AIPLA Files Amicus Brief with Court of Appeals for the Federal Circuit in In re: Xencor, Inc.

On October 6, 2023, the American Intellectual Property Law Association (AIPLA) filed an amicus brief with the Court of Appeals for the Federal Circuit in In re: Xencor, Inc., a case on appeal from the U.S. Patent and Trademark Office’s Patent Trial and Appeal Board. The case concerns the Board’s rejection of patent claims directed to a treatment method involving administration of an antibody containing certain amino acid substitutions that increase the antibody’s half-life. The Board rejected the claims for lack of written description and as indefinite.

AIPLA’s amicus brief addresses the Board’s analysis of a means-plus-function claim directed to the treatment method. Xencor had argued that the specification discloses a specific antibody that corresponds to the recited means and that its structure is sufficiently described because the antibody was known in the art at the time of the invention. The Board rejected Xencor’s argument that the specification discloses any structure embodying the claimed “means for binding” a particular protein. The Board offered commentary on the written description requirement for means-plus-function claims, noting such claims, by statute, are construed to cover “equivalents” of structures disclosed in the specification, and therefore are “genus claims.” The Board then noted that, even if the specification had sufficiently disclosed the specific antibody as Xencor had argued, this one structure may not satisfy the written description requirement because the claimed means was not restricted to this specific antibody.

In its brief, AIPLA urges the Federal Circuit not to adopt a bright-line rule that disclosure of an antibody’s structure is insufficient to support a means-plus-function claim merely because under Section 112(f) the “means” element includes “equivalents” of the disclosed structure(s).  The brief explains that existing precedent analyzing structural equivalents, both under Section 112(f) and under the closely-related doctrine of equivalents, provides a framework for determining structural equivalence in the antibody context. The brief further argues that allowing means-plus-function claiming in the antibody space (or any other technology field) advances sound patent policy—it provides patentees protection from unscrupulous copyists and yet it does not preclude innovators from developing their own novel means to achieve the claimed function in a different or improved way.