Daiichi Sankyo Co. said Tuesday it has signed an accord with U.S. biotechnology firm Amplimmune Inc. to cooperate in developing a therapeutic protein for treatment of autoimmune diseases.

Under the deal with the Maryland-based firm, Daiichi Sankyo will pay Amplimmune "more than $50 million" to reimburse past and planned research costs for the protein codenamed AMP-110 originally developed by the U.S. venture firm and gain an option to acquire its development program, it said.

Autoimmune diseases arise from an inappropriate immune response by a body against its own cells. The immune system mistakes such cells as a pathogen and attacks them.

Daiichi Sankyo said AMP-110 will block an inflammatory differentiation of T cells. The two firms expect to begin a Phase 1 clinical study of the protein in the first half of this year, it said.

The deal qualifies Amplimmune to get additional milestone payments during the collaboration period.

Daiichi Sankyo will decide whether to use the exclusive option and pay an undisclosed option fee to acquire the program to continue developing the AMP-110 when a proof-of-concept study in a Phase 2 clinical test is completed, it added.