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Recent Federal Circuit Decisions Address the “Tangential Relation” Exception to Prosecution History Estoppel

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Ajinomoto Co., Inc. v. Int’l Trade Comm’n, Appeal No. 2018-1590 (Fed. Cir. Aug. 6, 2019)

Eli Lilly & Co. v. Hospira, Inc., Appeal No. 2018-2128 (Fed. Cir. Aug. 9, 2019)

Prosecution history estoppel typically forecloses a patent owner’s ability to claim infringement on equivalents in the territory between the original claim language and the finalized claim language.[1] In two recent cases, however, the Federal Circuit showed its willingness to apply the tangential relation exception to prosecution history estoppel and find infringement under the doctrine of equivalents.

Ajinomoto Co., Inc. v. International Trade Commission involved U.S. Patent No. 7,666,655 (“the ‘655 patent”), which claims E. coli bacteria genetically engineered to increase their production of L-amino acids during fermentation. During prosecution, the ‘655 patent was initially rejected for lack of an adequate written description of what changes would occur during the patented process and lack of enablement as to how to alter sequences of the E. coli bacteria to produce the desired results. In response to the rejection, the applicants (collectively, “Ajinomoto”) amended the claim to read “replacing the native promoter that precedes a DNA encoding said protein . . . with a more potent promoter” instead of “by alteration of expression regulation sequence of said DNA.”[2]

Ajinomoto subsequently filed a complaint with the International Trade Commission against CheilJedang Corp., CJ America, Inc., and PT CheilJedang Indonesia (collectively, “CJ”) for patent infringement, alleging that CJ used three different strains of E. coli to produce the same L-amino acids covered in its patent. The Commission, relying on the “tangential relation” exception to prosecution history estoppel, determined that while some of CJ’s later strains were infringing, their later strains were not. Ajinomoto and CJ both appealed to the Federal Circuit.

The case went before Circuit Judges Dyk, Moore, and Taranto, and the majority affirmed the Commission’s decision holding that two of CJ’s strains of E. coli were equivalents and thus infringing under the doctrine of equivalents. The court agreed with the Commission’s conclusion that Ajinomoto had successfully invoked the tangential relation exception. That is, the purpose for the narrowing amendment was to limit the set of proteins within the claim’s scope, and this change was only tangentially related to the accused equivalent, which related to choosing among several DNA sequences within the same protein. As such, Ajinomoto was not barred by prosecution history estoppel from claiming infringement under the doctrine of equivalents.

Judge Dyk, dissenting in part, stated that the court should have followed the “very narrow” construal of the tangential relation exception “consistently described” by the court, that the reason for the narrowing amendment was directly related to the equivalent, and that the exception therefore did not apply.

In Eli Lilly & Co. v. Hospira, Inc., decided three days later, the Federal Circuit again addressed the tangential relation exception. Eli Lilly involved two appeals pertaining to the infringement of U.S. Patent No. 7,772,209 (“the ‘209 patent”). The invention of the ‘209 patent is an improved method of treating lung cancer and mesothelioma with antifolates, using a combination of pemetrexed disodium, methylmalonic acid, and folic acid. The original language of a parent application included broad claims to methods of administering an antifolate in conjunction with a methylmalonic acid, with or without folic acid. After the claims were rejected as either anticipated or obvious, Eli Lilly narrowed the language “antifolate” to “pemetrexed disodium” and cancelled its dependent claim limited to pemetrexed disodium.

Eli Lilly sued Hospira and Dr. Reddy’s Laboratories (DRL) in the Southern District of Indiana, alleging that their filings of drug applications for different pemetrexed salts—pemetrexed ditromethamine—constituted infringement. The district court found both literal infringement and infringement under the doctrine of equivalents.

On appeal, Circuit Judges Lourie, Moore, and Taranto reversed the district court’s finding of literal infringement. However, the panel agreed that Eli Lilly could succeed under the doctrine of equivalents. The panel reasoned that the amendment of the claim language served to distinguish pemetrexed from antifolates in general, while the accused equivalents related to the particular types of salt to which pemetrexed is complexed. Accordingly, the court determined that the two were only tangentially related and that the reason for the amendment was not to relinquish other functionally identical salts in potential patent litigation. Once again, the court showed a willingness to apply flexibility to the prosecution history estoppel and doctrine of equivalents analysis, stating “We do not demand perfection from patent prosecutors, and neither does the Supreme Court.”

[1] Under this doctrine, “[a] patentee’s decision to narrow his claims through amendment may be presumed to be a general disclaimer of the territory between the original claim and the amended claim.” Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722, 740 (2002).

[2] The original application recited “[t]he bacterium according to claim 1, wherein said activities of proteins . . . is enhanced by transformation of said bacterium with DNA coding for the protein . . . or by alteration of expression regulation sequence of said DNA on the chromosome of the bacterium” (emphasis added).