Be careful what you wish for: Method of treatment claim for an antibody genus found to satisfy both written description and enablement requirement (Teva v Eli Lilly)
Rose Hughes
Be careful what you wish for: Method of treatment claim for an antibody genus found to satisfy both written description and enablement requirement (Teva v Eli Lilly)
In a remarkable departure from what we might have expected it to do following Amgen v Sanofi, the US Court of Appeals of the Federal Circuit in Teva v Eli Lilly upheld a jury verdict finding that a method of treatment claim for a broad genus of antibody satisfied both the written description and enablement requirement. The Federal Circuit found a clear distinction between these requirements as applied to antibody claims per se (as in Amgen v Sanofi), and method of treatment claims for a known genus of antibodies. There is a lot to unpack in this case, but at the end we are left with the question of whether the decision signals the start of a shift in US patentability requirements for antibodies towards a more EPO-style approach.
Legal background: Written description and enablement of antibody claims
In the US, a patent specification must contain a "written description" of the invention, and of the manner and process of making and using it, in such full, clear, concise, and exact terms as to "enable" any person skilled in the art to make and use the same (35 U.S.C. § 112).
The written description requirement has been understood by the US courts as requiring the patent specification to describe the invention such that it reasonably conveys to a skilled person that the inventor had possession of the claimed subject matter as of the filing date. For a functionally-defined genus, this typically requires disclosure of a representative number of species. The enablement requirement requires that the specification teaches those skilled in the art how to make and use the full scope of the claimed invention without undue experimentation.
Both the written description and enablement requirement have been interpreted very strictly in the US, particularly as applied to antibody inventions defined by broad functional definitions, such as binding of a genus of antibodies to a particular epitope (IPKat). The US Supreme Court decision in Amgen v Sanofi was broadly understood as ruling out claims of this type for antibodies and other biologics.
The US versus European approach to functional antibody claims
In contrast to the US, the EPO Boards of Appeal have still been broadly happy in recent years to uphold broad antibody claims without any structural or sequence limitations. At its heart, the divergence between the US and Europe hinges on differing interpretations of what constitutes routine work by a skilled person.
In the US, a functional genus of a biologic might be considered to lack enablement due to an unpredictable and very high number of candidates. This was a key justification presented by the Supreme Court for its finding lack of enablement in Amgen v Sanofi. The Supreme Court cited an analogy whereby the process of antibody discovery was compared to trying to find all the combinations of a "combination lock with 100 tumblers, each of which can be set to 20 different positions." By contrast, in Europe, the time required for a skilled person to find all of the possible antibodies within a broad claim does not translate into a fundamental lack of sufficiency if the necessary assays for testing the antibodies are available to the skilled person.
Case background: Antibody headaches
The case in Teva v Eli Lilly involved Teva's patents US 8,586,045, US 9,884,907 and US 9,884,908. The patents related to methods of using humanised anti-CGRP antagonist antibodies to treat headache. The patents included, for example a claim for "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.", i.e. a method of treatment claim not limited to any particular antibody sequence.
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| Antibody headaches |
Teva sued Eli Lilly alleging that the sale of Eli Lilly's blockbuster migraine medication, Emgality (galcanezumab), infringed the patents. Teva itself markets a competing humanised anti-CGRP monoclonal antibody under the brand name Ajovy (fremanezumab). The antibodies have different sequences but bind the same CGRP target.
At trial, the jury found that Eli Lilly wilfully infringed the claims and failed to prove them invalid. However, the District Court granted Judgment as a Matter of Law (JMOL) that the claims were invalid for lacking both written description and enablement. Teva appealed this decision to the Federal Circuit.
Written description: Humanisation is routine
On Written description, Eli Lilly argued that the specification failed to disclose a representative number of species of the claimed genus of humanised anti-CGRP antagonist antibodies, noting that only one humanised version was disclosed. Following Amgen v Sanofi, we might broadly expect such an attack to succeed.
However, applying the case law from Herschler (In re Herschler, 591 F.2d 693 (CCPA 1979)) and Ajinomoto (Ajinomoto Co. v. ITC, 932 F.3d 1342 (Fed. Cir. 2019)), the Federal Circuit distinguished between claims to a genus itself and claims drawn to the use of a known genus as part of a different invention. The Federal Circuit observed that a reasonable jury could have found that anti-CGRP antagonist antibodies and methods of making them were well known in the prior art and, significantly, that humanisation was a routine procedure. Additionally, the Federal Circuit reasoned that a jury would have found that a skilled artisan would understand from the specification that all humanised anti-CGRP antagonist antibodies treat headache. For this Kat, this is a remarkable departure from what we usually expect to see from the Federal Circuit with respect to written description and antibody genus claims.
Enablement: All humanised antibodies would work and making more would be extra credit
Turning to enablement, Eli Lilly argued that the claims were not enabled because of the very large number of possible candidate antibodies defined by the claim. As such, Eli Lilly argued, the specification left the skilled artisan with a "research assignment" of screening and testing candidates to determine which antagonise CGRP, amounting to undue experimentation.
The Federal Circuit rejected this argument and notably distinguished the case from Amgen v Sanofi (IPKat) and Idenix (Idenix Pharmaceuticals LLC v. Gilead Sciences Inc. (941 F.3d 1149)). The Federal Circuit's reasoning once again hinged on the fact that the claims were not to the antibodies themselves, but to methods of treating headache. The court particularly found that:
"Given that anti-CGRP antagonist antibodies (and methods of making them) were already well known, humanizing them would have been routine, such humanized antibodies themselves are not claimed here, and all of them work in the claimed method, 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 Federal Circuit thus concluded that JMOL of no enablement was improper. Crucially, this conclusion was dictated by the procedural standard. Because it was undisputed that a reasonable jury could have found that all humanised anti-CGRP antagonist antibodies treat headache, the court concluded that no extensive, undue screening was legally required.
The European perspective: Composition of matter versus medical use
Interestingly, the case law in Europe demonstrates the risks of relying on broad functional definitions for a therapeutic molecule in a claim directed to use in a method of treatment. The EPO requires that a claimed therapeutic effect be credible across the entire scope of the claim. As such, claims that define the therapeutic molecule with a broad functional definition may be vulnerable to attack in light of post-published data that undermines the link between the broad claim and the purported technical effect (IPKat). This principle was recently demonstrated in T 0709/23 relating to treating itch in cats. In this case, the Patentee's own post-published data revealed that an antibody falling within the broad functional claim did not actually provide the claimed therapeutic effect (IPKat).
In this context, the Federal Circuit's reasoning in the present case that "a skilled artisan would have understood from the specification that all humanised anti-CGRP antagonist antibodies treat headache" is notable. Broad claims such as this are possible in Europe, however the applicant must convince the EPO that claimed therapeutic effect is credible over the whole scope of the claim. In Europe, the question would be asked whether a skilled person would have substantiated doubt that all possible anti-CGRP antagonist antibodies really would treat headache, in view of the data provided in the application as filed.
The value of broad method of treatment patents
In Amgen v Sanofi, the Supreme Court famously confirmed that "the more a party claims for itself the more it must enable". In this context, a method of treatment patent such as that at issue in Eli Lilly v Teva will be narrower than a product patent like that in Amgen v Sanofi. However, method of treatment patents can themselves be very broad.
Undoubtedly, a claim to a method of treatment will generally be considered less valuable than a product claim, given that a product claim will protect the product for any indication, whereas method of treatment claims protect only that particular use. However, method of treatment claims will often expire far later than the original composition of matter patent, and can be used to protect the main (or even only) commercialised indication for the drug product. A method of treatment claim not limited by sequence can also protect not only your product but also competitor products binding the same target for the same indication, and thereby prevent market erosion from both biosimilars and fast-follower competition. It is curious therefore that the Federal Circuit in Teva v Eli Lilly considers a different enablement standard to apply to method of treatment claims for a broad genus of antibodies.
Final thoughts
Importantly, the Federal Circuit was not making its own independent, matter-of-law factual findings regarding antibody science. Rather, it was reviewing the District Court's grant of JMOL which overturned the original jury verdict. Therefore, the question for the Federal Circuit was whether a reasonable jury could have concluded that Eli Lilly failed to meet this high evidentiary burden.
Nonetheless, Teva v Eli Lilly represents a remarkable shift away from the "undue experimentation" test emphasised in Amgen v Sanofi. To this Kat, the reasoning that anti-CGRP antagonist antibodies were already known doesn't justify the difference of approach for product versus method of treatment claims, from a scientific perspective. Methods and assays for making new antibodies for a known target are not affected by how many existing antibodies happen to have been disclosed. If the genus comprises millions of possible antibodies, a few hundred antibodies having been disclosed in the art is a drop in the ocean. The disclosure of these few antibodies doesn't fundamentally affect (or speed up) the skilled person's ability to make all the new antibodies falling under the broad genus. Furthermore, finding antibodies binding a particular target that are also effective at treating a particular disease is much harder, requiring far more experimentation, than finding antibodies that merely bind the target.
Finally, when it comes to antibody inventions, we must be careful what we wish for. Whilst many in the field have lamented the difficulty of claiming anything other than specific antibody sequences following Amgen v Sanofi, the US has nonetheless maintained a more lenient attitude to the non-obviousness of antibody inventions than the EPO. In Europe it is becoming increasingly difficult to patent any antibody, even when the claims are limited to the full binding sequence of the lead antibody, in view of the EPO's requirement that the invention solves a technical problem in view of prior art antibodies. The EPO argues that generating antibodies to a known target is routine. It is therefore generally easier to get a patent covering your lead antibody in the US than it is in Europe. However, the fact that the Federal Circuit allowed a jury verdict to stand on the premise that humanising antibodies to a known target is "routine" potentially foreshadows a shift by the US in a more European-like direction.
In light of this, as a general principle, before filing a patent application for an antibody or genus of antibodies, it is always good idea to establish why what you have is actually an invention and what problem you have solved, regardless of your jurisdictions of interest.
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- Will functional antibody inventions find new life in the US with mean-plus-function claims? (Ex parte Chamberlain, Appeal No. 2022-001944) (Jun 2024)
- UPC takes strong stance on therapeutic antibody inventions (Sanofi v Amgen, UPC_CFI_1/2023) (July 2024)
- Patentee's own post-published data undermines the credibility of their broad cat antibody patent (T 0709/23) (Oct 2025)
- EPO pharma case law trends 2025: Antibodies and biologics (Nov 2025)
- UPC Court of Appeal tackles broad functional antibody claims (UPC_CoA_529/2024) (1 Dec 2025)