Under the collaboration, the two companies will develop an HIV-specific therapeutic vaccine using Gritstone's prime-boost vaccine platform of self-amplifying mRNA (SAM) and adenoviral vectors along with antigens developed by Gilead.

Gilead will make a $60 million payment at closing of the agreement, including a $30 million cash payment upfront and a $30 million equity investment at a premium. In addition, Gilead will be responsible for conducting a phase I study for the HIV-specific therapeutic vaccine. It also holds an exclusive license to develop and commercialize the HIV-specific vaccine.

If that option is exercised and if certain clinical, regulatory, and commercial milestones are met, Gritstone will be eligible to receive up to an additional $725 million, as well as tiered royalties on net sales after the therapeutic vaccine is commercialized.

In other Gilead news, the company has increased its ownership share in Arcus Biosciences from approximately 13% to 19.5% by purchasing over 5.6 million additional shares of its common stock at the purchase price of $39 per share. Arcus said it will use the $220 million in proceeds to support development of its four clinical-stage molecules for cancer treatment. The partnership was established in July 2020 for the development of next-generation cancer immunotherapies.