Functional cure in an occult hepatitis B virus infection patient on sequential therapy: A case report

Abstract

BACKGROUND

Occult hepatitis B virus infection (OBI) is defined by the detection of replication-competent hepatitis B virus (HBV) DNA in the liver and/or blood despite the absence of detectable hepatitis B surface antigen (HBsAg) using conventional serological assays. Although OBI has been well-documented in individuals with resolved HBV infection or those receiving immunosuppressive therapy, reports of its occurrence during sequential antiviral treatment remain scarce. This report describes a case of chronic hepatitis B (CHB) transitioning through OBI during sequential combination therapy before ultimately achieving a functional cure. This case provides new insights into the emergence of OBI as a transitional phase during CHB treatment and emphasizes the importance of monitoring its clinical significance.

CASE SUMMARY

A 33-year-old Chinese male was diagnosed with HBV infection in 2001. The patient first presented in 2012 with abnormal liver function tests and received initial treatment with conventional interferon therapy, which failed to achieve a virological response. Antiviral therapy was subsequently switched to entecavir monotherapy. By August 2019, the patient exhibited an HBsAg level of 29.93 IU/mL with undetectable HBV DNA (< 25 IU/mL). At this point, combination therapy with entecavir and pegylated interferon α (PEG-IFN α) was initiated. Remarkably, while HBsAg declined to 0.42 IU/mL by April 2020, a paradoxical HBV DNA rebound to 173 IU/mL was observed. The regimen was consequently modified to tenofovir alafenamide and PEG-IFN α. By October 2020, the patient achieved HBsAg seroconversion (HBsAg 0.01 IU/mL, hepatitis B surface antibody 52.18 mIU/mL) for the first time, while maintaining low-level viremia (37 IU/mL), consistent with transition to OBI. The patient was then switched to PEG-IFN α monotherapy. In November 2021, he discontinued PEG-IFN α therapy, and one month later, both HBV DNA (< 10 IU/mL) and HBsAg (< 0.05 IU/mL) were negative. This response has been sustained through follow-up.

CONCLUSION

This case study illustrates the efficacy of sequential combination therapy in achieving functional cure in CHB patients, including those with a prolonged infection history. It highlights OBI as a transitional yet underrecognized phase during sequential antiviral therapy. While the patient ultimately achieved functional cure, the transient persistence of HBV DNA despite HBsAg clearance suggests the need for continued monitoring. This case provides new insights into OBI development during treatment and underscores the importance of further research into its long-term implications.

Key Words: Chronic hepatitis B; Occult hepatitis B virus infection; Sequential combined therapy; Functional cure; Case report

Core Tip: This case illustrates the emergence of occult hepatitis B infection (OBI) as a distinct transitional phase during sequential combination therapy for chronic hepatitis B. Unlike previously reported cases where OBI develops in individuals with resolved infection, this case suggests that antiviral therapy itself may induce an OBI-like state before achieving functional cure. As OBI has been associated with potential reactivation risks. Understanding the mechanisms behind treatment-induced OBI will be crucial in refining therapeutic strategies and improving long-term hepatitis B virus management.

INTRODUCTION

Hepatitis B virus (HBV) infection is a significant global health problem. Worldwide, an estimated 254 million people are chronic carriers of hepatitis B surface antigen (HBsAg), of which approximately 20%-40% require antiviral therapy based on current guideline recommendations[1]. Approved anti-HBV therapies include interferon (IFN) and nucleos(t)ide analogues (NAs), both of which improve clinical outcomes in chronic hepatitis B (CHB) infection[2]. However, neither therapy is universally effective when used alone. IFN has a low HBsAg seroconversion (3% to 5%) and potential adverse effects, while NAs primarily suppress HBV DNA replication but often require lifelong treatment[3,4].

The current therapeutic goal is a functional cure, defined as sustained HBsAg loss (< 0.05 IU/mL) and undetectable HBV DNA at the end of treatment. Combination therapy is frequently employed to achieve this goal, as numerous studies have demonstrated its effectiveness in restoring the host's antiviral immune response and eliminating the virus[5].

Occult hepatitis B virus infection (OBI) is characterized by the persistence of replication-competent HBV DNA in the liver and/or blood despite the absence of detectable serum HBsAg (< 0.05 IU/mL). It has been observed in individuals with resolved HBV infection, those receiving immunosuppressive therapy, and patients undergoing antiviral treatment. While OBI is generally considered a low-replication state, its clinical implications remain uncertain, particularly regarding the risk of viral reactivation, transmission, and liver disease progression[6]. The occurrence of OBI during antiviral therapy is not well understood, and its role as a transitional phase in HBV treatment has not been extensively studied.

Here, we present a case of CHB that transitioned through OBI during sequential combination therapy before ultimately achieving functional cure. This case provides new insights into the significance of OBI during treatment and underscores the need for continued monitoring.

CASE PRESENTATION

Chief complaints

A 33-year-old Chinese male presented to the Department of Infectious Diseases of the First Affiliated Hospital of Zhengzhou University in August 2019 with 18 years of CHB and recurrent liver function abnormalities for 3 months.

History of present illness

The patient was diagnosed with HBV infection in 2001, presenting as HBsAg-positive, hepatitis B e antigen (HBeAg)-positive, and hepatitis B c antibodies-positive, with normal liver function tests, and was not treated. In 2012, he developed abnormal liver function and was treated with short-acting IFN, but the response was poor, leading to a switch to entecavir (ETV) antiviral therapy. In May 2019, the patient again presented with abnormal liver function. The alanine aminotransferase (ALT) was 50 IU/L and the aspartate aminotransferase was 51 IU/L. Hepatoprotective medications were given.

History of past illness

The patient did not have a history of diabetes, hypertension, heart disease, tuberculosis, chronic hepatitis C virus infection, or any other diseases.

Personal and family history

The patient did not have a history of smoking or alcohol consumption, and there was no familial history of similar diseases.

Physical examination

The patient’s body temperature was 36.9 °C, pulse was 79 beats per minute, respiratory rate was 18 breaths per minute, and blood pressure was 129/79 mmHg. The patient exhibited no liver palms or spider angiomas, and jaundice was not observed in either the skin or sclera. The abdomen appeared flat, with no visible abdominal wall varicosities and no tenderness or rebound tenderness noted. The liver and the spleen were not palpable. The patient had no ascites and no edema in both lower limbs.

Laboratory examinations

Laboratory examinations are shown in Table 1. Changes in serum HBsAg and HBV DNA are shown in Figure 1. Test results and changes throughout treatment were tallied using GraphPad Prism 9 software.

Figure 1 Changes of serum hepatitis B surface antigen, hepatitis B virus DNA. HBsAg: Hepatitis B surface antigen; HBV: Hepatitis B virus.

Table 1 Evolution of hepatitis B pentameter and liver function during the treatment of patients with chronic hepatitis B.

Weeks		Treatment regimen	HBV-DNA (IU/mL)	HBsAg (0-0.05 IU/mL)	HBsAb (0-10 mIU/mL)	HBeAg (0-0.18 PEIU/mL)	HBeAb (1-999 S/CO)	HBcAb (0-1 S/CO)	ALT (0-40 U/L)	AST (0-40 U/L)	GGT (0-58 U/L)	CAP (< 238 dB/m)	LSM (2.5-7kPa)	AST/ALT
0		ETV	< 251	29.93	0.029	0.029	1.093	0.029	29	37	35	269	6.3	1.28
4		ETV + PEG	—	445.65	0.68	0.11	1.14	8.94	71	75	53	-	-	1.06
8		ETV + PEG	—	337.45	0.24	0.09	1.13	8.75	216	217	95	-	-	1.00
12		ETV + PEG	8.0E + 011	49.48	0.31	0.11	1.16	8.92	126	129	105	-	-	1.02
16		ETV + PEG	1.40E + 021	5.47	0.28	0.1	1.15	8.03	109	116	113	230	7.1	1.06
33		ETV + PEG	1.73E + 021	0.42	1.96	0.11	1.1	6.99	122	119	120	278	7.9	0.98
48		ETV + PEG	1.77E + 022	0.06	6	0.11	1.13	9.37	61	73	86	294	11.7	1.19
OBI phase	61	ETV + PEG	3.70E + 012	0.01	52.18	0.14	1.2	8.55	91	101	119	-	-	1.11
	72	ETV + PEG	9.20E + 012	0.01	142.41	0.14	1.3	9.32	98	119	117	253	9.8	1.21
	82	PEG	1.90E + 012	0	134.59	0.14	1.55	8.44	122	157	112	-	-	1.29
	91	PEG	1.10E + 012	0.01	82.28	0.13	1.3	7.12	73	90	119	-	-	1.23
	101	PEG	< 102	0.02	49.55	0.15	1.32	7.51	65	80	94	-	-	1.23
	115	PEG	4.10E + 012	0.02	58.37	0.18	1.54	7.53	30	72	120	-	-	2.40
120		D/C PEG for 1 months	< 102	0	89.18	0.22	1.43	7.64	-	-	-	-	-	-
129		D/C PEG for 3 months	< 102	0	91.6	0.16	1.36	6.37	26	29	34	-	-	1.12
140		D/C PEG for 6 months	< 102	0	112.26	0.14	1.32	8.73	23	25	33	-	-	1.09
154		D/C PEG for 9 months	-	0	123.62	0.16	1.34	7.05	18	26	28	-	-	1.44
174		D/C PEG for 13 months	< 102	0	44.04	0.15	1.42	6.49	20	26	26	176	7	1.30
188		D/C PEG for 17 months	< 102	0.03	30.84	0.18	1.46	6.61	20	30	30	-	-	1.60
212		D/C PEG for 23 months	< 251	0	8.11	0.17	1.02	6.31	20	29	30	239	5.9	1.45

¹Standard hepatitis B virus DNA assay: The lower limit of detection is 25 IU/mL.

²High-sensitivity hepatitis B virus DNA assay: The lower limit of detection is 10 IU/mL.

Detection method for hepatitis B serology panel - electrochemiluminescence immunoassay. HBV: Hepatitis B virus; HBsAb: Hepatitis B surface antibody; HBeAg: Hepatitis B e antigen; HBeAb: Hepatitis B e antibody; HBcAb: Hepatitis B core antibody; ALT: Alanine aminotransferase; AST: Aspartate aminotransferase; GGT: Glutamyltransferase; CAP: Controlled attenuation parameter; LSM: Liver stiffness measurements; ETV: Entecavir; PEG: Pegylated; D/C: Discontinued; OBI: Occult hepatitis B virus infection; S/CO: Signal-to-cutoff ratio.

Imaging examinations

Abdominal ultrasonography in the patient revealed a liver of normal size with a regular, homogeneous parenchymal structure and no focal lesions.

FINAL DIAGNOSIS

Based on the clinical presentation, laboratory findings, and exclusion of other causes, a diagnosis of CHB was established.

TREATMENT

In August 2019, laboratory tests showed HBsAg level of 29.93 IU/mL, HBeAg-negative (< 0.18 PEIU/mL), HBV DNA below the lower limit of detection (< 25 IU/mL), controlled attenuation parameter 269 dB/m and liver stiffness measurement 6.3 kPa. At this time, HBV DNA was negative (< 25 IU/mL), and HBsAg was at a low level, because ETV can potently inhibit HBV DNA replication but has a low clearance of HBsAg. Pegylated interferon α (PEG-IFN α) can promote HBsAg serological conversion by activating the immune system and breaking immune tolerance. Therefore, the combination of ETV and PEG-IFN α was given.

In November 2019, the patient presented with a biochemical episode of hepatitis B (ALT 126 U/L, aspartate aminotransferase 129 U/L). At this time, HBV DNA 80 IU/mL, HBsAg 49.48 IU/mL. The patient had no history of other medications (anti-tuberculosis medications, herbal medications, etc.) or recent alcohol consumption. His relevant examinations: Total bilirubin 11.4 μmol/L, albumin 47.1 g/L, for the time being, liver injury caused by HBV DNA virological breakthrough, fatty liver, and alcoholic liver disease were not considered. PEG-IFN α can cause hepatocellular injury and ALT elevation, most often occurring at 4-12 weeks of treatment, with ALT elevations typically ranging from 2-10 times the upper limit of normal. As the patient was in good general condition (no jaundice, normal coagulation), the combination therapy was continued.

Several test data points between weeks 16 and 33 of the combined treatment were missing due to unforeseen circumstances. In December 2019, the patient returned to his hometown of Wuhan, which was subsequently affected by the outbreak of coronavirus disease 2019 and placed under lockdown. As a result, the patient was unable to undergo the required tests during this period. However, the patient ensured that the treatment continued as scheduled by purchasing necessary medications in advance or having them mailed to maintain the course of treatment.

By April 2020, HBV DNA increased to 173 IU/mL while HBsAg decreased to 0.42 IU/mL. At this time, controlled attenuation parameter 278 dB/m and liver stiffness measurement 7.9 kPa. Given tenofovir alafenamide (TAF)’s superior efficacy in HBV DNA suppression and fibrosis progression delay, the treatment was adjusted to a combination of TAF and PEG-IFN α.

By October 2020, the patient’s HBsAg turned negative (< 0.05 IU/mL) for the first time, with hepatitis B surface antibody at 52.18 IU/mL, and HBV DNA remained detectable (37 IU/mL). The patient had transitioned to OBI, characterized by undetectable HBsAg despite persistent low-level HBV DNA. Given this development, therapy was continued with PEG-IFN α monotherapy to promote further viral suppression.

By November 2021, HBV DNA levels were still detectable at 41 IU/mL, while HBsAg remained negative (< 0.05 IU/mL). The patient subsequently discontinued PEG-IFN α therapy.

OUTCOME AND FOLLOW-UP

One month after the end of treatment, follow-up tests confirmed that both HBV DNA (< 10 IU/mL) and HBsAg (< 0.05 IU/mL) were negative, with hepatitis B surface antibody of 89.18 IU/mL and normalized liver function. Subsequent follow-up assessments showed sustained HBsAg loss (< 0.05 IU/mL), undetectable HBV DNA, and normal liver function, indicating achievement of functional cure.

DISCUSSION

Recent advancements in CHB treatment have led to a clearer understanding and wider use of NAs and PEG-IFN α in achieving functional cure[7]. A meta-analysis showed that sequential combination therapy performed better in HBsAg regression compared to initial combination therapy[8]. “The expert consensus on clinical cure (functional cure) of chronic hepatitis B” from China outlines a roadmap for achieving functional cure of CHB[9]. According to this roadmap, patients with low baseline HBsAg levels, HBeAg negativity, and sequential PEG-IFN α treatment are more likely to achieve functional cure. Additionally, patients with undetectable HBV DNA and HBsAg levels below 3000 IU/mL treated with direct-acting antivirals and sequential combination immunomodulators are strongly recommended, especially in HBeAg-negative patients with HBsAg levels below 1500 IU/mL. Furthermore, the ongoing SWAP study revealed a significantly lower rate of virological relapse in patients receiving sequential combination therapy with PEG-IFN α compared to switch or control groups[10]. In HBeAg-negative patients, discontinuing Nas might lead to a higher HBsAg clearance rate than continued use[11]. In this case, the patient had been receiving ETV treatment for 7 years, with the HBsAg level reaching 29.93 IU/mL at the end of the treatment. Despite this extended treatment period, viral suppression was not fully achieved. However, after initiating a combined treatment regimen, the patient ultimately achieved a functional cure, with a significant improvement in clinical outcomes.

OBI is commonly observed in individuals with resolved HBV infection or those undergoing immunosuppressive therapy[12,13], but its emergence during active antiviral treatment has not been extensively studied. In this case, the patient transitioned into an OBI state following sequential therapy with ETV, TAF, and PEG-IFN α, characterized by HBsAg clearance but persistent low-level HBV DNA before achieving functional cure.

The emergence of OBI during sequential combination therapy may be attributed to several mechanisms. One possible explanation is the suppression of HBsAg expression. Both PEG-IFN α and NAs effectively inhibit HBV replication and viral protein synthesis[14]. PEG-IFN α enhances immune-mediated clearance of HBsAg-producing hepatocytes[15], while NAs suppress HBV DNA replication[16]. As a result, HBsAg levels may decline below the detection limit while residual HBV DNA persists, leading to an OBI state. In addition to direct antiviral effects, host immune responses may also play a critical role in the development of OBI. Studies suggest that individuals with OBI exhibit stronger HBV-specific T-cell responses compared to those with overt infection[17]. This shift in the immune landscape could contribute to the suppression of viral replication without complete elimination, allowing for the persistence of low-level HBV DNA despite HBsAg clearance. Furthermore, epigenetic and genetic factors may influence OBI development during treatment. HBV covalently closed circular DNA is known to undergo epigenetic silencing rather than complete elimination, potentially reducing HBsAg production while maintaining low-level viral persistence[18]. Additionally, mutations in the HBV S regions may impair HBsAg detectability by altering antigen secretion or antigenicity. These genetic and epigenetic modifications could further contribute to an OBI-like state during antiviral therapy.

Although the patient ultimately achieved functional cure, the transient occurrence of OBI during antiviral therapy raises important clinical considerations. One of the primary concerns is the risk of HBV reactivation, particularly in individuals who become immunosuppressed or discontinue antiviral treatment. Previous studies have shown that OBI can serve as a potential reservoir for HBV reactivation, leading to progressive liver disease or fulminant hepatitis in high-risk populations[19,20]. Therefore, long-term monitoring of HBV DNA levels is crucial, even in patients who achieve HBsAg clearance. Another important consideration is the potential underestimation of OBI in clinical practice. Current monitoring strategies primarily focus on detecting HBsAg and HBV DNA, which may not be sufficient to identify OBI cases. During the OBI phase, the HBV genome exists as closed circular DNA and exhibits low replicative activity. As a result, HBV DNA can be detected intermittently in serum or plasma. Detection of HBV DNA using current routine methods may result in missed OBI. This highlights the need for revised clinical guidelines for more sensitive screening strategies, particularly in patients receiving antiviral therapy, especially those exhibiting signs of functional cure.

Additionally, the occurrence of OBI during sequential combination therapy raises questions about its role in the broader treatment landscape. It remains unclear whether OBI represents a transitional phase toward full viral eradication or a stable condition requiring long-term surveillance. Understanding whether OBI should be actively managed or simply monitored over time is essential for optimizing treatment strategies. Further research is needed to determine whether certain patient populations are more likely to develop OBI and whether its presence affects the long-term durability of functional cure.

CONCLUSION

To conclude, this case illustrates the emergence of OBI as a distinct phase during sequential combination therapy for chronic hepatitis B. Unlike previously reported cases where OBI develops in individuals with resolved infection, this case suggests that antiviral therapy itself may induce an OBI-like state before achieving functional cure. The persistence of low-level HBV DNA despite HBsAg clearance underscores the need for long-term monitoring, as OBI has been associated with potential reactivation risks. Understanding the mechanisms behind treatment-induced OBI will be crucial in refining therapeutic strategies and improving long-term HBV management.

ACKNOWLEDGEMENTS

We thank the patient for their participation and consent.