Renato Dulbecco. Portrait of Renato Dulbecco (born 1914), the Italian virologist who showed how certain viruses can transform normal cells into cancerous ones. These cancerous cells divide continuously because their genetic material has incorporated some of the virus' genes. The genes affected, oncogenes, produce protein growth factors which stimulate the growth and division of cancerous cells. For this work, Dulbecco shared the 1975 Nobel Prize for Physiology or Medicine with Baltimore and Temin, his former students. Dulbecco had worked for the Resistance during World War II, before emigrating to America in 1947. Photographed in 1995.