Human papillomavirus-like particles vaccine efficiently produced in a non-fermentative system based on insect larva

Platforms for Production of Protein-Based Vaccines: From Classical to Next-Generation Strategies

To date, vaccination has become one of the most effective strategies to control and reduce infectious diseases, preventing millions of deaths worldwide. The earliest vaccines were developed as live-attenuated or inactivated pathogens, and, although they still represent the most extended human vaccine types, they also face some issues, such as the potential to revert to a pathogenic form of live-attenuated formulations or the weaker immune response associated with inactivated vaccines. Advances in genetic engineering have enabled improvements in vaccine design and strategies, such as recombinant subunit vaccines, have emerged, expanding the number of diseases that can be prevented. Moreover, antigen display systems such as VLPs or those designed by nanotechnology have improved the efficacy of subunit vaccines. Platforms for the production of recombinant vaccines have also evolved from the first hosts, Escherichia coli and Saccharomyces cerevisiae, to insect or mammalian cells. Traditional bacterial and yeast systems have been improved by engineering and new systems based on plants or insect larvae have emerged as alternative, low-cost platforms. Vaccine development is still time-consuming and costly, and alternative systems that can offer cost-effective and faster processes are demanding to address infectious diseases that still do not have a treatment and to face possible future pandemics.

A Recombinant Baculovirus Efficiently Generates Recombinant Adeno-Associated Virus Vectors in Cultured Insect Cells and Larvae

Current large-scale recombinant adeno-associated virus (rAAV) production systems based on the baculovirus expression vector (BEV) remain complicated and cost-intensive, and they lack versatility and flexibility. Here we present a novel recombinant baculovirus integrated with all packaging elements for the production of rAAV. To optimize BEV construction, ribosome leaky-scanning mechanism was used to express AAV Rep and Cap proteins downstream of the PH and P10 promoters in the pFast.Bac.Dual vector, respectively, and the rAAV genome was inserted between the two promoters. The yields of rAAV2, rAAV8, and rAAV9 derived from the BEV-infected Sf9 cells exceeded 10⁵ vector genomes (VG) per cell. The BEV was shown to be stable and showed no apparent decrease of rAAV yield after at least four serial passages. The rAAVs derived from the new Bac system displayed high-quality and high-transduction activity. Additionally, rAAV2 could be efficiently generated from BEV-infected beet armyworm larvae at a per-larvae yield of 2.75 ± 1.66 × 10¹⁰ VG. The rAAV2 derived from larvae showed a structure similar to the rAAV2 derived from HEK293 cells, and it also displayed high-transduction activity. In summary, the novel BEV is ideally suitable for large-scale rAAV production. Further, this study exploits a potential cost-efficient platform for rAAV production in insect larvae.

In vivo production of recombinant proteins using occluded recombinant AcMNPV-derived baculovirus vectors

Trichoplusia ni insect larvae infected with vectors derived from the Autographa californica multiple nucleopolyhedrovirus (AcMNPV), are an excellent alternative to insect cells cultured in conventional bioreactors to produce recombinant proteins because productivity and cost-efficiency reasons. However, there is still a lot of work to do to reduce the manual procedures commonly required in this production platform that limit its scalability. To increase the scalability of this platform technology, a current bottleneck to be circumvented in the future is the need of injection for the inoculation of larvae with polyhedrin negative baculovirus vectors (Polh-) because of the lack of oral infectivity of these viruses, which are commonly used for production in insect cell cultures. In this work we have developed a straightforward alternative to obtain orally infective vectors derived from AcMNPV and expressing recombinant proteins that can be administered to the insect larvae (Trichoplusia ni) by feeding, formulated in the insect diet. The approach developed was based on the use of a recombinant polyhedrin protein expressed by a recombinant vector (Polh+), able to co-occlude any recombinant Polh- baculovirus vector expressing a recombinant protein. A second alternative was developed by the generation of a dual vector co-expressing the recombinant polyhedrin protein and the foreign gene of interest to obtain the occluded viruses. Additionally, by the incorporation of a reporter gene into the helper Polh+ vector, it was possible the follow-up visualization of the co-occluded viruses infection in insect larvae and will help to homogenize infection conditions. By using these methodologies, the production of recombinant proteins in per os infected larvae, without manual infection procedures, was very similar in yield to that obtained by manual injection of recombinant Polh- AcMNPV-based vectors expressing the same proteins. However, further analyses will be required for a detailed comparison of production yields reached by injection vs oral infections for different recombinant proteins. In conclusion, these results open the possibility of future industrial scaling-up production of recombinant proteins in insect larvae by reducing manual operations.

A Recombinant Viral Hemorrhagic Septicemia Virus Genotype IVb Glycoprotein Produced in Cabbage Looper Larvae Trichoplusia ni Elicits Antibody Response and Protection in Muskellunge

The Novirhabdovirus viral hemorrhagic septicemia virus (VHSV) genotype IVb has caused serious fish kills and become endemic throughout the Great Lakes basin of North America. This is troublesome since there are no protective vaccines currently approved against this deadly disease even though recombinant technology has become increasingly common. Herein, we explored the production of a recombinant VHSV-IVb glycoprotein, believed to be important for virus infectivity, and determined its ability to elicit protection against challenge with the wild virus strain. A recombinant baculovirus containing a 5' 6x polyhistidine tag embedded in the VHSV-IVb G gene was used to infect the larvae of the cabbage looper Trichoplusia ni. A sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of affinity-purified protein yielded apparent VHSV-IVb glycoprotein at the expected molecular weight of ~65 kDa. The recombinant protein (rG) was used successfully in coating microtiter plate wells in an indirect enzyme-linked immunosorbent assay (ELISA), and positive anti-VHSV-IVb antibodies in Muskellunge Esox masquinongy were capable of binding to both the rG and purified whole VHSV-IVb, indicating epitope resemblance. In addition, the rG elicited a protective response in Muskellunge during a VHSV-IVb immersion challenge, resulting in 80% relative percent survival. Our results demonstrate that cabbage looper larvae can serve as an excellent production system for apparently conformationally correct viral glycoprotein. The incorporation of a polyhistidine tag facilitates obtaining highly purified protein in a relatively high concentration, which has potential in the development of an efficacious subunit vaccine against this deadly virus. Received September 11, 2016; accepted March 10, 2017.

Protein Production with Recombinant Baculoviruses in Lepidopteran Larvae

With an increasing need for functional analysis of proteins, there is a growing demand for fast and cost-effective production of biologically active eukaryotic proteins. The baculovirus expression vector system (BEVS) is widely used, and in the vast majority of cases cultured insect cells have been the host of choice. A low cost alternative to bioreactor-based protein production exists in the use of live insect larvae as "mini bioreactors." In this chapter we focus on Trichoplusia ni as the host insect for recombinant protein production, and explore three different methods of virus administration to the larvae. The first method is labor-intensive, as extracellular virus is injected into each larva, whereas the second lends itself to infection of large numbers of larvae via oral inoculation. While these first two methods require cultured insect cells for the generation of recombinant virus, the third relies on transfection of larvae with recombinant viral DNA and does not require cultured insect cells as an intermediate stage. We suggest that small- to mid-scale recombinant protein production (mg-g level) can be achieved in T. ni larvae with relative ease.

Comparison of strategies for the production of FMDV empty capsids using the baculovirus vector system

Recombinant FMDV empty capsids have been produced in insect cells and larvae using the baculovirus expression system, although protein yield and efficiency of capsid assembly have been highly variable. In this work, two strategies were compared for the expression of FMDV A/Arg/01 empty capsids: infection with a dual-promoter baculovirus vector coding for the capsid precursor (P12A) and the protease 3C under the control of the polyhedrin and p10 promoters, respectively (BacP12A-3C), or a single-promoter vector coding the P12A3C cassette (BacP12A3C). Expression levels and assembly into empty capsids were analyzed in insect cells and larvae. We observed that the use of the single-promoter vector allowed higher levels of expression both in insect cells and larvae. Recombinant capsid proteins produced by both vectors were recognized by monoclonal antibodies (mAbs) directed against conformational epitopes of FMDV A/Arg/01 and proved to self-assemble into empty capsids (75S) and pentamers (12S) when analyzed by sucrose gradient centrifugation.

Head-to-head comparison of three vaccination strategies based on DNA and raw insect-derived recombinant proteins against Leishmania

Parasitic diseases plague billions of people among the poorest, killing millions annually, and causing additional millions of disability-adjusted life years lost. Leishmaniases affect more than 12 million people, with over 350 million people at risk. There is an urgent need for efficacious and cheap vaccines and treatments against visceral leishmaniasis (VL), its most severe form. Several vaccination strategies have been proposed but to date no head-to-head comparison was undertaken to assess which is the best in a clinical model of the disease. We simultaneously assayed three vaccination strategies against VL in the hamster model, using KMPII, TRYP, LACK, and PAPLE22 vaccine candidate antigens. Four groups of hamsters were immunized using the following approaches: 1) raw extracts of baculovirus-infected Trichoplusia ni larvae expressing individually one of the four recombinant proteins (PROT); 2) naked pVAX1 plasmids carrying the four genes individually (DNA); 3) a heterologous prime-boost (HPB) strategy involving DNA followed by PROT (DNA-PROT); and 4) a Control including empty pVAX1 plasmid followed by raw extract of wild-type baculovirus-infected T. ni larvae. Hamsters were challenged with L. infantum promastigotes and maintained for 20 weeks. While PROT vaccine was not protective, DNA vaccination achieved protection in spleen. Only DNA-PROT vaccination induced significant NO production by macrophages, accompanied by a significant parasitological protection in spleen and blood. Thus, the DNA-PROT strategy elicits strong immune responses and high parasitological protection in the clinical model of VL, better than its corresponding naked DNA or protein versions. Furthermore, we show that naked DNA coupled with raw recombinant proteins produced in insect larvae biofactories -the cheapest way of producing DNA-PROT vaccines- is a practical and cost-effective way for potential "off the shelf" supplying vaccines at very low prices for the protection against leishmaniases, and possibly against other parasitic diseases affecting the poorest of the poor.

Rotavirus A-specific single-domain antibodies produced in baculovirus-infected insect larvae are protective in vivo

Background

Single-domain antibodies (sdAbs), also known as nanobodies or VHHs, are characterized by high stability and solubility, thus maintaining the affinity and therapeutic value provided by conventional antibodies. Given these properties, VHHs offer a novel alternative to classical antibody approaches. To date, VHHs have been produced mainly in E. coli, yeast, plants and mammalian cells. To apply the single-domain antibodies as a preventive or therapeutic strategy to control rotavirus infections in developing countries (444,000 deaths in children under 5 years of age) has to be minimized their production costs.

Results

Here we describe the highly efficient expression of functional VHHs by the Improved Baculovirus Expression System (IBES® technology), which uses a baculovirus expression vector in combination with Trichoplusia ni larvae as living biofactories. Two VHHs, named 3B2 and 2KD1, specific for the inner capsid protein VP6 of Group A rotavirus, were expressed in insect larvae. The IBES® technology achieved very high expression of 3B2 and 2KD1, reaching 2.62% and 3.63% of the total soluble protein obtained from larvae, respectively. These expression levels represent up to 257 mg/L of protein extract after insect processing (1 L extract represents about 125 g of insect biomass or about 375 insect larvae). Larva-derived antibodies were fully functional when tested in vitro and in vivo, neutralizing Group A rotaviruses and protecting offspring mice against rotavirus-induced diarrhea.

Conclusions

Our results open up the possibility of using insects as living biofactories (IBES® technology) for the cost-efficient production of these and other fully functional VHHs to be used for diagnostic or therapeutic purposes, thereby eliminating concerns regarding the use of bacterial or mammalian cells. To the best of our knowledge, this is the first time that insects have been used as living biofactories to produce a VHH molecule.

New approaches to prophylactic human papillomavirus vaccines for cervical cancer prevention

The currently licensed human papillomavirus (HPV) vaccines are safe and highly effective at preventing HPV infection for a select number of papillomavirus types, thus decreasing the incidence of precursors to cervical cancer. It is expected that vaccination will also ultimately reduce the incidence of this cancer. The licensed HPV vaccines are, however, type restricted and expensive, and also require refrigeration, multiple doses and intramuscular injection. Second-generation vaccines are currently being developed to address these shortcomings. New expression systems, viral and bacterial vectors for HPV L1 capsid protein delivery, and use of the HPV L2 capsid protein will hopefully aid in decreasing cost and increasing ease of use and breadth of protection. These second-generation vaccines could also allow affordable immunization of women in developing countries, where the incidence of cervical cancer is high.

Insect larvae biofactories as a platform for influenza vaccine production

Increased production capacity is one of the most important priorities for seasonal and pandemic influenza vaccines. In the present study, we used a baculovirus-insect larvae system (considered small, living biofactories) to improve the production of recombinant influenza virus H1N1 hemagglutinin (HA). Insect larvae produced four-fold more HA protein than insect cells per biomass unit (1 g of fresh larvae weight). A single infected Trichoplusia ni larva produced up to 113 μg of soluble and easily purified recombinant HA, an amount similar to that produced by 1.2×10(8) Sf21 insect cells infected by the same baculovirus. The use of the KDEL endoplasmic reticulum retention signal fused to the HA protein further increased recombinant protein production. Larvae-derived HA was immunogenically functional in vaccinated mice, inducing the generation of hemagglutination inhibition antibodies and a protective immune response against a lethal challenge with a highly virulent virus. The productivity, scalability and cost efficiency of small, living biofactories based on insect larvae suggest a broad-based strategy for the production of recombinant subunit vaccines against seasonal or pandemic influenza as an alternative to fermentation technologies.