Transgenic non-human vertebrate for the expression of class-switched, fully human, antibodies
The present invention relates to humanisation of antibodies in vivo. The invention provides non-human vertebrates, cells, populations and methods useful for humanising chimaeric antibodies in vivo. Using the present invention it is possible straightforwardly and rapidly to obtain antigen-specific antibodies that are fully human (ie, comprising human variable and constant regions) and have undergone recombination, junctional diversification, affinity maturation and isotype switching in vivo in a non-human vertebrate system. Furthermore, such antibodies are humanised (eg, totally human)—and selected—totally in vivo, and as such the present invention harnesses in vivo filtering for expressibility, affinity and biophysical characteristics in the context of the desired human variable and constant region pairings. This is avoids problems of down-grading antibody characteristics when humanising the constant region of chimaeric antibodies in vitro.
1. A method of obtaining an antigen-specific antibody or antigen binding fragment thereof, said antibody comprising a human immunoglobulin heavy (IgH) chain comprising a human IgH chain variable region and a human IgH chain constant region, said antigen binding fragment comprising said human IgH chain variable region, the method comprising:
expressing said antibody or antigen binding fragment thereof from a cell comprising nucleic acid encoding said human IgH chain variable region of said antibody,
wherein said human IgH chain variable region is of a mouse whose genome comprises a gene locus for expression of antibody heavy chains, said locus comprising:
(a) an unrearranged human heavy chain variable region comprising human heavy chain variable region gene segments comprising a plurality of unrearranged human variable gene segments (VH), one or more unrearranged human D gene segments (D) and one or more human JH gene segments (JH) for expression of a plurality of human heavy chain variable domains; and (b) one or more human gamma heavy chain constant regions comprising gamma heavy chain constant region gene segments comprising a human CH2 gene segment and a human CH3 gene segment encoding gamma antibody heavy chains comprising (i) gamma heavy chain constant domains and (ii) human heavy chain variable domains;
wherein said unrearranged human heavy chain variable region of said mouse is upstream of and operably linked to said gamma heavy chain constant region and comprised by an IgH locus, and wherein said human CH2 and human CH3 gene segments are selected from the group consisting of
(i) a human IGHG1*01 CH2 gene segment and a human IGHG1*01 CH3 gene segment,
(ii) a human IGHG2*01 CH2 gene segment and a human IGHG2*01 CH3 gene segment,
(iii) a human IGHG3*01 CH2 gene segment and a human IGHG3*01 CH3 gene segment,
(iv) a human IGHG3*03 CH2 gene segment and a human IGHG3*03 CH3 gene segment,
(v) a human IGHG3*04 CH2 gene segment and a human IGHG3*04 CH3 gene segment
and
(vi) a human IGHG4*01 CH2 gene segment and a human IGHG4*01 CH3 gene segment, wherein the human CH2 and CH3 are in place of endogenous gamma heavy chain constant region DNA, such that said human heavy chain variable region gene segments are able to recombine for expression of an antibody heavy chain comprising a human gamma heavy chain antibody Fc region comprising a human gamma CH2 and a human gamma CH3 and a human heavy chain variable domain.
2. The method according to claim 1 , wherein said genome of said mouse comprises endogenous recombination activating gene 1 (RAG-1) and recombination activating gene 2 (RAG-2) genes.
3. The method according to claim 1 , wherein said unrearranged human variable region of said locus of said mouse comprises a plurality of unrearranged human D and/or JH gene segments.
4. The method according to claim 3 , wherein said plurality of unrearranged human D gene segments of said mouse comprises at least 5 different human D gene segments.
5. The method according to claim 4 , wherein said plurality of unrearranged human JH gene segments of said mouse, comprises at least 2 different human JH gene segments.
6. The method according to claim 1 , wherein said human gamma CH2 and human gamma CH3 gene segments of said mouse encode an inactive antibody Fc region.
7. The method according to claim 1 , wherein said human gamma CH2 and human gamma CH3 gene segments of said mouse encode an active antibody Fc region.
8. The method according to claim 1 , wherein said genome of said mouse comprises no human Cμ genes.
9. The method according to claim 1 , wherein said gamma heavy chain constant region at said endogenous IgH locus of said mouse comprises a human CH1 gene segment.
10. The method according to claim 1 , wherein said gamma heavy chain constant region at said endogenous IgH locus of said mouse does not comprise a human CH1 gene segment.
11. The method according to claim 10 , wherein light chain expression is inactive in said mouse when non-mu heavy chains are expressed in the mouse.
12. The method according to claim 1 , wherein said mouse comprises a human gamma-1 constant region comprising human CH1, human CH2 and human CH3.
13. The method according to of claim 12 , wherein said endogenous IgH locus of said mouse does not comprise a mouse gamma-1 constant region.
14. The method according to claim 1 , wherein said mouse does not express endogenous antibody heavy chains of said IgH gamma isotype.
15. The method according to claim 1 , wherein said human CH2 and human CH3 gene segments of said mouse are human CH2 gamma-1 and human CH3 gamma-1 gene segments.
16. The method according to claim 1 , wherein said human gamma constant region of said mouse comprises a human gamma CH1 gene segment in place of endogenous mouse gamma CH1 gene segment.