Correspondence George K. K. Lau, MD, Humanity and Health GI and Liver Clinic, Unit 1309, No. 9 Queen's Road Central, Hong Kong, SAR Tel: +852 28 184 300 Fax: +852 28 184 030 e-mail: email@example.com
HBeAg seroconversion, in association with undetectable levels of hepatitis B virus DNA as determined by polymerase chain reaction, is an important goal in the treatment of patients with HBeAg-positive chronic hepatitis B (CHB). Achievement of sustained HBeAg seroconversion at an early age (<40 years) is associated with a reduced incidence of hepatic complications, increased rates of HBsAg loss and seroconversion and improved survival rates, whether the seroconversion is spontaneous or treatment induced. Patients with HBeAg-positive CHB who achieve sustained HBeAg seroconversion and complete 6–12 months of consolidation therapy are eligible for stopping therapy. In randomized clinical studies involving patients with HBeAg-positive CHB, treatment with pegylated interferon (PegIFN)- α is associated with higher and more durable HBeAg seroconversion rates than are lamivudine and adefovir. More recently, newer generation oral nucleos(t)ide analogs (NAs) have become available. These include entecavir, telbivudine and tenofovir, and they demonstrate superior antiviral potency and efficacy. This review examines the importance of HBeAg seroconversion as an end point for therapy in the treatment of patients with HBeAg-positive CHB, and examines the rates and durability of HBeAg seroconversion with PegIFN and oral NA therapy. The mechanisms for enhanced HBeAg seroconversion rates with new-generation NAs are also discussed.
HBeAg seroconversion, whether spontaneous or treatment induced, is associated with clinical remission and a transition to inactive liver disease in patients with HBeAg-positive chronic hepatitis B (CHB) (1, 2). A reduction in liver fibrosis is noted upon liver biopsy, as is a lower incidence of cirrhosis and hepatocellular carcinoma (HCC) among patients who undergo spontaneous or treatment-induced HBeAg seroconversion (3–11). HBeAg seroconversion is also associated with a higher probability of HBsAg loss and seroconversion, which is considered to be a more permanent clinical remission of liver disease (12). Thus, the achievement and maintenance of HBeAg seroconversion, in association with polymerase chain reaction (PCR)-undetectable hepatitis B virus (HBV) DNA levels, is an important goal in the management of patients with HBeAg-positive CHB (13–15). Based on evidence demonstrating HBeAg seroconversion as a marker of a durable clinical remission of liver disease, major liver society treatment guidelines have adopted HBeAg seroconversion with sustained suppression of HBV DNA as an end point for treatment in patients with HBeAg-positive CHB who do not have cirrhosis or decompensated liver disease (13–15).
Treatment with interferon (IFN)-α has been the gold standard for promoting HBeAg seroconversion, yielding higher rates and greater durability after 1 year than that afforded by the first-generation oral nucleos(t)ide analogs (NAs) lamivudine and adefovir (3, 16–19). The higher rates of HBeAg seroconversion with IFN-based therapy are related to its dual antiviral and immunomodulatory effects. More recently, a new generation of more potent oral antiviral therapies, including entecavir, telbivudine and tenofovir, has now become available that has made the current paradigm of sustained viral suppression with HBeAg seroconversion an attainable goal. In registration studies, these agents demonstrated antiviral potency and efficacy superior to that of the older oral agents (5–7). HBeAg seroconversion rates at 2 years of treatment with entecavir and telbivudine are comparable to that induced by IFN-based therapy at 6 months after treatment (20, 21).
This review examines the importance of HBeAg seroconversion as an indication for cessation of therapy in patients with HBeAg-positive CHB. The rates of HBeAg seroconversion attained with pegylated interferon (PegIFN) and oral NA therapies and the durability of off-treatment response were discussed, as were the mechanisms of action of currently licensed agents and their potential impact on HBeAg seroconversion rates.
HBeAg seroconversion and the natural history of HBeAg-positive chronic hepatitis B
HBeAg seroconversion is a turning point in the natural history of the HBV infection. It signals a transition to the inactive carrier phase and the absence of clinically and biochemically detectable liver disease (1). Natural history and clinical cohort studies have consistently shown that the rate of liver disease complications and the risk of HCC are reduced measurably following spontaneous or treatment-induced HBeAg seroconversion (8–11, 22–25).
In a large, prospective cohort study that examined the relationship between HBsAg and HBeAg seropositivity and the development of HCC, seropositivity for HBeAg was the only factor associated with an increased risk of HCC (11). A total of 11 893 Asian men aged 30–65 years, who had no evidence of HCC at the time of enrolment, were followed for the development of HCC for 92 359 person-years. The incidence of HCC was higher among patients who were positive for both HBsAg and HBeAg (1169 cases per 100 000 person-years) than those among patients who were positive for HBsAg only (324 per 100 000 person-years) and patients who were negative for both HBsAg and HBeAg (39 per 100 000 person-years). Multivariate analysis adjusted for age, gender, the presence or absence of antibodies against the hepatitis C virus, cigarette smoking status and alcohol use found that the relative risk of HCC was higher among men who were seropositive for both HBsAg and HBeAg than those among men who were positive only for HBsAg and men who were negative for both HBsAg and HBeAg (11).
Additionally, delayed HBeAg seroconversion and relapse of hepatitis have been shown to be independent risk factors for cirrhosis (9, 26). In a prospective, longitudinal study of the natural history of HBeAg seroconversion involving 240 HBeAg-positive, asymptomatic, Taiwanese patients, Chu et al. (9) found the median age at HBeAg seroconversion to be 10 years older in patients who developed cirrhosis. Multivariate analysis of the factors associated with the risk of progression to cirrhosis after HBeAg seroconversion found older age at the time of seroconversion [hazard ratio (HR) per decade increase, 3.4; 95% confidence interval (CI), 1.4–8.2; P=0.006] and relapse after HBeAg seroconversion (HR, 20.5; 95% CI, 4.5–92.8; P<0.001) to be associated with an increased risk of progression to cirrhosis (9). Patients who experience delayed HBeAg seroconversion (after 40 years of age) may have a higher degree of hepatic fibrosis at the time of seroconversion, thereby increasing their risk of developing cirrhosis. This suggests that early spontaneous HBeAg seroconversion may reduce this risk. Evidence from natural history studies clearly demonstrates that spontaneous HBeAg seroconversion is associated with clinical remission of disease in up to 85% of HBeAg-positive patients with CHB (8, 9). HBeAg seroconversion is followed by a reduction in fibrosis and HBV DNA levels (27, 10) and marks the transition to a period of sustained inactive disease, particularly in patients who seroconvert before the age of 30 years and who maintain low or PCR-undetectable levels of HBV DNA (8–10). Yet, the annual rate of spontaneous seroconversion remains low, at ∼15% (8, 9, 28). The likelihood of inducing HBeAg seroconversion in HBeAg-positive patients with CHB may be improved with IFN-based or oral NA therapy. Long-term follow-up studies have shown that IFN-induced HBeAg seroconversion is closely linked to viral clearance, a better clinical prognosis and increased survival (22, 23, 29).
In long-term follow-up studies of IFN-α therapy administered to patients with HBeAg-positive CHB, HBeAg seroconversion was associated with a decreased risk of cirrhosis and HCC as well as an increased incidence of HBsAg loss (22–24). HBsAg loss occurs rarely and is believed to be related to full immunological control of the disease (30–32). In a long-term follow-up study involving 233 IFN-treated patients and 233 well-matched untreated controls, IFN-treated and -untreated HBeAg-positive patients who seroconverted showed a lower incidence of cirrhosis (P=0.041) and HCC (P=0.011) and a higher degree of HBsAg loss (P=0.03) than the untreated patients who remained HBeAg positive (22). Multivariate analysis of factors predictive of response showed that HBeAg seroconversion is an independent factor for better long-term outcomes.
Similar results have been reported by van Zonneveld et al. (24) in a study that evaluated the factors that influenced clinical outcome and survival in 165 HBeAg-positive patients with CHB who were treated with IFN-α. In this study, the rate of HBsAg loss was higher among IFN-treated patients who achieved HBeAg seroconversion than among nonresponders (52 vs 9%; P<0.001). These findings clearly demonstrate that early HBeAg seroconversion induced by IFN-based therapy is associated with clinical remission of disease and improved survival.
HBeAg seroconversion rates with currently approved antiviral therapies
The number of therapies available for the treatment of patients with CHB has increased over the last 2 years with the addition of PegIFN α-2a and three new-generation oral NAs: entecavir, telbivudine and tenofovir. PegIFN α-2a and the recently approved oral NAs have superceded conventional therapies, including IFN-α, lamivudine and adefovir, based on their superior potency and efficacy as demonstrated in pivotal randomized clinical studies (33). The following is a summary of the current data on HBeAg seroconversion rates in HBeAg-positive patients who have received PegIFN and oral NAs for the management of CHB.
Pegylated interferon α
Pegylated interferon α has immunomodulatory activity and has been shown to induce HBeAg seroconversion in up to 32% of patients with HBeAg-positive CHB at 6 months after treatment (Table 1) (3, 34–36). In a long-term follow-up analysis involving 150 Asian HBeAg-positive patients treated with a 48-week course of PegIFN α-2a, 39% of the patients achieved HBeAg seroconversion at 6 months after treatment, which was sustained in 83% of the patients at 12 months (36). The overall HBeAg seroconversion rate increased to 41% by 12 months after treatment because of delayed HBeAg seroconversion in a small proportion (15%) of patients who achieved HBeAg seroconversion 6–12 months after stopping therapy (36). Of patients with sustained HBeAg seroconversion at 12 months, 69% had HBV DNA levels <10 000 copies/ml, whereas 38% had HBV DNA levels ≤400 copies/ml.
Table 1. HBeAg seroconversion rates in patients treated with PegIFN α
Emerging evidence suggests that the HBV genotype may be an important and independent predictor of response to IFN-based therapy (37, 38). In studies of IFN-based therapy, HBV genotype A was associated with higher rates of HBeAg loss or even HBsAg clearance when compared with HBV genotype D or C (33, 39–43). Baseline HBV DNA and alanine aminotransferase (ALT) levels are predictive of HBeAg seroconversion with Peg IFN (35). Baseline ALT levels >5 × the upper limit of normal (ULN) and HBV DNA levels ≤9.81 log10 copies/ml are associated with higher rates of HBeAg seroconversion at 6 months after treatment in patients with HBeAg-positive CHB (36). More recently, on-treatment serum HBV DNA and HBeAg levels at weeks 12 and 24, respectively, of PegIFN α-2a therapy have been shown to correlate with the likelihood of HBeAg seroconversion at week 72 in HBeAg-positive patients (19).
HBeAg seroconversion rates of ∼20% have been reported in patients with treatment-naïve HBeAg-positive CHB after 1 year of oral NA therapy (Table 2) (5–7, 44–48). Lower HBeAg seroconversion rates of 12 and 17% have been reported after 1 year of adefovir and lamivudine treatment respectively (45, 49). Additionally, the durability of HBeAg seroconversion achieved following lamivudine treatment is low; the 3-year cumulative HBeAg relapse rate, as determined by the Kaplan–Meier method, was 54% for lamivudine (18). New-generation oral NAs, including entecavir, telbivudine and tenofovir, have demonstrated superior efficacy in suppressing HBV DNA levels compared with lamivudine and adefovir (5–7, 48, 50). Although comparable HBeAg seroconversion rates after 1 year of treatment with the newer oral NAs have been reported in large registration studies, consistently lower rates of HBeAg responses to entecavir have been reported in other studies, particularly among Asian patients (46–48). In a large randomized study (ETV-023) in which 519 nucleoside-naïve Chinese patients with CHB received entecavir (0.5 mg/day) or lamivudine (100 mg/day) for 48 weeks, HBeAg seroconversion rates at week 48 were 15 and 18% respectively (47). These findings are considerably lower than the 21% rate reported in one registration study of entecavir in which 58% of the patients were Asian (5). In a follow-up to their earlier study, Yao et al. (51) reported that 11% of patients receiving entecavir and 19% of patients receiving lamivudine underwent HBeAg seroconversion during the second year of treatment. In the cumulative confirmed analysis for all treated patients through 96 weeks, a higher proportion of entecavir-treated than lamivudine-treated patients achieved undetectable HBV DNA levels by PCR (79 vs 46%; P<0.0001), while similar proportions of entecavir-treated and lamivudine-treated patients achieved ALT normalization (95 vs 92%P=0.06) and HBeAg seroconversion (21 vs 23%, P>0.05) (Fig. 1) (51). Similar results have been reported in two smaller-scale 48-week studies involving primarily (>90%) Asian patients with HBeAg-positive CHB (46, 48). One study comparing entecavir (0.5mg/day) with adefovir (10 mg/day) in 132 patients with HBeAg-positive CHB found HBeAg seroconversion rates at 52 weeks of 15 and 22% respectively (48). Although entecavir resulted in a greater decrease from baseline HBV DNA levels than did adefovir through 2 years of treatment, the HBeAg seroconversion rates were 24 and 25% respectively (Fig. 1) (52).
Table 2. HBeAg seroconversion rates in patients treated with oral NAs
More recently, a long-term follow-up of continuous entecavir treatment has been reported (53, 54). In a cohort of 160 Chinese nucleoside-naïve patients, undetectable serum HBV DNA levels and ALT normalization were achieved by 89 and 86% of the patients, respectively, after 3 years of entecavir treatment (53). An additional 12% of patients achieved HBeAg seroconversion during the third year of treatment for an overall cumulative HBeAg seroconversion rate of 27% (53). An analysis of 98 treatment-naïve HBeAg-positive patients who received 5 years of continuous entecavir with a treatment gap of ≥35 days before recommencement of therapy showed that 94% of patients had HBV DNA of <300 copies/ml, 80% had normalized ALT levels and 17% achieved HBeAg seroconversion (54).
The HBeAg seroconversion rate at 1 and 2 years of treatment has also been reported for tenofovir, the most recently approved oral NA recently for HBV infection. A large randomized trial comparing tenofovir 300 mg/day and adefovir 10 mg/day for 48 weeks, involving 266 patients with HBeAg-positive CHB, of whom 36% were of Asian ethnicity, showed that HBeAg seroconversion occurred in 21 and 18% of patients respectively (Table 1) (7). In a follow-up analysis of the tenofovir-treated cohort, the HBeAg seroconversion rate increased to 26% at 2 years but remained unchanged during the third year of continuous tenofovir treatment (55, 56).
In contrast to other oral NAs, higher HBeAg responses have been reported after 1 year of telbivudine treatment, particularly in Asian patients (6, 44). In the GLOBE trial, the rates of HBeAg seroconversion after 1 year of treatment were similar between patients receiving telbivudine 600 mg/day and patients receiving lamivudine 100mg/day (22.5 and 21.5% respectively) (6). The rate of HBeAg seroconversion increased with continuous treatment in both treatment groups. At 2 years of treatment, 30 and 25% of the patients in the telbivudine and lamivudine arms, respectively, achieved HBeAg seroconversion (P=0.095) (21). In a subanalysis of the GLOBE trial, patients with baseline HBV DNA levels <9 log10 copies/mL and ALT levels ≥2 × ULN, who achieved undetectable HBV DNA levels by PCR at week 24 on treatment, achieved the highest rate of HBeAg seroconversion following 2 years of treatment with telbivudine (Fig. 2) (57).
In a second randomized phase III study that compared the safety and efficacy of telbivudine 600 mg/day with that of lamivudine 100 mg/day in 290 nucleoside-naïve Chinese patients with compensated HBeAg-positive or HBeAg-negative CHB, a higher proportion of telbivudine-treated than lamivudine-treated patients achieved HBeAg seroconversion (25 vs 18%; P=0.14) after 1 year of treatment (44). At 2 years, the rate of HBeAg seroconversion in the telbivudine and lamivudine treatment arms increased to 30 and 20% respectively (P=0.06) (Fig. 1) (58). In a long-term follow-up of HBeAg-positive patients who continued treatment with telbivudine, the overall cumulative HBeAg seroconversion rate after 3 years was 60% (59).
It must be noted that a direct comparison of HBeAg seroconversion rates among the various antiviral agents is limited in the absence of head-to-head randomized studies because results from different studies may be influenced by a variety of factors, including differences in the trial designs, patient populations, baseline patient characteristics and resistance rates. Kau et al. (38) recently summarized information regarding baseline and on-treatment factors that may influence the response to PegIFN α and NA therapy in patients with HBeAg-positive CHB (Table 3). Although baseline HBV DNA genotype and ALT levels may potentially influence response to oral NA therapy, on-treatment HBV DNA levels at week 24 appear to be the most robust predictor of response, including HBeAg seroconversion (21, 38, 57).
Table 3. Baseline predictors of response to antiviral therapy in patients with HBeAg-positive chronic hepatitis B
Mechanism of action of hepatitis B virus antiviral agents and HBeAg seroconversion
The ability to induce sustained rates of HBeAg and HBsAg seroconversion with a finite course of PegIFN therapy can be attributed to this agent's dual immunomodulatory and antiviral mode of action. Response to IFN treatment is associated with activation of the Th1 subset of cytokines [i.e., interleukin-2 (IL-2), IFN-γ, tumour necrosis factor-α (TNF-α)], which correlates with a rapid decline in HBV DNA and HBeAg serum levels in HBeAg-positive patients. In contrast, the induction of HBeAg seroconversion with NAs, which have a direct antiviral effect on HBV, requires prolonged therapy. This suggests that the suppression of HBV DNA levels alone is not always sufficient to induce clearance of the virus by the host immune system. However, preliminary data from recent studies suggest that the new-generation NAs, particularly telbivudine, can induce a Th1 cytokine response and reveal a potential correlation between HBV viraemia and impaired T-cell function (60, 61).
The ability to maintain sustained suppression of HBV replication and induce viral clearance is related to virus-specific T-cell reactivity and induction of the Th1 cytokine response (62, 63). Preliminary data from preclinical studies that investigated the immunomodulatory effects of telbivudine, lamivudine and adefovir in a murine hepatitis virus type 3 (MHV-3)-induced hepatitis model have recently been reported (61). Telbivudine treatment was associated with dose-dependent increases in the production of Th1 cytokines, including TNF-α, IL-12, IL-18 and IFN-γ, in MHV-3-induced macrophages, while the production of IL-10 was significantly inhibited. Treating the MHV-3-induced macrophages with lamivudine or adefovir did not increase the macrophage production of TNF-α. In vivo, serum levels of IFN-γ were elevated significantly in MHV-3-infected C3H mice after treatment with telbivudine, whereas serum levels of IL-4 decreased. These data collectively appear to suggest that telbivudine may possess immunomodulatory activity by preserving Th1 cytokine and inhibiting Th2 cytokine production in addition to its viral-suppressive effect (61).
Results from recent studies have also shown that the programmed death-1 (PD-1) molecule is upregulated in HBV-specific CD8 T cells and is associated with the dysfunction of these cells as well as high virological loads in patients with CHB (64). Decreasing expression of PD-1 may enhance the immune response to HBV infection. Preliminary evidence from a study examining the relationship among immune response, viral load and HBeAg seroconversion in patients with CHB undergoing therapy with telbivudine or lamivudine indicates a strong correlation between levels of HBV viraemia and the hyperexpression of PD-1 on all T cells (60). In this study, telbivudine-induced reductions in viral load and HBeAg seroconversion were independently associated with decreased PD-1 expression in HBV-specific CD8 T cells (60).
Thus, higher HBeAg seroconversion rates with the newer NAs may result from the ability of these agents, compared with conventional agents, to induce drastic suppression of HBV replication as well as cytokine production favouring the Th1 cytokine profile. Further studies are needed to explore the immunomodulatory effects of the newer NAs in addition to their antiviral effects in patients with CHB.
Durability of seroconversion
The durability of HBeAg seroconversion after stopping antiviral treatment is an important factor in the management of patients with CHB (65). HBeAg seroreversion (i.e., the reappearance of HBeAg) is associated with ALT elevation (66), viral rebound (67) and progression of chronic liver disease (68, 69). Lower rates of HBeAg reversion off treatment have been reported among patients treated with PegIFN compared with oral NAs (18, 70, 71). The 3-year cumulative HBeAg reversion rates of 32 and 54% have been reported in patients with genotype C HBV following cessation of a 24-week course of IFN and lamivudine therapy respectively (18). Pretreatment serum HBV DNA levels and a shorter duration of treatment after HBeAg seroconversion are independent risk factors for post-treatment relapse with lamivudine (70). Additionally, on-treatment serum HBV DNA levels at the time of HBeAg seroconversion may indicate a risk for HBeAg reversion (72–74). Quantitative assessment of serum HBV DNA levels by a PCR assay in 49 lamivudine-treated patients who exhibited HBeAg loss/seroconversion and received additional lamivudine therapy for 6 or 12 months demonstrated a lower rate of post-treatment reversion at 2 years in patients with undetectable serum HBV DNA levels (<200 copies/ml) than that in patients with HBV DNA levels ≥103 copies/ml at the time of drug cessation (37 vs 73%) (72). Thus, PCR-undetectable serum HBV DNA level at the time of treatment discontinuation is an important factor in the durability of HBeAg seroconversion.
Limited data are available on the off-treatment durability of HBeAg seroconversion achieved with the newer NAs. In a pooled analysis that assessed the durability of HBeAg seroconversion among HBeAg-positive patients who participated in GLOBE and study 015 and discontinued telbivudine treatment because of efficacy (i.e., they received ≥1 year of antiviral treatment and had HBV DNA <5 log10 copies/ml, with HBeAg loss maintained on treatment for ≥24 weeks), the post-treatment durability of HBeAg seroconversion with telbivudine was >85% by a Kaplan–Meier estimate after 52 weeks of off-treatment follow-up (47, 75). The off-treatment durability of HBeAg seroconversion for entecavir-treated patients with HBeAg-positive CHB who participated in a registrational phase III trial and discontinued treatment because of efficacy was 77% at week 96 (20). Long-term follow-up of HBeAg-positive patients treated with the newer NAs will be needed to assess the durability of HBeAg seroconversion induced by these agents.
Results from numerous clinical trials have shown that the sustained suppression of virological replication, as reflected by serum HBV DNA levels, is an important goal in the treatment of patients with CHB. For patients with HBeAg-positive CHB, HBeAg seroconversion is an important therapeutic end point because of its association with clinical remission of disease and a better long-term prognosis, especially when it occurs early during the course of the disease.
The treatment of patients with CHB continues to evolve, with the introduction of newer, more effective agents and the refinement of strategies for optimizing patient outcomes. PegIFN remains a good choice for younger HBeAg-positive patients with compensated liver disease and low ALT levels because of the high rate and durability of HBeAg and HBsAg seroconversion that can be achieved with a finite course of this drug. Clinical data suggest that high rates of sustainable HBeAg seroconversion and HBV DNA suppression can also be attained with a finite course of telbivudine, particularly in patients who have optimal baseline and on-treatment characteristics. Although preliminary preclinical evidence suggests that telbivudine may have dual antiviral and immunomodulatory effects that contribute to the higher rate of HBeAg seroconversion observed in patients with HBeAg-positive CHB, additional studies are required to confirm the potential immunomodulatory effects of this agent.
The achievement of treatment goals with a finite period of oral NA therapy has important socioeconomic implications for the patient and resource-constrained government-sponsored healthcare systems. Prolonged oral NA therapy is associated with high healthcare costs and an increased risk for developing drug resistance, which reduces the effectiveness of treatment. The ability to attain treatment goals with a finite course of oral NA therapy may allow cessation of treatment after a period of consolidation therapy. However, patients should continue to be monitored and treatment should be reinitiated if hepatitis is reactivated. This strategy may lead to improved quality of life, reduced risk of developing drug resistance and lower healthcare costs for the management of CHB. Data from long-term follow-up studies will provide additional information on the durability of response, HBsAg clearance and long-term clinical benefits of different anti-CHB therapies that will aid in further optimizing the management of CHB.