Patent ID: 7052873

Claim:
A method for preparing a humanized antibody, wherein a framework region (“FR”) in the humanized antibody is a FR naturally occurring in human antibodies, comprising the steps of: (1) obtaining a humanized antibody, wherein the humanized antibody has: i) six complementary determining regions (“CDRs”) of a first animal species; and ii) eight FRs of a second animal species, wherein one or more amino acid residues in one or more of the FRs have been substituted to retain antigen binding ability, with corresponding amino acid residues in FRs of the first animal species, and wherein said second animal species is human; (2) conducting a homology search using a database of amino acid sequence of FRs naturally occurring in human antibodies (“natural FRs”) in comparison with the amino acid sequence of the humanized antibody obtained in step (1), wherein the homology search is conducted over all 8FRs; (3) preparing a list of amino acid sequences of the natural FRs having the same as or at least 80% homology with the amino acid sequence of the FR, of the humanized antibody obtained in step (1), (4) selecting, from the list of step (3), a natural FR which has i) at corresponding positions the same amino acid residues as the amino acid residues introduced by the substitution in step (1); and ii) comprises an amino acid sequence that is the same as or has at least 80% homology with the FR sequence of the humanized antibody obtained in step (1); (5) if the amino acid sequence of the FR, in which amino acid residues have been substituted in step (1), of the humanized antibody obtained in step (1) has one or more amino acid residues that are different from amino acid residues at corresponding positions of the natural FR selected in step (4), replace said different amino acid residues in the FR sequence of the humanized antibody obtained in step (1) with corresponding amino acid residues in the natural FR; (6) constructing an expression vector expressing an amino acid sequence of the antibody obtained via steps (1) to (5); (7) culturing cells comprising an expression vector constructed in step (6); and (8) recovering from the culture the humanized antibody comprising the natural FR and 6 CDRs from the first animal species and wherein the recovered humanized antibody binds the same antigen that the antibody from the first animal species binds.