Allison's crucial insight was to block a protein on T cells that acts as a brake on their activation, freeing the T cells to attack cancer. Surgeon William Coley had developed an approach to treating cancer that involved injecting patients with a mixture of heat-killed bacteria in the hopes of stimulating the body's "resisting powers". Meanwhile, Honjo separately discovered a second protein on immune cells that also acted as a brake but with a different mechanism.
"Immunotherapy is now possibly the most important recent discovery for cancer therapy in general, as an alternative to chemo", he said.
Allison and Tashuka initially conceived that their discoveries may help treat chronic infections such as hepatitis B and C. The drugs created from their discoveries remain in trials for these conditions, but their most exciting application has come through the treatment of cancer. "It was one of those moments when we figured out that CTLA-4 was the brakes on the immune system".
The US Food and Drug Administration has already approved a number of immunotherapy treatments, including some targeting PD-1. He continues his own research, focusing on the details of immune response to cancer and identifying new targets for potential treatment.
Writing on his cancer centre's website, Allison said he was "honoured and humbled to receive this prestigious recognition". Honju works at Japan's Kyoto University.
Allison and Tasuku Honjo have jointly been awarded the Nobel Prize in medicine or physiology.
Prof Allison said it was "a great, emotional privilege to meet cancer patients who've been successfully treated with immune checkpoint blockade". This discovery has also proved to be effective in developing treatments.
While in theory it should work for most forms of cancer, it's most effective on those with the highest numbers of mutations such as melanomas, lung cancer and smoking, he added. Honjo, 76, is a distinguished professor at the Kyoto University Institute for Advanced Study and a professor in the department of immunology and genomic medicine at Kyoto University in Japan.
Dr. Allison told a news conference he was in a "state of shock" hours after learning from his son that he had won a Nobel prize. Experts previously thought that metastasis, when the cancer spreads to other organs and tissues, was untreatable, the Nobel committee's press release explains.