Tuberculosis Subunit Vaccination Provides Long-Term Protective Immunity Characterized by Multifunctional CD4 Memory T Cells

Improved vaccines capable of promoting long-term cellular immunity are urgently required for a number of diseases that remain global health problems. In the present study, we demonstrate that a tuberculosis subunit vaccine, Ag85B-ESAT-6/CAF01 (where ESAT-6 is early secreted antigenic target of 6 kDa and CAF01 is cationic adjuvant formulation 01), induces very robust memory CD4 T cell responses that are maintained at high levels for >1 year postvaccination. This long-term, vaccine-induced memory response protects against a challenge with Mycobacterium tuberculosis at levels that are comparable to or better than those of bacillus Calmette-Guérin. Characterization of the CD4 memory T cells by multicolor flow cytometry demonstrated that the long-lived memory population consisted almost exclusively of TNF-alpha(+)IL-2(+) and IFN-gamma(+)TNF-alpha(+)IL-2(+) multifunctional T cells. In addition, memory cells isolated >1 year postvaccination maintained a strong, vaccine-specific proliferative potential. Long-term memory induced by the BCG vaccine contained fewer multifunctional T cells and was biased toward effector cells mainly of the TNF-alpha(+)IFN-gamma(+)-coexpressing subset. Ag85B-ESAT-6/CAF01 vaccination very efficiently sustained multifunctional CD4 T cells that accumulated at the site of infection after M. tuberculosis challenge, whereas the response in unvaccinated animals was characterized by CD4 effector T cells. Our data demonstrate that adjuvanted subunit vaccines can promote long-term protective immune responses characterized by high levels of persisting multifunctional T cells and that the quality and profile of this response is sustained postinfection.