The Sn in preCore/Core was significantly higher at B than at TNR, and was non-significantly higher in TF than at TNR. These findings suggest a decrease in QA evolution, associated with LVD treatment failure. Boni et al reported that the immune response is enhanced when antiviral treatment controls HBV replication, but our patients were treatment nonresponders and therefore in a situation contrary to that of Boni’s population. In fact, most of our cases showed a decrease in QA complexity at TNR, which likely reflects attenuation of immune system activity at nonresponse. The possible relationship between QA complexity and antiviral therapy response was not tested in this study because responders, who have undetectable HBV-DNA levels after treatment, were not included. However, longitudinal UDPS study of our patients enabled examination of evolutionary patterns in the absence and presence of antiviral treatment, and this yielded conclusive results according to HBeAg status. Some patterns were identified: at baseline, QA complexity in HBeAg-positive patients was significantly lower than in those with fluctuating HBeAg. In addition, HBeAg-positive patients showed lower Core gene variability than those with fluctuating HBeAg at baseline and TF. In contrast, preCore MfAA was not significantly different between any of the groups, which could indicate that the host immune response mainly acts against Core epitopes in patients with fluctuating HBeAg. In fact, preCore variants and positive selection of Core variants were common in HBeAgnegative and fluctuating patients, in keeping with results from our previous studies. These findings may result from HBV adaptation under host immune pressure, or even be due to an effect of antiviral treatment on the Core gene. HBV QA evolution was analyzed in two periods, natural evolution and under NUC pressure. The significant negative correlation in QA complexity between the two periods suggests that changes occurring in natural evolution might be affected by the host immune response and determine the evolution of the same region under NUC treatment. We found that in most patients, the Nutlin-3 inquirer greater the complexity during natural evolution, the more homogeneous was the population after treatment, indicating that NUCs might also have some indirect effects on the preCore/Core region. However, this pattern was not observed in 2 of the 10 patients studied, probably due to the transient serconversion/seroreversion status of these cases. Apart from these differences, the main inverse pattern of QA evolution in the two periods may indicate the following: under immune pressure, a complex population evolves, rendering the QA less complex in a type of bottleneck phenomenon. The main limitation of this study is the small sample of 10 patients sequentially analyzed, which was related to our aim to characterize the HBV QA as accurately as possible by very high coverage.