 Bristol and Ono, which co-developed the first PD-1 antibody called Opdivo, filed the suit against Merck in September 2014, alleging that its sale of Keytruda, also a PD-1 antibody, infringed their patents in markets including the United States, parts of Europe, Australia and Japan.Merck will make an initial payment of $625 million to Bristol and Japan's Ono.The company will also pay a 6.5-percent royalty rate on Keytruda sales from January 2017 to December 2023, and a 2.5-percent rate for the subsequent three years.