186P Elevated CXCL10:IL-8 ratio in bronchoalveolar lavage fluid of immune checkpoint inhibitor-related pneumonitis

Immune checkpoint inhibitor (ICI) pneumonitis is the most common fatal immune-related adverse event (irAE) from PD-1/ PD-L1 blockade, and a diagnosis of exclusion. Based on single-cell transcriptomics, we identified pathogenic T-helper 17.1 cells in ICI-pneumonitis bronchoalveolar lavage fluid (BALF), putatively engaging with pro-inflammatory “M1-like” monocytes, as a key pathophysiologic mechanism. Herein, we present the cytokine profile of ICI-pneumonitis BALF, aiming to identify further mechanistic insights and diagnostic biomarkers. Levels of 22 cytokines (GM-CSF, Granzyme B, IFN-γ, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-10, IL-13, IL-15, IL-17A, IP-10, MCP-1, MIP-1α, MIP-1β, Perforin, sCD137, TNF-α, TNF-β) were measured in BALF supernatant of 17 ICI-pneumonitis and 6 controls from 23 independent patients at UZ Leuven (discovery), using Isoplexis’ CodePlex platform. Validation was performed in a published cohort of 13 ICI-pneumonitis and 6 controls from independent patients at Johns Hopkins University. Mann-Whitney U test (Benjamini-Hochberg corrected) was used to compare cytokine levels between groups. In the discovery cohort, we observed significantly lower levels of IL-8, IL-9, IL-10, IL-17A, CCL2, and sCD137 in ICI-pneumonitis BALF vs. controls. There was a trend towards higher levels of TNF-α and CXCL10 (p = 0.11; p = 0.16 respectively). Next, we investigated the biomarker potential of ratios of differentially abundant proteins, arguing that disbalance rather than absolute cytokine values provides a more meaningful readout for inflammation, while correcting for technical variability in BALF-derived data. We identified that a high CXCL10: IL-8 ratio distinguishes ICI-pneumonitis from control patients in the discovery cohort (ROC AUC 0.92) and in the validation cohort (ROC AUC 0.82). Bulk cytokine profiling identifies a high CXCL10: IL-8 ratio as a reproducible characteristic of ICI-pneumonitis BALF, in line with immunophenotypic data suggesting an interferon-γ driven immune response and absence of neutrophilic inflammation, respectively. The diagnostic utility of the CXCL10: IL-8 ratio in BALF to identify ICI-pneumonitis should be further investigated.