American James Allison and Japanese Tasuku Honjo won the 2018 Nobel Prize for Physiology or Medicine on Monday for game-changing discoveries about how to harness and manipulate the immune system to fight cancer.
The joint award to Allison and Honjo was given "for their discovery of cancer therapy by inhibition of negative immune regulation", the Nobel committee said.
Allison, a professor at the University of Texas MD Anderson Cancer Center, studied a protein that functions as a brake on the immune system.
Honjo, of Kyoto University, discovered a new protein, the ligand PD-1, which also acted as a brake on immune cells.
Researchers working under the direction of Allison and Honjo discovered methods of removing constraints on "T cells" that fight invaders by modulating immune responses.
Whereas both proteins have proven to be effective targets for treating different types of cancer, PD-1 has shown stronger results for the so-called immune checkpoint therapy, according to the Nobel Prize Foundation.
Allison, whose mother died of lymphoma, built on that research over the next 40 years, mostly in California and in Texas, where he is now chair of immunology at the MD Anderson Cancer Center. For many scientists, he said, a driving motivation "is simply to push the frontiers of knowledge".
Speaking to NPR in 2016, Allison said in his experiments on mice with cancer, he tinkered with one key molecule on the outside of T cells in the rodent's immune system.
Charles Swanton, chief clinician at the charity Cancer Research UK, said the scientists' work had revolutionised cancer and immunotherapy.
Research by Allison's team has meanwhile led to the development of a monoclonal antibody drug, which was approved by the US Food and Drug Administration (FDA) in 2011 for the treatment of melanoma.
"In some patients, this therapy is remarkably effective", Jeremy Berg, editor-in-chief of the Science family of journals, told The Associated Press.
Therapy developed from Honjo's work led to long-term remission in patients with metastatic cancer that had been considered essentially untreatable, the Nobel Assembly said. The economics laureate, which is not technically a Nobel but is given in honor of Alfred Nobel, the prizes' founder, will be announced next Monday.
Last year, U.S. geneticists Jeffrey Hall, Michael Rosbash and Michael Young were awarded the medicine prize for their research on the role of genes in setting the "circadian clock" which regulates sleep and eating patterns, hormones and body temperature.