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Court of Appeal Approves Reach-Through Claim

A recent decision of the UK Court of Appeal (FibroGen v Akebia [2021] EWCA Civ 1279) has provided clarification on the assessment of sufficiency for claims directed to a medical use of a functionally-defined compound. In doing so, the Court found a "reach-through" claim to be sufficient, even though it may cover the use of compounds that have not yet been invented.

The key claims related to use of a compound for treating anaemia. The compound was defined partly in structural terms (a very broadly defined class of carboxamides) and partly in functional terms (requiring that the compound "inhibits [HIF-PH] enzyme activity [… and increases] endogenous erythropoietin"). The functional terms therefore identified the so-called therapeutic target considered to embody the mechanism of action of the compound.

At first instance, the claims were found to be insufficient both for lack of plausibility and for placing an undue burden on the skilled person. It was held that the skilled person must both be able reasonably to predict that substantially all compounds that satisfy the structural definition will have therapeutic efficacy, and also be able to "identify substantially all compounds covered by the claim without undue burden" (a formidable prospect given the breadth of the structural definition).

In overturning the first instance judgement on plausibility, the appeal decision sets out a three-step test: a first step of identifying what falls within the scope of a claim; a second step of determining what it means to say the invention works; and a third step of assessing whether the invention can reasonably be predicted to work with substantially everything falling within the scope of the claim. Once the scope of the claims at issue was properly interpreted as including the functional limitations, it was reasonable to predict that therapeutic efficacy would be achieved (i.e., the invention would "work") for substantially all specific compounds satisfying the combination of structural and functional requirements.

Turning to undue burden, the "right test" is defined as follows: "If one has a claim with a functional feature which defines the claimed compounds, or a mix of such structural and functional features, it must be possible, without undue burden, both to identify compounds which satisfy the relevant test, and to find out whether any given compound satisfies the test."

Importantly, it is not necessary to establish that the skilled person can readily identify substantially all active compounds. Rather, it suffices that the skilled person can identify "some compounds beyond those named in the patent" and that it is possible "to work substantially anywhere within the whole claim". The evidence in this case indicated that these requirements were satisfied, and hence the claims were held to be sufficient.

The judgement therefore endorses an approach where sufficiency of disclosure is assessed in accordance with its technical contribution (in this case, a combination of structural terms and functional terms embodying the biological mechanism of action), rather than one that over-stresses a claim's breath or the amount of routine experimental work involved to validate all of its potential embodiments. This may be a welcome outcome to innovators in the life science and pharmaceutical fields, especially in circumstances where a technical contribution provided by an invention involves discovery of a new therapeutic target.