Bispecific t cell activating antigen binding molecules

A T cell activating bispecific antigen binding molecule comprising

• a) a first Fab molecule which specifically binds to a first antigen;
• b) a second Fab molecule which specifically binds to a second antigen, and wherein the variable domains VL and VH of the Fab light chain and the Fab heavy chain are replaced by each other;
• c) a third Fab molecule which specifically binds to the first antigen;
• and
• d) an Fc domain composed of a first and a second subunit capable of stable association;
• wherein
• (i) the first antigen is CD20 and the second antigen is CD3, particularly CD3 epsilon;
• (ii) the first Fab molecule under a) and the third Fab molecule under c) each comprise the heavy chain complementarity determining region (CDR) 1 of SEQ ID NO:
• 46, the heavy chain CDR 2 of SEQ ID NO:
• 47, the heavy chain CDR 3 of SEQ ID NO:
• 48, the light chain CDR 1 of SEQ ID NO:
• 49, the light chain CDR 2 of SEQ ID NO:
• 50 and the light chain CDR 3 of SEQ ID NO:
• 51, and the second Fab molecule under b) comprises the heavy chain CDR 1 of SEQ ID NO:
• 4, the heavy chain CDR 2 of SEQ ID NO:
• 5, the heavy chain CDR 3 of SEQ ID NO:
• 6, the light chain CDR 1 of SEQ ID NO:
• 8, the light chain CDR 2 of SEQ ID NO:
• 9 and the light chain CDR 3 of SEQ ID NO:
• 10;
• (iii) in the constant domain CL of the first Fab molecule under a) and the third Fab molecule under c) the amino acid at position 124 is substituted by lysine (K) (numbering according to Kabat) and the amino acid at position 123 is substituted by lysine (K) or arginine (R), particularly by arginine (R) (numbering according to Kabat), and wherein in the constant domain CH1 of the first Fab molecule under a) and the third Fab molecule under c) the amino acid at position 147 is substituted by glutamic acid (E) (numbering according to Kabat EU index) and the amino acid at position 213 is substituted by glutamic acid (E) (numbering according to Kabat EU index);
• and
• (iv) the first Fab molecule under a) is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the second Fab molecule under b), and the second Fab molecule under b) and the third Fab molecule under c) are each fused at the C-terminus of the Fab heavy chain to the N-terminus of one of the subunits of the Fc domain under d).