Gilead Sciences declined to exercise or defer its option on ABI-4334, a next-generation capsid assembly modulator for chronic hepatitis B (HBV) in its Phase 1b stage, as disclosed in Assembly Biosciences' 2025 year-end financial results456.
Assembly Biosciences has regained full control of ABI-4334 and initiated a structured process to find a new partner before advancing the program further45.
The decision occurred in March 2026, while Gilead continues collaboration with Assembly on herpes simplex virus (HSV) programs, having exercised options on ABI-5366 and ABI-1179 in 202525.
ABI-4334 showed positive topline results from its Phase 1b trial, demonstrating potent antiviral activity and a favorable safety profile in chronic HBV patients8.
The original 2023 partnership between Gilead and Assembly covered antivirals for HBV, HDV, herpesviruses, and beyond, but Gilead has other HBV efforts like a partnership with Hookipa Pharma14.
Sources:
1. https://www.gilead.com/news/news-details/2023/gilead-and-assembly-biosciences-establish-partnership-to-develop-next-generation-therapeutics-for-serious-viral-diseases
2. https://www.gilead.com/news/news-details/2025/gilead-sciences-exercises-option-to-license-assembly-biosciences-helicase-primase-inhibitor-programs-for-recurrent-genital-herpes
4. https://www.fiercebiotech.com/biotech/gilead-turns-down-chance-take-assemblys-phase-1-stage-hbv-antiviral
5. https://www.stocktitan.net/sec-filings/ASMB/10-k-assembly-biosciences-inc-files-annual-report-f6c41c7ce104.html
6. https://www.globenewswire.com/news-release/2026/03/19/3259423/0/en/Assembly-Biosciences-Reports-Year-End-2025-Financial-Results-and-Recent-Highlights.html
8. https://www.biospace.com/press-releases/assembly-biosciences-reports-positive-topline-results-from-phase-1b-clinical-trial-of-next-generation-investigational-capsid-assembly-modulator-abi-4334-in-chronic-hepatitis-b