Prosecution history estoppel can bar a claim of patent infringement under the doctrine of equivalents where a patentee’s statements lead a competitor to reasonably believe the patentee had surrendered the relevant subject matter, even if the argument was not actually required to secure allowance of the claim. The Federal Circuit reaffirmed that proposition this week in Amgen Inc. v. Coherus Biosciences Inc., No. 18-1993, slip op. at 9 (Fed. Cir. July 29, 2019). The Amgen v. Coherus decision comes after a series of other high-profile cases from the Federal Circuit this year limiting the application of the doctrine of equivalents, including Amgen Inc. v. Sandoz Inc., 923 F.3d 1023, 1029 (Fed. Cir. 2019) (“The doctrine of equivalents applies only in exceptional cases and is not ‘simply the second prong of every infringement charge, regularly available to extend protection beyond the scope of the claims.’”) and Duncan Parking Techs., Inc. v. IPS Group, Inc., 914 F.3d 1349, 1362 (Fed. Cir. 2019) (“[T]he doctrine of equivalents cannot be used to effectively read out a claim limitation . . . Because the public has a right to rely on the language of patent claims.”).
The Patent-in-Suit
The patent at issue—U.S. Patent No. 8,273,707 (“the ’707 Patent”)—is directed to a method of purifying proteins, using hydrophobic interaction chromatography (“HIC”) and buffered salt solutions employing specific two-salt combinations. Amgen, slip op. at 2. It “claims a process that . . . increases the ‘dynamic capacity’ of a HIC column,” to maximize the protein filtered through the column at any given time without increasing the concentration of a single salt in the buffer solution. Id. at 3. Each claim of the ’707 Patent requires a salt combination in the buffer solution chosen from: citrate and sulfate, citrate and acetate, or sulfate and acetate. Id. at 4.
During examination, the examiner rejected the then-pending ’707 Patent claims as obvious in view of U.S. Patent No. 5,231,178 (“Holtz”). Holtz disclosed using several salts to improve the interaction between proteins and the column matrix, and according to the examiner, “it would have been obvious for a person of ordinary skill to routinely optimize Holtz to achieve the claimed invention.” Id. at 4. In response, Amgen Inc. (“Amgen”) made three arguments:
- Holtz does not teach or suggest any combinations of salts;
- Holtz does not teach or suggest the particular combinations of salts recited in the pending claims; and
- Holtz does not teach dynamic capacity, much less increasing dynamic capacity.
Id. at 4–5. Amgen submitted an inventor declaration supporting each of these arguments. The examiner determined that Amgen had not sufficiently overcome his previous rejection. Id. at 5–6. Amgen responded again, but did not reiterate its “particular combinations” argument, and the examiner allowed the claims. Id. at 6.
The District Court Litigation
The Amgen v. Coherus case began in August 2016 after Coherus Biosciences Inc. (“Coherus”) filed its abbreviated Biologic License Application (“aBLA”) to market a biosimilar version of Amgen’s pegfilgrastim product Neulasta, which is a recombinant therapeutic protein that stimulates production of neutrophils, a type of white blood cell. Amgen, slip op. at 6. Amgen and Coherus engaged in the “patent dance,” exchanging the information required under the Biologics Price Competition and Innovation Act. Id. The exchange revealed that while Coherus’s manufacturing process included a chromatography buffer with a combination of...
