Cancer researchers have discovered a “master switch” that turns on immune system cells, called natural killer cells, that hunt down and destroy tumors.

The finding — by a team led by Dr. Nick Huntington, from the Walter and Eliza Hall Institute's Molecular Immunology Division — could pave the way to new therapies to target cancer by boosting the power of the body’s own natural defenses to fight tumors.

In a report describing the breakthrough published in the journal Immunity, Huntingtong said the switch — a protein called ID2 — works by allowing natural killer cells to become responsive to growth factors in the blood. Such growth factors keep natural killer cells active and alive, but if it is taken away these cells die.

"This is an exciting discovery because previous research has shown that these natural killer cells are really potent in killing tumors: breast and colon cancer and melanoma cells," Huntington said.

"We knew this switch — or master regulator — was essential for the natural killer cell development but we had no idea how this worked.

"If we can give an advantage to natural killer cells by boosting their activity or numbers or survival in the body then we can try to win that fight against cancer."
Natural killer cells are a type of white blood cell that delivers lethal toxic granules into cells that have become cancerous or infected, causing them to explode.

Huntington said the switch that controls them could also be manipulated to fight viral infections or to help patients whose immune systems have not developed properly because their bodies lack natural killer cells.

Conversely, the natural killer cell switch could potentially be turned off in cases where they prove damaging, such as when they prompt the rejection of donor stem cells in bone marrow transplants or produce signals that result in the potentially fatal toxic shock syndrome.

"We've basically identified how natural killer cells are born and how they're maintained in our body," Huntington said. "Now we know how to best keep them fit and healthy to keep us healthy."