Modified vaccinia Ankara-expressing Ag85A, a novel tuberculosis vaccine, is safe in adolescents and children, and induces polyfunctional CD4+ T cells.

Modified vaccinia Ankara-expressing Ag85A (MVA85A) is a new tuberculosis (TB) vaccine aimed at enhancing immunity induced by BCG. We investigated the safety and immunogenicity of MVA85A in healthy adolescents and children from a TB endemic region, who received BCG at birth. Twelve adolescents and 24 children were vaccinated and followed up for 12 or 6 months, respectively. Adverse events were documented and vaccine-induced immune responses assessed by IFN-gamma ELISpot and intracellular cytokine staining. The vaccine was well tolerated and there were no vaccine-related serious adverse events. MVA85A induced potent and durable T-cell responses. Multiple CD4+ T-cell subsets, based on expression of IFN-gamma, TNF-alpha, IL-2, IL-17 and GM-CSF, were induced. Polyfunctional CD4+ T cells co-expressing IFN-gamma, TNF-alpha and IL-2 dominated the response in both age groups. A novel CD4+ cell subset co-expressing these three Th1 cytokines and IL-17 was induced in adolescents, while a novel CD4+ T-cell subset co-expressing Th1 cytokines and GM-CSF was induced in children. Ag-specific CD8+ T cells were not detected. We conclude that in adolescents and children MVA85A safely induces the type of immunity thought to be important in protection against TB. This includes induction of novel Th1-cell populations that have not been previously described in humans.

Distinct, specific IL-17- and IL-22-producing CD4+ T cell subsets contribute to the human anti-mycobacterial immune response.

We investigated whether the proinflammatory T cell cytokines IL-17 and IL-22 are induced by human mycobacterial infection. Remarkably, >20% of specific cytokine-producing CD4(+) T cells in peripheral blood of healthy, mycobacteria-exposed adults expressed IL-17 or IL-22. Specific IL-17- and IL-22-producing CD4(+) T cells were distinct from each other and from Th1 cytokine-producing cells. These cells had phenotypic characteristics of long-lived central memory cells. In patients with tuberculosis disease, peripheral blood frequencies of these cells were reduced, whereas bronchoalveolar lavage fluid contained higher levels of IL-22 protein compared with healthy controls. IL-17 was not detected in this fluid, which may be due to suppression by Th1 cytokines, as PBMC IL-17 production was inhibited by IFN-gamma in vitro. However, Th1 cytokines had no effect on IL-22 production in vitro. Our results imply that the magnitude and complexity of the anti-mycobacterial immune response have historically been underestimated. IL-17- and IL-22-producing CD4(+) T cells may play important roles in the human immune response to mycobacteria.