UK COURTS GET FAMILIAR WITH US PATENT DOCTRINE

UK company Celltech obtained a patent for humanised antibodies from the USPTO. Before it was granted, Celltech licensed a US corporation, Medimmune, to develop, make, use and sell antibodies. Medimmune, who developed a humanised antibody which it sold under the trade name SYNAGIS, claimed that since its antibody would not have infringed Celltech’s patent it did not have to pay licence royalties. Celltech disgreed and sued for patent infringement, relying on the doctrine of equivalents, a rule of US patent law by which there might be infringement even if a product or process fell outside the literal meaning of the words of the claim when understood in their context.
Medimmune argued that Celltech could not invoke the doctrine of equivalents because of another feature of US patent law, the doctrine of prosecution history estoppel. Medimmune sought to rely on two types of prosecution history estoppel: (i) ’amendment estoppel’, which precludes a patentee from seeking protection for subject matter that was relinquished or distinguished in the course of the patent application and (ii) ’argument estoppel’, holds an applicant to the USPTO bound by unequivocal assertions he makes about the scope or meaning of his claims.
The trial judge, Jacob J, dismissed the infringement claim, holding that Celltech was bound by argument estoppel but not by amendment estoppel. Both parties appealed. The Court of Appeal today dismissed Celltech’s appeal but, by a 2-1 majority, allowed Medimmune’s cross-appeal. What is interesting here is the way the UK courts are gradually making themselves more at home with significant features of US patent law doctrine.