Novel vaccines to human rabies

Rabies virus large protein-derived T-cell immunogen facilitates rapid viral clearance and enhances protection against lethal challenge in mice

BACKGROUND

Rabies remains a devastating and fatal infectious disease worldwide. To date, vaccination is the most reliable and effective strategy for controlling rabies. However, despite the effectiveness of inactivated vaccines, cumbersome vaccination procedures and the high costs of post-exposure prophylaxis impose a significant economic burden, particularly in developing countries with limited access to vaccines. Therefore, there is an urgent need to develop a novel rabies vaccine that reduces costs while enhancing safety and efficacy.

METHODS

We developed a novel mRNA rabies vaccine called RABV-G-LT, which incorporates two immunogens: RABV-G, a glycoprotein designed mainly to elicit neutralizing antibody responses, and RABV-LT, a T-cell immunogen derived from the large protein of the rabies virus. Additionally, we evaluated the immunogenicity of RABV-G-LT in both mice and non-human primates.

RESULTS

The RABV-LT mRNA vaccination alone induced potent RABV-LT-specific T-cell responses and provided modest protection against rabies virus challenge in mice. Importantly, the dual-immunogen mRNA vaccine RABV-G-LT elicited vigorous and persistent neutralization antibody and T-cell responses, resulting in significantly more efficient clearance of the rabies virus in the brain and spinal cord. This conferred enhanced protection, evidenced by lesser initial weight loss and earlier recovery of body weight compared with the RABV-G mRNA or inactivated vaccine groups. Moreover, RABV-G-LT also mounted persistent strong antigen-specific T-cell and antibody immune responses in nonhuman primates.

CONCLUSIONS

Our study suggested that combining the T-cell immunogen and virus-neutralizing antibody immunogen was a practical approach to strengthening the defense against the rabies virus.

General public knowledge, attitudes, and practices about rabies and associated factors in Gomma district of Jimma zone, southwestern Ethiopia

BACKGROUND

Rabies is a disease of warm-blooded animals that affects the central nervous system and is almost invariably fatal once clinical signs develop. It is one of the most neglected tropical diseases in several areas of the world, including Ethiopia. Additionally, the burden of the disease is estimated to be high in Ethiopia, and public awareness contributes to prevention.

METHODS

A community-based cross-sectional study design was conducted from June-August 2023 in the Gomma district, Jimma zone, Oromia regional state, Ethiopia, to assess the knowledge, attitudes, and practices of communities towards rabies and associated risk factors using a structured questionnaire survey. A multi-stage sampling technique was used for the selection of the sampling units and a total of 140 participants were interviewed. The questionnaire parts included socio-demographics information, knowledge, attitudes, and practices of the community's respect for rabies management and control. The data was analyzed by Statistical Package for Social Science (SPSS) Version 20. Descriptive analyses were employed and multivariable logistic regression was used to calculate the association between independent and dependent variables (Knowledge, Attitudes, and Practice scores).

RESULTS

About 134 (95.7%) respondents had heard about rabies. Likewise, 75 (53.6%), 55 (39.3%), and 95 (67.9%) of the respondents had good knowledge, favorable attitudes, and good practices, respectively. Christians were more likely to have higher knowledge scores than Muslims (AOR = 6.876, CI = 1.750-27.016, p = 0.006). Respondents who knew someone's exposure had a higher knowledge score than those who did not (AOR = 6.208, CI = 2.750-14.012, p = 0.000). Moreover, Muslims were found to have a more favorable attitudes than Christians (AOR = 5.518, CI = 1.199-25.391, p = 0.028). Those who knew someone's exposure to rabies were found to have a more favorable attitudes than those who did not (AOR = 2.367, CI = 1.157-4.839, p = 0.018). Respondents who had favorable attitudes towards rabies were found to have more good practices than unfavorable attitudes (AOR = 3.267, CI = 1.391, 7.730, p = 0.005).

CONCLUSIONS

The study revealed a gap in knowledge among communities in the study area. Thus, rabies control activity and community awareness should be implemented with stakeholders.

Safety and efficacy assessment of an mRNA rabies vaccine in dogs, rodents, and cynomolgus macaques

Rabies is a lethal disease caused by the rabies virus (RABV), which causes acute neurological infections in mammals, including human beings. We previously reported that an mRNA vaccine (LVRNA001) encoding the rabies virus's glycoprotein induced strong protective immune responses to rabies in mice and dogs. Here, we further evaluate the safety of LVRNA001. First, we performed a confirmative efficacy study in dogs, which showed that LVRNA001 fully protected the animals from the virus, both pre- and post-infection. Moreover, using pre- and post-exposure prophylaxis murine models, we showed that LVRNA001, built from the CTN-1 strain, was able to protect against various representative RABV strains from the China I-VII clades. To evaluate the safety of the vaccine, chronic and reproductive toxicity studies were performed with cynomolgus macaques and rats, respectively. In a repeated-dose chronic toxicity study, vaccinated monkeys displayed no significant alterations in body weight, temperature, or hematological and biochemical markers. Lymphocyte subset measurement and histopathological examination showed that no toxicity was associated with the vaccine. The immunogenicity study in cynomolgus macaques demonstrated that LVRNA001 promoted the generation of neutralizing antibodies and Th1-biased immune response. Evaluation of reproductive toxicity in rats revealed that administration of LVRNA001 had no significant effects on fertility, maternal performance, reproductive processes, and postnatal outcomes. In conclusion, LVRNA001 can provide efficient protection against rabies virus infection in dogs and mice, and toxicity studies showed no significant vaccine-related adverse effects, suggesting that LVRNA001 is a promising and safe vaccine candidate for rabies prophylaxis and therapy.

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.

Rabies prevention practices and associated factors among household heads in Bure Zuria district, North West Ethiopia

Rabies is a zoonotic viral disease that can occur in all warm blooded animals including humans. Vaccinating dogs can protect people from contracting rabies. Despite the availability of effective human and animal rabies vaccines, rabies prevention and control efforts are inadequate. The aim of the study was to determine the level of rabies prevention practices and associated factors among household heads in Bure Zuria district, North-west Ethiopia. Community based cross-sectional study was conducted at Bure Zuria from June 1 to 30, 2020. A total of 609 participants were selected using simple random sampling technique. Simple and multiple binary logistic regressions were applied to identify associated factors of rabies prevention practices. Of 609 participants, 413 (67.8%) were male and 289 (47.5%) were 30-45 years old. The level of good prevention practices of rabies at Bure Zuria district was 43.3%. Being males (AOR = 2.69 (1.72-4.22)), age group 18-29 years (AOR = 2.70 (1.20-6.10)), ever bitten by dog, (AOR = 2.40 (1.56-3.68)), got training (AOR = 1.70 (1.08-2.68)), had dog (AOR = 2.92 (1.62-5.26)), with good knowledge AOR (95% CI) = 3.42 (2.19-5.32), with good attitude AOR (95% CI) = 1.78 (1.16-2.73) and have 1001-2000 AOR (95% CI) = 2.29 (1.39-3.79) and > 2000 AOR (95% CI) = 2.02 (1.28-3.18)) monthly income were more likely to have good prevention practices of rabies. In this study, we found that the level of good prevention practices of rabies was low in Bure Zuria district. Therefore; awareness creation trainings and multi-sectoral collaborations to prevent rabies are needed in the district, zone and at large region level.

Colloidal Manganese Salt Improves the Efficacy of Rabies Vaccines in Mice, Cats, and Dogs

Rabies, caused by rabies virus (RABV), remains a serious threat to public health in most countries worldwide. At present, the administration of rabies vaccines has been the most effective strategy to control rabies. Herein, we evaluate the effect of colloidal manganese salt (Mn jelly [MnJ]) as an adjuvant of rabies vaccine in mice, cats, and dogs. The results showed that MnJ promoted type I interferon (IFN-I) and cytokine production in vitro and the maturation of dendritic cells (DCs) in vitro and in vivo. Besides, MnJ serving as an adjuvant for rabies vaccines could significantly facilitate the generation of T follicular helper (Tfh) cells, germinal center (GC) B cells, plasma cells (PCs), and RABV-specific antibody-secreting cells (ASCs), consequently improve the immunogenicity of rabies vaccines, and provide better protection against virulent RABV challenge. Similarly, MnJ enhanced the humoral immune response in cats and dogs as well. Collectively, our results suggest that MnJ can facilitate the maturation of DCs during rabies vaccination, which can be a promising adjuvant candidate for rabies vaccines. IMPORTANCE Extending the humoral immune response by using adjuvants is an important strategy for vaccine development. In this study, a novel adjuvant, MnJ, supplemented in rabies vaccines was evaluated in mice, cats, and dogs. Our results in the mouse model revealed that MnJ increased the numbers of mature DCs, Tfh cells, GC B cells, PCs, and RABV-specific ASCs, resulting in enhanced immunogenicity and protection rate of rabies vaccines. We further found that MnJ had the same stimulative effect in cats and dogs. Our study provides the first evidence that MnJ serving as a novel adjuvant of rabies vaccines can boost the immune response in both a mouse and pet model.

Virus-like vesicles based on SFV-containing rabies virus glycoprotein make a safe and efficacious rabies vaccine candidate in a mouse model

Rabies is a fatal zoonosis causing encephalitis in mammals, and vaccination is the most effective method to control and eliminate rabies. Virus-like vesicles (VLVs), which are characterized as infectious, self-propagating membrane-enveloped particles composed of only Semliki Forest virus (SFV) replicase and vesicular stomatitis virus glycoprotein (VSV-G), have been proven safe and efficient as vaccine candidates. However, previous studies showed that VLVs containing rabies virus glycoprotein (RABV-G) grew at relatively low titers in cells, impeding their potential use as a rabies vaccine. In this study, we constructed novel VLVs by transfection of a mutant SFV RNA replicon encoding RABV-G. We found these VLVs could self-propagate efficiently in cell culture and could evolve to high titers (approximately 10⁸ FFU/ml) by extensive passaging 25 times in BHK-21 cells. Furthermore, we found that the evolved amino acid change in SFV nsP1 at positions 470 and 482 was critical for this high-titer phenotype. Remarkably, VLVs could induce robust type I IFN expression in BV2 cells and were highly sensitive to IFN-α. We found that direct inoculation of VLVs into the mouse brain caused lesser body weight loss, mortality and neuroinflammation compared with RABV vaccine strain. Finally, it could induce increased generation of germinal centre (GC) B cells, plasma cells (PCs) and virus-neutralizing antibodies (VNAs), as well as provide protection against virulent RABV challenge in immunized mice. This study demonstrated that VLVs containing RABV-G could proliferate in cells and were highly evolvable, revealing the feasibility of developing an economic, safe and efficacious rabies vaccine. IMPORTANCE VLVs have been shown to represent a more versatile and superior vaccine platform. In previous studies, VLVs containing the Semliki Forest Virus replicase (SFV nsP1-4) and rabies virus glycoprotein (RABV-G) grew to relatively low titers in cells. In our study, we not only succeeded in generating VLVs that proliferate in cells and stably express RABV-G, the VLVs that evolved grew to higher titers reaching 10⁸ FFU/ml. We also found that nucleic acid changes at positions 470 and 482 in nsP1 were vital for this high-titer phenotype. Moreover, the VLVs that evolved in our studies were highly attenuated in mice, induced potent immunity and protected mice from lethal RABV infection. Collectively, our study showed that high titers of VLVs containing RABV-G were achieved demonstrating that these VLVs could be an economical, safe, and efficacious rabies vaccine candidate.

Quantitative characterization of the B cell receptor repertoires of human immunized with commercial rabies virus vaccine

Humoral immunity is crucial for an efficient host immune response against rabies virus (RABV) infection. But the B cell receptor (BCR) repertoire in human after RABV vaccine immunization remained unclear. To study the BCR repertoires in peripheral blood mononuclear cells (PBMCs) of human immunized with rabies virus vaccine. In this study, we conducted BCR complementarity determining region 3 (CDR3) repertoires in 4 healthy volunteers before and after immunization with RABV vaccine by high-throughput sequencing. The bioinformatics analysis process was performed. The results showed that RABV vaccination changed the BCR diversity and the usage of V/J gene segments, as well as V-J pairing. B cell clone expansion was induced by the vaccination and sequences of high expand CDR3 aa clones were identified. To the best of our knowledge, we firstly quantitative characterized B cell receptor repertoire of human immunized with c rabies virus vaccine. It might provide us with new insights into B cell receptor condition after RABV vaccination.

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.

The COVID-19 Vaccine Landscape

The history of vaccine development spans centuries. At first, whole pathogens were used as vaccine agents, either inactivated or attenuated, to reduce virulence in humans. Safety and tolerability were increased by including only specific proteins as antigens and using cell culture methods, while novel vaccine strategies, like nucleic acid- or vector-based vaccines, hold high promise for the future. Vaccines have generally not been employed as the primary tools in outbreak response, but this might change since advances in medical technology in the last decades have made the concept of developing vaccines against novel pathogens a realistic strategy. Wandering the uncharted territory of a novel pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), we can learn from other human Betacoronaviridae that emerged in the last decades, SARS-CoV-1 and MERS-CoV. We can identify the most likely target structures of immunity, establish animal models that emulate human disease and immunity as closely as possible, and learn about complex mechanisms of immune interaction such as cross-reactivity or antibody-dependent enhancement (ADE). However, significant knowledge gaps remain. What are the correlates of protection? How do we best induce immunity in vulnerable populations like the elderly? Will the immunity induced by vaccination (or by natural infection) wane over time? To date, at least 149 vaccine candidates against SARS-CoV-2 are under development. At the time of writing, at least 17 candidates have already progressed past preclinical studies (in vitro models and in vivo animal experiments) into clinical development. This chapter will provide an overview of this rapidly developing field.

Outer membrane proteins of Salmonella typhimurium as an adjuvant in rabies vaccine

PURPOSE

The objective of the present study was to evaluate the immune-enhancing potential of Salmonella typhimurium outer membrane protein (OMP) and alum as adjuvants towards inactivated Vero cells rabies vaccine (FRV/K2).

MATERIALS AND METHODS

Six groups of female Sprague Dawley albino rats (10/group) were used in the evaluation of immunogenicity and safety of vaccines and adjuvants. Total immunoglobulin G secreted interferon-gamma (IFN-γ), and the percentage of proliferated CD4+ and CD8+ T cells were measured. Biochemical analysis and histopathological examination were used to test safety profiles.

RESULTS

OMP adjuvanted rabies vaccine (FRV/K2+OMP) (OMP combined locally prepared vaccine) induced significantly higher neutralizing antibodies on day 21 post-vaccination relative to free (FRV/K2) vaccine and alum adsorbed vaccine (FRV/K2+alum) (alum adsorbed locally prepared vaccine). (FRV/K2+OMP) induced a significantly higher level of IFN-γ on day 14 post-vaccination. CD8+ T cells were significantly higher post-vaccination with reference (RV), free (FRV/K2), and (FRV/K2+OMP) than (FRV/K2+alum). On the contrary, CD4+ T cells were significantly elevated post-vaccination with (FRV/K2+alum) at p<0.05. Biochemical analysis and histopathological examination revealed that OMP could be used safely as an adjuvant for the development of more effective rabies vaccines.

CONCLUSION

Outer membrane proteins adjuvanted rabies vaccines would be beneficial to induce rapid neutralizing antibodies and essential cytokines.

Rabies VLPs adjuvanted with saponin-based liposomes induce enhanced immunogenicity mediated by neutralizing antibodies in cattle, dogs and cats

We carried out an investigation on rabies virus-like particles (RV-VLPs) expressed in HEK293 cells using serum free medium. These RV-VLPs were formulated with two different adjuvants in order to analyse the enhancement of the triggered immune response and its stability. In experiments in mice, RV-VLPs showed an enhanced humoral immune response when injected with adjuvant, in contrast to the obtained for the RV-VLPs without adjuvant addition. Besides, higher titers of neutralizing antibodies were induced when RV-VLPs were formulated with LipoSap® in comparison with the obtained with Alhydrogel®. At the same time, the positive effect of this adjuvant in vaccine's potency and stability was demonstrated, showing that LipoSap® significantly increases the value obtained in NIH efficiency test for rabies vaccine, and proving that this value is maintained after 15 months storage at 4 °C. Further, we showed that RV-VLPs induces an immune response based on neutralizing antibodies when cat, dogs and bovines were vaccinated with only one dose of RV-VLPs. These results demonstrated that this vaccine candidate could be applied for the prevention of rabies in pets as well as for the control of paralytic rabies in cattle.

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.

Delivery of self-amplifying mRNA vaccines by cationic lipid nanoparticles: The impact of cationic lipid selection

Self-amplifying RNA (SAM) represents a versatile tool that can be used to develop potent vaccines, potentially able to elicit strong antigen-specific humoral and cellular-mediated immune responses to virtually any infectious disease. To protect the SAM from degradation and achieve efficient delivery, lipid nanoparticles (LNPs), particularly those based on ionizable amino-lipids, are commonly adopted. Herein, we compared commonly available cationic lipids, which have been broadly used in clinical investigations, as an alternative to ionizable lipids. To this end, a SAM vaccine encoding the rabies virus glycoprotein (RVG) was used. The cationic lipids investigated included 3ß-[N-(N',N'-dimethylaminoethane)-carbamoyl]cholesterol (DC-Chol), dimethyldioctadecylammonium (DDA), 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), 1,2-dimyristoyl-3-trimethylammonium-propane (DMTAP), 1,2-stearoyl-3-trimethylammonium-propane (DSTAP) and N-(4-carboxybenzyl)-N,N-dimethyl-2,3-bis(oleoyloxy)propan-1-aminium (DOBAQ). Whilst all cationic LNP (cLNP) formulations promoted high association with cells in vitro, those formulations containing the fusogenic lipid 1,2-dioleoyl-sn-3-phosphoethanolamine (DOPE) in combination with DOTAP or DDA were the most efficient at inducing antigen expression. Therefore, DOTAP and DDA formulations were selected for further in vivo studies and were compared to benchmark ionizable LNPs (iLNPs). Biodistribution studies revealed that DDA-cLNPs remained longer at the injection site compared to DOTAP-cLNPs and iLNPs when administered intramuscularly in mice. Both the cLNP formulations and the iLNPs induced strong humoral and cellular-mediated immune responses in mice that were not significantly different at a 1.5 µg SAM dose. In summary, cLNPs based on DOTAP and DDA are an efficient alternative to iLNPs to deliver SAM vaccines.

Nonclinical safety assessment of repeated administration and biodistribution of a novel rabies self-amplifying mRNA vaccine in rats

The novel self-amplifying mRNA (SAM) technology for vaccines consists of an engineered replication-deficient alphavirus genome encoding an RNA-dependent RNA polymerase and the gene of the target antigen. To validate the concept, the rabies glycoprotein G was chosen as antigen. The delivery system for this vaccine was a cationic nanoemulsion. To characterize the local tolerance, potential systemic toxicity and biodistribution of this vaccine, two nonclinical studies were performed. In the repeated dose toxicity study, the SAM vaccine was administered intramuscularly to rats on four occasions at two-week intervals followed by a four-week recovery period. SAM-related changes consisted of a transient increase in neutrophil count, alpha-2-macroglobulin and fibrinogen levels. Transient aspartate aminotransferase and alanine aminotransferase increases were also noted in females only. At necropsy, observations related to the elicited inflammatory reaction, such as enlargement of the draining lymph nodes were observed that were almost fully reversible by the end of the recovery period. In the biodistribution study, rats received a single intramuscular injection of SAM vaccine and then were followed until Day 60. Rabies RNA was found at the injection sites and in the draining lymph nodes one day after administration, then generally decreased in these tissues but remained detectable up to Day 60. Rabies RNA was also transiently found in blood, lungs, spleen and liver. No microscopic changes in the brain and spinal cord were recorded. In conclusion, these results showed that the rabies SAM vaccine was well-tolerated by the animals and supported the clinical development program.

Optimization and validation of a blocking ELISA for quantitation of anti-rabies immunoglobulins in multispecies sera

We developed a fast, rabies virus-free, in vitro method, based on a blocking ELISA (bELISA), to detect and accurately quantify anti-rabies glycoprotein antibodies in serum of several animal species. In this method, purified rabies virus-like particles (VLPs) are used as antigen to coat the plates, while the presence of specific rabies immunoglobulins is revealed through blocking the recognition of these VLPs by a biotinylated monoclonal antibody. A quality by design approach was carried out in order to optimize the method performance, improving the sensitivity and, thereby, reducing the limit of detection of this assay. After the method validation, we confirmed that the bELISA method is able to detect a concentration of 0.06 IU/mL rabies immunoglobulins, titer lower than the 0.5 IU/mL cutoff value established as indication for correct vaccination. Further, we assessed the correlation between bELISA, the MNT, and the Platelia methods, confirming the accuracy of this new assay. On the other hand, precision was evaluated, obtaining acceptable repeatability and intermediate precision values, showing that this bELISA could be proposed as a potential alternative method, replacing the gold standard techniques in vaccination schemes and becoming a routine control technique within regional rabies surveillance programs.

Quantity vs. quality: an assessment of the current pipeline for rabies

OBJECTIVES

To gain insight in the potential of the current pipeline for rabies to decrease the burden of disease by evaluating its relevance to high-risk countries.

METHODS

Rabies-related patent documents and clinical trials were retrieved from Espacenet and the WHO ICTRP, respectively. Data were cleaned, modulated and categorised into a pre-defined set of indicators those were used for (statistical) analyses on the number of patent applications, patent quality and type of stakeholders involved for different geographical areas.

RESULTS

Analysis of 583 unique patent families applied for in the period 1954-2017 showed a steep growth in the yearly number of patent applications. A significant portion of new patent applications concern Chinese patents with relatively low quality that are filed by a dispersed group of applicants. Excluding these patents, the number of patent applications has been virtually stable over the years. A shift is seen in public stakeholders becoming more prolific as patent applicants. This shift is also reflected in clinical trials; key sponsors of clinical trials include public and private stakeholders originating from high-risk rabies countries. The majority of clinical trials investigate adjustments to existing vaccines that may improve accessibility.

CONCLUSION

The results show a discrepancy between the quantity and quality of rabies patent applications that reflects national patent regulations rather than real progress in decreasing the burden of disease. This is in contrast to clinical trials, which focus on incremental innovations that are tested in clinical trials but may nevertheless have a potentially strong impact in high-risk countries.

Rabies and rabies immunobiological preparations: vaccinations Pasteur to the contemporary biotechnology

The review provides information on topical issues of rabies spread in the world and the Russian Federation, the stages of development and directions of improvement of available preventive anti-rabies immunobiological preparation used in medical practice for active and passive immunization against rabies. The current level of biotechnology development with the use of molecular biology and genetic engineering methods opens up prospects for the design of new safe effective anti-rabies drugs using recombinant technologies. Expanding the range of immunobiological drugs against rabies and their introduction into health practice will contribute to the elimination of human mortality from rabies.

Incorporating B cell activating factor (BAFF) into the membrane of rabies virus (RABV) particles improves the speed and magnitude of vaccine-induced antibody responses

B cell activating factor (BAFF) is a member of the tumor necrosis factor (TNF) superfamily of cytokines that links innate with adaptive immunity. BAFF signals through receptors on B cells, making it an attractive molecule to potentiate vaccine-induced B cell responses. We hypothesized that a rabies virus (RABV)-based vaccine displaying both antigen and BAFF on the surface of the same virus particle would target antigen-specific B cells for activation and improve RABV-specific antibody responses. To test this hypothesis, we constructed a recombinant RABV-based vector expressing virus membrane-anchored murine BAFF (RABV-ED51-mBAFF). BAFF was incorporated into the RABV particle and determined to be biologically functional, as demonstrated by increased B cell survival of primary murine B cells treated ex-vivo with RABV-ED51-mBAFF. B cell survival was inhibited by pre-treating RABV-ED51-mBAFF with an antibody that blocks BAFF functions. RABV-ED51-mBAFF also activated primary murine B cells ex-vivo more effectively than RABV as shown by significant upregulation of CD69, CD40, and MHCII on the surface of infected B cells. In-vivo, RABV-ED51-mBAFF induced significantly faster and higher virus neutralizing antibody (VNA) titers than RABV while not adversely affecting the longevity of the vaccine-induced antibody response. Since BAFF was incorporated into the virus particle and genome replication was not required for BAFF expression in-vivo, we hypothesized that RABV-ED51-mBAFF would be effective as an inactivated vaccine. Mice immunized with 250 ng/mouse of β-propriolactone-inactivated RABV-ED51-mBAFF showed faster and higher anti-RABV VNA titers compared to mice immunized with inactivated RABV. Together, this model stands as a potential foundation for exploring other virus membrane-anchored molecular adjuvants to make safer, more effective inactivated RABV-based vaccines.

A chimpanzee adenoviral vector-based rabies vaccine protects beagle dogs from lethal rabies virus challenge

Rabies continues to poses serious threats to the public health in many countries. The development of novel inexpensive, safe and effective vaccines has become a high priority for rabies control worldwide. We previously generated a novel recombinant rabies vaccine by cloning rabies virus glycoprotein into a chimpanzee adenoviral vector, termed ChAd68-Gp. The present study evaluated the immune responses and protection afforded by this vaccine in beagle dogs. The results demonstrated that intramuscular immunization with both low-dose and high-dose of ChAd68-Gp induced strong immune responses and provided complete protection in beagles even at low-dose. However, when administered orally, high-dose vaccination was protective while low-dose vaccination was ineffective. Further investigation indicated that the low-pH value of gastric juice in the stomach of beagles might decompose the adenovirus. Therefore, suitable formulation for adenovirus-based oral vaccine should be considered and developed. The chimpanzee adenovirus-vectored rabies vaccine ChAd68-Gp warrants extensive test for clinical application.

Staphylococcal enterotoxin C2 as an adjuvant for rabies vaccine induces specific immune responses in mice

Rabies vaccine administration is the most effective method to prevent the occurrence of rabies disease. However, administration of rabies vaccine without adjuvant always shows low efficiency. As a member of superantigen, staphylococcal enterotoxin C2 (SEC2) non-specifically activates T-cells at extremely low concentration. It enlightens us that SEC2 may be used as an adjuvant. We carried out the experiment that the mice received twice immunization with rabies vaccine in the presence or absence of SEC2 at 1-week interval. Serum and splenocytes from immunized mice were collected to measure the level of rabies-specific-IgG and the cell that secretes IFN-γ or IL-4. The promotion of antigen-specific splenocytes proliferation was also detected. Besides, a challenge test was performed to evaluate the protective efficiency of SEC2. It was shown that mice immunized with vaccine combined with SEC2 generated more specific anti-rabies-antibodies. The results for production of IFN-γ and IL-4, as well as the proliferation of splenocytes from immunized mice indicated SEC2 promoted the specific immune responses induced by rabies vaccine. Moreover, immunization of mice with vaccine combined with SEC2 provided efficient protection against the lethal rabies exposure. Taken together, our findings indicated that SEC2 can be served as an adjuvant for rabies vaccines.

Addition of C3d-P28 adjuvant to a rabies DNA vaccine encoding the G5 linear epitope enhances the humoral immune response and confers protection

Rabies DNA vaccines based on full-length glycoprotein (G) induce virus neutralizing antibody (VNA) responses and protect against the virus challenge. Although conformational epitopes of G are the main target of VNAs, some studies have shown that a polypeptide linear epitope G5 is also able to induce VNAs. However, a G5 DNA vaccine has not been explored. While multiple doses of DNA vaccines are required in order to confer a protective immune response, this could be overcome by the inclusion of C3d-P28, a molecular adjuvant is know to improve the antibody response in several anti-viral vaccine models. To induce and enhance the immune response against rabies in mice, we evaluated two DNA vaccines based on the linear epitope G5 of Rabies Virus (RABV) glycoprotein (pVaxG5 vaccine) and another vaccine consisting of G5 fused to the molecular adjuvant C3d-P28 (pVaxF1 vaccine). VNA responses were measured in mice immunized with both vaccines. The VNA levels from the group immunized with pVaxG5 decreased gradually, while those from the group vaccinated with pVaxF1 remained high throughout the experimental study. After challenge with 22 LD50 of the Challenge Virus Strain (CVS), the survival rate of mice immunized with pVaxG5 and pVaxF1 was increased by 27% and 50% respectively, in comparison to the PBS group. Furthermore, the in vitro proliferation of anti-rabies specific spleen CD4+ and CD8+ T cells from mice immunized with pVaxF1 was observed. Collectively, these results suggest that the linear G5 epitope is a potential candidate vaccine. Furthermore, the addition of a C3d-P28 adjuvant contributed to enhanced protection, the sustained production of VNAs, and a specific T-cell proliferative response.

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.

Barriers to innovation in human rabies prophylaxis and treatment: A causal analysis of insights from key opinion leaders and literature

Rabies is an essentially 100% fatal, zoonotic disease, caused by Lyssaviruses. Currently, the disease is vaccine-preventable with pre- and post-exposure prophylaxis (PrEP and PEP). Still, rabies virus is estimated to cause up to 60,000 human deaths annually, of which the vast majority occurs in rural Asia and Africa, due to the inaccessibility of prophylaxis and non-existence of treatment. Despite these unmet clinical needs, rabies control mainly focuses on the sylvatic reservoir and drug innovation receives relatively little attention compared to other neglected tropical diseases (NTDs). As such, the lag of innovation in human rabies prophylaxis and treatment cannot be explained by limited return on investment alone. Strategies countering rabies-specific innovation barriers are important for the acceleration of innovation in human rabies prophylaxis and treatment. Barriers throughout society, science, business development and market domains were identified through literature review and 23 semi-structured interviews with key opinion leaders worldwide. A subsequent root cause analysis revealed causal relations between innovation barriers and a limited set of root causes. Finally, prioritization by experts indicated their relative importance. Root causes, which are fundamental to barriers, were aggregated into four types: market and commercial, stakeholder collaboration, public health and awareness, and disease trajectory. These were found in all domains of the innovation process and thus are relevant for all stakeholders. This study identifies barriers that were not previously described in this specific context, for example the competition for funding between medical and veterinary approaches. The results stress the existence of barriers beyond the limited return on investment and thereby explain why innovation in human rabies medication is lagging behind NTDs with a lower burden of disease. A re-orientation on the full spectrum of barriers that hinder innovation in rabies prophylaxis and treatment is necessary to meet unmet societal and medical needs.

Rabies vaccine development by expression of recombinant viral glycoprotein

The rabies virus envelope glycoprotein (RVGP) is the main antigen of rabies virus and is the only viral component present in all new rabies vaccines being proposed. Many approaches have been taken since DNA recombinant technology became available to express an immunogenic recombinant rabies virus glycoprotein (rRVGP). These attempts are reviewed here, and the relevant results are discussed with respect to the general characteristics of the rRVGP, the expression system used, the expression levels achieved, the similarity of the rRVGP to the native glycoprotein, and the immunogenicity of the vaccine preparation. The most recent studies of rabies vaccine development have concentrated on in vivo expression of rRVGP by viral vector transduction, serving as the biotechnological basis for a new generation of rabies vaccines.

Rabies Control and Treatment: From Prophylaxis to Strategies with Curative Potential

Rabies is an acute, fatal, neurological disease that affects almost all kinds of mammals. Vaccination (using an inactivated rabies vaccine), combined with administration of rabies immune globulin, is the only approved, effective method for post-exposure prophylaxis against rabies in humans. In the search for novel rabies control and treatment strategies, live-attenuated viruses have recently emerged as a practical and promising approach for immunizing and controlling rabies. Unlike the conventional, inactivated rabies vaccine, live-attenuated viruses are genetically modified viruses that are able to replicate in an inoculated recipient without causing adverse effects, while still eliciting robust and effective immune responses against rabies virus infection. A number of viruses with an intrinsic capacity that could be used as putative candidates for live-attenuated rabies vaccine have been intensively evaluated for therapeutic purposes. Additional novel strategies, such as a monoclonal antibody-based approach, nucleic acid-based vaccines, or small interfering RNAs (siRNAs) interfering with virus replication, could further add to the arena of strategies to combat rabies. In this review, we highlight current advances in rabies therapy and discuss the role that they might have in the future of rabies treatment. Given the pronounced and complex impact of rabies on a patient, a combination of these novel modalities has the potential to achieve maximal anti-rabies efficacy, or may even have promising curative effects in the future. However, several hurdles regarding clinical safety considerations and public awareness should be overcome before these approaches can ultimately become clinically relevant therapies.

An mRNA Vaccine Encoding Rabies Virus Glycoprotein Induces Protection against Lethal Infection in Mice and Correlates of Protection in Adult and Newborn Pigs

Rabies is a zoonotic infectious disease of the central nervous system (CNS). In unvaccinated or untreated subjects, rabies virus infection causes severe neurological symptoms and is invariably fatal. Despite the long-standing existence of effective vaccines, vaccine availability remains insufficient, with high numbers of fatal infections mostly in developing countries. Nucleic acid based vaccines have proven convincingly as a new technology for the fast development of vaccines against newly emerging pathogens, diseases where no vaccine exists or for replacing already existing vaccines. We used an optimized non-replicating rabies virus glycoprotein (RABV-G) encoding messenger RNA (mRNA) to induce potent neutralizing antibodies (VN titers) in mice and domestic pigs. Functional antibody titers were followed in mice for up to one year and titers remained stable for the entire observation period in all dose groups. T cell analysis revealed the induction of both, specific CD4+ as well as CD8+ T cells by RABV-G mRNA, with the induced CD4+ T cells being higher than those induced by a licensed vaccine. Notably, RABV-G mRNA vaccinated mice were protected against lethal intracerebral challenge infection. Inhibition of viral replication by vaccination was verified by qRT-PCR. Furthermore, we demonstrate that CD4+ T cells are crucial for the generation of neutralizing antibodies. In domestic pigs we were able to induce VN titers that correlate with protection in adult and newborn pigs. This study demonstrates the feasibility of a non-replicating mRNA rabies vaccine in small and large animals and highlights the promises of mRNA vaccines for the prevention of infectious diseases.

Current Developments and Future Prospects for Plant-Made Biopharmaceuticals Against Rabies

Rabies is a prevalent health problem in developing countries. Although vaccines and immunoglobulin treatments are available, their cost and multiple-dose treatments restrict availability. During the last two decades, plants have served as a low-cost platform for biopharmaceuticals production and have been applied to fight against rabies during the last two decades. Herein, I provide a description of the state of the art in the development of plant-made pharmaceuticals against rabies and identify key prospects for the field in terms of novel strategies, immunogen design, and therapeutic antibodies production.

Development of broad-spectrum human monoclonal antibodies for rabies post-exposure prophylaxis

Currently available rabies post-exposure prophylaxis (PEP) for use in humans includes equine or human rabies immunoglobulins (RIG). The replacement of RIG with an equally or more potent and safer product is strongly encouraged due to the high costs and limited availability of existing RIG. In this study, we identified two broadly neutralizing human monoclonal antibodies that represent a valid and affordable alternative to RIG in rabies PEP. Memory B cells from four selected vaccinated donors were immortalized and monoclonal antibodies were tested for neutralizing activity and epitope specificity. Two antibodies, identified as RVC20 and RVC58 (binding to antigenic site I and III, respectively), were selected for their potency and broad-spectrum reactivity. In vitro, RVC20 and RVC58 were able to neutralize all 35 rabies virus (RABV) and 25 non-RABV lyssaviruses. They showed higher potency and breath compared to antibodies under clinical development (namely CR57, CR4098, and RAB1) and commercially available human RIG. In vivo, the RVC20-RVC58 cocktail protected Syrian hamsters from a lethal RABV challenge and did not affect the endogenous hamster post-vaccination antibody response.

Development of Rabies Virus-Like Particles for Vaccine Applications: Production, Characterization, and Protection Studies

Rabies is a viral infection of the central nervous system for which vaccination is the only treatment possible. Besides preexposure, vaccination is highly recommended for people living in endemic areas, veterinarians, and laboratory workers. Our group has developed rabies virus-like particles (RV-VLPs) with immunogenic features expressed in mammalian cells for vaccine applications. In this chapter the methods to obtain and characterize a stable HEK293 cell line expressing RV-VLPs are detailed. Further, analytical ultracentrifugation steps to purify the obtained VLPs are developed, as well as western blot, dynamic light scattering, and immunogold electron microscopy to analyze the size, distribution, shape, and antigenic conformation of the purified particles. Finally, immunization protocols are described to study the immunogenicity of RV-VLPs.

Immunoenhancement with flagellin as an adjuvant to whole-killed rabies vaccine in mice

Vaccination is the most effective method for preventing rabies virus (RABV) infection in both humans and animals; however, no satisfactory vaccine has been developed for use worldwide. In the present study, we investigated the immunoadjuvant properties of Salmonella Typhimurium flagellin (FljB, FliC, and FljB'-FliC) to improve immune responses against the rabies vaccine (RV) and the protective efficacy of the whole-killed rabies vaccine (WKRV) with or without flagellins in BALB/c mice. We also compared the differences among the three flagellins in terms of immunoadjuvant properties to RV. FljB can cause the WKRV to induce stronger humoral and cellular immune responses than WKRV alone or WKRV with FliC or FljB'-FliC can. Mice immunized with WKRV and FljB produced higher levels of virus-neutralizing antibody (VNA) against RABV than those in the other groups did. Although mice in all treatment groups survived RABV challenge, the body weight loss in the group immunized with WKRV and FljB was lower than in the other groups. These results indicate that FljB is a promising adjuvant for use in the development of effective rabies vaccines.

Immunogenic virus-like particles continuously expressed in mammalian cells as a veterinary rabies vaccine candidate

Rabies is one of the most lethal infectious diseases in the world, with a mortality approaching 100%. There are between 60,000 and 70,000 reported annual deaths, but this is probably an underestimation. Despite the fact that there are vaccines available for rabies, there is a real need of developing more efficacious and cheaper vaccines. This is particularly true for veterinary vaccines because dogs are still the main vector for rabies transmission to human beings. In a previous work, we described the development and characterization of rabies virus-like particles (RV-VLPs) expressed in HEK293 cells. We showed that RV-VLPs are able to induce a specific antibodies response. In this work, we show that VLPs are able to protect mice against virus challenge. Furthermore, we developed a VLPs expressing HEK-293 clone (sP2E5) that grows in serum free medium (SFM) reaching high cell densities. sP2E5 was cultured in perfusion mode in a 5 L bioreactor for 20 days, and the RV-VLPs produced were capable of triggering a protective immune response without the need of concentration or adjuvant addition. Further, these VLPs are able to induce the production of rabies virus neutralizing antibodies. These results demonstrate that RV-VLPs are a promising rabies vaccine candidate.

Incorporation of membrane-anchored flagellin or Escherichia coli heat-labile enterotoxin B subunit enhances the immunogenicity of rabies virus-like particles in mice and dogs

Rabies remains an important worldwide public health threat, so safe, effective, and affordable vaccines are still being sought. Virus-like particle-based vaccines targeting various viral pathogens have been successfully produced, licensed, and commercialized. Here, we designed and constructed two chimeric rabies virus-like particles (cRVLPs) containing rabies virus (RABV) glycoprotein (G), matrix (M) protein, and membrane-anchored flagellin (EVLP-F) or Escherichia coli heat-labile enterotoxin B subunit (EVLP-L) as molecular adjuvants to enhance the immune response against rabies. The immunogenicity and potential of cRVLPs as novel rabies vaccine were evaluated by intramuscular vaccination in mouse and dog models. Mouse studies demonstrated that both EVLP-F and EVLP-L induced faster and larger virus-neutralizing antibodies (VNAs) responses and elicited greater numbers of CD4⁺ and CD8⁺ T cells secreting IFN-γ or IL-4 compared with a standard rabies VLP (sRVLP) containing only G and M. Moreover, cRVLPs recruited and/or activated more B cells and dendritic cells in inguinal lymph nodes. EVLP-F induced a strong, specific IgG2a response but not an IgG1 response, suggesting the activation of Th1 class immunity; in contrast, Th2 class immunity was observed with EVLP-L. The significantly enhanced humoral and cellular immune responses induced by cRVLPs provided complete protection against lethal challenge with RABV. Most importantly, dogs vaccinated with EVLP-F or EVLP-L exhibited increased VNA titers in sera and enhanced IFN-γ and IL-4 secretion from peripheral blood mononuclear cells. Taken together, these results illustrate that when incorporated into sRVLP, membrane-anchored flagellin, and heat-labile enterotoxin B subunit possess strong adjuvant activity. EVLP-F and EVLP-L induce significantly enhanced RABV-specific humoral and cellular immune responses in both mouse and dog. Therefore, these cRVLPs may be developed as safe and more efficacious rabies vaccine candidate for animals.

Knowledge, attitudes and practices (KAP) about rabies prevention and control: a community survey in Tanzania

Background

Despite being entirely preventable, canine rabies still kills 55,000 people/year in developing countries. Information about local beliefs and practices can identify knowledge gaps that may affect prevention practices and lead to unnecessary deaths.

Methodology/Principal Findings

We investigated knowledge, attitudes and practices related to rabies and its prevention and control amongst a cross-section of households (n = 5,141) in urban and rural areas of central, southern and northern Tanzania. Over 17% of respondents owned domestic dogs (average of 2.3 dogs/household),>95% had heard about rabies, and>80% knew that rabies is transmitted through dog bites. People who (1) had greater education, (2) originated from areas with a history of rabies interventions, (3) had experienced exposure by a suspect rabid animal, (4) were male and (5) owned dogs were more likely to have greater knowledge about the disease. Around 80% of respondents would seek hospital treatment after a suspect bite, but only 5% were aware of the need for prompt wound cleansing after a bite. Although>65% of respondents knew of dog vaccination as a means to control rabies, only 51% vaccinated their dogs. Determinants of dog vaccination included (1) being a male-headed household, (2) presence of children, (3) low economic status, (4) residing in urban areas, (5) owning livestock, (6) originating from areas with rabies interventions and (7) having purchased a dog. The majority of dog-owning respondents were willing to contribute no more than US$0.31 towards veterinary services.

Conclusions/Significance

We identified important knowledge gaps related to, and factors influencing the prevention and control of rabies in Tanzania. Increasing knowledge regarding wound washing, seeking post-exposure prophylaxis and the need to vaccinate dogs are likely to result in more effective prevention of rabies; however, greater engagement of the veterinary and medical sectors is also needed to ensure the availability of preventative services.

Rabies remains a major public health problem in Africa and Asia, although means to control and prevent the disease are available through mass dog vaccination and provision of post-exposure prophylaxis to people exposed to bites by suspect rabid animals. Here we report the results of an extensive community survey on knowledge, attitudes and practices related to rabies control and prevention, covering rural and urban settings in central, northern and southern Tanzania. Our results showed that the majority of people across Tanzania had heard about rabies and knew that it is transmitted by dog bites, but most lacked comprehensive knowledge about key practices, such as the need for wound cleansing, which could prevent unnecessary deaths from the disease. In other circumstances, knowledge (for example, about the need to vaccinate dogs to control rabies) did not reflect good practice. In order to address the knowledge gaps identified by this study, there is a need for interventions aimed at increasing awareness, focusing on simple messages and targeting the community as a whole. This information could be channelled through media, community meetings and professionals including community leaders, health workers, teachers, livestock officers and clinicians.

Engineering, expression in transgenic plants and characterisation of E559, a rabies virus-neutralising monoclonal antibody

Rabies post-exposure prophylaxis (PEP) currently comprises administration of rabies vaccine together with rabies immunoglobulin (RIG) of either equine or human origin. In the developing world, RIG preparations are expensive, often in short supply, and of variable efficacy. Therefore, we are seeking to develop a monoclonal antibody cocktail to replace RIG. Here, we describe the cloning, engineering and production in plants of a candidate monoclonal antibody (E559) for inclusion in such a cocktail. The murine constant domains of E559 were replaced with human IgG1κ constant domains and the resulting chimeric mouse-human genes were cloned into plant expression vectors for stable nuclear transformation of Nicotiana tabacum. The plant-expressed, chimeric antibody was purified and biochemically characterized, was demonstrated to neutralize rabies virus in a fluorescent antibody virus neutralization assay, and conferred protection in a hamster challenge model.

Rabies virus-like particles expressed in HEK293 cells

Rabies is an infectious viral disease with a mortality rate close to 100%. Currently, there is a need to generate cheaper and more immunogenic vaccines for the effective prevention of rabies, mostly in developing countries. Virus-like particles have been widely used in viral vaccine production due to their high immunogenicity and safety during the production process. Rabies virus glycoprotein is the major antigen to trigger a protective immune response and the only protein capable of generating virus neutralizing antibodies. In this study we describe the development of a recombinant stable cell line for the production of rabies virus-like particles (RV-VLPs) expressing the rabies virus glycoprotein by lentivirus-based transduction of HEK293 cells. Protein expression was analyzed by flow cytometry, fluorescence microscopy, western blot and ELISA. Particles were purified from culture supernatant and their size and morphology were studied. Furthermore, mice were immunized with RV-VLPs, formulated with adjuvant, and these particles were able to produce a specific antibody response, demonstrating that these virus-like particles present a promising rabies vaccine candidate.

Safety and serological response to a matrix gene-deleted rabies virus-based vaccine vector in dogs

Dogs account for the majority of human exposures and deaths due to rabies virus (RABV) worldwide. In this report, we show that a replication-deficient RABV-based vaccine in which the matrix gene is deleted (RABV-ΔM) is safe and induces rapid and potent VNA titers after a single inoculation in dogs. Average VNA titers peaked at 3.02 or 5.11 international units (IU/ml) by 14 days post-immunization with a single dose of 10(6) or 10(7) focus forming units (ffu), respectively, of RABV-ΔM. By day 70 post immunization, all dogs immunized with either dose of vaccine showed VNA titers >0.5IU/ml, the level indicative of a satisfactory immunization. Importantly, no systemic or local reactions were noted in any dog immunized with RABV-ΔM. The elimination of dog rabies through mass vaccination is hindered by limited resources, requirement for repeat vaccinations often for the life of a dog, and in some parts of the world, inferior vaccine quality. Our preliminary safety and immunogenicity data in dogs suggest that RABV-ΔM might complement currently used inactivated RABV-based vaccines in vaccination campaigns by helping to obtain 100% response in vaccinated dogs, thereby increasing overall vaccination coverage.

ICAM-1-based rabies virus vaccine shows increased infection and activation of primary murine B cells in vitro and enhanced antibody titers in-vivo

We have previously shown that live-attenuated rabies virus (RABV)-based vaccines infect and directly activate murine and human primary B cells in-vitro, which we propose can be exploited to help develop a single-dose RABV-based vaccine. Here we report on a novel approach to utilize the binding of Intracellular Adhesion Molecule-1 (ICAM-1) to its binding partner, Lymphocyte Function-associated Antigen-1 (LFA-1), on B cells to enhance B cell activation and RABV-specific antibody responses. We used a reverse genetics approach to clone, recover, and characterize a live-attenuated recombinant RABV-based vaccine expressing the murine Icam1 gene (rRABV-mICAM-1). We show that the murine ICAM-1 gene product is incorporated into virus particles, potentially exposing ICAM-1 to extracellular binding partners. While rRABV-mICAM-1 showed 10-100-fold decrease in viral titers on baby hamster kidney cells compared to the parental virus (rRABV), rRABV-mICAM-1 infected and activated primary murine B cells in-vitro more efficiently than rRABV, as indicated by significant upregulation of CD69, CD40, and MHCII on the surface of infected B cells. ICAM-1 expression on the virus surface was responsible for enhanced B cell infection since pre-treating rRABV-mICAM-1 with a neutralizing anti-ICAM-1 antibody reduced B cell infection to levels observed with rRABV alone. Furthermore, 100-fold less rRABV-mICAM-1 was needed to induce antibody titers in immunized mice equivalent to antibody titers observed in rRABV-immunized mice. Of note, only 10³ focus forming units (ffu)/mouse of rRABV-mICAM-1 was needed to induce significant anti-RABV antibody titers as early as five days post-immunization. As both speed and potency of antibody responses are important in controlling human RABV infection in a post-exposure setting, these data show that expression of Icam1 from the RABV genome, which is then incorporated into the virus particle, is a promising strategy for the development of a single-dose RABV vaccine that requires only a minimum of virus.

High prevalence of antibodies against canine adenovirus (CAV) type 2 in domestic dog populations in South Africa precludes the use of CAV-based recombinant rabies vaccines

Rabies in dogs can be controlled through mass vaccination. Oral vaccination of domestic dogs would be useful in the developing world, where greater vaccination coverage is needed especially in inaccessible areas or places with large numbers of free-roaming dogs. From this perspective, recent research has focused on development of new recombinant vaccines that can be administered orally in a bait to be used as adjunct for parenteral vaccination. One such candidate, a recombinant canine adenovirus type 2 vaccine expressing the rabies virus glycoprotein (CAV2-RG), is considered a promising option for dogs, given host specificity and safety. To assess the potential use of this vaccine in domestic dog populations, we investigated the prevalence of antibodies against canine adenovirus type 2 in South African dogs. Blood was collected from 241 dogs from the Gauteng and KwaZulu-Natal provinces. Sampled dogs had not previously been vaccinated against canine adenovirus type 1 (CAV1) or canine adenovirus type 2 (CAV2). Animals from both provinces had a high percentage of seropositivity (45% and 62%), suggesting that CAV2 circulates extensively among domestic dog populations in South Africa. Given this finding, we evaluated the effect of pre-existing CAV-specific antibodies on the efficacy of the CAV2-RG vaccine delivered via the oral route in dogs. Purpose-bred Beagle dogs, which received prior vaccination against canine parvovirus, canine distemper virus and CAV, were immunized by oral administration of CAV2-RG. After rabies virus (RABV) infection all animals, except one vaccinated dog, developed rabies. This study demonstrated that pre-existing antibodies against CAV, such as naturally occurs in South African dogs, inhibits the development of neutralizing antibodies against RABV when immunized with a CAV-based rabies recombinant vaccine.

Enhancement of humoral and cellular immune responses by monophosphoryl lipid A (MPLA) as an adjuvant to the rabies vaccine in BALB/c mice

The development of effective vaccines against the rabies virus could prevent infection with this fatal virus. However, the current rabies vaccine fails to provide a full range of protection because of its limited ability to elicit a cellular immune response and the requirement for repeat vaccination. Monophosphoryl lipid A (MPLA) is well known as a potent adjuvant to enhance immune responses against virus infection. Here we investigated the efficacy of MPLA as an adjuvant to improve the humoral and cellular immune responses to the rabies vaccine in BALB/c mice. Supplementation of the rabies vaccine with MPLA significantly accelerated the production of specific antibodies by 10 days compared to the original vaccines. Furthermore, MPLA promoted the induction of stronger cellular immune responses by the rabies vaccine, including the production of IL-4, IFN-γ and the activation of CD4⁺/CD8⁺ T cells, than those elicited without MPLA. Collectively, our findings indicated that MPLA enhances humoral and cellular immunity and is a promising adjuvant for the development of more effective rabies vaccines.

The emergence of wildlife species as a source of human rabies infection in Brazil

Forty-five human rabies virus isolates from a wide geographical area of Brazil were characterized using an anti-nucleoprotein monoclonal antibody panel and by partial nucleotide sequencing analysis of the nucleoprotein gene. Three major antigenic groups related to the antigenic variants maintained in domestic dogs, vampire bats and marmosets were identified. Phylogenetic analyses revealed that the viruses from dog-related cases segregated into four sister clades: three associated with dog-endemic cycles in Brazil and one with the crab-eating fox cycle in the northeastern region of the country. The vampire bat- and marmoset-related viruses formed two independent groups. The topology of these clades was conserved when these samples were compared to virus representatives of the currently reported rabies endemic cycles in the Americas. These results indicated the presence of multiple endemic transmission cycles maintained in four different reservoirs, domestic dogs, crab-eating foxes, vampire bats and marmosets, which are being transmitted directly to humans and should be considered as a high-risk for rabies infection.

A new rabies vaccine based on a recombinant ORF virus (parapoxvirus) expressing the rabies virus glycoprotein

The present study describes the generation of a new Orf virus (ORFV) recombinant, D1701-V-RabG, expressing the rabies virus (RABV) glycoprotein that is correctly presented on the surface of infected cells without the need of replication or production of infectious recombinant virus. One single immunization with recombinant ORFV can stimulate high RABV-specific virus-neutralizing antibody (VNA) titers in mice, cats, and dogs, representing all nonpermissive hosts for the ORFV vector. The protective immune response against severe lethal challenge infection was analyzed in detail in mice using different dosages, numbers, and routes for immunization with the ORFV recombinant. Long-term levels of VNA could be elicited that remained greater than 0.5 IU per ml serum, indicative for the protective status. Single applications of higher doses (10(7) PFU) can be sufficient to confer complete protection against intracranial (i.c.) challenge, whereas booster immunization was needed for protection by the application of lower dosages. Anamnestic immune responses were achieved by each of the seven tested routes of inoculation, including oral application. Finally, in vivo antibody-mediated depletion of CD4-positive and/or CD8-posititve T cell subpopulations during immunization and/or challenge infection attested the importance of CD4 T cells for the induction of protective immunity by D1701-V-RabG. This report demonstrates another example of the potential of the ORFV vector and also indicates the capability of the new recombinant for vaccination of animals.

Developing plant-based vaccines against neglected tropical diseases: where are we?

Neglected tropical diseases (NTDs) impair the lives of 1 billion people worldwide, and threaten the health of millions more. Although vaccine candidates have been proposed to prevent some NTDs, no vaccine is available at the market yet. Vaccines against NTDs should be low-cost and needle-free to reduce the logistic cost of their administration. Plant-based vaccines meet both requirements: plant systems allow antigen production at low cost, and also yield an optimal delivery vehicle that prevents or delays digestive hydrolysis of vaccine antigens. This review covers recent reports on the development of plant-based vaccines against NTDs. Efforts conducted by a number of research groups to develop vaccines as a mean to fight rabies, cysticercosis, dengue, and helminthiasis are emphasized. Future perspectives are identified, such as the need to develop vaccination models for more than ten pathologies through a plant-based biotechnological approach. Current limitations on the method are also noted, and molecular approaches that might allow us to address such limitations are discussed.

Passive immunity in the prevention of rabies

Prevention of clinical disease in those exposed to viral infection is an important goal of human medicine. Using rabies virus infection as an example, we discuss the advances in passive immunoprophylaxis, most notably the shift from the recommended polyclonal human or equine immunoglobulins to monoclonal antibody therapies. The first rabies-specific monoclonal antibodies are undergoing clinical trials, so passive immunisation might finally become an accessible, affordable, and routinely used part of global health practices for rabies. Coupled with an adequate supply of modern tissue-culture vaccines, replacing the less efficient and unsafe nerve-tissue-derived rabies vaccines, the burden of this disease could be substantially reduced.

Treatment of rabies in the 21st century: curing the incurable?

Despite the extreme case fatality attributable to rabies, reports of survivors provide a faint glimpse of a possibility of overcoming this deadly disease, even after clinical symptoms manifest. At present, no existing approach fulfills modern medical criteria for the optimal therapy of rabies. Until new efficacious antiviral compounds and optimized treatment protocols are developed, animal population management and vaccination of major reservoirs and vectors, minimization of the risk of viral exposures, and appropriate and early postexposure prophylaxis, remain the hallmarks of modern public health intervention.

Oral immunisation of mice with a recombinant rabies virus vaccine incorporating the heat-labile enterotoxin B subunit of Escherichia coli in an attenuated Salmonella strain

To investigate effective new rabies vaccines, a fusion protein consisting of the rabies virus (RV) glycoprotein and the heat-labile enterotoxin B subunit of Escherichia coli (LTB) was successfully constructed and delivered in a live attenuated Salmonella strain LH430. Mice were immunised with LH430 carrying pVAX1-G, pVAX1-G-LTB or pVAX1-ori-G-LTB. The antibody titres of mice immunised with oral LH430 carrying pVAX1-G-LTB or pVAX1-ori-G-LTB were significantly higher than those of pVAX1-G-immunised mice. The results of the challenge with the rabies virus standard strain (CVS-11) showed that the LH430 strain carrying the G-LTB gene induced immunity and elevated IL-2 levels in immunised mice ((∗∗)P<0.01), whereas LH430 carrying pVAX1-G did not contribute to protection. These results show that LH430 carrying recombinant G-LTB could provide overall immunity against challenge with CVS-11 and should be considered to be a potential rabies vaccine.