Production of a recombinant mouse monoclonal antibody in transgenic silkworm cocoons

In the present study, we describe the production of transgenic silkworms expressing a recombinant mouse mAb in their cocoons. Two transgenic lines, L‐ and H‐, were generated that carried cDNAs encoding the L‐ and H‐chains of a mouse IgG mAb, respectively, under the control of the enhancer‐linked sericin‐1 promoter. Cocoon protein analysis indicated that the IgG L‐ or H‐chain was secreted into the cocoons of each line. We also produced a transgenic line designated L/H, which carried both cDNAs, by crossing the L‐ and H‐lines. This line efficiently produced the recombinant mAb as a fully assembled H 2 L 2 tetramer in its cocoons, with negligible L‐ or H‐chain monomer and H‐chain dimer production. Thus, the H 2 L 2 tetramer was synthesized in, and secreted from, the middle silk gland cells. Crossing of the L/H‐line with a transgenic line expressing a baculovirus‐derived trans ‐activator produced a 2.4‐fold increase in mAb expression. The recombinant mAb was extracted from the cocoons with a buffer containing 3  m urea and purified by protein G affinity column chromatography. The antigen‐binding affinity of the purified recombinant mAb was identical to that of the native mAb produced by a hybridoma. Analysis of the structure of the N ‐glycans attached to the recombinant mAb revealed that the mAb contained high mannose‐, hybrid‐ and complex‐type N ‐glycans. By contrast, insect‐specific paucimannose‐type glycans were not detected. Fucose residues α‐1,3‐ and α‐1,6‐linked to the core N ‐acetylglucosamine residue, both of which are found in insect N ‐glycans, were not observed in the N ‐glycans of the mAb.