9. Treatment of hepatitis B infections

Florian van Bömmel, Johannes Wiegand, Thomas Berg

Introduction

Individuals with hepatitis B virus (HBV) infection carry a significantly increased risk of life-threatening complications such as hepatic decompensation, liver cirrhosis and hepatocellular carcinoma (HCC) (Beasley 1988). The goal of treatment of chronic HBV infection is to improve survival of the infected person by preventing progression to liver cirrhosis or end-stage liver disease, HCC and death; and prevention of transmission of HBV to others (EASL 2017, Terrault 2016, Sarin 2016). Long term observational studies of the natural course of HBV infections have shown that the level of serum HBV DNA correlates higher with the risk of developing late sequel as cirrhosis and HCC as compared to other patient or virus related factors (Chen 2006, Iloeje 2006) (Figure 1). Moreover, it has now become apparent that deep and continuous suppression of HBV replication can revert liver fibrosis or even cirrhosis in most patients (Chan 2010b, Schiff 2011, Marcellin 2013).

Three categories of cure have been defined for HBV infections: virological, functional (also referred to as immunologic cure), and partial cure. Virological cure means the suppression of the replication of HBV to undetectable levels, and it has become the major goal in treatment of chronic HBV infections. HBeAg seroconversion is another treatment endpoint, provided that HBV replication remains durably suppressed to low levels. The loss of HBsAg or HBsAg seroconversion to anti-HBs can be considered as stable remission of HBV infections and it is often referred to as functional cure. However, this goal is difficult to achieve by available treatment options. Complete clearance of HBV from an infected liver is impossible or achieve by current treatment options because even after HBsAg seroconversion the HBV infections will persist on cellular levels.

Two drug classes are available for the treatment of chronic HBV infections: the immune modulator interferon α (standard or pegylated (PEG)-INF α) as well as nucleoside or nucleotide analogues (NA), which act as reverse transcriptase inhibitors of the HBV polymerase. Currently, the nucleoside analogues lamivudine (LAM), telbivudine (LdT), entecavir (ETV) and the acyclic nucleotide analogues adefovir dipivoxil (ADV) and tenofovir in the two formulations tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF) are available. Due to this broad spectrum of therapeutic options and by employing laboratory tests, ultrasound and risk calculators, disease progression and complications can be prevented in many patients if the infection is diagnosed early and treated effectively. A number of regional and international treatment guidelines for HBV infections have been published over the last decade, each one reflecting regional differences in access to drugs, laboratory tests and health care. New therapies aiming at increasing the rate of HBsAg seroconversions or even eradicating chronic HBV infections continue to be developed, but yet in early stages of clinical studies.

Goals of treatment

Due to persistence of episomal covalently closed circular DNA (cccDNA), a template of the HBV genome located in the nucleus of infected hepatocytes, a complete eradication of HBV infection is currently impossible (Rehermann 1996). Reactivation of a HBV infection can occur in certain circumstances from these nuclear reservoirs even decades after HBsAg loss, for instance during immunosuppressive therapy. Accordingly, the aim of treatment of chronic hepatitis B is currently not to eradicate the infection but to reduce complications such as liver failure and HCC and to increase survival (EASL 2017, Cornberg 2011, KASL 2013, Terrault 2016, WHO 2015, Sarin 2016). In patients with acute hepatitis B, preventing the risk of acute liver failure is the main treatment goal. These aims can be approached by successful long term suppression of the HBV replication. Ideally, an immunologic control over the infection can be achieved. Immunologic control includes serologic response, which is characterised by seroconversion of HBeAg to anti-HBe or by loss of HBsAg, as well as a stage of low level replication during which, even in absence of serologic response, an indication for retreatment is not given. This goal can be referred to as sustained immune control.

To determine the success of antiviral therapy surrogate markers are used during and after treatment. These parameters include virologic parameters (serological status of HBeAg and HBsAg, HBsAg levels, HBV DNA levels) and patient-related parameters (aminotransferases, liver histology).

Endpoints of treatment

Suppression of HBV replication. In two large long-term studies a close correlation of baseline HBV DNA levels and subsequent disease progression was demonstrated. In the REVEAL study, 3774 untreated HBV-infected individuals were followed over a mean time period of 11.4 years in Taiwan (Chen 2006, Iloeje 2006). HBV DNA levels at baseline were the strongest predictors of cirrhosis and HCC development (Figure 1). In multivariate models, the relative risk of cirrhosis increased when HBV DNA reached levels greater than 300 copies/mL, independent of whether patients were negative or positive for HBeAg. In addition, individuals with HBV DNA levels ≥10⁴ copies/mL (or ≥2,000 IU/mL) were found to have a 3-15 fold greater incidence of HCC as compared to those with a viral load <10⁴ copies/mL. On the other hand, suppression of HBV DNA over some years shows a time dependent reversion of liver fibrosis as well as a decrease of the HCC risk.

The regression of liver fibrosis during antiviral treatment was impressively demonstrated in a subanalysis of two trials evaluating 348 patients who underwent biopsies before and after five years of TDF monotherapy (Figure 2) (Marcellin 2013). Of those patients, 88% experienced an improvement in overall liver histology as measured by an improvement of at least two points in the Knodell score of HAI (histologic activity index) (Figure 5). Of the 94 patients who had cirrhosis at the start of therapy, 73% experienced regression of cirrhosis, and 72% had at least a two-point reduction in fibrosis scoring. The positive effect of and effective antiviral treatment on liver histology was also shown in a subgroup of 59 patients from a rollover study including two phase III trials on the efficacy of ETV in treatment-naïve patients. Liver biopsies taken at baseline and after a median treatment duration of 6 years (range, 3-7 years) showed a histologic improvement, defined as a decrease of 2 points or greater in the Knodell necroinflammatory score in absence of worsening of the Knodell fibrosis score in 96% of patients. In addition, an improvement of more than 1 point in the Ishak fibrosis score was seen in 88% of patients, including all 10 patients who had advanced fibrosis or cirrhosis when they entered the phase III studies (Chang 2010a).

The decrease of HCC incidence in HBV infected individuals during antiviral treatment was illustrated by results of a retrospective analysis comparing HBV infected individuals receiving with those not receiving antiviral treatment between 1997 and 2010 in Taiwan (Wu 2014). Among the patients receiving treatment with NAs, the incidence rate of HCCs over 7 years of follow up was 7.3 % as compared to 22.9% among patients without antiviral treatment. However, the HCC risk is not affected immediately after the initiation of antiviral treatment. Thus, the incidence of HCCs was shown to start decreasing after 5 years of effective HBV DNA suppression by either entecavir or tenofovir, and after eight years of treatment it was similar to individuals without HBV infection in a multicentric European cohort (Papatheodoridis 2017, Papatheodoridis 2018). The presence of liver cirrhosis strongly determines the remaining HCC risk. However, also patients with liver cirrhosis show a decreasing incidence in HCC development during treatment (Su 2016). Overall, these data indicate that with potent NAs HCC risk can be reduced but not eliminated.

Estimating the individual risk for HCC development during effective long term treatment with NAs is currently an important challenge for the treating physician. Several soring systems have been proposed including the CU-HCC-, GAG-HCC- und REACH-B-Score. A comparison of the performance of these three scores in Asian individuals receiving ETV for the treatment of chronic HBV infections found them to be equally precise in predicting HCC development (Wong 2013). For European individuals, the PAGE-B score, which is based on different parameters, seems to allow a more precise prediction as compared to the other scores (Papatheodorides 2014). An overview of the different scoring systems is given in table 1. Although the interpretation of the cut off results of those scores and the corresponding management strategies have not definitely been defined yet, those risk calculators can be used for evidence-based personalised tailoring of monitor algorithms of chronically HBV infected individuals.

Based on these observations, a durable suppression of HBV replication monitored by HBV DNA levels in serum has become the most urgent aim in the treatment of HBV infections (Cornberg 2011, EASL 2017, Terrault 2016, Sarin 2016, WHO 2015). Treatment is recommended to be continues until one of the following end-point has been achieved:

HBeAg seroconversion. In HBeAg positive patients, seroconversion from HBeAg to anti-HBe was found to be a reliable surrogate marker for prognosis of chronic HBV infection leading in many cases to an inactive HBsAg carrier state (Figure 3). In these patients, HBsAg remains detectable but HBV replication continues at low or even undetectable levels and transaminases are generally within normal ranges.

HBeAg seroconversions that appear during antiviral treatment can be considered asa lasting immune response in the majority of patients. In a meta-analysis in 76% of patients achieving HBeAg seroconversion this was stable after treatment discontinuation (Papatheodoridis 2016). On the other hand, long-term observations reveal that HBeAg seroconversion cannot always be taken as a guarantee of long-term remission. A reactivation of the disease with “sero-reversion” (HBeAg becoming detectable again) as well as a transition to HBeAg negative chronic hepatitis B with increased, often fluctuating, HBV DNA levels, can occur in 30-50% of patients (Hadziyannis 1995, Hadziyannis 2001, Hadziyannis 2006, van Hees 2018). Therefore, HBeAg seroconversion should only be regarded as a treatment endpoint in conjunction with durable and complete suppression of HBV replication.

The age of an individual in which an HBeAg seroconversion occurs seems to have an important influence on the development of complications of HBV infections. In a recent long-term observational study in 483 HBeAg positive patients achieving spontaneous HBeAg seroconversion, it was shown that over 15 years after HBeAg seroconversion the incidence of cirrhosis and HCC was lower for patients who had achieved HBeAg seroconversion at an age <30 years old compared to patients achieving seroconversion at an age >40 years old (Chen 2010). This observation raises the question whether HBeAg seroconversions appearing during antiviral treatment in patients older than 40 years might also be associated with a higher remaining risk of complications compared to patients achieving HBeAg seroconversion at a younger age.

There is ongoing discussion whether and how long a consolidation treatment (6-12 months) should be maintained following HBeAg seroconversion. As a result, Asian guidelines recommend stopping treatment after HBeAg seroconversion, whereas American and European guidelines favour treatment continuation, but allow discontinuation in selected patients with close subsequent monitoring.

HBsAg loss. Because HBsAg loss or seroconversion is associated with a complete and definitive remission of the activity of chronic hepatitis B and an improved long-term outcome, it is currently regarded as stable remission of HBV infections or a “functional cure”, although HBV cccDNA still persists in infected hepatocytes and reactivations may occur. Unfortunately, HBsAg loss can be induced in only a limited number of patients by treatment (in up to 10% of HBeAg positives and in <1% of HBeAg negatives). This is not improved even by long term treatment with NAs up to eight years (Marcellin 2014). The probability of HBsAg seroclearance during therapy with NAs is linked to a decrease in HBsAg levels during the early treatment period. As HBsAg levels remain unchanged in most patients during the first years of treatment it seems therefore unlikely that a longer duration of NA treatment will further increase rates of HBsAg losses (Figure 4) (Marcellin 2011).

Sustained immune control. The term “sustained immune control” can be used to describe a stage that follows the discontinuation of treatment for hepatitis B and applies to both, NA or PegIFN based treatments. Sustained immune control and it should be equated with “absence of virological treatment indication” and refers to a stage with low HBV replication (ideally < 2.000 IU/mL) and normal ALT levels in spite of detectable HBsAg (and possibly HBeAg). However, durability of this immune control is not guaranteed due to the fluctuating course of HBeAg negative chronic hepatitis B.

For treatment with PEG-IFN α in both, HBeAg positive and -negative patients, inducing an immune control status, characterised by persistent suppression of viral replication with HBV DNA levels <2,000 IU/mL and normalisation of ALT levels was defined as another, combined treatment endpoint (Marcellin 2009). If this condition is maintained over time, it increases the probability of HBsAg loss and reduces the development of liver fibrosis and HCC. Late relapse beyond 6 months post-treatment has been described, but a sustained response at 1 year post-treatment appears to be durable through long-term follow-up (Marcellin 2009). However, the immune control status needs to be regularly monitored, and treatment needs to be re-introduced in case of increase of HBV replication. Immune control defined as “absence of treatment indication” was recently shown to be an important end point after discontinuation of long term antiviral treatment in HBeAg negative patients (Berg 2017). For patients presenting any signs of liver fibrosis or family history of HCC, immune control should not be regarded as the treatment endpoint but rather the complete suppression of HBV replication.

Criteria for treatment response

Virologic response

• Sustained decrease of HBV DNA, to at least <2,000 IU/mL (corresponding to <10,000 copies/mL), ideally to <60 IU/mL (<300 copies/mL).
• Sustained HBeAg seroconversion in HBeAg positive patients.
• Ideally, loss of HBsAg with or without appearance of anti-HBs.

Biochemical response

• Sustained ALT normalisation.

Histologic response

• Reduction of fibrosis (histological staging).
• Reduction of inflammatory activity (histological grading).

Potential long-term effects

• Avoidance of cirrhosis, hepatocellular carcinoma (HCC), transplantation, and death.

Indication for antiviral therapy

Treatment of acute hepatitis B

Acute hepatitis B resolves spontaneously in 95-99% of cases (McMahon 1985, Tassopoulos 1987, Liaw 2009). Therefore, treatment of acute HBV infections with the currently available drugs is generally not indicated. In patients with a potentially life-threatening disease course as severe or fulminant acute hepatitis B antiviral treatment should, however, be considered as there are observations suggesting that antiviral treatment might reduce mortality in patients experiencing fulminant hepatitis during acute HBV infection. Thus, in a trial comparing treatment with LAM 100 mg/day versus no treatment in 80 Chinese patients with fulminant hepatitis B, a mortality of 7.5% was found in patients receiving LAM treatment compared to 25% in the control group (p=0.03) (Yu 2010). The result of this and another study also demonstrated that the earlier the treatment was initiated, the better were the results obtained (Kumar 2007). A rapid decline of HBV DNA load was a good predictor for treatment outcome (Kumar 2007). In contrast, a lower mortality was not seen when antiviral therapy was initiated late in the course of severe acute hepatitis B in patients with already manifested acute liver failure and advanced hepatic encephalopathy (Wang 2014). Several case reports from Europe also indicate that patients with severe and fulminante hepatitis B may benefit from early antiviral therapy with LAM or other NAs by reducing the need for high-urgency liver transplantation (Tillmann 2006). As a result, antiviral treatment of fulminant or severe acute hepatitis B with NA is recommended by current treatment guidelines (Terrault 2015, EASL 2017, WHO 2015, Sarin 2016). Interferon therapy is contraindicated in patients with acute HBV infection because of the risk of liver failure by increasing the inflammatory activity of the HBV infection (Tassopoulos 1997). The endpoint of treatment of acute HBV infections is HBsAg clearance (EASL 2017, WHO 2015, Sarin 2016).

Treatment of chronic hepatitis B

All individuals with detectable HBV DNA should be considered as potential candidates for antiviral therapy (EASL 2017, Terrault 2016, Chen 2006, Iloeje 2006). There is widespread agreement that the decision whether to initiate treatment should be made on the criteria: 1) serum HBV DNA levels, 2) ALT elevation and 3) histologic changes of liver tissue (Akarca 2008, Carosi 2011, Cornberg 2011, KASL 2012, EASL 2017, Terrault 2016, Sarin 2016). Indication for treatment should also take into account age, health status, family history of HCC or cirrhosis and extrahepatic manifestations. Differentiation between HBeAg positive and HBeAg negative chronic hepatitis B is not necessary anymore for treatment indication, although with respect to the choice of the appropriate antiviral drug (NAs vs. interferon α) these criteria may be still useful. Current recommendations for treatment indications may vary across different regions, and the criteria of different national and international societies are displayed in Table 1 (Akarca 2008, Carosi 2011, Colle 2007, Cornberg 2011, EASL 2017, Buster 2008, KASL 2012, Terrault 2016, WHO 2015, Sarin 2016). In comparison with previous recommendations, in most of these guidelines the most relevant factor for a decision to initiate treatment has shifted from histological proven disease activity to the serum level of HBV DNA. Thus, most guidelines now recommend antiviral treatment for patients with HBV DNA levels >2,000 IU/mL (corresponding to >10,000 copies/mL) in association with a sign of ongoing hepatitis (elevated ALT levels or liver fibrosis demonstrated by liver histology greater than A1/F1 or, alternatively, non-invasive tools such as liver elastography or serologic algorithms such as fibrotest).

The question which indications are needed to start antiviral treatment in patients with liver cirrhosis is answered controversially across different treatment guidelines. Most guidelines agree upon recommending treatment for all patients with liver cirrhosis or high-grade liver fibrosis and any measurable HBV DNA (Cornberg 2011, KASL 2012, EASL 2017, Sarin 2016). The WHO guidelines recommend treatment initiation in all patients with cirrhosis, even if the HBV DNA level is low or undetectable (WHO 2015), which is a more practical approach for settings in which quantification of HBV DNA is unavailable. In other treatment guidelines antiviral treatment is recommended for patients with chronic HBV infection and compensated cirrhosis, if HBV DNA levels are greater than 2,000 IU/mL, regardless of ALT levels (Terrault 2016, Sarin 2016). The decision path for antiviral treatment proposed by the German guidelines is depicted in Figure 2 (Cornberg 2011). In patients with decompensated cirrhosis with Child-Pugh score B or C, standard or pegylated interferon-α is contraindicated. For patients without liver cirrhosis, the treatment indication is linked to disease stages:

Inactive chronic HBsAg carriers (or patients with HBeAg negative HBV infection), characterised by negative HBeAg and pos-itive anti-HBe, HBV DNA levels <2,000 IU/mL and serum aminotransferases within normal ranges do not have an indication for antiviral therapy (Brunettto 2011, EASL 2017, WHO 2015, Terrault 2016, Sarin 2016). However, differentiation between true inactive HBsAg carriers and patients with chronic HBeAg negative hepatitis may be difficult in some cases and HBV DNA needs to be monitored on a regular basis. Elevated transaminases are no reliable parameter for assessing the stage of liver fibrosis and long-term prognosis of HBV-infected patients. On the other hand, even in patients with normal or slightly elevated aminotransferases there can be a significant risk for the development of HBV associated complications (Chen 2006, Iloeje 2006, Kumar 2008). HBsAg levels may be helpful to predict reactivation of HBV replication and inflammatory activity (Martinot-Peignoux 2013). It is reasonable to assess fibrosis progression by non-invasive methods or to perform a liver biopsy in these individuals and to control the levels of HBV DNA and ALT at three-month intervals and start treatment if moderate inflammation or advanced fibrosis becomes evident (Table 1).

HBV immune tolerant patients (or patients with HBeAg positive HBV infection) are mostly under 30 years old and can be recognised by their high HBV DNA levels, detectable HBeAg, normal ALT levels and minimal or absence of significant histological changes. The risk of disease progression in these individuals is very low (Tseng 2015). According to most practice guidelines, immediate therapy is not required as long as severe fibrosis development can be ruled out (Akarca 2007, Balik 2008, Carosi 2008, Buster 2008, Cornberg 2011, EASL 2017, KASL 2012, Terrault 2016, Sarin 2016). The WHO guidelines represent an exemption in this point as they do not advice antiviral treatment in immunotolerant individuals only up to an age of 30 years. Indeed, regarding the long lead in time for HCC development, it can be assumed that immune tolerant HBV with elevated risk for HCC development such as positive family history and patients from high endemic areas like East Asia or Africa may benefit from early antiviral therapy despite normal ALT levels. Treatment with either TDF or a combination of TDF plus emtricitabine was recently shown to be equally effective in suppressing HBV replication in in Asian immune tolerant patients with high-level viraemia (Chan 2014). However, the HBeAg loss rates were only 2-6% after 195 weeks of treatment and thus lower as in immune active patients. Studies are under way to further clarify this issue, especially to answer the question whether early intervention with antiviral therapy will positively influence the long-term risk for HCC.

How to treat

Therapy of chronic Hepatitis B is possible with either PEG-INF α or with NA. (Figure 6).
The option of PEG-INF α treatment should be considered for all patients. However, if a patient does not fulfil the criteria for a higher likelihood of response to treatment with PEG-INF α, has contraindications, or is intolerant to PEG-INF α, long-term therapy with an NA is recommended (Figure 6). If a NA is chosen, several parameters have to be considered prior to therapy: the antiviral efficacy of the drug, the resistance barrier, potential side effects and the stage of liver disease. The preferred regimens are ETV, TDF or TAF as monotherapies as first line treatment as recommended in guidelines due to their strong antiviral efficacy and low rate (ETV) or to date even absence (TDF, TAF) of reported resistance (EASL 2017, WHO 2015, Terrault 2016, Sarin 2016). LAM, ADV and LdT are still licensed, but due to their weaker antiviral performance and substantial risk of resistance development no longer recommended for treatment of hepatitis B (EASL 2017).

However, if the initial viral load is low and liver cirrhosis has been excluded, any approved NA may be used for treatment. (Table 3).

Treatment options

Currently available drugs for the treatment of HBV infections are listed in table 4. Because of a limited tolerability due to adverse events, duration of treatment with PEG-IFN α via subcutaneous injection is limited to a period of up to 48 weeks. NAs are orally administered and can achieve suppression of HBV DNA in almost all patients, but they have to be used for an undefined period unless one of the endpoints is achieved (see above). Planned discontinuation of long term NA treatment represents a novel approach to induce immune control in HBeAg negative patients. The efficacy of NAs can be hampered by emergence of HBV resistance. Response rates during treatment with different drugs are shown in Figure 7.

Interferons

INF α is a natural occurring cytokine with immune modulatory, anti-proliferative and antiviral activity. During treatment, the therapeutic efficacy of INF α can often be clinically recognised by a self-limited increase of ALT levels to at least twice the baseline levels. These ALT flares are often associated with virologic response.

The main aim of INF α treatment is to induce a long-term remission after a finite treatment duration. Response to IFN α can be either HBeAg seroconversion or durable suppression of HBV DNA to low or undetectable levels. In these responders the chance for HBsAg loss in the long-term is relatively high.

Standard INF α. Standard IFN α was approved for treatment of chronic hepatitis B in 1992. IFN α is applied in dosages ranging from 5 million units (MU) to 10 MU every other day or thrice weekly. In a meta-analysis, a significant improvement in endpoints was shown in patients with HBeAg positive chronic hepatitis B being treated with standard IFN compared to untreated patients (Craxí 2003). Complete remission of fibrotic changes was observed in some patients and the loss of HBsAg occurred comparatively often. Furthermore, there was a trend towards reduction of hepatic decompensation (treated 8.9% vs. untreated 13.3%), hepatocellular carcinoma (1.9 vs. 3.2%), and liver associated deaths (4.9 vs. 8.7%) (Craxí 2003).

A significant decrease in ALT and in HBV DNA serum levels was also shown for standard IFN α in the treatment of HBeAg negative chronic hepatitis B (Brunetto 2003). However, a high percentage (25-89%) of these patients relapses after the end of treatment showing elevation of ALT levels and a return of HBV DNA levels. The relapse rate seems to be higher when treatment duration is short (16 to 24 weeks) compared to longer treatment (12 to 24 months). A retrospective comparison of IFN therapies lasting from 5 to 12 months showed that with longer treatment the chance of a long-term response was 1.6 times higher (normalisation of ALT, HBV DNA <1x10⁶ copies/mL 1-7 years after end of therapy). The overall response rates were 54% at the end of therapy, 24% at 1 year after therapy, and 18% 7 years after therapy (Manesis 2001).

Patients with long-term response to treatment have a more favourable course than patients who were untreated, unresponsive, or who had a relapse interferon α therapy with respect to progression to liver cirrhosis, liver associated deaths, and development of hepatocellular carcinoma (Brunetto 2003, Lampertico 2003). However, due to higher antiviral efficacy PEG-IFN α should be preferred to standard IFN α.

PEG-INF α. The addition of a polyethylene glycol molecule to the IFN resulted in a significant increase in half-life, thereby allowing administration once weekly. Two types of subcutaneously administered PEG-IFN α were developed: PEG-IFN α-2a and PEG-IFN α-2b, of which PEG-IFN α-2a was licensed for the treatment of chronic HBV infections in a weekly dose of 180 µg for 48 weeks in both HBeAg positive and HBeAg negative patients. However, PEG-IFN α-2b shows similar efficacy. After one year on treatment with PEG-IFN α-2a and α-2b, 22% to 27% of patients were reported to achieve HBeAg seroconversion (Janssen 2005, Lau 2005).

The safety profiles of standard IFN α and PEG-IFN α are similar. Following therapy termination a relatively high relapse rate is to be expected (>50%). The dose of 180 µg per week applied for 48 weeks was recently shown to exert a stronger antiviral efficacy compared to administration for 24 weeks or to administration of 90 µg per week (Liaw 2011). Treatment durations longer than 48 weeks are not recommended in current guidelines.

PEG-IFN α in HBeAg positive patients. Four randomised, controlled studies investigating the efficacy of PEG-IFN α in HBeAg positive patients have been conducted (Crespo 1994, Chan 2005, Janssen 2005, Lau 2005). These studies compared 180 µg PEG-INF α per week to standard IFN, LAM, and/or a combination treatment with PEG-INF α + LAM for 48 weeks. Sustained HBeAg seroconversion at the end of follow-up (week 72) was significantly higher in patients treated with PEG-IFN α-2a alone or in combination with LAM than in patients treated with LAM alone (32% and 27% versus 19%) (Marcellin 2004).

PEG-IFN α in HBeAg negative patients. The efficacy and safety of 48 weeks treatment with 180 µg PEG-IFN α-2a once weekly plus placebo, plus 100 mg LAM daily, or LAM alone was compared in 177, 179, and 181 HBeAg negative patients, respectively. After 24 weeks of follow-up, the percentage of patients with normalisation of ALT levels or HBV DNA levels below 20,000 copies/mL was significantly higher with PEG-IFN α-2a monotherapy (59% and 43%, respectively) and PEG-IFN α-2a plus LAM (60% and 44%) than with LAM monotherapy (44% and 29%); the rates of sustained suppression of HBV DNA below 400 copies/mL were 19% with PEG-IFN α-2a monotherapy, 20% with combination therapy, and 7% with LAM alone (Lau 2005).

Prolongation of PEG-IFN α treatment beyond 48 weeks may increase sustained response rates in HBeAg negative patients. This was found in an Italian study in 128 mainly genotype D–infected HBeAg negative patients who were randomised to either treatment with 180 µg PEG-IFN α-2a per week for 48 weeks or an additional treatment with PEG-IFN α-2a at the dose of 135µg per week for another 48 weeks. Additionally, in a third arm patients received combination treatment with PEG-IFN α-2a 180µg/week and LAM 100 mg/day, followed by 48 weeks of PEG-IFN α-2a in the dosage of 135 µg/week. As a result, 48 weeks after the end of treatment 26% of patients who had received 96 weeks of PEG-IFN α-2a containing treatment showed HBV DNA levels <2,000 IU/mL as compared to only 12% of the patients who had received PEG-IFN α-2a for 48 weeks. Combination with LAM showed no additional effect (Lampertico 2013). However, prediction of response and management of side effects during prolonged treatment with PEG-IFN α has not yet been established and it is not recommended for clinical practice.

Importantly, it was shown that PEG-IFN α obviously induces immune modulatory effects which lead to considerable HBsAg clearance rates during the long–term follow-up period after treatment termination. In a study, 97 HBeAg positive patients with chronic HBV infection who had received treatment with standard IFN α were retrospectively analysed for a median period of 14 (range, 5-20) years. During the observation period, 28 patients (29%) of this cohort lost HBsAg (Moucari 2009). In another study in 315 HBeAg negative patients who were treated with either PEG-IFN α-2a, LAM 100 mg or a combination of both drugs for 48 weeks, three years after the end of treatment, the rate of HBsAg loss was 8.7% in those who had been treated with PEG-IFN α-2a alone or in combination with LAM while no patient treated with LAM as monotherapy cleared HBsAg (Marcellin 2009a). Of the patients who had received a PEG-IFN α-2a and who still had undetectable HBV DNA three years after treatment, 44% had lost HBsAg.

Nucleoside and nucleotide analogues

NAs inhibit HBV replication by competing with the natural substrate deoxyadenosine triphosphate (dATP) and causing termination of the HBV DNA chain prolongation. They represent two different subclasses of reverse transcriptase inhibitors: while both are based on purines or pyrimidines, acyclic nucleotide analogues have an open (acyclic) ribose ring that confers greater binding capacity to resistant HBV polymerase strains.

The treatment duration for NAs is not defined but a short-term application of these agents for 48 weeks is associated with prompt relapse in viraemia and they should be administered for longer periods. Treatment efficacy of NAs is defined by complete suppression of HBV DNA levels in serum. This should be achieved within 6-12 months if agents with high risk for resistance development as LAM, ADV, and LdT are used.

Effective long-term control of HBV replication with NAs is associated with a reduction of long-term complications such as liver cirrhosis and the development of HCC, especially in patients with liver cirrhosis (Toy 2009, Hosaka 2012) (Figure 8). Studies with different NAs have demonstrated that suppression of HBV replication is associated with a significant decrease in histologic inflammatory activity and fibrosis, including partial reversion of liver cirrhosis (Chen 2006, Iloeje 2006, Mommeja-Marin 2003, Chen 2010, Marcellin 2011, Schiff 2011). With increasing treatment duration HBeAg seroconversion rates increase, but even after 8 years of treatment they do not exceed 40-50% of treated patients (Liaw 2000, Lok 2000). There is also evidence that effective inhibition of HBV replication can reduce HBV cccDNA, possibly running parallel to the decline in serum HBsAg levels (Werle-Lapostolle 2004, Wursthorn 2006).

As treatment of HBeAg negative patients does not lead to an endpoint in most patients even after after more than a decade of therapy with NAs new concepts are assessed. Discontinuation of long term NA treatment may represent a novel approach to induce sustained immune control as well as serologic response in a significant proportion of HBeAg negative patients (van Bömmel 2018).

Lamivudine (LAM). LAM, a (-) enantiomer of 2’ -3’ dideoxy-3’-thiacytidine, is a nucleoside analogue that was approved for the treatment of chronic HBV infection in 1988 with a daily dose of 100 mg. This dose was chosen based on a preliminary trial that randomly assigned 32 patients to receive 25, 100, or 300 mg of LAM daily for a total of 12 weeks (Dienstag 1995). In this study the dose of 100 mg was more effective than 25 mg and was similar to 300 mg in reducing HBV DNA levels. LAM exerts its therapeutic action in its phosphorylated form. By inhibiting both the RNA- and DNA-dependent DNA polymerase activities, the synthesis of both the first strand and the second strand of HBV DNA are interrupted.

Long-term LAM treatment is associated with an increasing rate of antiviral drug resistance reaching approximately 70% after 5 years in patients with HBeAg positive HBV infections. Therefore, in many guidelines LAM is not considered a first-line agent in the treatment of chronic HBV infection any more. However, LAM still may play a role in combination regimens or in patients with mild chronic hepatitis B expressing low levels of HBV DNA (<10⁵ copies/mL). An early and complete virologic response to LAM within 6 months of therapy (<400 copies/mL) constitutes a prerequisite for long-term control of HBV infection without the risk of developing resistance.

Adefovir dipivoxil (ADV). Adefovir dipivoxil was approved for treatment of chronic hepatitis B in the US in 2002 and in Europe in 2003. It is an oral diester prodrug of adefovir, an acyclic nucleotide adenosine analogue that is active in its diphosphate form. Because the acyclic nucleotide already contains a phosphate-mimetic group, it needs only two, instead of three, phosphorylation steps to reach the active metabolite stage. ADV was the first substance with simultaneous activity against wild type, pre-core, and LAM-resistant HBV variants. It is active in vitro against a number of DNA viruses other than HBV and retroviruses (i.e., HIV). The dose of 10 mg per day was derived from a study comparing 10 mg versus 30 mg/d. The higher dosage leads to stronger suppression of HBV DNA levels but also to renal toxicity with an increase of creatinine levels (Hadziyannis 2003).

ADV was the first acyclic nucleotide that was widely used in the treatment of LAM resistant HBV infections. However, the antiviral effect of ADV in the licensed dosage of 10 mg/day is rather weak as compared to other available antivirals (Figure 7); this disadvantage makes ADV vulnerable to HBV resistance (Hadziyannis 2006a). For this, ADV should not be used as first line monotherapy.

Telbivudine (LdT). Telbivudine is a thymidine analogue which is active against HBV but at least in vitro not active against other viruses, including HIV and hepatitis C virus (HCV). LdT at 600 mg/day expresses higher antiviral activity compared to either LAM at 100 mg/day or ADV at 10 mg/day (Figure 7). More patients achieved HBeAg loss within 48 weeks compared to other NAs.

LdT was reported to be non-mutagenic, non-carcinogenic, non-teratogenic, and to cause no mitochondrial toxicity. A favourable safety profile at a daily dose of 600 mg was demonstrated (Hou 2008, Lai 2007). However, CK elevations were observed more often as compared to the group treated with LAM and neurotoxicity may be an issue when LdT is administered in combination with PEG-INF α (Fleischer 2009). Thus, in the GLOBE trial, during a period of 104 weeks grades 3/4 elevations in CK levels were observed in 88 of 680 (12.9%) patients who received LdT and in 28 of 687 (4.1%) patients who received LAM (p<0.001) (Liaw 2009). However, rhabdomyolysis was not observed. Peripheral neuropathy was described in 9 of 48 (18.75%) patients who received combination therapy of PEG-INF α and LdT and only in 10 of 3500 (0.28%) patients who received LdT monotherapy (Goncalves 2009).

In comparison to other NAs, some patients receiving treatment with LdT were shown to experience an increase in GFR rates. This effect was most pronounced in patients with mild renal insufficiency (Sun 2013). However, it is not clear if this translates into a clinical benefit of LdT.

Resistance to LdT has been found to occur in up to 21% of patients after 2 years of treatment (Tenney 2009), predominantly in those who did not achieve undetectable HBV DNA level by 24 weeks of treatment (Zeuzem 2009). LdT shows cross-resistance to LAM and ETV. As a consequence LdT should not be used in LAM or ETV refractory patients.

Entecavir (ETV). Entecavir, a cyclopentyl guanosine nucleoside analogue, is a selective inhibitor of HBV replication and was approved in 2006. Entecavir blocks all three polymerase steps involved in the replication process of the hepatitis B virus: first, base priming; second, reverse transcription of the negative strand from the pregenomic messenger RNA; third, synthesis of the positive strand of HBV DNA. In comparison to all other nucleoside and nucleotide analogues, ETV is more efficiently phosphorylated to its active triphosphate compound by cellular kinases. It is a potent inhibitor of wild-type HBV but is less effective against LAM-resistant HBV mutants. Therefore, ETV was approved at a dose of 0.5 mg per day for treating naïve HBeAg positive and HBeAg negative patients, but at the dose of 1 mg per day for patients with prior treatment with LAM (Lai 2005, Sherman 2008).

Treatment-naïve HBeAg positive patients achieved undetectable HBV DNA levels in 67%, 74% and 94% after one, two and five years of therapy, respectively (Figure 5, Figure 9) (Chang 2010). Long-term studies in ETV responding patients demonstrated that response was maintained in nearly all these patients over an observational period of up to six years. So far, the rate of resistance at six years of treatment is estimated to be approximately 1.2% for treatment-naïve patients (Tenney 2009). Loss of HBsAg occurs in 5% of treatment-naïve individuals after two years of ETV therapy (Gish 2010). A non-randomised Italian study in a mixed population of predominantly HBeAg negative patients could demonstrate undetectable HBV DNA levels in 91% and 97% of patients at 1 and 2 years of ETV treatment, respectively (Lampertico 2010).

In LAM-resistant patients ETV is less potent. Only 19% and 40% of these patients achieved undetectable HBV DNA after one and two years, respectively, despite an increased dose of 1 mg/day (Gish 2007, Sherman 2008). Due to cross-resistance up to 45% of patients with LAM resistance develop resistance against ETV after 5 years of treatment (Tenney 2009).

ETV has a favourable tolerability profile and can be easily adjusted to renal function. However, ETV may cause severe lactic acidosis in patients with impaired liver function and a MELD score of >20 points (Lange 2009).

Tenofovir (TFV). Tenofovir is available in two different formulas. It is an acyclic nucleoside phosphonate, or nucleotide analogue, and structurally closely related to ADV. TFV has selective activity against retroviruses and hepadnaviruses and is approved for the treatment of HIV infection and chronic hepatitis B. Tenofovir disoproxil fumarate (TDF), an ester prodrug form of tenofovir (PMPA; (R)-9-(2-phosphonylmethoxypropyl) showed marked antiviral efficacy over eight years (HBV DNA <400 copies/mL) in almost all treatment-naïve -negative and -positive patients (Table 5). HBeAg loss and HBeAg seroconversion were found in 47% and 31% of patients, respectively. Of the HBeAg positive patients remaining under observation for 8 years, 8.5% experienced HBsAg loss (Marcellin 2014). Other clinical studies showing a high efficacy of TDF in LAM-resistant HBV (van Bömmel 2010, Levrero 2010). Due to possibly existing cross-resistance to ADV, the efficacy of TDF might be hampered by the presence of ADV resistance in patients with high HBV viraemia; however, a breakthrough of HBV DNA during TDF treatment in patients with previous ADV failure or in treatment-naïve patients was not been observed (van Bömmel 2010, Levrero 2010, Berg 2014).

TDF is generally well tolerated and not associated with severe side effects. For HBV monoinfected, treatment-naïve patients, renal safety during TDF monotherapy was investigated in three studies. In a randomised study comprising HBeAg negative patients, none of 212 patients treated with TDF for six years and none of 112 patients who were treated with ADV for one year and then switched to TDF for five years had a decrease in GFR to levels of <50 ml/min or an increase of serum creatinine levels to >0.5 mg/dL (Buti 2015). In a similar study in HBeAg positive patients, of 130 patients treated with TDF for 3 years and of 76 patients treated with ADV for one year and consecutively with TDF for 2 years, only one patients showed an increase in serum creatinine levels >0.5 mg/dL starting at year two (Heathcote 2011). In a sub-analysis of both studies in 152 HBeAg positive and HBeAg negative Asian patients, no increase of serum creatinine >0.5 mg/dL or of eGFR <50 ml/min was found in up to 3 years of TDF treatment (Liaw 2009a). In addition, a benefit in renal function was found in treated patients when compared to untreated patients with HBV infection, which might reflect a lower incidence of glomerulonephritis caused by HBsAg induced immune complexes in treated patients (Mauss 2011).

Tenofovir alafenamide fumarate (TAF, or (9-[®-2-[[(S)-[[(S)-1-(isopropoxycarbonyl)ethyl]amino] phenoxyphosphinyl]methoxy]propyl]adenin), was approved for the treatment of HBV infections in 2016. TAF is following a novel pro-drug mechanism of action and has a higher bioavailability and increased plasma stability compared to TDF. The resulting lower daily dose of 25 mg (vs. 245 mg for TDF) has been shown to be as effective as the TDF formulation in both HBeAg positive patients, but with fewer negative effects on bone and kidney biomarkers (Buti 2016, Chan 2016). Thus, in both studies, patients receiving TAF experienced a significantly smaller mean decrease in spine and hip bone mineral density at week 48 compared to patients receiving TDF. The median decrease in estimated glomerular filtration rate (eGFR) from baseline to week 48 was smaller in the TAF treated patients, although the clinical relevance of this observation remains under debate.

The use of tenofovir in HIV-coinfected patients is discussed in detail in Chapter 15.

Combination therapy as first-line treatment. Combination treatments with different NAs or NAs with PEG-IFN α were studied in different patient cohorts. However, in most trials combinations were not superior to mono therapies, and due to insufficient knowledge how to choose patients that will benefit from first line combination treatments they are currently not recommended.

There is only one study comparing a combination therapy with LAM and ADV to LAM monotherapy in untreated patients (Sung 2008). In this study, there was no difference in the virologic and biochemical response between both groups. However, the rate of LAM resistance was much lower in the combination group.

A study assessing the combination of LAM with LdT showed no benefit for combination therapy (Lai 2005).

In another trial, 379 treatment-naïve patients were randomised to receive either ETV 0.5 mg/day as monotherapy (n = 186) or in combination with TDF (n = 198) (Lok 2012). By week 96, 76 % of patients in the monotherapy and 83 % in the combination arm showed suppression of HBV DNA below 50 IU/mL (p = 0.088). In a post hoc subgroup analysis, combination therapy was superior to ETV as monotherapy in HBeAg positive patients with baseline HBV DNA > 8 log IU/mL. In a double-blind study in 126 HBeAg positive immune tolerant individuals with high levels of HBV DNA (mean 8.41 log₁₀ IU/mL) were randomly assigned to two arms given either oral TDF 300 mg per day and placebo (n = 64) or a combination of TDF and emtricitabine (200 mg, n = 62) for 192 weeks. At week 192, 55% of patients in the TDF monotherapy group and 76% of patients in the combination group had levels of HBV DNA <69 IU/mL (p=0.016). However, HBeAg seroconversion or HBsAg loss was reported in only few patients and this was not different across both groups (Chan 2014).

Especially in patients with liver cirrhosis, a fast and complete suppression of HBV replication is desirable. A monotherapy with ETV was found to be as safe and effective as monotherapy with TDF, and an addition of emtricitabine to TDF showed no improvement in response (Liaw 2011). Therefore, in these patients as well, combination treatment is currently not recommended.

Although a combination of NAs and PEG IFN α theoretically represents a more promising approach as two different mechanisms of action could potentially be synergistic, the results from clinical studies do not support this strategy. A more pronounced on-treatment virologic response at week 48 of treatment was observed with combination therapy as compared to LAM or PEG-IFN α alone in one study (Chan 2005). But a combination of LAM plus PEG-IFN α failed to demonstrate serologic or clinical benefit when evaluated at the end of follow-up in most studies (Janssen 2005).

Combination therapies of PEG-IFN α with more potent NAs such as ETV or TDF may be more attractive. A combination treatment of ETV and PEG-IFN 2α after 4 years of complete response to ETV was found to be superior to continuation of ETV treatment by HBeAg and HBsAg loss and seroconversion rates (Ning 2014). A recent randomised study investigating the efficacy of a combination treatment of PEG-IFN α and TDF alone or in combination in 740 patients with chronic hepatitis B found that patients treated with TDF plus PEG-IFN 2α for 48 weeks achieved significantly higher rates of HBsAg loss at week 72 (9.1%) than patients treated with either TDF (0%) or PEG-IFN 2α (2.8%) at week 72 (Marcellin 2016). However, due to the short follow up of these patients and the low rate of HBsAg losses overall, a combination treatment of NAs plus PEG-INF α can still not be recommended.

Combination treatment with LdT and PEG-INF α is contraindicated. Peripheral neuropathy was described in 9 of 48 (18.8%) patients who received combination therapy of PEG-INF α and LdT, as compared to only in 10 of 3,500 (0.28%) patients who received LdT monotherapy (Goncalves 2009).

Choosing the right treatment option

At first, the feasibility of PEG-IFN α therapy should be evaluated (Figure 6). However, if a patient does not fulfil the criteria for PEG-IFN α, has contraindications or low likelihood for response, or is intolerant to interferon, long-term therapy with NAs is recommended. If an NA is chosen several parameters have to be considered prior to therapy: the antiviral efficacy of the drug, the durability of response, the resistance barrier, expected side effects and the stage of liver disease.

If the initial viral load is low and liver cirrhosis has been excluded, any approved NA may be used, however, more recent guidelines recommend the use of either ETV or TDF for first-line treatment (EASL 2017, WHO 2015, Terrault 2016, Sarin 2016). The use of LAM should be restricted to patients with mild fibrosis and HBV DNA levels <2,000 IU/mL (or <10⁴ copies/mL). For patients with high-level HBV replication (>2x10⁸ IU/mL or >10⁹ copies/mL) only drugs with a high genetic barrier should be used (i.e., ETV or TDF) (Table 4).

Prognostic factors for treatment response

Several factors are associated with long-term remission and may help to guide treatment decisions. Pre-treatment factors predictive of HBeAg seroconversion are low viral load, high ALT levels (above 2-5 x ULN) and high histological grading (Flink 2006, Hadziyannis 2006a, Lai 2007, Perrillo 1990, Perrillo 2002, Wong 1993, Yuen 2007, Zoulim 2008, Buster 2009). These general baseline predictors are relevant especially for treatment regimens with PEG-IFN α but may in part be relevant also for NAs (Table 6).

A pooled analysis from the two largest trials using PEG-IFN α-2a or -2b in chronic hepatitis B tried to calculate a score predicting successful interferon therapy based on an individual patient’s characteristics (viral load, ALT level, HBV genotype, age, gender). However, this approach may only be feasible in HBeAg positive patients (Buster 2009).

HBV genotypes and treatment response. HBV genotypes have been shown to be associated with IFN α treatment success. Patients with HBV genotype A, prevalent in northern Europe and the US, show a much higher rate of HBeAg and HBsAg seroconversion than patients with HBV genotype D, prevalent in the south of Europe, or the HBV genotypes B or C originating from Asia (Keeffe 2007, Wiegand 2008). During treatment with nucleos(t)ide analogues, suppression of HBV replication and induction of HBeAg loss can be achieved regardless of the present genotype. However, HBsAg loss was almost exclusively observed in patients with genotypes A or D.

During antiviral therapy, the decrease of HBV DNA levels from baseline is the most important tool in monitoring treatment efficacy. Complete response to antiviral therapy is defined as suppression of HBV DNA below the limit of detection as measured by a sensitive real time PCR assay (Figure 10). Incomplete suppression is characterised by persistent HBV replication despite antiviral therapy. Ongoing HBV replication should be avoided to prevent the selection of resistant HBV strains by replication of the virus in the presence of drug in the so-called “plateau phases”. A breakthrough of HBV DNA despite continuous NA treatment may be caused by viral resistance; however, if NAs with high genetic barrier against resistance as ETV or TFD are used, non-adherence to the antiviral treatment is more likely. Measuring of HBV DNA kinetics early during therapy will help to guide antiviral treatment and to establish early stopping rules or add-on strategies to avoid antiviral failure (Figure 10).

Incomplete or partial virologic response to NAs is defined as a decrease of HBV DNA >1 log₁₀ IU/mL but remaining measurable (Lavanchy 2004) (Figure 10). The definition of partial response depends on the type of treatment; thus, for agents with a high genetic barrier against resistance like ETV or TDF partial response is defined after 12 months and for substances with a low genetic barrier like LAM or LdT, after 6 months of monotherapy. In case of partial response to a drug with a low genetic barrier, an appropriate rescue therapy should be initiated. By current guidelines, a combination treatment with an NA is recommended for these patients. However, it was recently shown that patients with partial response to LAM or to ADV have a high probability of responding to TDF monotherapy, without risking the development of resistance (Heathcote 2011, Marcellin 2011b, van Bömmel 2010, Berg 2014). Patients with a partial response to ADV were also shown to have a high probability of responding to a subsequent monotherapy with ETV, irrespective of the presence of mutations associated with HBV resistance to ADV (Leung 2009, Leung 2009a).

For patients with partial response to a drug with a high genetic barrier as ETV or TDF, current guidelines also recommend the initiation of a combination treatment. However, this might be necessary only in a minority of patients, as recently published long-term studies have shown that the continuation of a first-line monotherapy with ETV or TDF increases the percentage of patients with undetectable HBV DNA over time without leading to resistance development (Chang 2010, Marcellin 2011b, Snow-Lampert 2011, Marcellin 2014) (Figure 9). Thus, during monotherapy with TDF in HBeAg positive and HBeAg negative patients, an increase of patients with complete suppression of HBV DNA between the end of the first and the end of the fifth year of treatment from 81% and 90% to 100% was shown. For monotherapy with ETV at 1 mg/day, an increase from 55% to 91% and 94% after the fourth and fifth years was demonstrated (Chang 2010). In case of incomplete viral suppression at week 48, a continuation of monotherapy with TDF or ETV 1 mg is advisable as long as HBV DNA levels decrease continuously. However, the debate on whether switching or adding a second drug as optimal management is not yet resolved.
Since only 30-35% of all patients treated with PEG-IFN α reach HBeAg seroconversion after 48 weeks, it has been assessed how to predict the probability of response to PEG-IFN α by kinetics of HBV DNA during treatment. In one retrospective analysis early prediction of stable seroconversion was possible by week 12 of therapy if HBV DNA had reached levels below 5 log₁₀ UI/mL within this short treatment period (Fried 2005). In 53% of these patients, HBeAg seroconversion was observed while patients with HBV DNA levels of 5 to 9 log₁₀ copies/mL or levels above 9 log₁₀ IU/mL achieved HBeAg seroconversion in only 17% and 14%, respectively.
Time point of HBeAg loss. In one study with 172 patients who were treated with PEG-IFN α-2b as monotherapy or in combination with LAM, the loss of HBeAg within the first 32 weeks of treatment was shown to be an on-treatment predictor for HBsAg loss during a mean period of 3.5 years after the end of treatment. HBsAg loss was found in 36% of the patients with early HBeAg loss and only in 4% of the patients with HBeAg loss after 32 weeks of treatment (Buster 2009).

HBsAg levels and treatment response. Response of HBeAg positive and HBeAg negative patients to PEG-IFN treatment can be predicted by measuring HBsAg levels before and changes of HBsAg levels during treatment (Figure 11).

During PEG-IFN treatment for HBeAg positive chronic HBV infection, an absence of a decline in HBsAg levels at week 12 of treatment reduces the probability of response to <5% in one study (Sonnefeld 2010). In the NEPTUNE trial investigating the predictive value of HBsAg levels in 114 HBeAg positive patients receiving PEG-IFN α-2a over 48 weeks, it was shown that in patients achieving suppression of HBsAg to levels <1,500 IU/mL after 12 weeks of treatment, the chance of reaching HBeAg seroconversion, suppression of HBV DNA to levels <2,000 IU/mL and HBsAg loss 6 months after treatment was 58%, 52% and 10%, compared to 42%, 31% and 0% in patients with HBsAg levels between 1,500-20,000 IU/mL. In this study, patients still showing HBsAg levels >20,000 IU/mL after 12 weeks of treatment achieved none of the endpoints (Liaw 2011). Beyond that, the probability of HBeAg loss rose to 68% in patients with elevation of ALT levels >2 x the upper limit of normal at treatment initiation (Figure 12).

Also, in HBeAg negative patients the decrease of HBsAg after 12 weeks of PEG-IFN α treatment can predict long-term response. This prediction can be made even more precise regarding the kinetics of both HBsAg and HBV DNA. In another study comprising 48 patients who were treated with PEG-IFN α-2a, a decrease in serum HBsAg levels of 0.5 and 1 log₁₀ IU/mL at weeks 12 and 24 of therapy was associated with a positive predictive value for HBsAg loss of 90% and 97% at week 96 after treatment, respectively (Moucari 2009).

Monitoring before and during antiviral therapy

Before therapy, HBV DNA levels should be measured with a highly sensitive assay. These results should be reassessed 1-2 months after initiation of therapy. In addition, ALT levels reflecting the inflammatory activity as well as creatinine levels to monitor eventual renal toxicity of NAs should be measured. HBV genotyping is only recommended in patients who are considered candidates for treatment with IFN. HBV resistance testing can be useful in patients with prior failure to more than one NA, but this is not a standard diagnostic approach.

During therapy, HBV DNA, ALT and creatinine levels should be measured initially, after 4 to 6 weeks and then every 3 months. The early identification of viral resistance and an early adjustment of therapy are crucial. Patients with suppression of HBV replication to levels <300 copies/mL (60 IU/mL) for at least 2 years may be scheduled at 6 months intervals (Table 7). However, no studies have been performed that support this procedure.

HBsAg and, in HbeAg positive patients, HBeAg and anti-HBe should also be measured once HBV DNA levels have become undetectable to detect serologic response).

Because the risk for HCC development remains increased even in patients with complete viral suppression during long-term treatment with NA, these patients should regularly receive ultrasound examinations (Papatheodoridis 2014). For the estimation of the individual risk of HCC development, newly introduced score systems can be helpful (see below).

Treatment duration and stopping rules

After loss of HBsAg or seroconversion to anti-HBs antiviral treatment patients can be safely withdrawn from treatment with NAs. This was demonstrated in a recent study assessing the long-term outcome of patients withdrawing from NA treatment after HBsAg clearance. In this study, 27 (5%) out of 520 CHB patients who received NA for prolonged periods ultimately lost serum HBsAg and were subsequently followed for a mean of 44 (12–117) months (Chen 2014).

In HBeAg positive patients continuous treatment with nucleos(t)ide analogues is necessary as long as HBeAg seroconversion is not achieved. Even after seroconversion antiviral therapy should be continued for at least another 12 months to reduce the risk of “sero-reversion” upon stopping the nucleos(t)ide analogue therapy (EASL 2017, WHO 2015, Terrault 2016).

Criteria for optimal treatment duration with NAs are still lacking for patients with HBeAg negative chronic hepatitis B. Therefore, currently unlimited treatment with NAs is recommended. Discontinuation of NA treatment may be considered in selected patients (see below). In patients with liver cirrhosis oral antiviral treatment should not be discontinued at any time point because of the risk of liver decompensation during a virologic and inflammatory rebound.

PEG-IFN α should be administered for 48 weeks in HBeAg positive and HBeAg negative patients. If no decrease in HBV DNA or/and in HBsAg levels can be noted after 12 weeks of treatment, response becomes unlikely and treatment may be stopped early in agreement with the patient.

Controlled cessation of long-term treatment with NAs in HBeAg negative patients

In HBeAg negative patients receiving antiviral treatment, HBsAg loss occurs only occasionally (<1%). Safety and costs of long term treatment with NAs are a concern for these patients. Current recommendations regarding treatment termination follow different strategies. Thus, AASLD guidelines state that NA treatment should be continued in HBeAg negative patients until HBsAg loss, while APASL guidelines recommend that treatment may be withdrawn after at least 2 years of treatment with undetectable HBV DNA (EASL 2017, Terrault 2016, Sarin 2016). EASL guidelines are the first to mention discontinuation of NA treatment as approach to increase immunologic response. All three guidelines recommend excluding patients with cirrhosis from treatment termination unless they have cleared HBsAg. After stopping long-term NA-treatment, a virologic and a biochemical relapse of the HBV infection is common, but some patients have been shown to clear HBsAg following this relapse, and others to develop a stable, low-level replicating HBV infection with no indication for further antiviral treatment (Figure 13). In the FINITE study, the first randomised study to assess the efficacy of NA discontinuation in HBeAg negative patients, the primary endpoint was not relapse in HBV DNA levels, but the rates of HBsAg loss and long-term immunological control defined as HBV DNA levels <2,000 IU/mL (Berg 2017). For this, patients were assessed week 144 after withdrawal of monotherapy with tenofovir (TDF). Patients included in the study had HBV DNA at undetectable levels for ≥3.5 years and were randomly assigned to either stop (n = 21) or continue (n = 21) TDF. After discontinuation of TDF, HBV DNA became detectable in all patients. However, a total of 62% (n = 13) remained off-therapy until week 144 (Figure 14). Four patients (19%) experienced HBsAg loss. Eight patients had to restart therapy with TDF due to ALT flares.

Prediction of response to NA discontinuation has not yet been established yet. HBsAg levels may be a marker to guide treatment cessation in HBeAg negative patients. The effect of stopping therapy after a long-term ADV treatment of 4 to 5 years with complete viral suppression was evaluated in a small cohort of Greek patients (Hadziyannis 2008). Despite the fact that all patients suffered a slight virologic relapse within 3 months of stopping therapy, most patients went below detection over the following 4 years without any therapy. Moreover, 28% of the patients lost HBsAg. Loss of HBsAg after stopping treatment was associated with low HBsAg titres at the time point of treatment withdrawal; however, due to the few currently available experiences stopping rules have not been established so far. Also other studies have found the association between low HBsAg levels at the time point of treatment withdrawal and HBsAg loss or consolidation of the HBV infection thereafter. HBsAg levels of <2 log₁₀ IU/mL at treatment withdrawal were associated with a lower relapse rate after 1–2 years (15% vs. 85%) (Liang 2011).

The predictors of off-treatment response were recently assessed in a meta-analysis including 25 studies with more than 1700 patients in whom NAs were discontinued (Papatheodoridis 2016). The duration of suppression of HBV DNA was shown to be the most important predictor of a durable off-therapy, and the probability of a viral relapse was lower in patients with suppression of HBV DNA for 24 months compared to 12 months (36% vs. 75%). Low HBsAg levels at the time point of treatment cessation were shown to be another positive predictor of treatment response (Wang 2016). However, more prospective studies are certainly needed for validation of these observations and for the refined definition of termination of NA treatment. Severe liver damage due to ALT flares was only observed in patients with cirrhosis so far (Papatheodoridis 2016).

Management of HBV resistance

Resistance development. The mechanism of action of NAs is a competitive inhibition of the HBV polymerase. During treatment with these substances, HBV variants bearing mutations within the HBV polymerase gene may become selected from the HBV quasispecies, a phenomenon which is defined as genotypic resistance.

Phenotypic resistance is defined as decreased susceptibility (in vitro testing) to inhibition by antiviral drugs associated with genotypic resistance (Figure 15).

Cross-resistance of HBV to antiviral treatment has been described within the groups of nucleoside and nucleotide analogues, respectively (Figure 16). If a resistant population becomes the majority in an individual, treatment might fail and a viral breakthrough during treatment may appear which may be associated with severe and sometimes fatal reactivation (Zoulim 2012).

Theoretically, all available NAs may select resistant HBV strains. However, resistance is very rare in treatment-naïve patients who receive substances with strong antiviral activity, i.e., TDF or ETV, but resistance rates against LdT, ADV and especially LAM are significantly higher (Figure 14).

Interestingly, for patients treated with TDF no resistance has ever been reported, not even in patients who were pretreated with ADV, although ADV resistance-associated mutations might slightly decrease response to TDF (van Bömmel 2012, Kitrinos 2014, Berg 2014).

Detection of HBV resistance. Generally, a confirmed re-increase of HBV DNA >1 log from nadir during treatment with nucleoside/nucleotide analogues is considered being a potential viral breakthrough caused by HBV resistance (Figure 10). Genotypic resistance testing is not available to most treating physicians and is generally not recommended (Cornberg 2011, EASL 2017, Terrault 2016). However, genotypic resistance testing might be helpful in individual cases. It has to be considered that most viral breakthroughs in treatment-naïve patients receiving ETV or TDF are the result of adherence issues. Therefore, patient adherence should be assessed before genotypic resistance testing is done.

Avoidance of HBV resistance. HBV resistance occurs most frequently in patients treated with LAM, LdT or ADV, therefore many guidelines discourage physicians to use these NAs in first line treatment. The selection of resistant HBV strains becomes more likely if HBV DNA levels do not become suppressed to undetectable levels within 6 months of treatment with these NAs. Therefore, in patients undergoing treatment with these substances, who show detectable HBV DNA after 6 to 12 months of treatment, the treatment should be adjusted (Cornberg 2011, EASL 2017, Terrault 2016). Also, patients with high viral load (>10⁹ copies/mL) are at increased risk of resistance and should not be treated with these substances. First-line treatment with ETV or TDF is recommended by many guidelines to avoid HBV resistance (Cornberg 2011, EASL 2017, Terrault 2016, WHO 2015).

Treatment of HBV resistance. Generally, resistance against a nucleoside analogue should be treated with a nucleotide analogue and vice versa (Figure 13). In real life, treatment with TDF has been shown to suppress most kinds of HBV variants associated with resistance against either nucleoside or nucleotide analogues. Thus, a switch to a monotherapy with TDF was shown to be very effective in patients with resistance to LAM and also in patients with resistance to ADV in European and in Asian patients (van Bömmel 2010, Huang 2017). In a randomised study, it was shown that patients with resistance to LAM did not show better response to a combination treatment of TDF plus emtricitabine as compared to TDF monotherapy (Fung 2014). In another study, it was observed that monotherapy with TDF was superior to entecavir-adefovir combination treatment in NA resistant patients with suboptimal response to lamivudine-adefovir (Lee 2017). However, some of these patients with genotypic ADV resistance, especially those with HBV DNA levels >10⁷ copies/mL showed delayed or incomplete response to TDF (van Bömmel 2010). ETV was shown to be effective as monotherapy in patients with resistance to ADV. General recommendations for the management of HBV resistance are given in Table 8.

The combination of ADV and LAM in the presence of LAM resistance delays the development of ADV resistance considerably compared to switching to ADV monotherapy (Lampertico 2007). However, combination treatment consisting of one nucleotide and one nucleoside analogue is not necessary for the majority of patients if TDF is available. However combination of TDF with a nucleoside analogue might be useful in patients with multiple pre-treatments who have accumulated different resistance mutations (Petersen 2012, van Bömmel 2012). In a therapeutic setting where TDF is unavailable a combination treatment with ADV should be inititiated if resistance to LAM, LdT or ETV occurs.

Treatment of HBV infections in special populations

Pregnancy. Globally, the vertical transmission from the mother to the newborn is the most frequent cause of HBV infection, and the highest risk is during delivery. A combination of hepatitis B immunoglobulin and vaccination given within 12 hours after birth can reduce the risk of perinatal transmission from >90 to <10% (WHO 2015). Still for a neonate born to a mother with high levels of HBV DNA (>200,000 IU/mL) the risk of perinatal transmission is considerable. Therefore, antiviral treatment is generally recommended in these women (Cornberg 2011, EASL 2017, Terrault 2016, WHO 2015). PEG-IFN α is contraindicated in pregnant women. Antivirals studied in pregnant women are LAM, LdT and TDF. In pregnant women with high levels of HBV DNA, LAM treatment during the last trimester of pregnancy was reported to reduce the risk of intrauterine and perinatal transmission of HBV if given in addition to passive and active vaccination by HBIg and HBV (van Zonneveld 2003). LdT administered for an average of 15 weeks at the end of pregnancy plus active-passive immunisation to neonates reduced vertical transmission rates from 23% to 4% compared to immunisation alone (Han 2011). Because of its high antiviral potency, TDF is often considered the treatment of choice.

The risk of teratogenicity of NAs is assessed by a classification based on data gathered in clinical trials as well as through the FDA Pregnancy Registry. TDF and LdT are listed as pregnancy category B drugs and LAM, whereas ADV and ETV as category C drugs. However, other side effects for the new born cannot completely be ruled out. A recent study reported that bone mineral content of infants of HIV infected mothers exposed to TDF (N=74) was 12% lower than that of infants not exposed to TDF (n=69) (Siberry 2015). Although the significance of this observation is yet unclear, antiviral treatment during pregnancy should be carefully monitored and limited to the second and third trimester. However, the optimal treatment duration has not been studied. As exacerbations of the HBV infection may occur, women with HBV should be monitored closely after delivery (ter Borg 2008).

Immunosuppression. During immunosuppressive treatment, a reactivation of an asymptomatic or inactive HBV infection can occur in 20% to 50% of patients (Lok 2009). Reactivations can occur in HBsAg carriers, but also in HBsAg negative but anti–hepatitis B core antibody (HBc)–positive patients. These reactivations are characterised by an increase in HBV replication followed by an increase in liver inflammation during immune reconstitution resulting in liver damage or even liver failure in some patients (Feld 2010, Roche 2011).

HBV reactivation was especially frequently observed during treatment with corticosteroids and antitumour necrosis factor therapies (i.e., infliximab, etanercept, adalimumab), anti-CD20 therapies (i.e., rituximab-containing chemotherapy) and trans-arterial chemoembolisation for HCC (Vassilopoulos 2007, Moses 2006, Park 2005, Rutgeerts 2009, Mallet 2015).

Prior to initiating immunosuppressive therapies, screening for HBV infection is recommended (Lok 2009, EASL 2017). Pre-emptive treatment with nucleoside/nucleotide analogues should be initiated in all patients with active HBV infection before any immunosuppressive treatment. HBsAg positive inactive HBV carriers have a diminished risk of HBV reactivation and mortality when pre-emptive treatment is conducted. Inactive carriers receiving immunosuppressive treatment with methotrexate or azathioprine in monotherapy represent an exemption as these patients have a low risk of HBV reactivation (Mallet 2016).

HBsAg negative/anti-HBc positive patients should only receive pre-emptive treatment if treatment with rituximab or human stem cell therapy is planned (Lok 1991, Zurawska 2012).

If available, a highly potent antiviral as ETV or TDF should be used for pre-emptive treatment. This recommendation is based on some recent reports revealing lower rates of HBV reactivation in patients treated with ETV as compared to patients treated with LAM. However, reactivations may still occur albeit in a low frequency. This was recently demonstrated in a randomised controlled trial of HBsAg negative/anti-HBc positive patients receiving chemotherapy including an anti-CD20 agent. In these patients, HBV reactivation occurred in 18% of the untreated compared to 2% of those patients receiving prophylaxis with ETV (p<0.05) (Lau 2003).

Novel treatments for HBV infections

The complete eradication of HBV from infected individuals cannot be achieved by any of the currently available treatment strategies, and this is due to persistence of HBV cccDNA. Trials investigating the possibility of improving outcomes in the treatment of HBV infections by combination treatment of PEG-IFN α with NAs in different doses and durations and by using novel NAs are ongoing. Besifovir (LB80380) is an acyclic nucleotide phosphonate with a molecular structure similar to that of ADV and TDF. In a phase IIb, open-label, multicentre study in114 treatment naïve patients randomised to besifovir 90 mg or 150 mg daily or to ETV 0.5 mg daily for 48 weeks, an equally strong antiviral activity as compared to ETV was shown for besifovir. Thus, suppression of HBV DNA to undetectable levels was found in 64, 63 and 58 %, and HBeAg seroconversion in 11, 15 and 9.5 %, respectively (Lai 2014). Of note, 94% of patients receiving besifovir had reduced serum L-carnitine, but the L-carnitine levels returned to normal with supplement.

Numerous novel substances are under investigation which might offer more potent suppression of HBV replication and, ideally, even eradication of the infection. Multiple strategies are being followed, some of which are targeting the innate or the adaptive immune system and some targeting the HBV replication cycle at different steps and to date it is not clear which approach is more promising. (Figure 17). Some of these novel drugs are investigated in pre-clinical or in early clinical studies and preliminary results have already been published for some approaches.

Thus, restoring the production of antiviral cytokines, which is often impaired in HBV infected individuals is followed by stimulation of toll like receptors (TLRs) which are located on plasmacytoid dendritic cells and myeloid cells. In HBV infected woodchucks it has been shown that treatment with the oral TLR7 agonist GS-9620 was followed by a marked decrease in serum HBsAg levels. HBsAg seroconversion occurred in several of these animals (Menne 2015). In contrast, in a trial in 26 patients with chronic HBV infection there was no effect of different doses of GS-9620 on HBsAg levels when given over 24 weeks (Boni 2016). However, stimulating effects of the HBV specific immune response were demonstrated including the acquisition of an activated natural killer cell type.

Interruption of HBV replication by interference with different key mechanisms of the HBV replication cycle is also currently investigated. The use of RNAi to inhibit the replication of HBV has been evaluated in animal models.

The siRNA molecules ARC-520 (phase II: NCT02604212 and NCT02604199; Arrowhead Research Corporation, Pasadena, CA, USA), ARB-1467 (phase II: NCT02631096; Arbutus Biopharma, Burnaby, British Columbia, Canada) and ALN-HBV (phase I/II: NCT02826018; Alnylam, Cambridge, MA, USA) are currently investigated in in clinical trials, The compound ARC-520 was shown to induce a durable and deep suppression of HBV proteins and HBV DNA in a phase II study (Yuen 2015). The nucleic acid polymer (NAP) Rep2139 (Replicor, Montreal, Quebec, Canada), has been shown to inhibit the secretion of HBsAg by an unidentified mechanism. Its combination with pegIFN-α in clinical trials (NTC02233075) has been shown to result in a significant suppression of HBsAg and HBV DNA levels and a high rate of HBsAg seroconversion.

It is likely that these substances will be used in combination with either NAs or PEG-IFN α and there is a need for new bio markers which reflect the level of HBV replication and the efficacy of these new compounds when HBV DNA is suppressed to undetectable levels. For this purpose, new markers such as quantitative HBeAg, HBV core-related antigen (HBVcrAg) and HBV RNA are currently under investigation and these molecules might be useful to tailor individual treatments and to increase response rates in the future.

An important goal for new drugs for treatment of HBV infections will be to move patients closer towards complete eradication of HBV. To date it seems, however, too early to predict the role of those novel compounds in future HBV treatments, but this fast developing field of research deserves continuous attention.

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