Existing problems and new advice on stage criteria of natural history for chronic hepatitis B

Abstract

The natural stages of chronic hepatitis B can be divided into four stages according to changes in virology, biochemistry, and pathology. However, there have been significant differences in the recommended stage criteria in the several major guidelines for chronic hepatitis B, especially regarding the immune tolerance phase. Inconsistent standards of indicators for different stages resulted in some problems, such as incorrect stage, uncertain stages and poor comparation of related studies. We propose suggestions for revisions to the stage criteria for CHB based on recent researches, including three stages: immune tolerance stage, immune clearance stage, and immune control stage. These revision suggestions rationalize some of the existing problems with the stage criteria for CHB and can significantly reduce the number of patients in the “uncertain stage” or “gray zone,” which is particularly valuable in guiding clinical practice. However, further clinical studies with large samples are needed to confirm these suggestions.

Chronic hepatitis B virus (HBV) infection is a global problem that poses a threat to human health. Studies have shown that chronic HBV infection is a long-term process of interaction and struggle between the body’s immunity and the HBV, leading to repeated fluctuations of intrahepatic inflammation and liver fibrosis in some patients, accompanied by changes in viral indicators, such as HBeAg, HBsAg, and HBV DNA [1]. According to these changes in virology, biochemistry, and pathology, the natural stages of chronic HBV infection can be divided into four stages: immune tolerance stage, immune clearance stage, immune control stage, and reactivation stage [2]. However, there have been significant differences in the recommended stage criteria in the guidelines for chronic HBV infection issued by European Association for the Study of the Liver(EASL), American Association for the Study of Liver Disease(AASLD), Asian Pacific Association for The Study of the Liver(APASL), and China Medical Association(CMA), especially regarding the immune tolerance stage [3–6]. These differences have influenced academic communication and prevention and treatment of chronic HBV infection worldwide. Therefore, there is an urgent need to revise and improve the natural stages of chronic HBV infection. Here, we summarize the relevant research on the natural stages of chronic HBV infection and existing problems. Some revision suggestions are proposed to guide the clinical practice of chronic HBV infection better.

Research process and controversy regarding the stages of chronic HBV infection

The natural history of chronic HBV infection are different and mainly depends on the interaction between the virus and the host [7]. Chu et al. [8] first suggested that the natural stages of chronic HBV infection should be divided into three phases: immune tolerance, immune clearance, and inactive phase. The immune tolerance phase, which was recognized as the initial stage of perinatally acquired chronic HBV infection is characterized by the presence of HBeAg, very high serum levels of HBV DNA, and normal ALT. The following immune clearance phase is associated with elevated ALT levels and decreasing serum levels of HBV DNA and HBeAg. After HBeAg seroconversion, most patients enter the “inactive” phase, characterized by persistently normal serum ALT and low HBV DNA. Subsequently, Lok et al. reported that chronic HBV infection might be divided into four stages: immune tolerance stage, immune clearance stage, immune control stage, and reactivation stage according to the levels of alanine transaminase (ALT), HBV DNA, HBeAg, HBsAg and the degree of pathological damage of liver tissue [2]. However, the hepatitis may relapse because of reactivation of HBV with either HBeAg seroreversion or development of HBeAg-negative hepatitis with precore or basal core prompter mutations. The immunopathogenesis of HBeAg-negative hepatitis is similar to that of HBeAg-positive hepatitis. Therefore, this phase is considered a variant of immune clearance phase [9].

HBV-specific T and B lymphocyte dysfunction is crucial for clinical outcomes and prognosis evaluation in chronic HBV infection [10]. However, due to the high heterogeneity of chronic HBV infection and the complexity of the immune response, there have yet to be any clear immune indicators based on T and B lymphocytes for clinical classification (or for the clinical infection stages) [11]. It was previously believed that the immune tolerance phase lacked an HBV-specific immune response, resulting in liver histology damage. In recent years, some scholars have raised doubts based on fundamental and clinical research evidence [12]. Regarding fundamental research, HBV-specific T cells and hepatocyte clones in liver tissue have been found in the immune tolerance stage [13, 14]. In the clinical aspect, many liver biopsy studies have found that some “immune tolerance stage” patients had various degrees of inflammation and fibrosis in the liver tissue [15, 16]. Given this, EASL proposed reclassifying chronic HBV infection into five stages and no longer use the four stages of CHB in 2017. Later, this new classification was adopted by the Chronic Hepatitis B Prevention Guidelines of CMA (2019) and Treatment Algorithm for Managing Chronic Hepatitis B Virus Infection in the United States: 2021 Update [6, 17]. However, consensus has yet to be reached on the definition and criterion of the immune phase of CHB [18, 19].

Effects and problems with the natural stage criteria for chronic hepatitis B

Problems with the natural stages of chronic hepatitis B

Significant differences in the definitions of stage indicators in different guidelines

The chronic HBV stages are mainly based on virology, biochemical, and histological indicators. Virology indicators include HBV DNA, HBsAg, and HBeAg. Inflammatory indicators primarily include ALT or AST and pathological changes in liver tissue. However, the relevant EASL, AASLD, APASL, and CMA guidelines define these stage indicators differently (Tables 1, 2 and 3). Notably, the upper normal limit of ALT used to define immune tolerance varied considerably among different guidelines ranging from 40 U/L (APASL 2016 and EASL 2017 and USA Algorithm 2021), to 35 U/L for men 25 U/L for women (AASLD 2018), and 30 U/L for men and 19 U/L for women (WHO 2015, UK 2017, USA Algorithm 2021). The use of high-normal ALT criteria may misdiagnose immune active phase as immune tolerance phase, especially for patients over 40 [20].

Table 1.

Definition of immune tolerance stage issued guideline of EASL, AASLD, APASL and CMA

	EASL (2017)	AASLD (2018)	APASL (2015)	CMA (2019)
HBsAg	High	-	-	> 1 × 104 IU/ml
HBeAg	positive	positive	positive	positive
HBVDNA	> 107 IU/ml	very high (typically > 1 million IU/mL)	> 1 × 104 IU/ml	> 2 × 107 IU/ml
ALT	Normal	Normal or minimally elevated ALT and/or AST	Normal (1-2ULN)	Normal
Liver biopsy	no or minimal	no fibrosis and minimal inflammation	minimal histological changes	no or minimal

Table 2.

Definition of immune clearance stage issued guideline of EASL, AASLD, APASL and CMA

	EASL (2017)	AASLD (2018)	APASL (2015)	CMA (2019)
HBsAg	High/intermediate	positive	positive	positive
HBeAg	positive	positive or negative	positive	positive
HBVDNA	104 ~107 IU/ml	HBeAg + > 2 × 104 IU/ml	> 2 × 107 IU/ml	> 2 × 104 IU/ml
		HBeAg- > 2 × 103 IU/ml
ALT	Elevated	Elevated ALT and/or AST (Intermittently or persistently)	Elevated	Elevated
Liver biopsy	Moderate/severe	Moderate/severe	Moderate/severe	obvious inflammation and/or fibrosis

Table 3.

Definition of immune control stage issued guideline of EASL, AASLD, APASL and CMA

	EASL (2017)	AASLD (2018)	APASL (2015)	CMA (2019)
HBsAg	Low	Positive	Positive	< 1 × 103 IU/ml
HBeAg	Negative	Negative	Negative	Negative
HBVDNA	< 2,000 IU/ml	< 2,000 IU/ml	< 2,000 IU/ml	< 2,000 IU/ml
ALT	Normal	Normal (Persistently)	Normal	Normal
Liver biopsy	None	absence of significant	None/minimal	None/minimal
		necroinflammation	inflammation/	inflammation/
		variable levels of fibrosis	Various fibrosis	Various fibrosis

HBeAg

HBeAg might inhibit HBV-specific immunity. A decrease in the HBeAg level is the first step to initiate HBV-specific immunity [21]. Yang et al. [22] showed that HBeAg could inhibit the function of T cells by inducing the expansion of monocyte-like myeloid-derived immunosuppressive cells (mMDSCs), thus leading to persistent HBV infection. CHB patients have a high level of HBeAg during the immune tolerance stage. However, being HBeAg-positive is generally regarded as the standard for the immune tolerance stage without considering it quantitatively. This may be related to the lack of reliable quantitative detection methods for HBeAg [14]. Our recent results showed that the cutoff value of the semi-quantitative level of HBeAg (1335S/CO) has high sensitivity and specificity for distinguishing patients with immune tolerance from those with immune clearance [23].

HBV DNA

HBV DNA quantification is the leading indicator that reflects the level of virus replication in HBV-infected patients. It is also one of the critical indicators for determining the stage of CHB. The level of HBV DNA in serum is generally 20 ~ 10⁹ IU/mL detected by fluorescent quantitative PCR. Currently, the standards recommended by various guidelines for patients in the immune tolerance stage vary from > 1 × 10⁶ to > 2 × 10⁷ IU/mL. HBV DNA at > 10⁹ IU/mL has been recommended by the World Gastrointestinal Society (WGS) [24]. For patients in the immune control stage, the EASL Guidelines (2017 edition), the AASLD Guidelines (2018 edition), the CMA Guidelines (2019 edition), and the WGO Guidelines (2015 edition) all recommend HBV DNA at < 2000 IU/mL. It is also should be emphasized that HBV DNA > 2000 IU/ml can be detected in some patients with HBeAg negative chronic infection (inactive carrier). But the EASL 2017 guidelines emphasized that HBV DNA level can be between 2000 to 20,000 IU/ml in some patients with HBeAg negative infection (inactive carriers) [25]. The recent Chinese Guidelines (2022 edition) recommend HBV DNA at < 20 IU/mL in patients with immune control, which is significantly lower than in other guidelines [26]. This standard may be more reasonable.

HBsAg

HBsAg is the most critical indicator for diagnosing HBV infection. In recent years, the complete quantitative determination of HBsAg has also been widely used to guide the clinical treatment of CHB. Although the quantitative detection of HBsAg contributes to the natural stages of CHB, the level of HBsAg was included as the evaluation index in a few studies [27, 28]. HBsAg's current quantitative detection range is 0.05–5.2 × 10⁵ IU/mL by Architect QT assay (Abbott Laboratories, IL, USA). The CMA Guidelines for the Prevention and Treatment of Chronic Hepatitis B(2019 and 2017 version) recommended that the level of HBsAg is more than 1 × 10⁴ IU/mL in patients in the immune tolerance phase. Many scholars believe the HBsAg level should be more than 4.5 ~ 5.0 log IU/mL [29, 30]. However, whether the relevant standards reflect the state of “immune tolerance” still lacks evidence from a large sample of evidence-based medicine. HBsAg originates from cccDNA and integrated HBV DNA, especially in HBeAg-negative chronic HBV-infected patients [31]. More than 50% of HBsAg originates from integrated HBV. The standard of HBsAg recommended by CMA and EASL is < 1000 IU/mL during the immune control stage. HBsAg levels of many patients that are persistently HBV DNA-negative are > 1000 IU/mL.

Further clarification of the relationship between HBV stage and disease status

Most HBeAg-positive CHB patients enter the immune control phase after HBeAg serological conversion. A few patients may experience HBeAg-negative CHB due to genetic mutations and other factors (also known as the immune escape phase). These patients may also re-enter the immune control phase. Patients who enter the immune control phase may also experience reactivation due to factors such as immune deficiency (reactivation phase). There is currently no specific definition for the reactivation period. Di Bisceglie et al. defined HBV reactivation as the sudden increase in HBV replication in previously inactive or concealed HBV-infected patients, usually accompanied by liver injury manifested by the elevation of serum ALT and/or bilirubin [32]. Wang et al. [33] reported that not all HBeAg-negative CHB patients enter the reactivation phase from HBeAg-negative carriers. However, HBeAg serum conversion can occur in HBeAg-positive CHB patients who are still in a sustained immune activity state. The WHO expert committee believes chronic HBV infection reactivation is not equivalent to HBeAg-negative CHB [34].

Severe liver injury does not always accompany the immune clearance stage of CHB patients

The pathogenesis of CHB is mainly related to the dysfunction of the HBV-specific immune response [10]. Research has shown that there are two main mechanisms of CD8⁺ T lymphocytes to eliminate HBV: a cytotoxic mechanism and a noncytotoxic mechanism. Guidotti et al. reported that the antiviral potential of the CTL is primarily mediated by noncytotoxic mechanisms that involve the intrahepatic specific production of IFN- γ by HBV-specific CTL cells that recruit antigen nonspecific inflammatory cells, which implies liver damage is initiated by the CTL [35]. In patients with CHB, the ability of HBV-specific CD8⁺ T lymphocytes to secrete IFN-γ decreases, but the cytotoxic activity to kill cells is partially preserved, leading to repeated episodes of liver inflammation. On the one hand, this leads to liver inflammation and damage, gradually accumulating liver fibrosis lesions, and ultimately, cirrhosis and liver cancer [36]. On the other hand, it may partially or entirely eliminate the HBV, manifested by the decrease or negative HBV DNA and/or HBsAg levels [37]. If the killing mechanism is dominant, it may cause severe liver damage. If noncytotoxic mechanisms prevail, the virus can be cleared, but liver tissue is not damaged, or the damage is minimal. Therefore, there may be different consequences from the long-term struggle between the body and HBV, which are mainly manifested in the following four situations: (1) the virus is cleared, and the liver has no or slight damage; (2) there is virus clearance, but liver damage is severe; (3) the virus has not been cleared, and there is no or mild damage to the liver; or (4) the virus was not cleared, and the liver is severely damaged (Fig. 1). These studies suggested that some patients in the immune clearance stage may not have obvious liver pathological damage. There are limitations in judging whether it is immune clearance based on the degree of liver pathological damage.

Fig. 1.

Different consequences from the long-term struggle between the body and HBV infection

Impact of inconsistent stage criteria for chronic HBV infection

Inconsistent standards of indicators for different stages resulting in incorrect stage

ALT is an essential indicator in determining the stages of chronic HBV infection. However, the level of ALT is not always consistent with the degree of inflammation and fibrosis in the liver [38, 39]. Some studies have shown that approximately 30% of patients clinically diagnosed to be in the immune tolerance stage have noticeable liver tissue lesions according to liver biopsy [40]. Moreover, the dynamic process between different stages requires follow-up observation. Although most scholars believe there should be no apparent liver pathological damage in the immune tolerance phase, few previous studies have included the pathological changes of liver tissue in the evaluation criteria of the immune tolerance phase. Patients with liver fibrosis above stage 1 were excluded from the initial liver biopsy in the immune tolerance phase in Hui et al.’ study [41]. In those who stayed in the immune-tolerant phase in their study, disease progression was minimal during the follow-up process. Patients have also been misdiagnosed as being in the immune control stage. Approximately one-third of patients have significant liver damage in the immune control stage.

Inconsistent standards for indicators of each stage lead to different results

There is a large gap between the definitions of the immune tolerance and immune clearance stages, affecting the comparison of different results. Most studies use only virology and biochemical indicators to judge the immune tolerance stage, leading to differences in results or even opposite conclusions. This explains why most studies have reported a minimum risk of hepatocellular carcinoma(HCC) in immune-tolerant patients. One specific study from Korea showed a conflicting result that untreated immune-tolerant patients had higher HCC risks than HBeAg positive immune-active patients treated with nucleos(t)ide analogues [42–44]. Previous studies have shown that CHB patients in the immune control phase have a low risk of developing HCC [45]. However, some recent studies found that some patients with low viral load still have a higher risk of developing cirrhosis and HCC [46, 47].

Inconsistent standards in the stage criteria have led to some “uncertain stages”

The stage can been determined according to stage indicator levels using the current guidelines, leading to some patients not being classified into one of the four stages. In other words, there is a “gray zone.” Some studies have reported that the percentage of standard uncertainty in the stage defined according to the AASLD 2018 chronic hepatitis B guidance is 28 to 39% [48, 49]. Gan’ et al. reported that there were 50.0%, 28% and 37.4% chronic HBV infection patients in the grey zone according to criteria of EASL, AASLD and CMA. Patients in the “gray zone” still have a risk of disease progression or HCC [50]. Hence, patients in the uncertain stage also require treatment [51]. Currently, some patients in the immune control stage have low viremia(HBV DNA < 2000 IU/ml but > 20 IU/ml). Patients who are low viremia may need to be excluded. Hence, patients with persistent negative HBV DNA are “real” patients in the immune control stage.

Suggested revisions for stage criteria for chronic HBV infection

The recovery of immune function plays a crucial role in the functional or spontaneous cure of chronic hepatitis B [52]. Some patients may have decreased or cleared the virus. Still, there may not be apparent liver tissue damage or liver fibrosis due to the noncytotoxic mechanism of HBV clearance. Therefore, regardless of the ALT level, as long as the levels of HBeAg, HBsAg, or HBV DNA begin to decrease, the patient has entered the immune clearance stage. Moreover, even if HBeAg undergoes serological conversion, as long as HBV DNA is still positive, the infection should be classified as being in the immune clearance stage and diagnosed as CHB. Some patients may be dominated by cytotoxicity and have severe liver damage. Some patients may be dominated by noncytotoxicity and have mild liver damage. The level of HBsAg in the natural stages of CHB is somewhat affected due to the presence of two sources of HBsAg (cccDNA expression and integrated HBV DNA expression) [53]. This is mainly manifested as persistent HBV DNA-negative but still HBsAg higher levels in some patients.

Based on the above studies, the author believes that the stage criteria for the natural course of chronic HBV infection need to be redefined. Patients with high levels of HBV DNA, HBsAg, and HBeAg, normal ALT levels, and no or mild inflammation or fibrosis in the liver tissue have been classified as being in the immune tolerance stage. The immune control stage is characterized by a positive HBsAg, continuously negative HBV DNA, normal ALT, and no inflammation or varying degrees of liver fibrosis in the liver tissue. Between the two stages, all patients with HBsAg who are HBV DNA-positive, HBeAg-positive or-negative and a normal or elevated ALT may be classified as being in the immune clearance stage and require antiviral treatment. According to the stage criteria, patients in the immune tolerance phase and immune control phase can be followed up and observed. Antiviral therapies should be used when these patients enter the immune clearance phase. This suggestion contradicts most international guidelines, but differs little from 2022 CMA guidelines. which recommend antiviral therapy for immune clearance patients with detectable HBV DNA, regardless of ALT levels, if the patient is over 30 years old, has a family history of HBV-related cirrhosis or hepatocellular carcinoma, non-invasive or histological examinations showing significant inflammation (G ≥ 2) or fibrosis (F ≥ 2), or extrahepatic HBV manifestations.

In summary, we propose suggestions for revisions to the stage criteria for CHB, including three stages: immune tolerance stage, immune clearance stage, and immune control stage. The reactivation of CHB mainly refers to the reactivation under immunosuppressive conditions, which is a particular stage of chronic HBV infection. Some scholars also believe that it is an adverse reaction to the use of immunosuppressive drugs. The specific standards are shown in Table 4. These revision suggestions rationalize some of the existing problems with the stage criteria for CHB and can significantly reduce the number of patients in the “uncertain stage” or “gray zone,” which is particularly valuable in guiding clinical practice. However, further clinical studies with large samples are needed to confirm these suggestions. In the future, it is still necessary to explore immune indicators to evaluate the natural stages of chronic Hepatitis B to guide antiviral therapy and improve patient prognosis.

Table 4.

New suggestions in the staging of natural history of chronic hepatitis B

Indicator	Immune tolerance	Immune clearanceb		Immune control
		HBeAg positive	HBeAg negative
ALT	normala	Elevated or normal	Elevated or normal	normal
HBsAg(IU/ml)	> 2 × 104	positive	positive	positive
HBeAg(S/CO)	> 1350	positive	negative	negative
HBVDNA(IU/ml)	> 2 × 107	positivec	positive	negative
Liver biopsy	None or minimal	Variable necroinflammation and/or fibrosis	Variable necroinflammation and/or fibrosis	No significant necroinflammation, variable fibrosis

^aUpper limit of normal value of ALT < 40U/L

^bDiagnosis of immune clearance: elevated ALT and positive HBV DNA, regardless of HBV DNA level, or normal ALT and positive HBV DNA with levels below or equal to 2 × 10⁷ IU/mL

^cHBVDNA > 10–20 IU/ml

Author’s contributions

XT concept and write this manuscript.

Funding

No.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Yes.

Competing interests

The authors declare no competing interests.