In an appeal from the District of Delaware, the Federal Circuit (Judges Moore, Plager, and Wallach) vacated and remanded the district court’s judgment of non-infringement based on erroneous claim construction. In particular, the Federal Circuit held that the district court erred in construing the terms “antibody” and “antibody fragment.”

In 2017, Baxalta Inc. sued Genentech Inc. asserting that Genentech’s Helimbra® (emicizumb-kxwh) product used to treat the blood clotting disorder hemophilia infringes claims 1, 4, 17, and 19 of U.S. Patent No. 7,033,590 (the “’590 patent”). Claim 1 is provided below for reference.

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

Baxalta and Genentech disputed the construction of the terms “antibody” and “antibody fragment” (among other terms not at issue on appeal). Baxalta argued that the term “antibody” should be construed as “[a] molecule having a specific amino acid sequence comprising two heavy chains (H chains) and two light chains (L chains),” while Genentech argued that it should instead be construed as “[a]n immunoglobulin molecule, having a specific amino acid sequence that only binds to the antigen that induced its synthesis or very similar antigens, consisting of two identical heavy chains (H chains) and two identical light chains (L chains).” The district court adopted Genentech’s construction of antibody, relying on a specific passage in the ’590 patent, i.e., 5:56-63, and an amendment made by Baxalta during the prosecution of the patent.

With regard to the term “antibody fragment,” Baxalta argued that it should be construed as “[a] portion of a molecule having a specific amino acid sequence comprising two heavy chains (H chains) and two light chains (L chains),” while Genentech argued that it should instead be construed as “[a] fragment of an antibody which partially or completely lacks the constant region” and that the term “excludes all other forms of anti-body derivatives.” The district court, relying on a passage in the ’590 patent, construed the term as “a fragment of an antibody which partially or completely lacks the constant region; the term ‘antibody fragment’ excludes bispecific antibodies.” Based on the district court’s constructions, Baxalta and Genentech stipulated to non-infringement of the asserted claims of the ’590 patent. Baxalta appealed, arguing that the district court erroneously construed the terms “antibody” and “antibody fragment.”

The Federal Circuit agreed with Baxalta and vacated the district court decision. In particular, with regard to the term “antibody,” the Federal Circuit looked to the claims, the written description, and the prosecution history of the ’590 patent in support of its finding that the district court’s construction was erroneous. For example, nothing in the plain language of claim 1 limits the term “antibody” to a specific antibody consisting of two identical heavy chains and two identical light chains or an antibody that only binds the antigen that induced its synthesis or very similar antigens. Further, the Federal Circuit held that each of the claimed “antibodies” in the dependent claims also fall outside the district court’s construction. In other words, the district court’s construction, which excluded explicitly claimed embodiments, is inconsistent with the plain language of the claims. In this regard, the Federal Circuit held that the plain language of the dependent claims weighed heavily in favor of adopting Baxalta’s broader claim construction. The Federal Circuit also found that the written description provides specific disclosures of many different types of “antibodies” that do not comport with the district court’s construction.

The Federal Circuit further found that the prosecution history was insufficient to overcome the meaning of “antibody” that was discerned from the claims and the written description. More specifically, there were no clear statements in the prosecution history regarding what scope, if any, was given up when the patentee substituted “antibody fragment” for “antibody derivative.” The Federal Circuit also held that term “antibody fragment” was erroneously construed for similar reasons as the term “antibody.”

As a practice point, parties should keep in mind to not solely rely on prosecution history or cherry-picked passages in the specification during claim construction but, instead, should also consider the totality of specification as well as the plain language of the claims.