Abstract
To characterize cytotoxic T lymphocytes (CTLs) that appeared in circulation during lamivudine therapy, we analyzed HBV‐specific CTLs using HLA‐A24 tetramer and HBcAg‐specific Th1 cells in patients receiving lamivudine therapy. Six patients (HLA‐A24^+^) with chronic hepatitis B, six patients (HLA‐A24^−^) with chronic hepatitis B, and six patients (HLA‐A24^+^) with chronic hepatitis C were studied. In addition to known CTL epitopes (C117 and P756), three epitopes were confirmed as CTL epitopes (C23, S89, S226) by chromium release assay and by staining intracellular perforin. CTLs specific for P756 were most frequently found at pre‐treatment. During lamivudine therapy, increase in the frequencies of HLA‐tetramer^+^ cells was found for C117, S89, and S226. Recovery of CTLs was observed earlier in patients with HBeAg^−^/anti‐HBe^+^ compared with those with HBeAg^+^/anti‐HBe^−^. HBcAg‐specific Th1 cells did not increase significantly up to 8 weeks. T cell lines from patients with chronic hepatitis B had a lower level of proliferation (0‐ to 24.9‐fold expansion by in vitro stimulation) and a higher ability to produce interferon‐γ (0–84% except for S89), while perforin‐positive cells showed low frequencies (0–50% except for S89). In conclusion, these results suggest that lamivudine therapy induces mainly CTLs that were less frequent before the therapy. Since recovered CTLs maintained the ability to produce interferon‐γ in response to peptides, these CTLs apparently contribute to the efficacy of lamivudine therapy in patients with hepatitis B. J. Med. Virol. 74:425–433, 2004. © 2004 Wiley‐Liss, Inc.