Patent ID: 8785138

Claim:
In a method for selecting a monovalent ligand of human CD28 receptor which blocks the binding of B7.1 or B7.2 proteins to said CD28 receptor without activating said receptor, comprising the steps of: (i) providing candidate monovalent ligands of said CD28 receptor, wherein said ligands are selected from the group consisting of Fv, Fab and scFv fragments of an anti-CD28 antibody, and recombinant proteins comprising said fragments and a heterologous polypeptide, (ii) testing said candidate ligands for the ability to block the binding of B7.1 and B7.2 to said CD28 receptor and for the ability to activate said receptor, and (iii) selecting the ligands which block the binding of B7.1 or B7.2 to said CD28 receptor without activating said receptor, the improvement comprises an additional method step between steps (i) and (ii), wherein the additional step comprises providing a human CD28 receptor or a fragment thereof comprising the conformational epitope formed by the stretches of amino acids of SEQ ID NO:2, SEQ ID NO:3 and SEQ ID NO:4 of said CD28 receptor, testing said candidate ligands for binding to said epitope, and selecting ligands which bind to said epitope.