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A Phase 2 Trial of Tobevibart plus Elebsiran in Hepatitis D
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November 9, 2025
N Engl J Med
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Abstract
Background
Both tobevibart (a monoclonal antibody) and elebsiran (a small interfering RNA) target hepatitis B virus surface antigen (HBsAg). Their efficacy and safety in the treatment of chronic hepatitis D virus (HDV) infection are unknown.
Methods
In this ongoing, phase 2, open-label trial, we randomly assigned participants to receive tobevibart plus elebsiran every 4 weeks or tobevibart monotherapy every 2 weeks. The primary end point was a combined response, defined by an HDV RNA level below the limit of detection or a decrease in the HDV RNA level of at least 2 log10 IU per milliliter from baseline (virologic response) and normalization of the alanine aminotransferase (ALT) level, at week 24.
Results
At week 24, a combined response was observed in 47% of participants (15 of 32) who received tobevibart plus elebsiran and in 70% of participants (23 of 33) who received tobevibart, with a virologic response in 100% (32 of 32) and 82% (27 of 33), respectively, and normalization of the ALT level in 47% (15 of 32) and 76% (25 of 33). At week 48, a combined response was observed in 56% of participants (18 of 32) with tobevibart plus elebsiran and 61% of participants (20 of 33) with tobevibart; undetectable HDV RNA (also known as target not detected, or TND; no amplification during reverse-transcriptase–polymerase-chain-reaction assay) in 66% (21 of 32) and 48% (16 of 33), respectively; normalization of the ALT level in 56% (18 of 32) and 61% (20 of 33); and an HBsAg level below 10 IU per milliliter in 91% (29 of 32) and 21% (7 of 33). No ALT flares were observed in participants starting tobevibart and elebsiran simultaneously or receiving tobevibart monotherapy. Through week 48, a total of 81% of participants who received tobevibart plus elebsiran and 94% of those who received tobevibart had at least one adverse event, primarily influenza-like illness and chills.
Conclusions
In this phase 2 trial, tobevibart plus elebsiran as well as tobevibart monotherapy decreased HDV RNA and ALT levels through week 48. Treatment with tobevibart plus elebsiran was associated with a high incidence of undetectable HDV RNA and of a decrease in the HBsAg level.
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