The antigen-specific memory CD8⁺ T-cell response induced by BCG in cattle resides in the CD8⁺γ/δTCR^-CD45RO⁺ T-cell population

Tuberculosis (TB) remains a worldwide leading cause of death among infectious diseases. Development of safer and more efficacious vaccines requires a basic understanding of the protective mechanisms induced by BCG. Here we show that vaccination of cattle with BCG induces CD8⁺γ/δTCR^-CD45RO⁺ T-cells that can produce IFN-γ, up-regulate transcription and expression of perforin, lyse BCG-infected monocyte-derived macrophages (MoMφ{symbol}) and contribute to a reduction in the number of intracellular mycobacteria. We also observed BCG-induced CD8⁺ responses in vivo. After infection of cattle with Mycobacterium bovis, CD8⁺γ/δTCR^-CD45RO⁺ cells responded more strongly to M. bovis-infected MoMφ{symbol} than to BCG-infected MoMφ{symbol}. These results indicate that the antigen-specific CD8⁺ memory response resides in the CD8⁺γ/δTCR^-CD45RO⁺ cell population.