Key Takeaways
- The written description and enablement analyses are context-dependent; claim type may affect the written description and enablement analyses.
- Biotechnology companies should think beyond composition of matter claims and develop strategies to prosecute method of treatment claims that are sufficiently supported by the specification.
- Be mindful of the interplay between different patent proceedings. Lilly's own prior statements that anti-CGRP antagonist antibodies were "well known" and "replete" in the prior art, made during IPR proceedings to invalidate Teva's composition claims, were used against Lilly in this district court litigation to support the validity of Teva's method claims.
On April 16, 2026, the United States Court of Appeals for the Federal Circuit issued a decision in Teva Pharmaceuticals International GmbH v. Eli Lilly and Company, No. 2024-1094, applying the written description and enablement requirements under 35 U.S.C. § 112 to claims directed to the use of a genus of antibodies to treat headaches. The opinion, authored by Judge Prost, reversed the district court's grant of judgment as a matter of law ("JMOL") of invalidity and reinstated a jury verdict that had found Teva's headache-treatment patents valid and willfully indirectly infringed by Lilly via its Emgality® product.
Background: The Headache Patents and the Antibody Patents
At trial, Teva asserted three patents (the "headache patents") that claim methods of treating headache by administering humanized anti-CGRP antagonist antibodies. For example, one asserted claim recites "[a] method for reducing incidence of or treating headache in a human, comprising administering to the human an effective amount of an anti-CGRP antagonist antibody, wherein said anti-CGRP antagonist antibody is a . . . humanized monoclonal antibody."
Notably, Teva also held a separate group of patents, the "antibody patents," which claimed humanized anti-CGRP antagonist antibodies themselves. In inter partes review proceedings before the Patent Trial and Appeal Board (the "Board"), Lilly successfully challenged the antibody patents as unpatentable for obviousness. In doing so, Lilly argued to the Board that anti-CGRP antagonist antibodies were "well known in the art," that the prior art was "replete with exemplary disclosures" of such antibodies, and that humanization "was a well-established and routine procedure" by the November 2006 priority date. The Board found the antibody patents' claims unpatentable, and the Federal Circuit affirmed. The headache patents, however, survived the IPR proceedings.
The District Court's JMOL of Invalidity
At trial in the District of Massachusetts, a jury found that Lilly willfully infringed the headache patents and failed to prove the asserted claims invalid for lack of written description or enablement. Lilly then moved for JMOL of invalidity, which the district court granted, concluding as a matter of law that the claims were invalid for failure to meet the written description and enablement requirements of § 112. The district court acknowledged that the jury could have permissibly found that murine anti-CGRP antagonist antibodies were known in the art, that humanization was routine, and that a person of ordinary skill would have understood from the specification that all humanized anti-CGRP antagonist antibodies would treat headache. However, the district court concluded that the claims were invalid because the specification’s disclosure of only one humanized anti-CGRP antagonist antibody was insufficient to demonstrate written description of the entire genus of antibodies recited in the claims, and excessive experimentation was needed because the actual number of humanized antibodies that could antagonize CGRP was unknowable, rendering the claims invalid for lack of enablement.
The Federal Circuit's Written Description Analysis
In reversing the district court’s grant of JMOL, the Federal Circuit relied on precedent involving a claim that “pertains to a well-known genus that is not, itself, the invention.”
First, in Ajinomoto Co. v. ITC, 932 F.3d 1342 (Fed. Cir. 2019), the Federal Circuit found that a claim covering a method of producing particular amino acids from a bacterium having “a more potent promoter” for a particular gene met the written description requirement. The court explained that the patent's invention was the identification of a specific gene function, not the well-known techniques for enhancing that function with more potent promoters, and that "the genus of more potent promoters was already well explored" in the art.
Second, in In re Herschler, 591 F.2d 693 (CCPA 1979), the Court of Customs and Patent Appeals (the Federal Circuit’s predecessor) found adequate written description for a method claim directed to enhancing skin penetration with a genus of steroidal agents, even though only one species was disclosed, because a skilled artisan would have understood that any member of the genus would work in the claimed method. The Herschler court repeatedly distinguished between claims to a genus itself, particularly a novel one, and claims involving a known genus used as part of a different invention.
Third, the plurality opinion in In re Fuetterer, 319 F.2d 259 (CCPA 1963), found that a claim to a composition for tire-tread stock complied with § 112. The claimed composition included “an inorganic salt that is capable of holding a mixture . . . . in colloidal suspension in water.” The Patent and Trademark Office rejected the claim because not all inorganic salts have this function. In upholding the claim, the CCPA emphasized that the invention was the combination of recited components, not the discovery that certain inorganic salts have colloid-suspending properties.
Applying this framework, the Federal Circuit held that the headache patents "make clear that their claimed invention is the use of anti-CGRP antagonist antibodies, or humanized versions thereof, to treat headache—not such antibodies themselves." The court found that a reasonable jury could have concluded that anti-CGRP antagonist antibodies and methods of making them were well known, that humanization was routine, and that a skilled artisan would have understood from the specification that all humanized anti-CGRP antagonist antibodies treat headache. Based on these findings, the specification's disclosure of several murine antibodies, one humanized antibody (G1, the active ingredient in Teva's Ajovy® product), and prior-art humanization methods were sufficient to constitute a representative number of species for purposes of the claimed method.
Distinguishing the Composition-Claim Precedent
Lilly argued that the distinction between method claims and composition claims was "a semantic distinction without a difference," relying on University of Rochester v. G.D. Searle & Co., 358 F.3d 916 (Fed. Cir. 2004), and Ariad Pharmaceuticals, Inc. v. Eli Lilly & Co., 598 F.3d 1336 (Fed. Cir. 2010) (en banc). The Federal Circuit disagreed. The court explained that in Rochester, the specification "did not disclose any compounds usable in the claimed methods, nor was there any evidence that such compounds were known," and in Ariad, the specification likewise failed to adequately disclose the molecules recited in the method claims. The court noted that neither case involved claims that recite a well-known genus used as part of a different invention.
The court also rejected Lilly’s argument (relying on AbbVie Deutschland GmbH & Co. v. Janssen Biotech, Inc., 759 F.3d 1285 (Fed. Cir. 2014)) that the written description requirement demands disclosure of an antibody structurally similar to the accused product. The court observed that the representativeness inquiry "accounts for the specific circumstances of the invention" and that AbbVie did not involve a well-known genus used as part of a different invention.
Enablement: Method Claims Survive Where Composition Claims May Not
The Federal Circuit's enablement analysis followed a parallel logic. Lilly's primary argument was that the number of candidate antibodies for the genus of humanized anti-CGRP antagonist antibodies was very large and that the specification did not teach a skilled artisan how to determine in advance which ones would antagonize CGRP, leaving only a burdensome "research assignment" of screening and testing.
The court acknowledged that this argument "might be more persuasive if the asserted claims were to the genus of humanized anti-CGRP antagonist antibodies themselves" and noted that such a case would resemble Amgen Inc. v. Sanofi, 598 U.S. 594 (2023), where the Supreme Court found composition claims to a genus of antibodies non-enabled because the specification failed to teach a skilled artisan how to find the claimed antibodies without unreasonable experimentation. Similarly, in Baxalta Inc. v. Genentech, Inc., 81 F.4th 1362 (Fed. Cir. 2023), composition claims with "materially indistinguishable" facts from those in Amgen were found non-enabled.
The Federal Circuit determined that the headache patents' method claims are different. Because the claims are directed to the use of humanized anti-CGRP antagonist antibodies for treating headache, "the more relevant 'research assignment' in this case would have been determining which humanized anti-CGRP antagonist antibodies treat headache." According to the court, that assignment was completed: the specification disclosed that all such antibodies work for that purpose. The court concluded that, given the well-known status of the antibodies and the routine nature of humanization, "undertaking to find or make all of them would—in the context of these claims—be more akin to extra credit than a necessary research assignment left to others to complete."
The court also distinguished Idenix Pharmaceuticals LLC v. Gilead Sciences Inc., 941 F.3d 1149 (Fed. Cir. 2019), a case in which a claim to a method of using a genus of nucleosides to treat hepatitis C was found not enabled because the evidence failed to support a finding that all members of the genus were effective for that purpose. In contrast, it was undisputed that a reasonable jury could have found that all humanized anti-CGRP antagonist antibodies recited in the headaches patents would work to treat headache.
On June 17, 2026, Eli Lilly filed a Petition for Rehearing En Banc in the Federal Circuit. We will continue to monitor developments in this litigation.
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