<scp>HCV</scp>‐infected hepatocytes drive <scp>CD</scp>4⁺<scp>CD</scp>25⁺<scp>F</scp>oxp3⁺ regulatory <scp>T</scp>‐cell development through the <scp>T</scp>im‐3/<scp>G</scp>al‐9 pathway

HCV is remarkable at disrupting human immunity to establish chronic infection. The accumulation of Treg cells at the site of infection and upregulation of inhibitory signaling pathways (such as T-cell Ig and mucin domain protein-3 (Tim-3) and galectin-9 (Gal-9)) play pivotal roles in suppressing antiviral effector T (Teff) cells that are essential for viral clearance. While Tim-3/Gal-9 interactions have been shown to negatively regulate Teff cells, their role in regulating Treg cells is poorly understood. To explore how Tim-3/Gal-9 interactions regulate HCV-mediated Treg-cell development, here we provide pilot data showing that HCV-infected human hepatocytes express higher levels of Gal-9 and TGF-β, and upregulate Tim-3 expression and regulatory cytokines TGF-β/IL-10 in co-cultured human CD4(+) T cells, driving conventional CD4(+) T cells into CD25(+) Foxp3(+) Treg cells. Additionally, recombinant Gal-9 protein can transform TCR-activated CD4(+) T cells into Foxp3(+) Treg cells in a dose-dependent manner. Importantly, blocking Tim-3/Gal-9 ligations abrogates HCV-mediated Treg-cell induction by HCV-infected hepatocytes, suggesting that Tim-3/Gal-9 interactions may regulate human Foxp3(+) Treg-cell development and function during HCV infection.