After his medical internship US Army Service (1945–48), and working at the military hospital of Nancy, he became a researcher at Columbia University College of Physicians and Surgeons (1948–50). He performed research in Paris (1950–56), relocated to New York University (1956–68), moved to the National Institutes of Health (1968–70), then joined Harvard University medical school (1970–91) where he became the Fabyan Professor of comparative Pathology, concurrently serving the Dana-Farber Cancer Institute, Boston (1980). He began studies of allergies in 1948, and discovered the Ir (immune response) genes that govern transplant rejection (1960s). Counting different editions, he is an author of over 300 books and articles