Antigen binding polypeptides

A process for preparing a recombinant antigen binding polypeptide that is immunoreactive with (or specifically binds to) a target antigen, said antigen binding polypeptide comprising a VH domain and a VL domain, said VH domain comprising hypervariable loops H1, H2 and H3, wherein said VH domain polypeptide is paired with a VL domain comprising hypervariable loops L1, L2 and L3, wherein each of the hypervariable loops H1-H3 and L1-L3 are obtained from a conventional antibody of a Lama species by active immunization of the Lama species with the target antigen, wherein said conventional antibody is a heterotetrameric IgG antibody composed of two identical light chains and two identical heavy chains, and wherein at least one of the hypervariable loops H1, H2, L1, L2 and L3 exhibits a predicted or actual canonical fold structure which is identical or substantially identical to a canonical fold structure of a corresponding H1, H2, L1, L2 or L3 hypervariable loop which occurs in a human antibody, said process comprising the steps of:

• (a) isolating a nucleic acid from a Lama species encoding at least one hypervariable loop of the VH and/or the VL domain of a conventional antibody of a Lama species immunoreactive with said target antigen;
• (b) preparing a polynucleotide comprising a nucleotide sequence encoding hypervariable loop(s) having amino acid sequence identical to the hypervariable loop(s) encoded by the nucleic acid isolated in step (a), which polynucleotide encodes an antigen binding polypeptide comprising a VH domain and a VL domain that is immunoreactive with (or specifically binds to) said target antigen, wherein said VH domain comprises hypervariable loops H1, H2 and H3, wherein said VH domain polypeptide is paired with a VL domain comprising hypervariable loops L1, L2 and L3, wherein each of the hypervariable loops H1-H3 and L1-L3 are obtained from a conventional antibody of a Lama species by active immunization of the Lama species with the target antigen, wherein said conventional antibody is a heterotetrameric IgG antibody composed of two identical light chains and two identical heavy chains, and wherein at least one of the hypervariable loops H1, H2, L1, L2 and L3 exhibits a predicted or actual canonical fold structure which is identical or substantially identical to a canonical fold structure of a corresponding H1, H2, L1, L2 or L3 hypervariable loop which occurs in a human antibody;
• and
• (c) expressing said antigen binding polypeptide from the recombinant polynucleotide of step (b), wherein said antigen binding polypeptide is not identical to the conventional antibody of a Lama species of part (a).

A method of producing an antigen binding polypeptide immunoreactive with a target antigen, the method comprising steps of:

• a) preparing an expression vector encoding a polynucleotide molecule encoding a VH domain and/or a VL domain of an antigen binding polypeptide, said VH domain comprising hypervariable loops H1, H2 and H3, and said VL domain comprising hypervariable loops L1, L2 and L3, wherein said VH domain and/or said VL domain are each fused to one or more IgG constant domains of a human antibody, wherein each of the hypervariable loops H1-H3 and L1-L3 are obtained from a conventional antibody of a Lama species by active immunization of the Lama species with the human target antigen, wherein said conventional antibody is a heterotetrameric IgG antibody composed of two identical light chains and two identical heavy chains, and wherein at least one of the hypervariable loops H1, H2, L1, L2 and L3 exhibits a predicted or actual canonical fold structure which is identical or substantially identical to a canonical fold structure of a corresponding H1, H2, L1, L2 or L3 hypervariable loop which occurs in a human antibody;
• b) introducing said expression vector into host cell or cell-free expression system under conditions which permit expression of the encoded antigen binding polypeptide;
• and
• c) recovering the expressed antigen binding polypeptide.