Characterization of Mycobacterium tuberculosis-specific Th22 cells and the effect of tuberculosis disease and HIV co-infection

Abstract

ABSTRACTThe development of a highly effective tuberculosis (TB) vaccine is likely dependent on our understanding of what constitutes a protective immune response to TB. Accumulating evidence suggests that CD4+ T cells producing IL-22, a distinct subset termed ‘Th22’ cells, may contribute to protective immunity to TB. Thus, we characterized Mycobacterium tuberculosis (Mtb)-specific Th22 (and Th1 and Th17) cells in 72 individuals with latent tuberculosis infection (LTBI) or TB disease, with and without human immunodeficiency virus (HIV)-1 infection. We investigated the functional properties (IFN-γ, IL-22 and IL-17 production), memory differentiation (CD45RA, CD27 and CCR7) and activation profile (HLA-DR) of Mtb-specific CD4+ T cells. In HIV-uninfected individuals with LTBI, we detected abundant IFN-γ producing CD4+ T cells (median: 0.93%) and IL-22-producing CD4+ T cells (median: 0.46%) in response to Mtb. The frequency of IL-17 producing CD4+ T cells was much lower, at a median of 0.06%. Consistent with previous studies, IL-22 was produced by a distinct subset of CD4+ T cells and not co-expressed with IL-17. Mtb-specific IL-22 responses were markedly reduced (median: 0.08%) in individuals with TB disease and HIV co-infection compared to IFN-γ responses. Mtb-specific Th22 cells exhibited a distinct memory and activation phenotype compared to Th1 and Th17 cells. Furthermore, Mtb-specific IL-22 was produced by conventional CD4+ T cells that required T cell receptor (TCR) engagement. In conclusion, we confirm that Th22 cells contribute substantially to the immune response to TB. Depletion of Mtb-specific Th22 cells during HIV co-infection may contribute to increased risk of TB disease.