In a Report and Recommendation issued December 7, 2017, Magistrate Judge Burke in the District of Delaware recommended that Amgen's BPCIA complaint for infringement against Coherus Biosciences Inc. be dismissed with prejudice on the ground that prosecution history estoppel barred Amgen from bringing claims for infringement under the doctrine of equivalents.

In August 2016, Coherus filed an abbreviated Biologics License Application (aBLA), seeking Food and Drug Administration approval to market a biosimilar form of Amgen's pegfilgrastim product, Neulasta®. Pegfilgrastim is a modified form of granulocyte colony stimulating factor that promotes the creation of white blood cells. After Coherus filed its aBLA, Amgen and Coherus engaged in the exchange of information dictated by the BPCIA, i.e., "the patent dance," and ultimately agreed–pursuant to 42 U.S.C. § 262(l)(6)(A)–that a single Amgen patent, U.S. Patent No. 8,273,707 (the "'707 patent"), would be included in the lawsuit.

The '707 patent generally discloses a process for purifying proteins by using column chromatography to separate the proteins of interest from other components. The methods of the '707 patent include treating the protein mixture with a combination of salts prior to filtering on the column. Critically, both of the independent claims of the '707 patent require the use of a combination of salts in the loading solution, which must be selected from one of citrate and sulfate, citrate and acetate, or sulfate and acetate.

The salt combination limitations were added by amendment to the claims of the '707 patent during patent prosecution after Amgen's claims were rejected as obvious in view of a single reference, Holtz. Holtz was described as teaching a method for purifying a protein by column chromatography; it also discloses salts, such as the citrate, sulfate and acetate salts for use in protein purification. To overcome the obviousness rejection, Amgen argued that Holtz failed to teach combinations of salts to increase the dynamic capacity of a purification column, let alone the "particular combinations of salts recited in the pending claims." (emphasis in original). Following a second rejection based on Holtz, Amgen reiterated this distinction and submitted a declaration from one of its named inventors to further support its position. Amgen's claims were subsequently granted.

However, the manufacturing process set forth by Coherus for its biosimilar pegfilgrastim product utilized a different combination of salts not claimed by the '707 patent. As a result, Amgen was forced to assert infringement under the doctrine of equivalents theory. In its motion to dismiss, Coherus argued that Amgen was foreclosed from arguing equivalence by virtue of prosecution history estoppel. More specifically, Coherus argued that, by narrowing its claims during prosecution to include only the three disclosed salt combinations, Amgen disavowed alternative combinations.

On review, the court found that Amgen clearly and unmistakably surrendered processes using combinations of salts other than those specifically identified in the claims of the '707 patent. In so doing, the court acknowledged that, had Amgen distinguished its claims from Holtz based solely on the use of a combination of salts, as opposed to the use of a single salt, then no estoppel would apply. But in light of Amgen's repeated emphasis that its particular combinations of salts provided enhanced benefits over the prior art, including through an inventor declaration that described test results for those particular salt combinations, Amgen was barred from arguing that its claims could reach further.

Amgen Inc., Amgen Manufacturing Limited v. Coherus Biosciences Inc., No. 17-546-LPS-CJB

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