One possible explanation is that the suppression BGJ398 ic50 of serum HBV–DNA does not accurately reflect the host immune control and clearance of covalently closed circular DNA (cccDNA) inside the liver. Quantitative serum HBsAg has attracted a lot of research interest in recent years. Earlier reports in HBeAg-positive patients suggested that the level of serum HBsAg was associated with intrahepatic cccDNA levels, and that the

change in serum HBsAg after peg-interferon therapy could also reflect the change in cccDNA levels.7 Although HBsAg is a viral protein, the clearance of HBsAg requires host immunity. In untreated patients, HBsAg levels decline with immune clearance,8 and low HBsAg levels (< 100 IU/mL) predict spontaneous HBsAg seroclearance.9 In patients on antiviral treatment, HBsAg levels decline more dramatically with peg-interferon, an immune modulator, than nucleos(t)ide analogs, which are potent inhibitors of HBV–DNA replication.10 With this background, serum HBsAg is a logical candidate to predict and guide the response of peg-interferon therapy. Several studies, including the post-hoc analysis of the multicenter ZVADFMK trials

on peg-interferon α-2a, have shown an association of on-treatment HBsAg level and response to peg-interferon.10 In HBeAg-positive patients, an HBsAg level of < 1500 IU/mL at weeks 12 and 24 is associated with a > 50% chance of HBeAg seroconversion, while an HBsAg level of > 20 000 IU/mL usually predicts non-response. Sirolimus In a study in Hong Kong, a > 1 log reduction in HBsAg at week 24 was also a predictor of response.11 In HBeAg-negative patients, a reduction in HBsAg, rather than any absolute HBsAg level, is more predictive of response to peg-interferon.10 The exact reason why HBsAg is used differently in HBeAg-positive and -negative patients is unclear. This might be related to the poor

relationship between HBsAg level and cccDNA in HBeAg-negative patients, in contrast to those who are HBeAg positive.12 Even if we can predict the response to peg-interferon using on-treatment HBsAg levels, the key question is: what is next? For the 20% poor on-treatment responders, one can stop peg-interferon early and shift to an oral antiviral agent. What can we do for the remaining 80% of patients who are starting to respond? Can we further improve the response for the on-treatment responders, particularly those with intermediate HBsAg response? Combination with lamivudine does not seem to improve the sustained response to peg-interferon.3,13 More data are required before combination with entecavir or tenofovir can be recommended (a trial with telbivudine was discontinued because of unexpected toxicity). In a recent study evaluating the effect of a lower dose (90 mcg weekly) and shorter duration (24 weeks) of peg-interferon α-2a in HBeAg-positive patients, it was clear that the standard 180 mcg weekly dosing for 48 weeks is needed to achieve the best sustained response.