A DNA sequence encoding the Cynomolgus (Macaca fascicularis) CD3E extracellular domain (Met 1-Asp 117) was fused with the C-terminal his-tagged Fc region of human IgG1 at the C-terminus, constructed the plasmid 1; A DNA sequence encoding the Cynomolgus (Macaca fascicularis) CD3D extracellular domain (Met 1-Ala 105) with the C-terminal flag-tagged Fc region of human IgG1 at the C-terminus, constructed the plasmid 2. The two plasmids were co-expressed and the CD3E&CD3D heterodimer was purified.