Claim Amendment to Avoid Unrelated Prior Art Protein Is Unrelated to Codon-Randomized Versions of Protein-at-Issue and Do Not Trigger Prosecution History Estoppel Under the Tangential Exception

In Ajinomoto Co. v. Int’l Trade Comm’n, Nos. 2018-1590, 2018-1629 (Fed. Cir. Aug. 6, 2019), the Federal Circuit applied the tangential relation exception to the doctrine of prosecution history estoppel in its doctrine of equivalents analysis. The claims at issue recite alternative descriptions of the claimed protein: “(A) comprising the amino acid sequence shown in SEQ ID NO:2, or (B) comprising an amino acid sequence encoded by a nucleotide sequence that hybridizes with the nucleotide sequence of SEQ ID NO:1 under stringent conditions.” The Commission found that the protein encoded by a codon-randomized gene of the respondent’s strain was an equivalent of SEQ ID NO:2.

Initially, the Federal Circuit noted that the originally filed claim 1 recited a different (B) alternative, i.e., an amino acid sequence including deletion, substitution, insertion, or addition of one or several amino acids in SEQ ID NO:2. During prosecution, to overcome an anticipation rejection over an unrelated prior-art E. coli YfiK protein technically covered by the original (B) alternative, applicants amended (B) to recite an amino acid sequence encoded by a nucleotide sequence that hybridizes with the nucleotide sequence of SEQ ID NO:1 under stringent conditions. The court concluded that the objective rationale for the amendment was to limit the scope of (B) so that it no longer covered the unrelated YfiK prior-art protein and had nothing to do with choosing among several DNA sequences in the redundant genetic code corresponding to the protein at issue in the case (i.e., application of codon-randomization). Accordingly, the court affirmed the Commission’s finding of infringement under DOE.