GENERATION OF HEAVY-CHAIN ONLY ANTIBODIES IN TRANSGENIC ANIMALS

1 - 34 . (canceled)

35 . A method for increasing the diversity of V H heavy chain-only antibodies in a transgenic non-human mammal comprising the steps of

a) providing a transgenic non-human mammal whose genome comprises more than one heterologous V H heavy chain locus, wherein each heterologous V H heavy chain locus comprises V H gene segments, D gene segments, and J gene segments, and a gene segment encoding a heavy chain constant region which, when expressed, does not include a functional C H 1 domain and

b) expressing a V H heavy chain-only antibody from at least one of said loci in B-cells,

wherein said V H gene segments do not encode camelid VHH domains, and wherein said heterologous V H heavy chain loci are present on the same or different chromosomes, and the expression of a heterologous V H locus is determined by allelic exclusion.

36 . The method of claim 35 , wherein each heavy chain locus comprises one V H gene segment.

37 . The method of claim 35 , wherein each V H gene segment is different from all other V H gene segments.

38 . The method of claim 35 , wherein the V H gene segments are of human origin.

39 . The method of claim 35 , wherein the multiple V H heavy chain loci comprise any number or combination of the 39 functional human V gene segments.

40 . The method of claim 39 , wherein each different V H heavy chain locus is present as a single copy in the genome of the transgenic non-human mammal.

41 . The method of claim 35 , wherein each V H heavy chain locus comprises from one to forty D gene segments.

42 . The method of claim 35 , wherein the D gene Segments are human D gene segments.

43 . The method of claim 35 , wherein each V H heavy chain locus comprises from one to twenty J gene segments.

44 . The method of claim 35 , wherein the J gene segments are human J gene segments.

45 . The method of claim 35 , wherein each V H heavy chain locus comprises one or more human V H gene segments, twenty-five functional human D gene segments and 6 human J gene segments.

46 . The method of claim 35 , wherein each gene segment encoding a heavy chain constant region comprises one or more heavy chain constant region exons of the Cδ, Cγ 1-4 , Cμ, Cε or Cα 1-2 classes, with the proviso that at least one of the heavy chain constant region gene segments does not express a C H 1 domain.

47 . The method of claim 35 , wherein the heavy chain constant region is of human origin.

48 . The method of claim 45 , wherein the heavy chain constant region is of human origin.

49 . The method of claim 35 , wherein the transgenic non-human mammal is a rodent.

50 . The method of claim 45 , wherein the transgenic non-human mammal is a rodent.

51 . The method of claim 49 , wherein the rodent is a mouse.

52 . A transgenic non-human mammal comprising more than one heterologous V H heavy chain locus as defined in claim 35 .

53 . A transgenic non-human mammal comprising more than one heterologous V H heavy chain locus as defined in claim 45 .

54 . A method for the production of heavy chain-only antibodies comprising:

a) immunising a transgenic non-human mammal of claim 52 with an antigen; and

b) isolating antigen-specific heavy chain-only antibodies.

55 . A method for the production of heavy chain-only antibodies comprising:

a) immunising a transgenic non-human mammal of claim 53 with an antigen; and

b) isolating antigen-specific heavy chain-only antibodies.

56 . A method of producing high affinity, antigen-specific V H heavy chain-only antibodies comprising:

a) immunising a transgenic non-human mammal according to claim 52 with an antigen;

b) generating B-cell hybridomas;

c) selecting cells expressing antigen-specific heavy chain-only antibody; and

d) isolating antigen-specific heavy chain-only antibody.

57 . A method of producing high affinity, antigen-specific V H heavy chain-only antibodies comprising:

a) immunising a transgenic non-human mammal according to claim 53 with an antigen;

b) generating B-cell hybridomas;

c) selecting cells expressing antigen-specific heavy chain-only antibody; and

d) isolating antigen-specific heavy chain-only antibody.