Killer T cells find meaningful encounters through iMATEs

Regulatory T cells suppress TLR9-induced formation of intrahepatic myeloid-cell aggregates for T cell population expansion in liver

Toll-like receptor (TLR) 9 ligand has been reported to induce the formation of intrahepatic myeloid-cell aggregates for T cell population expansion (iMATEs), which enhances responses of cytotoxic T lymphocytes (CTLs). However, little is known about how the formation of iMATEs is regulated. Previously, various studies have demonstrated that regulatory T cells (Tregs) can suppress CTL responses through soluble cytokines or co-inhibitory molecules. It's unclear whether and how Tregs regulate the formation of iMATEs. In this study, we investigated whether Tregs are involved in regulating TLR9-induced iMATEs formation and the mechanisms behind it by using different gene knockout mice and blocking antibodies. We observed that intravenous injection of TLR9 ligand CpG induced significant iMATEs formation, accompanied by a marked increase in the number of Tregs infiltrating the liver as well as upregulation of IL-10 in both peripheral blood and liver. Importantly, depletion of Tregs either by anti-CD4, anti-CD25 blocking antibodies or diphtheria toxin (DT) in DEREG transgenic mice resulted in enhanced CpG-induced iMATEs formation. Conversely, knocking out IL-10 led to increased intrahepatic Treg infiltration and decreased CpG ODN-induced iMATEs formation. Consistently, depleting Kupffer cells (KCs), one of the main source of IL-10, also resulted in reduced formation of iMATEs. In conclusion, our results suggest that IL-10 suppresses Treg infiltration in the liver and thus promote CpG ODN-induced iMATEs formation. These results fill the gap in our understanding of the intrahepatic regulation mechanism of iMATEs formation.

TLR9-Mediated Conditioning of Liver Environment Is Essential for Successful Intrahepatic Immunotherapy and Effective Memory Recall

Immune defense against hepatotropic viruses such as hepatitis B (HBV) and hepatitis C (HCV) poses a major challenge for therapeutic approaches. Intrahepatic cytotoxic CD8 T cells that are crucial for an immune response against these viruses often become exhausted resulting in chronic infection. We elucidated the T cell response upon therapeutic vaccination in inducible transgenic mouse models in which variable percentages of antigen-expressing hepatocytes can be adjusted, providing mosaic antigen distribution and reflecting the varying viral antigen loads observed in patients. Vaccination-induced endogenous CD8 T cells could eliminate low antigen loads in liver but were functionally impaired if confronted with elevated antigen loads. Strikingly, only by conditioning the liver environment with TLR9 ligand prior and early after peripheral vaccination, successful immunization against high intrahepatic antigen density with its elimination was achieved. Moreover, TLR9 immunomodulation was also indispensable for functional memory recall after high frequency antigen challenge. Together, the results indicate that TLR9-mediated conditioning of liver environment during therapeutic vaccination or antigen reoccurrence is crucial for an efficacious intrahepatic T cell response.