Drafting antibody claims at the European Patent Office (EPO) is a high-stakes balancing act. How do you define an antibody broadly enough to capture future developments, but specifically enough to ensure a technical effect is “credible” across the entire scope?

The recent decision T 0655/24 (Genmab A/S) provides a masterclass in using a hybrid approach to overcome inventive step hurdles.

The Drafting Dilemma

• Structure-Only (CDRs/Partial sequences): These claims are often vulnerable. If changes in the framework regions could materially affect the antibody’s properties (like affinity or activity), the EPO may argue the technical effect isn’t credible across the full scope.
• Full Sequence (VH/VL): While safer, this is often too narrow, leaving your invention open to minor modifications that bypass the patent.

The T 0655/24 Solution: The Hybrid Approach

The proprietor successfully defended claims by combining a limited structural definition with functional limitations that reflected the technical contribution.

The claim featured:

• Structural mutations: Specific Fc mutations (L234F, L235E, and D265A), and
• Functional Parameters: The Fc region must not bind Fcγ receptors, and the plasma clearance rate must not deviate by more than 10% from the wild-type protein.

Why did this work?

By including functional criteria, the claim automatically “polices” its own scope. If an opponent argues that additional mutations might negate the technical effect, those variants simply fall outside the claim because they wouldn’t meet the functional requirements. This aligns the claimed scope with the actual technical contribution.

This approach is explicitly supported by the EPO Examination Guidelines (G-II, 6.1.4), which allow for sequences with less than 100% identity when combined with clear functional features.

Practical Takeaways for Patent Strategy

Based on the findings in T 0655/24, consider these strategies for your next antibody filing:

• Avoid Structure-Only Vulnerability: Do not rely solely on partial structural definitions (like CDRs) if the technical effect could be affected by variations elsewhere in the molecule. Such claims are frequently revoked on appeal because the effect isn’t “credible” across the full scope.
• Implement “Self-Policing” Claims: Combine structural features with functional limitations to exclude non-working embodiments. This ensures that the claimed scope remains commensurate with the actual technical contribution, protecting the inventive step.
• Use Relative vs. Absolute Limitations: A key success in T 0655/24 was defining the plasma clearance rate relative to a reference antibody rather than an absolute value. This ensures the mutations don’t worsen stability in any given Fc domain context without unnecessarily restricting the claim to a fixed number.
• Align Scope with Contribution: Ensure functional limitations precisely reflect the technical effect you are relying on for your inventive step argument. If you claim an “improvement,” you must provide experimental evidence (like the CD69 expression assays in this case) that makes that improvement credible across a wide concentration range.
• Leverage EPO Guidelines: Use Guideline G-II, 6.1.4 to justify claiming antibodies with less than 100% sequence identity by pairing them with a clear functional feature. This allows for variation in non-essential positions while capturing the inventive core.