Patents

Case Note Celltech Chiroscience Ltd. v Medimmune Inc.

John Lambert

Oct 1998
Last Updated 1 March 2004

In this fascinating case, the English courts had to apply the US doctrine of equivalents as mitigated by the countervailing doctrine of prosecution history estoppel. The point arose because a licence with an English choice of law and jurisdiction clause required the defendant licensee to pay a royalty to the claimant upon sales covered by a US patent. The defendant's product fell outside the plain words of the claim but the patentee claimed that it still fell within the patent because the doctrine of equivalents extends the scope to cover equivalent matter. The defendant replied that prosecution history estoppel prevents a patentee from asserting the doctrine of equivalents to contradict amendments, or representations to the US Patent and Trade Mark Office ("USPTO") as to the scope, of a claim. In 2000 the Court of Appeals for the Federal Circuit had restricted the doctrine of equivalents in Festo Corp v Shoketsu KKK 234 F.3d 558 holding a patentee to the language of his amendment. In May 2002, however, the US Supreme Court overturned the Federal Circuit substituting for the restriction a rebuttable presumption against the choice of equivalents in a judgment that even the Circuit Court finds difficulty to apply. The task in Celltech of balancing conflicting doctrines of a very different patent law that are still in flux must have been far from enviable for the judge.

The Facts

The patent for which the licence was granted covered antibodies upon which parts that fasten onto antigens known as complementarily determining regions taken from mice are grafted at particular positions on human antigens. In the original application to the USPTO a number of amino acid residues from mice or humans at various positions was claimed. Following citation of an earlier application, the claim was narrowed to specify such residue at only one specified position. The defendant's product differed from the specification only in one respect. The residue at the specified position in its product was human whereas in the specification it was murine. The patentee contended that the substitution of human for murine residue was equivalent to what had been claimed in its patent. The defendant replied that the patentee was estopped from claiming such equivalent by its amendment.

The Judgment

Jacob J found that the amendment was irrelevant to the amendment claimed. It had reduced the number of positions for the grafting of the complimentary determining regions that the patentee could claim but did not address the question of whether the residue had to be human or murine. However, in distinguishing its invention from the prior art the patentee had told the USPTO on more than one occasion that a human residue at the specified position (which had been disclosed in the earlier invention) would fall outside its claim. The judge found that the claimant was bound by that representation and held that the claimant's reliance upon the doctrine of equivalents was precluded.

Evidence of US Law

Another interesting feature of this case is that the judge found himself receiving submissions on US Law as though he were a US District Court judge. As he observed at para [8] of his judgment, foreign law is treated as a question of fact in England and it is normally proved by evidence from foreign lawyers. It appears that in this case counsel had agreed that the judge could read the US cases without the aid of a US lawyer. There is a lot to be said for that approach. Experts in foreign legal systems do not come cheap and, as the judge noted, cross-examination of American experts would consist of bouncing points of argument off which could just as easily be submitted to him. On the other hand, it has to be remembered that the US legal tradition is very different from our own. Moreover as a decision on US law is a decision on fact it is hard to see how a finding on American law could be challenged on appeal even if palpably wrong. This is not something that should be followed in every case.

The Appeal

Both sides appealed with Jacob J's permission. The claimant contended that the judge had been wrong to hold that it was estopped from relying on the doctrine of equivalents by an aspect of file wrapper estoppel known as "argument estoppel". The defendant argued that it could also have succeeded on another aspect of the doctrine known as "amendment estoppel." By a 2 to 1 majority (Sir Andrew Morritt V-C and Longore LJ, Arden LJ dissenting) dismissed the claimant's appeal and allowed the defendant's cross-appeal).

Practical Observation

It might also be said that specifying the products to be manufactured under the licence rather than a blanker reference to the US patent might have avoided the need for this litigation altogether.