Elevated Soluble LAG-3 in Chronic Hepatitis B and T-Cell Responses to Checkpoint Blockade.

[BACKGROUND & AIMS] LAG-3 is an inhibitory immune checkpoint implicated in T-cell dysfunction, but the significance of soluble LAG-3 (sLAG-3) in chronic hepatitis B (CHB) remains unclear. Whether checkpoint blockade can restore intrahepatic antiviral T-cell function during HBV antigen clearance also remains to be defined.

[METHODS] We combined clinical sample analysis, liver transcriptomics, single-cell datasets, and a hydrodynamic HBV mouse model to characterize LAG-3-associated immune alterations in CHB. The effects of anti-PD-1 and anti-LAG-3 treatment on antigen clearance, T-cell distribution, phenotype, and HBV-specific effector responses were further evaluated in vivo.

[RESULTS] Serum sLAG-3 was elevated in CHB and correlated with markers of liver injury, whereas soluble immune checkpoint profiles were broadly altered across HBV-related liver diseases. In CHB liver tissue, multiple checkpoint-related genes, including LAG3, together with ADAM10 and ADAM17, were upregulated, and single-cell analysis localized LAG3 mainly to T-cell subsets. In HBV mice, LAG-3-positive immune cells accumulated within intrahepatic immune clusters during antigen clearance, accompanied by progressive enrichment of intrahepatic T cells expressing PD-1, LAG-3, CD39, TIM-3, and TOX. Checkpoint blockade exerted compartment-specific effects. Anti-PD-1 accelerated antigen clearance, advanced the alanine aminotransferase flare, and increased intrahepatic CD8 T-cell frequency, whereas anti-LAG-3 reduced intrahepatic LAG-3 expression and CD8 T-cell frequency. Both treatments reshaped T-cell distribution and phenotype across blood, liver, and spleen, but neither restored intrahepatic HBV-specific IFN-γ responses.

[CONCLUSIONS] Elevated sLAG-3 is a feature of CHB and is associated with liver injury. PD-1 and LAG-3 blockade induce distinct, compartment-specific T-cell responses during HBV antigen clearance, but do not restore intrahepatic antiviral effector function.