In a somewhat controversial decision in the United Kingdom, the House of Lords held that a metabolite formed in the human body, but whose existence was unknown at the time of filing a patent application directed to that metabolite, may be relevant prior art against such a patent application. In the case of Merrill Dow Pharmaceuticals Inc. v. H.N. Norton[1] the issue in suit was whether the fact that a prior patent had described a compound for use as an antihistamine and had stated that ingestion of that compound would "produce a chemical reaction in ... the body ... having an antihistamine effect" constituted prior art against a claim to a metabolite of the first compound which was formed in the liver of persons taking that compound. The metabolite was more effective than the original compound. The case came before the courts because after the expiration of their original patent, the patentees brought an infringement action under their second patent against persons who were selling the original product on the ground that this was contributory infringement of their second patent because of the metabolization of the first product when it was ingested. For some reason that is not clear the question of validity of the second patent was taken up as a preliminary issue. The House of Lords agreed with the lower courts that in order for something to constitute prior art in English law, there was no need to know what that something was. It was sufficient that what was disclosed to the public was a description "sufficient to work the invention". In the present case, the first patent "enabled the public to work the invention by making the ... metabolite in their livers. The fact that they would not have been able to describe the chemical reaction in those terms did not mean that they were not working the invention".

This decision is to be contrasted with the parallel case in the Munich Oberlandesgericht, where under German law the court could only address the question of infringement and not validity (validity issues being the exclusive jurisdiction of a different court). In this case the Court simply held that the claims to the metabolite in the patentee's second patent could not be construed in such a way as to make unlawful the sale of the product covered by the first patent once this had expired. Logically this seems a sounder basis than that of the House of Lords, but the situation as a whole shows the problems that can arise when validity issues are isolated from those relating to claim scope for the purposes of infringement.[2]

The difference in conclusion reached by the Hose of Lords and the EPO's Appeal Board in respect of European Patent 182442 have been noted briefly above[3]. The claim in question reads as follows:

The first key difference between the EPO and the House of Lords was whether this claim was properly supported by a priority document that disclosed

However, there was no actual demonstration of expression of HBcAg or HBsAg nor any data on the production of a polypeptide with antigen specificity. Shortly after the priority date claimed, the DNA sequences coding for certain polypeptides falling within the definition in the claim were published by a third party.

The EPO stated that for there to be support "the disclosure of the essential elements must be expressly, or be directly and unambiguously implied by the text. Missing elements which are to be recognized as essential only later on are thus not part of the disclosure. However, it concluded that in the present case the criteria for accepting the claimed priority date were met. The Board held that notwithstanding the missing data noted above, it was "directly and unambiguously implied by the text that the expressed product could be a protein displaying antigen specificity" of one or more known HBV antigens depending on the HBV DNA fragment used. A simple experimental approach could lead to the expression of polypeptides as defined in these claim. The House of Lords on the other hand followed its decision in Asahi Kasei Kogyo KK's Application[4] and concluded that there was a lack of enabling disclosure in the priority document. "If the claims include a number of discrete methods or products, the patentee must enable the invention to be performed in respect of each of them". The House of Lords concluded that the disclosure of the priority document in fact only supported the possibility of producing certain polypeptides having the desired characteristics and therefore did not support an claim covering production of all polypeptides having these characteristics and so the claim to priority failed. However, as noted earlier, the gut reason why the House felt it necessary to conclude that the patent was invalid was that they felt that it was just too broad.[5] It felt that the EPO Board had simply failed to address this aspect of the case and that its own decision was consistent with the EPO's decision in the Exxon[6] case.

Once the earliest priority date was lost, it was conceded that the patent was obvious over the cited art.[7] The House also held the patent invalid for insufficiency of disclosure for reasons analogous to those applied to the priority date question.

As in the Merrill Dow case, it can be seen how the impact of what are essentially questions of claim scope seen from the perspective of an infringement situation impact on the question of validity.

These decisions raise the question therefore of whether the EPO Boards of Appeals by virtue of their lack of contact with infringement situations may be taking a too strongly pro-patent position in some respects and whether some greater concern for the proper scope of a claim might be desirable in EPO proceedings.[8]