Heterodimeric proteins

A heterodimeric antibody comprising:

• a) a first monomer comprising:
• i) a first variant Fc domain;
• and
• ii) a single chain Fv region (scFv) that binds a first antigen, wherein said scFv region comprises a first variable heavy domain, a first variable light domain and a scFv linker, wherein said scFv linker covalently attaches said first variable heavy domain and said first variable light domain;
• and
• b) a second monomer comprising a VH-CH1-hinge-CH2-CH3 monomer, wherein VH is a second variable heavy domain and CH2-CH3 is a second variant Fc domain;
• and
• c) a light chain comprising a second variable light domain (VL) and a constant light chain region;
• wherein said VH and VL bind a second antigen, wherein said second variant Fc domain comprises amino acid substitutions N208D/Q295E/N384D/Q418E/N421D, wherein said first and second variant Fc domains each comprise amino acid substitutions E233P/L234V/L235A/G236del/S267K and M428L/N434S;
• and wherein said first variant Fc domain comprises amino acid substitutions S364K/E357Q and second variant Fc domain comprises amino acid substitutions L368D/K370S, wherein numbering is according to the EU index as in Kabat.