BACKGROUND: Chronic hepatitis B is associated with virus-specific and global T-cell dysfunction. We hypothesized that therapeutic reduction in serum HBV DNA, ALT, and HBsAg would restore HBV-specific T-cell function and modify T-cell regulatory phenotype, with associated posttreatment ALT flare. METHODS: HBV-specific T-cell lymphoproliferative responses and global T-cell phenotype were prospectively examined at baseline, weeks 24, 48, 192, 216, and 240 in 34 adults with immune-active chronic hepatitis B treated with 192 weeks of tenofovir alone (n=21) or combined with pegylated interferon (PegIFN) in the first 24 weeks (n=13). HBV-specific T-cell IFNγ responses at weeks 0, 24, and 48 were examined by ELISpot assay ex vivo in 24 patients. Posttreatment flare was defined by serum ALT >5 times the upper limit of normal. RESULTS: Tenofovir therapy did not promote sustained induction of HBV-specific T-cell proliferative responses, regardless of PegIFN therapy or decreased serum HBsAg, HBV DNA, or ALT levels. Instead, HBV-specific T-cell IFNγ responses declined significantly by 48 weeks of therapy (p=0.008). Posttreatment ALT flare was associated with higher baseline %PD1+/CD8 (p=0.019), %PD1+/CD4 (p=0.039), and %CTLA4+/CD4 (p=0.003) T cells compared to non-flares, but without associated HBsAg loss or increased HBV-specific T-cell responsiveness. CONCLUSION: HBV-specific T-cell function was not restored after 192 weeks of tenofovir therapy and did not correlate with HBsAg levels before, during, or after therapy. Baseline global T-cell regulatory phenotype was a predictor for ALT flare post-therapy without associated HBsAg decline. These findings support the need for more novel immune-modulatory approaches to enhance HBV-specific T-cell responsiveness.