The discoveries led to the creation of a multibillion-dollar market for new cancer medicines. In particular, drugs targeting PD-1 blockade have proved a big commercial hit, offering new options for patients with melanoma, lung and bladder cancers.
US drugmakers Merck & Co and Bristol-Myers Squibb currently lead the field after winning drug approvals in 2014, but Roche, AstraZeneca, Pfizer and Sanofi are also fielding rivals.
Sales of such medicines, which are given as infusions, are expected to reach some $15 billion this year, according to Thomson Reuters' consensus forecasts. Some analysts see eventual revenues of $50 billion.
Honjo, who is now 76, told a news conference in Tokyo he was honoured to get the Nobel, but that his work was not yet done. "I would like to keep on doing my research ...so that this immune treatment could save more cancer patients," he said.
Allison also said he was "honored and humbled" by the award.
"I never dreamed my research would take the direction it has," he said in a statement on his university's website.
"It's a great, emotional privilege to meet cancer patients who've been successfully treated with immune checkpoint blockade. They are living proof of the power of basic science."
Commenting on Monday's award, Dan Davis, an immunologist at Britain's University of Manchester, said "this game-changing cancer therapy" has "sparked a revolution in thinking about the many other ways in which the immune system can be harnessed or unleashed to fight cancer and other illnesses."
Charles Swanton, chief clinician at the charity Cancer Research UK, said the scientists' work had revolutionised cancer and immunotherapy.
"The booming field of immunotherapy that these discoveries have precipitated is still relatively in its infancy, so it's exciting to consider how this research will progress in the future and what new opportunities will arise," he said.