Pienaar, Elsje

Purpose Mycobacterium avium complex lung disease (MAC-LD) represents the most common form of nontuberculous mycobacterial lung infection, particularly affecting women and older adults. Clinical management remains challenging, including prediction and differentiation between progressive and non-progressive disease. Overexpression of PD-1 pathways have been reported in progressive disease, and we hypothesize that PD-1 inhibition can restore antigen-specific immune responses detectable by FluoroSpot assay. Methods Peripheral blood mononuclear cells from 22 participants, including progressive and non-progressive MAC-LD patients, healthy controls, and individuals with latent tuberculosis infection (LTBI) were stimulated with nontuberculous mycobacteria and Mycobacterium tuberculosis antigens. Cytokine secretion of interferon-gamma (IFN-γ) and interleukin-2 (IL-2) were quantified using dual FluoroSpot assay, with and without PD-1 blockade. Results Progressive MAC-LD cases demonstrated significant increases in glycopeptidolipid (GPL)- and PPD-stimulated IFN-γ responses following PD-1 blockade, which was not seen in healthy controls, LTBI, or non-progressive MAC-LD patients. After GPL stimulation and in the presence of anti-PD-1, the number of IFN-γ responses increased from 25% to 75% in samples from progressive MAC-LD patients. This supports an association between PD-1–mediated T-cell dysfunction and disease progression. Mycobacterial MTB300 peptide pool antigen failed to discriminate MAC-LD from healthy controls, underscoring antigen specificity. Conclusions Our pilot study demonstrates that IFN-γ FluoroSpot assays, particularly when combining GPL or PPD stimulation and PD-1 inhibition, may help identify progressive MAC-LD. These findings also support other studies reporting that immune checkpoint dysregulation can be present in some patients with progressive and severe MAC-LD patients. Additional studies are warranted to determine its pathogenic role.