Protection following pulmonary DNA immunization is independent of the peripheral T-cell supply. (a) Mice were immunized by the pulmonary route with PEI-DNA-gp120, and 6 weeks later the mice were treated with FTY720. The following day the mice were challenged by intranasal instillation of a lethal dose (2 × 106 PFU) of vaccinia virus-gp160. Five days later, lungs and ovaries were harvested and assessed for viral titers. (b) The average percentages ± s.e. of circulating T cells in the blood of 5–7 mice per group with or without FTY720 treatment. (c) The total numbers of tetramer-positive CD8+ T cells (mean±s.e.) before FTY720 treatment, 1 day post treatment and 5 days following intranasal vaccinia virus-gp160 challenge. (d) Viral titers in the lungs and ovaries of unimmunized, pulmonary immunized, and pulmonary immunized+FTY720-treated mice that were challenged intranasally with vaccinia virus-gp160. Data represent means of 3–5 mice per group±s.e. BAL, broncho-alveolar lavage; MLN, mediastinal lymph nodes; PEI-DNA-gp120, polyethyleneimine-DNA-gp120 complexes; PFU, plaque-foming units.