system. Toxic chemo-therapies and radiation therapies disable cancer, at least in theory, long enough for the immune system to catch up with the cancer and complete the job of treatment. Some cancers, such as melanoma and prostate cancer, are now treated with vaccines to augment the power of the immune system, with varying degrees of success.

Dr. Irving Weissman and his colleagues at the Stanford University School of Medicine in Palo Alto, California, have discovered that one of the ways cancers evade the immune system is by producing relatively high levels of a protein called CD47.

In healthy blood cells, this chemical protects the cell against attack by the immune system as it circulates through the blood stream. it essentially serves as a "don't eat me" signal to white blood cells that otherwise would attack the tumor. In cancerous cells, excessive production of this chemical, above three times as much as is produced by healthy cells, prevents the immune system from detecting the cancer, and allows the cancerous cells that survive radiation and chemotherapy to reproduce and form new tumors.

Actually, it took four years for Weissman and colleagues to realize what they had discovered. And it took another nine years for them to be able to demonstrate in the scientific literature that they had discovered a cancer-killer that attacks most solid tumors in humans. But their research has reached the point that clinical testing is on the way soon.

Blocking CD47 Allows the Immune System Literally to Eat Cancer Cells

Weissman and his collaborators originally found that CD47 protected leukemia and lymphoma cells from the action of the immune system. Recent experiments have found that CD47 protects other kinds of cancers, too.

The research team took samples of solid tumors, sliced them up, and created cancer cell tissue cultures. They then exposed the cancer cells to macrophages, the relatively large white blood cells that have the function of surrounding and ingesting germs, foreign matter, and dead or diseased cells.

When Weissman and colleagues placed white blood cells in the same test tube as untreated cancer cells, the macrophages essentially didn't notice the cancer cells were there. They did not destroy the cells. But when Weissman and colleagues pre-treated the cancer cells with a CD47 inhibitor, the macrophages devoured the cells and eliminated the cancer. It is actually the immune system that kills the cancer, not the drug. The drug only allows the immune system to "know" that cancer is present.

Continue reading after recommendations

  • Kim D, Wang J, Willingham SB, Martin R, Wernig G, Weissman IL. Anti-CD47 antibodies promote phagocytosis and inhibit the growth of human myeloma cells.Leukemia. 2012 Dec. 26(12):2538-45. doi: 10.1038/leu.2012.141. Epub 2012 May 30. PMID: 22648449 [PubMed - indexed for MEDLINE]
  • Willingham SB, Volkmer JP, Gentles AJ, Sahoo D, Dalerba P, Mitra SS, Wang J, Contreras-Trujillo H, Martin R, Cohen JD, Lovelace P, Scheeren FA, Chao MP, Weiskopf K, Tang C, Volkmer AK, Naik TJ, Storm TA, Mosley AR, Edris B, Schmid SM, Sun CK, Chua MS, Murillo O, Rajendran P, Cha AC, Chin RK, Kim D, Adorno M, Raveh T, Tseng D, Jaiswal S, Enger PØ, Steinberg GK, Li G, So SK, Majeti R, Harsh GR, van de Rijn M, Teng NN, Sunwoo JB, Alizadeh AA, Clarke MF, Weissman IL. The CD47-signal regulatory protein alpha (SIRPa) interaction is a therapeutic target for human solid tumors. Proc Natl Acad Sci U S A. 2012 Apr 24.109(17):6662-7. doi: 10.1073/pnas.1121623109. Epub 2012 Mar 26.
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