Transgenic Non-Human Vertebrate for the Expression of Class-Switched, Fully Human, Antibodies

Abstract

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 (i.e., 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 (e.g., 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 avoids problems of down-grading antibody characteristics when humanising the constant region of chimaeric antibodies in vitro.

I claim: 
     
         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) a heavy chain constant region comprising one or more human gamma constant regions selected from the group consisting of gamma-1, gamma-2, gamma-3 and gamma-4, wherein each of said one or more human gamma constant regions comprises CH2, CH3, M1 and M2 gene segments, 
 said (a) and (b) 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 is upstream of and operably linked to said gamma heavy chain constant region and comprised by an IgH locus, wherein one or more of said human CH2 and human CH3 gene segments are in place of the respective CH2 and CH3 gene segments 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 a gamma antibody heavy chain comprising a human gamma heavy chain antibody Fc region comprising a human CH2 and a human 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 antibody Fc region. 
     
     
         7 . The method according to  claim 6 , wherein said human gamma CH2 and human gamma CH3 gene segments of said mouse encode an inactive Fc region. 
     
     
         8 . The method according to  claim 6 , wherein said human gamma CH2 and human gamma CH3 gene segments of said mouse encode an active Fc region. 
     
     
         9 . The method according to  claim 6 , wherein said genome of said mouse comprises no human Cμ genes. 
     
     
         10 . The method according to  claim 1 , wherein said gamma-1 constant region of said mouse comprises a human CH1 gene segment. 
     
     
         11 . The method according to  claim 6 , wherein said gamma-1 constant region of said mouse does not comprise a human CH1 gene segment. 
     
     
         12 . The method according to  claim 11 , wherein light chain expression is inactive in said mouse when non-mu heavy chains are expressed in the mouse. 
     
     
         13 . The method according to  claim 12 , wherein said IgH locus comprises said human CH2 and human CH3 gene segments which are in place of corresponding endogenous non-mu heavy chain constant region gene segments of the same non-mu isotype. 
     
     
         14 . The method according to  claim 6 , wherein said human gamma CH2 and human gamma CH3 gene segments are in place of endogenous gamma constant region DNA in said genome of said mouse, whereby the human gamma CH2 and CH3 gene segments are functional to encode a gamma antibody Fc region. 
     
     
         15 . The method according to  claim 1 , wherein said heavy chain constant region comprising one or more human gamma constant regions of said mouse comprises a human gamma-1 constant region comprising human CH1, human CH2 and human CH3. 
     
     
         16 . The method according to of  claim 15 , wherein said endogenous IgH locus of said mouse does not comprise a mouse gamma-1 constant region. 
     
     
         17 . The method according to  claim 1 , wherein said mouse does not express endogenous antibody heavy chains of a non-mu isotype. 
     
     
         18 . The method according to  claim 6 , wherein said human gamma constant region of said mouse comprises a human CH1 gene segment. 
     
     
         19 . The method according to  claim 1 , wherein said human gamma constant region of said mouse does not comprise a human CH1 gene segment. 
     
     
         20 . 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. 
     
     
         21 . The method according to  claim 6 , wherein said human CH2 and human CH3 gene segments of said mouse are human CH2 gamma-1 and human CH3 gamma-1 gene segments. 
     
     
         22 . The method according to  claim 6 , 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. 
     
     
         23 . The method according to  claim 1 , wherein said mouse is homozygous for insertion of the human DNA in first and second copies of an IgH antibody locus. 
     
     
         24 . The method of  claim 1 , wherein said one or more human gamma constant regions of said mouse further comprise the poly-A immediately 3′ of CH3 or M2. 
     
     
         25 . A method of obtaining an antigen-specific antibody comprising a human immunoglobulin heavy (IgH) chain, a human antibody heavy (IgH) chain or antigen binding fragment thereof, said 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, heavy chain 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 transgenic mouse contacted with said antigen, said mouse comprising in its germline a chimeric homozygous immunoglobulin heavy chain locus; wherein the germline of said mouse 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) a non-mu heavy chain constant region comprising non-mu heavy chain constant region gene segments comprising a human CH2 gene segment and a human CH3 gene segment encoding non-mu antibody heavy chains comprising
 (i) non-mu 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 non-mu heavy chain constant region and comprised by an IgH locus and said human CH2 and human CH3 gene segments are in place of endogenous non-mu heavy chain constant region DNA, such that said human heavy chain variable region gene segments are able to recombine for expression of a non-mu antibody heavy chain comprising a human non-mu heavy chain antibody Fc region comprising a human CH2 and a human CH3 and a human heavy chain variable domain, wherein in said genome, human DNA is incorporated in place of endogenous Ig antibody loci DNA, “and wherein said human variable region gene segments are positioned to recombine to human VDJ gene segments and would be operably linked to endogenous mouse constant region if present. 
   
     
     
         26 . The method according to  claim 25 , wherein said genome of said mouse comprises endogenous recombination activating gene 1 (RAG-1) and recombination activating gene 2 (RAG-2) genes. 
     
     
         27 . The method according to  claim 25 , wherein said unrearranged human variable region of said locus of said mouse comprises a plurality of unrearranged human D and/or JH gene segments. 
     
     
         28 . The method according to  claim 27 , wherein said plurality of unrearranged human D gene segments of said mouse comprises at least 5 different human D gene segments. 
     
     
         29 . The method according to  claim 28 , wherein said plurality of unrearranged human JH gene segments of said mouse, comprises at least 2 different human JH gene segments. 
     
     
         30 . The method according to  claim 25 , wherein said non-mu constant region of said locus of said mouse comprises a human gamma constant region comprising a human gamma CH2 gene segment and a human gamma CH3 gene segment, wherein said human gamma CH2 and human gamma CH3 gene segments encode an antibody Fc region. 
     
     
         31 . The method according to  claim 30 , wherein said CH2 and CH3 gene segments of said mouse encode an inactive Fc region. 
     
     
         32 . The method according to  claim 30 , wherein said CH2 and CH3 gene segments of said mouse encode an active Fc region. 
     
     
         33 . The method according to  claim 30 , wherein said genome of said mouse comprises no human Cμ genes. 
     
     
         34 . The method according to  claim 25 , wherein said non-mu heavy chain constant region of said mouse comprises a human CH1 gene segment. 
     
     
         35 . The method according to  claim 30 , wherein said gamma constant region of said mouse does not comprise a human CH1 gene segment. 
     
     
         36 . The method according to  claim 35 , wherein light chain expression is inactive in said mouse when non-mu heavy chains are expressed in the mouse. 
     
     
         37 . The method according to  claim 36 , wherein said IgH locus comprises said human CH2 and human CH3 gene segments are in place of corresponding endogenous non-mu heavy chain constant region gene segments of the same non-mu isotype. 
     
     
         38 . The method according to  claim 30 , wherein said human gamma CH2 and human gamma CH3 gene segments are in place of endogenous gamma constant region DNA in said genome of said mouse, whereby the human gamma CH2 and CH3 gene segments are functional to encode a gamma antibody Fc region. 
     
     
         39 . The method according to  claim 25 , wherein said human non-mu constant region of said mouse comprises a human gamma-1 constant region comprising human CH1, human CH2 and human CH3. 
     
     
         40 . The method according to of  claim 39 , wherein said mouse does not comprise a mouse gamma-1 constant region. 
     
     
         41 . The method according to  claim 25 , wherein said mouse does not express endogenous antibody heavy chains of said non-mu isotype. 
     
     
         42 . The method according to  claim 30 , wherein said human gamma constant region of said mouse comprises a human CH1 gene segment. 
     
     
         43 . The method according to  claim 25 , wherein said non-mu heavy chain constant region of said mouse does not comprise a human CH1 gene segment. 
     
     
         44 . The method according to  claim 25 , wherein said human CH2 and human CH3 gene segments of said mouse are human CH2 gamma-1 and human CH3 gamma-1 gene segments. 
     
     
         45 . The method according to  claim 30 , wherein said human CH2 and human CH3 gene segments of said mouse are human CH2 gamma-1 and human CH3 gamma-1 gene segments. 
     
     
         46 . The method according to  claim 30 , wherein said human non-mu constant region of said mouse comprises a human gamma CH1 gene segment in place of endogenous mouse gamma CH1 gene segment. 
     
     
         47 . The method according to  claim 25 , wherein said mouse is homozygous for insertion of the human DNA in first and second copies of an endogenous IgH antibody locus. 
     
     
         48 . A method of obtaining a nucleic acid encoding a human antibody heavy (IgH) chain variable region, the method comprising:
 obtaining or copying a nucleic acid encoding said human IgH chain variable region of said antibody,   wherein said human IgH chain variable region is of a transgenic mouse contacted with said antigen, said mouse comprising in its germline a chimeric homozygous immunoglobulin heavy chain locus; wherein the germline of said mouse 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) a non-mu heavy chain constant region comprising non-mu heavy chain constant region gene segments comprising a human CH2 gene segment and a human CH3 gene segment encoding non-mu antibody heavy chains comprising
 (i) non-mu 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 non-mu heavy chain constant region and comprised by an IgH locus, and wherein said human CH2 and human CH3 gene segments are in place of endogenous non-mu heavy chain constant region DNA, such that said human heavy chain variable region gene segments are able to recombine for expression of a non-mu antibody heavy chain comprising a human non-mu heavy chain antibody Fc region comprising a human CH2 and a human CH3 and a human heavy chain variable domain, wherein in said genome, human DNA is only in place of endogenous Ig antibody loci DNA. 
     
     
         49 . The method according to  claim 48 , wherein said genome of said mouse comprises endogenous recombination activating gene 1 (RAG-1) and recombination activating gene 2 (RAG-2) genes. 
     
     
         50 . The method according to  claim 48 , wherein said unrearranged human variable region of said locus of said mouse comprises a plurality of unrearranged human D and/or JH gene segments. 
     
     
         51 . The method according to  claim 50 , wherein said plurality of unrearranged human D gene segments of said mouse comprises at least 5 different human D gene segments. 
     
     
         52 . The method according to  claim 51 , wherein said plurality of unrearranged human JH gene segments of said mouse, comprises at least 2 different human JH gene segments. 
     
     
         53 . The method according to  claim 48 , wherein said non-mu constant region of said locus of said mouse comprises a human gamma constant region comprising a human gamma CH2 gene segment and a human gamma CH3 gene segment, wherein said human gamma CH2 and human gamma CH3 gene segments encode an antibody Fc region. 
     
     
         54 . The method according to  claim 53 , wherein said CH2 and CH3 gene segments of said mouse encode an inactive Fc region. 
     
     
         55 . The method according to  claim 53 , wherein said CH2 and CH3 gene segments of said mouse encode an active Fc region. 
     
     
         56 . The method according to  claim 53 , wherein said genome of said mouse comprises no human Cμ genes. 
     
     
         57 . The method according to  claim 48 , wherein said non-mu heavy chain constant region of said mouse comprises a human CH1 gene segment. 
     
     
         58 . The method according to  claim 53 , wherein said gamma constant region of said mouse does not comprise a human CH1 gene segment. 
     
     
         59 . The method according to  claim 58 , wherein light chain expression is inactive in said mouse when non-mu heavy chains are expressed in the mouse. 
     
     
         60 . The method according to  claim 59 , wherein said IgH locus comprises said human CH2 and human CH3 gene segments are in place of corresponding endogenous non-mu heavy chain constant region gene segments of the same non-mu isotype. 
     
     
         61 . The method according to  claim 53 , wherein said human gamma CH2 and human gamma CH3 gene segments are in place of endogenous gamma constant region DNA in said genome of said mouse, whereby the human gamma CH2 and CH3 gene segments are functional to encode a gamma antibody Fc region. 
     
     
         62 . The method according to  claim 48 , wherein said human non-mu constant region of said mouse comprises a human gamma-1 constant region comprising human CH1, human CH2 and human CH3. 
     
     
         63 . The method according to of  claim 62 , wherein said endogenous IgH locus of said mouse does not comprise a mouse gamma-1 constant region. 
     
     
         64 . The method according to  claim 48 , wherein said mouse does not express endogenous antibody heavy chains of said non-mu isotype. 
     
     
         65 . The method according to  claim 53 , wherein said human gamma constant region of said mouse comprises a human CH1 gene segment. 
     
     
         66 . The method according to  claim 48 , wherein said non-mu heavy chain constant region of said mouse does not comprise a human CH1 gene segment. 
     
     
         67 . The method according to  claim 48 , wherein said human CH2 and human CH3 gene segments of said mouse are human CH2 gamma-1 and human CH3 gamma-1 gene segments. 
     
     
         68 . The method according to  claim 53 , wherein said human CH2 and human CH3 gene segments of said mouse are human CH2 gamma-1 and human CH3 gamma-1 gene segments. 
     
     
         69 . The method according to  claim 53 , wherein said human non-mu constant region of said mouse comprises a human gamma CH1 gene segment in place of endogenous mouse gamma CH1 gene segment. 
     
     
         70 . The method according to  claim 48 , wherein said mouse is homozygous for insertion of the human DNA in first and second copies of an endogenous IgH antibody locus. 
     
     
         71 . The method of  claim 48 , wherein in said method of obtaining a nucleic acid encoding a human IgH chain variable region, said nucleic acid encoding said human IgH chain variable region is upstream of a nucleotide sequence encoding a human constant region. 
     
     
         72 . The method of  claim 71 , further comprising expressing a human IgH chain, where said human IgH chain is expressed by said nucleic acid encoding said human IgH chain variable region upstream of said nucleotide sequence encoding said human constant region. 
     
     
         73 . The method of  claim 72 , further comprising isolating (i) said human IgH chain expressed by said nucleic acid encoding said human IgH chain variable region upstream of said nucleotide sequence encoding said human constant region or (ii) an antibody comprising said human IgH chain of (i). 
     
     
         74 . The method of  claim 73 , further comprising formulating a pharmaceutical composition comprising said isolated human IgH chain or an antibody comprising said human IgH chain. 
     
     
         75 . The method of  claim 71 , further comprising inserting said nucleic acid encoding said human IgH chain variable region upstream of a nucleotide sequence encoding a human constant region into a vector. 
     
     
         76 . The method of  claim 48 , further comprising inserting said nucleic acid encoding said human IgH chain variable region into a vector. 
     
     
         77 . The method of  claim 76 , wherein said vector is an expression vector. 
     
     
         78 . The method of  claim 76 , further comprising inserting the vector of  claim 93  into a host cell. 
     
     
         79 . The method of  claim 77 , further comprising inserting the expression vector of  claim 94  into a host cell. 
     
     
         80 . The method of  claim 1 , wherein said human gamma-1 constant region of said mouse comprises a human IGHG1*01 CH2 gene segment and a human IGHG1*01 CH3 gene segment. 
     
     
         81 . The method of  claim 1 , wherein said human gamma-2 constant region of said mouse comprises a human IGHG2*01 CH2 gene segment and a human IGHG2*01 CH3 gene segment. 
     
     
         82 . The method of  claim 1 , wherein said gene locus of said mouse comprises a human gamma-3 constant region and/or a human gamma-4 constant region. 
     
     
         83 . The method of  claim 82 , wherein said human gamma-3 constant region of said mouse comprises a human IGHG3*04 CH2 gene segment and a human IGHG3*04 CH3 gene segment. 
     
     
         84 . The method of  claim 1 , wherein said gene locus of said mouse comprises a human alpha constant region. 
     
     
         85 . The method of  claim 1 , wherein said gene locus of said mouse comprises a human delta constant region. 
     
     
         86 . The method of  claim 1 , wherein said gene locus of said mouse comprises a human epsilon constant region. 
     
     
         87 . The method of  claim 1 , wherein said gamma-1 and/or gamma-2 constant region of said mouse excludes a CH1 gene segment. 
     
     
         88 . The method of  claim 1 , wherein said gene locus of said mouse comprises a nucleotide sequence selected from the group consisting of:
 (a) a nucleotide sequence consisting of the sequence from human gamma-3 to (and including) human gamma-4 constant regions;   (b) a nucleotide sequence consisting of the sequence from human gamma-3 to (and including) human gamma-2 constant regions;   (c) a nucleotide sequence consisting of the sequence from human gamma-3 to (and including) human gamma-1 constant regions;   (d) a nucleotide sequence consisting of the sequence from human gamma-1 to (and including) human gamma-4 constant regions;   (e) a nucleotide sequence consisting of the sequence from human gamma-1 to (and including) human gamma-2 constant regions; and   (f) a nucleotide sequence consisting of the sequence from human gamma-2 to (and including) human gamma-4 constant regions.   
     
     
         89 . The method of  claim 1 , wherein said gene locus of said mouse comprises a nucleotide sequence selected from the group consisting of:
 (i) a nucleotide sequence consisting of the sequence from human delta to (and including) human gamma-4 constant regions;   (ii) a nucleotide sequence consisting of the sequence from human delta to (and including) human gamma-2 constant regions;   (iii) a nucleotide sequence consisting of the sequence from human delta to (and including) human alpha-1 constant regions;   (iv) a nucleotide sequence consisting of the sequence from human delta to (and including) human gamma-1 constant regions; and   (v) a nucleotide sequence consisting of the sequence from human delta to (and including) human gamma-3 constant regions.   
     
     
         90 . The method of  claim 25 , wherein said human gamma-1 constant region of said mouse comprises a human IGHG1*01 CH2 gene segment and a human IGHG1*01 CH3 gene segment. 
     
     
         91 . The method of  claim 25 , wherein said human gamma-2 constant region of said mouse comprises a human IGHG2*01 CH2 gene segment and a human IGHG2*01 CH3 gene segment. 
     
     
         92 . The method of  claim 25 , wherein said gene locus of said mouse comprises a human gamma-3 constant region and/or a human gamma-4 constant region. 
     
     
         93 . The method of  claim 92 , wherein said human gamma-3 constant region comprises a human IGHG3*04 CH2 gene segment and a human IGHG3*04 CH3 gene segment. 
     
     
         94 . The method of  claim 25 , wherein said gene locus of said mouse comprises a human alpha constant region. 
     
     
         95 . The method of  claim 25 , wherein said gene locus of said mouse comprises a human delta constant region. 
     
     
         96 . The method of  claim 25 , wherein said gene locus of said mouse comprises a human epsilon constant region. 
     
     
         97 . The method of  claim 25 , wherein said gamma-1 and/or gamma-2 constant region of said mouse excludes a CH1 gene segment. 
     
     
         98 . The method of  claim 25 , wherein said gene locus of said mouse comprises a nucleotide sequence selected from the group consisting of:
 (a) a nucleotide sequence consisting of the sequence from human gamma-3 to (and including) human gamma-4 constant regions;   (b) a nucleotide sequence consisting of the sequence from human gamma-3 to (and including) human gamma-2 constant regions;   (c) a nucleotide sequence consisting of the sequence from human gamma-3 to (and including) human gamma-1 constant regions;   (d) a nucleotide sequence consisting of the sequence from human gamma-1 to (and including) human gamma-4 constant regions;   (e) a nucleotide sequence consisting of the sequence from human gamma-1 to (and including) human gamma-2 constant regions; and   (f) a nucleotide sequence consisting of the sequence from human gamma-2 to (and including) human gamma-4 constant regions.   
     
     
         99 . The method of  claim 25 , wherein said gene locus of said mouse comprises a nucleotide sequence selected from the group consisting of
 (i) a nucleotide sequence consisting of the sequence from human delta to (and including) human gamma-4 constant regions;   (ii) a nucleotide sequence consisting of the sequence from human delta to (and including) human gamma-2 constant regions;   (iii) a nucleotide sequence consisting of the sequence from human delta to (and including) human alpha-1 constant regions;   (iv) a nucleotide sequence consisting of the sequence from human delta to (and including) human gamma-1 constant regions; and   (v) a nucleotide sequence consisting of the sequence from human delta to (and including) human gamma-3 constant regions.   
     
     
         100 . The method of  claim 48 , wherein said human gamma-1 constant region of said mouse comprises a human IGHG1*01 CH2 gene segment and a human IGHG1*01 CH3 gene segment. 
     
     
         101 . The method of  claim 48 , wherein said human gamma-2 constant region of said mouse comprises a human IGHG2*01 CH2 gene segment and a human IGHG2*01 CH3 gene segment. 
     
     
         102 . The method of  claim 48 , wherein said gene locus of said mouse comprises a human gamma-3 constant region and/or a human gamma-4 constant region. 
     
     
         103 . The method of  claim 102 , wherein said human gamma-3 constant region comprises a human IGHG3*04 CH2 gene segment and a human IGHG3*04 CH3 gene segment. 
     
     
         104 . The method of  claim 48 , wherein said gene locus of said mouse comprises a human alpha constant region. 
     
     
         105 . The method of  claim 48 , wherein said gene locus of said mouse comprises a human delta constant region. 
     
     
         106 . The method of  claim 48 , wherein said gene locus of said mouse comprises a human epsilon constant region. 
     
     
         107 . The method of  claim 48 , wherein said gamma-1 and/or gamma-2 constant region of said mouse excludes a CH1 gene segment. 
     
     
         108 . The method of  claim 48 , wherein said gene locus of said mouse comprises a nucleotide sequence selected from the group consisting of:
 (a) a nucleotide sequence consisting of the sequence from human gamma-3 to (and including) human gamma-4 constant regions;   (b) a nucleotide sequence consisting of the sequence from human gamma-3 to (and including) human gamma-2 constant regions;   (c) a nucleotide sequence consisting of the sequence from human gamma-3 to (and including) human gamma-1 constant regions;   (d) a nucleotide sequence consisting of the sequence from human gamma-1 to (and including) human gamma-4 constant regions;   (e) a nucleotide sequence consisting of the sequence from human gamma-1 to (and including) human gamma-2 constant regions; and   (f) a nucleotide sequence consisting of the sequence from human gamma-2 to (and including) human gamma-4 constant regions.   
     
     
         109 . The method of  claim 48 , wherein said gene locus of said mouse comprises a nucleotide sequence selected from the group consisting of
 (i) a nucleotide sequence consisting of the sequence from human delta to (and including) human gamma-4 constant regions;   (ii) a nucleotide sequence consisting of the sequence from human delta to (and including) human gamma-2 constant regions;   (iii) a nucleotide sequence consisting of the sequence from human delta to (and including) human alpha-1 constant regions;   (iv) a nucleotide sequence consisting of the sequence from human delta to (and including) human gamma-1 constant regions; and   (v) a nucleotide sequence consisting of the sequence from human delta to (and including) human gamma-3 constant regions.   
     
     
         110 . 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) a heavy chain constant region comprising the human gamma-1 constant region, wherein said human gamma constant region comprises CH2, CH3, M1 and M2 gene segments,   said (a) and (b) encoding gamma-1 antibody heavy chains comprising (i) gamma-1 heavy chain constant domain and (ii) human heavy chain variable domains;   
       wherein said unrearranged human heavy chain variable region is upstream of and operably linked to said human gamma-1 heavy chain constant region and comprised by an IgH locus, wherein said human CH2 and human CH3 gene segments physically replace the respective CH2 and CH3 gene segments of endogenous mouse gamma-1 heavy chain constant region DNA, such that said human heavy chain variable region gene segments are able to recombine for expression of a gamma-1 antibody heavy chain comprising a human gamma-1 heavy chain antibody Fc region comprising a human CH2 and a human CH3 and a human heavy chain variable domain. 
     
     
         111 . 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,   wherein said mouse has been produced comprising:
 (i) targeted insertion of said human IgH chain variable region and said human IgH chain constant region DNA at the endogenous IgH locus of an ES cell of a bacterial artificial chromosomes (BAC), wherein said BAC comprises the entire sequence of human constant region DNA, 
 (ii) implanting the ES cell produced in (i) into a donor blastocyst, 
 (iii) implanting the blastocyst produced in (iii) into a foster mother; 
 (iv) selecting mice with germline transmission of said human constant region DNA 
 thereby producing mice having said human constant region DNA integrated at the endogenous mouse IgH locus, 
   (a) wherein said human IgH chain variable region comprises 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) wherein said human IgH chain constant region comprises a heavy chain constant region comprising the human gamma constant region, wherein said human gamma constant region comprises CH2, CH3, M1 and M2 gene segments,   said (a) and (b) encoding gamma antibody heavy chains comprising (i) gamma heavy chain constant domain and (ii) human heavy chain variable domains;   
       wherein said unrearranged human heavy chain variable region is upstream of and operably linked to said human gamma heavy chain constant region and comprised by an IgH locus, wherein said human CH2 and human CH3 gene segments are in place of the respective CH2 and CH3 gene segments of endogenous mouse gamma heavy chain constant region DNA, such that said human heavy chain variable region gene segments are able to recombine for expression of a gamma antibody heavy chain comprising a human gamma heavy chain antibody Fc region comprising a human CH2 and a human CH3 and a human heavy chain variable domain.