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Updated: Jan 12, 2026

Generation of Induced Regulatory T Cells from Primary Human Naïve and Memory T Cells
Published on: April 16, 2012
TCR signaling via NFATc1 constrains IL-15-induced bystander activation of human memory CD8+ T cells
Hoyoung Lee1, So-Young Kim2, Sang-Hoon Kim1
1Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea; The Center for Viral Immunology, Korea Virus Research Institute, Institute for Basic Science (IBS), Daejeon 34126, Republic of Korea.
Abstract:
Human memory CD8+ T cells can undergo T cell receptor (TCR)-independent activation by interleukin-15 (IL-15) in a bystander manner. Bystander-activated CD8+ T cells contribute to host tissue injury through natural killer (NK)-like cytotoxicity during viral infections. However, detailed mechanisms underlying IL-15-induced bystander activation remain to be elucidated. In this study, we investigated the molecular regulation of bystander activation and NK-like cytotoxicity of human CCR7- memory CD8+ T cells. We found that TCR signals suppressed characteristic features of IL-15-induced CD8+ T cell activation. Ionomycin also suppressed IL-15-induced expression of NKG2D and NK cytotoxicity genes, indicating that Ca2+-calcineurin signaling suppressed bystander activation. Mechanistically, NFATc1 bound to AP-1, limiting its ability to induce expression of NK cytotoxicity-related genes. We also defined an IL-15-induced bystander activation gene set, which was validated in bystander CD8+ T cells from patients with hepatitis A virus infection. Our findings open avenues for investigating bystander CD8+ T cell activation and its regulation in pathological conditions.
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