Reply:
Authors: Chao-Wei Hsu, Chau-Ting Yeh
Journal: Hepatology (2011)

We appreciate Seyed Mohamad Jazayeri and Seyed Moayed Alavian's interest in our article1 and their generous sharing of the data regarding spontaneous hepatitis B surface antigen (HBsAg) mutations in genotype D patients. Indeed, mutations on the hepatitis B virus (HBV) surface protein do occur spontaneously in patients who have not been treated by any antiviral agents. In this study, we did not include a control group of untreated patients to examine whether the two identified mutations occurred spontaneously. However, we clarify that in the two reported patients, longitudinal samples have been tested, including two samples obtained 3 months apart before treatment.1 No corresponding mutation was found before interferon (IFN) therapy or during the HBsAg-positive period after initiation of IFN therapy. The fact that these two mutations only developed after IFN treatment at the HBsAg-negative stage indicated that at least in these two patients, the HBsAg mutations were very likely selected by antiviral treatment. We also appreciate Tai-Chung Tseng and Jia-Horng Kao's interest in our report and the two questions they raised: whether a small percentage (14.3%) of the HBsAg-negative mutant sT125A was responsible for HBsAg loss in one patient and whether the sW74* mutant could replicate competently in the other patient. Regarding the first question, a low titer of serum HBsAg was still detectable in the patient if a more sensitive, quantitative HBsAg assay was applied.1 In these two patients, multiple HBsAg mutations were identified. For the viruses not carrying the sT125A mutation, it was possible that a combination of other mutations led to the detection failure of HBsAg by the less sensitive, qualitative test. An alternate possibility is that one or some of these mutants exerted a dominant negative effect for an HBsAg secretion defect, resulting in HBsAg retention in hepatocytes. At least two recent studies have demonstrated such a phenomenon.2, 3 It is certainly possible that peginterferon could generate a similar effect through epigenetic, genetic, or other subcellular modifications in the hepatocytes. Regarding the second question, we clarify that the sW74* mutation is caused by a point mutation in the nucleotide sequence, which is a silent mutation in the polymerase reading frame. During the course of chronic hepatitis, host immunity against HBV gradually recovers, resulting in three phases of clinical presentation: immune tolerance, immune clearance, and residual phases. In a small but significant proportion of patients, even spontaneous HBsAg clearance can occur, accompanied by development of the pre-S/S mutations.4 It is therefore not surprising that in some treatment-naïve patients, mutations located near or on the "a" determinant can emerge, with coexistence of HBsAg and anti-HBs antibody. This might represent the ability of HBV to adapt during the course of recovering host immunity. In patients receiving polymerase inhibitors for anti-HBV therapy, long-term suppression of HBV-DNA could lead to increase of humoral or cell-mediated immunity. In patients receiving IFN-based agents, host immunity could be enhanced through immune modulation. Both treatments result in more powerful selection pressure for HBsAg mutants. The immune escape–like, HBsAg-negative mutants have been reported in patients receiving antiviral therapies including thymosin, lamivudine, and IFN.1, 5, 6 These observations suggest that the current therapeutic strategies are indeed effective in combating HBV. However, to fight back, HBV can develop mutations not just for drug resistance, but also for escape from the recovering/enhancing host immunity.7 Chao-Wei Hsu M.D.*, Chau-Ting Yeh M.D., Ph.D.*, * Liver Research Center, Chang Gung Memorial Hospital and Chang Gung University School of Medicine, Toayuan, Taiwan.