César Milstein, an Argentine biochemist exiled in the United Kingdom after being affected by political repression in Argentina, and Georges Köhler, a German immunologist, develop in 1975 at the MRC Laboratory of Molecular Biology in Cambridge a technique that solves a fundamental problem of applied immunology: how to produce large quantities of a single, identical, specific antibody directed against one particular molecular target. Until then, antibodies obtained from immunized animals were always a heterogeneous mixture of distinct molecules recognizing multiple parts of the antigen, limiting their precision as diagnostic or research tools. Milstein and Köhler fuse antibody-producing cells — which naturally die after a limited time in culture — with cancerous myeloma cells, immortal in laboratory culture, generating hybrids called "hybridomas" that combine both properties: they produce a single type of antibody indefinitely and without limit. The hybridoma technique quickly becomes a fundamental tool of modern biomedicine, used in pregnancy tests, infection diagnostic tests, identification of cancer cell types, and as the basis of numerous modern therapeutic drugs based on monoclonal antibodies, used against cancers, autoimmune diseases, and viral infections. Milstein and Köhler deliberately decided not to patent the technique, allowing its free and immediate adoption by laboratories worldwide.