Recruitment of neutrophils to the airways, and their pathological conditioning therein, drive tissue damage and coincide with the loss of lung function in patients with cystic fibrosis (CF). So far, these key processes have not been adequately recapitulated in models, hampering drug development. Here, we hypothesized that the migration of naïve blood neutrophils into CF airway fluid in vitro would induce similar functional adaptation to that observed in vivo, and provide a model to identify new therapies. We used multiple platforms (flow cytometry, bacteria-killing, and metabolic assays) to characterize functional properties of blood neutrophils recruited in a transepithelial migration model using airway milieu from CF subjects as an apical chemoattractant. Similarly to neutrophils recruited to CF airways in vivo, neutrophils migrated into CF airway milieu in vitro display depressed phagocytic receptor expression and bacterial killing, but enhanced granule release, immunoregulatory function (arginase-1 activation), and metabolic activities, including high Glut1 expression, glycolysis, and oxidant production. We also identify enhanced pinocytic activity as a novel feature of these cells. In vitro treatment with the leukotriene pathway inhibitor acebilustat reduces the number of transmigrating neutrophils, while the metabolic modulator metformin decreases metabolism and oxidant production, but fails to restore bacterial killing. Interestingly, we describe similar pathological conditioning of neutrophils in other inflammatory airway diseases. We successfully tested the hypothesis that recruitment of neutrophils into airway milieu from patients with CF in vitro induces similar pathological conditioning to that observed in vivo, opening new avenues for targeted therapeutic intervention.

Bacteria colonize cystic fibrosis (CF) airways, and while T cells with appropriate antigen specificity are present in draining lymph nodes, they are conspicuously absent from the lumen. To account for this absence, we hypothesized that polymorphonuclear neutrophils (PMNs), recruited massively into the CF airway lumen and actively exocytosing primary granules, also suppress T-cell function therein. Programmed Death-Ligand 1 (PD-L1), which exerts T-cell suppression at a late step, was expressed bimodally on CF airway PMNs, delineating PD-L1hi and PD-L1lo subsets, while healthy control (HC) airway PMNs were uniformly PD-L1hi. Blood PMNs incubated in CF airway fluid lost PD-L1 over time, and in coculture, antibody blockade of PD-L1 failed to inhibit the suppression of T-cell proliferation by CF airway PMNs. In contrast with PD-L1, arginase 1 (Arg1), which exerts T-cell suppression at an early step, was uniformly high on CF and HC airway PMNs. However, arginase activity was high in CF airway fluid and minimal in HC airway fluid, consistent with the fact that Arg1 activation requires primary granule exocytosis, which occurs in CF, but not HC, airway PMNs. In addition, Arg1 expression on CF airway PMNs correlated negatively with lung function and positively with arginase activity in CF airway fluid. Finally, combined treatment with arginase inhibitor and arginine rescued the suppression of T-cell proliferation by CF airway fluid. Thus, Arg1 and PD-L1 are dynamically modulated upon PMN migration into human airways, and, Arg1, but not PD-L1, contributes to early PMN-driven T-cell suppression in CF, likely hampering resolution of infection and inflammation.

Highlights d Neutrophils recruited to cystic fibrosis airways undergo de novo RNA transcription d Neutrophil adaptation to CF airways leads to downregulation of their antimicrobial genes d Transcriptional blockade restores CF airway neutrophil bactericidal capacity

Dendritic cells (DCs) are key regulators of host immunity that are capable of inducing either immune tolerance or activation. In addition to their well-characterized role in shaping immune responses to foreign pathogens, DCs are also known to be critical for the induction and maintenance of anti-tumor immune responses. Therefore, it is important to understand how tumors influence the function of DCs and the quality of immune responses they elicit. Although the majority of studies in this field to date have utilized either immortalized DC lines or DC populations that have been generated under artificial conditions from hematopoietic precursors in vitro, we wished to investigate how tumors impact the function of already differentiated, tissue-resident DCs. Therefore, we used both an ex vivo and in vivo model system to assess the influence of melanoma-derived factors on DC maturation and activation. In ex vivo studies with freshly isolated splenic DCs, we demonstrate that the extent to which DC maturation and activation are altered by these factors correlates with melanoma tumorigenicity, and we identify partial roles for tumor-derived transforming growth factor (TGF)β1 and vascular endothelial growth factor (VEGF)-A in the altered functionality of DCs. In vivo studies using a lung metastasis model of melanoma also demonstrate tumorigenicity-dependent alterations to the function of lung-resident DCs, and skewed production of proinflammatory cytokines and chemokines by these tumor-altered cells is associated with recruitment of an immune infiltrate that may ultimately favor tumor immune escape and outgrowth.

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Our data establish relationships between resistin levels in the plasma and sputum of CF patients that correlate with disease status, and identify resistin as a novel mechanistic link between neutrophilic inflammation and lung disease in CF.

Dendritic cells function as potent regulators of both innate and adaptive immunity to tumors and the regulatory activities of these cells are tightly linked to their maturation and activation status. Despite the critical role played by dendritic cells in the induction of anti-tumor immune responses, the number of dendritic cells that can be isolated from experimental animals is limiting and often precludes in-depth analyses of these cells. To overcome this limitation, dendritic cell lines have been established and have facilitated the experimental study of dendritic cell biology. In this study we compare the dendritic cell lines DC2.4 and JAWSII as in vitro model systems for studying the influence of melanoma-derived factors on dendritic cell maturation and activation. Using flow cytometry and ELISA analyses, we evaluate the expression of costimulatory/MHC class II molecules and proinflammatory cytokines/chemokines by these dendritic cell lines in their resting state and following LPS stimulation in the presence or absence of B16-F1 melanoma-derived factors. Results: We demonstrate that soluble B16-F1-derived factors suppress the LPSinduced upregulation of CD40, CD80, CD86 and MHC class II on both the DC2.4 and JAWSII dendritic cell lines. Interestingly, LPS-induced secretion by DC2.4 cells of the proinflammatory cytokines/chemokines TNF-α, IP-10, MIP-1α, MIP-1β and MCP-1 is also altered by B16-F1-derived factors, whereas JAWSII cell cytokine/chemokine production is affected to a lesser extent by such factors, with only IL-1β and IP-10 production being suppressed. Conclusions/Recommendations: We conclude that melanoma-derived factors can suppress dendritic cell maturation/activation and that the DC2.4 and JAWSII dendritic cell lines are effective in vitro models for future studies that aim to (1) identify factors that influence both the susceptibility and the resistance of dendritic cells to tumor-mediated immunosuppression and (2) investigate the influence of tumor-altered dendritic cells on the quality of anti-tumor T cell responses.

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