6.1.3 Definition by target antigen and further functional features 

In addition to being functionally defined by their target antigen, antibodies can be further characterised by functional features defining their other properties, for example binding affinity, neutralising properties, induction of apoptosis, internalisation, inhibition or activation of receptors.

An antibody may also be claimed by reference to its epitope, i.e. the structurally defined part of the antigen that it specifically binds to. Claims are sometimes directed to antibodies defined by their ability to compete with a reference antibody which is disclosed for the first time in the application. However, this property will normally not be sufficient to identify antibodies in the state of the art. In such cases, a complete search cannot be carried out (B‑VIII, 3) and an invitation under Rule 63(1) to indicate subject-matter for search is sent (B‑VIII, 3.1).

In all these cases, if there is no indication to the contrary, it is to be assumed that a prior-art antibody binding the same target antigen will have the claimed functional properties. A novelty objection may therefore be raised and the burden of proof lies with the applicant (cf. G‑VI, 5).

The application must enable the skilled person to produce further antibodies having the claimed functional property without undue burden (see F‑III, 1 and F-III, 4). In addition, the functional definition must allow the skilled person to easily and unambiguously verify whether they are working inside or outside the scope of the claim. The claim should therefore normally include the relevant characteristics of the method used to determine and define the functional property (see F‑IV, 4.11).