Rabies virus glycoprotein serology ELISA for measurement of neutralizing antibodies in sera of vaccinated human subjects

One-dose intradermal rabies booster enhances rabies antibody production and avidity maturation

The incidence of rabies in Thailand reached its peak in 2018 with 18 human deaths. Preexposure prophylaxis (PrEP) vaccination is thus recommended for high-risk populations. WHO has recently recommended that patients who are exposed to a suspected rabid animal and have already been immunized against rabies should receive a 1-site intradermal (ID) injection of 0.1 mL on days 0 and 3 as postexposure prophylaxis (PEP). In Thailand, village health and livestock volunteers tasked with annual dog vaccination typically receive only a single lifetime PrEP dose and subsequent boosters solely upon confirmed animal bites. However, the adequacy of a single PrEP dose for priming and maintaining immunity in this high-risk group has not been evaluated. Therefore, our study was designed to address two key questions: (1) sufficiency of single-dose PrEP-to determine whether a single ID PrEP dose provides adequate long-term immune protection for high-risk individuals exposed to numerous dogs during their vaccination duties. (2) Booster efficacy for immune maturation-to investigate whether one or two additional ID booster doses effectively stimulate a mature and sustained antibody response in this population. The level and persistence of the rabies antibody were determined by comparing the immunogenicity and booster efficacy among the vaccination groups. Our study demonstrated that rabies antibodies persisted for more than 180 days after cost-effective ID PrEP or the 1st or the 2nd single ID booster dose, and adequate antibody levels were detected in more than 95% of participants by CEE-cELISA and 100% by indirect ELISA. Moreover, the avidity maturation of rabies-specific antibodies occurred after the 1st single ID booster dose. This smaller ID booster regimen was sufficient for producing a sufficient immune response and enhancing the maturation of anti-rabies antibodies. This safe and effective PrEP regimen and a single visit involving a one-dose ID booster are recommended, and at least one one-dose ID booster regimen could be equitably implemented in at-risk people in Thailand and other developing countries. However, an adequate antibody level should be monitored before the booster is administered.

A time-resolved fluorescence immunoassay for rapid and precise automatic quality control of human papillomavirus type 68 VLPs in human papillomavirus vaccine

The effectiveness and necessity of human papillomavirus (HPV) vaccination to prevent HPV infection and cervical cancer are increasingly recognized by people. The 15-valent HPV vaccine, which protects against almost high-risk types of HPV viruses identified by WHO, has attracted much attention. However, as the valence of vaccines increases, quality control in the HPV vaccine production process is facing more challenges. The precise quality control of the HPV type 68 virus-like particles (VLPs), one of the unique components of the 15-valent HPV vaccine that distinguishes it from existing vaccines, is the new requirement for vaccine manufacturers. Here we developed a novel time-resolved fluorescence immunoassay (TRFIA) for rapid and precise automatic quality control of HPV68 VLPs in HPV vaccine. Two murine monoclonal antibodies specifically targeting the HPV68 L1 protein were used to establish a classical sandwich assay. Except for pretreating the vaccine sample, the whole analysis process was performed by a fully automated machine, which saves detection time and gets rid of manual error. Multiple experiments established that the current novel TRFIA can efficiently and reliably analyses HPV68 VLPs. Present novel TRFIA has exhibited merits with speed, robustness, high sensitivity with a minimum detection value of 0.08 ng/mL, considerable accuracy, a wide detection range (up to 1000 ng/mL) and excellent specificity. It is also expected to provide a new detection method for quality control for each HPV type VLPs. To summarize, the novel TRFIA is of great interest for application in HPV vaccine quality control.

Evaluation of In-House ELISA for Antirabies Antibodies Detection in Domestic Canine

Indonesia is known to be endemic for rabies in several areas, especially in Sumatra, Kalimantan, Sulawesi, and Flores Islands. Currently, vaccinating dogs has been shown to be the most cost-effective strategy for preventing rabies in humans. Postvaccination monitoring should be carried out to evaluate the success of vaccination by measuring antibody titers in serum of vaccinated dogs. Serological methods for monitoring rabies-specific antibody titers can be carried out using enzyme-linked immunosorbent assay (ELISA) methods as recommended by the World Organization for Animal Health (WOAH). Therefore, the development of the in-house ELISA (BukTi-Vet) that we have carried out in order to support postvaccination monitoring in dogs needs to be evaluated for its diagnostic performance compared to commercial ELISA kits. The diagnostic performance of each ELISA kit was evaluated using 111 known positive and 47 negative serums. Each known positive and negative serum will be tested using the three rabies ELISA kits used in this study. BukTi-Vet is an in-house ELISA for the detection of rabies-specific IgG antibodies that have been developed with sensitivity, specificity, and accuracy of 98.19%, 97.87%, and 98.1%, respectively. Based on the value of its positive and negative clinical utility index, BukTi-Vet is excellent for use in immunoassays directed for confirmatory (0.97) as well as screening (0.94) tests. BukTi-Vet shows a very good agreement with both Platelia II and RFFIT, so it is convincing to be further refined into a diagnostic kit. Tests of field sera from dogs vaccinated with various vaccines should be performed to provide more complete information on diagnostic performance. BukTi-Vet showed a very good agreement with RFFIT, while Pusvetma and Platelia II only showed good agreement. The average value of BukTi-Vet compatibility with RFFIT can reach 94%.

A combination vaccine against SARS-CoV-2 and H1N1 influenza based on receptor binding domain trimerized by six-helix bundle fusion core

Background

Increasing severe morbidity and mortality by simultaneous or sequential infections with SARS-CoV-2 and influenza A viruses (IAV), especially in the elderly and obese patients, highlight the urgency of developing a combination vaccine against COVID-19 and influenza.

Methods

Self-assembling SARS-CoV-2 RBD-trimer and Influenza H1N1 HA1-trimer antigens were constructed, upon the stable fusion core in post-fusion conformation. Immunogenicity of SARS-CoV-2 RBD-trimer vaccine and H1N1 HA1-trimer antigens candidates were evaluated in mice. Protection efficacy of a combination vaccine candidate against SARS-CoV-2 and IAV challenge was identified using the K18-hACE2 mouse model.

Findings

Both the resultant RBD-trimer for SARS-CoV-2 and HA1-trimer for H1N1 influenza fully exposed receptor-binding motifs (RBM) or receptor-binding site (RBS). Two-dose RBD-trimer induced significantly higher binding and neutralizing antibody titers, and also a strong Th1/Th2 balanced cellular immune response in mice. Similarly, the HA1-trimer vaccine was confirmed to exhibit potent immunogenicity in mice. A combination vaccine candidate, composed of RBD-trimer and HA1-trimer, afforded high protection efficacy in mouse models against stringent lethal SARS-CoV-2 and homogenous H1N1 influenza co-infection, characterized by 100% survival rate.

Interpretation

Our results represent a proof of concept for a combined vaccine candidate based on trimerized receptor binding domain against co-epidemics of COVID-19 and influenza.

Funding

This project was funded by the Strategic Priority Research Program of CAS (XDB29040201), the National Natural Science Foundation of China (81830050, 81901680, and 32070569) and China Postdoctoral Science Foundation (2021M703450).

A Comparative Evaluation of the Estimation of Rabies Virus Antibodies among Free-Roaming, Vaccinated Dogs in Bengaluru, India

Vaccination is the practical solution for the prevention of rabies in dogs. Assessment of the immunogenicity of vaccination includes estimation of specific rabies virus neutralizing antibodies (VNA) in the target species. We undertook a study to estimate the levels of VNA in free-roaming dogs with a history of rabies vaccination in Bengaluru city, India. We compared the rapid fluorescent focus inhibition test (RFFIT) and an in-house quantitative indirect ELISA (iELISA). The study area comprised the jurisdiction of Bruhat Bengaluru Mahanagara Palike (BBMP), the Bengaluru civic body. The BBMP, along with several non-government organizations (NGO), were conducting a trap- neuter- vaccinate- release program for the prevention of dog rabies. Serum samples were collected from 250 free-roaming dogs from representative regions of BBMP, of which 125 had a VNA titre of 0.5 IU or more by the RFFIT. Furthermore, 126 dogs showed percent positivity values (PP values) more than the cut off PP value of 57.1 by the iELISA, accounting for 50.4% of satisfactory post-vaccinal serum conversion. The sensitivity and specificity of the iELISA was 94.4% and 95.2%, respectively. Based on these data, a quantitative iELISA may be a complementary tool for sero-monitoring immune responses of free-ranging animals after rabies vaccination.

A comparative review of serological assays for the detection of rabies virus-specific antibodies

Rabies is a major public health problem with a fatality rate close to 100%, caused by a virus of the Lyssavirus genus, of which rabies virus (RABV) is the prototype. Nonetheless, the complete prevention can be achieved by the induction of neutralizing antibodies by pre- or post-exposure prophylaxis. According to the world health organization (WHO) and World Organization for animal health (OIE), serum titers of rabies virus neutralizing antibodies (RVNA) that are higher or equal to 0.5 international units (IU)/ml indicate adequate immune response after vaccination against rabies. Currently, RFFIT and FAVN are the gold standard tests recommended by both WHO and OIE for detecting and quantitating RVNA in biological samples from individuals or animals previously vaccinated and/or subjects suspected of having been infected by RABV. Although the tests RFFIT and FAVN are efficient, they are time-consuming, labor-intensive manual tests and not cost-effective for routine use. Following the previously mentioned, approaches with alternative methods have been developed to detect RVNA or rabies-specific antibodies in human or animal serum, but with variable success. This work summarizes the advances in the serological assays for the detection of neutralizing antibodies or rabies antibodies and assesses the individual immune status after vaccination against rabies, as well as the mechanisms of RABV neutralization mediated by antibodies. Therefore, the main alternative methods for the determination of RABV or rabies-specific antibodies are exposed, with promising results, besides being easy to execute, of low cost, and representing a possibility of being applied, according to the proposal of each test to the network of Rabies Surveillance Laboratories.

Review of Detection and Quantification of Rabies Virus Antibodies

Rabies is an almost invariably fatal disease. According to the World Health Organization (WHO), rabies virus neutralizing antibody (RVNA) titers of ≥0.5 IU/mL are considered adequate for rabies protection. Therefore, detection and quantification of RABV antibodies are important. Many methods have been developed for detecting RABV antibodies. In the present study, we reviewed several methods of detecting RABV antibodies in human and animal samples and evaluated and compared their performance. Of 34 methods, 5 demonstrated unsatisfactory sensitivity or specificity. The others exhibited sensitivity and specificity of ≥75%. The correlation coefficient for five of eight methods was >0.8. The Bland-Altman mean bias of five of five methods was <±2.0. The kappa values of 25 of 28 methods were higher than 0.4, demonstrating at least moderate agreement. Analysis of the performance of these methods emphasized that any new technology should be considered carefully and objectively before being used as an appropriate and applicable alternative.

Detection and quantification of anti-rabies glycoprotein antibodies: current state and perspectives

Rabies is an ancient fatal disease with no other available treatment than post-exposure vaccination, where the bite of infected animals, mainly dogs, is the leading cause of its transmission to human beings. In this context, global vaccination campaigns of companion animals, as well as wildlife reservoirs vaccination, are key factors to achieve the "Zero by 30" plan that pursues the eradication of dog-mediated human rabies by 2030. Rabies virus-neutralizing antibodies (VNAs) play an essential role in the disease protection, as it correlates with an adequate immune response and allows evaluating pre- or post-exposure prophylaxis efficacy. Hence, counting with reliable, accurate, and robust serological tests is of paramount importance. Currently, RFFIT and FAVN are the gold standard VNAs tests recommended by both the WHO and the OIE. Despite these methodologies are efficient and widely used, they present several drawbacks, as they are less easily to standardize and require the use of live rabies virus, containment facilities, and skilled professionals. Thus, in this review, we describe the state-of-the-art of alternative analytical methodologies currently available for rabies serology, with novel approaches based on pseudotyped recombinant viruses and emphasizing in the antigen binding methodologies that detect and quantify antibodies against the rabies glycoprotein. We discussed the wide range of assays that are interesting tools for a faster measurement of anti-rabies glycoprotein antibodies and, in some cases, less complex and more versatile than the gold standard methods. Finally, we discussed the key issues during the design and optimization steps of ELISA assays, highlighting the importance of validation and standardization procedures to improve rabies serology tests and, as a consequence, their results. KEY POINTS: • An exhaustive revision of rabies serology testing was made. • No rabies serology assay can be thought as better than others for all intents and purposes. • The validation procedure guarantees reliable and consistent results among the globe.

Determining the Specific Activity of Anti-Rabies Sera and Immunoglobulin Using Atomic Force Microscopy of Cell Cultures

BACKGROUND

Mouse neutralization test is widely used to determine the level of anti-rabies antibodies, but it is labor-intensive and time consuming. Alternative methods for determining the neutralizing activity of anti-rabies sera and immunoglobulin in cell cultures are also known. Methods such as FAVN and RFFIT involve the use of fluorescent diagnostics. Determination of Cytopathic Effect (CPE) is often complicated due to features of rabies virus replication in cells. Atomic Force Microscopy (AFM) is able to detect the interaction of the virus with the cell at an early stage. Therefore, in this study, a method has been developed for determining the specific activity of anti-rabies sera and immunoglobulin using AFM of cell cultures.

METHODS

The method is based on the preliminary interaction of rabies virus with samples of rabies sera or immunoglobulin drug, adding the specified reaction mixture to cell culture (Vero or BHK-21), and then measuring the surface roughness of the cells using AFM. AFM was carried out in the intermittent contact mode by the mismatch method in the semi-contact mode. The results were compared with the values obtained in the mouse neutralization test. The consistency of the results obtained by both methods was evaluated by Bland-Altman method.

RESULTS

The increment in the surface roughness of the cells is a consequence of the damaging effect of the virus, which is weakened as a result of its neutralization by rabies antibodies. A dilution allowing 50% suppression of the increase in the surface roughness of cells was selected as the titer of rabies sera or immunoglobulin. In this case, the recommended range for determining the antibody titer is from 1:100 to 1:3000.

CONCLUSION

For the first time, a new methodological approach in virology and pharmaceutical research is presented in this study. The use of the proposed methodological technique will reduce the time from 21 to 2 days to obtain results in comparison with the mouse neutralization test; also, fewer laboratory animals are required in this approach which is in agreement with 3 R Principle.

Systematic Booster after Rabies Pre-Exposure Prophylaxis to Alleviate Rabies Antibody Monitoring in Individuals at Risk of Occupational Exposure

Pre-exposure rabies prophylaxis (PrEP) is recommended for people at frequent or increased risk of professional exposure to lyssavirus (including rabies virus). PrEP provides protection against unrecognized exposure. After the primary vaccination, one's immune response against rabies may decline over time. We aimed to evaluate the immune response to rabies in individuals immunized for occupational reasons before and after a booster dose of the rabies vaccine. With this aim, we retrospectively documented factors associated with an inadequate response in individuals vaccinated for occupational purposes. Our findings analyzed data from 498 vaccinated individuals and found that 17.2% of participants had an inadequate antibody titration documented after their primary vaccination without the booster, while inadequate response after an additional booster of the vaccine was evidenced in 0.5% of tested participants. This study showed that a single booster dose of vaccine after PrEP conferred a high and long-term immune response in nearly all individuals except for rare, low responders. A systematic rabies booster after primary vaccination may result in alleviating the monitoring strategy of post-PrEP antibody titers among exposed professionals.

Peptide enzyme-linked immunosorbent assay (pELISA) as a possible alternative to the neutralization test for evaluating the immune response to IBV vaccine

BACKGROUND

Infectious bronchitis virus (IBV), a coronavirus, is one of the most important poultry pathogens worldwide due to its multiple serotypes and poor cross-protection. Vaccination plays a vital role in controlling the disease. The efficacy of vaccination in chicken flocks can be evaluated by detecting neutralizing antibodies with the neutralization test. However there are no simple and rapid methods for detecting the neutralizing antibodies.

RESULTS

In this study, a peptide enzyme-linked immunosorbent assay (pELISA) as a possible alternative to the neutralization test for evaluating the immune response to IBV vaccine was developed. The pELISA could indirect evaluate neutralizing antibody titers against different types of IBV in all tested sera. The titers measured with the pELISA had a coefficient of 0.83 for neutralizing antibody titers.

CONCLUSIONS

The pELISA could detect antibodies against different types of IBV in all tested sera. The pELISA has the potential to evaluate samples for IBV-specific neutralizing antibodies and surveillance the infection of IBV.

Glycosylation is required for the neutralizing activity of human IgG1 antibodies against human rabies induced by pre-exposure prophylaxis

Rabies lyssavirus (RABV) neutralizing IgG antibodies confer protection after rabies vaccination, although how the RABV-specific antibodies neutralize the virus is still unknown. As changes in the antibody's carbohydrate chain can interfere with its effector functions, we compared the glycosylation patterns of both neutralizing and non-neutralizing IgG1 induced by pre-exposure prophylaxis to human rabies and analyzed their influence on in vitro antibody neutralizing activities. Specific IgG1 were purified from human serum using affinity chromatography. Purity and avidity were analyzed by SDS-PAGE and indirect ELISA using NH₄SCN respectively. The N-linked oligosaccharide chain of the purified IgG antibody was evaluated using a lectin-based ELISA assay with a panel of seven lectins. The activity of purified IgG1 and neutralizing IgG1 deglycosylated by PNGase F enzyme were analyzed using the rapid fluorescent focus inhibition test. The purified IgG1 showed an electrophoretic pattern compatible with human IgG. All of the antibodies recognized RABV, although neutralizing IgG1 had a higher avidity (RAI = 80%) than non-neutralizing IgG1 (RAI = 30%). The neutralizing IgG1 also showed higher binding to WFA, ECA, WGA, and ConA lectins, indicating possible different N-acetylgalactosamine, galactose, N-acetylglucosamine, and mannose contents. Non-neutralizing IgG1, on the other hand, showed strong binding at UEA-1 and SNA, which bind to fucose and sialic acid residues respectively. Different glycosylation profiles were also observed in Fab and Fc fragments from neutralizing and non-neutralizing IgG1, although the deglycosylated IgG1 lost its neutralizing activity. Our results suggest that antibody glycosylation is important for neutralizing RABV in vitro, since neutralizing IgG1 has a different glycosylation profile than non-neutralizing IgG1. Further research will be needed to better evaluate the differential glycosylation patterns between IgG1 antibodies following vaccination.

A time-resolved fluoroimmunoassay for assessing rabies antibody titers in the sera of vaccinated human subjects

Several studies have investigated the use of simple in vitro tests for the assessment of rabies antibody titers in serum samples from vaccinated human subjects, which would allow the effectiveness of rabies vaccination to be conveniently evaluated. To this end, a novel time-resolved fluoroimmunoassay (TRFIA) for the assessment of rabies antibody titers was established in this study for evaluating the effectiveness of protection against rabies. The TRFIA had a satisfactory limit of detection value (0.035 IU/mL) under optimal conditions. Additionally, the application of the TRFIA was demonstrated in 68 serum samples with satisfactory results. The coefficient variations (CVs) were all <10%, and the recoveries were in the range of 90-110%. The correlation coefficient of titer values obtained using the present TRFIA and the rapid fluorescent focus inhibition test (RFFIT) was 0.733, with a coincidence rate regarding the evaluation results (protected or not protected by vaccination) of 100%. The preliminary results confirmed that the TRFIA had a higher performance than an enzyme-linked immunosorbent assay (ELISA), and could potentially replace the ELISA. Based on these results, the novel TRFIA appears to be a convenient tool for the evaluation of rabies vaccination results based on serum samples from vaccinated human subjects.

Immune response to rabies post-exposure prophylaxis in patients with non-HIV secondary immunodeficiencies

BACKGROUND

This study sought to determine the proportion of individuals with non-HIV secondary immunodeficiencies presenting inadequate antibody titers after rabies post-exposure prophylaxis (PEP) and to identify variables associated with inadequate response.

METHODS

A retrospective review of the records of immunocompromised patients having received a full course of PEP after a rabies exposure and having been tested for post-PPE antibody titers in two French Antirabies Clinics, between 2013 and 2018, was conducted. Antibody titers < 0.5 EU/ml (ELISA) were classified as inadequate.

RESULTS

A total of 28 individuals were included, 6 had inadequate post-PPE titers. None of the tested variable was independently associated with inadequate titers.

CONCLUSIONS

Inadequate response was unpredictable and not explained either by the characteristics of patients or by the PEP regimen they received. These findings support the WHO recommendation to systematically assess post-PEP response in immunocompromised patients to detect non-responders, who might require an additional dose.

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.