In addition to the functional definition by the antigen it binds to, claims directed to antibodies can be further characterised by functional features defining further properties of the antibodies; for example, the binding affinity, neutralising properties, induction of apoptosis, internalisation of receptors, inhibition or activation of receptors (c.f. e.g. T 299/86, Reasons 3 - 6, and T 1300/05, Reasons 4 - 7).
If an antibody is claimed exclusively by functional features and the prior art discloses in an enabling manner an antibody directed to the same antigen using an immunisation and screening protocol that arrives at antibodies having the claimed properties, it has to be assumed that the prior-art antibody inherently displays the same functional properties as the claimed antibody, which thus lacks novelty (cf. G-VI, 6). On the other hand, if the antibody is defined by unusual parameters, care has to be taken that these do not disguise a lack of novelty (F-IV, 4.11.1). In both these cases the burden of proof of novelty resides with the applicant.
If an antibody is defined exclusively by functional properties, it has to be carefully assessed whether the application provides an enabling disclosure across the whole scope claimed and whether the functional definition allows the skilled person to clearly determine the limits of the claim.