French drugmaker Sanofi has signed a definitive agreement to buy Synthorx, a US clinical-stage US biotech focused on cancer and autoimmune disorders, for $68 per share. The cash offer is worth about $2.5 billion.

The California company’s lead immuno-oncology product candidate, THOR-707, is in clinical development in multiple solid tumor types as a single agent and in combination with immune checkpoint inhibitors.

The transaction unanimously approved by both companies’ board, is subject to customary closing conditions, including the tender of at least a majority of the outstanding shares of Synthorx common stock and the expiration or termination of the waiting period under the US Hart-Scott-Rodino Antitrust Act.

Sanofi said the acquisition of the La Jolla-based biotech fits perfectly with its strategy to build a portfolio of high-quality assets and to lead with innovation. “Additionally,” said CEO Paul Hudson, the purchase reflects the drugmaker’s goal to build its oncology franchise with potentially practice-changing medicines and novel combinations.

Synthorx’s lead immuno-oncology product candidate, THOR-707, a variant of interleukin-2 (IL-2), is in clinical development in multiple solid tumor types as a single agent and in combination with immune checkpoint inhibitors.

Sanofi see this drug as having potential to become the best-in-class IL-2 therapeutic for this treatment of solid tumors as it demonstrates improved pharmacology and less frequent dosing and therapeutic superiority when compared to other IL-2 compounds.

Adding THOR-707 and Synthorx’s other earlier-stage cytokine programs to the Paris drugmaker’s platform will enhance its position in oncology and in immuno-oncology, Sanofi said.

“By selectively expanding the numbers of effector T-cells and natural killer cells in the body, THOR-707 can be combined with our current oncology medicines and our emerging pipeline of immuno-modulatory agents for treating cancer,” John Reed, global head of research & development at Sanofi commented.

Alone or in combination with other existing company platforms, including the Paris company’s Nanobody technology, Sanofi expects Synthorx’s Genetic Alphabet platform to facilitate development of a wide range of novel biologics, including drug conjugates, protein fusions and multi-specific biologics, with applications beyond oncology and extending to other therapeutic areas.