A DNA sequence encoding the human IL27B (NP_005746.2)(Met1-Lys229) was fused with a flag tag at the C-terminus, constructed the plasmid 1; A DNA sequence encoding the human IL12A (NP_000873.2)(Met1-Ser219) was fused with a polyhistidine tag at the C-terminus, constructed the plasmid 2. The two plasmids were co-expressed and the human IL27B&IL12A heterodimer was purified.