Enablement Requirements for Antibody Claims to be Reviewed by US Supreme Court

In a development which will be of interest to biotech companies, particularly those working in the antibody field, the US Supreme Court has unexpectedly agreed to review the standard for enablement of “genus” claims (e.g. claims which define a product by its function rather than by its structure, and therefore cover multiple products which are not specifically defined in the patent). Although applicable to all areas of technology, this is an issue which overwhelmingly impacts pharmaceuticals and biotechnology, particularly in respect of antibodies and other antigen-binding molecules.


As is common to all jurisdictions, US patent law requires that a patent contains an enabling disclosure of its claimed subject matter. In the US, this is known as the ‘enablement’ requirement, which derives from 35 USC § 112(a), which states:

“The specification shall 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 which it pertains … to make and use the same”

The test for enablement applied by the US Federal Circuit to genus claims is that the specification should allow those skilled in the art “to reach the full scope of claimed embodiments” (i.e. to identify and make all or nearly all embodiments of the claimed invention) “without substantial time and effort”.

In the fields of pharmaceuticals and biotechnology, it is common to seek to claim products based on their functionality rather than their structure, e.g. binding to or inhibiting a newly-identified target for treatment of a certain disease. In the case of antibodies and other antigen-binding molecules, it is common to try to obtain protection based on the epitope they recognise. While claiming an antibody that binds a particular epitope may enable the skilled person to “make and use” that invention (i.e. to generate further antibodies binding the specified epitope), given the inherent unpredictability of which antibody sequences will bind a particular epitope, it is essentially impossible to enable the skilled person to identify all antibodies falling within the claim without substantial time and effort. This has contributed to “genus” claims of this type becoming essentially unobtainable in the USA, and existing patents containing such claims becoming unenforceable.

The Supreme Court has now agreed to review the test for enablement employed by the Federal Circuit, which may result in a lower barrier being applied to the assessment of enablement. If so, this could make it easier to obtain and enforce claims to antibodies defined by their function rather than their structure in the US, although it appears that the standard of assessment for written description will not be considered.

Background of the Case

The Supreme Court referral arises from a long-running patent battle between Amgen on the one hand and Sanofi and Regeneron on the other, in relation to anti-PCSK9 antibodies, which can be used for treatment of high cholesterol. LDL (“bad cholesterol”) is removed from the blood by the LDL receptor (LDLR) in the liver. PCSK9 binds LDLR and causes its degradation, preventing removal of LDL from the blood. Amgen obtained a US patent which covers its specific anti-PCSK9 antibody product, Repatha®, as well as two broader patents for antibodies which (i) bind to PCSK9 at any of the residues through which it interacts with LDLR, and (ii) block the interaction between PCSK9 and LDLR.

Sanofi and Regeneron also have an antibody against PCSK9, on the market under the trade name Praluent®. Back in 2014, Amgen sued Sanofi and Regeneron for infringement of its two broad patents, which claimed antibodies to PCSK9 based on their binding site and inhibitory activity (hereafter, “the Amgen patents”). Sanofi and Regeneron countersued for invalidity on the grounds of lack of enablement, lack of written description and obviousness.

Infringement of the Amgen patents is not under dispute, but the case turns on the Amgen patents’ validity. At first instance, a jury in the Delaware District Court found that the patents were valid, but Sanofi and Regeneron appealed and in a landmark 2017 judgement, the Court of Appeals for the Federal Circuit reversed the decision of the District Court and remanded the case for retrial in respect of written description and enablement (Amgen Inc. v. Sanofi, No. 17-1480 (Fed. Cir. 2017)), resulting in a tightening of the law on written description. The current test for written description is that the inventors must demonstrate possession of the invention at the filing date, which in respect of genus claims has been held to mean that a patent must disclose “a representative” number of species falling within the genus, or structural features common to the members of the genus to enable its members to be “visualised and recognised”. Many companies working in the antibody field (and related technologies) will be familiar with the difficulties in meeting the written description requirement for broad, functionally-defined claims.

Following remand of the case back to the District Court, a jury again found Amgen’s patents to meet both the requirements for enablement and written description. However, a District Court judge overturned the jury’s decision in respect of enablement.

Amgen again appealed to the Federal Circuit, but the Federal Circuit rejected the appeal, finding that the proper test for enablement of a claim that includes a functional requirement is whether the specification enables the skilled person to reach the full scope of claimed embodiments without time and effort, and that the Amgen patents failed this test (Amgen Inc. v. Sanofi, Aventisub LLC, No. 20-1074 (Fed. Cir. 2021)).

Amgen subsequently petitioned the Supreme Court to review the decision of the Federal Circuit, requesting that the Court review the test applied by the Federal Circuit in respect of genus claims, which Amgen argued to be inconsistent with statute law. The Solicitor General, representing the Federal Government, made submissions to the Court that the test applied by the Federal Circuit is correct, and should not be reviewed, but unexpectedly the Supreme Court decided nonetheless to take the case. A decision is expected next summer.

Possible Impact

It is hard to say what impact a change in enablement law might make to the prospects for genus claims. The legal question taken up for review by the Supreme Court relates narrowly to enablement, and so it seems unlikely that the Court will also consider the standard applied to the written description requirement, although this derives from the same section of patent law (indeed, at the same time as accepting the Amgen referral, the Court refused to consider a petition from Juno Therapeutics to review the written description standard, arising from their battle with Gilead in Juno Therapeutics, Inc. v. Kite Pharma, Inc.). Many companies in the biotech field will be familiar with the difficulty in obtaining broad genus claims in view of the onerous written description requirements. Unless the Supreme Court chooses to consider the § 112(a) requirements as a whole, victory for Amgen on the enablement standard alone may have a limited impact on practice in the field.