Interventions: ISA104 vs placebo. ISA104 is a therapeutic synthetic long peptide (SLP) vaccine for chronic HBV (peptide-based immunotherapy). Mechanism of action: SLPs are taken up by dendritic cells and processed for MHC class I and II presentation, leading to cross-priming and expansion of HBV-specific CD8+ cytotoxic T lymphocytes and CD4+ helper (Th1) cells. Goal is to restore/boost exhausted antiviral T-cell responses in cHBV patients on nucleos(t)ide analogs, enabling CTL-mediated killing of HBV-infected hepatocytes and improved immune control of HBV. Cells/pathways targeted: dendritic cell antigen processing and cross-presentation, adaptive cellular immunity via MHC I/II–TCR pathways, activation of HBV-specific CD8+ T cells and CD4+ Th1 cells with IFN-γ–driven antiviral activity. Comparator: saline placebo.