CD4 and infection: In summary, our present results showed that aerosolized boosting of γ-irradiated BCG is able to elicit Th1-biased immune responses, including antigen-specific memory CD4+ T cells concomitantly producing IFN-γ, TNF-α, and IL-2, as well as the IFN-γ response, via both the local and systemic immune systems and to eventually confer improved protection against hypervirulent Mtb HN878 infection following BCG s.c. priming and boosting.