Compositions and methods for simultaneous bivalent and monovalent co-engagement of antigens

1. An antibody analog comprising:

a) a first heavy chain and an associated light chain, wherein said first heavy and light chains form a first antigen binding site, wherein the C-terminus of the CH3 domain of said first heavy chain is covalently attached to a C-terminal variable heavy domain, wherein said first heavy chain comprises a first variant Fc domain;

b) a second heavy chain and an associated light chain, wherein said second heavy and light chains form a second antigen binding site, wherein the C-terminus of the CH3 domain of said second heavy chain is covalently attached to a C-terminal variable light domain; wherein said second heavy chain comprises a second variant Fc domain;

such that said C-terminal variable heavy and light domains form a third antigen binding site, wherein said first and second variant Fc domains are different, and wherein the first and second variant Fc domains have amino acid substitutions selected from the following pairs:

A

B

K409E and

L368K;

S364D/K370G and

S364Y/K370R;

S364D and

Y349K;

K409D and

L368K;

K392E and

D399K;

S364E and

Y349K;

L368E/K409E and

L368K;

S364E/F405A and

Y349K/T394F;

S364H and

Y349K;

P395T/V397S/F405A and

T394F;

T394S/P395V/P396T/V397E/F405S and

T394F;

V397S/F405A and

T394F;

S364H/D401K/F405A and

Y349T/T394F/T411E;

L351K/S364H/D401K and

Y349T/L351E/T411E;

S364H and

Y349T;

S364H/D401K and

Y349T/T411E;

S364H/T394F and

Y349T/F405A;

S364H/F405A and

Y349T/T394F;

F405A and

T394F;

S364E/T394F and

Y349K/F405A;

V397T/F405S and

T394F;

S364E/F405S and

Y349K/T394Y;

S364E/T411E/F405A and

Y349K/T394F/D401K;

S364E/T411E and

Y349K/D401K;

L351E/S364D and

Y349K/L351K;

L351E/S364E and

Y349K/L351K;

Y349C/S364E and

Y349K/S354C;

S364H/F405A/T411E and

Y349T/T394F/D401K;

S364D/T394F and

Y349K/F405A

and wherein numbering is according to the EU index as in Kabat and wherein the substitution(s) of column A and column B are in different heavy chains selected from the first heavy chain and the second heavy chain.

2. The antibody analog of claim 1 , wherein the first and second variant Fc domains have amino acid substitutions selected from the following pairs:

C

D

S364E/F405A and

Y349K/T394F;

S364H/D401K and

Y349T/T411E;

S364H/T394F and

Y349T/F405A;

S364E/T394F and

Y349K/F405A;

S364E/T411E and

Y349K/D401K;

S364D/T394F and

Y349K/F405A;

S364H/F405A and

Y349T/T394F

and wherein the substitution(s) of column C and column D are in different heavy chains selected from the first heavy chain and the second heavy chain.

3. An antibody analog according to claim 1 wherein two of said antigen binding sites are the same and the third is different.

4. An antibody analog according to claim 1 wherein the antigen bound by said third antigen binding site is CD3.

5. An antibody analog according to claim 1 wherein the antigen bound by said third antigen binding site is FcγRIIb.

6. An antibody analog according to claim 1 wherein all three of said antigen binding sites are the same.

7. An antibody analog according to claim 1 wherein said the C-terminus of said C-terminal variable heavy domain is covalently attached to a CH1 domain and wherein said C-terminus of said C-terminal variable light domain is covalently attached to a CL domain.

8. An antibody analog according to claim 1 wherein said first and second Fc domains further comprise at least one substitution that reduces binding to at least one FcγR receptor.

9. An antibody analog according to claim 1 wherein said first and second Fc domains further comprise at least one substitution that increases binding to at least one FcγR receptor.

10. An antibody analog according to claim 1 wherein said first and second Fc domains further comprise at least one substitution that increases binding to the FcRn receptor.