Method for obtaining april-binding peptides, process for producing the peptides, april-binding peptides obtainable with said method/process and use of the april-binding peptides

A method of selecting an APRIL-binding antibody that detects APRIL in a human sample, comprising:

• providing a library of candidate APRIL-binding antibodies;
• contacting the candidate APRIL-binding antibodies with an APRIL polypeptide immobilized on a solid support, wherein said APRIL polypeptide comprises an APRIL receptor-binding region of APRIL, and wherein the APRIL polypeptide is bound to an APRIL-binding region of an APRIL receptor;
• selecting an APRIL-binding antibody that binds to the APRIL polypeptide.

A method for performing an ex vivo diagnostic test for the presence of APRIL in a human sample, comprising:

• contacting a human sample with an APRIL-binding antibody selected according to the method of claim 1;
• and
• detecting binding between APRIL polypeptides present in the human sample and the APRIL-binding antibody.

A method for performing an ex vivo diagnostic test for the presence of APRIL in a human sample, comprising:

• contacting a human sample with an APRIL-binding antibody which binds to APRIL in complex with BCMA or TACI and to uncomplexed APRIL;
• and
• detecting binding between APRIL polypeptides present in the human sample and the APRIL-binding antibody.