Side-by-side comparison of gene-based smallpox vaccine with MVA in nonhuman primates

The Re-Emergence of Mpox: Old Illness, Modern Challenges

The Mpox virus (MPXV) is known to cause zoonotic disease in humans. The virus belongs to the genus Orthopoxvirus, of the family Poxviridae, and was first reported in monkeys in 1959 in Denmark and in humans in 1970 in the Congo. MPXV first appeared in the U.S. in 2003, re-emerged in 2017, and spread globally within a few years. Wild African rodents are thought to be the reservoir of MPXV. The exotic trade of animals and international travel can contribute to the spread of the Mpox virus. A phylogenetic analysis of MPXV revealed two distinct clades (Central African clade and West African clade). The smallpox vaccine shows cross-protection against MPXV infections in humans. Those who have not previously been exposed to Orthopoxvirus infections are more vulnerable to MPXV infections. Clinical manifestations in humans include fever, muscle pain, headache, and vesicle formation on the skin of infected individuals. Pathognomonic lesions include ballooning degenerations with Guarnieri-like inclusions in vesicular epithelial cells. Alterations in viral genome through genetic mutations might favor the re-emergence of a version of MPXV with enhanced virulence. As of November 2023, 92,783 cases and 171 deaths have been reported in 116 countries, representing a global public health concern. Here, we provide insights on the re-emergence of MPXV in humans. This review covers the origin, emergence, re-emergence, transmission, pathology, diagnosis, control measures, and immunomodulation of the virus, as well as clinical manifestations. Concerted efforts of health professionals and scientists are needed to prevent the disease and stop its transmission in vulnerable populations.

Mpox vaccination and treatment: a systematic review

The Human monkeypox virus (mpox) belongs to the Poxviridae family, characterized by double-stranded DNA. A 2022 outbreak, notably prevalent among men who have sex with men, was confirmed by the World Health Organization. To understand shifting prevalence patterns and clinical manifestations, we conducted a systematic review of recent animal and human studies. We comprehensively searched PubMed, Scopus, Web of Science, Cochrane Library, and Clinicaltrials.gov, reviewing 69 relevant articles from 4,342 screened records. Our analysis highlights Modified Vaccinia Ankara - Bavarian Nordic (MVA-BN)'s potential, though efficacy concerns exist. Tecovirimat emerged as a prominent antiviral in the recent outbreak. However, limited evidence underscores the imperative for further clinical trials in understanding and managing monkeypox.

A multivalent mRNA monkeypox virus vaccine (BNT166) protects mice and macaques from orthopoxvirus disease

In response to the 2022 outbreak of mpox driven by unprecedented human-to-human monkeypox virus (MPXV) transmission, we designed BNT166, aiming to create a highly immunogenic, safe, accessible, and scalable next-generation vaccine against MPXV and related orthopoxviruses. To address the multiple viral forms and increase the breadth of immune response, two candidate multivalent mRNA vaccines were evaluated pre-clinically: a quadrivalent vaccine (BNT166a; encoding the MPXV antigens A35, B6, M1, H3) and a trivalent vaccine (BNT166c; without H3). Both candidates induced robust T cell responses and IgG antibodies in mice, including neutralizing antibodies to both MPXV and vaccinia virus. In challenge studies, BNT166a and BNT166c provided complete protection from vaccinia, clade I, and clade IIb MPXV. Furthermore, immunization with BNT166a was 100% effective at preventing death and at suppressing lesions in a lethal clade I MPXV challenge in cynomolgus macaques. These findings support the clinical evaluation of BNT166, now underway (NCT05988203).

Biology of Variola Virus

Variola virus is an anthroponotic agent that belongs to the orthopoxvirus family. It is an etiological agent of smallpox, an ancient disease that caused massive mortality of human populations. Twentieth century has witnessed the death of about 300 million people due to the unavailability of an effective vaccine. Early detection is the primary strategy to prevent an outbreak of smallpox. Variola virus forms the characteristic pus-filled pustules and centrifugal rash distribution in the infected patients while transmission occurs mainly through respiratory droplets during the early stage of infection. No antiviral drugs are approved for variola virus till date. Generation of first-generation vaccines helped in the eradication of smallpox which was declared by the World Health Organization.

Neutralization Determinants on Poxviruses

Smallpox was a highly contagious disease caused by the variola virus. The disease affected millions of people over thousands of years and variola virus ranked as one of the deadliest viruses in human history. The complete eradication of smallpox in 1980, a major triumph in medicine, was achieved through a global vaccination campaign using a less virulent poxvirus, vaccinia virus. Despite this success, the herd immunity established by this campaign has significantly waned, and concerns are rising about the potential reintroduction of variola virus as a biological weapon or the emergence of zoonotic poxviruses. These fears were further fueled in 2022 by a global outbreak of monkeypox virus (mpox), which spread to over 100 countries, thereby boosting interest in developing new vaccines using molecular approaches. However, poxviruses are complex and creating modern vaccines against them is challenging. This review focuses on the structural biology of the six major neutralization determinants on poxviruses (D8, H3, A27, L1, B5, and A33), the localization of epitopes targeted by neutralizing antibodies, and their application in the development of subunit vaccines.

An mpox virus mRNA-lipid nanoparticle vaccine confers protection against lethal orthopoxviral challenge

Mpox virus (MPXV) caused a global outbreak in 2022. Although smallpox vaccines were rapidly deployed to curb spread and disease among those at highest risk, breakthrough disease was noted after complete immunization. Given the threat of additional zoonotic events and the virus's evolving ability to drive human-to-human transmission, there is an urgent need for an MPXV-specific vaccine that confers protection against evolving MPXV strains and related orthopoxviruses. Here, we demonstrate that an mRNA-lipid nanoparticle vaccine encoding a set of four highly conserved MPXV surface proteins involved in virus attachment, entry, and transmission can induce MPXV-specific immunity and heterologous protection against a lethal vaccinia virus (VACV) challenge. Compared with modified vaccinia virus Ankara (MVA), which forms the basis for the current MPXV vaccine, immunization with an mRNA-based MPXV vaccine generated superior neutralizing activity against MPXV and VACV and more efficiently inhibited spread between cells. We also observed greater Fc effector TH1-biased humoral immunity to the four MPXV antigens encoded by the vaccine, as well as to the four VACV homologs. Single MPXV antigen-encoding mRNA vaccines provided partial protection against VACV challenge, whereas multivalent vaccines combining mRNAs encoding two, three, or four MPXV antigens protected against disease-related weight loss and death equal or superior to MVA vaccination. These data demonstrate that an mRNA-based MPXV vaccine confers robust protection against VACV.

Development of a specific MPXV antigen detection immunodiagnostic assay

Human monkeypox (mpox) has recently become a global public health emergency; however, assays that detect mpox infection are not widely available, largely due to cross-reactivity within the Orthopoxvirus genus. Immunoassay development was largely confined to researchers who focus on biothreats and endemic areas (Central and West Africa) until the 2022 outbreak. As was noted in the COVID-19 pandemic, antigen detection assays, integrated with molecular assays, are necessary to help curb the spread of disease. Antigen-detecting immunoassays offer the advantage of providing results ranging from within min to h and in lateral flow formats; they can be deployed for point-of-care, home, or field use. This study reports the development of an mpox-specific antigen detection immunoassay developed on a multiplexed, magnetic-bead-based platform utilizing reagents from all research sectors (commercial, academic, and governmental). Two semi-quantitative assays were developed in parallel and standardized with infectious mpox virus (MPXV) cell culture fluid and MPXV-positive non-human primate (NHP) sera samples. These assays could detect viral antigens in serum, were highly specific toward MPXV as compared to other infectious orthopoxviruses (vaccinia virus, cowpox virus, and camelpox virus), and exhibited a correlation with quantitative PCR results from an NHP study. Access to a toolbox of assays for mpox detection will be key for identifying cases and ensuring proper treatment, as MPXV is currently a global traveler.

Immunogenic proteins and potential delivery platforms for mpox virus vaccine development: A rapid review

Since May 2022, the mpox virus (MPXV) has spread worldwide and become a potential threat to global public health. Vaccines are important tools for preventing MPXV transmission and infection in the population. However, there are still no available potent and applicable vaccines specifically for MPXV. Herein, we highlight several potential vaccine targets for MPVX and emphasize potent immunogens, such as M1R, E8L, H3L, A29L, A35R, and B6R proteins. These proteins can be integrated into diverse vaccine platforms to elicit powerful B-cell and T-cell responses, thereby providing protective immunity against MPXV infection. Overall, research on the MPXV vaccine targets would provide valuable information for developing timely effective MPXV-specific vaccines.

Cross-reactive immune responses to monkeypox virus induced by MVA vaccination in mice

Mpox (monkeypox) infection cases increased recently in non-Mpox outbreak areas, potentially causing an international threat. The desire to defend against a potential outbreak has led to renewed efforts to develop Mpox vaccines. In this report, mice were immunized with various doses of modified vaccinia virus Ankara (MVA) to evaluate the cross-reactive immune response of MVA immunization against protective antigens of the current monkeypox virus. We demonstrated that MVA induced specific antibodies against protective antigens (A29, A35, B6, M1, H3, and I1), mediating the neutralization abilities against the MVA and the monkeypox virus (MPXV). Moreover, recombinant protective antigens of the MPXV elicited cross-binding and cross-neutralizing activities for MVA. Hence, the MVA induced cross-reactive immune responses, which may guide future efforts to develop vaccines against the recent MPXV. Notably, compared to the other protective antigens, the predominant A29 and M1 antigens mediated higher cross-neutralizing immune responses against the MVA, which could serve as antigen targets for novel orthologous orthopoxvirus vaccine.

The assessment on cross immunity with smallpox virus and antiviral drug sensitivity of the isolated mpox virus strain WIBP-MPXV-001 in China

Since May 2022, human mpox cases have increased unexpectedly in non-endemic countries. The first imported case of human mpox in Hong Kong was reported in September 2022. Here we report the isolation and identification of MPXV from the vesicle swabs of this patient. In this research, the vesicle swabs were inoculated in Vero and Vero E6 cells. In addition to observing cytopathic effects (CPEs) in Vero or Vero E6 cells, the isolated virus was identified as mpox virus (MPXV) using quantitative Real-Time PCR (RT-PCR), transmission electron microscopy, and high-throughput sequencing. The experiment also assessed the cross-protective efficacy of sera from the smallpox vaccinated population and preliminarily assessed the inhibitory effect of anti-smallpox virus drugs against MPXV. CPEs can be observed on Vero E6 cells at 24 hours and Vero cells at 48 hours. The virus particles could be observed by transmission electron microscope, showing typical orthopoxvirus morphology. In addition, F3L and ATI genes which from MPXV A39R, B2R, HA genes which from orthopoxvirus were confirmed by conventional PCR and Sanger sequencing. The next generation sequencing (NGS) suggests that the MPXV strain belongs to B.1 branch of the West African linage, and has a highly identity with the sequence of the 2022 ongoing outbreak. PRNT₅₀ results showed that 26.7% of sera from individuals born before 1981 who had been immunized with smallpox were positive, but no MPXV-neutralizing antibodies were found in sera from individuals born later. All four anti-smallpox virus drugs evaluated demonstrated inhibition of mpox virus.

Monkeypox virus quadrivalent mRNA vaccine induces immune response and protects against vaccinia virus

Monkeypox has been declared a public health emergency by the World Health Organization. There is an urgent need for efficient and safe vaccines against the monkeypox virus (MPXV) in response to the rapidly spreading monkeypox epidemic. In the age of COVID-19, mRNA vaccines have been highly successful and emerged as platforms enabling rapid development and large-scale preparation. Here, we develop two MPXV quadrivalent mRNA vaccines, named mRNA-A-LNP and mRNA-B-LNP, based on two intracellular mature virus specific proteins (A29L and M1R) and two extracellular enveloped virus specific proteins (A35R and B6R). By administering mRNA-A-LNP and mRNA-B-LNP intramuscularly twice, mice induce MPXV specific IgG antibodies and potent vaccinia virus (VACV) specific neutralizing antibodies. Further, it elicits efficient MPXV specific Th-1 biased cellular immunity, as well as durable effector memory T and germinal center B cell responses in mice. In addition, two doses of mRNA-A-LNP and mRNA-B-LNP are protective against the VACV challenge in mice. And, the passive transfer of sera from mRNA-A-LNP and mRNA-B-LNP-immunized mice protects nude mice against the VACV challenge. Overall, our results demonstrate that mRNA-A-LNP and mRNA-B-LNP appear to be safe and effective vaccine candidates against monkeypox epidemics, as well as against outbreaks caused by other orthopoxviruses, including the smallpox virus.

Monkeypox Virus in Animals: Current Knowledge of Viral Transmission and Pathogenesis in Wild Animal Reservoirs and Captive Animal Models

Mpox, formerly called monkeypox, is now the most serious orthopoxvirus (OPXV) infection in humans. This zoonotic disease has been gradually re-emerging in humans with an increasing frequency of cases found in endemic areas, as well as an escalating frequency and size of epidemics outside of endemic areas in Africa. Currently, the largest known mpox epidemic is spreading throughout the world, with over 85,650 cases to date, mostly in Europe and North America. These increased endemic cases and epidemics are likely driven primarily by decreasing global immunity to OPXVs, along with other possible causes. The current unprecedented global outbreak of mpox has demonstrated higher numbers of human cases and greater human-to-human transmission than previously documented, necessitating an urgent need to better understand this disease in humans and animals. Monkeypox virus (MPXV) infections in animals, both naturally occurring and experimental, have provided critical information about the routes of transmission; the viral pathogenicity factors; the methods of control, such as vaccination and antivirals; the disease ecology in reservoir host species; and the conservation impacts on wildlife species. This review briefly described the epidemiology and transmission of MPXV between animals and humans and summarizes past studies on the ecology of MPXV in wild animals and experimental studies in captive animal models, with a focus on how animal infections have informed knowledge concerning various aspects of this pathogen. Knowledge gaps were highlighted in areas where future research, both in captive and free-ranging animals, could inform efforts to understand and control this disease in both humans and animals.

Potential threat of human pathogenic orthopoxviruses to public health and control strategies

Orthopoxviruses (OPXVs) belong to a group of nucleo-cytoplasmic large DNA viruses. Human pathogenic OPXVs (hpOPXVs) include at least five viruses, among which smallpox virus and monkeypox virus are the most dangerous viral pathogens. Both viruses are classified as category-one human infectious pathogens in China. Although smallpox was globally eradicated in the 1980 s, it is still a top biosecurity threat owing to the possibility of either being leaked to the outside world from a laboratory or being weaponized by terrorists. Beginning in early May 2022, a sudden outbreak of monkeypox was concurrently reported in more than 100 disparate geographical areas, representing a public health emergency of international concern, as declared by the World Health Organization (WHO). In this review, we present the reasons for hpOPXVs such as monkeypox virus presenting a potential threat to public health. We then systematically review the historical and recent development of vaccines and drugs against smallpox and monkeypox. In the final section, we highlight the importance of viromics studies as an integral part of a forward defense strategy to eliminate the potential threat to public health from emerging or re-emerging hpOPXVs and their variants.

Immunization of mice with vaccinia virus Tiantan strain yields antibodies cross-reactive with protective antigens of monkeypox virus

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The first study describing the cross-reactivity of antibodies elicited by a Chinese smallpox vaccine against MPXV.

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Mice immunized with vaccinia virus Tiantan strain yield antibodies cross-reactive with MPXV protective antigens.

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Cross-reactivities of VTT-elicited antibodies against monkeypox protective antigens are ranging from 33% to 94%.

Single Dose of Recombinant Chimeric Horsepox Virus (TNX-801) Vaccination Protects Macaques from Lethal Monkeypox Challenge

The ongoing global Monkeypox outbreak that started in the spring of 2022 has reinforced the importance of protecting the population using live virus vaccines based on the vaccinia virus (VACV). Smallpox also remains a biothreat and although some U.S. military personnel are immunized with VACV, safety concerns limit its use in other vulnerable groups. Consequently, there is a need for an effective and safer, single dose, live replicating vaccine against both viruses. One potential approach is to use the horsepox virus (HPXV) as a vaccine. Contemporary VACV shares a common ancestor with HPXV, which from the time of Edward Jenner and through the 19th century, was extensively used to vaccinate against smallpox. However, it is unknown if early HPXV-based vaccines exhibited different safety and efficacy profiles compared to modern VACV. A deeper understanding of HPXV as a vaccine platform may allow the construction of safer and more effective vaccines against the poxvirus family. In a proof-of-concept study, we vaccinated cynomolgus macaques with TNX-801, a recombinant chimeric horsepox virus (rcHPXV), and showed that the vaccine elicited protective immune responses against a lethal challenge with monkeypox virus (MPXV), strain Zaire. The vaccine was well tolerated and protected animals from the development of lesions and severe disease. These encouraging data support the further development of TNX-801.

The virology of human monkeypox virus (hMPXV): A brief overview

First described in 1958, the human monkeypox virus (hMPXV) is a neglected zoonotic pathogen closely associated with the smallpox virus. The virus usually spreads via close contact with the infected animal or human and has been endemic mostly in parts of the African continent. However, with the recent increase in trade, tourism, and travel, the virus has caused outbreaks in countries outside Africa. The recent outbreak in 2022 has been puzzling given the lack of epidemiological connection and the possible sexual transmission of the virus. Furthermore, there is limited understanding of the structural and pathogenetic mechanisms that are employed by the virus to invade the host cells. Henceforth, it is critical to understand the working apparatus governing the viral-immune interactions to develop effective therapeutical and prophylactic modalities. Hence, in the present short communication, we summarize the previously reported research findings regarding the virology of the human monkeypox virus.

Animal Models Used in Monkeypox Research

Monkeypox is an emerging zoonotic disease with a growing prevalence outside of its endemic area, posing a significant threat to public health. Despite the epidemiological and field investigations of monkeypox, little is known about its maintenance in natural reservoirs, biological implications or disease management. African rodents are considered possible reservoirs, although many mammalian species have been naturally infected with the monkeypox virus (MPXV). The involvement of domestic livestock and pets in spillover events cannot be ruled out, which may facilitate secondary virus transmission to humans. Investigation of MPXV infection in putative reservoir species and non-human primates experimentally uncovered novel findings relevant to the course of pathogenesis, virulence factors and transmission of MPXV that provided valuable information for designing appropriate prevention measures and effective vaccines.

Evaluation of Virulence in Cynomolgus Macaques Using a Virus Preparation Enriched for the Extracellular Form of Monkeypox Virus

The 2022 global human monkeypox outbreak emphasizes the importance of maintaining poxvirus research, including enriching a basic understanding of animal models for developing and advancing therapeutics and vaccines. Intravenous administration of monkeypox virus in macaques is arguably one of the best animal models for evaluating the efficacy of medical countermeasures. Here we addressed one criticism of the model, a requirement for a high-titer administration of virus, as well as improving our understanding of monkeypox virus pathogenesis. To do so, we infected macaques with a challenge dose containing a characterized inoculum enriched for the extracellular form of monkeypox virus. Although there were some differences between diseases caused by the enriched preparation compared with a relatively similar unpurified preparation, we were unable to reduce the viral input with the enriched preparation and maintain severe disease. We found that inherent factors contained within the serum of nonhuman primate blood affect the stability of the monkeypox extracellular virions. As a first step to study a role of the extracellular form in transmission, we also showed the presence of this form in the oropharyngeal swabs from nonhuman primates exposed to monkeypox virus.

Effect of Monkeypox Virus Preparation on the Lethality of the Intravenous Cynomolgus Macaque Model

For over two decades, researchers have sought to improve smallpox vaccines and also develop therapies to ensure protection against smallpox or smallpox-like disease. The 2022 human monkeypox pandemic is a reminder that these efforts should persist. Advancing such therapies have involved animal models primarily using surrogate viruses such as monkeypox virus. The intravenous monkeypox model in macaques produces a disease that is clinically similar to the lesional phase of fulminant human monkeypox or smallpox. Two criticisms of the model have been the unnatural route of virus administration and the high dose required to induce severe disease. Here, we purified monkeypox virus with the goal of lowering the challenge dose by removing cellular and viral contaminants within the inoculum. We found that there are advantages to using unpurified material for intravenous exposures.

Lipid nanoparticle delivery of unmodified mRNAs encoding multiple monoclonal antibodies targeting poxviruses in rabbits

Poxviruses are a large and complex family of viruses with members such as monkeypox virus and variola virus. The possibility of an outbreak of monkeypox virus (or a related poxvirus) or the misuse of variola virus justifies the development of countermeasures. Furthermore, poxviruses can be a useful surrogate for developing technology involving antibody therapies. In our experiments, we explored the feasibility of utilizing unmodified mRNA that encodes three previously described monoclonal antibodies, c8A, c6C, and c7D11, as countermeasures to smallpox in a relatively large (>3 kg) laboratory animal (rabbits). We confirmed in vitro translation, secretion, and biological activity of mRNA constructs and identified target monoclonal antibody levels from a murine vaccinia virus model that provided a clinical benefit. Individually, we were able to detect c7D11, c8A, and c6C in the serum of rabbits within 1 day of an intramuscular jet injection of lipid nanoparticle (LNP)-formulated mRNA. Injection of a combination of three LNP-formulated mRNA constructs encoding the three different antibodies produced near equivalent serum levels compared with each individual construct administered alone. These data are among the first demonstrating the feasibility of launching multiple antibodies using mRNA constructs in a large, nonrodent species. Based on empirically derived target serum level and the observed decay rate, the antibody levels attained were unlikely to provide protection.

A nucleic acid-based orthopoxvirus vaccine targeting the vaccinia virus L1, A27, B5 and A33 proteins protects rabbits against lethal rabbitpox virus aerosol challenge

In the age of COVID, nucleic acid vaccines have garnered much attention, at least in part, because of the simplicity of construction, production, and flexibility to adjust and adapt to an evolving outbreak. Orthopoxviruses remain a threat on multiple fronts, especially as emerging zoonosis. In response, we developed a DNA vaccine, termed 4pox, that protected nonhuman primates against monkeypox virus (MPXV) induced severe disease. Here, we examined the protective efficacy of the 4pox DNA vaccine delivered by intramuscular (i.m.) electroporation (EP) in rabbits challenged with aerosolized rabbitpox virus (RPXV), a model that recapitulates the respiratory route of exposure and low dose associated with natural smallpox exposure in humans. We found that 4pox vaccinated rabbits developed immunogen-specific antibodies, including neutralizing antibodies and did not develop any clinical disease, indicating protection against aerosolized RPXV. In contrast, unvaccinated animals developed significant signs of disease, including lesions, and were euthanized. These findings demonstrate that an unformulated, non-adjuvanted DNA vaccine delivered (i.m.) can protect against an aerosol exposure. Importance The eradication of smallpox and subsequent cessation of vaccination has left a majority of the population susceptible to variola virus or other emerging poxvirus. This is exemplified by human monkeypox, as evidenced by the increase in reported endemic and imported cases over the past decades. Therefore, a malleable vaccine technology that can be mass produced, and doesn't require complex conditions for distribution and storage is sought. Herein, we show that a DNA vaccine, in the absence of a specialized formulation or adjuvant, can protect against a lethal aerosol insult of rabbitpox virus.

IMVAMUNE® and ACAM2000® Provide Different Protection against Disease When Administered Postexposure in an Intranasal Monkeypox Challenge Prairie Dog Model

The protection provided by smallpox vaccines when used after exposure to Orthopoxviruses is poorly understood. Postexposu re administration of 1st generation smallpox vaccines was effective during eradication. However, historical epidemiological reports and animal studies on postexposure vaccination are difficult to extrapolate to today’s populations, and 2nd and 3rd generation vaccines, developed after eradication, have not been widely tested in postexposure vaccination scenarios. In addition to concerns about preparedness for a potential malevolent reintroduction of variola virus, humans are becoming increasingly exposed to naturally occurring zoonotic orthopoxviruses and, following these exposures, disease severity is worse in individuals who never received smallpox vaccination. This study investigated whether postexposure vaccination of prairie dogs with 2nd and 3rd generation smallpox vaccines was protective against monkeypox disease in four exposure scenarios. We infected animals with monkeypox virus at doses of 10⁴ pfu (2× LD₅₀) or 10⁶ pfu (170× LD₅₀) and vaccinated the animals with IMVAMUNE^® or ACAM2000^® either 1 or 3 days after challenge. Our results indicated that postexposure vaccination protected the animals to some degree from the 2× LD₅₀, but not the 170× LD₅ challenge. In the 2× LD₅₀ challenge, we also observed that administration of vaccine at 1 day was more effective than administration at 3 days postexposure for IMVAMUNE^®, but ACAM2000^® was similarly effective at either postexposure vaccination time-point. The effects of postexposure vaccination and correlations with survival of total and neutralizing antibody responses, protein targets, take formation, weight loss, rash burden, and viral DNA are also presented.

Particle-specific neutralizing activity of a monoclonal antibody targeting the poxvirus A33 protein reveals differences between cell associated and extracellular enveloped virions

Only a small subset of the hundreds of proteins encoded by the poxvirus genome have been shown to be effective as vaccine and/or therapeutic targets. One of these proteins is A33. Here we assess and dissect the ability of an anti-A33 humanized monoclonal antibody, c6C, to affect vaccinia virus infection in vitro. Enveloped virions (EV) released from infected cells can be sensitive or resistant to neutralization by c6C indicating there are different types of EV particles, extracellular enveloped virions (EEV) and released cellular-associated virions (rCEV), that are biologically distinct. Through a combination of plaque phenotype, confocal imaging, and neutralization assays, we found that c6C differentially affects EV from two different virus strains, IHD-J and WR. Evidence for an anti-A33 resistant EV particle, and strain differences in this phenotype, provides a logical answer as to why certain functional assays in the literature have been unable to detect anti-viral effects of anti-A33 antibodies.

Preclinical pharmacokinetic evaluation to facilitate repurposing of tyrosine kinase inhibitors nilotinib and imatinib as antiviral agents

Background

Several tyrosine kinase inhibitors (TKIs) developed as anti-cancer drugs, also have anti-viral activity due to their ability to disrupt productive replication and dissemination in infected cells. Consequently, such drugs are attractive candidates for “repurposing” as anti-viral agents. However, clinical evaluation of therapeutics against infectious agents associated with high mortality, but low or infrequent incidence, is often unfeasible. The United States Food and Drug Administration formulated the “Animal Rule” to facilitate use of validated animal models for conducting anti-viral efficacy studies.

Methods

To enable such efficacy studies of two clinically approved TKIs, nilotinib, and imatinib, we first conducted comprehensive pharmacokinetic (PK) studies in relevant rodent and non-rodent animal models. PK of these agents following intravenous and oral dosing were evaluated in C57BL/6 mice, prairie dogs, guinea pigs and Cynomolgus monkeys. Plasma samples were analyzed using an LC-MS/MS method. Secondarily, we evaluated the utility of allometry-based inter-species scaling derived from previously published data to predict the PK parameters, systemic clearance (CL) and the steady state volume of distribution (Vss) of these two drugs in prairie dogs, an animal model not tested thus far.

Results

Marked inter-species variability in PK parameters and resulting oral bioavailability was observed. In general, elimination half-lives of these agents in mice and guinea pigs were much shorter (1–3 h) relative to those in larger species such as prairie dogs and monkeys. The longer nilotinib elimination half-life in prairie dogs (i.v., 6.5 h and oral, 7.5 h), facilitated multiple dosing PK and safety assessment. The allometry-based predicted values of the Vss and CL were within 2.0 and 2.5-fold, respectively, of the observed values.

Conclusions

Our results suggest that prairie dogs and monkeys may be suitable rodent and non-rodent species to perform further efficacy testing of these TKIs against orthopoxvirus infections. The use of rodent models such as C57BL/6 mice and guinea pigs for assessing pre-clinical anti-viral efficacy of these two TKIs may be limited due to short elimination and/or low oral bioavailability. Allometry-based correlations, derived from existing literature data, may provide initial estimates, which may serve as a useful guide for pre-clinical PK studies in untested animal models.

Intranasal monkeypox marmoset model: Prophylactic antibody treatment provides benefit against severe monkeypox virus disease

Concerns regarding outbreaks of human monkeypox or the potential reintroduction of smallpox into an immunological naïve population have prompted the development of animal models and countermeasures. Here we present a marmoset model of monkeypox and smallpox disease utilizing a relevant poxvirus via a natural exposure route. We found that 1000 plaque forming units (PFU) of Monkeypox virus was sufficient to recapitulate smallpox disease, to include an incubation period of approximately 13 days, followed by the onset of rash, and death between 15 and 17 days. Temporally accurate manifestation of viremia and oral shedding were also features. The number of lesions ranged from no lesions to 299, the most reported in a marmoset exposed to a poxvirus. To both evaluate the efficacy of our antibodies and the applicability of the model system, marmosets were prophylactically treated with two monoclonal antibodies, c7D11 and c8A. Of three marmosets, two were completely free of disease and a single marmoset died 8 days after the mock (n = 1) or PBS control(s) (n = 2). Evaluation of the serum levels of the three animals provided a possible explanation to the animal succumbing to disease. Interestingly, more females had lesions (and a greater number of lesions) and lower viral burden (viremia and oral shedding) than males in our studies, suggesting a possible gender effect.

Challenges and Achievements in Prevention and Treatment of Smallpox

Declaration of smallpox eradication by the WHO in 1980 led to discontinuation of the worldwide vaccination campaign. The increasing percentage of unvaccinated individuals, the existence of its causative infectious agent variola virus (VARV), and the recent synthetic achievements increase the threat of intentional or accidental release and reemergence of smallpox. Control of smallpox would require an emergency vaccination campaign, as no other protective measure has been approved to achieve eradication and ensure worldwide protection. Experimental data in surrogate animal models support the assumption, based on anecdotal, uncontrolled historical data, that vaccination up to 4 days postexposure confers effective protection. The long incubation period, and the uncertainty of the exposure status in the surrounding population, call for the development and evaluation of safe and effective methods enabling extension of the therapeutic window, and to reduce the disease manifestations and vaccine adverse reactions. To achieve these goals, we need to evaluate the efficacy of novel and already licensed vaccines as a sole treatment, or in conjunction with immune modulators and antiviral drugs. In this review, we address the available data, recent achievements, and open questions.

Validation of a pan-orthopox real-time PCR assay for the detection and quantification of viral genomes from nonhuman primate blood

BACKGROUND

In 1980, smallpox disease was eradicated from nature and Variola virus, the etiological agent of smallpox, was confined to two laboratories, one located in Russia (Moscow) later moved to VECTOR (Novosibirsk, Siberia) and one in the United States (CDC Atlanta). Vaccinations among the general public ceased shortly after the successful eradication campaign, resulting in an increasingly immunologically susceptible population. Because of the possibility of intentional reintroduction of Variola virus and the emergence of other pathogenic poxviruses, there is a great need for the development of medical countermeasures to treat poxvirus disease. It is highly likely that the U.S. FDA "animal rule" will be necessary for regulatory approval of these interventions. Therefore, relevant animal models and the associated supporting assays will require development to stand up to regulatory scrutiny.

METHODS

An optimized real time PCR assay for the detection of orthopoxviruses has been developed by researchers at the United States Army Research Institute of Infectious Diseases (USAMRIID). To support animal studies that will be used to support approval of medical countermeasures by the U.S. FDA, the assay was designed to quantitate poxvirus genomic DNA in a nonhuman primate (cynomolgus macaque) blood matrix as a measurement of viremia. This manuscript describes the validation of the process, including DNA extraction from whole blood anticoagulated with EDTA, for obtaining and quantitating monkeypox genomes by evaluating precision, accuracy, the standard curve, specificity, robustness and stability of the assay and/or components of the assay.

RESULTS

The assay had a lower limit of quantitation of 50 genome copies/5 uL sample, upper limit of quantitation of 5 × 10⁷ GC/5uL sample and a limit of detection of 2.5 genome copies /5uL sample. The assay was specific for orthopoxvirus. Matrix effects were detected and suggest the presence of PCR inhibitor(s) that was co-extracted with the target DNA.

CONCLUSIONS

The assay has been validated for the purpose of quantitating monkeypox viral load in blood from cynomolgus macaques. This assay has and will continue to support submissions to the FDA for approval of antiviral therapeutics for smallpox.

Defending against smallpox: a focus on vaccines

Smallpox has shaped human history, from the earliest human civilizations well into the 20th century. With high mortality rates, rapid transmission, and serious long-term effects on survivors, smallpox was a much-feared disease. The eradication of smallpox represents an unprecedented medical victory for the lasting benefit of human health and prosperity. Concerns remain, however, about the development and use of the smallpox virus as a biological weapon, which necessitates the need for continued vaccine development. Smallpox vaccine development is thus a much-reviewed topic of high interest. This review focuses on the current state of smallpox vaccines and their context in biodefense efforts.

TLR3 and TLR9 agonists improve postexposure vaccination efficacy of live smallpox vaccines

Eradication of smallpox and discontinuation of the vaccination campaign resulted in an increase in the percentage of unvaccinated individuals, highlighting the need for postexposure efficient countermeasures in case of accidental or deliberate viral release. Intranasal infection of mice with ectromelia virus (ECTV), a model for human smallpox, is curable by vaccination with a high vaccine dose given up to 3 days postexposure. To further extend this protective window and to reduce morbidity, mice were vaccinated postexposure with Vaccinia-Lister, the conventional smallpox vaccine or Modified Vaccinia Ankara, a highly attenuated vaccine in conjunction with TLR3 or TLR9 agonists. We show that co-administration of the TLR3 agonist poly(I:C) even 5 days postexposure conferred protection, avoiding the need to increase the vaccination dose. Efficacious treatments prevented death, ameliorated disease symptoms, reduced viral load and maintained tissue integrity of target organs. Protection was associated with significant elevation of serum IFNα and anti-vaccinia IgM antibodies, modulation of IFNγ response, and balanced activation of NK and T cells. TLR9 agonists (CpG ODNs) were less protective than the TLR3 agonist poly(I:C). We show that activation of type 1 IFN by poly(I:C) and protection is achievable even without co-vaccination, requiring sufficient amount of the viral antigens of the infective agent or the vaccine. This study demonstrated the therapeutic potential of postexposure immune modulation by TLR activation, allowing to alleviate the disease symptoms and to further extend the protective window of postexposure vaccination.

The optical, photothermal, and facile surface chemical properties of gold and silver nanoparticles in biodiagnostics, therapy, and drug delivery

Nanotechnology is a rapidly growing area of research in part due to its integration into many biomedical applications. Within nanotechnology, gold and silver nanostructures are some of the most heavily utilized nanomaterial due to their unique optical, photothermal, and facile surface chemical properties. In this review, common colloid synthesis methods and biofunctionalization strategies of gold and silver nanostructures are highlighted. Their unique properties are also discussed in terms of their use in biodiagnostic, imaging, therapeutic, and drug delivery applications. Furthermore, relevant clinical applications utilizing gold and silver nanostructures are also presented. We also provide a table with reviews covering related topics.

Assessment of the protective effect of Imvamune and Acam2000 vaccines against aerosolized monkeypox virus in cynomolgus macaques

To support the licensure of a new and safer vaccine to protect people against smallpox, a monkeypox model of infection in cynomolgus macaques, which simulates smallpox in humans, was used to evaluate two vaccines, Acam2000 and Imvamune, for protection against disease. Animals vaccinated with a single immunization of Imvamune were not protected completely from severe and/or lethal infection, whereas those receiving either a prime and boost of Imvamune or a single immunization with Acam2000 were protected completely. Additional parameters, including clinical observations, radiographs, viral load in blood, throat swabs, and selected tissues, vaccinia virus-specific antibody responses, immunophenotyping, extracellular cytokine levels, and histopathology were assessed. There was no significant difference (P > 0.05) between the levels of neutralizing antibody in animals vaccinated with a single immunization of Acam2000 (132 U/ml) and the prime-boost Imvamune regime (69 U/ml) prior to challenge with monkeypox virus. After challenge, there was evidence of viral excretion from the throats of 2 of 6 animals in the prime-boost Imvamune group, whereas there was no confirmation of excreted live virus in the Acam2000 group. This evaluation of different human smallpox vaccines in cynomolgus macaques helps to provide information about optimal vaccine strategies in the absence of human challenge studies.

Utilizing poxviral vectored vaccines for antibody induction-progress and prospects

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Poxviral vectors are now regarded as robust tools for B cell and antibody induction.

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Antibody responses can be induced against the vector as well as a transgene.

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Increasing application is seen in heterologous prime–boost immunization regimes.

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Effective veterinary poxviral vaccine products are now licensed.

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Promising results of antibody induction are being reported in human clinical trials.

Over the last decade, poxviral vectors emerged as a mainstay approach for the induction of T cell-mediated immunity by vaccination, and their suitability for human use has led to widespread clinical testing of candidate vectors against infectious intracellular pathogens and cancer. In contrast, poxviruses have been widely perceived in the vaccine field as a poor choice of vector for the induction of humoral immunity. However, a growing body of data, from both animal models and recent clinical trials, now suggests that these vectors can be successfully utilized to prime and boost B cells and effective antibody responses. Significant progress has been made in the context of heterologous prime–boost immunization regimes, whereby poxviruses are able to boost responses primed by other vectors, leading to the induction of high-titre antigen-specific antibody responses. In other cases, poxviral vectors have been shown to stimulate humoral immunity against both themselves and encoded transgenes, in particular viral surface proteins such as influenza haemagglutinin. In the veterinary field, recombinant poxviral vectors have made a significant impact with numerous vectors licensed for use against a variety of animal viruses. On-going studies continue to explore the potential of poxviral vectors to modulate qualitative aspects of the humoral response, as well as their amenability to adjuvantation seeking to improve quantitative antibody immunogenicity. Nevertheless, the underlying mechanisms of B cell induction by recombinant poxviruses remain poorly defined, and further work is necessary to help guide the rational optimization of future poxviral vaccine candidates aiming to induce antibodies.