A Subset of Mycobacteria-Specific CD4⁺ IFN-γ⁺ T Cell Expressing Naive Phenotype Confers Protection against Tuberculosis Infection in the Lung

Failure of the most recent tuberculosis (TB) vaccine trial to boost bacillus Calmette-Guérin-mediated anti-TB immunity despite the induction of Th1-specific central memory cell and effector memory cell responses highlights the importance of identifying optimal T cell targets for protective vaccines. In this study, we describe a novel, Mycobacterium tuberculosis -specific IFN-γ + CD4 + T cell population expressing surface markers characteristic of naive-like memory T cells (T NLM ), which were induced in both human (CD45RA + CCR7 + CD27 + CD95 - ) and murine (CD62L + CD44 - Sca-1 + CD122 - ) systems in response to mycobacteria. In bacillus Calmette-Guérin-vaccinated subjects and those with latent TB infection, T NLM were marked by the production of IFN-γ but not TNF-α and identified by the absence of CD95 expression and increased surface expression CCR7, CD27, the activation markers T-bet, CD69, and the survival marker CD74. Increased tetramer-positive T NLM frequencies were noted in the lung and spleen of ESAT-6 1-20 -specific TCR transgenic mice at 2 wk postinfection with M. tuberculosis and progressively decreased at later time points, a pattern not seen with TNF-α + CD4 + T cells expressing naive cell surface markers. Importantly, adoptive transfer of highly purified T NLM alone, from vaccinated ESAT-6 1-20 -specific TCR transgenic mice, conferred equivalent protection against M. tuberculosis infection in the lungs of Rag -/- mice when compared with total memory populations (central and effector memory cells). Thus, T NLM may represent a memory T cell population that, if optimally targeted, may significantly improve future TB vaccine responses.