Domain-exchanged antibody

1. A bispecific domain-exchanged antibody comprising a first dimer and a second dimer, each dimer comprising a light chain (LC) and a heavy chain (HC), wherein the LC and HC are each formed from antibody domains selected from the group consisting of VL, VH, CL, CH1, CH2, and CH3, comprising:

a) a first LC paired with a first HC to form the first dimer, the first dimer having a first binding site that recognizes a first epitope, wherein:

i) the first LC comprises the following domains in order from N-terminus to C-terminus: VL-CH3 LC , wherein CH3 LC is a CH3 domain; and

ii) the first HC comprises the following domains in order from N-terminus to C-terminus: VH-CH3 HC1 -CH2-CH3 HC2 , wherein CH3 HC1 and CH3 HC2 are each CH3 domains, further comprising a hinge between the CH3 HC1 and the CH2 domains,

wherein CH3 LC binds to CH3 HC1 thereby forming a first CH3 pair; and

b) a second LC paired with a second HC to form the second dimer, the second dimer having a second binding site that recognizes a second epitope different from the first epitope, wherein:

iii) the second LC comprises the following domains in order from N-terminus to C-terminus: VL-CL; and

iv) the second HC comprises the following domains in order from N-terminus to C-terminus: VH-CH1-CH2-CH3, further comprising a hinge between the CH1 domain and the CH2 domains,

wherein the CH2 domain of the first dimer binds the CH2 domain of the second dimer, and the CH3 HC2 domain of the first dimer binds the CH3 domain of the second dimer, thereby forming a second CH3 pair and an Fc region of the antibody,

wherein the CH3 domains of the first CH3 pair each comprise a mutation according to one of the following embodiments v) to ix) and the CH3 domains of the second CH3 pair each comprise a mutation according to one of the following embodiments v) to ix), the mutations of the CH3 domains of the first CH3 pair being different from the mutations of the CH3 domains of the second CH3 pair:

v) one CH3 domain of the CH3 pair and the other CH3 domain of the same CH3 pair respectively comprise a complementary knob and hole mutation;

vi) a cysteine residue of one CH3 domain of the CH3 pair is covalently linked to a cysteine residue of the other CH3 domain of the same CH3 pair, thereby introducing an interdomain disulfide bridge;

vii) one CH3 domain of the CH3 pair and the other CH3 domain of the same CH3 pair each comprises alternating segments of human IgA and IgG CH3 sequences;

viii) one CH3 domain of the CH3 pair and the other CH3 domain of the same CH3 pair each comprises one or more mutations where a repulsive charge suppresses heterodimer formation; or

ix) one CH3 domain of the CH3 pair and the other CH3 domain of the same CH3 pair respectively each comprise mutations from the group consisting of:

T350V:L351Y:F405A:Y407V/T350V:T366L:K392L:T394W,

T350V:L351Y:F405A:Y407V/T350V:T366L:K392M:T394W,

L351Y:F405A:Y407V/T366L:K392M:T394W,

F405A:Y407V/T366L:K392M:T394W, and

F405A:Y407V/T366L:T394W,

wherein numbering is according to the EU index of Kabat.

2. The antibody of claim 1 , wherein the antibody further comprises an additional CH3 domain on the C-terminus of the CH3 HC2 domain of the first dimer and an additional CH3 domain on the C-terminus of the CH3 domain of the second dimer.

3. The antibody of claim 1 , wherein the knob Of and hole mutation is selected from the group consisting of T366Y/Y407′T, F405A/T394′W, T366Y:F405A/T394′W:Y407′T, T366W/Y407′A, and S354C:T366W/Y349′C:T366'S:L368′A:Y407′V, wherein numbering is according to the EU index of Kabat.

4. The antibody of claim 1 , wherein the interdomain disulfide bridge links the C-terminus of the CH3 domain of the second dimer and the CH3 HC2 domain of the first dimer.

5. The antibody of claim 1 , wherein the one or more mutations comprising a repulsive charge that suppresses heterodimer formation are selected from the group consisting of K409D/D399′K, K409D/D399′R, K409E/D399′K, K409E/D399′R, K409D:K392D/D399′K:E356′K and K409D:K392D:K370D/D399′K:E356′K:E357′K, wherein numbering is according to the EU index of Kabat.

6. The antibody of claim 1 , wherein the antibody is an effector-function competent antibody comprising a Fc gamma receptor binding site and/or a C1q binding site located in any of the CH2 and/or CH3 domains.

7. The antibody of claim 1 , wherein the antibody is an effector-negative antibody comprising a Fc region deficient in binding to an Fc gamma receptor and/or C1q.

8. The antibody of claim 1 , wherein the antibody comprises a pH-dependent FcRn binding site located in any of the CH2 and/or CH3 domains.

9. The antibody of claim 1 , wherein the first binding site recognizes CD3 or CD16, and wherein the second binding site recognizes EGFR.

10. The antibody of claim 1 , wherein at least one of the CH3 LC or the CH3 HC1 domains of the first CH3 pair comprises at least one mutation at the FcRn binding site to reduce pH-dependent FcRn binding, wherein the at least one mutation is selected from the group consisting of a H433A mutation and a H435A mutation, wherein the numbering is according to the EU index of Kabat.

11. The antibody of claim 1 , wherein the CH2 and/or CH3 domains of the antibody are of human origin, are humanized, or are functionally active variants thereof with at least 60% sequence identity to the respective human IgG1 antibody domains.

12. The antibody of claim 1 , wherein the interdomain disulfide bridge links the C-terminus of CH3 L c domain and the CH3 H ci domain of the first CH3 pair.