Illustration of the Japanese physician and immunologist Tasuku Honjo (born 1942). In the early 1980s Honjo discovered the mechanism (class switch recombination) by which B cell immune cells switch the type of antibody they produce according to the antigen presented to them. While working on another type of immune cell, T cells, he discovered the cell surface protein programmed death-1 (PD-1), which he showed to be an immune checkpoint molecule that prevented T cells from attacking healthy cells. He also showed one of the ligands (targets) for PD-1, known as PD-L1, was over expressed on cancer cells allowing them to avoid detection by T cells. Honjo showed that blocking PD-L1 enhanced T cell response to cancers and lead to tumour shrinkage. Drugs targeting PD-L1 have been developed to treat numerous cancers. Honjo was awarded a share of the 2018 Nobel Prize in Physiology or Medicine for his work on cancer immunotherapies along with James P. Allison.