Background/Purpose: Immune checkpoint inhibitors (ICI) have advanced the field of cancer therapeutics. By blocking the negative co-stimulation of T cells, ICI augment the anti-tumor immune response. However, ICI can elicit inflammatory reactions termed immune-related adverse events (irAEs). We previously reported that ICI therapy is associated an abrupt onset, oftentimes severe irAE resembling Sjögren’s syndrome (Warner et al., 2019). Herein we aimed to characterize the inflammatory infiltrate of labial salivary gland biopsies (LSGB) from patients with ICI sicca.

Methods: Patients with ICI sicca (ICI, n=21) and healthy volunteers (HV, n=9) underwent saliva assessments, medical workup, and LSGBs. We measured the surface area of acini and fibrosis with histochemical stains and the density of IHC stains in LSGB using QuPath_2.0. Transcriptional profiling of immune markers was determined using RNA sequencing. Dissociated LSGB were subjected to 4h PMA/ionomycin stimulation and subsequent flow cytometry analysis. In patients with available dissociated tissues, single cell (sc)RNA sequencing was performed. 

Results: LSGB form ICI sicca patients demonstrated architectural distortion including the most common findings of reduced density of acini (p=0.01), variable fibrosis (p= 0.07), and mild-to-severe sialadenitis composed chiefly of T lymphocytes. In some patients, destruction of PD-L1⁺ epithelia with marked effacement of gland architecture was observed. IHC demonstrated the ICI inflammatory infiltrate was composed increased numbers of CD8⁺ (p=0.039), CD4⁺ (p=0.078), and CD3⁺ (p=0.05) T lymphocytes. RNA sequencing exhibited significantly higher PD-1 expression in the ICI LSGB (p=0.02) with higher CD8 and CD39 expression (p=0.05). CD3, CD4, 4-1BB, TIM3, GzmB, FOXP3 and PDL1 were all upregulated in the ICI group but did not reach statistical significance. Flow cytometry confirmed increased infiltration with CD3⁺ with significant increases in activated cytotoxic T cells (CD8⁺CD107a⁺). scRNAseq and confocal immunofluorescence microscopy confirmed increased density of CD8⁺PD-1⁺CD39⁺ T cells in the ICI LSGB.

Conclusion: The histopathology of ICI induced sialadenitis consists primarily of a T cell infiltrate with parenchymal destruction with patchy fibrosis. IHC analysis combined with the transcriptional data show the presence of cytotoxic T-cell population (CD8, 4-1BB, TIM3, GrzB) with a chronic antigen exposure phenotype (PD-1, CD39). Further investigation is necessary to determine if this T-cell population is causing the sicca or if it constitutes a reactive population.

Example of severe sialadenitis induced by anti-PD-L1 therapy . Total effacement of the gland architecture with injury to the acini and ducts is evident. The infiltrate is composed chiefly of T cells without B cells. CD4 cells predominate, although infiltration of the acini and ducts is seen.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/cytotoxic-t-cells-with-a-chronic-antigen-exposure-phenotype-drive-immune-checkpoint-inhibitor-sicca/