Georges Kohler, 48, Medicine Nobel Winner

Georges Kohler, co-inventor of one of the most important techniques of biotechnology, for which he shared the Nobel Prize in Medicine in 1984, died on Wednesday in Freiburg, Germany. He was 48.

The cause was heart failure, said Dr. Marinus Lamers, a colleague of his at the Max Planck Institute for Immune Biology in Freiburg.

Dr. Kohler invented a method of forcing immune system cells to make pure antibodies against a chosen antigen, instead of the profusion of different agents that usually greet an invading virus or bacterium. These pure proteins, known as monoclonal antibodies, laid the foundation of a multimillion-dollar industry that supplies them for diagnosing disease organisms and targeting specific tissues of the body.

The invention was made in 1974 when Dr. Kohler, then a young postdoctoral student, was working with his mentor, Dr. Cesar Milstein at the Laboratory of Molecular Biology in Cambridge, England. The British Government, which supported the laboratory, did not recognize the extraordinary commercial significance of the technique and failed to patent it.

Some discoveries just drop into a scientist's lap, while others require a lifetime's dedicated pursuit. Dr. Kohler was dedicated to solving a single problem, but also lucky in making such a great discovery so early in his career.

For his doctoral thesis at the Institute of Immunology in Basel, Switzerland, he studied the powerful diversity of the immune system, establishing that the mouse can generate a thousand different types of antibodies against a single site on a foreign protein.

This very diversity made the immune system hard to study, since biologists could not reliably produce useful amounts of any one antibody. Moving to Cambridge after hearing a lecture by Dr. Milstein in Basel, Dr. Kohler conceived a way of creating a line of cells that would produce a single pure antibody.

His idea was to inject a mouse with a powerful antigen and extract the antibody-producing white blood cells from its spleen. The white blood cells, known as lymphocytes, would then be fused with a kind of cancerous cell known as a myeloma. If by blind chance the right lymphocyte should be selected -- one producing the antibody against the injected antigen -- then the cancerous half of the hybrid cell would keep it alive indefinitely in the test tube, forming daughter cells that were locked into producing the same pure antibody.

Although both he and Dr. Milstein believed the experiment was a long shot, they decided Dr. Kohler should try it anyway. Around Christmas 1974, Dr. Kohler's first batch of fused cells was ready to be challenged with an antigen: halos would emerge around their wells if they were producing antibodies.

As Dr. Kohler described the discovery several years later, he prepared the cells and went home for dinner, waiting three hours for the test to develop. He asked his wife, Claudia, to go back with him to the laboratory, so as to commiserate if the results were negative, as he expected. "We went down into the basement of the institute, which has no windows," he said. "I looked at the first two plates. I saw these halos. That was fantastic. I shouted. I kissed my wife, I was all happy. It was the best result I could think of."

For reasons not well understood at the time, the lymphocytes engaged in producing the antibody were also particularly prone to fuse with the myelomas, explaining the success of the experiment. Dr. Kohler had created a powerful general method for raising pure antibodies against any antigen of interest. In principle these pure antibodies, because of their remarkable specificity, could be used to diagnose disease, or to carry therapeutic agents to particular body tissues.

As the importance of the invention became clearer, the scientific establishment at first assumed that Dr. Milstein, a well-known immunologist, must have done all the work, even though the original paper was signed jointly and, in the style of scientific articles, gave no clue as to which author had done what. In 1980 Columbia University gave its $20,000 Horwitz Prize to Dr. Milstein alone for inventing the technique "with an associate, George [ sic ] Kohler." The General Motors Cancer Research Foundation, too, awarded its $100,000 Sloan prize to his mentor the following year for the technique "which Dr. Cesar Milstein developed."

Dr. Kohler, a shy and gentle man, did not complain of these oversights but insisted on his own role in the discovery, that of conceiving and executing the experiment. "I believe I was the driving force in it, but it is also true to say that I would not have thought about this problem in any other laboratory than Cesar Milstein's and I wouldn't have been encouraged to do the experiment by anyone else but Cesar Milstein," he wrote in a memorandum in 1981.

Prize committees then began to include Dr. Kohler in the kudos they showered down on the monoclonal antibody technique, also known as the hybridoma technique. In 1984 the Lasker Prize, whose jurors often succeed in anticipating Nobel awards, included Dr. Milstein, Dr. Kohler and Michael Potter, who developed the myeloma cells used by Dr. Kohler. Later the same year the biologist's ultimate accolade, the Nobel Prize for Medicine, was awarded to three immunologists, including Dr. Milstein and Dr. Kohler.

Georges Kohler was born on April 17, 1946, in Munich. He graduated from Freiburg University in 1971, then went to Basel. After leaving Cambridge, Dr. Kohler returned to the Institute of Immunology in Basel, where he worked from 1976 to 1983. In 1984 he moved to the Max Planck Institute for Immune Biology in Freiburg, where he was director.

Dr. Kohler further refined the technique for making hybridoma cells but had no interest in developing it commercially, a task he viewed as routine. He remained keenly interested in research and in developing new immunologic techniques. At Freiburg he and his colleagues studied the B cells of the immune system and the receptors with which they respond to the hormone interleukin. They found the receptors had a major role in the human response to parasitic infections.

In his view of science Dr. Kohler distinguished between ideas, which are cheap, and the arduous experiments needed to test them. "I have many ideas, but often they don't work," he said in an interview in the journal Science in 1981. "In discoveries, the most important thing is to do the experiment."

Dr. Kohler is survived by his wife and three children.