Insect Cell Glycosylation Patterns in the Context of Biopharmaceuticals

Abstract

The baculovirus expression vector system (BEVS) was originally described in 1983 [1]. This binary expression system consists of a lepidopteran insect cell or insect host and a recombinant baculoviral vector encoding one or more proteins of interest (for reviews see [2–7]). The insect cell lines used in the BEVS are derived from pupae, larvae or eggs of a wide variety of lepidopteran insect species. The most commonly used cell lines are derived from Trichoplusia ni (BTI-TN-5B1-4, commercially available as High Five [8]) andSpodoptera frugiperda (IPLB-Sf21AE [9] and Sf9 [6]). These immortalized cell lines can be grown as adherent cultures in T-flasks or as suspension cultures in Fernbach flasks, spinner flasks, or in airlift, stirred-tank or WAVE bioreactors. Baculovirus vectors are recombinant viruses that can productively infect insect, but not mammalian cells. Recombinant baculoviruses can be produced using several different approaches involving either homologous recombination [10, 11] or DNA transposition [12]. Genes encoding the protein of interest in baculovirus expression vectors are typically placed under the control of strong transcriptional promoters derived from the very late baculoviral polyhedrin or p10 genes. Alternatively, they can be placed under the control of weaker promoters derived from baculoviral late (e.g., p6.9) [13] or immediate early (e.g., ie1) promoters [14]. Recombinant baculovirus vectors are used to infect insects or insect cells, thus inducing production of the recombinant protein as a by-product of the infection process. Recombinant protein production is transient because baculovirus infections are cytolytic. Nonetheless, the BEVS can produce recombinant proteins at very high levels due to amplification of the vector and the extraordinary strength of the very late gene promoters typically used to drive foreign gene expression. Furthermore, the BEVS is a eukaryotic system that can produce soluble, biologically active recombinant proteins with coand post-translational modifications, including glycosylation.