As previously reported the US Supreme Court, in Mayo v. Prometheus, recently invalidated Prometheus’s diagnostic claims - directed to a method of optimizing the treatment of autoimmune diseases, based on the level of a certain therapeutic metabolite in a patient after initial treatment - under the judicial "laws of nature" exclusion in US patent law. The decision has broad implications for the level of patent coverage available in the USA, in fields such as diagnostics and personalised medicine.

Prometheus’ claimed invention involved (a) administering a drug to an appropriate patient, and (b) determining the level of the relevant metabolite in the patient, "wherein" levels above or below specific recited amounts indicated a need to respectively decrease or increase the dose of drug subsequently administered to the patient. The metabolite in question is produced from the administered drug in the body, and variation in this natural process meant that doctors had previously had difficulty in determining the appropriate dose.

The Court decided that the correlation between the level of metabolite and the effect on the patient was itself an un-patentable law of nature, and that Prometheus’s claims did not add enough to the stated law of nature to qualify as patent-eligible. In particular, the Court stated that the steps of the claims added "nothing specific to the laws of nature other than what is well-understood, routine, conventional activity, previously engaged in by those in the field. And since they are steps that must be taken in order to apply the laws in question, the effect is simply to tell doctors to apply the law somehow when treating their patients".

The key term above appears to be ‘specific’. Based on our recent experience, it is the breadth of claim scope which now seems to be USPTO examiners’ main concern when dealing with this type of claim. Therefore, limiting such claims, for example by adding the use of a specific probe or antibody in the diagnostic method, may help overcome this type of objection. For example, in the case of Prometheus, an additional step of using a specific assay to test for the level of metabolite might have been enough to move the claim outside the "laws of nature" exclusion.

There is still no guidance on quite how specific the limitation has to be, however. For example, in the scenario where you add a step of assaying for a particular protein in the blood using an antibody, do you need to specify a particular antibody, or can the antibody be defined functionally? It may be some time before there is a cohesive practice for prosecution of these types of claims in the USA.

In Europe, pharmacogenomics claims also face challenges, and the EPO is still seeking to clarify the boundaries of what is allowable. The battleground in Europe is novelty and whether the invention identifies a novel patient group. The EPO have indicated that claims defining a preferred patient-group only by statistical correlation of a marker (e.g. a SNP) with a preferential outcome (e.g. improved efficacy) will typically lack novelty.

On the other hand, if an invention identifies a new direct technical effect between drug and disease, a claim incorporating that effect may be considered novel. For example, the discovery that drug X can treat disease Y by inhibiting neovascularisation as well as by the known route of immune activation could form the basis of a novel claim since the discovery allows for treatment of a new patient group (immune compromised sufferers of disease Y).