Addressing an infringement determination under the doctrine of equivalents (DOE), the US Court of Appeals for the Federal Circuit found that the “tangential relation” exception to the doctrine of prosecution history estoppel (PHE) applied and thus infringement under DoE was not precluded. Ajinomoto Co., Inc. v. Int’l Trade Comm’n, Case Nos. 18-1590, -1629 (Fed. Cir. Aug. 6, 2019) (Taranto, J) (Dyk, J, concurring in part, dissenting in part).

Ajinomoto filed a complaint against CJ CheilJedang with the US International Trade Commission (ITC), alleging that CJ violated § 337 by importing certain animal-feed-grade L-tryptophan products produced by a process that infringed Ajinomoto’s patent. The patent covered a method of using genetically engineered Escherichia coli bacteria to increase their production of aromatic L-amino acids, such as L-tryptophan. The ITC determined that CJ’s earlier E. coli strains did not infringe, but that CJ’s two later strains did. The ITC also found that the patent was not invalid for lack of written description. Ajinomoto appealed the ITC’s claim construction underlying the determination of no infringement by the earlier strains. CJ cross-appealed the determination of infringement by the later strains and rejection of the validity challenge.

The Federal Circuit affirmed. Turning first to the ITC’s finding of no infringement by the earlier E. coli strains, the Court agreed with the ITC’s claim construction of the term “replacing the native promoter . . . with a more potent promoter.” After reviewing the intrinsic evidence, the Court found that this term meant removing the entire native promoter as a unit rather than replacement by mutagenesis of a single nucleotide of the promoter. The Court noted that this was “a case where the applicants surrendered more than may have been necessary” by changing the word “alteration” (which would have covered mutations to single nucleotides) to “replacing.”

Turning to the ITC’s infringement determination by the later E. coli strains, the Federal Circuit rejected CJ’s two arguments on appeal: (1) that PHE barred Ajinomoto from relying on the DOE and (2) that the later strains could not be found to be equivalents under the function-way-result test. The Court noted that CJ’s argument involved an unusual circumstance because the infringement determination rested not on finding an equivalent of the new claim language but on finding an equivalent that was not itself altered by the amendment at issue. The Court agreed that the “tangential relationship” exception to the DOE—which asks “whether the [patentee’s objectively apparent] reason for the narrowing amendment was peripheral, or not directly relevant, to the alleged equivalent”—applied. The Court then proceeded to find that substantial evidence supported the ITC’s finding of equivalence under the function-way-result test.

Finally, the Federal Circuit affirmed the ITC’s rejection of the validity challenge for lack of written description, finding that the patent disclosed a representative number of species and common structural features. In doing so, the Court stated that the patent disclosed four examples of potent promoters and incorporated art that disclosed 14 additional potent promoters along with a general methodology for determining promoter strength in E. coli bacteria such that a skilled artisan could make relatively predictable changes to the native promoter to arrive at a more potent promoter.

Judge Dyk dissented only as to the majority’s conclusion that Ajinomoto had successfully rebutted the presumption of PHE under the “tangential relation” exception. Noting that the Federal Circuit has consistently described this exception as “very narrow,” he stated that the majority’s analysis ignored how the patentee deliberately elected to narrow the claims to avoid anticipating prior art (a prior art protein based on its encoding nucleotide sequence that does not meet the newly claimed hybridization requirement), and that rationale was directly related to the accused equivalent (a protein made by an encoding nucleotide sequence that does not meet the newly claimed hybridization requirement).