The 2018 Nobel Prize in Physiology or Medicine was awarded to Dr. Tasuku Honjo, Distinguished Professor at Kyoto University. His research won recognition for the discovery of a substance that suppressed the function of the immune system which contributed to the development of a promising new cancer treatment. It began with the accidental discovery of a protein called PD-1 found on immune cells. Honjo's meticulous research uncovered that it operates as a brake for the immune cells. Cancer cells being attacked bind to PD-1 and signal the immune cells to stop attacking. Honjo contributed to the development of the breakthrough cancer treatment drug Opdivo, by finding a way to protect PD-1 from cancer cells. Find out about Honjo's research of more than 20 years from the discovery of PD-1 to the successful clinical application of Opdivo.