On June 8, 2019, Fresenius Kabi filed a petition for inter partes review challenging the validity of U.S. Patent No. 9,643,997, entitled “Capture purification processes for proteins expressed in a non-mammalian system.” The challenged claims in the patent, owned by Amgen Inc., relate to processes for purifying recombinant proteins expressed in a non-native limited solubility form. The petition for inter partes review argues that the ’997 patent is invalid as anticipated and obvious. This patent is also the subject of an IPR proceeding brought by Kashiv Biosciences. Amgen has asserted the patent with respect to one or both of its biologics NEULASTA® (pegfilgrastim) and Neupogen® (filgrastim) in BPCIA litigations against each of Adello, Sandoz, Mylan, and Pfizer.