A DNA sequence encoding the extracellular domain (Met1-Asp108) of mouse CD3E (NP_031674.1) was fused with the C-terminal polyhistidine tagged Fc region of human IgG1 at the C-terminus, constructed the plasmid 1; A DNA sequence encoding the extracellular domain (Met1-Ser116) of mouse CD3G (NP_033980.1) was fused with the Fc region of human IgG1 at the C-terminus, constructed the plasmid 2. The two plasmids were co-expressed and the mouse CD3E/CD3G heterodimer was purified.