Upholding summary judgment of no literal infringement, the U.S. Court of Appeals for the Federal Circuit reversed summary judgment of non-infringement under the doctrine of equivalents reasoning that the accused tumor diagnostic fell within a grey area, which the district court failed to consider. Goldenberg v. Cytogen, Inc., Case No. 03-1409 (Fed. Cir. June 23, 2004) (Gajarsa, J.) (Prost, J., concurring-in-part, dissenting-in-part).
Immunomedics sued Cytogen alleging infringement of U.S. Pat. No. 4,460,559 (the `559 patent) both literally and under the doctrine of equivalents. The claimed invention is directed to a method for detecting tumors by targeting intracellular marker substances associated with tumor cells using a radio labeled antibody. Cytogen’s ProstaScint targets tumors using an antibody specific to an intracellular portion of prostate specific membrane antigen (PSMA), and a transmembrane antigen having both an intracellular and extra cellular domain.
The district court construed the term "intracellular marker substance" to mean an antigen existing within a cell, relying on the intrinsic record repeatedly distinguishing intracellular antigens from cell surface antigens. Granting summary judgment of non-infringement, the district court characterized PSMA to be a cell surface antigen, finding it to be outside the literal scope of the claims. Immunomedics’ argument that PSMA could be both a cell surface and intracellular marker substance was found insufficient to show equivalence because it did not address the distinction between cell surface and intracellular antigens.
Affirming the district court’s construction, the Federal Circuit rejected interpretations that included portions of an antigen located inside a cell, reasoning in part, that the `559 patent describes 26 antigens wholly within the cell and suitable as marker substances and is silent as to the use of antigen portions. Relying on dictionary definitions for the meaning of "intracellular," the Court concluded that an intracellular marker substance must be wholly internal to a cell, affirming no literal infringement because PSMA does not exist wholly within a cell.
Reversing summary judgment of no infringement by equivalence the Court rejected the view that antigens are categorized as either cell surface or intracellular and that an antigen not falling into either category such as PSMA cannot be an equivalent as a matter of law. The Court reasoned that transmembrane antigens appear to be in a category not addressed by the `559 patent and PSMA could be found an equivalent to either category. Finding that Immunomedics presented a sufficient factual dispute, i.e., whether the PSMA-specific antibody in ProstaScint functioned to target a tumor cell by binding to an antigen located in a cell, the Court remanded the case for further proceedings.
Concurring on the issue of equivalents infringement, Judge Prost dissented with respect to the issues of claim construction and no literal infringement. Viewing references to subunits in the patent as a fragment, Judge Prost’s claim construction would encompass portions of an antigen located inside the cell.
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