By: IPP Bureau
Last updated : December 24, 2025 7:26 pm
Under the 2023 collaboration agreement, Assembly Bio will receive $35 million for Gilead’s exercise of the HSV program option
Gilead Sciences has taken a major step in antiviral innovation.
The global biopharma leader has exercised its option to exclusively license Assembly Biosciences’ herpes simplex virus (HSV) helicase-primase inhibitor programs, including long-acting investigational drugs ABI-1179 and ABI-5366 for recurrent genital herpes.
The programs mark the first advancement under the ongoing Gilead-Assembly R&D collaboration, aimed at building a novel antiviral pipeline and addressing critical unmet medical needs.
Genital herpes, caused by HSV, affects over four million people in the US and Europe, causing painful lesions, social stigma, and increasing the risk of HIV acquisition. No new therapies for HSV have been approved in the US or Europe in over 25 years.
“At Gilead, we develop novel antiviral therapeutics that aim to deliver meaningful solutions that improve the lives of people affected by serious viral infections.
"Our research partnership with Assembly Bio has been highly fruitful, and we are excited to continue the clinical development of our herpes simplex virus candidates,“ said Jared Baeten, Senior Vice President, Clinical Development, Virology Therapeutic Area Head, Gilead Sciences. “Collaborations and partnerships are key in the pursuit of life-changing innovations.”
ABI-1179 and ABI-5366 are long-acting inhibitors targeting the viral helicase-primase enzyme, essential for herpes virus replication. Phase 1b interim data showed strong antiviral activity and clinical improvements, including significant reductions in virus-positive lesions. Both compounds also demonstrated pharmacokinetic and safety profiles supportive of once-weekly oral dosing.
“We are pleased Gilead has opted in to advance the helicase-primase program for recurrent genital herpes,” said Jason Okazaki, CEO and President of Assembly Bio.
“This milestone reflects the strength of our collaboration and the potential of our antiviral pipeline. With Gilead’s proven track record in developing and commercializing antiviral medicines, exercising this option is an important step forward as they take control of ABI-5366 and ABI-1179 and advance closer to delivering long-awaited new treatment options to patients suffering from recurrent genital herpes.”
Under the 2023 collaboration agreement, Assembly Bio will receive $35 million for Gilead’s exercise of the HSV program option. Gilead now holds an exclusive license to ABI-5366 and ABI-1179 and will lead clinical development and commercialization.
Assembly Bio remains eligible for up to $330 million in regulatory and commercial milestones, as well as tiered royalties on net sales, and retains the option to share US costs and profits for the program in the future.