Sanofi v Amgen: comparing antibody patent litigation at the UPC, EPO and in the United States

The long-running global dispute between Sanofi/Regeneron and Amgen over the validity of patents covering therapeutic antibodies against PCSK9, a key protein in cholesterol metabolism, has become a defining case study in biotechnology patent litigation across key jurisdictions.

With key decisions from the United States Supreme Court, the European Patent Office (EPO), and the Unified Patent Court (UPC), the dispute illustrates sharply contrasting approaches to broad functional antibody claims, and highlights evolving law that will influence future biotechnology innovations.

Background

The patents at issue relate to monoclonal antibodies that bind to proprotein convertase subtilisin/kexin type 9 (PCSK9), a key regulator of cholesterol metabolism. By blocking PCSK9’s interaction with LDL receptors (LDLRs) on liver cells, such antibodies increase LDL receptor recycling and reduce circulating LDL cholesterol.

Antibody innovation often involves identifying and characterising specific binding epitopes and functional blocking properties, and so patent claims are frequently drafted in broad functional or epitope-defined terms.

As such, the core legal issue across jurisdictions has been whether broad claims covering entire classes of antibodies, rather than specific sequences, satisfy the relevant patentability requirements.

United States: Enablement as the primary constraint

In the US, the dispute culminated in a landmark Supreme Court decision of Amgen Inc. v Sanofi, 598 U.S. 594 (2023).

The Court focused on the issue of enablement, the requirement under 35 U.S.C. § 112(a) that a patent specification describes the claimed invention sufficiently so that a person skilled in the art can make and use the invention without undue experimentation.

The Supreme Court unanimously held that Amgen’s broad functional claims were not enabled because the patent did not provide enough information to enable the full scope of all claimed antibodies beyond the specific examples disclosed. As the Court explained, claiming an “entire class” of antibodies and only disclosing a limited number amounted to “little more than…research assignments”.

The decision makes clear that in the US, broad functional antibody claims must be supported by a specification that enables their full scope, and that genus claims encompassing several undisclosed embodiments face substantial risk.

Whilst enablement is typically a challenge before the USPTO, with the skilled person needing to be provided with numerous examples, in Europe, Applicants and Proprietors typically find that inventive step is a greater hurdle as one skilled in the art would usually consider generating antibodies to be routine.

Europe: Inventive Step at the EPO and UPC

Europe offers two key venues to challenge patents: the EPO for opposition proceedings immediately post-grant, and the UPC, a centralised court system for infringement and revocation actions across participating EU states.

The EPO: The structured problem-solution approach

Sanofi and Regeneron opposed Amgen’s European Patent EP 3 666 797 before the EPO, challenging the validity of its medical use claims.

At the EPO, inventive step is assessed using the well-established problem-solution approach (PSA). This structured methodology requires identification of the closest prior art, formulation of the objective technical problem, and evaluation of whether the skilled person, starting from the closest prior art and faced with the objective problem, would have arrived at the claimed solution in an obvious manner.

Applying this approach, the EPO Opposition Division upheld the patent as granted, finding that the claimed antibodies were not rendered obvious by the prior art when analysed through the problem-solution approach. In particular, the Opposition Division framed the objective technical problem as not merely “providing anti-PCSK9 antibodies”, but more narrowly as providing antibodies with the claimed functional blocking properties that would be therapeutically effective. As such, they concluded that while the closest prior art (Lagace) “…provides a suggestion to use antibodies that block the interaction of PCSK9 to LDLR in the treatment of hypercholesterolemia, it does not provide the skilled person with a reasonable expectation of success that using said antibodies would be indeed therapeutically effective”. An appeal from this decision by the opponents is ongoing before the EPO’s Board of Appeal.

Unified Patent Court (UPC) Proceedings: A developing but converging approach

In parallel, Sanofi and Regeneron initiated revocation proceedings before the UPC against the same European patent.

First instance: Central Division revokes the patent

In July 2024, the UPC Munich Central Division rendered the first substantive revocation decision at the UPC (UPC_CFI_1/2023). It found Amgen’s ‘797 patent invalid for lack of inventive step. The court held that at the priority date, the development of therapeutic antibodies against PCSK9 would have been routine to a skilled person and thus not inventive over prior art teaching the value of targeting PCSK9.

While the decision referred to concepts familiar from an EPO perspective, it did not strictly adhere to the structured PSA, demonstrating the UPC’s willingness to apply its own procedural and substantive framework. In particular, the Central Division selected the “realistic starting point” as opposed to the “closest prior art”, and formulated the “underlying” technical problem rather than the “objective” technical problem. Furthermore, in contrast to the EPO’s Opposition Division, the Central Division held that generating and selecting the claimed antibodies was a “matter of routine” for the skilled person, and that they would have had a reasonable chance of success in obtaining the antibodies without involving an inventive step. Accordingly, the Central Division appeared to characterise the invention more broadly as the routine development of antibodies against a known target, compared to the EPO’s Opposition Division who focused more on the claimed functional and therapeutic properties of the antibodies. See our previous article, “Sanofi v Amgen: UPC revokes Amgen’s antibody patent in its first revocation order”, for a detailed analysis of the decision.

UPC Court of Appeal: Convergence with the EPO

On 25 November 2025, the UPC Court of Appeal overturned the revocation decision and held that Amgen’s antibody patent is valid (UPC_CoA_529/2024), with the appeal judgement confirming that the patent meets the requirements of novelty and inventive step. While the Court of Appeal did not formally adopt the EPO’s PSA, see our earlier Article here, its reasoning reflects a movement towards convergence with EPO practice.

A notable feature of the Court of Appeal’s approach is that it first considered the object of the invention (i.e., the objective problem), before assessing the realistic starting point from the prior art. This contrasts with the EPO’s PSA, where the objective technical problem is formulated only after identifying the closest prior art.

Furthermore, the Court of Appeal clarified that the assessment must consider whether the skilled person would, rather than merely could, have arrived at the claimed invention, and that a structured reasoning process is necessary to avoid hindsight.

Applying these principles to the present case, the Court of Appeal stated that in order for the claim to lack inventiveness the skilled person “needed a sufficient indication that an antibody approach would cause a noticeable improvement of the medical condition of the patient suffering from hypercholesterolemia and similar diseases, for it to have a reasonable expectation of success.” (emphasis added).

Taking into account a disclosure in the prior art that “PCSK9 can function both extracellularly and intracellularly, but we do not know which pathway predominates under normal and/or pathologic conditions” the Court of Appeal concluded that the skilled person would not have reasonably predicted whether the antibody (i.e., extracellular) route would lead to a therapeutically effective treatment of hypercholesterolemia and similar diseases.

The Court of Appeal also addressed sufficiency of disclosure and clarified that the UPC and EPO standards for functional antibody claims can be aligned, contrasting sharply with the stricter US enablement requirement. It is worth noting, however, that in Amgen Inc. v Sanofi, 598 U.S. 594 (2023), the US Supreme Court considered broad antibody genus claims directed to the antibodies per se. By contrast, the European patent assessed by the EPO and the UPC did not contain the same antibody per se claims, but instead contained narrower “medical use” claims, focused on the therapeutic use of the claimed antibodies in treating or preventing conditions such as hypercholesterolemia.

Jurisdictional contrasts and practical implications

The Sanofi v Amgen dispute highlights a fundamental divergence between Europe and the US in the patentability of broad functional antibody claims. In the US, the decisive issue was enablement, with the US Supreme Court adopting a strict standard that places significant constraints on broad functional antibody claims. In Europe, by contrast, assertions of a lack of sufficiency were unsuccessful and so the central debate focused on inventive step. In this case, both the EPO and the UPC found the claims to define inventive subject matter, thereby demonstrating a willingness to uphold functionally defined antibody claims where they reflect a genuine and non-obvious technical contribution.

For patent applicants, these differences carry substantial practical implications. In the US, detailed disclosure and representative examples are essential to support broad claims. In Europe, however, carefully drafted functional or epitope-based claims remain viable, but opposition and revocation proceedings provide powerful mechanisms for centralised validity challenges.

As UPC case law continues to develop, its emerging alignment with the EPO suggests a gradual consolidation of standards for inventive step, bringing greater coherence and predictability to antibody patent litigation within Europe. At the same time, the divergence from the position adopted by the United States Supreme Court is becoming increasingly pronounced. For biotechnology applicants, this divergence underscores the need for carefully considered global patent strategies that anticipate materially different thresholds for claim breadth, disclosure and validity.