Mycobacterium bovis BCG induces similar immune responses and protection byrectal and parenteral immunization routes

We compared cellular immune responses to rectal, subcutaneous, and intrader mal administration of Mycobacterium bovis BCG for 5 to 20 weeks in mice, gu inea pigs, and macaques. Strong lymphoproliferative responses were induced in spleen cells after in vitro stimulation with purified protein derivative in guinea pigs and macaques, whatever the route of immunization. Comparabl e high numbers of gamma interferon- and tumor necrosis factor alpha-produci ng cells were found in the spleen after rectal, subcutaneous, and intraderm al immunization of mice and macaques. Similar levels of precursors of cytot oxic T lymphocytes specific for mycobacterial antigens were observed in mic e for all immunization routes. In macaques, cytotoxic activity, determined only at the end of the experiment (20 weeks), was similar after rectal and intradermal immunization. Six months after immunization, rectal and subcuta neous routes induced in mice similar levels of protective immunity against challenge with a virulent Mycobacterium tuberculosis strain (H37Rv), Rectal immunization gave immune responses and protective capacity similar to thos e for parenteral immunization and seemed to be a promising new route of vac cination against tuberculosis; in our study, immunization via the rectal ro ute never induced side effects associated with parenteral routes (axillary adenitis) and could also effectively reduce the risks of viral transmission associated with unsafe injections in the developing world.