CD8+ T cells in Hashimoto's thyroiditis-associated papillary thyroid carcinoma.

Papillary thyroid carcinoma (PTC) is the most common thyroid malignancy and frequently coexists with Hashimoto's thyroiditis (HT). Clinical observations indicate that HT-PTC tends to display less aggressive clinicopathological features; however, the immune characteristics underlying this phenomenon remain incompletely defined. In this study, we combined transcriptomic analysis with experimental validation to investigate CD8+ T cell features in HT-PTC. Analysis of TCGA data showed increased CD8+ T cell infiltration in HT-PTC compared with non-HT-PTC. In surgically resected specimens from our center, primary CD8+ T cells derived from HT-PTC were further characterized. Tumor-derived CD8+ T cells maintained cytokine secretion capacity and showed lower expression of TIM-3 and LAG-3, together with higher Granzyme B levels. In coculture assays, these cells were associated with reduced proliferation and migration of thyroid cancer cells. Overall, CD8+ T cells in HT-PTC exhibited no pronounced exhaustion-associated feature pattern and retained functional activity. This immune profile may be linked to the relatively less aggressive behavior observed in HT-PTC and provides a biological reference for future immune-informed risk stratification strategies.