Bivalent, bispecific antibodies

1. A bivalent, bispecific antibody, comprising:

a) the light chain and heavy chain of an antibody specifically binding to a first antigen; and

b) the light chain and heavy chain of an antibody specifically binding to a second antigen, wherein constant domains CL and CH1 from the antibody specifically binding to a second antigen are replaced by each other.

2. The antibody according to claim 1 ,

wherein the CH3 domain of one heavy chain and the CH3 domain of the other heavy chain each meet at an interface;

wherein the CH3 domain of one heavy chain is altered so that within the original interface the CH3 domain of one heavy chain that meets the original interface of the CH3 domain of the other heavy chain within the bivalent, bispecific antibody, an amino acid residue is replaced with an amino acid residue having a larger side chain volume, thereby generating a protuberance within the interface of the CH3 domain of one heavy chain which is positionable in a cavity within the interface of the CH3 domain of the other heavy chain; and

wherein the CH3 domain of the other heavy chain is altered so that within the original interface of the second CH3 domain that meets the original interface of the first CH3 domain within the bivalent, bispecific antibody an amino acid residue is replaced with an amino acid residue having a smaller side chain volume, thereby generating a cavity within the interface of the second CH3 domain within which the protuberance within the interface of the first CH3 domain is positionable.

3. The antibody according to claim 2 , wherein the amino acid residue having a larger side chain volume is selected from the group consisting of arginine (R), phenylalanine (F), tyrosine (Y), tryptophan (W).

4. The antibody according to claim 2 , wherein the amino acid residue having a smaller side chain volume is selected from the group consisting of alanine (A), serine (S), threonine (T), valine (V).

5. The antibody according to claim 3 , wherein the amino acid residue having a smaller side chain volume is selected from the group consisting of alanine (A), serine (S), threonine (T), valine (V).

6. The antibody according to claim 2 , wherein both CH3 domains are further altered by the introduction of cysteine (C) as amino acid in the corresponding positions of each CH3 domain.

7. The antibody according to claim 3 , wherein both CH3 domains are further altered by the introduction of cysteine (C) as amino acid in the corresponding positions of each CH3 domain.

8. The antibody according to claim 4 , wherein both CH3 domains are further altered by the introduction of cysteine (C) as amino acid in the corresponding positions of each CH3 domain.

9. The antibody according to claim 1 , wherein one of the CH3 domains is replaced by a constant heavy chain domain CH1; and the other CH3 domain is replaced by a constant light chain domain CL.

10. A method for the preparation of a bivalent, bispecific antibody according to claim 1 comprising the steps of:

a) transforming a host cell with

vectors comprising nucleic acid molecules encoding the light chain and heavy chain of an antibody specifically binding to a first antigen

vectors comprising nucleic acid molecules encoding the light chain and heavy chain of an antibody specifically binding to a second antigen, wherein the constant domains CL and CH1 from the antibody specifically binding to a second antigen are replaced by each other;

b) culturing the host cell under conditions that allow synthesis of said antibody; and

c) recovering said antibody from said culture.

11. A composition comprising a bivalent, bispecific antibody according to claim 1 and at least one pharmaceutically acceptable excipient.

12. A composition comprising a bivalent, bispecific antibody according to claim 6 and at least one pharmaceutically acceptable excipient.

13. A composition comprising a bivalent, bispecific antibody according to claim 9 and at least one pharmaceutically acceptable excipient.