Sequential therapy with antisense oligonucleotide and immune modulator as HBV cure

Sequential therapy combining antisense oligonucleotides (ASOs) and immune modulators represents a promising strategy to achieve a functional cure for chronic hepatitis B virus (HBV). Below, I will explain each component, the significance of this approach, and how it addresses the limitations of current therapies:

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### **1. What is an Antisense Oligonucleotide (ASO)?**

Antisense oligonucleotides are short, synthetic strands of nucleic acids designed to bind specifically to messenger RNA (mRNA) sequences in cells. By binding to target mRNA, ASOs can block its translation into proteins or promote its degradation, effectively silencing gene expression. In the context of HBV, the ASO **bepirovirsen** specifically targets the HBV mRNA responsible for producing viral proteins, including hepatitis B surface antigen (HBsAg). This leads to a reduction in viral antigen levels, which is a critical step in disrupting the virus's ability to evade the immune system.

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### **2. What is an Immune Modulator?**

Immune modulators are therapies that enhance or regulate the immune system's ability to fight infections or diseases. In HBV treatment, **pegylated interferon-alpha (PegIFN)** is an example of an immune modulator. PegIFN works by:

• Activating immune cells such as cytotoxic T cells and natural killer (NK) cells.
• Promoting antiviral mechanisms that inhibit HBV replication.
• Enhancing the immune system's ability to clear infected cells.

PegIFN is particularly effective when the immune system is given a "head start," such as through prior reduction of viral antigens using ASOs.

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### **3. Definition of HBV Cure**

A functional cure for HBV is defined as:

• Durable loss of hepatitis B surface antigen (HBsAg) from the bloodstream.
• Undetectable HBV DNA levels.
• No need for lifelong antiviral therapy.

This does not necessarily mean complete eradication of the virus but rather achieving sustained remission where the immune system can control the infection without continuous medical intervention.

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### **4. Limitations of Present Therapies for HBV Cure**

Current therapies for HBV, such as nucleos(t)ide analogs (NAs) and PegIFN monotherapy, have significant limitations:

• **Nucleos(t)ide Analogs (NAs):** These suppress HBV replication but do not directly target viral antigens like HBsAg. They rarely lead to HBsAg clearance and require lifelong treatment.
• **PegIFN Monotherapy:** Although PegIFN can achieve HBsAg loss in a subset of patients, its efficacy is limited, especially in patients with high levels of HBsAg. Relapse rates after treatment discontinuation are high.
• **Immune Exhaustion:** Chronic HBV infection is characterized by immune tolerance or exhaustion due to persistent high levels of HBsAg. This makes it difficult for the immune system to mount an effective response.

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### **5. How Sequential Therapy Helps**

The sequential therapy combining **bepirovirsen** and **PegIFN** addresses these limitations by leveraging the complementary mechanisms of the two agents:

#### **Step 1: Reduction of Viral Antigens with Bepirovirsen**

• Bepirovirsen lowers HBsAg and other viral antigens in the bloodstream by targeting HBV mRNA.
• This reduction in antigen levels alleviates immune tolerance and rejuvenates exhausted immune cells, creating an environment where the immune system can respond more effectively.

#### **Step 2: Immune Boost with PegIFN**

• After the antigen load is reduced, PegIFN is introduced to stimulate the immune system and promote clearance of infected cells and residual virus.
• PegIFN works more effectively in patients with low HBsAg levels, as shown in real-world data and clinical studies.

#### **Clinical Results from Sequential Therapy**

• In the B-Together trial, among patients who achieved low or undetectable HBsAg and HBV DNA levels after bepirovirsen treatment, **59% maintained viral suppression** after 24 weeks of subsequent PegIFN therapy.
• This sustained response rate is higher than what is typically achieved with PegIFN monotherapy, highlighting the synergistic effect of sequential treatment.

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### **6. Mechanistic Complementarity**

The success of sequential therapy lies in the complementary mechanisms of action:

• **Bepirovirsen:** Targets viral replication and antigen production, reducing immune suppression caused by persistent HBsAg.
• **PegIFN:** Activates immune pathways to clear the virus and infected cells, promoting long-term control of HBV.

Together, these agents create a therapeutic strategy that addresses both viral suppression and immune restoration, which are critical for achieving a functional cure.

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### **7. Implications for Cure Research**

Sequential therapy supports the paradigm that lowering the antigen load is a prerequisite for successful immune-mediated HBV clearance. This approach mirrors the "inactive carrier state," where antigen levels are minimal, allowing the immune system to maintain control over the infection. It also opens new avenues for treating other chronic viral infections characterized by immune exhaustion.

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### **8. Limitations and Future Directions**

While promising, this approach has limitations:

• **Study Design Challenges:** The lack of a monotherapy control arm in trials makes it difficult to quantify PegIFN's incremental benefit over ASO therapy alone.
• **Safety Concerns:** Both bepirovirsen and PegIFN have manageable side effects, but their combined use requires careful monitoring.
• **Real-World Validation:** Larger phase 3 trials and real-world studies are needed to confirm the findings and optimize dosing intervals for maximal immune restoration.

Future research should focus on refining the sequential therapy protocol, exploring its applicability to broader patient populations, and adapting the model to other chronic viral infections.

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### **9. Key Conclusion**

Sequential therapy combining **bepirovirsen** (to reduce viral antigens) and **PegIFN** (to boost immune clearance) represents a significant step forward in HBV cure research. By addressing both immune exhaustion and viral persistence, this strategy offers hope for achieving sustained remission and a functional cure for chronic HBV infection.