The Federal Circuit affirmed a district court decision barring Amgen from asserting an infringement claim under the doctrine of equivalents against Coherus Biosciences because Amgen disclaimed all combinations not identified in its claims during prosecution.

Amgen sued Coherus in the District Court for the District of Delaware for infringement of its U.S. Patent No. 8,273,707 after Coherus filed an abbreviated Biologic License Application (aBLA) for approval of a biosimilar of Amgen’s Neulasta product. The ’707 patent claims methods of purifying proteins using Hydrophobic Interaction Chromatography (HIC). More specifically, the ’707 patent claims methods for purifying proteins on columns that include as a first step “mixing a preparation containing the protein with a combination of a first salt and a second salt.” The claims of the ’707 patent further specify “the first and second salts are selected from the group consisting of citrate and sulfate, citrate and acetate, and sulfate and acetate, respectively.”

During prosecution, the claims of the ’707 patent were rejected in view of the Holtz reference, which generally disclosed several salts that can be used to improve the hydrophobic interactions between a protein and a column matrix. Amgen responded that Holtz does not teach (1) combining multiple salts, (2) combining the particular salts recited in the claims or (3) using any combination of salts for increasing the dynamic capacity of a HIC. Amgen submitted a declaration to the PTO to emphasize further the importance of its particular combination of salts, which improved the cost-effectiveness of commercial manufacturing and increased the dynamic capacity of the column. Amgen also argued more broadly that Holtz failed to disclose any combination of salts. In a response to a second rejection, Amgen reiterated its broader response to Holtz, but did not repeat its emphasis on the particular combination of salts disclosed in the claims. The examiner allowed Amgen’s claims after receiving Amgen’s second response.

Amgen’s complaint against Coherus asserted that Coherus infringed the ’707 patent under the doctrine of equivalents, because Coherus’s aBLA indicated that Coherus manufactured its biosimilar product using a salt combination other than the three specified in the ’707 patent claims. Coherus successfully moved pursuant to Rule 12(b)(6) to dismiss Amgen’s complaint in the District Court, arguing that Amgen was barred from asserting infringement under the doctrine of equivalents based on prosecution history estoppel.

On appeal, the Federal Circuit affirmed the district court’s dismissal of Amgen’s complaint, and held that Amgen “clearly and unmistakably surrendered unclaimed salt combinations during prosecution.” Specifically, Amgen emphasized that Holtz did not disclose the particular salt combinations claimed in the ’707 patent multiple times during prosecution. The Court rejected Amgen’s argument that it distinguished Holtz more broadly on the ground that Holtz does not disclose any combination of salts. In doing so, the Court noted that “while Amgen did assert multiple reasons for why Holtz is distinguishable, [its] precedent instructs that estoppel can attach to each argument.” Similarly, the Court also held that prosecution history estoppel still applied even though Amgen only included the “particular combinations” argument in its response to the examiner’s first rejection, and not the second—“clear assertions made during prosecution in support of patentability, whether or not actually required to secure allowance of the claim, may also create an estoppel.”

Amgen Inc., Amgen Manufacturing Ltd. V. Coherus Biosciences Inc., No. 2018-1993, (Fed. Cir. July 29, 2019)

Practice Tip

Statements made at any point during the course of prosecution, even if not required to secure allowance of the claims and even where alternative arguments are presented, can support application of prosecution history estoppel. Thus, it is important to avoid narrow lines of argument during prosecution, when broader distinctions can be made between pending claims and prior art. And, to the extent an applicant has made a clear disavowal of claim scope during prosecution, this case demonstrates that prosecution history estoppel may be a viable defense even at the 12(b)(6) stage.