Multispecific antigen binding fragments and multispecific antibodies derived therefrom comprising mutant CH1 and CL-kappa domains

1. A multispecific antigen-binding fragment comprising at least two Fab fragments with different CH1 and CL domains, wherein said Fab fragments comprise:

a. a mutated Fab fragment consisting of:

i. the VH and VL domains of an antibody recognizing an epitope of interest;

ii. a CH1 domain of a human immunoglobulin comprising substitution of the leucine residue at position 143 of said CH1 domain with a glutamine residue and substitution of the serine residue at position 188 of said CH1 domain with a valine residue; and

iii. a CL-kappa domain of a human immunoglobulin comprising substitution of the valine residue at position 133 of said CL domain with a threonine residue and substitution of the serine residue at position 176 of said CL domain with an valine residue; and

b. at least a Fab fragment which is selected from the group consisting of

b1) a mutated Fab fragment consisting of:

i. the VH and VL domains of an antibody recognizing an epitope of interest;

ii. a CH1 domain of a human immunoglobulin comprising substitution of the threonine residue at position 192 of said CH1 domain with a glutamic acid residue; and

iii. a CL-kappa domain of a human immunoglobulin by comprising substitution of the asparagine residue at position 137 of said CL domain with a lysine residue and substitution of the serine residue at position 114 of said CL domain with an alanine residue;

b2) a mutated Fab fragment consisting of:

i. the VH and VL domains of an antibody recognizing an epitope of interest;

ii. a CH1 domain of a human immunoglobulin comprising substitution of the leucine residue at position 124 of said CH1 domain with an alanine residue and substitution of the leucine residue at position 143 of said CH1 domain with a glutamic acid residue; and

iii. a CL-kappa domain of a human immunoglobulin comprising substitution of the valine residue at position 133 of said CL domain with a tryptophan residue;

b3) a mutated Fab fragment consisting of:

i. the VH and VL domains of an antibody recognizing an epitope of interest;

ii. a CH1 domain of a human immunoglobulin comprising substitution of the valine residue at position 190 of said CH1 domain with an alanine residue; and

iii. a CL-kappa domain of a human immunoglobulin comprising substitution of the leucine residue at position 135 of said CL domain with a tryptophan residue, and substitution of the asparagine residue at position 137 of said CL domain with an alanine residue; and

b4) a wild-type Fab fragment consisting of wild-type CH1 and wild-type CL domains of an immunoglobulin, and the VH and VL domains of an antibody recognizing an epitope of interest;

wherein the position numbers used for the CH1 and CL domains refer to Kabat numbering and each Fab fragment recognizes a different epitope of interest, and said Fab fragments are tandemly arranged in any order, the C-terminal end of the CH1 domain of the first Fab fragment being linked to the N-terminal end of the VH domain of the following Fab fragment through a polypeptide linker.

2. The multispecific antigen-binding fragment of claim 1 , wherein said Fab fragments comprise:

a. a mutated Fab fragment consisting of:

i. the VH and VL domains of an antibody recognizing an epitope of interest;

ii. a CH1 domain of a human immunoglobulin comprising substitution of the leucine residue at position 143 of said CH1 domain with a glutamine residue and substitution of the serine residue at position 188 of said CH1 domain with a valine residue; and

iii. a CL-kappa domain of a human immunoglobulin comprising substitution of the valine residue at position 133 of said CL-kappa domain with a threonine residue and substitution of the serine residue at position 176 of said CL-kappa domain with a valine residue; and

b. a Fab fragment consisting of:

i. the VH and VL domains of an antibody recognizing an epitope of interest;

ii. a CH1 domain of a human immunoglobulin comprising substitution of the threonine residue at position 192 of said CH1 domain with a glutamic acid residue; and

iii. a CL-kappa domain of a human immunoglobulin comprising substitution of the asparagine residue at position 137 of said CL domain with a lysine residue and substitution of the serine residue at position 114 of said CL domain with an alanine residue.

3. The multispecific antigen-binding fragment of claim 1 , wherein the polypeptide linker has a length of at least 20 amino-acids.

4. The multispecific antigen-binding fragment of claim 1 , wherein the polypeptide linker comprises all or part of the sequence of the hinge region of one or more immunoglobulin(s) selected among IgA, IgG, and IgD.

5. The multispecific antigen-binding fragment of claim 1 , wherein the polypeptide linker has the sequence of SEQ ID NO:9.

6. A multispecific antibody having two identical antigen-binding arms, each consisting of the multispecific antigen-binding fragment of claim 1 .

7. A multispecific antibody having two identical antigen-binding arms and an immunoglobulin-like structure, wherein the multispecific antibody comprises:

a. two identical antigen-binding arms, with each consisting of the multispecific antigen-binding fragment of any of claims 1 to 5 ,

b. the dimerized CH2 and CH3 domains of an immunoglobulin; and

c. the hinge region of an IgA, IgG, or IgD, linking the C-terminal ends of CH1 domains of the antigen-binding arms to the N-terminal ends of the CH2 domains.

8. An isolated polynucleotide comprising a sequence encoding the heavy chain of the multispecific antibody of claim 6 , wherein when the heavy chain is paired with complementary VL domains, the VH region/VL region pairs form antigen binding sites.

9. An isolated host-cell transformed with a polynucleotide encoding the heavy chain of the multispecific antigen-binding fragment of claim 1 and at least two polynucleotides encoding two different light chains, wherein the first light chain pairs specifically with a first VH/CH1 region of said heavy chain and the second light chain pairs specifically with a second VH/CH1 region of said heavy chain.

10. The isolated host cell of claim 9 , wherein at least one of said light chains is the light chain of a mutated Fab fragment.

11. A method of preparing a multispecific antigen-binding fragment wherein the method comprises culturing the isolated host-cell of claim 9 and recovering said antigen-binding fragment from the culture.

12. A therapeutic composition comprising the multispecific antigen-binding fragment of claim 1 and a pharmaceutically acceptable vehicle.

13. A therapeutic composition comprising a multispecific antibody of claim 6 and a pharmaceutically acceptable vehicle.