Protecting the epitope, not just the antibody: why Australian antibody claims can have substantial strategic value

A common form of functional claiming is to define an antibody by its ability to bind a particular antigen or epitope. Such claims are commercially valuable for at least the following reasons:

• They can capture structurally different competing antibodies.
  Since such claims are not limited by sequence and therefore can encompass a structurally diverse range of antibody sequences.
• They can make designing around the patent considerably harder
  If the commercially important biology depends on engaging a particular region of the target, a competitor cannot necessarily avoid the claim simply by developing a new antibody sequence. That is especially important where efficacy is epitope-dependent.
• They can protect a genus rather than merely a molecule
  This is commercially valuable since the protected asset instead of being antibody X is significantly broader to encompass antibodies that interact with a specific part of target Y.
• They may cover later developed antibodies
  A later antibody may have different variable-region sequences, affinity, format or engineering but still operate through the patented epitope. A properly drafted epitope claim may therefore remain relevant despite subsequent antibody optimisation.
• They can protect the underlying biological discovery
  The invention may lie not in the antibody sequence but in the discovery that engaging a particular epitope produces an advantageous biological outcome. An epitope claim can align the patent scope much more closely with that inventive contribution.

When it comes to defining a genus of antibodies based on a newly defined epitope, Australia has diverged from the United States. The Australian Patent Office Manuel of Practice and Procedure indicates that a claim to an antibody specifically binding a new epitope may be enabled where the applicant discloses the epitope and shows that antibodies can be raised against it. IP Australia’s Manual expressly provides an example in which such a claim is fully enabled because raising antibodies to the epitope constitutes a principle of general application across the claim scope, although the Manual cautions that its examples are guidance and each case must be considered on its own facts.

The Australian approach contrasts strongly with the United States and more particularly, the U.S. Supreme Court’s decision in Amgen Inc. v. Sanofi, 598 U.S. 594 (2023). As US practitioners will be aware, the Court held that where a patent claims an entire class, the specification must enable the skilled person to make and use that class, established a demanding enablement standard for claims directed to a functionally defined antibody genus.

The Australian approach to epitope-defined antibody claims

The Australian Patent Office’s Manual of Practice and Procedure specifically recites:

Claim 1 to an antibody that specifically binds epitope A would be fully enabled where the applicant had disclosed the epitope and shown that antibodies can be raised against it. This is because raising antibodies to that epitope is a principle that can be generally applied to produce antibodies over the whole scope of the claim. The specification need only disclose one such antibody.

The rationale is that raising antibodies against a disclosed epitope represents a principle of general application across the scope of the claim. Thus, the analysis focuses on whether identification of the epitope provides the skilled person with a general teaching that enables antibodies across the claim scope to be produced without undue burden.

This is significant because the claim is directed to the antibody composition itself and defines the antibody principally by its binding function. In the example given by the Manual, enablement does not depend upon limiting the genus to antibodies sharing particular complementarity-determining region (CDR) or variable-region sequences.

However, the Manual also provides a contrasting example involving a claim to an antibody that binds Epitope A and comprises “one or more” of six disclosed CDRs. Such a claim would generally impose an undue burden because the skilled person would first need to generate antibodies that bind the epitope and then sequence those antibodies to determine which fall within the claimed subset. Hence, disclosure of the epitope would not provide a principle of general application for selectively producing antibodies containing one or more of the recited CDRs.

The distinction reflects an important feature of the Australian enablement analysis. A broad claim is not enabled merely because the skilled person possesses the technical ability to generate and test a large number of antibody candidates. Rather, the disclosure must provide a principle that can reasonably be applied across the claim scope without undue burden.

Accordingly, under current Australian Patent Office practice, identification of a new epitope may provide the general principle necessary to support broad protection for antibodies binding that epitope. This contrasts with the treatment of comparable functional genus claims in the United States following Amgen Inc. v. Sanofi.

Implications for Australian and U.S. claim drafting

The divergence between Australian and U.S. practice supports a jurisdiction-specific approach to antibody claim drafting.

For Australian prosecution, applicants should consider whether a newly identified epitope can support a composition claim to antibodies binding that epitope under the general-principle reasoning reflected in the Australian Patent Office Manual.

Therefore, where an epitope claim matters, the specification should ideally disclose, where experimental evidence permits;

• the complete antigen sequence and an unambiguous residue-numbering convention;
• the epitope residues identified experimentally;
• which residues are critical to binding versus merely contacting the antibody;
• whether the epitope is linear or discontinuous/conformational;
• variants of the epitope definition, for example combinations of 3, 4, 5, etc. critical residues;
• exemplary antibodies recognising the epitope;
• sequence diversity among those antibodies, if available;
• functional consequences of binding the epitope;
• methods suitable for determining whether another antibody binds the relevant epitope;
• competition data against the exemplified antibody; and
• structure-function evidence showing why the epitope represents a principle of general application, rather than an observation unique to one antibody.

For Applicants seeking protection in both Australia and the U.S, it is not simply that Australia permits broader antibody claims than the U.S., rather, the two countries place the inventive contribution at different points. Australian practice may permit the discovery of a new epitope itself to support a broad antibody genus where that discovery provides a principle of general application. In the United States, Amgen makes an equivalent composition claim considerably more difficult.

The decision in Teva Pharmaceuticals GmBH v Eli Lilly & Co No. 2024-1094 (Fed. Cir. Apr. 16, 2026) provides a potentially important alternative where the inventive contribution lies in using an independently established antibody genus for a new therapeutic purpose. This will be discussed in a follow on article.