Gilead Sciences has agreed to acquire a 49.9% equity interest in Tizona Therapeutics, a clinical-stage developer of immunotherapies for cancers, for $300m.

Along with the 49.9% stake, the California-based biopharmaceutical firm also received an exclusive option to acquire the remaining stake in Tizona for an additional payment of up to $1.25bn, which includes the option exercise fee and potential future milestone payments.

Gilead Sciences chairman and chief executive officer Daniel O’Day said: “Tizona is pursuing first-in-class cancer immunotherapies that could make an important difference in oncology by helping patients who don’t respond to current checkpoint inhibitors.

“This agreement with Tizona adds to the significant progress we’ve made in the first half of this year in building out a strong and diverse immuno-oncology pipeline. We now have multiple opportunities to develop novel therapies that will improve the treatment of cancer.”

Tizona has developed its investigational antibody TTX-030 in partnership with AbbVie

Under the terms of the transaction agreement, Gilead has the option to acquire the remaining stake in Tizona, after the completion of a Phase 1b study of its investigational antibody TTX-080.

Tizona would spin-off TTX-030, its investigational anti-CD39 antibody, developed in partnership with AbbVie, into a separate entity before closing the transaction.

TTX-080 is a potential medicine that works against HLA-G, a novel and emerging immune checkpoint expressed across various types of cancers. The drug has been granted the US Food and Drug Administration (FDA) Investigational New Drug (IND) approval.

Furthermore, Tizona intends to begin a Phase 1 clinical trial of TTX-080, both as a monotherapy and in combination with other agents in patients with advanced cancers, in the third quarter of 2020.

The transaction is expected to be completed, subject to antitrust clearance under the Hart-Scott-Rodino Antitrust Improvements Act and other customary closing conditions, in the third quarter of 2020.

Tizona chief executive officer Scott Clarke said: “Gilead’s support will enable Tizona to accelerate and broaden our TTX-080 clinical programme while also enabling us to rapidly advance our rich, first-in-class preclinical portfolio and target validation efforts.

“Our mission is dedicated to translating novel scientific insights into first-in-class immunotherapies and Gilead is a partner that shares our passion for science and delivering breakthrough innovation to people with cancer.”

In June this year, Gilead Sciences has agreed to buy a 49.9% stake and hold an exclusive option to acquire the remaining equity in Pionyr Immunotherapeutics for $275m.