Title: IL-2 Produced by HBV-specific T cells as a Biomarker of Viral Control and Predictor of Response to PD-1 Therapy Across Clinical Phases of Chronic Hepatitis B

Background: HBV-specific T cells are functionally exhausted in chronic Hepatitis B virus (HBV) infection. Immune checkpoint blockade targeting PD-1/PD-L1 can rescue HBV-specific T cells and potentially achieve functional cure.

Purpose: Our study aimed to identify an ex vivo assay that might predict chronic hepatitis B (CHB) patients responsive to checkpoint inhibitor therapy.

Method: We enrolled immunotolerant (IT), HBeAg+ immune-active (IA+), HBeAg- immune-active (IA-), inactive carriers (IC) and functionally cured (FC) patients to test ex vivo PD-1 blockade on HBV-specific T cell functionality. PBMCs were stimulated with overlapping peptides covering HBV proteins +/- anti-PD-1 blocking. Functional T cells were measured using a 2-color FluoroSpot assay for IFN-gamma and IL-2. An interferon response capacity assay, which predicts overall survival in cancer patients treated with checkpoint inhibitors, was used to correlate potential outcomes of PD-1 therapy with IL-2 restoration.

Results: Ex vivo IFN-gamma+ responses did not differ across phases. IL-2+ responses were significantly higher among patients with better viral control: IC and FC patients. PD-1 blockade preferentially restored IL-2+ responses across all patient cohorts. HBeAg negative status was associated with significantly higher functional restoration. IL-2 restoration by ex vivo PD-1 blockade significantly correlated with the interferon response capacity.

Conclusion: We demonstrate that IL-2 production was associated with better viral control and superior to IFN-gamma as a marker of T cell restoration across the clinical phases. Correlation of IL-2 restoration following PD-1 blockade with the interferon response capacity suggests we may be able to predict immunological outcomes in CHB patients without measuring HBV-specific T cell magnitude or function.