Standardization of a neutralizing anti-vaccinia antibodies titration method: an essential step for titration of vaccinia immunoglobulins and smallpox vaccines evaluation

Characterizing Aptamer Interaction with the Oncolytic Virus VV-GMCSF-Lact

Aptamers are currently being investigated for their potential to improve virotherapy. They offer several advantages, including the ability to prevent the aggregation of viral particles, enhance target specificity, and protect against the neutralizing effects of antibodies. The purpose of this study was to comprehensively investigate an aptamer capable of enhancing virotherapy. This involved characterizing the previously selected aptamer for vaccinia virus (VACV), evaluating the aggregation and molecular interaction of the optimized aptamers with the recombinant oncolytic virus VV-GMCSF-Lact, and estimating their immunoshielding properties in the presence of human blood serum. We chose one optimized aptamer, NV14t_56, with the highest affinity to the virus from the pool of several truncated aptamers and built its 3D model. The NV14t_56 remained stable in human blood serum for 1 h and bound to VV-GMCSF-Lact in the micromolar range (Kd ≈ 0.35 μM). Based on dynamic light scattering data, it has been demonstrated that aptamers surround viral particles and inhibit aggregate formation. In the presence of serum, the hydrodynamic diameter (by intensity) of the aptamer-virus complex did not change. Microscale thermophoresis (MST) experiments showed that NV14t_56 binds with virus (EC50 = 1.487 × 109 PFU/mL). The analysis of the amplitudes of MST curves reveals that the components of the serum bind to the aptamer-virus complex without disrupting it. In vitro experiments demonstrated the efficacy of VV-GMCSF-Lact in conjunction with the aptamer when exposed to human blood serum in the absence of neutralizing antibodies (Nabs). Thus, NV14t_56 has the ability to inhibit virus aggregation, allowing VV-GMCSF-Lact to maintain its effectiveness throughout the storage period and subsequent use. When employing aptamers as protective agents for oncolytic viruses, the presence of neutralizing antibodies should be taken into account.

Orthopoxvirus Seroprevalence and Infection Susceptibility in France, Bolivia, Laos, and Mali

To determine a demographic overview of orthopoxvirus seroprevalence, we tested blood samples collected during 2003-2019 from France (n = 4,876), Bolivia (n = 601), Laos (n = 657), and Mali (n = 255) for neutralizing antibodies against vaccinia virus. In addition, we tested 4,448 of the 4,876 samples from France for neutralizing antibodies against cowpox virus. We confirmed extensive cross-immunity between the 2 viruses. Seroprevalence of antibodies was <1% in Bolivia, <5% in Laos, and 17.25% in Mali. In France, we found low prevalence of neutralizing antibodies in persons who were unvaccinated and vaccinated for smallpox, suggesting immunosenescence occurred in vaccinated persons, and smallpox vaccination compliance declined before the end of compulsory vaccination. Our results suggest that populations in Europe, Africa, Asia, and South America are susceptible to orthopoxvirus infections, which might have precipitated the emergence of orthopoxvirus infections such as the 2022 spread of monkeypox in Europe.

The Influence of an Elevated Production of Extracellular Enveloped Virions of the Vaccinia Virus on Its Properties in Infected Mice

The modern approach to developing attenuated smallpox vaccines usually consists in targeted inactivation of vaccinia virus (VACV) virulence genes. In this work, we studied how an elevated production of extracellular enveloped virions (EEVs) and the route of mouse infection can influence the virulence and immunogenicity of VACV. The research subject was the LIVP strain, which is used in Russia for smallpox vaccination. Two point mutations causing an elevated production of EEVs compared with the parental LIVP strain were inserted into the sequence of the VACV A34R gene. The created mutant LIVP-A34R strain showed lower neurovirulence in an intracerebral injection test and elevated antibody production in the intradermal injection method. This VACV variant can be a promising platform for developing an attenuated, highly immunogenic vaccine against smallpox and other orthopoxvirus infections. It can also be used as a vector for designing live-attenuated recombinant polyvalent vaccines against various infectious diseases.

Effect of the Route of Administration of the Vaccinia Virus Strain LIVP to Mice on Its Virulence and Immunogenicity

The mass smallpox vaccination campaign has played a crucial role in smallpox eradication. Various strains of the vaccinia virus (VACV) were used as a live smallpox vaccine in different countries, their origin being unknown in most cases. The VACV strains differ in terms of pathogenicity exhibited upon inoculation of laboratory animals and reactogenicity exhibited upon vaccination of humans. Therefore, each generated strain or clonal variant of VACV needs to be thoroughly studied in in vivo systems. The clonal variant 14 of LIVP strain (LIVP-14) was the study object in this work. A comparative analysis of the virulence and immunogenicity of LIVP-14 inoculated intranasally (i.n.), intradermally (i.d.), or subcutaneously (s.c.) to BALB/c mice at doses of 108, 107, and 106 pfu was carried out. Adult mice exhibited the highest sensitivity to the i.n. administered LIVP-14 strain, although the infection was not lethal. The i.n. inoculated LIVP-14 replicated efficiently in the lungs. Furthermore, this virus was accumulated in the brain at relatively high concentrations. Significantly lower levels of LIVP-14 were detected in the liver, kidneys, and spleen of experimental animals. No clinical manifestations of the disease were observed after i.d. or s.c. injection of LIVP-14 to mice. After s.c. inoculation, the virus was detected only at the injection site, while it could disseminate to the liver and lungs when delivered via i.d. administration. A comparative analysis of the production of virus-specific antibodies by ELISA and PRNT revealed that the highest level of antibodies was induced in i.n. inoculated mice; a lower level of antibodies was observed after i.d. administration of the virus and the lowest level after s.c. injection. Even at the lowest studied dose (106 pfu), i.n. or i.d. administered LIVP-14 completely protected mice against infection with the cowpox virus at the lethal dose. Our findings imply that, according to the ratio between such characteristics as pathogenicity/immunogenicity/protectivity, i.d. injection is the optimal method of inoculation with the VACV LIVP-14 strain to ensure the safe formation of immune defense after vaccination against orthopoxviral infections.

Using the Ground Squirrel (Marmota bobak) as an Animal Model to Assess Monkeypox Drug Efficacy

In experiments to study the sensitivity of ground squirrels (Marmota bobak) to monkeypox virus (MPXV) at intranasal challenge, expressed pox-like clinical symptoms (hyperthermia, lymphadenitis, skin rash all over the body and mucous membranes and others) were observed 7-9 days post-infection. The 50% infective dose (ID50 ) of MPXV for these marmots determined by the presence of clinical signs of the disease was 2.2 log10 PFU. Some diseased marmots (about 40%) died 13-22 days post-infection, and the mortality rate was weakly dependent on MPXV infective dose. Lungs with trachea were primary target organs of marmots challenged intranasally (with ~30 ID50 ). The pathogen got to secondary target organs of the animals mainly via the lymphatic way (with replication in bifurcation lymph nodes). Lungs with trachea, nasal mucosa and skin were the organs where the maximum MPXV amounts accumulated in these animals. Evidences of the pathogen presence and replication were revealed in these and subcutaneously infected marmots in the traditional primary target cells for MPXV (macrophages and respiratory tract epitheliocytes), as well as in some other cells (endotheliocytes, plasmocytes, fibroblasts, reticular and smooth muscle cells). Our use of this animal species to assess the antiviral efficacy of some drugs demonstrated the agreement of the obtained results with those described in scientific literature, which opens up the prospects of using marmots as animal models for monkeypox to develop therapeutic and preventive anti-smallpox drugs.

The Possibility of Using the ICR Mouse as an Animal Model to Assess Antimonkeypox Drug Efficacy

As a result of the conducted experimental studies on intranasal challenge of ICR mice, rabbits and miniature pigs (even in the maximum variant) with the doses of 4.0-5.5 lg PFU of monkeypox virus (MPXV), some clinical signs such as purulent conjunctivitis, blepharitis and ruffled fur were found only in mice. The 50% infective dose (C ID50 ) of MPXV for these animals estimated by the presence of external clinical signs was 4.8 lg PFU, and L ID50 estimated by the virus presence in the lungs of mice 7 days post-infection taking into account its 10% application in the animal respiratory tract was 1.4 lg PFU. When studying the dynamics of MPXV propagation in mice challenged intranasally with 25 L ID50 of MPXV, the maximum pathogen accumulation was revealed in nasal cavity, lungs and brain: 5.7 ± 0.1, 5.5 ± 0.1 and 5.3 ± 0.3 lg PFU/ml, respectively. The pathomorphological examination of these animals revealed the presence and replication of the pathogen in the traditional primary target cells for MPXV (mononuclear phagocyte system cells and respiratory tract epitheliocytes) as well as in some other types of cells (endothelial cells, reticular cells, connective tissue cells). Our use of these animals to assess the antiviral efficacy of some drugs demonstrated the agreement of the results (a significant positive effect of NIOCH-14 and ST-246) with those described in scientific literature, which opens up the prospects of using ICR mice as animal models for monkeypox to develop preventive antismallpox drugs.

New effective chemically synthesized anti-smallpox compound NIOCH-14

Antiviral activity of the new chemically synthesized compound NIOCH-14 (a derivative of tricyclodicarboxylic acid) in comparison with ST-246 (the condensed derivative of pyrroledione) was observed in experiments in vitro and in vivo using orthopoxviruses including highly pathogenic ones. After oral administration of NIOCH-14 to outbred ICR mice infected intranasally with 100 % lethal dose of ectromelia virus, it was shown that 50 % effective doses of NIOCH-14 and ST-246 did not significantly differ. The 'therapeutic window' varied from 1 day before infection to 6 days post-infection (p.i.) to achieve 100-60 % survival rate. The administration of NIOCH-14 and ST-246 to mice resulted in a significant reduction of ectromelia virus titres in organs examined as compared with the control and also reduced pathological changes in the lungs 6 days p.i. Oral administration of NIOCH-14 and ST-246 to ICR mice and marmots challenged with monkeypox virus as compared with the control resulted in a significant reduction of virus production in the lungs and the proportion of infected mice 7 days p.i. as well as the absence of disease in marmots. Significantly lower proportions of infected mice and virus production levels in the lungs as compared with the control were demonstrated in experiments after oral administration of NIOCH-14 and ST-246 to ICR mice and immunodeficient SCID mice challenged with variola virus 3 and 4 days p.i., respectively. The results obtained suggest good prospects for further study of the chemical compound NIOCH-14 to create a new smallpox drug on its basis.

Highly immunogenic variant of attenuated vaccinia virus

The LIVPΔ6 strain of vaccinia virus (VACV) was created by genetic engineering on the basis of previously obtained attenuated 1421ABJCN strain by target deletion of the A35R gene encoding an inhibitor of antigen presentation by the major histocompatibility complex class II. 1421ABJCN is the LIVP strain of VACV with five inactivated virulence genes encoding hemagglutinin (A56R), γ-interferon-binding protein (B8R), thymidine kinase (J2R), complement-binding protein (C3L), and Bcl2-like inhibitor of apoptosis (N1L). The highly immunogenic LIVPΔ6 strain could be an efficient fourth-generation attenuated vaccine against smallpox and other orthopoxvirus infections.

Using ICR and SCID mice as animal models for smallpox to assess antiviral drug efficacy

The possibility of using immunocompetent ICR mice and immunodeficient SCID mice as model animals for smallpox to assess antiviral drug efficacy was investigated. Clinical signs of the disease did not appear following intranasal (i.n.) challenge of mice with strain Ind-3a of variola virus (VARV), even when using the highest possible dose of the virus (5.2 log10 p.f.u.). The 50 % infective doses (ID50) of VARV, estimated by the virus presence or absence in the lungs 3 and 4 days post-infection, were 2.7 ± 0.4 log10 p.f.u. for ICR mice and 3.5 ± 0.7 log10 p.f.u. for SCID mice. After i.n. challenge of ICR and SCID mice with VARV 30 and 50 ID50, respectively, steady reproduction of the virus occurred only in the respiratory tract (lungs and nose). Pathological inflammatory destructive changes were revealed in the respiratory tract and the primary target cells for VARV (macrophages and epithelial cells) in mice, similar to those in humans and cynomolgus macaques. The use of mice to assess antiviral efficacies of NIOCH-14 and ST-246 demonstrated the compliance of results with those described in scientific literature, which opens up the prospect of their use as an animal model for smallpox to develop anti-smallpox drugs intended for humans.

Development of human monoclonal antibodies against diseases caused by emerging and biodefense-related viruses

Polyclonal antibodies have a century-old history of being effective against some viruses; recently, monoclonal antibodies (mAbs) have also shown success. The humanized mAb Synagis (palivizumab), which is still the only mAb against a viral disease approved by the US FDA, has been widely used as a prophylactic measure against respiratory syncytial virus infections in neonates and immunocompromised individuals. The first fully human mAbs against two other paramyxoviruses, Hendra and Nipah virus, which can cause high (up to 75%) mortality, were recently developed; one of them, m101, showed exceptional potency against infectious virus. In an amazing pace of research, several potent human mAbs targeting the severe acute respiratory syndrome coronavirus S glycoprotein that can affect infections in animal models have been developed months after the virus was identified in 2003. A potent humanized mAb with therapeutic potential was recently developed against the West Nile virus. The progress in developing neutralizing human mAbs against Ebola, Crimean-Congo hemorrhagic fever, vaccinia and other emerging and biodefense-related viruses is slow. A major problem in the development of effective therapeutic agents against viruses, including therapeutic antibodies, is the viruses' heterogeneity and mutability. A related problem is the low binding affinity of crossreactive antibodies able to neutralize a variety of primary isolates. Combinations of mAbs or mAbs with other drugs, and/or the identification of potent new mAbs and their derivatives that target highly conserved viral structures, which are critical for virus entry into cells, are some of the possible solutions to these problems, and will continue to be a major focus of antiviral research.

Validation of an immunoperoxidase monolayer assay for total anti–Vaccinia virus antibody titration

Vaccinia virus (VACV) has been associated with zoonotic exanthemic outbreaks affecting bovids and human beings, with significant public health and economic impacts. Rapid and reliable diagnostic methods are needed to detect and epidemiologically monitor antibodies to VACV. The current study describes the development of an immunoperoxidase monolayer assay (IPMA) for detection of total VACV antibodies in bovine serum. The assay was validated by comparison with a plaque reduction neutralization test (PRNT). Kappa index of agreement, diagnostic sensitivity, specificity, and accuracy of the IPMA were −1.008, 100%, 96%, and 98%, respectively, when compared with PRNT on 148 field bovine sera. Repeatability tests on 32 field-positive serum samples revealed that intraclass coefficient correlation was 0.86. In experimentally infected cattle, VACV antibodies were detectable by IPMA 4 days postinfection, which was more than 2 weeks earlier than with the PRNT, indicating that IPMA could be a more sensitive test than the latter. In 4 naturally VACV-diseased cows monitored for 13 months, IPMA could detect VACV antibodies up to 13 months, a longer time than PRNT. The IPMA is simpler to produce and perform when compared with PRNT and is time saving and suitable for large-scale surveys of VACV infection in bovine.

Deletion of major nonessential genomic regions in the vaccinia virus Lister strain enhances attenuation without altering vaccine efficacy in mice

The vaccinia virus (VACV) Lister strain was one of the vaccine strains that enabled smallpox eradication. Although the strain is most often harmless, there have been numerous incidents of mild to life-threatening accidents with this strain and others. In an attempt to further attenuate the Lister strain, we investigated the role of 5 genomic regions known to be deleted in the modified VACV Ankara (MVA) genome in virulence in immunodeficient mice, immunogenicity in immunocompetent mice, and vaccine efficacy in a cowpox virus challenge model. Lister mutants were constructed so as to delete each of the 5 regions or various combinations of these regions. All of the mutants replicated efficiently in tissue culture except region I mutants, which multiplied more poorly in human cells than the parental strain. Mutants with single deletions were not attenuated or only moderately so in athymic nude mice. Mutants with multiple deletions were more highly attenuated than those with single deletions. Deleting regions II, III, and V together resulted in total attenuation for nude mice and partial attenuation for SCID mice. In immunocompetent mice, the Lister deletion mutants induced VACV specific humoral responses equivalent to those of the parental strain but in some cases lower cell-mediated immune responses. All of the highly attenuated mutants protected mice from a severe cowpox virus challenge at low vaccine doses. The data suggest that several of the Lister mutants combining multiple deletions could be used in smallpox vaccination or as live virus vectors at doses equivalent to those used for the traditional vaccine while displaying increased safety.

Poxvirus infection in a cat with presumptive human transmission

The present report describes a case of generalized cowpox virus infection with necrotizing facial dermatitis in a cat and a likely transmission to an animal keeper. The viral aetiology was confirmed by histopathology, immunohistochemistry, PCR, virus isolation, DNA sequencing and electron microscopy. Histopathological examination of the cat's skin revealed a severe, necrotizing dermatitis with ballooning degeneration and hyperplasia of epithelial cells with pathognomonic cytoplasmic eosinophilic inclusion bodies. Additionally, at post-mortem examination, a systemic poxvirus infection was detected affecting pancreas, thymus, lymph node, liver and lung. The human patient's skin biopsy revealed an ulcerative dermatitis with epidermal hyperplasia and ballooning degeneration. Serological investigation displayed a high orthopoxvirus-specific antibody titre in the human patient. Environmental factors increase the natural reservoir host population for cowpox viruses, such as voles, which results in a higher risk of infection for cats and subsequently for humans. Due to this zoonotic potential, a cowpox virus infection must be considered as an aetiological differential in cases of necrotizing dermatitis in cats.

Control of vaccinia virus skin lesions by long-term-maintained IFN-gamma+TNF-alpha+ effector/memory CD4+ lymphocytes in humans

Vaccinia virus (VV) vaccination is used to immunize against smallpox and historically was considered to have been successful if a skin lesion formed at the vaccination site. While antibody responses have been widely proposed as a correlate of efficacy and protection in humans, the role of cellular and humoral immunity in VV-associated skin lesion formation was unknown. We therefore investigated whether long-term residual humoral and cellular immune memory to VV, persisting 30 years after vaccination, could control VV-induced skin lesion in revaccinated individuals. Here, we have shown that residual VV-specific IFN-gamma+TNF-alpha+ or IFN-gamma+IL-2+ CD4+ lymphocytes but not CD8+ effector/memory lymphocytes expressing a skin-homing marker are inversely associated with the size of the skin lesion formed in response to revaccination. Indeed, high numbers of residual effector T cells were associated with lower VV skin lesion size after revaccination. In contrast, long-term residual VV-specific neutralizing antibody (NAbs) titers did not affect skin lesion formation. However, the size of the skin lesion strongly correlated with high levels of NAbs boosted after revaccination. These findings demonstrate a potential role for VV-specific CD4+ responses at the site of VV-associated skin lesion, thereby providing new insight into immune responses at these sites and potentially contributing to the development of new approaches to measure the efficacy of VV vaccination.

Natural human infections with Vaccinia virus during bovine vaccinia outbreaks

BACKGROUND

Bovine vaccinia is an exanthematic disease caused by Vaccinia virus (VACV). This zoonosis has been associated with several cases of bovine infection, particularly in milk herds. Farmers, milkers and their close contacts developed lesions on the hands, forearms, legs and face accompanied by fever, headache, malaise, myalgia and axillary, inguinal and cervical lymphadenopathy. VACV infections have a significant public health impact due to their occupational character, high frequency of transmission and the improper medical treatment often applied.

OBJECTIVES

To study natural human infection by VACV and to analyze clinical and epidemiological aspects, emphasizing the patients' immunological status.

STUDY DESIGN

Ninety-eight individuals from rural properties with bovine vaccinia (BV) outbreaks who were at risk due to contact were submitted to epidemiological and clinical studies. From these individuals, 54 sera were analyzed by serological and molecular procedures. This study was conducted in Rio de Janeiro State from September 2002 to October 2006.

RESULTS

The clinical frequency of infection was 52.0%, with 57.4% ELISA and 43.0% PRNT-positive reactions. DNAemia was detected in 18.5% of the analyzed sera, and 50% of smallpox-vaccinated individuals developed symptoms.

CONCLUSIONS

This study confirms the high clinical frequency of human VACV infection, even among vaccinated individuals. The infection was related to detection of IgG- or IgM-specific antibodies that correlates in most of the cases with positive PRNT. The DNAemia suggests viremia during VACV natural infections. Our data indicate that patients vaccinated against smallpox may no longer be protected.

Phenotypic and genetic diversity of the traditional Lister smallpox vaccine

As an initial step in the development of a second-generation smallpox vaccine derived from the Lister strain, to be prepared for a variola virus threat, diversity of the traditional vaccine was examined by characterizing a series of ten viral clones. In vitro and in vivo phenotypic studies showed that the biological behavior of the clones diverged from each other and in most cases diverged from the vaccinia virus (VACV) Lister parental population. Taken together, these results demonstrate the heterogeneity of the viral population within the smallpox vaccine and highlight the difficulty in choosing one clone which would meet the current requirements for a safe and effective vaccine candidate.

Short- and long-term immunogenicity and protection induced by non-replicating smallpox vaccine candidates in mice and comparison with the traditional 1st generation vaccine

This study assessed three non-replicating smallpox vaccine candidates (modified vaccinia Ankara (MVA), NYVAC and HR) for their immunogenicity and ability to protect mice against an intranasal cowpox virus challenge and compared them with the traditional replicating vaccine. A single immunisation with the non-replicating vaccines induced a complete protection from death at short-term, but was not fully protective when mice were challenged 150 days post-vaccination with protection correlated with the specific neutralizing antibodies and CD4(+) T-cells responses. Prime-boost vaccination enabled effective long-term protection from death for mice vaccinated with MVA, but protection from disease and CD4(+) T-cell level were lower than the ones induced by the traditional vaccine over the long-term period. Further investigations are necessary with MVA to determine the optimal conditions of immunisation to induce at long-term immunogenicity and protection observed with the 1st generation smallpox vaccine.

Accuracy and repeatability of a micro plaque reduction neutralization test for vaccinia antibodies

The detection of neutralizing antibodies against vaccinia virus is a valuable tool for the investigation of previous smallpox vaccination. Compulsory smallpox vaccination ended in Brazil during the early 1970s, although the vaccine was available until the late 1970s. The threat of smallpox as a biological weapon has called the attention of public health authorities to the need for an evaluation of the immune status of the population. Based on our previous experience with a micro plaque reduction neutralization test (PRNT) for the evaluation of yellow fever immunity, a similar test was developed for the detection and quantification of vaccinia neutralizing antibodies. A cross-sectional study to test the repeatability and validity of plaque reduction neutralization test (PRNT) for vaccinia antibodies was performed in 182 subjects divided into two categories: subjects above 31 years old and the other > or = 35 years old. Cases were subjects considered to have been vaccinated with vaccinia virus if they declared vaccination history or evidenced vaccination marks. The assay is carried out in 96-well plates, provides results within 30 h, is easily performed, has good sensitivity (92.7%) and specificity (90.8), excellent repeatability (ICC 0.89 (0.88; 0.92)) and is thus suitable for use in mass screening of a population's antibody levels.

Intranasal cowpox virus infection of the mouse as a model for preclinical evaluation of smallpox vaccines

The intranasal infection of mice with cowpox virus (CPXV) has been evaluated as a model for smallpox infection in man. Administration of a lethal dose of CPXV allowed time for development of T-cell responses but antibodies could not be detected before death occurred. In contrast, infection with a sublethal dose was associated with an early T-cell response followed by neutralising antibodies which correlated with virus clearance. Comparison of two first generation smallpox vaccines revealed no significant differences in terms of immunogenicity, protection and post-challenge virus clearance. These studies show that the CPXV/mouse model is valuable for the initial assessment of smallpox vaccines.

Establishment of a national network of validated and qualified laboratories for neutralizing anti-vaccinia antibodies titration

A Proficiency Testing Study (PTS) was organized in France by the French Health Products Safety Agency (Afssaps) aiming at assessing the performance of laboratories in performing a neutralizing anti-vaccinia antibodies titration method by plaque reduction neutralization test (PRNT). The ultimate goal was to establish a national network of qualified and validated laboratories. Five laboratories were included in the PTS and four submitted their data. Three samples of human sera containing various immunoglobulin concentrations (a "high" serum: s-576, a "medium" serum: Ref-19584 and a "low" serum: s-483) were tested by PRNT as described in a procedure supplied by Afssaps and developed in each laboratory during preliminary assays. Data were sent to Afssaps which performed the statistical analysis. The overall performance of the four participating laboratories was satisfactory. This allowed the four participating laboratories to be validated and then to be qualified by the Ministry of Health. Finally a national network for anti-vaccinia immunoglobulins titration was established.