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Dr. Enders pondered while he puttered with cowpox virus in tissue cultures of chick embryo cells. Through an ordinary binocular microscope, he could see that the cells were damaged and began to fall apart as the virus multiplied. Others had seen this phenomenon; to the thoughtful Dr. Enders its significance eventually became clear and astonishingly simple: the nature and amount of cell damage were indexes to the nature and amount of viral activity. "It seems incredibly obvious now," he says.
A World War II project diverted Dr. Enders to mumps, which was feared as a menace to troops. He produced a moderately satisfactory killed-virus vaccine that helped him form his now firm opinion that a vaccine made from a live but attenuated virus is better than any made with killed virus: "I don't think you can do better than nature itself does when it gives you the disease." Back at tissue culture after the war, Enders was joined by two research fellows. Drs. Frederick C. Robbins and Thomas Weller. The work was bedeviled by bacteria contaminating the cultures, making them useless before a slow-starting virus multiplied. Virologists began adding antibiotics to their cultures to keep out bacteria; Enders hit upon a particularly successful combination of penicillin and streptomycin. Yet even in uncontaminated cultures, Enders failed to isolate and grow the obstreperous measles virus.
Culture in Human Embryo. Then came a lucky break. The lab happened to have some poliovirus tucked away. This had hitherto refused to grow except in brain cells, which are unsafe as a culture for a human vaccine because nerve-cell proteins can kill the vaccinated person. Enders suggested growing it in cultures of muscle and skin from human embryos recovered in therapeutic abortions. It worked. Watching the cell-damage effect, the Harvard researchers could see that the virus was multiplying. The virus could still cause paralytic polio. But when serum from a recent polio patient was mixed with the virus in tissue culture, the cells were protected. The antibodies were at work. In guarded, highly technical language in Science, meaningful only to other virologists, the three researchers reported their success.
It meant that poliovirus could at last be grown in a way to make a safe vaccine, and the discovery led the University of Pittsburgh's Dr. Jonas E. Salk to the next step, developing a formaldehyde-killed vaccine. It also meant a 1954 Nobel Prize, which Enders insisted that Robbins and Weller share with him equally.
Success in Measles. An ever more insistent backer of live-virus vaccines, Enders was a bit dismayed that the U.S. took up killed-virus polio vaccine with such zest. He experimented for a while attenuating poliovirus, sent a sample to the University of Cincinnati's Dr. Albert Sabin (who went on to make workable live-virus polio vaccines), then turned back to basic research. In 1954 another of his research fellows, Thomas Peebles, fulfilled Enders' longstanding dream of growing measles virus (obtained from a prep school student named David Edmonston) in tissue culture. This time, aiming for a safe and effective live-virus product, Enders decided to keep control of the vaccine project in his own lab.