Mirum Pharmaceuticals, Inc. / Bluejay Therapeutics, Inc.

Chronic hepatitis delta virus (HDV) infection

70K US cases/yr · $1.5B Analyst peak sales estimate, HDV global (2024 consensus) · 70-80% 5-year cirrhosis rate, untreated chronic HDV

Disease Overview

Chronic hepatitis delta virus (HDV) infection is the most severe form of viral hepatitis, requiring hepatitis B virus (HBV) co-infection for viral replication because HDV uses the HBV surface antigen (HBsAg) envelope to package its genome. Chronic HDV accelerates progression to cirrhosis, hepatic decompensation, and hepatocellular carcinoma by a factor of 2-to-3 versus HBV mono-infection, with 5-year cirrhosis rates of 70-80% in untreated patients. Global prevalence estimates range from 12 to 20 million HDV-infected individuals, with approximately 70,000 to 110,000 chronically infected patients in the United States, though CDC screening rates remain low and actual prevalence is likely understated. There is no FDA-approved therapy for chronic HDV in the United States. Pegylated interferon alfa has historically been used off-label with modest virologic response rates (25-30%) and significant tolerability limitations. Bulevirtide (Hepcludex, Gilead), an HBV/HDV entry inhibitor, received EMA conditional marketing authorization in 2020 but received an FDA Complete Response Letter in 2022 and remains unapproved in the US. The HDV landscape is defined by an acute regulatory white space and well-defined unmet medical need, with Mirum's acquisition of Bluejay centered on brelovitug (formerly BJT-778), a fully human IgG1 monoclonal antibody neutralizing HBsAg/HDV virions with Phase 2 SOLSTICE data showing high rates of HDV RNA undetectability. Breakthrough Therapy and PRIME designations support accelerated development; pivotal AZURE trial readouts expected 2H 2026 and BLA filing targeted for 2027.

Competitive Landscape

The HDV competitive landscape is thin but increasingly contested. Bulevirtide (Hepcludex, Gilead) is the only approved HDV therapy in Europe (EMA 2020, conditional) and received an FDA Complete Response Letter in 2022 related to manufacturing, leaving a US regulatory window open. Pegylated interferon alfa (Pegasys, Roche) is used off-label. Emerging therapies include lonafarnib (Eiger BioPharmaceuticals, prenylation inhibitor, received FDA CRL in 2024 and Eiger filed for bankruptcy), JNJ-3989 (Johnson & Johnson/Arrowhead, GalNAc-siRNA targeting HBV/HDV), elebsiran (GSK/Arrowhead, siRNA), bepirovirsen (GSK, antisense oligonucleotide for HBV with HDV read-through potential), and Replicor's nucleic acid polymers REP 2139. Brelovitug is differentiated as a neutralizing mAb targeting HBsAg/HDV virions directly, with Phase 2 data showing deep HDV RNA suppression and favorable safety versus interferon-containing regimens. Mirum's acquisition rationale centers on (1) filling a US regulatory white space with an orphan HDV asset, (2) leveraging Mirum's existing rare-liver-disease commercial infrastructure built around Livmarli (maralixibat) and Cholbam (cholic acid), and (3) diversifying beyond pediatric cholestasis into adult rare liver disease.