Manufacturing Pharmaceutical-Grade Interferons Using Silkworm- Baculovirus System

Abstract

To develop feline and canine interferons as medicine for companion animal, silkworm-baculovirus expression system was established as a manufacturing technology. Thus produced interferons were successfully cleared for a sale in commercial market. For expression of feline interferon in the silkworm, recombinant Bombyx mori nucleopolyhedrovirus (BmNPV) was constructed carrying feline interferon cDNA. When the recombinant BmNPV was injected to silkworm larvae, as much as 1.2 × 10 8 unit/mL of feline interferon was produced in their hemolymph. This productivity is 100–fold higher than those of E. coli, yeast and mammalian cell expression system. Similarly, canine interferon-γ was produced in the largest amount in silkworm. Two or more forms of interferons were produced due to various processing in silkworm. For feline interferon, two forms of protein molecule resulting from two different cleavage sites in signal peptide sequence was solved by reconstitution of a single amino acid in signal sequence. In the case of canine interferon- γ, several variations were produced due to glycosylation pattern and C-terminal degradation, but removal of glycosylation sites and elimination of C-terminal 16 amino acids sequence from native sequence lead to uniformity of the expressed protein. Drug formulated two recombinant animal interferons were approved as a treatment of viral diseases and atopic dermatitis by regulatory authorities. Especially, feline interferon is now sold in 20 countries including Japan and Europe.