CD4 and infection: In our study, the BCG s.c.-immunized group also showed more generation of multifunctional CD4+ T cells producing IFN-γ+TNF-α+IL-2+ at 5 weeks post-Mtb challenge than the infection-only control group (Fig 5A), indicating the presence of ready-to-be expanded multifunctional memory CD4+ T cells and that their rapid expansion following the recognition of Mtb infection is critical for vaccine development.