Antigen binding polypeptides

1. A library of expression vectors comprising cDNA sequences encoding VH and VL domains of camelid conventional antibodies from a camelid actively immunized with a target antigen.

2. A method of producing the library of expression vectors of claim 1 , said method comprising the steps:

a) amplifying regions of nucleic acid molecules encoding VH and/or VL domains of camelid conventional antibodies to obtain amplified gene segments, each gene segment containing a sequence of nucleotides encoding a VH domain or a sequence of nucleotides encoding a VL domain of a camelid conventional antibody, and

b) cloning the gene segments obtained in a) into expression vectors, such that each expression vector contains at least a gene segment encoding a VH domain and/or a gene segment encoding a VL domain, whereby a library of expression vectors is obtained.

3. The method of claim 2 wherein the nucleic acid amplified in step a) comprises cDNA or genomic DNA prepared from lymphoid tissue of a camelid, said lymphoid tissue comprising one or more B cells, lymph nodes, spleen cells, bone marrow cells, or a combination thereof.

4. The method of claim 3 wherein the lymphoid tissue comprises one or more B cells selected for expression of camelid conventional antibodies with desired antigen binding properties.

5. The method of claim 4 wherein the target antigen is selected from the group consisting of: human antigens, viral antigens, bacterial antigens and target antigens of therapeutic or diagnostic importance.

6. The method of claim 2 , wherein step b) comprises cloning gene segments encoding VH and VL domains into expression vectors to produce a library of expression vectors, wherein each expression vector in the library comprises a gene segment encoding a VH domain and a gene segment encoding a VL domain and directs expression of an antigen binding polypeptide comprising said VH domain and said VL domain.

7. The method of claim 2 wherein the expression vectors in the library are selected from the group consisting of phage vectors, phagemid vectors, yeast, mammalian expression vectors and bacterial expression vectors.

8. The method of claim 2 wherein the camelid is llama or alpaca.

9. A method of producing the library of expression vectors of claim 1 , said method comprising the steps:

a) actively immunizing a camelid, thereby raising conventional camelid antibodies against a target antigen;

b) preparing cDNA or genomic DNA from a sample comprising lymphoid tissue (e.g. circulating B cells) from said immunised camelid;

c) amplifying regions of said cDNA or genomic DNA to obtain amplified gene segments, each gene segment comprising a sequence of nucleotides encoding a VH domain or a sequence of nucleotides encoding a VL domain of a camelid conventional antibody; and

d) cloning the gene segments obtained in c) into expression vectors, such that each expression vector contains a gene segment encoding a VH domain and a gene segment encoding a VL domain and directs expression of an antigen binding polypeptide comprising said VH domain and said VL domain, whereby a library of expression vectors is obtained.

10. The method of claim 9 wherein the expression vectors obtained in step d) direct expression of said VH domain and said VL domain in the form of an antigen binding polypeptide selected from the group consisting of: scFVs, Fabs and antibodies.

11. The method of claim 9 wherein the expression vectors in the library are selected from the group consisting of phage vectors, phagemid vectors, yeast, mammalian expression vectors and bacterial expression vectors.

12. The method of claim 9 wherein the camelid is llama or alpaca.

13. An expression vector comprising cDNA sequences encoding a VH and VL domain of a camelid conventional antibody from a camelid actively immunized with a target antigen.

14. A method of producing the expression vector of claim 13 , the method comprising steps of:

i) preparing a library of expression vectors, wherein each vector in said library comprises a gene segment encoding a VH domain and a gene segment encoding a VL domain, wherein at least one of said VH domain or said VL domain is from a camelid conventional antibody, and wherein each vector in said library directs expression of an antigen binding polypeptide comprising said VH domain and VL domain;

ii) screening antigen binding polypeptides encoded by said library for immunoreactivity with said target antigen, and thereby producing the expression vector.

15. The method of claim 14 wherein the library of step i) is prepared by

a) actively immunizing a camelid, thereby raising conventional camelid antibodies against a target antigen;

b) preparing cDNA or genomic DNA from a sample comprising lymphoid tissue (e.g. circulating B cells) from said immunised camelid;

c) amplifying regions of said cDNA or genomic DNA to obtain amplified gene segments, each gene segment comprising a sequence of nucleotides encoding a VH domain or a sequence of nucleotides encoding a VL domain of a camelid conventional antibody; and

d) cloning the gene segments obtained in c) into expression vectors, such that each expression vector contains a gene segment encoding a VH domain and a gene segment encoding a VL domain and directs expression of an antigen binding polypeptide comprising said VH domain and said VL domain, whereby a library of expression vectors is obtained.

16. The method of claim 14 comprising the further step of iii) cloning the gene segment encoding the VH domain of the vector selected in part (ii) and the gene segment encoding the VL domain of the vector selected in part (ii) into a further expression vector, in operable linkage with a sequence of nucleotides encoding one or more constant domains of a human antibody, thereby producing an expression vector encoding a chimeric antigen binding polypeptide comprising the VH and VL domains selected in step ii) fused to one or more constant domains of a human antibody.

17. The method of claim 16 wherein the gene segment encoding the VH domain of the vector selected in part (ii) and/or the gene segment encoding the VL domain of the vector selected in part (ii) is engineered to introduce one or more changes in the nucleotide sequence encoding said VH and/or said VL domain, prior to cloning into the further expression vector.

18. The method of claim 14 further including a light chain shuffling process comprising the following steps:

iii) preparing a second library of expression vectors, wherein each vector in the library contains a gene segment encoding the VH domain of the expression vector selected in step ii) and a gene segment encoding a VL domain;

iv) screening antigen binding polypeptides encoded by said second library for immunoreactivity with said target antigen, and thereby selecting an expression vector encoding an antigen binding polypeptide immunoreactive with said target antigen.

19. The method of claim 18 comprising the further step of v) cloning the gene segment encoding the VH domain of the vector selected in part (iv) and the gene segment encoding the VL domain of the vector selected in part (iv) into a further expression vector, in operable linkage with a sequence of nucleotides encoding one or more constant domains of a human antibody, thereby producing an expression vector encoding a chimeric antigen binding polypeptide comprising the VH and VL domains selected in step iv) fused to one or more constant domains of a human antibody.

20. The method of claim 19 wherein the gene segment encoding the VH domain of the vector selected in part (iv) and/or the gene segment encoding the VL domain of the vector selected in part (iv) is engineered to introduce one or more changes in the nucleotide sequence encoding said VH and/or said VL domain, prior to cloning into the further expression vector.

21. The method of claim 18 further including a heavy chain shuffling process comprising the following steps:

v) preparing a third library of expression vectors, wherein each vector in the library contains a gene segment encoding the VL domain of the expression vector selected in step iv) and a gene segment encoding a VH domain;

vi) screening antigen binding polypeptides encoded by said third library for immunoreactivity with said target antigen, and thereby selecting an expression vector encoding an antigen binding polypeptide immunoreactive with said target antigen.

22. The method of claim 21 comprising the further step of vii) cloning the gene segment encoding the VH domain of the vector selected in part (vi) and the gene segment encoding the VL domain of the vector selected in part (vi) into a further expression vector, in operable linkage with a sequence of nucleotides encoding one or more constant domains of a human antibody, thereby producing an expression vector encoding a chimeric antigen binding polypeptide comprising the VH and VL domains of the vector selected in step vi) fused to one or more constant domains of a human antibody.

23. The method of claim 22 wherein the gene segment encoding the VH domain of the vector selected in part (vi) and/or the gene segment encoding the VL domain of the vector selected in part (vi) is engineered to introduce one or more changes in the nucleotide sequence encoding said VH and/or said VL domain, prior to cloning into the further expression vector.

24. A method of producing the expression vector of claim 13 , said method comprising the steps:

a) actively immunizing a camelid (Llama or alpaca), thereby raising conventional camelid antibodies against a target antigen;

b) preparing cDNA or genomic DNA from a sample comprising lymphoid tissue (e.g. circulating B cells) from said immunised camelid;

c) amplifying regions of said cDNA or genomic DNA to obtain amplified gene segments, each gene segment comprising a sequence of nucleotides encoding a VH domain or a sequence of nucleotides encoding a VL domain of a camelid conventional antibody;

d) cloning the gene segments obtained in c) into expression vectors, such that each expression vector contains a gene segment encoding a VH domain and a gene segment encoding a VL domain and directs expression of an antigen binding polypeptide comprising said VH domain and said VL domain, thereby producing a library of expression vectors;

e) screening antigen binding polypeptides encoded by the library obtained in step d) for immunoreactivity with said target antigen, and thereby selecting an expression vector encoding an antigen binding polypeptide immunoreactive with said target antigen;

f) optionally performing a light chain shuffling step and/or a heavy chain shuffling step to select an expression vector encoding a potency-optimised antigen binding polypeptide immunoreactive with said target antigen;

g) optionally subjecting the gene segment encoding the VH domain of the vector selected in step e) or step 1) and/or the gene segment encoding the VL domain of the vector selected in step e) or step 1) to germlining and/or codon optimisation; and

h) cloning the gene segment encoding the VH domain of the vector selected in part e) or

f) or the germlined and/or codon optimised VH gene segment produced in step g) and the gene segment encoding the VL domain of the vector selected in part e) or f) or the germlined and/or codon optimised VL gene segment produced in step g) into a further expression vector, in operable linkage with a sequence of nucleotides encoding one or more constant domains of a human antibody, thereby producing the expression vector.

25. A composition comprising an expression vector comprising a cDNA sequence encoding a camelid VH domain and an expression vector comprising a cDNA sequence encoding a camelid VL domain, wherein the camelid VH and VL domains are from a camelid actively immunized with a target antigen.

26. The composition of claim 1 , wherein the target antigen is a human antigen.

27. The composition of claim 13 , wherein the target antigen is a human antigen.

28. The composition of claim 25 , wherein the target antigen is a human antigen.