The possibility of achieving durable immune control with safe drug discontinuation in patients treated with NAs is a pressing issue in clinical practice. In view of the different mechanisms of action and advantages of IFN and NA, it has become a hot topic of research to obtain satisfactory or desirable therapeutic endpoints for CHB patients by using timely combination or sequential therapy. The dilemma of NA antiviral therapy is that NA targets the viral polymerase and has little effect on the body’s antiviral immune response, resulting in CHB patients not easily obtaining HBeAg or HBsAg serological conversion and a high relapse rate after drug discontinuation, in addition, there is also the problem of drug resistance that plagues all NA therapy, etc. The level of HBsAg decreases very slowly during NA therapy, and it is necessary to obtain a negative HBsAg or serological conversion through NA therapy. The rate of HBsAg conversion or serologic conversion during NA treatment is very slow, and it takes a long time and is very low. Korean scholar Cho et al. predicted the time to obtain HBsAg serological conversion by NA treatment by calculating the kinetic changes of HBsAg during NA treatment in 1006 patients with primary CHB, and found that HBeAg-positive and HBeAg-negative patients needed 87 and 73 years, respectively, to clear HBsAg with NA treatment, implying lifelong treatment. Currently, most patients treated with NA are able to maintain negative viral tests, but the E antigen seroconversion rate is low. In order to improve the treatment response of these patients and help them achieve the desired endpoint of HBsAg clearance or serologic conversion early, many scholars have started to explore the treatment regimen of combined or sequential use of interferon. 2, NA and IFN combination therapy The theoretical basis of NA combined with IFN therapy lies in the fact that NA can rapidly inhibit viral replication, reduce viral protein synthesis and help restore the body’s immune response, thus helping to improve the immunomodulatory effects of interferon. The current status of NA combination IFN therapy research can be summarized as the following models: 1. initial combination; 2. sequential use; 3. single use and then combination; 4. combination and then single use, so the classification is described. 2.1 Initial combination 2.1.1 Initial combination in patients with E antigen-positive CHB Lau et al. randomized 814 patients to receive pegylated interferon 2a in combination with LAM, pegylated interferon alone and lamivudine alone in a registration trial study of pegylated interferon 2a for 48 weeks of treatment and 24 weeks of discontinuation follow-up, and showed that: the initial combination group and the pegylated interferon alone group The E antigen seroconversion rates at 24 weeks of discontinuation were 27% and 32%, respectively, which were significantly higher than the 19% in the lamivudine alone group, but the difference between the initial combination and monotherapy groups was not significant; Janssen et al. showed by treating 130 patients with the initial combination and 136 patients with pegylated interferon alone for 52 weeks that at 26 weeks of discontinuation, the E antigen seroconversion rates in both groups were 29% and negative S-antigen conversion rate of 7% in both groups, with no statistical difference seen. However, a study by Cao et al. in 2013 showed that in two groups of patients treated with pegylated interferon in combination with ADV and in combination with LAM for 96 weeks, respectively, with 24 weeks of discontinuation, the E antigen seroconversion rate was 74% and 71%, and the S antigen seroconversion rate was 22% and 33%, respectively. 2.1.2 Initial combination in E antigen-negative patients Tangkijvanich et al. in Thailand initially combined PEG-IFN-α2a and entecavir (ETV) for the treatment of HBeAg-negative chronic hepatitis B and compared the efficacy with PEG-IFN-α2a monotherapy. Interim results were reported at the 2013 APASL Annual Meeting. The study enrolled 76 patients with primary HBeAg-negative chronic hepatitis B who were randomized to PEG-IFN-α in combination with entecavir and PEG- IFN-α monotherapy. The results showed that at the end of treatment, the HBV DNA undetectable rate was significantly higher in the combination therapy group than in the monotherapy group; however, combination therapy was not superior to PEG- IFN-α monotherapy in terms of HBsAg levels and HBsAg clearance. 2.2 NA sequential pegylated interferon A study conducted by Prof. Ning Qin et al. in 2014 on switching to PEG-IFN-α after ETV treatment aimed to achieve higher treatment goals with sequential PEG-IFN-α in patients who did not achieve HBeAg seroconversion with entecavir therapy while achieving safe discontinuation of the drug. The results showed that sequential PEG-IFN-α treatment with entecavir resulted in higher HBsAg clearance and HBeAg seroconversion rates than in patients who continued with entecavir alone. Further analysis showed that patients with HBsAg <200 IU/mL treated with entecavir sequential PEG-IFN-α for 12 weeks were more likely to achieve HBsAg conversion and HBeAg seroconversion; patients with HBsAg ≥1500 IU/mL were very unlikely to achieve HBsAg conversion and HBeAg seroconversion. This may provide a basis for the implementation and patient selection of nucleoside (acid) analogue sequential PEG-IFN-α regimens, but validation in larger samples is still needed. 2.3 NA alone then combined with interferon The ARES study included patients with compensated HBeAg-positive CHB treated with ETV monotherapy and randomized to either the add-on PEG-IFN treatment group or the continued ETV monotherapy group. As a result, the response rate was 19% vs. 10% for patients in the PEG-IFN and monotherapy groups, respectively (P=0.095). After correction for HBV DNA levels, the addition of PEG-IFN treatment was significantly associated with response. Disease remission was achieved after discontinuation in 11 (13%) and 2 (2%) patients in the PEG-IFN- and monotherapy groups, respectively (P=0.007), and HBeAg serologic conversion rates were 26% and 13% in the two groups at week 96, respectively (P=0.036). The addition of PEG-IFN treatment resulted in more significant reductions in HBsAg, HBeAg and HBV DNA levels than ETV monotherapy, and the combination regimen was very safe and well tolerated by patients. In a retrospective study by Prof. Guojun Li, 192 patients who applied NA therapy for 2 years and did not achieve HBeAg disappearance, 83 patients received combination therapy for 48 weeks and 109 patients received NAs to continue monotherapy for 48 weeks, and all patients received 24-week discontinuation follow-up with HBsAg testing during and after treatment. The results showed that HBsAg levels at baseline, 12 weeks and 24 weeks were strong predictors of treatment response in the combination group. Among patients with HBsAg <1000 IU/mL at baseline, 100% achieved a complete response and 91% achieved HBsAg clearance. Among patients with HBsAg >1000 IU/mL, the response rate was significantly lower in patients whose HBsAg did not decline at 12 weeks of treatment. However, patients with HBsAg levels decreasing >0.5log IU/mL at 12 weeks or >1.5log IU/mL at 24 weeks still had a chance of achieving a treatment response, suggesting that baseline HBsAg levels and the rate of HBsAg decline can predict response to combination therapy. Whether pegylated interferon alpha (PEG-IFN-α) combined with nucleoside (acid) analogue (NA) therapy enhances antiviral efficacy in chronic hepatitis B (CHB) remains to be clarified. In the plenary session of EASL 2014, Su from Taiwan, China, gave a congress presentation (abstract number: 0113) reporting on a phase IV, randomized, placebo (PBO) controlled, double-blind study evaluating the efficacy of PEG-IFN-α2a in combination with adefovir (ADV) or entecavir (ETV) for the treatment of HBeAg-positive chronic hepatitis B. A total of 280 patients with CHB were enrolled in the study, and 263 (94%) completed treatment. There were 3 treatment groups: (i) ADV 10 mg/d plus PBO-ETV; (ii) ETV 0.5 mg/d plus PBO-ADV; or (iii) both PBOs; after 6 weeks of treatment with the above regimen, all patients received PEG-IFN-α2a (180 μg/week) and continued treatment for 46 weeks (the first 2 weeks were overlapping treatment). The results revealed that the treatment was well tolerated, with low withdrawal rates in all three groups due to adverse events or laboratory abnormalities. The proportion of patients who experienced HBeAg serologic conversion ranged from 21% to 27% at the end of treatment and from 23% to 36% at the 24-week follow-up after the end of treatment. No statistically significant rates of HBeAg serologic conversion at the end of treatment or after 24 weeks of follow-up were seen at this time. The investigators concluded that “PEG-IFN-α2a combined with NA therapy was well tolerated, but after 24 weeks of follow-up, the combination therapy did not improve the HBeAg serologic conversion rate obtained with PEG-IFN-α2a alone.” A small study recently published in the journal Eur J Gastroenterol Hepatol by the group of Professor Gao Zhiliang at the Third Hospital of Sun Yat-sen University in China offers an alternative regimen of short-term treatment with PEG-IFN-α2a combined with response-guided lamivudine. The protocol was: initial treatment with PEG-IFN-α2a (135 μg/week); at 12 weeks of treatment, if HBV DNA remained above 1 × 105 copies/mL and HBeAg remained positive, lamivudine was added for 12 weeks; lamivudine was then discontinued and PEG-IFN-α2a was continued for a total duration of 52 weeks. The patient subgroups and treatment results from this study showed that the HBeAg seroconversion rate was up to 75% in the early responders who did not need the combination of lamivudine, while the HBeAg seroconversion rate also increased to 38% in those who needed the combination. The overall virologic response rate at the end of treatment with this regimen was 59%, the HBeAg seroconversion rate was 47%, and the HBsAg disappearance rate was 3%. Only 32 patients were included in this study, and the optimal duration of combination therapy remains to be determined, but it is still evident that adjustment of the treatment regimen through a response-guided approach to combination therapy is beneficial in improving outcomes and warrants further study in a large population. The current status of PEG-IFN-α combined with nucleoside (acid) analog therapy can be summarized as follows: (i) to date, there are still no data from controlled trials to support that the initial and parallel combination of PEG-IFN-α and nucleoside (acid) analogs can increase the response rate after drug discontinuation; (ii) patients with partial immune function recovery after viral load reduction with nucleoside (acid) analog therapy can be selected combination PEG-IFN-α therapy; and (iii) the addition of PEG-IFN-α early or late in the nucleoside (acid) analogue application has yielded promising results.” In order for more patients to achieve a durable response after drug discontinuation, investigators wanted to find strategies to further improve durable response rates. Numerous studies have first identified baseline factors affecting response to PEG-IFN-α treatment, including host factors (age, ALT levels) and viral factors (HBV DNA levels, HBsAg levels, HBV genotype), which provide a strong basis for the optimal timing of treatment prior to treatment. Based on the RGT strategy, investigators have conducted exploratory studies on the selection of different treatment regimens (standard therapy, extended interferon therapy, combined NA therapy, etc.) according to treatment response, and their effectiveness has been initially verified. As research progresses, there is a consensus on the significance of the combination of HBsAg and HBV DNA. However, the time points and thresholds for the observation of these two indicators have not been standardized, and the effectiveness and safety of optimized treatment regimen application have not been validated by prospective studies.