Accelerated induction of mycobacterial antigen-specific CD8⁺T cells in theMycobacterium tuberculosis-infected lung by subcutaneous vaccination withMycobacterium bovisbacille de Calmette et Guérin

P>Both CD4+ and CD8+ T cells are important in protection against Mycobacterium tuberculosis infection. To evaluate the effect of vaccination with Mycobacterium bovis bacille Calmette-Guerin (BCG) on the CD8+ T-cell response to pulmonary M. tuberculosis infection, we analyzed the kinetics of CD8+ T cells specific to the mycobacterial Mtb32a(309-318) epitope, which is shared by M. tuberculosis and M. bovis BCG, in the lung of mice infected with M. tuberculosis. The CD8+ T cells were detected by staining lymphocytes with pentameric major histocompatibility complex (MHC) class I H-2Db-Mtb32a(209-318) peptide complex and were analysed by flow cytometry. Mtb32a-specific CD8+ T cells became detectable on day 14, and reached a plateau on day 21, in the lung of M. tuberculosis-infected unvaccinated mice. Subcutaneous vaccination with M. bovis BCG in the footpads induced Mtb32a-specific CD8+ T cells in the draining lymph nodes (LNs) on day 7 and their numbers further increased on day 14. When M. bovis BCG-vaccinated mice were exposed to pulmonaryinfection with M. tuberculosis 4 weeks after vaccination, the Mtb32a-specific CD8+ T cells in the infected lung became detectable on day 7 and reached a plateau on day 14, which was 1 week earlier than in the unvaccinated mice. The pulmonary CD8+ T cells from the BCG-vaccinated M. tuberculosis-infected mice produced interferon-gamma in response to Mtb32a(209-318) peptide on day 7 of the infection, whereas those of unvaccinated mice did not. The results demonstrate that induction of mycobacterial antigen-specific protective CD8+ T cells in the M. tuberculosis-infected lung is accelerated by subcutaneous vaccination with M. bovis BCG.