American James Allison and Japanese Tasuku Honjo won the 2018 Nobel Prize for Physiology or Medicine for discoveries leading to new approaches in harnessing the immune system to fight cancer, the award-giving body said on Monday.

“Allison and Honjo showed how different strategies for inhibiting the brakes on the immune system can be used in the treatment of cancer,” the Nobel Assembly at Sweden’s Karolinska Institute said, on awarding the prize of 9 million Swedish crowns ($1 million).

Both laureates studied proteins that prevent the body and its main immune cells, known as T-cells, from attacking tumor cells effectively.

Honjo, professor at Kyoto University since 1984, separately discovered a second protein on immune cells and revealed that it too operated as a brake, but with a different mechanism.