Anti-cd28 x anti-enpp3 antibodies

A heterodimeric antibody comprising:

• a) a first monomer comprising:
• i) a single chain variable fragment (scFv);
• and
• ii) a first Fc domain, wherein the scFv is covalently attached to the N-terminus of the first Fc domain using a domain linker;
• b) a second monomer comprising, from N-terminal to C-terminal, a VH1-CH1-hinge-CH2-CH3, wherein VH1 is a first variable heavy domain and CH2-CH3 is a second Fc domain;
• and
• c) a light chain comprising, from N-terminal to C-terminal, VL1-CL, wherein VL1 is a first variable light domain and CL is a constant light domain,
• wherein the scFv comprises a second VH domain (VH2), a scFv linker, and a second variable light domain (VL2),
• wherein the VH1 and the VL1 together form a first antigen binding domain (ABD) and the VH2 and the VL2 together form a second ABD, and
• wherein one of the first ABD and second ABD is a CD28 binding domain and the other of the first ABD and second ABD is a Ectonucleotide Pyrophosphatase/Phosphodiesterase 3 (ENPP3) binding domain.

A heterodimeric antibody comprising:

• a) a first monomer comprising an amino acid sequence of SEQ ID NO:745;
• b) a second monomer comprising an amino acid sequence of SEQ ID NO:746;
• and
• c) a light chain comprising an amino acid sequence of SEQ ID NO:747.