by Chris Holman
ImmunoGen, Inc. v. Hirshfeld, 2022 WL 885774, (Fed. Cir. Mar. 25, 2022) (nonprecedential)
The patent application at issue in this case claims a method of treating a cancer patient by administering mirvetuximab (an immunoconjugate drug) “at a dose of 6 milligrams (mg) per kilogram (kg) of adjusted ideal body weight (AIBW) of the patient.” The purported invention arose out of the discovery that administration of mirvetuximab at the recited dosage significantly reduces the severe ocular side effects that were observed during Phase 1 clinical trials when the drug was administered at a dose of 7 mg per kg of the patient’s total body weight (“TBW”). After the Patent Trial and Appeal Board (“Board”) affirmed the examiner’s rejection of the pending claims for obviousness and obviousness-type double patenting, the applicant (ImmunoGen) filed a § 145 suit in the Eastern District of Virginia challenging the rejections. The district court determined on summary judgment that the claims are “fatally indefinite and fatally obvious” as a matter of law. On appeal, the Federal Circuit vacated the grant of summary judgment and remanded for further proceedings.
The district court’s indefiniteness ruling was based on the claims’ recitation of “AIBW,” a term which the court found was not defined in the application in manner that would inform a skilled artisan, with reasonable certainty, as to the scope of the invention (the Nautilus standard). The application defines AIBW as “a size descriptor that accounts for sex, total body weight, and height.” It further defines ideal body weight (“IBW”), which is used to calculate AIBW, as “an estimate of weight corrected for sex and height, and optionally frame size.” The AIBW and IBW definitions each includes a specific formula, introduced by the phrase “for example,” for calculating the respective values.
The formulas are reproduced below in the form of equations:
AIBW = IBW + 0.4(Actual weight in kg – IBW)
IBW (male) = 0.9(Height in centimeters) – 88
IBW (female) = 0.9(Height in centimeters) – 92
These “example” formulas were also reproduced in Example 4 of the application, which relates to the dosing of mirvetuximab.
In support of its decision finding the claims indefinite, the district court relied primarily on the fact that the definitions section of the application preceded the AIBW formula with the language “for example,” which the court found “ma[de] clear that there are multiple ways to calculate AIBW,” thereby “leav[ing] a skilled artisan to wonder or to guess whether the formula provided is the only one covered by the ’809 Application.” This uncertainty was, in the view of the district court, compounded by: (1) similar “for example” language accompanying the IBW formula; (2) the disclosure that IBW corrects “for sex and height, and optionally frame size”; and the incorporation by reference in its entirety of “Green,” an article that discloses several methods for calculating IBW and lists correction factors, each specific to a different drug, that can be used to adjust IBW to AIBW.
On appeal, the Federal Circuit found that the material factual findings underlying the district court’s definiteness ruling were far from undisputed. In particular, ImmunoGen had identified other intrinsic evidence a skilled artisan would consider in determining the scope of the claims, including that: (1) the claims and specification are drawn to a specific dosing regimen for a specific immunoconjugate, which is significant in light of expert testimony that the correction factor used to calculate AIBW is drug-specific; (2) Example 4 describes dosing mirvetuximab in accordance with the claimed method and uses the same AIBW and IBW formulas disclosed in the definitions section; and (3) during the prosecution of the ’809 Application, the USPTO never disputed the definiteness, or gave any indication it failed to understand the meaning, of the now-allegedly indefinite term. ImmunoGen also presented extrinsic evidence regarding the knowledge of a skilled artisan. For instance, both parties’ experts testified that AIBW dosing involves drug-specific formulas and correction factors.
The Federal Circuit also found that the district court had erred in concluding that there was no disputed question of material fact with respect to obviousness. It was undisputed that AIBW dosing had not previously been used for mirvetuximab, or for that matter any other immunoconjugate drug.
If on remand the court ultimately finds the claims indefinite for defining a critical claim limitation in terms of an “example,” it would not be the first time that the Federal Circuit has flagged this as an issue. In Interval Licensing LLC v. AOL, Inc., 766 F.3d 1364 (Fed. Cir. 2014), the Federal Circuit held claims invalid for indefiniteness because the specification failed to adequately define the claim limitation “unobtrusive manner that does not distract a user.” While “recognizing that a patent which defines a claim phrase through examples may satisfy the definiteness requirement,” the court “decline[d] to cull out a single “e.g.” phrase from a lengthy written description to serve as the exclusive definition of a facially subjective claim term.” The court observed that “[h]ad the phrase been cast as a definition instead of as an example—if the phrase had been preceded by “i.e.” instead of “e.g.”—then it would help provide the clarity that the specification lacks.”
Still, I think that Interval Licensing can be readily distinguished over ImmunoGen, in that Interval Licensing’s “unobtrusive manner that does not distract the user” claim limitation seems much more “facially subjective” than ImmunoGen’s “adjusted ideal body weight.”