A study of the effect of chemical inactivants on the epitopes of Rift Valley fever virus glycoproteins using monoclonal antibodies

Safety and immunogenicity of inactivated Rift Valley Fever Smithburn viral vaccine in sheep

BACKGROUND

The live-attenuated Rift Valley Fever Smithburn (SB) vaccine is one of the oldest products widely used in ruminants for control of RVF infections. Vaccinations with RVF Smithburn result in residual pathogenic effect and is limited for use in non-pregnant animals. Commercially available RVFV inactivated vaccines are considered safer options to control the disease. These products are prepared from virulent RVFV isolates and present occupational safety concerns. This research study evaluates the ability of an inactivated SB vaccine strain to elicit neutralising antibody response in sheep.

METHODS

The RVF Smithburn vaccine was inactivated with binary ethylenimine at 37 °C. Inactivated RVFV cultures were adjuvanted with Montande™ Gel-01 and aluminium hydroxide (Al (OH)3) gel for immunogenicity and safety determination in sheep. The commercial RVF inactivated vaccine and a placebo were included as positive and negative control groups, respectively.

RESULTS

Inactivated RVFV vaccine formulations were safe with all animals showing no clinical signs of RVFV infection and temperature reactions following prime-boost injections. The aluminium hydroxide formulated vaccine induced an immune response as early as 14 days post primary vaccination with neutralising antibody titre of 1:20 and a peak antibody titre of 1:83 was reached on day 56. A similar trend was observed in the animal group vaccinated with the commercial inactivated RVF vaccine obtaining the highest antibody titre of 1:128 on day 56. The neutralizing antibody levels remained within a threshold for the duration of the study. Merino sheep vaccinated with Montanide™ Gel-01-Smithburn were characterised with overall lower immune response when compared to aluminium hydroxide vaccine emulsions.

CONCLUSIONS

These finding suggests that the inactivated RVF Smithburn vaccine strain adjuvanted with aluminium-hydroxide can be used an alternative to the products prepared from virulent RVFV isolates for protection of ruminants against the disease. The vaccine can further be evaluated for safety in pregnant ewes.

Hydrophobic Rose Bengal Derivatives Exhibit Submicromolar-to-Subnanomolar Activity against Enveloped Viruses

Rose Bengal (RB) is an anionic xanthene dye with multiple useful biological features, including photosensitization properties. RB was studied extensively as a photosensitizer, mostly for antibacterial and antitumor photodynamic therapy (PDT). The application of RB to virus inactivation is rather understudied, and no RB derivatives have been developed as antivirals. In this work, we used a synthetic approach based on a successful design of photosensitizing antivirals to produce RB derivatives for virus photoinactivation. A series of n-alkyl-substituted RB derivatives was synthesized and evaluated as antiviral photosensitizers. The compounds exhibited similar 1O2 generation rate and efficiency, but drastically different activities against SARS-CoV-2, CHIKV, and HIV; with comparable cytotoxicity for different cell lines. Submicromolar-to-subnanomolar activities and high selectivity indices were detected for compounds with C4-6 alkyl (SARS-CoV-2) and C6-8 alkyl (CHIKV) chains. Spectrophotometric assessment demonstrates low aqueous solubility for C8-10 congeners and a significant aggregation tendency for the C12 derivative, possibly influencing its antiviral efficacy. Initial evaluation of the synthesized compounds makes them promising for further study as viral inactivators for vaccine preparations.

Metal-Organic Framework Encapsulated Whole-Cell Vaccines Enhance Humoral Immunity against Bacterial Infection

The increasing rate of resistance of bacterial infection against antibiotics requires next generation approaches to fight potential pandemic spread. The development of vaccines against pathogenic bacteria has been difficult owing, in part, to the genetic diversity of bacteria. Hence, there are many potential target antigens and little a priori knowledge of which antigen/s will elicit protective immunity. The painstaking process of selecting appropriate antigens could be avoided with whole-cell bacteria; however, whole-cell formulations typically fail to produce long-term and durable immune responses. These complications are one reason why no vaccine against any type of pathogenic E. coli has been successfully clinically translated. As a proof of principle, we demonstrate a method to enhance the immunogenicity of a model pathogenic E. coli strain by forming a slow releasing depot. The E. coli strain CFT073 was biomimetically mineralized within a metal-organic framework (MOF). This process encapsulates the bacteria within 30 min in water and at ambient temperatures. Vaccination with this formulation substantially enhances antibody production and results in significantly enhanced survival in a mouse model of bacteremia compared to standard inactivated formulations.

Staphylococcus aureus derived hyaluronic acid and bacillus Calmette-Guérin purified proteins as immune enhancers to rabies vaccine and related immuno-histopathological alterations

Purpose

One of the essential goals regarding the successful control of rabies infection is the development of a safe, effective, and inexpensive vaccine. the current study aimed to evaluate the inactivation potential of β-propiolactone (βPL), binary ethyleneimine (BEI), and hydrogen peroxide (H₂O₂).

Materials and Methods

Estimating the inactivation kinetics of βPL, BEI, and H₂O₂ revealed that the tested inactivants could completely and irreversibly inactivate rabies virus within 2, 12, and 4 hours, respectively while maintaining its viral immunogenicity. The potency of βPL, BEI, and H₂O₂ inactivated vaccines was higher than the World Health Organization acceptance limit and were in the order of 3.75, 4.21, and 3.64 IU/mL, respectively. Monitoring the humoral and cellular immunity elicited post-immunization using Staphylococcus aureus derived hyaluronic acid (HA) and bacillus Calmette-Guérin purified protein derivative (PPD) adjuvanted rabies vaccine candidates were carried out using enzyme-linked immunosorbent assay.

Results

Results demonstrated that both adjuvants could progressively enhance the release of anti-rabies total immunoglobulin G as well as the pro-inflammatory mediators (interferon-gamma and interleukin-5) relative to time. However, a higher immune response was developed in the case of HA adjuvanted rabies vaccine compared to PPD adjuvanted one. The harmful consequences of the tested adjuvants were considered via investigating the histopathological changes in the tissues of the immunized rats using hematoxylin and eosin stain. Lower adverse effects were observed post-vaccination with HA and PPD adjuvanted vaccines compared to that detected following administration of the currently used alum as standard adjuvant.

Conclusion

Our findings suggested that HA and PPD could serve as a promising platform for the development of newly adjuvanted rabies vaccines with elevated immune enhancing potentials and lower risk of health hazards.

Validation of a binary ethylenimine (BEI) inactivation procedure for biosafety treatment of foot-and-mouth disease viruses (FMDV), vesicular stomatitis viruses (VSV), and swine vesicular disease virus (SVDV)

Binary ethylenimine (BEI) has been widely used as a virucide to inactivate viruses. For regulatory exclusion of a select agent, the United States Federal Select Agent Program (FSAP) requires an inactivation procedure that renders a select agent non-viable but allows the select agent to retain antigenic characteristics for future use must be validated, and the inactivated agent must be confirmed by a viability testing. In this curve-based validation study, we examined impacts of BEI concentration, treatment temperature, and time on our in-house inactivation procedures of Foot-and-Mouth Disease Virus (FMDV), Vesicular Stomatitis Virus (VSV), and Swine Vesicular Disease Virus (SVDV). The inactivation efficacy was confirmed by virus titration and 3 consecutive blind passages on the monolayers of susceptible cells. A linear correlation between the virus titer reduction and BEI concentration, treatment time, and temperature was established. The results confirmed our in-house BEI inactivation procedure of two doses of 1.5 mM BEI treatment at 37 °C, 1st dose for 24 h, then 2nd dose for 6 more hours for a total of 30 h BEI contact time, can ensure complete inactivation of FMDV, VSV, and SVDV.

An effective inactivant based on singlet oxygen-mediated lipid oxidation implicates a new paradigm for broad-spectrum antivirals

Emerging viral pathogens cause substantial morbidity and pose a severe threat to health worldwide. However, a universal antiviral strategy for producing safe and immunogenic inactivated vaccines is lacking. Here, we report an antiviral strategy using the novel singlet oxygen (¹O₂)-generating agent LJ002 to inactivate enveloped viruses and provide effective protection against viral infection. Our results demonstrated that LJ002 efficiently generated ¹O₂ in solution and living cells. Nevertheless, LJ002 exhibited no signs of acute toxicity in vitro or in vivo. The ¹O₂ produced by LJ002 oxidized lipids in the viral envelope and consequently destroyed the viral membrane structure, thus inhibiting the viral and cell membrane fusion necessary for infection. Moreover, the ¹O₂-based inactivated pseudorabies virus (PRV) vaccine had no effect on the content of the viral surface proteins. Immunization of mice with LJ002-inactiviated PRV vaccine harboring comparable antigen induced more neutralizing antibody responses and efficient protection against PRV infection than conventional formalin-inactivated vaccine. Additionally, LJ002 inactivated a broad spectrum of enveloped viruses. Together, our results may provide a new paradigm of using broad-spectrum, highly effective inactivants functioning through ¹O₂-mediated lipid oxidation for developing antivirals that target the viral membrane fusion process.

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LJ002 efficiently generates ¹O₂ in solution and living cells.

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LJ002 oxidizes lipids in the viral envelope, thus inhibiting fusion between the virus and cell membrane.

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LJ002-inactivated PRV vaccine has no effect on the content of antigens on the viral surface.

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LJ002-inactivated PRV vaccine elicits a strong neutralizing antibody response.

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LJ002 can inactivate a broad spectrum of enveloped viruses.

The Potential of Influenza HA-Specific Immunity in Mitigating Lethality of Postinfluenza Pneumococcal Infections

Influenza virus infections pre-dispose an individual to secondary pneumococcal infections, which represent a serious public health concern. Matching influenza vaccination was demonstrated helpful in preventing postinfluenza bacterial infections and associated illnesses in humans. Yet, the impact of influenza hemagglutinin (HA)-specific immunity alone in this dual-infection scenario remains elusive. In the present study, we assessed the protective effect of neutralizing and non-neutralizing anti-hemagglutinin immunity in a BALB/c influenza-pneumococcus superinfection model. Our immunogens were insect cell-expressed hemagglutinin-Gag virus-like particles that had been differentially-treated for the inactivation of bioprocess-related baculovirus impurities. We evaluated the potential of several formulations to restrain the primary infection with vaccine-matched or -mismatched influenza strains and secondary bacterial replication. In addition, we investigated the effect of anti-HA immunity on the interferon status in mouse lungs prior to bacterial challenge. In our experimental setup, neutralizing anti-HA immunity provided significant but incomplete protection from postinfluenza bacterial superinfection, despite effective control of viral replication. In view of this, it was surprising to observe a survival advantage with non-neutralizing adaptive immunity when using a heterologous viral challenge strain. Our findings suggest that both neutralizing and non-neutralizing anti-HA immunity can reduce disease and mortality caused by postinfluenza pneumococcal infections.

Photodynamic inactivation of selected bovine viruses by isomeric cationic tetra-platinated porphyrins

Porphyrin-based photodynamic processes have been used for the inactivation of microorganisms and treatment of tumors. The virucidal activity of porphyrins 3-PtTPyP and 4-PtTPyP was investigated against bovine viruses representative of the main structural groups (enveloped/non-enveloped, DNA/RNA: BVDV, BoHV-1, BAV and BEV), and against two epitheliotropic viruses (VSV and VACV). Viral suspensions were incubated at 0.91 [Formula: see text]mol [Formula: see text] L[Formula: see text] and exposed to a white-light LED array source (25 mW [Formula: see text] cm[Formula: see text]; 90 J [Formula: see text] cm[Formula: see text] for 0, 15, 30 and 60 min followed by determination of the remaining virus titers. Porphyrin 3-PtTPyP reduced almost 6 log of VSV and 3.5 log of BVDV titers after 15 min and complete virus photoinactivation was achieved after 30 min. 4-PtTPyP at 0.91 [Formula: see text]mol [Formula: see text] L[Formula: see text] produced reduction of titers of all enveloped virus depending on the time of light irradiation. No virucidal activity of any of the porphyrins was observed for non-enveloped viruses and these results showed the potential of porphyrins to inactivate viruses in premises.

Evaluation of Different Stabilizers and Inactivating Compounds for the Enhancement of Vero Cell Rabies Vaccine Stability and Immunogenicity: In Vitro Study

Inactivation of rabies virus is essential for rabies vaccine preparation where the inactivating compound that is currently recommended for rabies vaccine preparation is β-propiolactone (β-PL). This compound is considered better than phenol and formalin but it is expensive and potentially carcinogenic. Data revealed that Ascorbic acid (AA) with cupric ions could yield complete and irreversible inactivation of rabies virus without adversely affecting its antigenicity. Additionally, the results of testing the vaccine potency with the selected inactivating compounds were comparable (P<0.05), and ED50 was higher than the recommended World Health Organization (WHO) limits. The use of HemaGel (plasma substitute) for testing vaccine stabilization was compared with the currently used vaccine stabilizers (human albumin and lactose). HemaGel yielded better stability than the other tested stabilizers. Monitoring of cellular and humoral immune responses indicated that both the total IgG level against rabies vaccine and the IFN and IL5 levels obtained with the HemaGel-stabilized vaccines were higher than those obtained with human albumin- and lactose-stabilized vaccine candidates.

Chemical-free inactivated whole influenza virus vaccine prepared by ultrashort pulsed laser treatment

There is an urgent need for rapid methods to develop vaccines in response to emerging viral pathogens. Whole inactivated virus (WIV) vaccines represent an ideal strategy for this purpose; however, a universal method for producing safe and immunogenic inactivated vaccines is lacking. Conventional pathogen inactivation methods such as formalin, heat, ultraviolet light, and gamma rays cause structural alterations in vaccines that lead to reduced neutralizing antibody specificity, and in some cases, disastrous T helper type 2-mediated immune pathology. We have evaluated the potential of a visible ultrashort pulsed (USP) laser method to generate safe and immunogenic WIV vaccines without adjuvants. Specifically, we demonstrate that vaccination of mice with laser-inactivated H1N1 influenza virus at about a 10-fold lower dose than that required using conventional formalin-inactivated influenza vaccines results in protection against lethal H1N1 challenge in mice. The virus, inactivated by the USP laser irradiation, has been shown to retain its surface protein structure through hemagglutination assay. Unlike conventional inactivation methods, laser treatment did not generate carbonyl groups in protein, thereby reducing the risk of adverse vaccine-elicited T helper type 2 responses. Therefore, USP laser treatment is an attractive potential strategy to generate WIV vaccines with greater potency and safety than vaccines produced by current inactivation techniques.

Effect of formaldehyde inactivation on poliovirus

Inactivated polio vaccines, which have been used in many countries for more than 50 years, are produced by treating live poliovirus (PV) with formaldehyde. However, the molecular mechanisms underlying virus inactivation are not well understood. Infection by PV is initiated by virus binding to specific cell receptors, which results in viral particles undergoing sequential conformational changes that generate altered structural forms (135S and 80S particles) and leads to virus cell entry. We have analyzed the ability of inactivated PV to bind to the human poliovirus receptor (hPVR) using various techniques such as ultracentrifugation, fluorescence-activated cell sorting flow cytometry and real-time reverse transcription-PCR (RT-PCR). The results showed that although retaining the ability to bind to hPVR, inactivated PV bound less efficiently in comparison to live PV. We also found that inactivated PV showed resistance to structural conversion in vitro, as judged by measuring changes in antigenicity, the ability to bind to hPVR, and viral RNA release at high temperature. Furthermore, viral RNA from inactivated PV was shown to be modified, since cDNA yields obtained by RT-PCR amplification were severely reduced and no infectious virus was recovered after RNA transfection into susceptible cells. Importance: This study represents a novel insight into the molecular mechanisms responsible for poliovirus inactivation. We show that inactivation with formaldehyde has an effect on early steps of viral replication as it reduces the ability of PV to bind to hPVR, decreases the sensitivity of PV to convert to 135S particles, and abolishes the infectivity of its viral RNA. These changes are likely responsible for the loss of infectivity shown by PV following inactivation. Techniques used in this study represent new approaches for the characterization of inactivated PV products and could be useful in developing improved methods for the production and quality control testing of inactivated polio vaccines. Measuring the antigenicity, capsid stability, and RNA integrity of inactivated PV samples could help establishing the optimal balance between the loss of infectivity and the preservation of virus antigenicity during inactivation.

Ebolavirus nucleoprotein C-termini potently attract single domain antibodies enabling monoclonal affinity reagent sandwich assay (MARSA) formulation

BACKGROUND

Antigen detection assays can play an important part in environmental surveillance and diagnostics for emerging threats. We are interested in accelerating assay formulation; targeting the agents themselves to bypass requirements for a priori genome information or surrogates. Previously, using in vitro affinity reagent selection on Marburg virus we rapidly established monoclonal affinity reagent sandwich assay (MARSA) where one recombinant antibody clone was both captor and tracer for polyvalent nucleoprotein (NP). Hypothesizing that the closely related Ebolavirus genus may share the same Achilles' heel, we redirected the scheme to see whether similar assays could be delivered and began to explore their mechanism.

METHODS AND FINDINGS

In parallel we selected panels of llama single domain antibodies (sdAb) from a semi-synthetic library against Zaire, Sudan, Ivory Coast, and Reston Ebola viruses. Each could perform as both captor and tracer in the same antigen sandwich capture assay thereby forming MARSAs. All sdAb were specific for NP and those tested required the C-terminal domain for recognition. Several clones were cross-reactive, indicating epitope conservation across the Ebolavirus genus. Analysis of two immune shark sdAb revealed they also targeted the C-terminal domain, and could be similarly employed, yet were less sensitive than a comparable llama sdAb despite stemming from immune selections.

CONCLUSIONS

The C-terminal domain of Ebolavirus NP is a strong attractant for antibodies and enables sensitive sandwich immunoassays to be rapidly generated using a single antibody clone. The polyvalent nature of nucleocapsid borne NP and display of the C-terminal region likely serves as a bountiful affinity sink during selections, and a highly avid target for subsequent immunoassay capture. Combined with the high degree of amino acid conservation through 37 years and across wide geographies, this domain makes an ideal handle for monoclonal affinity reagent driven antigen sandwich assays for the Ebolavirus genus.

Induction of heterosubtypic cross-protection against influenza by a whole inactivated virus vaccine: the role of viral membrane fusion activity

BACKGROUND

The inability of seasonal influenza vaccines to effectively protect against infection with antigenically drifted viruses or newly emerging pandemic viruses underlines the need for development of cross-reactive influenza vaccines that induce immunity against a variety of virus subtypes. Therefore, potential cross-protective vaccines, e.g., whole inactivated virus (WIV) vaccine, that can target conserved internal antigens such as the nucleoprotein (NP) and/or matrix protein (M1) need to be explored.

METHODOLOGY/PRINCIPAL FINDINGS

In the current study we show that a WIV vaccine, through induction of cross-protective cytotoxic T lymphocytes (CTLs), protects mice from heterosubtypic infection. This protection was abrogated after depletion of CD8+ cells in vaccinated mice, indicating that CTLs were the primary mediators of protection. Previously, we have shown that different procedures used for virus inactivation influence optimal activation of CTLs by WIV, most likely by affecting the membrane fusion properties of the virus. Specifically, inactivation with formalin (FA) severely compromises fusion activity of the virus, while inactivation with β-propiolactone (BPL) preserves fusion activity. Here, we demonstrate that vaccination of mice with BPL-inactivated H5N1 WIV vaccine induces solid protection from lethal heterosubtypic H1N1 challenge. By contrast, vaccination with FA-inactivated WIV, while preventing death after lethal challenge, failed to protect against development of disease and severe body weight loss. Vaccination with BPL-inactivated WIV, compared to FA-inactivated WIV, induced higher levels of specific CD8+ T cells in blood, spleen and lungs, and a higher production of granzyme B in the lungs upon H1N1 virus challenge.

CONCLUSION/SIGNIFICANCE

The results underline the potential use of WIV as a cross-protective influenza vaccine candidate. However, careful choice of the virus inactivation procedure is important to retain membrane fusion activity and full immunogenicity of the vaccine.

Development and characterization of monoclonal antibodies against Rift Valley fever virus nucleocapsid protein generated by DNA immunization

This paper describes the generation of monoclonal antibodies directed to immunogenic nucleoprotein N epitopes of Rift Valley fever virus (RVFV), and their application in diagnostics, both for antibody detection in competitive ELISA and for antigen capture in a sandwich ELISA. Monoclonal antibodies (mAbs) were generated after DNA immunization of Balb/c mice and characterized by western blot, ELISA and cell immunostaining assays. At least three different immunorelevant epitopes were defined by mAb competition assays. Interestingly, two of the mAbs generated were able to distinguish between RVFV strains from Egyptian or South African lineages. These monoclonal antibodies constitute useful tools for diagnosis, especially for the detection of serum anti-RVFV antibodies from a broad range of species by means of competitive ELISA.

Display of peptides on the surface of tobacco mosaic virus particles

In this review, we focus on the potential that tobacco mosaic virus (TMV) has as a carrier for immunogenic epitopes, and the factors that must be considered in order to bring products based on this platform to the market. Large Scale Biology Corporation developed facile and scaleable methods for manufacture of candidate peptide display vaccines based on TMV. We describe how rational design of peptide vaccines can improve the manufacturability of particular TMV products. We also discuss downstream processing and purification of the vaccine products, with particular attention to the metrics that a product must attain in order to meet criteria for regulatory approval as injectable biologics.

Immunogenicity of formaldehyde and binary ethylenimine inactivated infectious bursal disease virus in broiler chicks

Infectious bursal disease virus (IBDV) was inactivated by two different chemicals--formaldehyde and binary ethylenimine (BEI). Formaldehyde was used at 0.1% and 0.2%, while BEI was used at concentrations of 0.001 and 0.002 mol/L. These four vaccines were tested for their efficiency in generating humoral immune response in different groups of broiler chicks. Both BEI-inactivated vaccines gave relatively higher antibody titers and were almost twice as efficient as formaldehyde-inactivated ones.

Inactivation of infectious bursal disease virus by binary ethylenimine and formalin

In this experiment conducted to study the inactivation dynamics of infectious bursal disease virus (IBDV) by binary ethylenimine (BEI) in comparison with formalin, IBDV was isolated from the bursa of infected chickens and its confirmation was done by agar gel precipitation test. Viral suspensions were subjected to inactivation with BEI and formalin for pre-set time intervals. BEI was employed at concentrations of 0.001 and 0.002 mol/L while formalin was used at 0.1% and 0.2%. Sampling was done at 6, 12, 24, 36 and 48 h of incubation and samples were tested for their inactivation status in 9-day-old embryonated eggs and 3-week-old broiler chickens. IBDV was completely inactivated by 0.001 and 0.002 mol/L BEI after 36 h of incubation at 37 degrees C, whereas formalin at 0.1% and 0.2% concentrations inactivated IBDV in 24 h.

Production and characterization of monoclonal antibodies against binary ethylenimine inactivated Nipah virus

Nipah virus, a zoonotic paramyxovirus which emerged recently was chemically inactivated using binary ethylenimine (BEI). The inactivated virus was concentrated and purified by sucrose gradient centrifugation. The gradient fractions were examined by electron microscopy and Western immunoblot, and gradient fraction containing mainly Nipah matrix (M) and nucleocapsid (N) proteins was used for immunizing BALB/c mice to generate hybridomas. Screening of the resultant hybridoma clones identified five strongly positive clones producing IgG monoclonal antibodies (mAbs) reactive to the Nipah virus antigen. The protein specificity of these mAbs was determined by Western immunoblot using Nipah virus and recombinant Nipah virus proteins expressed in mammalian cells. Four mAbs reacted with Nipah N protein and one reacted with Nipah M protein. None of the mAbs neutralized Nipah virus infectivity in vitro. However, all mAbs recognized Nipah virus in ELISA and immunofluorescence assay. F45G2 mAb was most suitable for immunohistochemistry on long term formalin-fixed Nipah virus infected swine tissues. Three of the anti-nucleocapsid mAbs (F45G2, F45G3 and F45G6) showed cross-reactivity with closely related Hendra virus N protein in both immunofluorescence and Western Immunoblot assays. Two of the mAbs were specific for the Nipah virus only, F45G4 (anti-N) and F45G5 (anti-M), and could be used in the primary identification of Nipah virus. The use of these immunoreagents to develop new diagnostic assays is discussed.

Relationship between the immune response and protection conferred by new designed inactivated vaccines against ovine enzootic abortion in a mouse model

Chlamydophila abortus is a gram-negative obligate intracellular bacterium and the etiological agent of ovine enzootic abortion (OEA), an economically important disease in many countries. Inactivated vaccines have been reported to induce immunity in ewes and they have been used for many years. However, some outbreaks have been reported in correctly vaccinated flocks, so it is clear that new vaccines are necessary to address adequate protection and to avoid the shedding of the microorganism. This idea lead us to design inactivated vaccines, in a previously established mouse model, evaluating different inactivation procedures and new adjuvants. To assess the protection conferred, the results were analyzed on the basis of clinical signs and the isolation of C. abortus from spleen. These findings were correlated with the immune response induced by the vaccines, as determined by the production of C. abortus-specific IFN-gamma and IL-4 from splenocyte cultures and the detection of IgG isotypes in serum. BEI was found to be the best C. abortus-inactivation procedure. The inactivated vaccines adjuvated with QS-21 (QS) or Montanide 773 (M7) induced the best protection both against homologous and heterologous challenge, with an adequate (Th1-like) immune response. Finally, these selected vaccines were evaluated in a pregnant mouse model, in which they were seen to confer good protection and to avoid the C. abortus persistence in uterus after delivery. With these results, this mouse model could be considered as an adequate tool for selecting and optimizing effective vaccines against OEA.

Effect of gamma-irradiation on serum samples on the diagnostic performance of ELISA methods for the detection of trypanosomal antibodies

The study investigated the effect of gamma-irradiation on bovine serum samples on the ability of enzyme-linked immunosorbent assay (ELISA) methods to detect trypanosomal antibodies. The serum samples were analysed using two standardised indirect ELISA systems. Higher measurement values were observed for most gamma-irradiated antibody positive and negative test samples. Using cut-off points, determined from the analysis of a non-irradiated trypanosomal antibody-negative population, the gamma-irradiated sera data showed that there was an increased risk of misclassifying samples as false positive or cross-reactive due to increased analytical sensitivity and decreased analytical specificity. The intraplate precision and agreement between tested and expected values of measurements were not altered throughout. The impact on the assays' diagnostic performance was estimated by analysing diagnostic sensitivity, diagnostic specificity and related parameters. The data demonstrated that although there was a bias of higher measurement values after gamma-irradiation, this could be compensated after readjustment of the cut-off points to obtain best separation of antibody-positive and -negative samples. Thus, for each assay, no significant difference of the diagnostic proficiency was found before and after gamma-irradiation. The practical implications are discussed of a serum sterilisation procedure using (60)Co gamma-rays for routine sample testing, assay validation and trypanosomosis monitoring and tsetse-fly control and eradication programmes.

Effect of different baculovirus inactivation procedures on the integrity and immunogenicity of porcine parvovirus-like particles

We have demonstrated earlier the usefulness of recombinant porcine parvovirus (PPV) virus-like particles (VLPs) as an efficient recombinant vaccine for PPV. Here, we have demonstrated that preparations of PPV VLPs could be contaminated by recombinant baculoviruses. Since these baculoviruses can be a problem for the registration and safety requirements of the recombinant vaccine, we have tested different baculovirus inactivation strategies, studying simultaneously the integrity and immunogenicity of the VLPs. These methods were pasteurization, treatment with detergents and alkylation with binary ethylenimine (BEI). The structural and functional integrity of the PPV VLPs after the inactivation treatments were analyzed by electron microscopy, hemagglutination, double antibody sandwich (DAS)-ELISA and immunogenicity studies. Binary ethylenimine and Triton X-100 inactivated particles maintained all the original structural and antigenic properties. In addition, PPV VLPs were subjected to size-exclusion chromatography to analyze the presence of VP2 monomers or any other contaminant. The resulting highly purified material was used as the standard of reference to quantify PPV VLPs in order to determine the dose of vaccine by DAS-ELISA. After immunization experiments in guinea pigs, the antibody titers obtained with all the inactivation procedures were very similar. Triton X-100 treatment was selected for further testing in animals because of the speed, simplicity and safety of the overall procedure.

Production of a highly immunogenic subunit ISCOM vaccine against Bovine Viral Diarrhea Virus

Bovine Viral Diarrhea Virus (BVDV) is a major pathogen of cattle in most countries. The main reservoir of virus in herds are BVDV persistently infected animals, which arise as a result of infection of the bovine fetus early in gestation. The spread of virus to the unborn fetus may be prevented by vaccination of the dam. We describe in this report the production and initial testing of an inactivated subunit vaccine against BVDV. The vaccine is based on production of antigen in primary bovine cell cultures, extraction of antigens from infected cells with detergent, chromatographic purification, concentration, and insertion of antigens into immune stimulating complexes (ISCOMs). Vaccines based on two different Danish strains of BVDV were injected into calves and the antisera produced were tested for neutralising activity against a panel of Danish BVDV strains. The two vaccines induced different neutralisation responses, which seem to partly complement each other. The implication of these observations for successful vaccination against BVDV is discussed.

Comparison of two different methods for inactivation of viruses in serum

In order to compare protocols for inactivation of viruses potentially present in biological specimens, three different model viruses were treated in bovine serum by two different inactivation methods: samples were subjected either to chemical inactivation with ethylenimine (El) at concentrations of 5 and 10 mM at 37 degrees C for periods up to 72 h or to electron-beam irradiation in frozen and liquid form with doses varying between 11 and 46 kGy. The chemical inactivation resulted in nonlinear tailing curves in a semilogarithmic plot of virus titer versus inactivation time showing non-first-order kinetics with respect to virus titer. The time for inactivation of 7 log10 units of porcine parvovirus (PPV) was about 24 h for both El concentrations, whereas 5 log10 units of bovine viral diarrhea virus (BVDV) was inactivated in 2 h for both El concentrations and 6 log10 units of porcine enterovirus (PEV) was inactivated within 3 h. The inactivation with electron-beam irradiation resulted in almost linear curves in a semilogarithmic plot of virus titer versus irradiation dose, reflecting a first-order inactivation. The rate of inactivation was almost twice as fast in the liquid samples compared to the rate in frozen ones, giving values of the doses needed to reduce virus infectivity 1 log10 unit for inactivation of PPV of 11.8 and 7.7 kGy for frozen and liquid samples, respectively, whereas the corresponding values for BVDV were 4.9 and 2.5 kGy, respectively, and those for PEV were 6.4 and 4.4 kGy, respectively. The nonlinear inactivation with El makes it impossible to extrapolate the curves beyond the virus detection limit and thereby predict the necessary time for complete inactivation, i.e., to a level beyond the detection limit, of virus in a given sample. The first-order inactivation obtained with electron-beam irradiation makes such a prediction possible and justifiable. The two methods are discussed with respect to their different kinetics and applicability under different circumstances and criteria for inactivation, and considerations for choice of method are discussed.

Activity of antibodies against Salmonella dublin, Toxoplasma gondii, or Actinobacillus pleuropneumoniae in sera after treatment with electron beam irradiation or binary ethylenimine

Viral contamination of biological material may constitute a risk when samples are exchanged between countries, and it may be necessary to subject the material to an inactivation treatment. The present study investigated possible adverse effects on antibody activity subsequent to either electron beam irradiation or binary ethylenimine (BEI) treatment. The treatments were performed with sera obtained from pigs or cattle. For each treatment level, the posttreatment activity was plotted against the pretreatment activity, and regression analyses were carried out. The slope of the regression line was used as an estimate for the relative posttreatment activity. For a Toxoplasma gondii indirect enzyme-linked immunosorbent assay (ELISA) and agglutination assay as well as for a Salmonella dublin indirect ELISA, the posttreatment activity was more than 89% of the pretreatment activity when the samples were irradiated in the frozen state (on dry ice) with up to 46. kGy or when they were treated with 5 or 10 mM BEI for up to 48 h. The samples were more sensitive to irradiation in the liquid state. Thus, samples irradiated with 22.6 kGy retained 98% of their activity in the indirect ELISA when they were irradiated in the frozen state on dry ice but only 35% of their activity when they were irradiated in the liquid state at 0 degrees C. The patterns seen in an S. dublin blocking ELISA and an Actinobacillus pleuropneumoniae complement fixation assay differed in that samples with a low level of pretreatment activity were subject to a relatively greater decrease in activity than samples with a high level of pretreatment activity. The complement fixation assay was particularly sensitive to irradiation of serum. It is concluded that serum samples retain sufficient activity by both methods of virus inactivation, especially when used in indirect ELISA or in the T. gondii agglutination assay.