Patent ID: 7175996

Claim:
A method of identifying heteromeric variable region binding fragments comprising the steps of: a) providing: (i) a donor heteromeric variable region binding fragment comprising donor complementarity determining region reference sequences and a donor framework sequence wherein said donor variable region binding fragment binds an antigen and (ii) an acceptor framework sequence; b) comparing said donor framework sequence with said acceptor framework sequence; c) identifying one or more framework positions wherein said donor and said acceptor sequences are different; d) constructing a population of overlapping oligonucleotides said population of oligonucleotides encoding a population of overlapping fragments of a variable region of an antibody chain wherein said population of overlapping fragments comprise i) complementarity determining region sequences wherein at least one donor complementarity-determining region sequences is altered with respect to a donor complementarity-determining region reference sequence using codon based mutagenesis and ii) acceptor framework sequences modified by substitution with the donor amino acid more of said identified positions, iii) said population of oligonucleotides comprising between 10 and 10 8 different species; e) extending the overlapping oligonucleotides to create a population of extended oligonucleotides encoding a population of acceptor variable regions; f) generating a population of heteromeric variable region binding fragments comprising expressing said population of extended oligonucleotides to create a population of variable regions of antibody chains; g) identifying individual heteromeric variable region binding fragments wherein said heteromeric variable region binding fragments bind the same antigen as said donor heteromeric variable region binding fragment.