4. STUDY POPULATION 4.1 Population Healthy volunteers, 18 - 55 yr old. 4.2 Inclusion criteria The subjects must be healthy adults, aged 18 - 55 years old. 4.3 Exclusion criteria Subjects are excluded when they are from tuberculosis endemic countries, if they have been in contact with tuberculosis patients or if they already have been vaccinated with BCG. The subjects are excluded from the study if they suffer for any disease, including intercurrent infections. Subjects are not allowed to use any medication except oral anticonceptive agents.