Heteromultimers with reduced or silenced effector function

1. A heteromultimer comprising an IgG Fc construct having a first and a second Fc polypeptide, each Fc polypeptide comprising a modified lower hinge region, wherein:

a. the modified lower hinge region of the first Fc polypeptide comprises the amino acid modifications L234K/L235K and the modified lower hinge region of the second Fc polypeptide comprises the amino acid modifications L234A/L235A; or

b. the modified lower hinge region of the first Fc polypeptide comprises the amino acid modifications L234K/L235K and the modified lower hinge region of the second Fc polypeptide comprises the amino acid modifications L234D/L235E; or

c. the modified lower hinge region of the first Fc polypeptide comprises the amino acid modifications E233A/L234R/L235R and the modified lower hinge region of the second Fc polypeptide comprises the amino acid modifications E233A/L234D/L235E, or

d. the modified lower hinge region of the first Fc polypeptide comprises the amino acid modifications E233K/L234R/L235R and the modified lower hinge region of the second Fc polypeptide comprises the amino acid modifications L234D/L235E; or

e. the modified lower hinge region of the first Fc polypeptide comprises the amino acid modifications E233K/L234A/L235K and the modified lower hinge region of the second Fc polypeptide comprises the amino acid modifications E233A/L234K/L235A; or

f. the first Fc polypeptide comprises the amino acid modifications E233K/L234R/L235R/D265S and the second Fc polypeptide comprises the amino acid modifications L234D/L235E/D265S; or

g. the first Fc polypeptide comprises the amino acid modifications E233K/L234R/L235R/E269K and the second Fc polypeptide comprises the amino acid modifications L234D/L235E/E269K; or

h. the first Fc polypeptide comprises the amino acid modifications E233K/L234R/L235R/K322A and the second Fc polypeptide comprises the amino acid modifications L234D/L235E/K322A; or

i. the first Fc polypeptide comprises the amino acid modifications E233K/L234R/L235R/P329W and the second Fc polypeptide comprises the amino acid modifications L234D/L235E/P329W; or

j. the first Fc polypeptide comprises the amino acid modifications E233K/L234R/L235R/E269K/D265S/K322A and the second Fc polypeptide comprises the amino acid modifications L234D/L235E/E269K/D265S/K322A; or

k. the first Fc polypeptide comprises the amino acid modifications E233K/L234R/L235R/E269K/D265S/K322E/E333K and the second Fc polypeptide comprises the amino acid modifications L234D/L235E/E269K/D265 S/K322E/E333K,

wherein the IgG Fc construct displays reduced binding to the FcγRIa, FcγRIIa, FcγRIIb and FcγRIIIa receptors as compared to a corresponding parent IgG Fc construct,

wherein the IgG Fc construct is an IgG1, IgG3 or IgG4 Fc construct,

and wherein the numbering of amino acids is according to the EU index as in Kabat.

2. The heteromultimer according to claim 1 , wherein the IgG Fc construct is aglycosylated or deglycosylated.

3. The heteromultimer according to claim 1 , wherein

one of the first and second Fc polypeptides comprises the CH3 amino acid modifications T366L/N390R/K392M/T394W and the other Fc polypeptide comprises the CH3 amino acid modifications L351Y/S400E/F405A/Y407V.

4. The heteromultimer according to claim 1 , wherein the heteromultimer further comprises at least one antigen-binding construct fused to the IgG Fc construct.

5. The heteromultimer according to claim 4 , wherein the at least one antigen-binding construct is a Fab fragment, an scFv, an sdAb, an antigen binding peptide, an Fc fusion protein, or a protein or fragment thereof capable of binding the antigen.

6. The heteromultimer according to claim 4 , comprising one or two antigen-binding constructs.

7. The heteromultimer according to claim 1 , wherein the IgG Fc construct is linked to one or more toxic drug molecules or one or more heterologous polypeptides.

8. The heteromultimer according to claim 7 , wherein the one or more heterologous polypeptides are selected from enzymes and toxins.

9. The heteromultimer according to claim 1 , wherein the IgG Fc construct is an IgG1 Fc construct.

10. A pharmaceutical composition comprising the heteromultimer according to claim 1 and a pharmaceutically acceptable carrier.

11. The heteromultimer according to claim 1 , wherein the IgG Fc construct further displays reduced binding to C1q protein as compared to the corresponding parent IgG Fc construct.

12. The heteromultimer according to claim 1 , wherein one of the first and second Fc polypeptides comprises the CH3 amino acid modifications L351Y/F405A/Y407V and the other Fc polypeptide comprises the CH3 amino acid modifications T366L/K392M/T394W.

13. The heteromultimer according to claim 1 , wherein one of the first and second Fc polypeptides comprises the CH3 amino acid modifications L351Y/F405A/Y407V and the other Fc polypeptide comprises the CH3 amino acid modifications T366L/K392L/T394W.

14. The heteromultimer according to claim 1 , wherein one of the first and second Fc polypeptides comprises the CH3 amino acid modifications T350V/L351Y/F405A/Y407V and the other Fc polypeptide comprises the CH3 amino acid modifications T350V/T366L/K392L/T394W.

15. The heteromultimer according to claim 1 , wherein one of the first and second Fc polypeptides comprises the CH3 amino acid modifications T350V/L351Y/F405A/Y407V and the other Fc polypeptide comprises the CH3 amino acid modifications T350V/T366L/K392M/T394W.

16. The heteromultimer according to claim 1 , wherein one of the first and second Fc polypeptides comprises the CH3 amino acid modifications T350V/L351Y/S400F/F405A/Y407V and the other Fc polypeptide comprises the CH3 amino acid modifications T350V/T366L/N390R/K392M/T394W.