The Tangential Exception to the Presumption of Prosecution History Estoppel 

August 19, 2019

The Federal Circuit has consistently described the “tangential” exception to the presumption of prosecution history estoppel as “very narrow.” Only a few Federal Circuit decisions have found proof of the tangential exception sufficient to rebut the presumption of prosecution history. The Federal Circuit in a split decision in Ajinomoto Co., Inc. v. ITC did so on August 6, 2019. This decision is of particular interest because of the significant differences in the majority and dissent’s analyses of this issue.

Ajinomoto Co. Inc., a producer of amino acids, brought an ITC action against CheilJedang Corp. (CJ), a Korean food company, under Section 337 of the Tariff Act of 1930 seeking to exclude from entry into the United States certain L-tryptophan products that allegedly infringed U.S. Patent No. 7,666,655. The ‘655 patent claims genetically engineered E. coli bacteria that have increased production of aromatic-L-amino acids, including L-tryptophan. In particular, the ’655 patent identifies a specific gene in the E. coli genome, the yddG gene, that encodes the yddG protein involved in the export of aromatic L-amino acids. L-tryptophan is an essential amino acid that animals cannot synthesize and is used as an animal feed supplement.

During the ITC proceedings, CJ made a new bacterial strain (later second strain) by using a technique that takes advantage of the redundancy of the genetic code. Specifically, CJ made a synthetic yddG gene with a DNA sequence that differs from the naturally occurring yddG gene, but encodes the same yddG protein. That gene did not hybridize with the E. coli yddG gene, thus avoiding the literal scope of the ’655 patent claims.

Under the doctrine of prosecution history estoppel, a narrowing of a claim through amendment is presumed to be a general disclaimer of the territory between the original claim and the amended claim. The patentee may rebut that presumption by showing: (1) the equivalent was unforeseeable at the time of the application, (2) the rationale for the amendment bears no more than a tangential relation to the equivalent in question, or (3) some other reason suggesting that the patentee could not reasonably be expected to have described the equivalent. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722, 740 (2002).

On appeal, claim 20 of the ‘655 patent was the only claim at issue. Claim 20 reads:

20. A method for producing an aromatic L-amino acid, which comprises cultivating the bacterium according to any one of claims 9-12, 13, 14, 15-18, or 19.

Claim 20 depends on claim 9, which includes a protein limitation, i.e., “in which said protein consists of the amino acid sequence of SEQ ID NO: 2.” The commission found that the yddG protein encoded by the codon-randomized non-E. coli yddG gene of CJ’s later second strain is an equivalent of SEQ ID NO: 2 (the amino-acid sequence of the E. coli yddG protein), and thus met the protein limitation of claim 9. Claim 9 issued from application claim 12, which was added during prosecution. Claims 9 contains the SEQ ID NO: 2 language of the (A) limitation of claim 1.

            Claim 1 originally recited:

... bacterium ... enhanced by enhancing activity of a protein as defined in the following (A) or (B) ...:

(A) a protein which comprises the amino acid sequence shown in SEQ ID NO: 2 in Sequence listing;

(B) a protein which comprises an amino acid sequence including deletion, substitution, insertion or addition of one or several amino acids in the amino acid sequence shown in SEQ ID NO: 2 . ...

The examiner rejected claim 1 as anticipated by a reference which disclosed the E. coli “yfiK gene product” (i.e., the E. coli yfiK protein) — which differed from SEQ ID NO: 2 by deletion, substitution, insertion, or addition of several amino acids.

In response to overcome the prior art, the patentee amended limitation (B) of claim 1 to read:

(B) a protein which comprises an amino acid that is encoded by a nucleotide sequence that hybridizes with the nucleotide sequence of SEQ ID NO: l . …

CJ’s argument for prosecution history estoppel involves what the majority characterized as “an unusual circumstance.” The infringement determination does not rest on finding an equivalent of the new claim language — the (nucleotide) SEQ ID NO: 1 language. Rather, it rests on finding an equivalent of the (amino-acid) SEQ ID NO: 2 language in claim 9, which was not altered by the amendment at issue. Ajinomoto therefore contended that, in this circumstance, prosecution history estoppel does not apply at all. However, CJ argued that prosecution history estoppel indirectly applies to the “SEQ ID NO: 2” element of claim 9 and limits the range of equivalents that is available for that claim term because Ajinomoto narrowed the protein element of its claims by referring to its DNA sequence and hybridization instead of its amino acid sequence.

The Federal Circuit, quoting from Festo, stated the test for the “tangential relation” exception is “‘whether the reason for the narrowing amendment was peripheral, or not directly relevant, to the alleged equivalent.’” The majority determined that the rationale for the amendment was to limit the set of proteins within the claim’s scope so the claim no longer included the prior-art E. coli yfiK protein and more generally, that the amended claim no longer allowed as wide a range of amino acid alterations as the original claim. The majority stated that the reason for the narrowing amendment “had nothing to do with choosing among several DNA sequences in the redundant genetic code that correspond to the same protein.” The majority explained that the non-E. coli yddG protein is identical whether produced from the codon-randomized or the non-codon-randomized version of the non-E. coli yddG gene.

Judge Dyk dissented. Judge Dyk reasoned that “the patentee deliberately chose to redefine the claimed proteins in terms of the ability of their encoded nucleotide sequences to hybridize with SEQ ID NO: 1 under the claimed conditions.” He stated that the amended claim excluded the prior art protein “because it was made based on a nucleotide sequence that did not meet the newly added hybridization requirement.” Judge Dyk wrote that the “accused equivalent is similarly not covered by the amended claims because it is produced based on an encoding nucleotide sequence that does not hybridize with SEQ ID NO: 1 under the claimed conditions.” Thus, Judge Dyk concluded that the narrowing amendment is not tangential to the accused equivalent and that the “equivalent is directly related to the reason for the amendment — to exclude those proteins made by an encoding nucleotide sequence that does not hybridize with SEQ ID NO: 1 under the specified conditions.”

CJ also contended that Ajinomoto forfeited reliance on the tangential relation exception because Ajinomoto did not rely upon that exception until the commission exercised its discretion to raise the exception. Because the commission gave the parties an adequate opportunity to address the exception, the Federal Circuit rejected CJ’s waiver argument.

Take Away

In designing around a claim, competitors often rely on an equivalent to a limitation that was narrowed by amendment during prosecution to avoid prior art. A lesson from this decision is that competitors must also carefully consider whether the reason for the claim amendment will be considered only tangential to the equivalent at issue.



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