To develop a safe and effective RSV vaccine, many strategies and platforms have been applied in pre-clinical and clinical phases (26) . Many RSV vaccine candidates specifying target antigens employed two envelop proteins, G attachment protein and F fusion protein, because these antigens are known to induce protective immunity against live RSV infection. However, in the BALB/c mouse model, immunization of G protein expressed from recombinant vaccinia virus elicited Th2-biased responses, which was responsible for the vaccine-enhanced diseases (27) . Thus, G protein has been falsely regarded as a bad target antigen for a long time, although it could induce strong neutralizing antibody responses upon immunization. Recently, it has been suggested that G protein itself is not the cause of vaccine-enhanced diseases and the proper balance between RSV-specific Th1 and Th2 responses is rather an important factor controlling both safety and efficacy of G-targeted RSV vaccine. Using appropriate platforms and/or adjuvants, this balance could be achieved with G-targeted vaccines. For example, we have recently demonstrated that mucosal immunization of recombinant adenovirus vac-cine expressing the core domain of G successfully induced protective immunity without vaccine-induced diseases (9) .