BacMam Platform for Vaccine Antigen Delivery

Recombinant Protein Production in Suspension Mammalian Cells Using the BacMam Baculovirus Expression System

Mammalian cell lines are one of the best options when it comes to the production of complex proteins requiring specific glycosylation patterns. Plasmid DNA transfection and stable cell lines are frequently used for recombinant protein production, but they are expensive at large scale or can become time-consuming, respectively. The BacMam baculovirus (BV) is a safe and cost-effective platform to produce recombinant proteins in mammalian cells. The process of generating BacMam BVs is straightforward and similar to the generation of "insect" BVs, with different commercially available platforms. Although there are several protocols that describe recombinant protein expression with the BacMam BV in adherent cell lines, limited information is available on suspension cells. Therefore, it is of relevance to define the conditions to produce recombinant proteins in suspension cell cultures with BacMam BVs that facilitate bioprocess transfer to larger volumes. Here, we describe a method to generate a high titer BacMam BV stock and produce recombinant proteins in suspension HEK293 cells.

Identification of African swine fever virus-like elements in the soft tick genome provides insights into the virus' evolution

BACKGROUND

African swine fever virus (ASFV) is a most devastating pathogen affecting swine. In 2007, ASFV was introduced into Eastern Europe where it continuously circulates and recently reached Western Europe and Asia, leading to a socio-economic crisis of global proportion. In Africa, where ASFV was first described in 1921, it is transmitted between warthogs and soft ticks of the genus Ornithodoros in a so-called sylvatic cycle. However, analyses into this virus' evolution are aggravated by the absence of any closely related viruses. Even ancient endogenous viral elements, viral sequences integrated into a host's genome many thousand years ago that have proven extremely valuable to analyse virus evolution, remain to be identified. Therefore, the evolution of ASFV, the only known DNA virus transmitted by arthropods, remains a mystery.

RESULTS

For the identification of ASFV-like sequences, we sequenced DNA from different recent Ornithodoros tick species, e.g. O. moubata and O. porcinus, O. moubata tick cells and also 100-year-old O. moubata and O. porcinus ticks using high-throughput sequencing. We used BLAST analyses for the identification of ASFV-like sequences and further analysed the data through phylogenetic reconstruction and molecular clock analyses. In addition, we performed tick infection experiments as well as additional small RNA sequencing of O. moubata and O. porcinus soft ticks.

CONCLUSION

Here, we show that soft ticks of the Ornithodoros moubata group, the natural arthropod vector of ASFV, harbour African swine fever virus-like integrated (ASFLI) elements corresponding to up to 10% (over 20 kb) of the ASFV genome. Through orthologous dating and molecular clock analyses, we provide data suggesting that integration could have occurred over 1.47 million years ago. Furthermore, we provide data showing ASFLI-element specific siRNA and piRNA in ticks and tick cells allowing for speculations on a possible role of ASFLI-elements in RNA interference-based protection against ASFV in ticks. We suggest that these elements, shaped through many years of co-evolution, could be part of an evolutionary virus-vector 'arms race', a finding that has not only high impact on our understanding of the co-evolution of viruses with their hosts but also provides a glimpse into the evolution of ASFV.

Crude extracts of recombinant baculovirus expressing rabbit hemorrhagic disease virus 2 VLPs from both insect and rabbit cells protect rabbits from rabbit hemorrhagic disease caused by RHDV2

Vaccines against viral pathogens are often composed of recombinant proteins expressed in different systems. Such proteins expressed by recombinant baculoviruses have been proven to be effective for vaccination. Especially, after codon usage optimization high amounts of recombinant viral proteins can be obtained which can assemble to virus like particles (VLPs) spontaneously. In this study we compared two different codon usages of RHDV2-VP1 to improve the expression of recombinant VP1 of RHDV2 by recombinant baculoviruses after infection of insect SF9 cells or transduction of mammalian RK13 cells in order to gain high protein yields. Also the influence on the auto-assembly of RHDV2-VP1 to VLPs was investigated. Finally, the immunogenic potential of such recombinant vaccines against RHDV2 to induce a protective immune response in rabbits against RHDV2 should be characterized. There was no influence of different codon usages on RHDV2-VP1 gene expression in the respective cell lines detected. However, in insect cell line SF9 higher rates of recombinant VP1 were measured in comparison to the transduction of mammalian cells RK13. Auto-assembly of RHDV2-VP1 to VLPs was observed in both cell systems by electron microscopy. Finally, both RHDV-VP1 VLPs derived from mammalian and insect cells were able to induce a protective humoral immune response in rabbits against RHDV2.