Doctrine of Equivalents under Enzo Biochem Inc. v. Applera Corp.

| Robert J. Hilton, Ph.D.Eric Furman, Ph.D.

Before Prost, O’Malley, and Wallach. Appeal from the District of Connecticut (nonprecedential).

On August 2, 2017, the Federal Circuit affirmed a decision by the U.S. District Court for the District of Connecticut granting summary judgment in favor of Applera Corp. and Tropix, Inc. (“Applera”). This decision is the latest in a more than decade-long dispute between the parties.


Enzo Biochem, Inc., Enzo Life Sciences, Inc. and Yale University (“Enzo”) sued Applera in 2004 for patent infringement over six patents. After many years of litigation, Enzo limited its contention to U.S. Patent No. 5,449,767 (“the ’767 patent”). The ’767 patent relates to the use of nucleotide probes for detecting the presence of a target nucleic acid sequence in a sample or identifying an unknown nucleic acid sequence using nucleotide derivatives containing biotin, iminobiotin, lipoic acid, or other moieties covalently coupled to a pyrimidine or purine ring. Claim 1 is directed to a nucleotide marker, and the disputed language of Claim 1 recites:

  1. An oligo- or polynucleotide containing a nucleotide having the structure:

. . . wherein A comprises at least three carbon atoms and represents at least one component of a signaling moiety capable of producing a detectable signal . . .

Procedural History

During trial, Enzo asserted Claims 1, 8, 67, 68, and 70 of the ’767 patent, and the jury found that Applera infringed the claims at issue, awarding $48.6 million in damages. Applera appealed on an issue of claim construction, arguing that the claims relate only to indirect detection, whereas Applera’s products involve only direct detection. The Federal Circuit reversed the district court’s claim construction, agreeing that the claims only extend to producing an indirect detectable signal (by complexing with a second molecule having an indicator marker) and do not extend to producing a direct detectable signal (by detecting the marker itself) (780 F.3d 1149 (Fed. Cir. 2015); “Enzo II”). The Federal Circuit remanded to the district court to determine whether the accused product infringes under the proper claim construction. On remand, the district court concluded that the disputed claims only relate to indirect detection, as found by the Federal Circuit, and rejected Enzo’s doctrine of equivalent arguments. Enzo then appealed.

Federal Circuit Opinion

On appeal, Enzo conceded that Applera did not literally infringe the claims under the claim construction of indirect detection. Instead, Enzo argued that the claims were infringed under the doctrine of equivalents. The Federal Circuit rejected Enzo’s doctrine of equivalents argument and noted that a party can only prove infringement under the doctrine of equivalents when “every limitation of the asserted claim, including a limitation’s ‘equivalent,’ is found in the accused product, where an equivalent differs from the claimed limitation only insubstantially.” Quoting Ethicon EndoSurgery, Inc. v. U.S. Surgicla Corp., 149 F.3d 1309, 1315.

Here, however, the ’767 patent explained that indirect detection is superior to direct detection, which led to the claim construction ruling that the claims only cover indirect detection. The Federal Circuit explained that the “concept of equivalency cannot embrace a structure that is specifically excluded from the scope of the claims” (quoting Dolly, Inc. v. Spalding & Evenflow Cos., 16 F.3d 394, 400 (Fed. Cir. 1994)), concluding that “the same principle applies in this case; the concept of equivalency cannot embrace direct detection because it is ‘specifically excluded from the scope of the claims.’” In Enzo II, the Federal Circuit construed the claims as covering only indirect detection. Although Claim 1 does not explicitly exclude direct detection, the language “wherein A comprises at least three carbon atoms and represents at least one component of a signaling moiety capable of producing a detectable signal” indicates that the signaling moiety is composed of multiple parts. The Federal Circuit also noted that the specification does not support the inclusion of direct detection, and concluded that no reasonable jury could find, even under the doctrine of equivalents, that Applera’s accused products infringed Enzo’s patent claims.


Although this case is non-precedential, it highlights the difficulty of proving infringement under the doctrine of equivalent. Here, even though the claims do not explicitly exclude “direct detection,” the Federal Circuit concluded that direct detection was specifically excluded from the scope of the claims, primarily based on language from the specification.