^*When antibiotics first appeared in the late 1930s and 1940s, they performed like magic, and much of this research was abandoned; in the early 1960s, public health officials were declaring victory over infectious disease. Now, with dozens of strains of bacteria developing resistance to drugs, with viruses gaining resistance even faster, with such diseases as tuberculosis, once considered conquered, making comebacks, investigators have returned to searching for ways to stimulate the immune system against everything from infections to cancer.