Born at Munich in Germany, Köhler was educated at the University of Freiburg, receiving his doctorate in 1974. He then worked in Cambridge at the Medical Research Council Laboratory of Molecular Biology (1974–76) and at the Basel Institute for Immunology (1977–84). In 1985 he was appointed director of the Max Planck Institute for Immunology in Freiburg.

In 1975, Köhler's work at the MRC Laboratory in Cambridge with the molecular biologist César Milstein, yielded the first monoclonal antibody, i.e., antibody of one specific type manufactured by a culture of genetically identical cells, representing a single clone. This proved to be one of the major scientific breakthroughs of the decade, as anticipated by Köhler and Milstein in their letter to Nature briefly describing their achievement, published on August 7 1975: “Such cells can be grown in vitro in massive cultures to provide specific antibody. Such cultures could be valuable for medical and industrial use.”

The technique of Köhler and Milstein involved fusing a white blood cell (lymphocyte), which manufactures antibody but has a short lifespan, with a cancer cell, which ensures continuous production of the antibody. Specifically, lymphocytes were obtained from the spleen of a mouse that had previously been injected with sheep red blood cells (the antigen) to stimulate antibody production in the mouse cells. The lymphocytes were then mixed with cells from a bone-marrow tumor culture to create a hybridoma – an antibody-secreting cell line.

Köhler and Milstein later adapted their technique to produce a range of hybridoma cultures, each manufacturing pure antibody to specific known antigen. Monoclonal antibodies have revolutionized biological and medical diagnostic tests and assays and have found applications in various therapeutic techniques. Their great advantage is that they can be tailor-made to target a particular type of cell or subcellular component, and used as a vehicle for precision delivery of powerful drugs.

For their achievement, Köhler and Milstein shared the 1984 Nobel Prize for physiology or medicine with Niels Jerne.