MON-431 Novel T Cell Determinants of Female-Sex Bias in Autoimmune Thyroid Disease

Abstract Disclosure: R. Le: None. H. Willy: None. J. Olay: None. T.E. Angell: None. M. Lechner: None. Sexual dimorphism impacts the prevalence and severity of many inflammatory conditions, including autoimmune disease. Thyroid autoimmunity in particular affects nearly 15% of the population and show a strong female sex bias (8:1 female to male ratio). The chronic autoimmune attack in Hashimoto’s thyroiditis (HT) leads to hypothyroidism requiring life-long thyroid hormone replacement and has been associated with increased cognitive dysfunction, depression, pregnancy complications, and cardiovascular disease. Immune drivers of the female-sex bias in autoimmune thyroid disease remain uncertain. We hypothesize that the female predisposition of HT is driven by sex-specific differences in T cell conversion from stem-like progenitors to terminally differentiated effectors with killing function. To investigate this hypothesis, we compared immune infiltrates in human thyroid specimens between men (n=4) and women (n=7) with HT (TPO antibody positive; similar age distribution and thyroid hormone status across sexes) using single cell RNA sequencing (5’ GEX + TCR). Mapping of the raw sequencing output was conducted using Cellranger (10x Genomics), with downstream analysis performed using Seurat (v5), Slingshot, and STARTRAC in RStudio. Our analysis revealed a diverse immune infiltrate in men and women, comprised of 23 distinct cell populations of immune cells, including CD8 T cells, CD4 T cells, and B cells. Subset analysis of CD8+ T cells revealed a population TCF7+ CD8+ T cells that convert within the thyroid to effector CD8+ T cells expressing effector molecules associated with activation (CXCR6, CD44) and killing ability (IFNG, PRF1, GZMK) (p<0.0001). In chronic viral infections, such TCF7+ CD8+ cells show self-renewal and serve to replenish the pool of cytotoxic effector cells to sustain the immune response. Our data suggests a similar role for TCF7+ CD8+ stem-like progenitors in autoimmune persistence in HT. Furthermore, our data show that women with HT have increased conversion of CD8+ stem-like progenitors to effectors, whereas men showed a higher density of progenitor CD8+ T cells. Genes required for stem-ness were increased in male CD8+ T cells, including TCF7 and BACH2. Conversely, female CD8+ T cells exhibited higher expression of effector-related genes, namely GZMK, CXCR6, PRF1, and IFNG. Notably, these gene expression patterns align with recently reported targets of androgens (male sex hormones) and X-linked epigenetic regulator UTX (encoded by KDM6A). In summary, we identify a key T cell axis in thyroid autoimmune pathogenesis that demonstrates sexual dimorphism and nominate TCF7 and BACH2 as potential therapeutic targets to reduce effector CD8+ T cell conversion in HT. Understanding the molecular underpinnings of sex differences is an important step toward developing strategies to halt autoimmune thyroid disease and reduce disease susceptibility in women. Presentation: Monday, July 14, 2025