10 years ago, a Stanford University School of Medicine researcher Irving Weissman found a protein on Leukemia cells, called CD47, which the cancer cells produce in inordinate amounts.
CD47 is a marker protein that acts as a signal to prevent the body’s immune system from attacking & destroying its cancerous cells as they circulate. It turns out, “CD47 isn’t just important on leukemias and lymphomas,” says Weissman. “It’s on every single human primary tumor that we tested.”
Scientists have since built an antibody, that blocks the CD47 protein. Once blocked, macrophages, a type of immune cell, no longer ignore the cancer cells, but instead engulf and destroy them.
Researchers have used the antibody in mice, with human tumors transplanted from breast, ovary, colon, bladder, brain, liver, and prostate cancers. In each case, the presence of the blocking antibody, allowed the mice immune systems to recognize, and destroy, the cancer cells. The tumors shrank, and did not spread to the rest of the body, and the mice remained cancer-free 4 months after the treatment stopped.
Although the macrophages in the treated mice also attacked ordinary blood cells, which express small amounts of CD47, the researchers found that the decrease in blood cells was short-lived; the animals turned up production of new blood cells to replace those they lost.
While treated mouse macrophages engulfed and destroyed cancer cells from all human tumor types, more research is still ongoing to determine whether the results hold true in humans themselves.
Proceedings of the National Academy of Sciences.