The Federal Circuit issued a decision in Baxalta Inc. v. Genentech, Inc., ___ F.3d __, 2020 WL 5048435 (Fed. Cir. Aug. 27, 2020) construing the terms “antibody” and “antibody fragment.” According to the decision:

• Antibody: An “immunoglobulin molecule having a specific amino acid sequence comprising two heavy chains (H chains) and two light chains (L chains).”
• Antibody Fragment: A “portion of an immunoglobulin molecule having a specific amino acid sequence comprising two heavy chains (H chains) and two light chains (L chains).”

While the definition of claim terms will necessarily depend on how they are used in the specification and claims, this decision gives guidance on what the courts believe is the plain meaning of these important terms.

The Decision

As background, the court noted that antibodies are, generally, Y-shaped structures that have two heavy chains (H chains) and two light chains (L claims). An antibody where the two H chains are identical and the two L chains are identical is called a “monospecific” antibody “because each H-L chain pair binds the same antigen.” Bispecific antibodies, on the other hand, have two different H chains and/or two different L chains.

The independent claim at issue disclosed “[a]n isolated antibody or antibody fragment thereof that binds Factor IX or Factor IXa and increases the procoagulant activity of Factor IXa.”

The District Court narrowly defined antibody as “an immunoglobulin molecule, having a specific amino acid sequence that only binds to the antigen that induced its synthesis or very similar antigens, consisting of large, identical heavy chains (H chains) and two light, also identical chains (L chains).” The Federal Circuit rejected this narrow construction, finding that:

• The plain language of the claim did not limit the term to monospecific antibodies or to antibodies that only bind the antigen that induced their synthesis.
• The District Court’s construction excluded claimed embodiments, such as bispecific antibodies and humanized antibodies.
• Statements in the specification did not limit the claims. Although background material in the specification described antibodies as monospecific, that generalized description in one section of the specification did not limit the claim term. The Federal Circuit cited the lack of limiting language such as “the invention is” and the express disclosure of bispecific, chimeric and humanized antibodies elsewhere in the specification.
• There was no “clear and unmistakable” disavowal of claim scope by replacing the term “antibody derivatives” with “antibody fragment” to resolve an enablement rejection. The term “antibody derivative” was not commonly used in the art and thus it was unclear whether the amendment to “antibody fragment” surrendered claim scope.

The District Court interpreted “antibody fragment” narrowly as “a fragment of an antibody which partially or completely lacks the constant region” and that “the term ‘antibody fragment’ excludes bispecific antibodies.” The Federal Circuit determined that general statements in the specification to that effect did not define “antibody fragments” as “partially or completely lacking a constant region” because the patentee did not clearly intend to define (or “redefine”) the term “antibody fragment” with those statements and thus the term’s plain and ordinary meaning would govern.