Tangential Relation Exception Rebuts Presumption Of Prosecution History Estoppel

  • August 1, 2019
Ajinomoto Co., v. ITC; CJ Cheiljedang Corp., v. ITC

In Ajinomoto, the Federal Circuit affirmed the International Trade Commission’s determination that application of the doctrine of equivalents was not barred by amendment-based prosecution history estoppel, where it determined that the alleged equivalent was no more than tangentially related to the reasons for the amendment.

Ajinomoto owns a patent directed to producing amino acids with genetically modified E. coli. Ajinomoto filed a complaint with the ITC, accusing CJ Cheiljedang of importing infringing amino acids produced by E. coli. The ITC reviewed the complaint, and determined that some strains of E. coli used by CJ were equivalent to the E. coli claimed in the patent.

CJ appealed the ITC’s determination to the Federal Circuit, arguing that Ajinomoto was barred from relying on the doctrine of equivalents because the patentee had narrowed the claims during prosecution through amendment. Specifically, CJ argued that an amendment limiting the claims to specific DNA sequences that encoded a particular protein produced in the claimed E. coli barred Ajinomoto from a “codon-randomized” DNA sequence used in the accused product. Because multiple codons may code for the same amino acid, a codon-randomized DNA sequence can produce an identical protein using different DNA than the non-randomized sequence.

The doctrine of prosecution history estoppel typically bars a patent owner from asserting the doctrine of equivalents for any limitation that was narrowed during prosecution by argument or amendment unless an exception applies. One such exception is where the reason for the narrowing amendment was peripheral, or not directly relevant, to the alleged equivalent.

The ITC found, and the Federal Circuit affirmed, that the tangential relation exception applied in this instance, because the reason for the amendment was found to be only to limit the scope of the protein, and not the many DNA sequences that may encode the protein, like codon-randomized variants. In other words, the Federal Circuit concluded that the amendment was only tangentially related to the purpose of the amendment.

In dissent, Judge Dyk took a different view, stating that the tangential relation exception should not apply because Ajinomoto deliberately chose to define proteins based on their encoding DNA. Judge Dyk considered that by excluding the prior art through limiting the encoding DNA, the amendment also excluded CJ’s accused equivalent.

Key takeaway: Prosecution history estoppel will not bar the use of the doctrine of equivalents for a limitation that was the subject of a narrowing amendment during prosecution, if the amendment was only tangentially related to the accused equivalent.


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