Antigen binding polypeptides

1. A process for preparing a chimeric antigen binding polypeptide that specifically binds to a human target antigen, said 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 said VH domain and 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, said process comprising:

(a) determining the nucleotide sequence encoding each of the hypervariable loops of the VH and/or the VL domain of a conventional antibody of a Lama species immunoreactive with said target antigen; and

(b) expressing a chimeric antigen binding polypeptide immunoreactive with said target antigen, said antigen binding polypeptide comprising a VH and a VL domain, wherein each of the hypervariable loops of the VH domain or the VL domain has an amino acid sequence encoded by the nucleotide sequence determined in part (a).

2. The process of claim 1 , wherein the conventional antibody of a Lama species of part (a) is obtained by immunising a Lama species, thereby raising a conventional antibody which is immunoreactive with said target antigen.

3. The process of claim 1 , wherein step (a) comprises determining the nucleotide sequence encoding the VH and/or the VL domain of a conventional antibody of a Lama species immunoreactive with said target antigen; and step (b) comprises expressing an antigen binding polypeptide immunoreactive with said target antigen, said antigen binding polypeptide comprising a VH and a VL domain, wherein at least one of the VH domain or the VL domain has an amino acid sequence encoded by the nucleotide sequence determined in part (a).

4. The process of claim 1 , wherein the antigen binding polypeptide expressed in step (b) comprises at least one constant domain of a non-camelid antibody, preferably a human antibody.

5. 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).

6. The process of claim 5 wherein (a) comprises isolating a nucleic acid of a Lama species encoding the VH domain and/or the VL domain of said antibody and altering the sequence of said nucleic acid such that it encodes a VH domain and/or a VL domain with one or more amino acid substitutions, deletions or additions.

7. The process of claim 5 wherein the recombinant polynucleotide prepared in step (b) additionally comprises a nucleotide sequence encoding one or more constant domains of a non-camelid antibody, preferably a human antibody.

8. The process of claim 5 wherein the Lama species is llama ( Lama glama ) or alpaca ( Lama pacos ).

9. The process of claim 5 wherein the target antigen is selected from the group consisting of: human antigens, viral antigens, bacterial antigens and a target antigens of therapeutic or diagnostic importance.

10. 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.

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

a) preparing an expression vector encoding an antigen binding polypeptide immunoreactive with a target antigen using the method of claim 10 ;

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.

12. The process of claim 1 wherein the Lama species is llama ( Lama glama ) or alpaca ( Lama pacos ).