By Fineline Cube 
US-based Gilead Sciences Inc. (Nasdaq: GILD) announced plans to acquire the HB-400 and HB-500 programs from its compatriot partner Hookipa Pharma Inc. for a total of USD 10 million. This strategic move expands Gilead’s portfolio in the development of therapeutic vaccines for chronic infectious diseases.
HB-400 Program
HB-400 is an arenavirus-based therapeutic vaccine targeting chronic hepatitis B virus (HBV). It comprises two viral vector components, GS-2829 and GS-6779, developed using Hookipa Pharma’s non-replicating arenavirus vector platform. These vectors, derived from lymphocytic choriomeningitis virus (LCMV) and vesicular stomatitis virus (VSV), are engineered to express HBV antigens. Phase I clinical trial data showed that both single and alternating vector administration were safe and well-tolerated, with dose-dependent immune responses and enhanced T-cell responses observed in some participants.
HB-500 Program
HB-500 is an arenavirus-based therapeutic vaccine targeting HIV. It employs two replication-competent vectors based on Pichinde virus (PICV) and lymphocytic choriomeningitis virus (LCMV). These vectors deliver HIV antigens from highly conserved regions of HIV-1 proteins. In January 2025, Hookipa announced the completion of enrollment for its Phase Ib clinical trial evaluating HB-500 in HIV, involving 30 participants. The trial is expected to reach its primary endpoint in the second half of 2025. Under a recently signed agreement, Hookipa will gradually wind down the Phase I study of HB-500.
Collaboration Background
Gilead’s partnership with Hookipa dates back to 2018, when Gilead first licensed Hookipa’s arenavirus immunotherapy platform for HBV and HIV. Although Gilead decided not to advance the resulting HIV candidate to clinical development in 2021, the collaboration was renegotiated in 2022. At that time, Gilead provided a USD 15 million upfront payment and a USD 5 million equity investment. The original agreement included potential payments of USD 10 million for program completion, up to USD 162.5 million in development milestones, and up to USD 65 million in commercial milestones.-Fineline Info & Tech