Highlights
– Pegylated interferon‑α2a (PegIFN‑α2a) added to siRNA JNJ‑73763989 (JNJ‑3989) produced marked declines in HBsAg in treatment‑naive, HBeAg‑positive chronic hepatitis B (CHB) patients.
– 11/54 (20.4%) participants achieved HBsAg seroclearance at least once; 6 maintained loss to follow‑up week 48 (FUW48), but no participant met the primary endpoint of sustained HBsAg loss 24 weeks after stopping all therapy.
– HBeAg seroclearance occurred in 16/53 (30.2%) at least once; 12 sustained to FUW48. The regimen had an acceptable safety profile with no deaths or serious adverse events.
Background and Unmet Need
Chronic hepatitis B virus (HBV) infection remains a major global health problem with significant risk of cirrhosis and hepatocellular carcinoma. Approved antiviral therapies — nucleos(t)ide analogues (NA) and interferon‑based regimens — suppress viral replication and reduce complications but only infrequently achieve functional cure, defined as sustained hepatitis B surface antigen (HBsAg) loss with or without seroconversion. This is particularly true in the HBeAg‑positive immune‑active phase, where treatments often reduce HBV DNA but have limited impact on HBsAg and HBeAg.
Contemporary curative strategies aim to both reduce viral antigen burden (to relieve immune exhaustion) and to restore antiviral immunity. Small interfering RNA (siRNA) therapies targeting viral transcripts markedly lower HBsAg production, while immunomodulatory agents such as pegylated interferon‑α (PegIFN‑α) can enhance innate and adaptive immune responses. Combining antigen‑reducing agents with immune stimulants is therefore a rational approach to increase rates of functional cure.
Study Design (REEF‑IT, NCT04439539)
REEF‑IT is a phase 2, open‑label study that evaluated the safety, antiviral activity and pharmacokinetics (PK) of PegIFN‑α2a added to JNJ‑73763989 (JNJ‑3989) with or without bersacapavir and with or without background NA therapy in untreated, HBeAg‑positive adult patients with chronic HBV.
Key elements:
- Population: 54 treatment‑naive adults with HBeAg‑positive chronic HBV (mean age 33.6 years; 52% male).
- Induction: JNJ‑3989 200 mg subcutaneously every 4 weeks plus NA ± bersacapavir 250 mg daily for 36–52 weeks.
- Add‑on: PegIFN‑α2a 180 μg weekly was added for 12 weeks after induction.
- Primary endpoint: Proportion of participants with HBsAg seroclearance 24 weeks after stopping all treatment, including NA.
- Secondary assessments: changes in HBsAg and HBeAg levels, seroclearance at other time points, safety, and PK.
Key Results
Disposition and baseline
Of 54 enrolled participants, 49 (91%) completed the study. Demographics indicated a young adult cohort (mean age 33.6 years) with slight male predominance (52%).
Primary outcome
No participant achieved the protocol‑specified primary endpoint of HBsAg seroclearance 24 weeks after complete treatment cessation (i.e., sustained off‑therapy functional cure). One participant met specified criteria for NA discontinuation during the study.
HBsAg kinetics and seroclearance
Despite failing to meet the primary endpoint, the regimen produced deep quantitative declines in HBsAg.
- Mean (SE) change from baseline in HBsAg: -2.85 (0.13) log10 IU/mL at end of induction.
- -3.61 (0.18) log10 IU/mL at end of treatment (induction + PegIFN‑α2a add‑on).
- -2.63 (0.26) log10 IU/mL at follow‑up week 48 (FUW48).
Seroclearance was observed transiently in a subset: 11/54 (20.4%) participants achieved HBsAg loss at least once during the study, and 6 of these maintained HBsAg loss through FUW48.
HBeAg outcomes
HBeAg seroclearance occurred in 16/53 (30.2%) participants at least once; of these, 12 maintained HBeAg loss through FUW48, suggesting that biologically meaningful antigenic responses were achievable in a subset.
Safety and tolerability
The safety profile was consistent with expectations for PegIFN‑α2a and investigational siRNA therapy:
- A similar proportion of participants experienced adverse events (AEs) during induction (83.3%), during PegIFN‑α2a add‑on (85.7%) and follow‑up (64.7%).
- No deaths or serious AEs were reported.
- Two participants discontinued PegIFN‑α2a due to tolerability.
Specific AE categories were not detailed in the summary provided here; however, pegylated interferon classically causes flu‑like symptoms, cytopenias, mood changes and laboratory abnormalities, whereas siRNA agents can be associated with injection‑site reactions and transient transaminase changes. Overall tolerability in REEF‑IT was described as acceptable.
Pharmacokinetics
Pharmacokinetic assessments were performed as part of the study; the primary manuscript reports PK data and interpretation. No unexpected pharmacokinetic safety signals were highlighted in the study summary.
Interpretation and Clinical Implications
The REEF‑IT results illustrate both the promise and the current limitations of combination strategies aimed at achieving functional cure in HBeAg‑positive CHB.
Key interpretive points:
- Biological proof of concept: The combination of potent antigen reduction with JNJ‑3989 and immune stimulation with PegIFN‑α2a produced deep quantitative HBsAg declines and led to transient HBsAg seroclearance in about one in five participants. HBeAg loss in ~30% supports meaningful antigenic and immunologic effects.
- Durability remains a hurdle: No participant met the prespecified durable off‑therapy HBsAg loss endpoint at 24 weeks post‑treatment. This highlights that deep antigen declines are necessary but not always sufficient for durable immune control; either longer or differently timed immunomodulation, additional immune‑restorative interventions, or broader patient selection may be required.
- Safety and feasibility: The regimen was generally tolerated; however, PegIFN‑α2a retains class‑dependent tolerability challenges that may limit broad adoption unless benefit is robust. Strategies that avoid systemic interferon or that use lower‑intensity immune modulators are being explored.
- Population and generalizability: The study enrolled treatment‑naive, HBeAg‑positive adults with a mean age of 33.6 years. Outcomes may differ in older patients, those with prior therapy, or with different viral genotypes and host backgrounds.
Mechanistic Rationale and Biomarker Considerations
siRNA agents such as JNJ‑3989 silence viral transcript production, lowering HBsAg and other viral proteins that contribute to immune exhaustion. Transient removal of antigenic burden can unmask virus‑specific T and B cell responses. PegIFN‑α2a exerts broad antiviral and immune‑stimulatory effects, including induction of interferon‑stimulated genes, enhancement of antigen presentation and activation of NK and T cells. The combined approach is therefore biologically plausible.
To optimize outcomes, future studies need integrated immune monitoring (e.g., HBV‑specific T cell function, B cell/anti‑HBs responses, innate immune markers) and host/viral biomarkers predictive of durability (baseline HBsAg, quantitative HBeAg, HBV RNA, HBcrAg). Identifying responders prospectively would improve therapeutic risk‑benefit balance.
Limitations
Important limitations that temper interpretation include the relatively small sample size, lack of a randomized control arm reported in the summary, heterogeneity in background therapy (± NA, ± bersacapavir), and relatively short duration of PegIFN‑α2a exposure (12 weeks). The primary endpoint was strict (HBsAg loss 24 weeks after stopping all therapy), which sets a high bar for phase 2 signal detection but is appropriate for functional cure assessment.
Next Steps and Research Priorities
Future development should focus on:
- Randomized trials comparing combination regimens with appropriate control arms to quantify incremental benefit and safety.
- Optimizing timing, duration and sequencing of antigen‑reduction and immune‑stimulation components.
- Combining siRNA with other immune‑restorative strategies (therapeutic vaccines, checkpoint modulation, TLR agonists) while carefully monitoring safety.
- Robust biomarker‑driven patient selection and integrated immune phenotyping to identify those most likely to achieve durable responses.
Conclusion
The REEF‑IT phase 2 study provides encouraging evidence that siRNA‑mediated antigen reduction augmented by pegylated interferon can induce deep declines in HBsAg and achieve transient seroclearance in a subset of treatment‑naive, HBeAg‑positive patients. However, durable off‑therapy functional cure at the prespecified 24‑week landmark was not achieved. These results support continued development of combination strategies for HBV cure and highlight the need for randomized trials, biomarker development, and alternative or adjunct immune‑restorative approaches to convert deep on‑treatment responses into durable cures.
Funding and Trial Registration
Trial registration: NCT04439539. Funding and detailed sponsor information are provided in the primary publication (Kennedy et al., Gut, 2025).
References
1. Kennedy PTF, Fung S, Buti M, Yilmaz G, Chuang WL, Asselah T, Kurosaki M, Jezorwski J, Klyashtornyy V, Verbinnen T, Kakuda TN, Lenz O, Guinard‑Azadian C, Biermer M. Peginterferon alpha‑2a add‑on to siRNA JNJ‑73763989 in untreated patients with HBeAg‑positive chronic hepatitis B virus (HBV) infection: the phase 2 REEF‑IT study. Gut. 2025 Nov 4:gutjnl‑2025‑336592. doi: 10.1136/gutjnl‑2025‑336592. PMID: 41193172.
2. European Association for the Study of the Liver. EASL 2017 Clinical Practice Guidelines on the management of hepatitis B virus infection. J Hepatol. 2017 Aug;67(2):370‑398. doi:10.1016/j.jhep.2017.03.021.
3. World Health Organization. Global hepatitis report 2017. Geneva: WHO; 2017.
4. Terrault NA, Lok AS, McMahon BJ, Chang KM, Hwang JP, Jonas MM, Brown RS Jr, Bzowej NH, Carey WD. Update on prevention, diagnosis, and treatment of chronic hepatitis B: AASLD 2018 hepatitis B guidance. Hepatology. 2018;67(4):1560‑1599.
Author note
This article is an evidence‑focused clinical interpretation of the REEF‑IT phase 2 study results (Kennedy et al., Gut 2025) intended for clinicians and researchers. For full protocol details, complete safety tables, and PK data, consult the original publication.