April 29, 2013

ARZERRA better way to respond?

Prosecution history estoppel in light of Biogen v. GlaxoSmithKline

          On April 16, 2013, the Federal Circuit affirmed a grant of summary judgment to GlaxoSmithKline (GSK) in a dispute with Biogen Idec over GSK’s Arzerra® treatment for chronic lymphocytic leukemia (CLL). The case’s holding, regarding prosecution history estoppel, has unsettling implications for patent prosecutors.

Biogen owns U.S. Patent No. 7,682,612 (‘612), which claims “[a] method of treating [CLL] in a human patient, comprising administering an anti-CD20 antibody…” At the time that Biogen filed the application for ‘612, only one region of CD20 was known to be susceptible to inhibition with antibodies, and Biogen’s Rituxan® is directed to that particular region. Subsequently, a second, smaller region of CD20 was discovered also to be susceptible to therapeutic inhibition. GSK’s Arzerra® is directed to this second region. In March 2010 Biogen sued GSK, alleging that Arzerra® infringed ‘612.

In a Markman hearing, Judge Roger Benitz of the Southern District of California ruled that the claim term “anti-CD20 antibody,” meant “rituximab and antibodies that bind to the same epitope of the CD20 antigen with similar affinity and specificity as rituximab,” the meaning suggested by GSK. Biogen v. GlaxoSmithKline, No. 10-CV-00608, 2011 U.S. Dist. LEXIS 120043, at *31 (S.D. Cal. Oct. 17, 2011). Biogen had proposed the more intuitive construction, “an antibody that binds to a cell surface CD20 antigen.” Id.

          The district court arrived at this less intuitive construction of “anti-CD20 antibody” based on an exchange between Biogen and the PTO during prosecution. The first Office Action rejected all of Biogen’s claims because Claim 1 was “drawn to ‘… an anti-CD20 antibody or fragment thereof.’” Under the PTO’ s “broadest reasonable interpretation” standard, “anti-CD20 antibody” was interpreted as “any and all anti-CD20 antibodies, no matter the specificity or affinity for the specific epitope on the circulating tumor cells.” The PTO conceded that “the specification is enabling for the application of RITUXAN®, RITUXIMAB® and 2B8-MX-DTPA in the treatment of hematologic malignancies,” but insisted that the disclosure did not enable treatment with “all other anti-CD20 antibodies, which may have different structural and functional properties.”

Biogen responded, not by amending the claims, but instead by arguing that “even though antibodies directed to the same antigen might have different affinities and functional characteristics, one of skill in the art could readily identify an antibody that binds to CD20 with similar affinity and specificity as does RITUXAN® using techniques that are well known in the art.” From this response, the district court concluded that Biogen was estopped from arguing that “anti-CD20 antibodies” meant anything other than “antibodies that bind to CD20 with similar affinity and specificity as does RITUXAN®.” Biogen stipulated that if this definition were used, GSK’s Arzerra® did not infringe. On this basis, the district court granted summary judgment of non-infringement and Biogen appealed to the Federal Circuit. Biogen v. GlaxoSmithKline, No. 2012-1120, slip op. at 7 (Fed. Cir. Apr. 16, 2013).

On appeal, Biogen offered two arguments as to why the Markman construction of “anti-CD20 antibody” was wrong:

(1) Under the standard set forth in Omega Eng’g. v. Raytek Corp., 334 F.3d 1314, 1323, 1326 (Fed. Cir. 2003), a patentee can only cede claim scope by a “clear and unmistakable” disavowal. Biogen argued that nothing in the quoted exchange between Biogen and the PTO rises to the level of a “clear and unmistakable” disavowal; and

(2) ‘612 had incorporated U.S. Patent No. 5,736,137 (‘137) by reference, and ‘137 says that “[a]s used herein, the term ‘anti-CD20 antibody’ is an antibody which specifically recognizes a cell surface non-glycosylated phosphoprotein of 35,000 Daltons… commonly referred to as CD20.” Therefore, Biogen argued, the explicit definition of “anti-CD20 antibody” in ‘137 should control.

In response to (1) Judges Reyna and Dyk held that the exchange between Biogen and the PTO was a “clear and unmistakable” disavowal of claim scope. Slip op. at 11. If this seems a surprising result, the majority notes that an applicant “can challenge an examiner’s characterization in order to avoid any chance for disclaimer, but the applicants in this case did not directly challenge the examiner’s characterization.” Id. Judge Plager’s dissent contends that “the applicants’ response was at worst a non-response to the examiner’s concern, and at best a statement that antibodies other than RITUXUN®[sic] and RITUXUN®[sic]-like antibodies that had similar affinity and specificity are included in the claims.” Slip op. at 17–18. A dissent, however, is not law. Evidently, going forward, applicants must make clear to disagree explicitly with an examiner’s characterization of enablement, or risk the possibility that an ambiguous response will constitute a disavowal of claim scope. It appears that the bar is falling for what can constitute “clear and unmistakable” disavowal.

Regarding argument (2), the majority held that ‘137’s “as used herein” language means that the definition applies only to the interpretation of ‘137. Slip op. at 13. The dissent pointed out that by incorporating ‘137 by reference, the ‘612 patent essentially includes all of ‘137’s text, so that the “herein” should apply to ‘612 as well, but the majority confined the “herein” to ‘137. Slip op. at 21. Patent drafters should keep this in mind in future. If one hopes to rely on a definition, one must set it forth in the patent text, and not merely rely on the presence of the definition in other patents or priority documents which are incorporated by reference.

The above article was written by Greg DeLassus, an associate in the St. Louis, MO office of Harness Dickey.  Greg can be reached at 314.446.7687 or gdelassus@hdp.com.