Johns Hopkins and Yale scientists have found that melanoma cells use a cloaking protein to hide from immune cells poised to attack the cancer. Nearly 40 percent of their sampling of melanoma tissues contained the B7-H1 protein, also called PD-L1, and scientists say it could be used as a target for new therapies.
For the study, described in the March 28 issue of Science Translational Medicine, the research team analyzed 150 samples of benign melanocytic lesions, and primary and metastatic melanomas, looking for expression of B7-H1 above a threshold of five percent. Of the samples, collected from patients at Johns Hopkins, 57 (38 percent) were positive for the B7-H1 cloaking protein.
Previous research by Yale scientist and B7-H1 discoverer Leiping Chen, Ph.D., formerly of Johns Hopkins, established that some melanoma cells express B7-H1, which renders the cells invisible to T-cells. These t-cells release interferon gamma, a potent signal to trigger cancer cell-killing. But it turns out that interferon gamma also prompts melanoma cells to make more B7-H1, further cloaking the melanoma cells from the immune system.
"It's a self-defeating process that may explain why immune cells penetrating melanomas can't kill them," says Janis Taube, M.D., assistant professor of dermatology and pathology at Johns Hopkins. "The immune cells are standing ready to attack, but the melanoma cells are holding them at bay by using the B7-H1 protein," she adds.