Abstract B039: T-cell–dominated interferon signaling drives immune checkpoint inhibitor–associated pneumonitis and reveals actionable cytokine targets

Abstract Immune checkpoint inhibitors (ICI) have revolutionized cancer therapy, improving patient survival for many cancers, by harnessing the immune system to target cancer cells, however, they can also mediate unwanted autoimmunity in healthy tissues, causing significant immune-related adverse events (IrAEs), including life-threatening ICI-pneumonitis. The underlying mechanisms driving lung IrAEs are not fully understood, thus identifying the critical pathways involved are vital in developing targetable strategies to prevent or treat these toxicities. This study aims to further explore the cellular and molecular mechanisms causing ICI pneumonitis using single-nuclei RNA sequencing. Lung tissue biopsies from patients with ICI pneumonitis, pulmonary graft-versus-host disease (GvHD), connective-tissue-disease–associated interstitial lung disease (CTD-ILD), and healthy controls were collected and underwent single-nuclei isolation, sequencing, followed by bioinformatic analysis of differential gene expression, and gene set enrichment analysis. ICI pneumonitis demonstrated a distinct predominance of CD8+ T cells, namely cytotoxic effectors, whereas CTD-ILD and pulmonary GvHD exhibited TRM CD4+T cells. Differential expression analysis revealed significant upregulation of CXCL9, CXCR3, CD8A, IL21R, GZMB, CD38, JAK3, and STAT1 in ICI pneumonitis, indicating enhanced T-cell recruitment and activation. Interestingly, ICI pneumonitis lungs also demonstrated a distinct inflammatory macrophage predominance, meanwhile CTD-ILD and GvHD lungs had a neutrophil-predominance. Gene set enrichment showed significant activation of interferon responses, and IL6-JAK/STAT3 signaling, and suppression of TNF-alpha and hypoxia pathways in ICI-pneumonitis. These findings were conserved when comparing ICI pneumonitis to healthy lungs, GvHD and CTD-ILD disease states as well, thus identifying actionable cytokine pathways, including IL-6 and JAK/STAT3 signaling, that correspond to targets of existing pharmaceuticals. In conclusion, ICI pneumonitis is driven by a CD8+ T-cell-dominant, interferon-activated inflammatory program within the lungs, revealing therapeutic opportunities to mitigate IrAEs without compromising anti-tumor immunity. Future directions include using spatial transcriptomics to further explore/validate our findings, the development of an ICI-pneumonitis mouse model, and planning for early-phase clinical evaluation of targetable cytokine pathways. Citation Format: Paytsar Topchyan, Nikhita Kathuria-Prakash, Jarod Olay, Leland Damron, Min Zhang, Gregory Fishbein, Willy Hugo, Dimitrios Stefanoudakis, Richard Watson, Melissa Lechner, Alexandra Drakaki. T-cell–dominated interferon signaling drives immune checkpoint inhibitor–associated pneumonitis and reveals actionable cytokine targets abstract. In: Proceedings of the AACR Immuno-Oncology Conference (AACR IO): Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2026 Feb 18-21; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2026;14(2 Suppl):Abstract nr B039.