Virus like particles (VLP) Expression platforms
Structure of capsid proteins is important to stimulate the immune response and it is depended on the post translational modification of different expression systems. The various expression systems such as prokaryotic (bacteria, yeast) or eukaryotic (baculovirus/insect cell, mammalian cell and plant) have been used to produce the VLP. In addition, cell-free expression systems have also been used successfully. Selecting a suitable system is important and system has both advantages and disadvantages (Fuenmayor et al. 2017).
1. Bacteria based virus like particles (VLP)
Bacteria are one of the most widely used systems for the non-enveloped virus like particles production. Escherichia coli-based expression system has advantages such as cost-effective, rapid cell growth and high protein expression level to produce safe VLP. However, prokaryotic expression system is not suitable for some protein due to the lack of PTM system. Various VLP vaccines produced by E. coli have been successfully used against infectious and non-infectious diseases.
2. Yeast based virus like particles (VLP)
Yeast is also most commonly used for VLPs production. Saccharomyces cerevisiae and Pichia pastoris, are the widely used yeast expression system. The yeast system has the advantages such as rapid cell growth, high yield, scalability, cost-effective, and PTM process.
3. Baculovirus/Insect cells (B/IC) based virus like particles (VLP)
The B/IC expression system is used to produce both enveloped- and non-enveloped-VLPs. The insect cell lines viz. Spodoptera frugiperda (Sf9/Sf21) and Trichoplusia ni (Tn5) is commonly used for VLP production. Due to its fast growth, it is convenient to produce the vaccines for outbreaks such as influenza virus. It has advantages such as high yield of proteins, complex PTM pathways. The Baculovirus/insect cell platform has been used to develop the vaccine against HIV 1, influenza virus A, Chikungunya virus, severe acute respiratory syndrome (SARS), Ebola virus, dengue fever virus, Rift Valley fever virus (RVFV), Norwalk virus and HCV.
4. Plants cells-based virus like particles (VLP)
Plant-based VLP platform is a versatile and cost effective. It has the advantages such as expression levels of up to 80% total soluble protein, low refining costs, and high-performance expression processing. Numerous studies on the VLP vaccines based on plant system have been effectively created. The plant viruses such as Tobaco Mosaic Virus (TMV), cucumber mosaic virus (CMV), alfalfa mosaic virus (AIMV), cowpea mosaic virus (CPMV), papaya mosaic virus (PapMV), and the potato X virus (PVX) have been used for the VLP platform.
5. Mammalian and avian cells-based virus like particles (VLP)
Animal cell expression systems is a valued platforms for producing the structural proteins of non-enveloped and enveloped VLPs. Animal cell platforms are most effective due to its complex and precise PTMs. The animal cell lines such as CHO, baby hamster kidney-21 (BHK-21), human embryonic kidney 293 (HEK293), CAP‐T cell line derived from human amniocytes, Vero 9, and east lansing line-0 (ELL-0) are widely used system for the VLPs production. Among them, CHO has been most commonly used and it has the advantage over other cell lines.
| Expression system | Advantages | Disadvantages |
|---|---|---|
| Bacteria | Cost-effective Scalable Fast growth High level of expression Genetically stable |
Poor immunogenic Absence of PTM Poor protein stability Presence of bacterial endotoxin |
| Yeast | Low cost no endotoxin contamination high density fermentation support some protein folding |
Low yield than bacteria Lack of mammalian PTM system High mannose modification |
| Insect cells | Uptake and deliver large amount of DNA High level of protein expression Support PTM Proper protein folding and assembly |
Difficult to scale up Production cost is high Baculovirus contamination possibility PTM not similar to mammalian system Incomplete protein modification |
| Mammalian cells | Proper PTM, protein folding and assembly | Large scale production Expression time Low yield Mycoplasma contamination |
| Plant cells | Highly scalable Cost effective High expression Proper folding and assembly |
Lower yield than mammalian cells Technical issues |
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