The Coming Age of Insect Cells for Manufacturing and Development of Protein Therapeutics

Abstract

Protein therapeutics is a rapidly growing segment of the pharmaceutical market. Currently, the majority of protein therapeutics are manufactured in mammalian cells for their ability to generate safe and efficacious human-like glycoproteins. The high cost of using mammalian cells for manufacturing has motivated a constant search for alternative host platforms. Insect cells have begun to emerge as a promising candidate, largely due to the development of the baculovirus expression vector system. While there are continuing efforts to improve insect-baculovirus expression for producing protein therapeutics, key limitations including cell lysis and the lack of homogeneous humanized glycosylation still remain. The field has started to see a movement toward virus-less gene expression approaches, notably the use of clustered regularly interspaced short palindromic repeats to address these shortcomings. This review highlights recent technological advances that are realizing the transformative potential of insect cells for the manufacturing and development of protein therapeutics.

Figure 1.

Timeline of approvals made by the FDA and EMA for recombinant protein therapeutics for human use overlaid with significant technological advances and regulation events.^,–

Figure 2.

Overview of the BEVS and strategies to address issues associated with product contamination and glycosylation. BEVS includes four major steps: (A) Cloning the gene of interest (GOI) into a transfer plasmid and transposing into the baculovirus genome in a specialized E. coli strain (DH10Bac). (B) Transfection of the purified recombinant baculovirus genome in insect cells to form recombinant baculovirus progeny (Note: direct homologous recombination in insect cells could also be used but is not shown for simplicity). (C) Amplification to generate high-titer viral stocks. (D) Expression of the target protein. The six strategies listed have been applied at one of the four steps.

Figure 3.

Comparison of the flipase-based recombination method and CRISPR for creating a stable cell line. Flipase-based recombination first requires the “tagging” integration of a reporter gene into a random location of the genome. High-expressing clones are isolated and expanded as master cell lines. A “targeting” integration exchanges the reporter with the target protein cassette(s) through the use of flipase. CRISPR in theory requires one round of site-specific integration of the target protein; thus, it could accelerate the creation of stable cell lines.