A35-29 CD8⁺ T-cell-driven Interferon Signaling Defines Immune Checkpoint Inhibitor-associated Pneumonitis and Reveals Actionable Cytokine Targets

Rationale

Immune checkpoint inhibitors (ICI) have become standard therapy across multiple malignancies, yet ICI-associated pneumonitis remains one of the most serious and life-threatening immune-related adverse events, frequently necessitating hospitalization, prolonged immunosuppression, and permanent discontinuation of life-prolonging cancer therapy. Current management relies on empiric corticosteroids, with limited mechanistic guidance and high morbidity. The cellular drivers of ICI pneumonitis and how they differ from other inflammatory lung diseases remain poorly defined, representing a major unmet clinical need.

Methods

We performed single-nuclei RNA sequencing on lung biopsies from patients with ICI pneumonitis, pulmonary graft-versus-host disease (GvHD), connective-tissue-disease-associated interstitial lung disease (CTD-ILD), and healthy controls. Immune cell composition, differential gene expression, and gene set enrichment analyses were used to elucidate disease-specific inflammatory programs.

Results

ICI pneumonitis exhibited a distinct immune architecture marked by a pronounced expansion of cytotoxic CD8⁺ T cells and proliferating T cells, in contrast to the predominance of TRM CD4⁺ T cells observed in CTD-ILD and pulmonary GvHD. CD8⁺ T cells in ICI pneumonitis showed increased expression of CXCL9, CXCR3, CD8A, GZMB, CD38, IL21R, JAK3, and STAT1, consistent with heightened recruitment, activation, and effector function. The myeloid compartment was dominated by inflammatory macrophages, whereas comparator diseases showed relative neutrophil enrichment. Gene set enrichment analysis demonstrated robust activation of type I and II interferon responses and IL6-JAK/STAT3 signaling, with relative suppression of TNF-alpha and hypoxia-associated pathways in ICI pneumonitis. These signatures were conserved across comparisons of ICI pneumonitis with healthy lungs, GvHD, and CTD-ILD.

Conclusions

ICI pneumonitis is driven by a CD8⁺ T-cell-dominant, interferon-activated inflammatory program that is mechanistically distinct from other immune-mediated lung diseases. Identification of convergent interferon and IL6-JAK/STAT3 signaling highlights immediately actionable pathways targeted by existing therapies, providing a rational framework for mechanism-based treatment strategies in a high-mortality toxicity with limited current options.

Figure. Single-nuclei RNA sequencing identifies a T-cell-dominant interferon response in immune checkpoint inhibitor-associated pneumonitis. UMAP visualization of lung single-nuclei RNA sequencing data shows clustering of major epithelial, stromal, myeloid, and lymphoid cell populations, alongside interferon-gamma (IFNG) expression across disease states. IFNG expression is markedly enriched in ICI-associated pneumonitis, localizing predominantly in T cell populations, compared to healthy control lungs and interstitial lung disease.

This abstract is funded by: Johnny Carson Foundation