By Jason Rantanen
Biogen Idec, Inc. v. Glxosmithkline (Fed. Cir. 2013)
Download Biogen v GSK
Panel: Dyk, Plager (dissenting), Reyna (author)
By the mid-1990's, it was well known that rituximab, an anti-CD20 antibody, could be used to treat certain cancers of the lymph nodes such as non-Hodgkins lymphoma. The anti-CD20 antibody binds to a portion of the CD20 antigen protein exposed on the cell surface and destroys the cell. Scientists from Biogen discovered that patients with another type of cancer, Chronic Lymphocytic Leukemia (CLL), could also be treated using anti-CD20 antibodies. Based on this discovery, Biogen obtained Patent No. 7,682,612. Claim 1 of the '612 patent reads:
1. A method of treating chronic lymphocytic leukemia in a human patient, comprising administering an anti-CD20 antibody to the patient in an amount effective to treat the chronic lymphocytic leukemia, wherein the method does not include treatment with a radiolabeled anti-CD20 antibody.
Biogen filed the application leading to the '612 patent in the late 1990s. At the time, scientists believed that only one large loop, or epitope, of the CD20 antigen was exposed on the cancerous cell's surface and that this was the only site that for an anti-CD20 antigen to bind to. Rituximab binds to this epitope. After Biogen filed its application, other scientists discovered that the CD20 antigen had a second small loop (originally thought to be hidden inside the cell) to which other, different anti-CD20 antibodies could bind. In 2002, Glaxosmithkline (GSK) developed a new anti-CD20 antigen that binds to the small loop. Because it binds to a different epitope, GSK's anti-CD20 antibody has different specificity and affinity characteristics than rituximab.
Biogen sued GSK for infringement of the '612 patent in 2010. The district court construed anti-CD20 antibody to mean "rituximab and antibodies that bind to the same epitope of the CD20 antigen with similar affinity and specificity as rituximab." Based on this construction, Biogen stiplated to noninfringement and appealed.
Prosecution History Disclaimer: The issue on appeal involved the the doctrine of prosecution history disclaimer. Prosecution history disclaimer applies when a "patentee unequivocally and unambiguously disavows a certain meaning to obtain a patent." Slip Op. at 8. In this circumstance, the doctrine "narrows the meaning of the claim consistent with the scope of the claim being surrendered," id. overcoming even the term's ordinary and customary meaning. Application of the doctrine helps serve a public notice function by allowing the public and competitors rely on definitive statements made during prosecution when launching a new product or designing-around a patented invention.
During an early stage of the prosecution of the '612 patent, the examiner rejected the presented claims on enablement grounds:
Claims 1 and 12 are broadly drawn to ‘. . . an anti-CD20 antibody or fragment thereof’. This is
broadly interpreted for examination purposes to be any and all anti-CD20 antibodies, no matter
the specificity or affinity for the specific epitope on the circulating tumor cells. While the specification is enabling for the application of RITUXAN®, RITUXIMAB® and 2B8-MX-DTPA in the treatment of hematologic malignancies, the specification is not enabling in the application of all other anti-CD20 antibodies, which may have different structural and functional properties.
In response, the applicant wrote:
Applicants respectfully submit 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. . . . With that knowledge in hand, the skilled artisan could readily produce anti-CD20 antibodies using similar techniques, and screen such antibodies for those having an affinity and functional activity similar to Rituxan®
Based on this exchange in the context of the prosecution history read as a whole, the majority agreed with the district court that prosecution disclaimer applied to limit the scope of "anti-CD20 antibody." "[R]ather than challenging the examiner’s understanding of the crucial terms, the applicants argued that the specification was enabling for anti-CD20 antibodies with similar affinity and specificity as Rituxan®." Slip Op. at 10. Nor was exact recitation of the examiner's own words necessary: "While disavowing statements must be “so clear as to show reasonable clarity and deliberateness,” Omega, 334 F.3d at 1325, this requirement does not require the applicant to parrot back language used by the examiner when clearly and deliberately responding to a particular grounds for rejection. If an applicant chooses, she 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." Slip Op. at 11.
Hierarchy of canons of claim construction: In the hierarchy of canons of claim construction, prosecution history disclaimer trumps the presumption of claim differentiation: "Our cases make clear  that where found, prosecution history disclaimer can overcome the presumption of claim differentiation." Id. at 12 (note that the court said "can overcome," leaving open a door for cirucumstances in which it might not).
Dissent: Writing in dissent, Judge Plager disagreed that this was an instance of prosecution history disclaimer. "[T]he give-and-take that is often part of the process of negotiation between an examiner and an applicant may result in less-than-clear understandings, as happened here. Making too much of such ambiguous statements 'does not advance the patent’s notice function or justify public reliance.'" Slip Op. at 16. For Judge Plager, the question is thus "whether the prosecution history makes it clear that using RITUXAN® [Biogen's branded version of rituximab]-like antibodies is the only way to practice the claimed invention, and that no other antibodies can be used." Id. In his view, the above quoted statements fail to meet the "clear and unmistakable" standard required for prosecution history estoppel.
The avoided question: By affirming the district court's claim construction, the CAFC avoided a battle over an extremely challenging issue: enablement in the context of after arising technologies and knowledge. Biogen's proposed construction was "an antibody that binds to a cell surface CD20 antigen." This construction would presumably encompass methods using antibodies that bind to the larger epitope (which Biogen discovered) as well as antibodies that bind to the smaller epitope (which Biogen did not). Since enablement is determined as of the filing date, this presents the classic patent law hypothetical: Inventor X invents one way of curing a type of cancer and then claims simply "a cure for cancer." Should inventor X be entitled to the claim? She's cured cancer, after all.