Human interleukin-2 production in insect (Trichoplusia ni) larvae: Effectsand partial control of proteolysis

Many eukaryotic proteins have been successfully expressed in insect cells i nfected with a baculovirus in which the foreign gene has been placed under the control of a viral promoter. This system can be costly at large scale d ue to the quality of virus stock, problems of oxygen transfer, and severity of large-scale contamination. To circumvent this problem, we have investig ated the expression of a foreign protein, human interleukin-2 (IL-2), in in sect larvae, Trichoplusia ni, infected with the baculovirus Autographa cali fornica nuclear polyhedrosis virus (AcNPV). The IL-2 gene was placed under control of the p10 promoter so that the polyhedra remained intact for effic ient primary infection. From our results, it was clear that early infection limited larval growth and late infection delayed product production until near pupation, hence infection timing was important. Also, the harvest time was crucial for obtaining high yield, because IL-2 production had a sharp optimal peak with a time of occurrence dependent on both temperature and th e initial a mount of infection virus. Specifically, we found that, by raisi ng the infection temperature to 30 degrees C, we more than doubled the prot ein productivity. Furthermore, a significant concern of the larvae/baculovi rus expression system has been the large amount of protease produced by the larvae, which adversely affects the protein yield. Therefore, we screened several protease inhibitors and characterized the larval protease specifici ty and timing to attenuate their impact. This report elucidates and delinea tes the factors that most directly impact protein yield in the larvae expre ssion system, using IL-2 as a model. (C) 1999 John Wiley & Sons, Inc. Biote chnol Bioeng 62: 175-182,1999.