Fusion protein

A fusion protein comprising two different first and second chains,

• wherein the first chain comprises two antibody variable regions VH1 and VH2, one antibody variable region VL2, and one antibody constant region CH1 or CL,
• the second chain comprises two antibody variable regions VL1 and VL3, one antibody variable region VH3, and one antibody constant region CL or CH1,
• the first and second chains contain a heterodimeric interaction, and
• a VH1/VL1 binding domain, a VH2/VL2 binding domain, and a VH3/VL3 binding domain, which are three combinatorial VH/VL binding domains formed within the fusion protein, have any binding ability selected from the following (provided that the three combinatorial VH/VL binding domains have different binding abilities from one another):
• (i) ability to bind to 5T4;
• (ii) ability to bind to a CD3 receptor complex;
• and
• (iii) ability to bind to PD-1, PD-L1, or LAG3.