The Doctrine of Equivalents After Festo

The Supreme Court’s decision in Festo removes some of the rigidity of the Federal Circuit’s “complete bar” approach to the doctrine of equivalents, but difficulties remain for biotechnology patent holders. The Court explicitly allows for the application of prosecution history estoppel to claims amended in response to enablement rejections and not just those amended to avoid prior art. Due to the uncertainty regarding enablement for nucleotide and amino acid sequences, applications in the field of biotechnology are virtually guaranteed to be amended during prosecution. Consequently, the Festo decision places an undue burden on applicants in the field of biotechnology: to specifically claim every possible variant of a nucleotide or amino acid sequence or risk finding out in court that minor non-functional substitutions in the claimed sequence were foreseeable, and therefore not covered by the doctrine of equivalents.