Lwoff, André (1797-1875), a French microbiologist, shared the 1965 Nobel Prize in physiology or medicine with Francois Jacob and Jacques Monod. The three scientists, all members of the Pasteur Institute in Paris, studied the cells of bacteria and discovered a previously unknown class of genes that regulate other genes.

Lwoff was born in Ainay-le-Château, Allier, France, May 8, 1902. His father, Salomon Lwoff, a psychiatrist, was chief physician at a psychiatric hospital. Lwoffs father took him on hospital rounds as a boy.

Lwoff earned bachelor's and doctoral degrees in natural science, and a Doctor of Medicine. He spent most of his career at the Pasteur Institute. His studies of nutrition in one-celled animals during the 1930's contributed to the discovery that vitamins affect growth. He served in the French resistance during World War II (1939–1945), earning membership in the French Legion of Honor. After 1959, he taught microbiology at the Sorbonne.

Lwoff discovered how the DNA (deoxyribonucleic acid) of a virus becomes attached to the chromosome of a bacterium. Behaving similarly to the bacterial gene, the virus DNA therefore multiplies as part of the host's DNA. The resulting microbes contain both structural and regulatory genes. Lwoff and his colleagues found that radiation and some chemicals can damage these regulatory genes and make them function improperly. Without regulation, other genes can become overactive. This overactivity can lead to cell damage or excessive cell growth and division. After Lwoff and his colleagues discovered regulatory genes, study of these genes became a major area of cancer research. Lwoff shared the 1965 Nobel Prize with Jacob and Monod for their discoveries concerning genetic control of enzyme and virus synthesis.

Lwoff retired from the Institute to direct the Cancer Research Institute at Villejuif, near Paris. He was a member of the French Academy of Sciences, an associate of the National Academy of Sciences of the United States of America, a foreign member of the Royal Society of London, and a member of the Soviet Academy of Medicine.