Stopping nucleos(t)ide analog treatment in chronic hepatitis B-Who and when?☆

Suzette Grace R.Kho-Herman ,Henry Lik-Yuen Chan

aInstitute of Digestive Disease,The Chinese University of Hong Kong,Hong Kong,China

bMakati Medical Center,Makati,Philippines

1.The dilemma-to stop or not to stop NA therapy

Despite the availability of an effective,prophylactic vaccine,hepatitis B virus(HBV)infection remains a signi ficant global health concern affecting more than 350 million of the world's population with high prevalence in the Asia-Paci fic region.A dynamic disease with variable natural history ranging from inactive to progressive liver disease,chronic hepatitis B(CHB)infection continues to be the major causative factor of liver complications,with an estimated 786,000 deaths annually due to cirrhosis,hepatic decompensation and hepatocellular carcinoma(HCC).1

The advent of nucleos(t)ide analogs(NAs)as one of the main treatments for CHB has led to better therapeutic strategies and dramatic improvement in prognosis.2,3These oral drugs have excellent safety pro files and are well tolerated by most patients including those with advanced and decompensated liver cirrhosis.NAs act by suppressing HBV DNA replication through inhibition of HBV polymerase reverse transcriptase activity.Most patients achieve biochemical remission and undetectable HBV DNA levels with long-term NA treatment.As a result,cirrhotic complications and HCC are reduced.Lamivudine,adefovir and telbivudine are associated with signi ficant drug resistance on prolonged use due to their low barrier of resistance;the subsequent viral relapse negates their clinical bene fits.Hence,entecavir and tenofovir,which are very potent and have minimal risk of drug resistance,are recommended as first-line NA treatment for CHB by all regional guidelines.4-6Tenofovir is most effective for treatment of lamivudine,telbivudine and entecavir resistance,whereas entecavir is the preferred treatment for adefovir resistance.In dif ficult cases with multi-drug resistance,a combination of tenofovir and entecavir can be used.7However,long-term use of tenofovir disoproxil fumarate can result in renal impairment and bone mineral density loss,and rare cases of Fanconi syndrome have been reported.Recently,tenofovir alafenamide,which is associated with much lower systemic exposure to tenofovir,has been found to have superior renal and bone safety pro files as compared to tenofovir disoproxil fumarate in two phase 3 studies.8,9

Most patients need long-term NA treatment,as viral relapse is common after stopping treatment.10Since cirrhotic patients have a much poorerhepatic reserve than others,discontinuing NA therapy is generally not recommended due to the risk of disease reactivation with hepatitis flare,which may result in potentially lifethreatening fulminant hepatitis.On the other end of the spectrum,there are a substantial number of patients continuously receiving NAs even when treatment is no longer needed.11The advantage of stopping NA treatment includes a finite duration of treatment,better patient compliance to therapy,reduction of financial costs and fewer treatment side effects.4

2.NA therapy recommendations by international guidelines

Criteria to stop NA therapy were proposed by the 2015 Asian Paci fic Association for the Study of the Liver(APASL)guidelines,2015 American Association for the Study of Liver Diseases(AASLD)guidelines and 2012 European Association for the Study of Liver(EASL)guidelines.4-6For hepatitis B e antigen(HBeAg)-positive patients who seroconvert to anti-HBe,NA therapy should be maintained for an additional year before stopping treatment,along with undetectable HBV DNA levels and persistently normal alanine aminotransferase(ALT)levels.The most updated APASL guideline recommends consolidation of NA for up to 3 years post-HBeAg seroconversion before stopping NA.5For cirrhotic patients,all three guidelines recommend long-term NA therapy irrespective of HBeAg status or anti-HBe seroconversion on treatment owing to the risk of hepatic decompensation and HCC.For patients with HBeAg-negative CHB,there are no clear data on the optimal duration of oral antiviral therapy.Hepatitis B surface antigen(HBsAg)seroclearance is the best marker to consider stopping therapy.Otherwise,the AASLD guideline recommends long-term treatment with NA until HBsAg seroclearance.4The APASL guideline suggests that NAs may be discontinued in HBeAg-negative patients without liver cirrhosis until(i)HBsAg loss following either anti-HBs seroconversion or at least a 12-month post-HBsAg clearance consolidation period;or(ii)after treatment for at least 2 years with undetectable HBV DNA levels documented on three separate occasions at 6 months apart.5The recently updated EASL guideline recommends consideration of stopping NA therapy in select non-cirrhotic patients who have been treated for over 3 years with undetectable HBV DNA levels(Table 1).6

3.Stopping NA therapy in different patient groups

3.1.HBsAg seroclearance

HBsAg clearance is the closest thing to HBV cure and is accompanied by a favorable prognosis with undetectable serum HBV DNA levels,normalization ofliverbiochemistriesand improved liver histology.In a Korean cohort of 5409 CHB patients treated with lamivudine or entecavir for a median of 6 years,HBsAg seroclearance was associated with a reduced risk of disease progression,HCC and mortality compared to patients who remained HBsAg-positive.12In a Taiwanese series,the clinical outcome of NA-induced HBsAg seroclearance was comparable to that of spontaneous HBsAg seroclearance.13After stopping NA therapy,HBsAg seroclearance tended to be durable in 93.9%patients at year 3;other patients only had low-level viremia with HBV DNA levels＜2000 IU/ml.

However,HBsAg seroclearance is an uncommon event in patients receiving NA therapy.In a 5-year follow-up cohort of HBeAg-positive patients on entecavir,HBsAg seroclearance only occurred in 3 of the 146 patients(2%).14In the pivotal study of tenofovir,the 5-year cumulative probability of HBsAg seroclearance was 10%in HBeAg-positive patients,but only 1 of the 375 HBeAg-negative patients had HBsAg seroclearance.15Patients infected with HBV genotypes A and D seem to have higher probabilities of HBsAg loss than those infected with HBV genotypes B and C.15Conversely,in another multicenter study of 126 immune tolerant patients,tenofovir with or without emtricitabine did not yield a single case of HBsAg seroclearance after 4 years of therapy.16According to mathematical models,HBsAg declines at a very slow rate in patients on NA treatment,and HBsAg seroclearance could only be attained after a period of approximately30-50yearsinHBeAg-positiveandHBeAgnegative CHB patients.16-18This is because NAs do not directly interfere with HBV covalently closed circular(ccc)DNA formation,which serves as the template for HBV replication inside the hepatocyte.As a result,if NA treatment is prematurely discontinued before HBsAg seroclearance,HBV viremia often rebounds.Recent evidence suggests that incomplete blockade of intracellular HBV DNA synthesis,which allows replenishment of the cccDNA pool while on NA treatment,is another reason for viral persistence.19

Loss of HBsAg does not indicate complete eradication of the virus as there is persistence of cccDNA within infected hepatocytes,a reservoir for HBV.Potential HCC development still persists and,therefore,long-term surveillance is still mandatory despite successful HBsAg clearance and stopping of NA therapy.4-6In The Risk Evaluation of Viral Load Elevation and Associated Liver Disease/Cancer-Hepatitis B virus(REVEAL-HBV)cohort,HCC still developed in 91.33 per 100,000 person-year of follow-up among 529 patients who had spontaneously cleared HBsAg without liver cirrhosis.20Similarly,in a Korean cohort of 110 patients who had HBsAg seroclearance after NA therapy,1 patient with underlying liver cirrhosis still developed HCC.12

Table 1Comparison between the different international guidelines regarding stopping NA therapy in CHB patients.

3.2.HBeAg-positive patients

Although HBeAg seroconversion is recommended as the serological marker to consider stopping NA therapy in HBeAg-positive patients,less than 50%of patients will undergo HBeAg seroconversion after long-term NA therapy.14,15The chance of HBeAg seroconversion is lower in patients who have partial responses to treatment,which is de fined as HBV DNA reduction＞1 log IU/ml,but remains detectable at 1 year of NA therapy.5In cohorts from Hong Kong and Korea,the rate of HBeAg seroconversion among partial responders to entecavir was 10%-20%at year 3.21,22For immune tolerant patients,the HBeAg seroconversion rate is even lower;4-year continuous treatment with tenofovir with or without emtricitabine only led to HBeAg seroconversion in 2.8%of patients.16All immune tolerant patients who stopped NA treatment but remained HBeAg-positive had rapid HBV DNA relapse at week 4 post-treatment.

In a systematic review of 733 HBeAg-positive patients who stopped NA therapy,the probability of off-therapy response,de fined as sustained HBeAg seroconversion with HBV DNA levels＜20,000 IU/ml,was 62.5%at month 12,53.4%at month 24 and 51.5%at month 36.10Although a 12-month post-HBeAg seroconversion consolidation is recommended bymost regional guidelines,it seems that extending the consolidation duration of NA treatment can improve the sustainability of HBeAg seroconversion.In a Chinese cohort of 101 HBeAg-positive patients who had combined responses(HBeAg seroconversion and undetectable HBV DNA levels)before stopping lamivudine therapy,the sustained combined response was much higher among patients who had 18 months of consolidation therapy(71.4%)than those who had 12-18 months(39%)or＜12 months(25.6%)of consolidation therapy.23In another collaborative study from Toronto and the Netherlands,among 35 patients who had stopped NA treatment after HBeAg seroconversion,the risk of viral relapse(HBV DNA＞2000 IU/ml)was reduced by approximately 50%beyond 2.9 years of consolidation therapy compared to 1 year.24This is the key evidence for the APASL recommendation to extend post-HBeAg seroconversion consolidation therapy from 1 year to 3 years before stopping NA treatment.5

3.3.HBeAg-negative patients

Discontinuation of NAs in HBeAg-negative patients tends to be less sustained than in HBeAg-positive patients.In a systematic review of 967 HBeAg-negative CHB patients who stopped NA therapy after at least 12 months of treatment,the probability of off-therapy response,de fined as HBV DNA levels＜20,000 IU/ml,was 43.7%at month 12,31.3%at month 24 and 30.1%at month 36.10This finding is in line with another systematic review including 22 studies with 1732 patients,which found that virologic relapse(HBV DNA levels＞2000 IU/ml)and clinical relapse(HBV DNA levels＞2000 IU/ml and elevated ALT levels)developed in ＜70%and ＜50%patients,respectively.25

The APASL guideline has a controversial recommendation that NA therapy can be stopped in HBeAg-negative patients if HBV DNA is undetectable on three separate occasions at 6 months apart.5This recommendation has remained in the APASL guideline since its earlier version in 2008.26The possibility to stop NA therapy in HBeAg-negative patients was supported by a small Greek case series of HBeAg-negative patients who had treatment stopped after 4-5 years of adefovir dipivoxil.27Among the 33 patients who discontinued adefovir therapy,13(39%)had HBsAg seroclearance in the subsequent 5.5-year follow-up.Several studies have been conducted to evaluate the APASL recommendation after its publication.A study from China included 60 HBeAg-negative patients who ful filled the APASL criteria and discontinued lamivudine;49.7%and 56.1%of patients had hepatitis relapse(de fined as HBV DNA＞10,000 copies/ml,approximately equal to＞2000 IU/ml)at 3 and 5 years post-treatment,respectively.28Hepatitis flare,de fined as elevated ALT levels,was seen in 90.3%of patients with hepatitis relapse.Another prospective study from Hong Kong also showed that 91.4%of 184 HBeAg-negative patients had virologic relapse(HBV DNA levels＞2000 IU/ml)within 1 year after stopping entecavir according to the APASL criteria.29As retreatment was allowed after virologic relapse in the Hong Kong study,only 25.8%of patients had elevated ALT and 11.7%had elevated ALT levels＞2 times the upper limit of normal.In Taiwan,a retrospective cohort of 95 HBeAg-negative patients showed 45.3%of patients developed clinical relapse(HBV DNA levels＞2000 IU/ml and ALT levels＞2 times the upper limit of normal)1 year after stopping entecavir according to the APASL criteria.30Another Taiwanese study of 161 patients who stopped entecavir showed 49.2%had clinical relapse and 81.7%had virologic relapse within 2 years.31In a long-term follow-up of 164 HBeAg-negative patients who had compensated cirrhosis and stopped entecavir according to the APASL recommendation,the cumulative incidence of HCC was 9.1%at 5 years,which was not signi ficantly different from patients who continued entecavir treatment after propensity score matching.32Taken together,discontinuation of NAs based on the HBV DNA criteria of the APASL guideline isa “halffullorhalfempty glass”consideration.33

Many factors are found to predict off-treatment virologic response,including lower baseline ALT levels,lower baseline HBV DNA levels,absence of baseline cirrhosis,younger age and female gender,however,most of these factors could not be reproduced in different patient cohorts.10In the Hong Kong study,patients who had detectable HBV DNA at week 12 off-treatment had a higher risk of virologic relapse with HBV DNA levels＞2000 IU/ml at week 48 post-treatment.29

4.New virologic markers to guide stopping NA therapy

4.1.HBsAg quanti fi cation

Quanti fication of HBsAg titers has recently been advocated as a marker for disease monitoring in CHB.Since HBsAg is one of the subviral replication products of cccDNA,levels appear to correlate with HBV transcriptional activity inside hepatocytes,acting as a surrogate marker of infected cells.34HBsAg titers vary during the natural course of CHB infection,and a lower HBsAg level can re flect an inactive carrier state.35In a few long-term follow-up studies in Asian HBeAg-negative CHB patients,HBsAg levels＜100 IU/ml and HBV DNA levels＜2000 IU/ml enabled prediction of an inactive HBV carrier state,which is associated a high probability of spontaneous HBsAg clearance and lower risk of HCC.36-39In other words,a low HBsAg level,probably＜100 IU/ml,may re flect good host immune control of HBV.

As opposed to pegylated interferon therapy,HBsAg decline among patients treated by NAs tends to be very slow.40However,a small proportion of patients have a rapid decline in HBsAg level in the first year of NA therapy,and these patients tend to have a high chance of subsequent HBsAg seroclearance.41,42Most data investigating the use of HBsAg level to guide stopping NA therapy are retrospective studies in HBeAg-negative CHB patients from Asian institutions.In a study from China including HBeAg-negative patients who stopped NA treatment,only 1 of 11(9%)patients who had HBsAg levels＜100 IU/ml at the end of treatment had virologic relapse(HBV DNA level＞1000 copies/ml,approximately equal to＞200 IU/ml)at 6 months post-treatment.43Another study from Taiwan evaluated patients who stopped lamivudine;2 of 30(6.7%)patients who had HBsAg levels＜200 IU/ml had virologic relapse up to 6 years post-treatment.44Unfortunately,HBsAg levels＜100 IU/ml are still not frequently seen in patients on NA treatment.In a prospective cohort of HBeAg-negative patients who stopped entecavir according to the APASL criteria in Hong Kong,only 10 of 184(5.4%)patients had HBsAg levels＜100 IU/ml after a mean of 3.06 years of entecavir treatment.29

As HBsAg level can be very low in HBeAg-negative patients,the absolute level of HBsAg alone sometimes cannot accurately predict hepatitis relapse.35A study in Taiwan showed that the cumulative incidence of virologic relapse was 39.6%and clinical relapse was 15.3%after stopping entecavir among 25 patients who received entecavir for over 3 years with end of treatment HBsAg levels＜100 IU/ml.31In a study in Hong Kong,both the absolute HBsAg level and decline of HBsAg from pre-treatment levels were found to be predictors of off-treatment virologic relapse.45Among HBeAg-negative patients who stopped lamivudine therapy,virologic relapse(HBV DNA levels＞200 IU/ml at 1 year post-treatment)was observed in none of the 5 patients who had HBsAg decline by＞1 log IU/ml with end of treatment HBsAg levels＜100 IU/ml;50%of the 8 patients who had either HBsAg decline by＞1 log IU/ml or HBsAg levels＜100 IU/ml had virologic relapse;and all 41 patients who had HBsAg decline＜1 log IU/ml and HBV DNA levels＞100 IU/ml had virologic relapse.

4.2.Hepatitis B core-related antigen(HBcrAg)

HBcrAg is a recently developed marker that measures a common amino acid sequence shared bydifferent HBV proteins,namely HBeAg,hepatitis B core antigen(HBcAg)and 22-kD precoreprotein.HBcrAg positivity has been found to correlate with intrahepatic HBV DNA and pregenomic RNA levels in patients under NA treatment,suggesting that it can be a serum virologic marker of active transcriptional activity of cccDNA in the liver.46In both treatmentnaïveand NA-treated patients,HBcrAg levels are associated with an increased risk of HCC.46,47Additionally,serum HBcrAg levels tend to correlate with serum HBV DNA levels but not serum HBsAg level in patients on NA treatment.48

An early study in Japan explored the use of HBcrAg to predict hepatitis reactivation after stopping lamivudine in a mixed cohort of 34 HBeAg-positive and HBeAg-negative patients.49After at least 6-17 months of lamivudine treatment,all patients had undetectable HBV DNA levels,and a higher serum HBcrAg level was associated with a higher probability of hepatitis reactivation(ALT elevation to＞80 U/L)within 12 months of stopping lamivudine.In a more recent Korean cohort of 45 HBeAg-positive and 68 HBeAgnegative CHB patients who stopped NA therapy according to the APASL criteria,end of treatment serum HBcrAg level was found to predict virologic relapse(HBV DNA levels＞2000 IU/ml)in HBeAgnegative but not HBeAg-positive patients.50End of treatment HBcrAg levels＞3.7 log IU/ml had an odds ratio of 3.75 for virologic relapse in HBeAg-negative patients compared to those with lower HBcrAg levels.

5.Retreatment of hepatitis relapse

To date,there is no recommendation on when one should restart treatment in patients with hepatitis relapse after stopping NA therapy.In previous cohorts,if retreatment was initiated when clinical relapse developed,i.e.,HBV DNA levels＞2000 IU/ml and ALT levels＞2 times the upper limit of normal,then 25%-48%of patients were re-treated.25In studies when retreatment was initiated for just virologic relapse,i.e.,HBV DNA levels＞2000 IU/ml without consideration of ALT level,up to 88.5%of patients were retreated.In general,re-treating patients with NA therapy is effective to suppress HBV DNA and normalize ALT levels,even when it is prescribed at clinical relapse.21,27,41,47A few reported patients who developed hepatic decompensation on clinical relapse were successfully rescued by NA retreatment.30,51,52

The need of retreatment for clinical relapse is challenged by a multicenter,randomized,controlled study conducted in Europe.53In this study,42 HBeAg-negative patients on tenofovir disoproxil fumaratewere randomized in a 1:1 ratioto either stop treatment or continue treatment.While very good viral suppression and biochemical remission were observed in the continue treatment group until week 144,no HBsAg loss was observed.Conversely,among the 21 patients who stopped tenofovir,all patients eventually had undetectable HBV DNA levels.At week 144,8 patients(38%)had re-initiation of treatment.Patients who stopped tenofovir had a much greater reduction in HBsAg level in the stop treatment group(median＞0.5 log IU/ml)than the continue treatment group(median=0.21 log IU/ml),and 4(19%)patients who stopped tenofovir had HBsAg seroclearance.

6.Conclusion

Stopping NA therapy in CHB remains a clinical challenge despite current guideline recommendations.The persistence of cccDNA in HBV-infected cells remains one of the main obstacles to complete eradication of the virus.Currently available antiviral treatments suppress viral replication and improve patient survival.However,they do not eradicate the virus,and the cccDNA pool leads to viral reactivation after treatment cessation.Although there are guidelines on when and in whom to stop NA therapy,a signi ficant proportion of patients will experience virologic and/or biochemical relapse.Newer biomarkers such as HBsAg and HBcrAg may provide better guidance on the timing of stopping NA therapy,but more work is needed to re fine their use.

Con flict of interest

H.L.-Y.Chan is an advisor and speaker for AbbVie,Bristol Myers Squibb,Gilead and Roche;a speaker for Echosens and Novartis;and has received an unrestricted grant for HBV research from Roche.Suzette Grace R.Kho-Herman has no con flicts of interest to declare.

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