On August 27, 2020, the United States Court of Appeals for the Federal Circuit (“CAFC”) issued an opinion reversing the decision of the United States District Court for the District of Delaware dismissing plaintiff Baxalta Inc.’s (“Baxalta”) infringement suit against Genetech, Inc. (“Genentech”). Baxalta Inc. v. Genentech, Inc., __ F.3d __ (Fed. Cir. Aug. 27, 2020).

Baxalta filed suit against Genentech alleging infringement of claims 1, 4, 17, and 19 of U.S. Patent No. 7,035,590 (the “’590 patent”), which relates to preparations used to treat hemophilia patients. Independent Claim 1 and dependent claims 4 and 19 (which are illustrative), recite: 

1. An isolated antibody or antibody fragment thereof that binds Factor IX or Factor IXa and increases the procoagulant activity of Factor IXa.

4. The antibody or antibody fragment according to claim 1, wherein said antibody or antibody fragment is selected from the group consisting of a monoclonal antibody, a chimeric antibody, a humanized antibody, a single chain antibody, a bispecific antibody, a diabody, and di-, oligo- or multimers thereof.

19. The antibody or antibody fragment according to claim 4, wherein the antibody is a humanized antibody.

At issue in the present suit were the district court’s construction of the terms “antibody” and “antibody fragment.” Baxalta argued that “antibody” should be construed broadly as “[a] molecule having a specific amino acid sequence comprising two heavy chains … and two light chains ….” Genentech argued for a narrower definition: “[a]n immunoglobulin molecule, having a specific amino acid sequence that only binds to the antigen … consisting of two identical heavy chains … and two identical light chains.”

The district court ultimately adopted Genentech’s narrow definition. Thereafter, the parties stipulated to non-infringement, and the court entered judgment in Genentech’s favor. Baxalta appealed the district court’s claim construction to the CAFC.

First, the CAFC considered whether the district court’s narrow definition of “antibody” was consistent with the claims of the ’590 patent. The district court held that the plain language of claim 1 limited the term “antibody” to the narrow definition. However, the CAFC ruled that the language of the dependent claims (e.g., claim 4) suggested that “antibody” should not be limited to Genentech’s narrow definition. While the district court came to the same conclusion, it suggested that the proper course of action would be to invalidate the inconsistent claims, rather than expand the independent claim. The CAFC disagreed, noting that the plain language of the dependent claims weighed heavily in favor of adopting Baxalta’s broader claim construction.

Next, the CAFC considered whether the district court’s definition of “antibody” was inconsistent with the written description of the patent. The district court relied heavily on Column 5 of the patent, which it ruled included a definition of antibodies consistent with Genentech’s proposal. The CAFC disagreed, holding that this was an isolated reading of the claims instead of a reading of “the specification as a whole.” Considering the entire specification, the CAFC ruled that Column 5 was a generalized introduction rather than a definitional statement. Further, the patent specification provided specific disclosures that did not comport with the district court’s construction. Accordingly, the CAFC ruled that the district court improperly construed the written description to support the narrow definition.

Finally, the CAFC considered whether the district court improperly interpreted the ’590 patent’s prosecution history to support its claim-construction ruling. Claims 1, 4, and 19 previously included the term “antibody derivatives,” but that term was replaced with “antibody fragments” during prosecution to cure an enablement issue. The definition of “antibody derivatives” included language that was inconsistent with Genentech’s narrow definition. The district court ruled that Baxalta’s removal of “antibody derivative” constituted a disclaimer of the term. The CAFC disagreed, citing precedent for the proposition that the doctrine of prosecution history should not be applied where the alleged disclaimer is less than clear. Rather, a disavowal must be both clear and unmistakable. The CAFC ruled that there was no clear statement in the prosecution history regarding what scope, if any, was given up due to the substitution of terms. Accordingly, the prosecution history did not support the district court’s construction of “antibody.”

Additionally, the CAFC reversed the district court’s construction of the term “antibody fragment.” The district court construed the term to mean “a fragment of an antibody which partially or completely lacks the constant region.” This reading was based on a portion of the written description which stated, “activating antibodies … may also include … e.g., … antibody fragments which partially or completely lack the constant region.” The CAFC ruled that the excerpt did not define the term as necessarily “partially or completely lack[ing] in the constant region,” as “the standard for lexicography is exacting, requiring the patentee to ‘clearly express an intent to redefine a term.’” The written description’s use of “may also include” and “e.g.,” showed that the patentee did not intend the excerpt to define “antibody fragment.” Accordingly, the CAFC reversed the district court’s construction.