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AT A GLANCE The diagnosis and progression of nontuberculous mycobacteria lung disease (NTN-LD) are important for clinical judgement but cannot easily be predicted. The immunological response of mono- and poly-functional T cells, a representative of host reactivity to NTM, could be a surrogate biomarker for disease and progression prediction. BACKGROUND Mycobacterium avium complex (MAC) and M. abscessus (MAB) induced lung disease (LD) have become a clinical concern. Predicting clinical disease relevance and progression is important, but suitable biomarkers are lacking. The host immune response of mono- and poly-functional T cells might aid in clinical judgement. METHODS We enrolled 140 participants, including 42 MAC-LD, 25 MAB-LD, 31 MAC airway colonization (MAC-Co), 15 MAB-Co patients, and 27 healthy controls. Their blood mono- and poly-functional T cells were measured and analyzed after in-vitro stimulation. RESULTS Patients with MAC-LD generally had lower total IFN-γ+, total TNF-α+ and triple-positive T cells but higher mono-IL-2+ expression than the controls and MAC-Co group. The MAB-LD group had lower total IL-2 and triple positive cells than the controls and colonization group. Multivariate analysis revealed that body mass index (BMI), mono-IL2+ CD4+ and triple positive-CD8+ cells (PMA stimulation) significantly predicted MAC-LD from the controls. By contrast, male gender and triple positive-CD4+ cells predicted MAC-LD from colonization. On the other hand, the triple positive-CD4+ cells (PMA stimulation) alone or together with the mock/MAB ratio of IL-2+/TNF-α+ CD4 cells could predict MAB-LD in the MAB-Co group or the controls. Among MAC/MAB-LD patients without anti-mycobacterial treatment, MAC-specific mono-IFN-γ+ CD4+ cells and PMA-induced triple positive-CD4+ cells were correlated with progression, with an area under the ROC curve of 0.875. CONCLUSIONS The patients with MAC/MAB-LD had attenuated poly-functional T cells. The triple-positive CD4+ cells could be useful in diagnosing disease from colonization. MAC-specific mono-IFN-γ+ CD4+ cells and triple positive-CD4+ might predict radiographic progression, which could be useful in making treatment decisions.