Celltech R & D Ltd. v Medimmune Inc

Under German patent law, infringement begins with the semantic meaning of the claims, construed in context. A variant outside that meaning is protected only if it works by equivalent means, the equivalence would be obvious to the skilled person, and the skilled person would regard the variant as the specific equivalent solution contemplated by the claim.

Clear claim limitations, including specified residues or dimensions, may exclude technically equivalent variants. A court cannot correct a patentee’s deliberate or apparent mistake by expanding the monopoly beyond the teaching of the claims. The patentee may choose narrower protection, and the reader is entitled to rely on that choice.

Celltech claimed royalties from Medimmune under a patent licence covering German patent rights. It alleged that Medimmune’s SYNAGIS antibody product infringed claim 1 of a European patent concerning humanised antibodies.

The product did not satisfy the claim’s semantic meaning because it retained an acceptor residue at heavy-chain position 23 instead of the required donor residue. Celltech argued that the residue was a conservative substitution and that the product was nevertheless an equivalent under German patent law. The court had to determine the scope of protection under the German approach implementing Article 69 EPC and the Protocol on its interpretation.

1. Claim construction and German law. The court had to apply German infringement law rather than assume that the result would be identical under English law. Under the approach derived from Formstein (BGHZ 98, 12), the claims are the essential basis for determining protection, interpreted with the description and drawings. The wording chosen by the patentee remains important to legal certainty.
2. Equivalent infringement. Following Custodial II (GRUR 2002, 527), a non-literal variant must satisfy three requirements: it must solve the problem with modified but objectively equivalent means; the skilled person must recognise the modified means as equivalent; and the skilled person must regard the variant as the specific equivalent solution indicated by the semantic content of the claim.
3. The third requirement was decisive. The patent consistently classified residue 23, together with certain other residues, as a mandatory donor residue. The claims and specification imposed a strict donor-only requirement. The skilled reader would understand that the patentee had deliberately limited the monopoly, even if the limitation was scientifically unnecessary or based on mistaken analysis. German law did not permit the court to correct that mistake.
4. The arguments based on conservative substitution, the structure of the antibody, and the discussion of Riechmann’s work did not alter that conclusion. The skilled reader would not infer that residue 23 could be acceptor where the patent expressly treated it as critical.
5. Alternatively, the court found that conservative substitution at residue 23 did not materially affect the antibody’s characteristics, so the first Custodial II question favoured Celltech. However, the substitution was not obvious to the skilled reader starting from the patent and common general knowledge. The proposed reasoning was an unfair step-by-step ex post facto analysis, contrary to British Westinghouse v Braulik ((1910) 27 RPC 209).
6. SYNAGIS therefore fell outside the scope of the patent claims. The claim for royalties failed. Since there was no infringement, there was no occasion to consider the Formstein objection.