In the early 1990s James Allison showed that CTLA-4 acts as an inhibitory molecule to restrict T-cell responses. In 1996, Allison was the first to show that antibody blockade of a T-cell inhibitory molecule (known as CTLA-4) could lead to enhanced anti-tumor immune responses and tumor rejection. Order of authorship in the original publication: Leach, Krummel, Allison.

In 2018 Allison shared the Nobel Prize in Physiology or Medicine with Tasuku Honjo “for their discovery of cancer therapy by inhibition of negative immune regulation.”  See also No. 14266.