Patent ID: 7973137

Claim:
A composition comprising a cell in which a molecular complex is bound to the surface of the cell, wherein the molecular complex comprises at least two first fusion proteins and at least two second fusion proteins, wherein: (a) each of the two first fusion proteins comprises an immunoglobulin heavy chain, wherein the immunoglobulin heavy chain comprises a variable region, and an extracellular portion of a first transmembrane polypeptide; and (b) each of the two second fusion proteins comprises an immunoglobulin light chain and an extracellular portion of a second transmembrane polypeptide; wherein the at least two first fusion proteins and the at least two second fusion proteins associate to form the molecular complex, wherein the molecular complex comprises two ligand binding sites, wherein each ligand binding site is formed by the extracellular domain of a first transmembrane polypeptide and the extracellular domain of a second transmembrane polypeptide, wherein the affinity of the molecular complex for a cognate ligand is increased at least two-fold over a dimeric molecular complex consisting of the first and the second fusion protein.