Galectin-1 Covers and Protects Malignant Gliomas from Natural Killer Cells

Brain tumors fly under the radar of the body's defense forces by coating their cells with extra amounts of a specific protein, new research shows. Like a stealth fighter jet, the coating means the cells evade detection by the early-warning immune system that should detect and kill them. The stealth approach lets the tumors hide until it's too late for the body to defeat them. The findings, made in mice and rats, show the key role of a protein called galectin-1 (see image) in some of the most dangerous brain tumors, called high-grade malignant gliomas. A research team from the University of Michigan (U-M) Medical School made the discovery and published it online on July 16, 2014 in Cancer Research. In a stunning example of scientific serendipity, the team uncovered galectin-1's role by pursuing a chance finding. They had actually been trying to study how the extra production of galectin-1 by tumor cells affects cancer's ability to grow and spread in the brain. Instead, they found that when they blocked cancer cells from making galectin-1, the tumors were eradicated; they did not grow at all. That's because the "first responders" of the body's immune system – called natural killer or NK cells – spotted the tumor cells almost immediately and killed them. But when the tumor cells made their usual amounts of galectin-1, the immune cells couldn't recognize the cancerous cells as dangerous. That meant that the immune system couldn't trigger the body's "second line of defense," called T cells – until the tumors had grown too large for the body to defeat. Team leader Pedro Lowenstein, M.D., Ph.D., of the U-M Department of Neurosurgery, says the findings open the door to research on the effect of blocking galectin-1 in patients with gliomas.