Massive monoclonal expansion of CD4 T-cells specific for aMycobacterium tuberculosisESAT-6 peptide

Abstract

T-cell responses towards tuberculin (purified protein derivative; PPD) or theMycobacterium tuberculosis-specific antigens early secretory antigenic target (ESAT)-6 and culture filtrate protein-10 are indicative of prior contact with mycobacterial antigens. In this study, we investigated the exceptional case of a 75-yr-old patient who devoted more than one-third of his CD4 T-cells against PPD and ESAT-6.Antigen-specific T-cells were characterised using flow cytometric intracellular cytokine staining, ELISPOT assay, proliferation assays, and T-cell receptor spectratyping.T-cell frequencies were far above those found in age-matched controls (median 0.33%, range 0.05–6.32%) and remained at high levels for >2 yrs. The patient initially presented with haemoptysis, but active tuberculosis was ruled out by repeated analysis of sputum and bronchoalveolar lavage fluid. Skin testing was negative and haemoptyses did not have aM. tuberculosis-related aetiology. Phenotypical and functional properties of specific T-cells were consistent with a terminally differentiated effector-memory phenotype with capacity to produce interferon-γ, interleukin-2 and tumour necrosis factor-α. Epitope mapping showed that the CD4 T-cells were directed against a single peptide from ESAT-6 (amino acid 5–20) that was presented in context of HLA-DR. T-cell receptor Vβ-spectratyping and sequencing of specific CD4 T-cells revealed a prominent peak fraction of monoclonal origin.In conclusion, similar to monoclonal gammopathies of undetermined significance, this may represent the first T-cell counterpart with known specificity againstM. tuberculosis.