Presenting multiple arguments in prosecution risks prosecution history estoppel on each of them
| November 8, 2019
Amgen Inc. v. Coherus BioSciences Inc.
July 29, 2019
Before Reyna, Hughes, and Stoll. Opinion by Stoll.
Summary
The CAFC affirmed a district court decision holding that Amgen had failed to state a claim and dismissed Amgen’s suit against Coherus for patent infringement under the doctrine of equivalents, in view of Amgen’s clear and unmistakable disclaimer of claim scope during prosecution.
Details
Amgen Inc. and Amgen Manufacturing Ltd. (“Amgen”) sued Coherus BioSciences Inc. for infringement of U.S. Patent No. 8,273,707 (the ‘707 patent). The patent relates to methods of purifying proteins using hydrophobic interaction chromatography (“HIC”), in which a buffered salt solution containing the desired protein is poured into a HIC column and the proteins are bound to a column matrix while the impurities are washed out. However, only a limited amount of protein can bind to the matrix. If too much protein is loaded on the column, some of the protein will be lost to the solution phase before elution.
Conventionally, a higher salt concentration in a buffer solution is provided to increase the dynamic capacity of the HIC column, but the higher salt concentration causes protein instability. Amgen’s ‘707 patent discloses a process that increases the dynamic capacity of a HIC column by providing combinations of salts instead of using a single salt.
According to the ‘707 patent, any one of the three combinations of salts – citrate and sulfate, citrate and acetate, or sulfate and acetate – allows for a decreased concentration of at least one of the salts to achieve a greater dynamic capacity without compromising the quality of the protein separation.
During prosecution, the Examiner rejected the claims as being obvious in view of U.S. Patent No. 5,231,178 (“Holtz”). In reply to the Examiner’s rejection, Amgen argued that:
(1) The pending claims recite a particular combination of salts. No combinations of salts are taught nor suggested in Holtz;
(2) No particular combinations of salts recited in the pending claims are taught or suggested in Holtz; and
(3) Holtz does not teach dynamic capacity at all.
Amgen also attached a declaration from the inventor. The declaration stated that the use of the three salt combinations leads to substantial increases in the dynamic capacity of a HIC column and “[use] of this particular combination of salts greatly improves the cost-effectiveness of commercial manufacturing by reducing the number of cycles required for each harvest and reducing the processing time for each harvest.”
The Examiner again rejected Amgen’s argument and took the position that the prior art does disclose salts used in a method of purification and that adjustment of conditions was within the skill of an ordinary artisan. This time, in response to the Examiner’s position, Amgen replied that Holtz does not disclose any combination of salts and does not mention the dynamic capacity of a HIC column. In particular, Amgen stated that it was a “lengthy development path” when choosing a working salt combination and that merely adding a second salt would not have been expected to result in the invention. The Examiner allowed the claims.
In 2016, Coherus sought FDA approval to market a biosimilar version of Amgen’s pegfilgrastim product. In 2017, Amgen sued Coherus for infringing the ‘707 patent under the doctrine of equivalents because Coherus’s process did not match any of the three explicitly recited salt combinations in the ‘707 patent. Coherus moved to dismiss Amgen’s complaint for failure to state a claim.
The district court agreed to dismiss the complaint. The district court noted that during prosecution, Amgen had distinguished Holtz by repeatedly arguing that Holtz did not disclose “one of the particular, recited combinations of salts” in the two responses and in the declaration. The district court held that “[t]he prosecution history, namely, the patentee’s correspondence in response to two office actions and a final rejection, shows a clear and unmistakable surrender of claim scope by the patentee.” In addition, the district court held that “by disclosing but not claiming the salt combination used by Coherus, Amgen had dedicated that particular combination to the public.”
Amgen appealed.
The CAFC affirmed the district Court’s dismissal and found that the “prosecution history estoppel has barred Amgen from succeeding on its infringement claim under the doctrine of equivalents.”
In the appeal, Amgen argued that it only had distinguished Holtz by stating that Holtz does not disclose increasing any dynamic capacity or mention any salt combination. Amgen also argued that the prosecution history should not apply here because the last response filed prior to allowance did not make the argument that Holtz failed to disclose the particular salt combinations.
Regarding Amgen’s first point – that during prosecution, only dynamic capacity had been used to distinguish Holtz – the CAFC noted the three grounds on which Amgen has relied for distinguishing Holtz, and the fact that Amgen had quoted the declaration in support of the particular combination of salts recited in the claims. The CAFC explained that “separate arguments create separate estoppels as long as the prior art was not distinguished based on the combination of these various grounds.”
The CAFC also disagreed with Amgen’s second point (that prosecution history estoppel should not apply because of their last response), commenting that “there is no requirement that argument-based estoppel apply only to arguments made in the most recent submission before allowance… We see nothing in Amgen’s final submission that disavows the clear and unmistakable surrender of unclaimed salt combinations made in Amgen’s response.”
The CAFC held that the prosecution history estoppel applied and affirmed the District Court’s order dismissing Amgen’s complaint for failure to state a claim. The CAFC did not discuss whether Amgen dedicated unclaimed salt combinations to the public.
Takeaway
- Prosecution history estoppel can be triggered, not only by narrowing amendments, but also by arguments, even without any amendments.
- Presenting multiple arguments does not eliminate the risk of triggering estoppel for each of them.
- When writing an argument, avoid using expressions that are not recited in the claims (when discussing the claimed invention) or the cited documents (when discussing the state of the art).
