TYPE I INTERFERON AND MITOCHONDRIAL DYSFUNCTION ARE ASSOCIATED WITH DYSREGULATED CYTOTOXIC CD8+ T CELL RESPONSES IN JUVENILE SYSTEMIC LUPUS ERYTHEMATOSUS

PV001 / #50 Poster Topic: AS01 - Adaptive Immunity Background/Purpose Juvenile systemic lupus erythematosus (JSLE) is an autoimmune condition which causes significant morbidity in children and young adults. While many aspects of immune dysfunction have been studied extensively in adult-onset SLE, there is limited and contradictory evidence of how cytotoxic CD8 + T cells contribute to disease pathogenesis, and studies exploring cytotoxicity in JSLE are rare. Methods Detailed characterization of peripheral blood CD8 + T cells was undertaken in JSLE patients (n=44, median age 22 years and disease duration 9 years) and age/sex-matched healthy controls (HC, n=68, median age 20 years). Multiparameter flow cytometric immunophenotyping, RNA sequencing, serum metabolomic profiling, cell culture assays/functional in vitro studies, and mitochondrial morphology studies were performed. Results Frequencies of CD8 + T cells expressing the cytotoxic mediator perforin and effector cytokines interferon (IFN)-γ and tumor-necrosis-factor (TNF)-α were reduced in JSLE vs HC, irrespective of treatment or disease activity. Transcriptomic and serum metabolomic analysis identified that upregulated type I IFN signaling, mitochondrial dysfunction and metabolic disturbances underpinned these observations (see Figure). Mechanistic studies demonstrated that alteration in these pathways lead to a deficiency in effector memory (EM) JSLE CD8 + T cells, which are enriched for cytotoxic mediator-expressing cells, due to enhanced apoptosis of these cells selectively in JSLE vs HC. Figure. Transcriptomic analysis reveals upregulation of IFN-α responses and potential metabolic and mitochondrial disturbances in CD8 + T cells in JSLE. (a) Volcano plot showing differences in gene expression from RNA sequencing of CD8+ T cells from JSLE (n=26) vs HC (n=29). Blue and red points represent statistically significant differentially expressed genes below the FDR adjusted p-value threshold of 0.05. Blue and red arrows indicate number of statistically significant downregulated and upregulated genes, respectively. (b) Bar plot showing -log10p values and enrichment ratios (ER) of summary enriched pathway GO BP ontology terms in CD8+ T cells in JSLE vs HC using the 147 significantly upregulated and 91 significantly downregulated genes (FDR adjusted p<0.05). Statistical significance of enrichment was determined using a p-value cut-off of 0.01 and a minimum enrichment score of 1.5. Terms highlighted in red and blue represent pathways of potential interest, derived from upregulated (red) and downregulated (blue) genes in JSLE vs HC. (c) Word cloud representing all words taken from significantly enriched pathways in Metascape GO enrichment and GSEA analysis of DEGs in CD8+ T cells in JSLE vs HC. Text size indicates the frequency of the word. Conclusions Cytotoxic capacity of CD8 + T cells is diminished in JSLE due to a numerical deficiency in EM CD8 + T cells, which is linked to mitochondrial defects, dysregulated type I IFN signaling, and increased apoptosis. Future studies are needed to understand the therapeutic implications of these findings.