Baruj Benacerraf, 90, a Venezuelan-born immunologist who became a leading scientist and academic administrator and won a Nobel Prize for shedding new light on how the human body fends off disease, died Aug. 2 at his home in Boston. He had pneumonia.

In 1980, Dr. Benacerraf earned the Nobel in the physiology or medicine category for studies that delineated the role of genes as regulators of the immune system. He shared the award with colleagues Jean Dausset of the University of Paris and George Snell of Jackson Laboratory in Bar Harbor, Maine.

In exploring the genetic basis of the body’s defenses, Dr. Bena­cerraf helped show how and why individuals differ in their ability to resist infection. His work led to understanding of the way the body might also attack itself, and of the acceptance or rejection of transplanted tissue.

His “seminal discoveries about genetic control of the immune system made possible much of what we now know about basic disease processes such as infection, autoimmune disorders and cancer,” said Edward J. Benz Jr., president of the Dana-Farber Cancer Institute in Boston.

Dr. Benacerraf was president of the institute from 1980 to 1992. Before settling in Boston, he directed an immunology laboratory at the National Institutes of Health in Bethesda from 1968 to 1970.

The asthma from which he suffered as a child was credited with prompting his interest in medicine and immunology. He developed a curiosity about hypersensitivity and why some substances irritate some people but not others.

Much of his career was spent in the Boston area, where he was a professor at Harvard Medical School from 1970 to 1991 as well as head of Dana-Farber. He was known for his ability to toggle among a variety of responsibilities as scientist and administrator. He supervised research, raised money and attracted talented staff members.

His heritage spanned four continents and several countries. His parents, Sephardic Jews, came from North Africa.

Baruj Benacerraf was born Oct. 29, 1920, in Caracas, Venezuela, where his father had gone to establish himself in finance and textiles. His early schooling was in France, where the family was living when the rise of the Nazis in Germany and the threat of war prompted their return to Venezuela.

For college, Dr. Benacerraf came to the United States, enrolling in Columbia University’s school of general studies. He received a bachelor’s degree in 1942 and applied to medical school.

As a Jew and a foreigner, he wrote in a biographical sketch, he found almost no place open to him at that time. Dozens of other medical schools turned him down. Through the intervention of a family friend, he obtained one of the last two unfilled spots in the entering class of the Medical College of Virginia, which is now part of Virginia Commonwealth University in Richmond.

He became a naturalized American citizen in 1943 and was drafted into the Army while in medical school. He finished medical school in three years, rather than four. He was sent to Europe after the war. In the French city of Nancy, he practiced what now, he said, would be called “community medicine.”

The next several years were complicated by his father’s poor health. His father had suffered a stroke, and Dr. Benacerraf struggled to maintain his burgeoning career in medical research while running the family enterprises. He said he was greatly limited in France because he was viewed as a foreigner, despite his early education there.

In 1956, he returned to the United States and launched his research career at New York University as an assistant professor of pathology. A mentor there helped Dr. Benacerraf establish his own laboratory and research support. At the same time, he managed a family bank. But as immunology developed in importance, he cut back on his business involvement.

In an important experiment, Dr. Benacerraf recognized the varying abilities of laboratory guinea pigs to respond to foreign cells, and through selective breeding, he managed to create separate lines, distinguished by possession or lack of a specific gene.

Such work pointed toward isolation of the genes that controlled immunity as part of research that gave new understanding of the processes of sickness and health.

In 1943, Dr. Benacerraf married Annette Dreyfus, whom he had met at Columbia. She was the niece of another Nobel laureate, Jacques Monod, who won the 1965 prize in physiology or medicine. She was also a descendant of Alfred Dreyfus, the French army captain whose court-martial in the 1890s was a key event in European political and social history.

Annette Dreyfus died in June. Dr. Benacerraf’s survivors include a daughter, Beryl Benacerraf, a professor at Harvard Medical School; a brother; and two grandchildren.