In Baxalta Inc. v. Genentech, the Fed. Cir. vacated the district court’s judgment of noninfringement and remanded based on an erroneous claim construction.  Baxalta had claimed an isolated antibody or antibody fragment to Factor IX or Factor IXa, increasing procoagulant activity.  A dependent claim specified a Markush group of antibody or antibody fragments, including a bispecific antibody.  The district court had adopted Genentech’s claim construction based on the specification of antibodies as consisting of identical heavy chains and identical light chains (monospecific), in spite of the patent claiming bispecific antibodies having different heavy chains and/or light chains.  The District court found estoppel based on Applicant’s amendment of “antibody derivative” to “antibody fragment” to address the Examiner’s enablement rejection.  The Fed. Cir’s. de novo review found the plain language of antibody to cover monospecific and bispecific antibodies, citing the dependent claim as specifically reciting a bispecific antibody.  The district court’s construction excluded many of the antibodies of the dependent claims and thus was inconsistent with the plain claim language.  The Fed. Cir. emphasized that claim construction requires consideration of the specification as a whole, rather than on an excerpt in isolation.  The Fed. Cir. found the change from “antibody derivative” to ”antibody fragment” to be a substitution of a known term for one less commonly used, as suggested by the Examiner.  Practice tip: Dependent claims are not just for validity.