Hibsago (Bepirovirsen): A Potentially Transformative Antisense Oligonucleotide for Chronic Hepatitis B
Hibsago (bepirovirsen) represents a significant breakthrough in hepatitis B treatment as the first therapy to achieve functional cure—defined as sustained HBsAg loss—in approximately 20% of patients after a finite 24-week treatment course, a goal that current standard therapies (nucleos(t)ide analogues) achieve in less than 0.33% annually. 1
What is Bepirovirsen and How Does It Work?
Bepirovirsen is a 20-mer antisense oligonucleotide that targets all hepatitis B virus (HBV) messenger RNAs, leading to degradation of viral transcripts and reduction in viral proteins 2, 3. Unlike current standard therapies with nucleos(t)ide analogues (entecavir, tenofovir) that only suppress viral replication without eliminating the virus, bepirovirsen has a multimodal mechanism of action 4:
- Direct antiviral effect: Reduces HBV DNA and viral protein production by degrading HBV mRNAs
- Immune activation: Induces innate immune responses through TLR8 signaling in Kupffer cells and macrophages, potentially facilitating killing of infected hepatocytes 5
- Cytokine induction: Triggers production of IFN-γ, TNF, and other pro-inflammatory cytokines that recruit and activate immune cells 6
Clinical Efficacy: The B-Well Phase 3 Trials
The most recent and highest quality evidence comes from two replicate phase 3 trials (B-Well 1 and B-Well 2) published in 2026 1:
Study Design:
- 1,834 patients with noncirrhotic chronic HBV infection
- All receiving stable nucleos(t)ide analogue therapy
- HBsAg levels 100-3000 IU/mL
- Randomized 2:1 to bepirovirsen 300 mg subcutaneous weekly for 24 weeks vs. placebo
- Nucleos(t)ide analogues discontinued at week 48
Primary Results at Week 72:
- B-Well 1: 20% (127/650) achieved functional cure with bepirovirsen vs. 0% (0/328) with placebo
- B-Well 2: 19% (106/570) achieved functional cure with bepirovirsen vs. 0% (0/286) with placebo
- Both results were statistically significant
This represents a paradigm shift, as current guidelines acknowledge that HBsAg loss—the optimal endpoint—occurs in only a minority of patients receiving standard antiviral therapy 7, 8.
Safety Profile
Common Adverse Events 1:
- Injection site reactions (most common)
- Grade 3+ adverse events in 16% during treatment (vs. 3% placebo)
- ALT elevations were the most common grade 3 adverse event (6% of patients)
Critical Safety Consideration: The ALT elevations observed with bepirovirsen appear to represent a therapeutic response rather than hepatotoxicity. Post-hoc biomarker analysis demonstrates that these ALT increases correlate with:
- Increased serum liver and apoptosis-specific proteins
- Evidence of infected hepatocyte killing
- HBsAg decreases and transient HBV DNA elevations
- More pronounced in responders than non-responders 4
This is fundamentally different from drug-induced liver injury and reflects the immune-mediated clearance of infected hepatocytes—a necessary step toward functional cure.
Clinical Significance in Context of Current Treatment Landscape
Current Standard of Care Limitations
According to the most recent EASL 2025 guidelines 9 and prior guidelines 7, 10, 8, current treatment with potent nucleos(t)ide analogues (entecavir, tenofovir):
- Achieves viral suppression (undetectable HBV DNA) in >90% after 3 years
- Requires lifelong therapy in most patients
- Achieves HBsAg loss in <0.33% annually 8
- Cannot eradicate cccDNA (the viral reservoir in hepatocyte nuclei)
- Leaves patients at continued risk for hepatocellular carcinoma even with viral suppression
Bepirovirsen's Transformative Potential
Finite Duration Therapy: Unlike nucleos(t)ide analogues requiring indefinite treatment, bepirovirsen offers a 24-week finite course with durable off-treatment response in responders 1.
Functional Cure: The 20% functional cure rate represents a 100-fold improvement over the <0.33% annual rate with current therapies 8, 1.
Addresses Unmet Need: Current guidelines acknowledge that "research is rapidly expanding in the area of curing HBV" and that achieving HBsAg loss remains a critical unmet need 8.
Patient Selection Based on Phase 3 Data
Optimal Candidates (based on B-Well trial inclusion criteria) 1:
- Noncirrhotic chronic HBV infection
- Currently on stable nucleos(t)ide analogue therapy
- HBsAg levels 100-3000 IU/mL (lower baseline HBsAg associated with better response)
- HBeAg-negative preferred (though both HBeAg-positive and negative were included)
Important Caveat: Patients with decompensated cirrhosis were excluded from trials and should continue lifelong nucleos(t)ide analogue therapy per guidelines 7, 9.
Monitoring Strategy During Treatment
Based on the safety profile and mechanism of action 1, 4:
- ALT monitoring every 2-4 weeks during the 24-week treatment period
- ALT elevations ≥2× ULN occurred in approximately 11 patients across trials
- These elevations were transient and self-resolving
- Do not discontinue therapy for ALT elevations alone unless accompanied by signs of hepatic decompensation
- Monitor HBsAg levels to assess virological response
- Continue monitoring for 48 weeks after treatment completion (when nucleos(t)ide analogues are discontinued in responders)
Broader Medical Significance
Public Health Impact
With 254 million people living with chronic HBV globally and 1.1 million deaths annually 11, a therapy achieving functional cure in 20% of treated patients could prevent:
- Progression to cirrhosis
- Hepatocellular carcinoma (HCC accounts for ~350,000 HBV-related deaths yearly) 11
- Need for liver transplantation
- Vertical transmission (by reducing maternal viral load)
Paradigm Shift in Treatment Goals
Current guidelines prioritize viral suppression as the main endpoint, with HBsAg loss as an "optimal" but rarely achieved goal 7, 9. Bepirovirsen makes functional cure a realistic treatment target for the first time, potentially changing the treatment paradigm from lifelong viral suppression to finite-duration curative therapy.
Comparison to Other Novel Agents
While multiple investigational agents are in development for HBV 8, 12, bepirovirsen is the first to demonstrate functional cure in phase 3 trials with statistically significant results 1. This positions it as the leading candidate for regulatory approval among novel HBV therapies.
Limitations and Unanswered Questions
Durability: Long-term follow-up beyond 72 weeks is needed to confirm durability of functional cure 3.
Non-responders: 80% of patients did not achieve functional cure—predictors of response and strategies for this population require further study 1.
Cirrhotic Patients: Safety and efficacy in compensated cirrhosis remain to be established, as phase 3 trials excluded cirrhotic patients 1.
Combination Strategies: Whether combining bepirovirsen with other novel agents (e.g., capsid assembly modulators, therapeutic vaccines) could improve response rates is under investigation 3.
Clinical Bottom Line
Bepirovirsen represents the most significant advance in hepatitis B treatment in over a decade, offering the first realistic path to functional cure with finite-duration therapy. For appropriately selected patients (noncirrhotic, on stable nucleos(t)ide analogues, HBsAg 100-3000 IU/mL), it achieves a 20% functional cure rate—a goal essentially unattainable with current standard therapies. The ALT elevations observed during treatment reflect therapeutic immune-mediated clearance of infected hepatocytes rather than toxicity. While 80% of patients do not achieve functional cure, even these patients may benefit from reduced HBsAg levels and enhanced immune responses. Pending regulatory approval, bepirovirsen will likely become a preferred option for patients meeting trial criteria who seek finite-duration therapy with curative intent, fundamentally changing the treatment landscape for chronic hepatitis B.