PD-L1 and PD-1 Are Associated with Clinical Outcomes and Alveolar Immune Cell Activation in ARDS.

The relationship between the Programmed Death-Ligand 1 (PD-L1)/Programmed Death-1 (PD-1) pathway, lung inflammation, and clinical outcomes in acute respiratory distress syndrome (ARDS) is poorly understood. We sought to determine whether PD-L1/PD-1 in the lung or blood is associated with ARDS and associated severity. We measured soluble PD-L1 (sPD-L1) in plasma and lower respiratory tract samples (ARDS1 (n = 59) and ARDS2 (n = 78)) or plasma samples alone (ARDS3 (n = 149)) collected from subjects with ARDS and tested for associations with mortality using multiple regression. We used mass cytometry to measure PD-L1/PD-1 expression and intracellular cytokine staining in cells isolated from bronchoalveolar lavage fluid (BALF) (n = 18) and blood (n = 16) from critically-ill subjects with or without ARDS enrolled from a fourth cohort. Higher plasma levels of sPD-L1 were associated with mortality in ARDS1, ARDS2, and ARDS3. In contrast, higher levels of sPD-L1 in the lung were either not associated with mortality (ARDS2) or were associated with survival (ARDS1). Alveolar PD-1POS T cells had more intracellular cytokine staining compared with PD-1NEG T cells. Subjects without ARDS had a higher ratio of PD-L1POS alveolar macrophages to PD-1POS T cells compared with subjects with ARDS. We conclude that sPD-L1 may have divergent cellular sources and/or functions in the alveolar vs. blood compartments given distinct associations with mortality. Alveolar leukocyte subsets defined by PD-L1/PD-1 cell-surface expression have distinct cytokine secretion profiles, and the relative proportions of these subsets are associated with ARDS.

The transcriptional and phenotypic characteristics that define alveolar macrophage subsets in acute hypoxemic respiratory failure.

The transcriptional and phenotypic characteristics that define alveolar monocyte and macrophage subsets in acute hypoxemic respiratory failure (AHRF) are poorly understood. Here, we apply CITE-seq (single-cell RNA-sequencing and cell-surface protein quantification) to bronchoalveolar lavage and blood specimens longitudinally collected from participants with AHRF to identify alveolar myeloid subsets, and then validate their identity in an external cohort using flow cytometry. We identify alveolar myeloid subsets with transcriptional profiles that differ from other lung diseases as well as several subsets with similar transcriptional profiles as reported in healthy participants (Metallothionein) or patients with COVID-19 (CD163/LGMN). We use information from CITE-seq to determine cell-surface proteins that distinguish transcriptional subsets (CD14, CD163, CD123, CD71, CD48, CD86 and CD44). In the external cohort, we find a higher proportion of CD163/LGMN alveolar macrophages are associated with mortality in AHRF. We report a parsimonious set of cell-surface proteins that distinguish alveolar myeloid subsets using scalable approaches that can be applied to clinical cohorts.