Rabies vaccine development by expression of recombinant viral glycoprotein

Single-injection subunit vaccine for rabies prevention using lentinan as adjuvant

Current rabies vaccines require 5 doses to provide full protection from the deadly virus, which significantly reduce the compliance of recipients. To minimize the number of immunizations herein single injection vaccines were developed. First a single injection vaccine was designed using rabies virus glycoprotein (G protein) as antigen. A time-controlled release system which uses dynamic layer-by-layer films as erodible coating was employed to accomplish multiply pulsatile releases of G protein. The single-injection vaccine elicits potent humoral and cellular immune responses comparable to the corresponding multi-dose ordinary vaccines because of their similar release pattern of G protein. To further improve its performance, a second single injection vaccine, in which lentinan was added as adjuvant, was designed. This single-injection vaccine again elicits humoral and cellular immune responses comparable to the corresponding multi-dose ordinary vaccines because of their similar release pattern of antigen and adjuvant. In addition, the second single-injection vaccine elicits higher level immune response and provides higher efficiency on virus inhibition than the first one because lentinan can booster immune response.

Developments in Rabies Vaccines: The Path Traversed from Pasteur to the Modern Era of Immunization

Rabies is a disease of antiquity and has a history spanning millennia ever since the first interactions between humans and dogs. The alarming fatalities caused by this disease have triggered rabies prevention strategies since the first century BC. There have been numerous attempts over the past 100 years to develop rabies vaccineswith the goal of preventing rabies in both humans and animals. Thepre-Pasteurian vaccinologists, paved the way for the actual history of rabies vaccines with the development of first generation vaccines. Further improvements for less reactive and more immunogenic vaccines have led to the expansion of embryo vaccines, tissue culture vaccines, cell culture vaccines, modified live vaccines, inactivated vaccines, and adjuvanted vaccines. The adventof recombinant technology and reverse genetics have given insight into the rabies viral genome and facilitated genome manipulations, which in turn led to the emergence of next-generation rabies vaccines, such as recombinant vaccines, viral vector vaccines, genetically modified vaccines, and nucleic acid vaccines. These vaccines were very helpful in overcoming the drawbacks of conventional rabies vaccines with increased immunogenicity and clinical efficacies. The path traversed in the development of rabies vaccines from Pasteur to the modern era vaccines, though, faced numerous challenges;these pioneering works have formed the cornerstone for the generation of thecurrent successful vaccines to prevent rabies. In the future, advancements in the scientific technologies and research focus will definitely lay the path for much more sophisticated vaccine candidates for rabies elimination.

Recombinant adeno-associated virus serotype 9 AAV-RABVG expressing a Rabies Virus G protein confers long-lasting immune responses in mice and non-human primates

Three or four intramuscular doses of the inactivated human rabies virus vaccines are needed for pre- or post-exposure prophylaxis in humans. This procedure has made a great contribution to prevent human rabies deaths, which bring huge economic burdens in developing countries. Herein, a recombinant adeno-associated virus serotype 9, AAV9-RABVG, harbouring a RABV G gene, was generated to serve as a single dose rabies vaccine candidate. The RABV G protein was stably expressed in the 293T cells infected with AAV9-RABVG. A single dose of 2 × 10¹¹ v.p. of AAV9-RABVG induced robust and long-term positive seroconversions in BALB/c mice with a 100% survival from a lethal RABV challenge. In Cynomolgus Macaques vaccinated with a single dose of 1 × 10¹³ v.p. of AAV9-RABVG, the titres of rabies VNAs increased remarkably from 2 weeks after immunity, and maintained over 31.525 IU/ml at 52 weeks. More DCs were activated significantly for efficient antigen presentations of RABV G protein, and more B cells were activated to be responsible for antibody responses. Significantly more RABV G specific IFN-γ-secreting CD4+ and CD8+ T cells, and IL-4-secreting CD4+ T cells were activated, and significantly higher levels of IL-2, IFN-γ, IL-4, and IL-10 were secreted to aid immune responses. Overall, the AAV9-RABVG was a single dose rabies vaccine candidate with great promising by inducing robust, long-term humoral responses and both Th1 and Th2 cell-mediated immune responses in mice and non-human primates.

Long-term humoral immunogenicity, safety and protective efficacy of inactivated vaccine against reindeer rabies

The core element of the reindeer rabies eradication strategy is regular application of vaccines to obtain and uphold a vaccination coverage sufficient for the ceasing of rabies virus transmission. This article presents the results of reindeer humoral immunity intensity and duration study after the immunization with two form of inactivated rabies vaccines (adjuvanted liquid vaccine and non-adjuvanted lyophilized vaccine) based on the Shchelkovo-51 rabies virus strain. Efficiency of post-vaccine immunity was assessed by measuring the animal blood serum virus-neutralizing antibody level in a neutralization test. The study determined the efficient rabies vaccine injection dose as equal to 3 ml. A single dose of 3 ml of these vaccines induced stable production of specific neutralizing antibodies in reindeer as early as 7 day after administration, and by 30 days after immunization, it significantly exceeded the minimal threshold level accepted by OIE. Two doses of vaccines administration with an interval of 30 days are required to achieve a strong immunity with the rabies-specific virus-neutralizing antibody titer of more than 0.5 IU/ml for at least 2 years. Our data do not support the benefit of an adjuvanted vaccine for the prevention of rabies in reindeer.

Production, purification, and characterization of recombinant rabies virus glycoprotein expressed in PichiaPink™ yeast

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The rabies virus glycoprotein was produced in the Pichia pastoris production strains PichiaPink™ .

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Different carbon sources were found able to support the RABV-G expression under the control of the constitutive GAP promoter.

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Culture parameters such as oxygen supply, pH or growth rate can affect the yield and the quality of the produced RABV-G.

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The purified RABV-G was found correctly glycosylated and able to mediate trimeric oligomerization.

The commonly used host for industrial production of recombinant proteins Pichia pastoris, has been used in this work to produce the rabies virus glycoprotein (RABV-G). To allow a constitutive expression and the secretion of the expressed recombinant RABV-G, the PichiaPink™ commercialized expression vectors were modified to contain the constitutive GAP promoter and the α secretion signal sequences. Recombinant PichiaPink™ strains co-expressing the RABV-G and the protein chaperone PDI, have been then generated and screened for the best producer clone. The influence of seven carbon sources on the expression of the RABV-G, has been studied under different culture conditions in shake flask culture. An incubation temperature of 30°C under an agitation rate of 250 rpm in a filling volume of 10:1 flask/culture volume ratio were the optimal conditions for the RABV-G production in shake flask for all screened carbon sources. A bioreactor Fed batch culture has been then carried using glycerol and glucose as they were good carbon sources for cell growth and RABV-G production in shake flask scale. Cells were grown on glycerol during the batch phase then fed with glycerol or glucose defined solutions, a final RABV-G concentration of 2.7 µg/l was obtained with a specific product yield (Y_P/X) of 0.032 and 0.06 µg/g(_DCW) respectively. The use of semi-defined feeding solution enhanced the production and the Y_P/X to 12.9 µg/l and 0.135 µg/g(_DCW) respectively. However, the high cell density favored by these carbon sources resulted in oxygen limitation which influenced the glycosylation pattern of the secreted RABV-G. Alternatively, the use of sucrose as substrate for RABV-G production in large scale culture, resulted in less biomass production and a Y_P/X of 0.310 µg/g_(DCW) was obtained. A cation exchange chromatography was then used for RABV-G purification as one step method. The purified protein was correctly folded and glycosylated and able to adopt trimeric conformation. The knowledges gained through this work offer a valuable insight into the bioprocess design of RABV-G production in Pichia pastoris to obtain a correctly folded protein which can be used during an immunization proposal for subunit Rabies vaccine development.

Interferon Inhibition Enhances the Pilot-Scale Production of Rabies Virus in Human Diploid MRC-5 Cells

Inactivated vaccines based on cell culture are very useful in the prevention and control of many diseases. The most popular strategy for the production of inactivated vaccines is based on monkey-derived Vero cells, which results in high productivity of the virus but has a certain carcinogenic risk due to non-human DNA contamination. Since human diploid cells, such as MRC-5 cells, can produce a safer vaccine, efforts to develop a strategy for inactivated vaccine production using these cells have been investigated using MRC-5 cells. However, most viruses do not replicate efficiently in MRC-5 cells. In this study, we found that rabies virus (RABV) infection activated a robust interferon (IFN)-β response in MRC-5 cells but almost none in Vero cells, suggesting that the IFN response could be a key limiting factor for virus production. Treatment of the MRC-5 cells with IFN inhibitors increased RABV titers by 10-fold. Additionally, the RABV titer yield was improved five-fold when using IFN receptor 1 (IFNAR1) antibodies. As such, we established a stable IFNAR1-deficient MRC-5 cell line (MRC-5^IFNAR1−), which increased RABV production by 6.5-fold compared to normal MRC-5 cells. Furthermore, in a pilot-scale production in 1500 square centimeter spinner flasks, utilization of the MRC-5^IFNAR1− cell line or the addition of IFN inhibitors to MRC cells increased RABV production by 10-fold or four-fold, respectively. Thus, we successfully established a human diploid cell-based pilot scale virus production platform via inhibition of IFN response for rabies vaccines, which could also be used for other inactivated virus vaccine production.

Production of Rabies VLPs in Insect Cells by Two Monocistronic Baculoviruses Approach

Rabies is an ancient zoonotic disease that still causes the death of over 59,000 people worldwide each year. The rabies lyssavirus encodes five proteins, including the envelope glycoprotein and the matrix protein. RVGP is the only protein exposed on the surface of viral particle, and it can induce immune response with neutralizing antibody formation. RVM has the ability to assist with production process of virus-like particles. VLPs were produced in recombinant baculovirus system. In this work, two recombinant baculoviruses carrying the RVGP and RVM genes were constructed. From the infection and coinfection assays, we standardized the best multiplicity of infection and the best harvest time. Cell supernatants were collected, concentrated, and purified by sucrose gradient. Each step was used for protein detection through immunoassays. Sucrose gradient analysis enabled to verify the separation of VLPs from rBV. Through the negative contrast technique, we visualized structures resembling rabies VLPs produced in insect cells and rBV in the different fractions of the sucrose gradient. Using ELISA to measure total RVGP, the recovery efficiency of VLPs at each stage of the purification process was verified. Thus, these results encourage further studies to confirm whether rabies VLPs are a promising candidate for a veterinary rabies vaccine.

Attachment and in vitro transfection efficiency of an anti-rabies Chitosan-DNA nanoparticle vaccine

In Mexico, urban rabies has been reduced during the last decade thanks to intensive canine control and vaccination campaigns; however, rabies transmitted by wild animals, especially by bats, has been increasing due to vampire bats feeding on livestock. Vampire bat populations has been controlled by culling with vampiricides, reducing indiscriminately other bat species. Hence, bat vaccination for rabies offers an alternative for culling. Nevertheless, available rabies vaccines are not suitable for their use in wildlife from emerging countries. This project presents an alternative for the use of plasmid vaccines using bio-nanotechnology, to create low-cost and accessible vaccines. To accomplish this goal, chitosan nanoparticles were synthesized by ionic gelation and conjugated by coacervation with a pDNA rabies vaccine to test their attachment efficiency. Also, the conjugate was functionalized with Protoporphyrin IX and Folic acid as biomarkers. The nanoparticles complex was characterized by ultraviolet visible spectroscopy, infrared spectroscopy, transmission electron microscopy, dynamic light scattering, and the Z potential was obtained. In vitro tests were performed on cell viability and transfection. The nanoparticles possessed a low polydispersity, a mean size of 118.5 ± 13.6 nm and a Z potential of 17.3 mV. The attachment efficiency was of 100% independent of pDNA added. In contrast to functionalized nanoparticles which showed a max attachment efficiency of 99.6% dependent of pDNA concentration and the method of functionalization. The conjugate did not influence the viability and they improved the transfection efficiency. Results suggest that these nanoparticles are easy to prepare, inexpensive, and exhibit potential for plasmid delivery as it improves transfection efficiency of pDNA vaccines.

Whole-Cell Vaccine Preparation: Options and Perspectives

Vaccines are biological preparations to elicit a specific immune response in individuals against the targetted microorganisms. The use of vaccines has caused the near eradication of many critical diseases and has had an everlasting impact on public health at a relatively low cost. Most of the vaccines developed today are based on techniques which were developed a long time ago. In the beginning, vaccines were prepared from tissue fluids obtained from infected animals or people, but at present, the scenario has changed with the development of vaccines from live or killed whole microorganisms and toxins or using genetic engineering approaches. Considerable efforts have been made in vaccine development, but there are still many diseases that need attention, and new technologies are being developed in vaccinology to combat them. In this chapter, we discuss different approaches for vaccine development, including the properties and preparation of whole-cell vaccines.

Bats in ecosystems and their Wide spectrum of viral infectious potential threats: SARS-CoV-2 and other emerging viruses

Bats have populated earth for approximately 52 million years, serving as natural reservoirs for a variety of viruses through the course of evolution. Transmission of highly pathogenic viruses from bats has been suspected or linked to a spectrum of potential emerging infectious diseases in humans and animals worldwide. Examples of such viruses include Marburg, Ebolavirus, Nipah, Hendra, Influenza A, Dengue, Equine Encephalitis viruses, Lyssaviruses, Madariaga and Coronaviruses, involving the now pandemic Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Herein, we provide a narrative review focused in selected emerging viral infectious diseases that have been reported from bats.

Construction and evaluation of recombinant Lactobacillus plantarum NC8 delivering one single or two copies of G protein fused with a DC-targeting peptide (DCpep) as novel oral rabies vaccine

Rabies remains an important public health threat in most developing countries. To develop a more effective and safe oral vaccine against rabies, we constructed recombinant Lactobacillus plantarum NC8 carrying one or two copies of the G gene with a dendritic cell-targeting peptide (DCpep) fused at the C-terminal designated NC8-pSIP409-sRVG or NC8-pSIP409-dRVG, respectively. The immunogenicity and protective efficacy of these recombinant Lactobacillus plantarum against RABV were evaluated by oral administration in a mouse model. The results showed that recombinant NC8-pSIP409-dRVG possessed more G protein, resulting in more functional maturation of DCs. After three cycle of oral immunization, NC8-pSIP409-dRVG induced significantly higher levels of specific IgG antibody and mixed Th1/Th2 with a strong Th1-biasd immune response in mice. Most importantly, although the titers of RABV neutralizing antibody (VNA) were below the threshold of 0.5 IU/mL, the NC8-pSIP409-dRVG could protect 60 % of inoculated mice against lethal RABV challenge. These data reveal that recombinant NC8-pSIP409-dRVG may be a novel and promising oral vaccine candidate to prevent and control of animal rabies.

Purification of rabies virus glycoprotein produced in Drosophila melanogaster S2 cells: An efficient immunoaffinity method

Most rabies vaccines are based on inactivated virus, which production process demands a high level of biosafety structures. In the past decades, recombinant rabies virus glycoprotein (RVGP) produced in several expression systems has been extensively studied to be used as an alternative vaccine. The immunogenic characteristics of this protein depend on its correct conformation, which is present only after the correct post-translational modifications, typically performed by animal cells. The main challenge of using this protein as a vaccine candidate is to keep its trimeric conformation after the purification process. We describe here a new immunoaffinity chromatography method using a monoclonal antibody for RVGP Site II for purification of recombinant rabies virus glycoprotein expressed on the membrane of Drosophila melanogaster S2 cells. RVGP recovery achieved at least 93%, and characterization analysis showed that the main antigenic proprieties were preserved after purification.

Recombinant Human Adenovirus Type 5 Co-expressing RABV G and SFTSV Gn Induces Protective Immunity Against Rabies Virus and Severe Fever With Thrombocytopenia Syndrome Virus in Mice

Both severe fever with thrombocytopenia syndrome (SFTS) and rabies are severe zoonotic diseases. As co-hosts of rabies virus (RABV) and SFTS virus (SFTSV), dogs and cats could not only be infected but also transmit the virus to human. Hence, developing a bivalent vaccine against both SFTS and rabies is urgently needed. In this study, we generated a recombinant replication-deficient human adenovirus type 5 (Ad5) co-expressing RABV G and SFTSV Gn (Ad5-G-Gn) and evaluated its immunogenicity and efficacy in mice. Ad5-G-Gn immunization activated more dendritic cells (DCs) and B cells in lymph nodes (LNs) and induced Th1-/Th2-mediated responses in splenocytes, leading to robust production of neutralizing antibodies against SFTSV and RABV. In addition, single dose of Ad5-G-Gn conferred mice complete protection against lethal RABV challenge and significantly reduced splenic SFTS viral load. Therefore, our data support further development of Ad5-G-Gn as a potential bivalent vaccine candidate against SFTS and rabies for dog and cat use.

A Bivalent Human Adenovirus Type 5 Vaccine Expressing the Rabies Virus Glycoprotein and Canine Distemper Virus Hemagglutinin Protein Confers Protective Immunity in Mice and Foxes

The development of a safe and efficient multivalent vaccine has great prospects for application. Both rabies virus (RABV) and canine distemper virus (CDV) are highly infectious antigens, causing lethal diseases in domestic dogs and other carnivores worldwide. In this study, a replication-deficient human adenovirus 5 (Ad5)-vectored vaccine, rAd5-G-H, expressing RABV glycoprotein (G) and CDV hemagglutinin (H) protein was constructed. The RABV G and CDV H protein of rAd5-G-H were expressed and confirmed in infected HEK-293 cells by indirect immunofluorescence assay. The rAd5-G-H retained a homogeneous icosahedral morphology similar to rAd5-GFP under an electron microscope. A single dose of 10⁸ GFU of rAd5-G-H administered to mice by intramuscular injection elicited rapid and robust neutralizing antibodies against RABV and CDV. Flow cytometry assays indicated that the dendritic cells and B cells in inguinal lymph nodes were significantly recruited in rAd5-G-H-immunized mice in comparison with the mock and rAd5-GFP groups. rAd5-G-H also activated the Th1- and Th2-mediated cell immune responses against RABV and CDV in mice, which contributed to 100% survival of a lethal-dose RABV challenge without any clinical signs. In foxes, a single dose of 10⁹ GFU of rAd5-G-H could elicit high levels of neutralizing antibodies against both RABV and CDV in comparison with the mock and rAd5-GFP groups. All foxes in the rAd5-GFP and mock groups died, while the foxes inoculated with rAd5-G-H all survived and showed no clinical signs of disease after being challenged with a lethal wild-type CDV strain. These results suggested that rAd5-G-H has great potential as a bivalent vaccine against rabies and canine distemper in highly susceptible dogs and wildlife animals.

Advances in RNA Vaccines for Preventive Indications: A Case Study of A Vaccine Against Rabies

There is a global need for effective and affordable rabies vaccines, which is unmet by current vaccines due to limitations in their production capacities, required administration schedules, storage requirements, and cost. Many different experimental approaches previously used for bacterial and viral vaccines have been applied to rabies, but with variable success. One of the most promising new concepts is the use of messenger RNA (mRNA) in encoding the main rabies virus antigen, the envelope glycoprotein (RABV-G). CureVac has applied their proprietary technology platform for the production of mRNA to this problem, resulting in the rabies vaccine candidate CV7201. Following preclinical studies in mice and pigs showing that CV7201 could induce neutralizing immune responses that protected against rabies virus, different dosages and routes of administration of CV7201 were tested in a phase 1 human study. This clinical study proved that mRNA vaccination was safe and had an acceptable reactogenicity profile, but immune responses depended on the mode of administration, and they did not unequivocally support CV7201 for further development as a prophylactic vaccine with this particular formulation. Further, preclinical studies using RABV-G mRNA encapsulated in lipid nanoparticles (LNPs) showed an improved response in both mice and nonhuman primates, and these encouraging results are currently being followed up in clinical studies in humans. This review summarizes the recent advances in mRNA vaccines against rabies.

Feline herpesvirus vectored-rabies vaccine in cats: A dual protection

In China, cats cause about 5% of human rabies cases. Rabies control in cats plays a role in achieving the ultimate goal of elimination of dog rabies-mediated human deaths. However, there is no cat-specific rabies vaccine in China yet. In this study, we constructed a recombinant rabies vaccine by using a felid herpesvirus 1 (FHV-1) isolate, and deleted the gI/E in the FHV-1 and replaced the region with a glycoprotein (G) of rabies virus (RABV) strain BD06 through homologous recombination. The recombinant virus FHV-RVG was recovered and purified, and the expression of RABV glycoprotein was verified by indirect immunofluorescent assay. For potency in cats, each animal was inoculated intranasally with 1 ml FHV-RVG at 10^6.5 TCID₅₀. Blood samples were collected at defined intervals for antibody titration. The animals were challenged by herpes and rabies after completion of vaccination on day 180 and day 194, respectively. Our results demonstrated all vaccinated cats generated antibodies against both FHV-1 and RABV, and reached an arbitrary protective titer > 0.5 IU/ml for rabies viral neutralizing antibody (VNA) by day 14 post inoculation (dpi) and titer peaked on 30 dpi with VNA at 24.5 ± 10.23 IU/ml. All vaccinated cats presented no clinical signs of FHV-1 infection and survived rabies challenge, while the control cats had severe rhinotracheitis and died from rabies after challenge. All this demonstrated that the FHV-based recombinant vaccine is effective in protection against both FHV-1 and RABV infections.

Production of Recombinant Rabies Virus Glycoprotein by Insect Cells in a Single-Use Fixed-Bed Bioreactor

A single-use fixed-bed bioreactor (iCELLis nano) can be used for cultivating non adherent insect cells, which can be then recovered for scaling up or for harvesting a membrane-associated viral glycoprotein with high quality in terms of preserved protein structure and biological function. Here, we describe the procedures for establishing genetically modified Drosophila melanogaster Schneider 2 (S2) cell cultures in the iCELLis nano bioreactor and for quantifying by ELISA the recombinant rabies virus glycoprotein (rRVGP) synthesized. By using the described protocol of production, the following performance can be regularly achieved: 1.7 ± 0.6 × 1E10 total cells; 2.4 ± 0.8 × 1E7 cells/mL and 1.2 ± 0.9 μg of rRVGP/1E7 cells; 1.5 ± 0.8 mg of total rRVGP.

A novel approach to a rabies vaccine based on a recombinant single-cycle flavivirus vector

The RepliVax® vaccine (RV) platform is based on flavivirus genomes that are rationally attenuated by deletion. These single-cycle RV vaccine candidates targeting flavivirus pathogens have been demonstrated to be safe, highly immunogenic, and efficacious in animal models, including non-human primates. Here we show utility of the technology for delivery of a non-flavivirus immunogen by engineering several West Nile-based RV vectors to express full-length rabies virus G protein. The rabies virus G protein gene was incorporated in place of different West Nile structural protein gene deletions. The resulting RV-RabG constructs were demonstrated to replicate to high titers (8 log₁₀ infectious particles/ml) in complementing helper cells. Following infection of normal cells, they provided efficient rabies virus G protein expression, but did not spread to surrounding cells. Expression of rabies virus G protein was stable and maintained through multiple rounds of in vitro passaging. A sensitive neurovirulence test in 2-3 day old neonatal mice demonstrated that RV-RabG candidates were completely avirulent indicative of high safety. We evaluated the RV-RabG variants in several animal models (mice, dogs, and pigs) and demonstrated that a single dose elicited high titers of rabies virus-neutralizing antibodies and protected animals from live rabies virus challenge (mice and dogs). Importantly, dogs were protected at both one and two years post-immunization, demonstrating durable protective immunity. The data demonstrates the potential of the RepliVax® technology as a potent vector delivery platform for developing vaccine candidates against non-flavivirus targets.