Allison, 70, of the University of Texas Austin, studied a known protein and developed the concept into a new treatment approach. He realized that if he could release that "brake", the immune system would wreak havoc on tumors.
Many of Allison's patients are alive and cancer free because of his approach.
According to his website, Honjo discovered a key protein - Programmed Cell Death Protein 1 - in controlling whether cells live or die, a central process in determining whether cells become cancerous and grow into tumors or behave normally. "I didn't set out to study cancer, but to understand the biology of T cells, these incredible cells [that] travel our bodies and work to protect us".
Prior to the discoveries made by this year's Nobel Prize for Medicine or Physiology winners, progress into clinical development of new cancer treatments was slow.
In the early 1990s, Allison had been studying a protein called CTLA-4, which sits in the outer layer - the membrane - of an active T-cell and behaves like an off-switch.
Researchers from the United States and Japan won the Nobel Prize in medicine on Monday for discoveries that help the body marshal its cellular troops to attack invading cancers.
"By stimulating the ability of our immune system to attack tumor cells, this year's #NobelPrize laureates have established an entirely new principle for cancer therapy". "A succession of graduate students, postdoctoral fellows and colleagues at MD Anderson, the University of California, Berkeley, and Memorial Sloan Kettering Cancer Center played important roles in this research".
Emery 'very happy' with Welbeck after match-winning brace for Arsenal
There's the club, the player and the team, and my focus is the team. "I think he is helping the team and we want this". The 27-year-old has scored four goals in six appearances for his club this season.
At the time, most doctors and scientists believed that the immune system could not be exploited to fight cancer, because cancer cells look too much like the body's own cells, and any attack against cancer cells would risk killing normal cells and creating serious side effects.
"I'm honored and humbled to receive this prestigious recognition", Allison said.
"I think this is just the tip of the iceberg - many more medicines like this are on the horizon", he said.
"I would like to keep on doing my research.so that this immune treatment could save more cancer patients", he said.
Meanwhile, Allison left UC Berkeley in 2004 for Memorial Sloan Kettering research center in NY to be closer to the drug companies shepherding his therapy through clinical trials, and to explore in more detail how checkpoint blockade works.
Meanwhile, the fact that the literature prize will not be handed over this year has grabbed several headlines.
Awards in physics, chemistry, peace and economics will follow.
The duo will share the Nobel prize sum of nine million Swedish kronor (about $1.01 million or 870,000 euros).