106. Elevated STAT3/PIM1 Expression in T Cell Subsets of Granulomatosis with Polyangiitis Patients

Background: Granulomatosis with polyangiitis (GPA) is an autoimmune disease characterized by inflammation of the microvasculature in various organs. Aberrations in several T cell subsets, both numerical and functional, have been identified in GPA patients. However, their significance for GPA pathogenesis remains unclear. Here, we applied single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs) to capture the transcriptional signatures of T cell subsets associated with active disease in GPA. Methods: PBMCs of active GPA patients (n=3) and healthy age-and sex-matched donors (n=3) were subjected to droplet-based scRNA-seq (10x Genomics). Analysis of scRNA-seq data was performed using BioTuring Browser (https://bioturing.com/bbrowser) and Seurat package. Validation of differentially expressed genes was subsequently performed by quantitative PCR (qPCR) on bulk flow-sorted naïve CD4+ T cells (CD4+Tnaive), CD4+ effector memory T cells (CD4+TEM), and CD4+ regulatory T cells (CD4+Tregs) derived from active and remission GPA patients and healthy donors. Results: Differential expression analysis of scRNA-seq datasets revealed that mRNA expression levels of the serine/threonine kinase; proviral integration site for Moloney murine leukemia virus (PIM1) and its transcription factor STAT3 were upregulated in T cells from active GPA patients including subpopulations of CD4+Tnaive, CD4+TEM, and CD4+Tregs. qPCR analysis of bulk flow-sorted CD4+Tnaive, CD4+TEM, and CD4+Tregs of active GPA patients confirmed elevated expression levels of PIM1 in all subsets compared to those of healthy controls whereas STAT3 expression was significantly upregulated in CD4+Tnaive and CD4+TEM subsets. Interestingly, qPCR analysis of CD4+Tnaive and CD4+TEM from remission patients demonstrated that PIM1 expression was still upregulated suggesting persistent T cell activation (figure 1). Conclusions: These data indicate that the STAT3/PIM1 signaling pathway is activated in T cells from GPA patients. Interestingly, previous studies have shown that PIM1 mediated phosphorylation of FOXP3 impairs the suppressive capacity of Tregs which may explain the defective Treg function known to exist in GPA patients (1,2). Further functional studies are warranted to determine whether PIM1 inhibition is a rational therapeutic approach in GPA. Disclosures: None Figure 1. PIM1 mRNA expression is upregulated in bulk sorted CD4+TEM in GPA patients with active disease and in remission compared to healthy controls. Kruskal-Wallis test (p