By Jason Rantanen

Amgen Inc v. Coherus Biosciences Inc. (Fed. Cir. 2019) 18-1993.Opinion.7-29-2019

Judges Reyna, Hughes, Stoll (author)

The doctrine of equivalents (“DOE”) may be every patent law student’s favorite doctrine to hate. (Edit: to clarify, I mean that it can be complicated not that it’s conceptually a “bad” doctrine.) I sometimes introduce it as “the rule against perpetuities – except more complicated and economically significant.” Under the DOE, a patent can be infringed even when the accused product or process doesn’t literally meet all the limitations of the claim.

Central to the DOE is prosecution history estoppel: a doctrine that prevents “a patentee from using the doctrine of equivalents to recapture subject matter surrendered from the literal scope of a claim during prosecution.” Slip Op. at 8, quoting Trading Techs. Int’l, Inc. v. Open E Cry, LLC, 728 F.3d 1309, 1322 (Fed. Cir. 2013). Because prosecution history estoppel is a question of law, it often functions as threshold question that is resolved before moving to the fact-specific equivalents analysis. Indeed, David Schwartz, Lee Petherbridge and others have argued that PHE is one of the key mechanisms that the Federal Circuit has used to limit the application of the doctrine of equivalents following Warner-Jenkinson.

Often when we think about prosecution-history estoppel, we think about amendment-based estoppel, which can arise when an applicant makes a narrowing amendment to a pending claim. This case involves one of the trickier aspects of PHE: argument-based estoppel.

Background

Amgen sued Coherus for infringement of Patent No. 8,273,707, which relates to methods of purifying proteins using hydrophobic interaction chromatography (“HIC”).” Slip Op. at 2. This process uses a combination of a buffered salt solution containing the protein that is poured into a HIC column. The proteins bind to column matrix and impurities are poured off. The ‘707 patent claims a process that increases the maximum amount of protein in solution that can be loaded into the HIC column by using certain combinations of salts “chosen form one of three pairs: citrate and sulfate, citrate and acetate, or sulfate and acetate.” Slip Op. at 4.

During prosecution (this gives rise to the PHE ruling), the examiner rejected the claims as obvious in view of a prior art patent that “disclosed several salts for improving hydrophobic interactions between a protein and the column matrix.” Slip Op. at 4. Amgen responded by pointing out that “the pending claims recite a particular combination of salts. No combinations of salts [are] taught nor suggested int eh Holtz et al. patent, nor [are] the particular combinations of salts recited in teh pending claims taught nor suggested in this reference.” Id. at 4-5. A supporting inventor declaration pointed out the three pairs above “reduced purification costs on a commercial scale as compared to using only a single salt.” Id. at 5. After another rejection, Amgen further pointed out that “choosing a working salt combinationw as a ‘lengthy development path’ and that ‘merely adding a second salt’ would not result in the invention” and the examiner allowed the claims. Id. at 6.

In 2016, Coherus filed an abbreviated Biological License Application for an Amgen product. Because Coherus’s protein purification method uses a chromatography buffer containing a salt combination, but not one of the specific combinations recited in Amgen’s claim, when Amgen sued for infringement in 2017, Amgen’s infringement theory rested on the doctrine of equivalents rather than literal infringement. The district court subsequently granted Coherus’s motion to dismiss on the pleadings for failure to state a claim.

Federal Circuit: Argument-based prosecution history estoppel applies here

On appeal, the Federal Circuit affirmed the application of argument-based estoppel. “To invoke argument-based estoppel, ‘the prosecution history must evince a clear and unmistakable surrender of subject matter.'” Slip Op. at 9, quoting Conoco, Inc. v. Energy & Envtl. Int’l, L.C., 460 F.3d 1349, 1363 (Fed. Cir. 2006). Here, the court held, argument-based estoppel applies “because Amgen clearly and unmistakably surrendered unclaimed salt combinations during prosecution.” Id. at 9. Amgen repeatedly pointed to the particular combinations of salts as important in distinguishing the prior art references. As a result, “a competitor would reasonably believe that Amgen surrendered unclaimed salt combinations.” Id. at 10 (internal quotation marks omitted).

Amgen’s primary argument, that it asserted other reasons for distinguishing the prior art reference, was not persuasive as “our precedent instructs that estoppel can attach to each argument.” Id. at 11. Nor was the court persuaded by Amgen’s argument that it’s last response before the claims were allowed did not contain the particular-salt-combination argument. But “[t]here is no requirement that argument-based estoppel apply only to arguments made in the most recent submission before allowance.” Id. at 11. For those seeking to avoid this outcome, note the court’s final words on the subject: “We see nothing in Amgen’s final submission that disavows the clear and unmistakable surrender of unclaimed salt combinations made in Amgen’s January 6, 2011 response.” (I’m curious: has any applicant ever disavowed an argument made earlier in prosecution? This seems like a risky strategy for getting claims allowed.)