Originally, the term “antibody” referred to an unknown entity in serum, which had the capacity to neutralize pathogenic bacteria. Ehrlich discovered that the socalled antibody had to be a discrete substance, and was the first to propose a theory on antibody formation (1 ). A few years later, he hypothesized that antibodies might be applied for selective treatment of cancer, provided that the antibody showed specificity for the tumor tissue (2 ). Later studies showed that antibodies could be produced against a wide variety of substances, including tumors.