In 1796, English physician Edward Jenner decided to investigate a tale he had often heard — that milkmaids infected with cowpox became immune to smallpox, a much more dangerous affliction. To test this theory, Jenner inoculated an eight-year-old boy with pus from the blisters of a milkmaid who had caught cowpox. Two months later, Jenner injected the boy with material from a smallpox lesion. The boy did not become ill, nor did the 22 people on whom Jenner later performed the same procedure.
Jenner had just made one of the most significant discoveries in medical history — a vaccine against smallpox, one of the greatest scourges humans have faced. But, his methodology would not make it past the ethical review boards that now govern research on human subjects.
Today, scientists testing experimental vaccines usually rely on laboratory experiments, measuring the immune responses of cells grown in Petri dishes, or animal studies, which dont always offer an accurate picture of the human immune response. Once vaccines become promising enough to test in humans, researchers can vaccinate volunteer subjects but cant purposely expose them to the pathogen. For example, in a recent study of an AIDS vaccine, researchers administered either the vaccine or a placebo to more than 16,000 volunteers in Thailand, then followed them for three years to see how many became infected.
That kind of study is useful but doesnt allow researchers to fully control the experimental conditions. Now, researchers at MIT and elsewhere are trying a new tactic — recreating the human immune system in a mouse. With mice that have human immune cells, you can “study immune response to pathogens that you cant give to people,” says Jianzhu Chen, the MIT biology professor leading this effort