Baculoviruses in Biotechnology

Baculoviruses, a family of large DNA viruses primarily infecting insects, have emerged as valuable tools in biotechnology with diverse applications. Among these, the Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is particularly noteworthy. The versatility of baculoviruses stems from their ability to serve as expression vectors for recombinant protein production, providing an efficient platform for the synthesis of biologically relevant proteins (Miller, 1997; Boucias et al., 1998).

The insect baculoviruses are split into two groups, the nucleopolyhedroviruses (NPVs) and the granuloviruses (GVs) with similar biotechnology oriented promise. They were first characterised as the jaundice causing agent of Bombyrix, the silkworm larvae. Their pathology has also been exploited against insects and is a major discipline is its own right (Federici, 1997).

One of the key applications of baculoviruses in biotechnology is their role as expression vectors for recombinant protein production. The baculovirus expression vector system (BEVS) is now widely used for heterologous protein expression due to its powerful functionality and easy access to commercial expression vectors (Felberbaum, 2015). It involves the insertion of a target gene into the baculovirus genome, facilitating the production of the desired protein in insect cells. Unlike bacterial and yeast expression systems, insect cells infected with baculovirus offer an environment conducive to proper protein folding and post-translational modifications. This is particularly crucial for the production of complex proteins that require specific folding patterns or post-translational modifications, such as glycosylation.

It is the case that laboratories prefer two strategies for protein production. One version is recombinant bacmid based on transposition in Escherichia coli (e.g., Bac-to-Bac), and another is homologous recombination in insect cells (e.g., flashBac). Th BEVS platform has many advantages:-

• flexible product design
• manufacturing speed
• safety
• scaleability

Nine BEVS-derived products have been approved – four for human use (Cervarix®, Provenge®, Glybera® and Flublok®) and five for veterinary use (Porcilis® Pesti, BAYOVAC CSF E2®, Circumvent® PCV, Ingelvac CircoFLEX® and Porcilis® PCV). 

The use of baculovirus expression systems in insect cells is advantageous for producing proteins that closely mimic their native counterparts. Mammalian-like post-translational modifications, including glycosylation patterns, are crucial for the biological activity and efficacy of certain therapeutic proteins. Baculovirus-infected insect cells provide a eukaryotic cellular environment, facilitating the production of recombinant proteins with proper folding and post-translational modifications. This is especially relevant in the pharmaceutical industry, where the production of biologically active proteins, such as antibodies and enzymes, is a critical aspect of drug development.

Furthermore, baculoviruses have been instrumental in the production of virus-like particles (VLPs). VLPs are non-infectious particles that mimic the structure of viruses but lack the viral genetic material. Baculovirus-infected insect cells can be engineered to express and assemble VLPs from various viruses, including influenza, human papillomavirus (HPV), and others. These VLPs serve as promising candidates for vaccine development, as they can elicit an immune response without the risks associated with live viral components. The baculovirus system provides a safe and effective platform for the production of VLP-based vaccines.

In the realm of vaccine development, baculoviruses have been employed to produce recombinant vaccines. The ability to express large quantities of viral antigens in insect cells infected with baculovirus makes this system a robust platform for vaccine manufacturing. Baculovirus-based vaccines have been developed for various diseases, demonstrating their potential in addressing global health challenges. This approach not only allows for the rapid and scalable production of vaccines but also offers a safer alternative to traditional vaccine manufacturing methods.

The specificity of baculoviruses to insect hosts has also been harnessed for biological pest control in agriculture. While this application is distinct from their role in biotechnology, it highlights the versatility of baculoviruses in addressing diverse challenges. Commercial formulations of baculovirus-based biopesticides are used to control insect pests in a targeted and environmentally friendly manner. These biopesticides have gained popularity as sustainable alternatives to chemical insecticides, as they are specific to certain insect species and have minimal impact on non-target organisms.

While baculoviruses have found success in various biotechnological applications, their use in gene therapy research is an area of ongoing exploration. Although not as common as viral vectors derived from adenoviruses or lentiviruses, baculovirus vectors are being investigated for their potential in gene delivery. The safety profile of baculoviruses, coupled with their ability to infect non-dividing cells, makes them intriguing candidates for certain gene therapy applications.

The Baculovirus Expression System (BEVS)

A recombinant baculovirus is designed as a vector to express heterologous genes (foreign genes if you like) into cultured insect cells and larvae. These heterologous genes are placed under transcriptional control of the strong polyhedrin promoter of the Autographa californica polyhedrosis virus (AcNPV). The mode of action is based on site specific transposition of an expression cassette i.e. pfast Bac with the gene of interest, into a baculovirus shuttle vector (the bacmid).

The gene of interest then is cloned into a pfast Bac donor plasmid. An expression cassette in the pfast Bac plasmid is flanked by left and right arms of Tn7 and also an SV40 polyadenylation signal to form a miniTn7.

The cloned pfast Bac is transformed in an E.coli host strain such as DH10Bac which contains a baculovirus shuttle vector bacmid having a mini-attTn7 target site. A helper plasmid allows transposition of the gene of interest from pfast to bacmid (shuttle vector). Transposition occurs between the mini-att Tn7 target site to generate a recombinant bacmid. This recombinant bacmid is then used to transfect insect cells.

In conclusion, baculoviruses have emerged as powerful tools in biotechnology, with diverse applications ranging from the production of recombinant proteins and virus-like particles to vaccine development and biological pest control. The unique attributes of baculovirus expression systems, such as their capacity for proper protein folding and post-translational modifications, make them indispensable in the production of biologically active proteins. As biotechnological research continues to advance, the applications of baculoviruses are likely to expand, offering innovative solutions to a wide array of challenges in medicine, agriculture, and beyond.

References

Boucias, D. G., Pendland, J. C., Boucias, D. G., & Pendland, J. C. (1998) Baculoviruses. Principles of Insect Pathology, pp. 111-146

Federici, B. A. (1997). Baculovirus pathogenesis. In The Baculoviruses . Boston, MA: Springer US. (pp. 33-59)

Felberbaum, R.S. (2015) The baculovirus expression system: A commercial manufacturing platform for viral vaccines and gene therapy vectors. Biotechnol. J. 10(5) pp. 702-714 (Article)

Miller, L. K. (Ed.). (1997). The Baculoviruses. Springer Science & Business Media.