Unusual features of vaccinia virus extracellular virion form neutralization resistance revealed in human antibody responses to the smallpox vaccine

The impact of orthopoxvirus vaccination and Mpox infection on cross-protective immunity: a multicohort observational study

BACKGROUND

Cross-reactive immune memory responses to orthopoxviruses in humans remain poorly characterised despite their relevance for vaccine design and outbreak control. We aimed to assess the magnitude, specificity, and durability of cross-reactive immune responses elicited by smallpox vaccines and mpox virus infection.

METHODS

We did a multicohort observational study involving participants from the USA, Brazil, and Portugal across four groups: Dryvax (first-generation smallpox vaccine) recipients vaccinated 40-80 years ago, JYNNEOS (third-generation smallpox vaccine) recipients vaccinated within the past year, a cohort receiving both vaccines, and patients infected with clade IIb mpox. Samples were analysed for systemic and mucosal humoral responses, neutralising antibody titres, viral antigen structural analysis, and T-cell cross-reactivity to vaccina virus, cowpox virus, and mpox virus. Statistical analyses included correlation assessments and comparisons across cohorts to determine the magnitude, longevity, and breadth of immune responses.

FINDINGS

Between July 7, 2022, and Aug 3, 2023, 262 participants were recruited, resulting in analysis of 378 samples. Both first-generation and third-generation smallpox vaccines elicited vaccinia virus-reactive and mpox virus-reactive antibodies, with the strongest responses targeting the less conserved extracellular virion antigens B5 and A33. Despite high concentrations of anti-mpox virus antibodies in the plasma, cross-neutralisation activity correlated with viral antigenic distance. Higher neutralisation was observed for cowpox virus than for mpox virus, which has lower antigenic conservation with vaccina virus. Complement-mediated neutralisation enhanced mpox virus neutralisation, overcoming the limitations of antigenic distance. Dryvax recipients sustained vaccina virus neutralisation titres for over 80 years, whereas cross-reactive responses did not show this durability. JYNNEOS-induced responses waned within a year. T-cell cross-reactivity was long-lasting, detected up to 70 years after vaccination. Booster vaccinations augmented the magnitude, breadth, and longevity of cross-neutralising responses.

INTERPRETATION

Our findings highlight the potential combined role of antibody effector functions and T-cell memory in cross-protection against orthopoxviruses. Complement-mediated neutralisation enhances cross-protection, overcoming antigenic distance. These Fc-mediated functions, along with T-cell responses, contribute to effective and long-lasting immunity conferred by smallpox vaccines against other orthopoxviruses.

FUNDING

Yale University and Stavros Niarchos Foundation Institute for Global Infectious Disease.

Research progress and development potential of oncolytic vaccinia virus

ABSTRACT

Oncolytic virotherapy is a promising therapeutic approach treating tumors, where oncolytic viruses (OVs) can selectively infect and lyse tumor cells through replication, while also triggering long-lasting anti-tumor immune responses. Vaccinia virus (VV) has emerged as a leading candidate for use as an OV due to its broad cytophilicity and robust capacity to express exogenous genes. Consequently, oncolytic vaccinia virus (OVV) has entered clinical trials. This review provides an overview of the key strategies used in the development of OVV, summarizes the findings from clinical trials, and addresses the challenges that must be overcome in the advancement of OVV-based therapies. Furthermore, it explores potential future strategies for enhancing the development and clinical application of OVV, intending to improve tumor treatment outcomes. The review aims to facilitate the further development and clinical adoption of OVV, thereby advancing tumor therapies.

Monkeypox virus H3L protein as the target antigen for developing neutralizing antibody and serological assay

The large number of atypical monkeypox (Mpox) cases caused by emerging monkeypox virus (MPXV) strains was recently found in countries and regions where the Mpox was not reported before. Diagnostic tools and therapeutic agents are important countermeasures for preventing Mpox outbreak. H3L protein is the important surface antigen of MPXV for binding to host cell receptors and mediating viral infection. A broad range of murine anti-MPXV H3L monoclonal antibodies (mAbs) recognizing various binding epitopes have been generated in the study. The rapid test composed of the mAbs 4-2A and 3-3F can specifically detect H3L protein and MPXV virion. The mAb 3-3F exhibited strong MPXV neutralizing activity in a complement-dependent manner. Notably, 3-3F binds to a unique epitope within residues 35-89 of H3L protein. The serum samples collected from Mpox patients barely bound to the N-terminal portion of H3L protein ranging from 2 to 89 residues, indicating that the content of the 3-3F-like antibody is very low in Mpox patient sera. In contrast, the seropositivity was mostly observed using the C-terminal portion of H3L protein ranging from 185 to 282 residues as the target antigen in the immunoblot analysis. Taken together, the anti-MPXV H3L mAb can be developed as the Mpox diagnostic and therapeutic agents. Furthermore, H3L protein is the promising biomarker for serological analysis. KEY POINTS: •Anti-H3L mAbs can cross-react with H3L proteins in MPXV and VACV virions. •The LFIA rapid test using the mAbs 4-2A and 3-3F can specifically detect MPXV. •MPXV was neutralized by mAb 3-3F in a complement-dependent manner.

Identification of mpox M1R and B6R monoclonal and bispecific antibodies that efficiently neutralize authentic mpox virus

In 2022, the monkeypox virus (mpox virus, MPXV) exhibited global dissemination across six continents, representing a notable challenge owing to the scarcity of targeted antiviral interventions. Passive immunotherapy, such as the use of monoclonal antibodies (mAbs) and bispecific antibodies (bsAbs), has emerged as a promising option for antiviral regimens. Here, we generated several mAbs against M1R and B6R of MPXV, and subsequently characterized the antiviral activity of these antibodies both in vitro and in vivo. Two neutralizing mAbs, M1H11 and M3B2, targeting M1R, and one B6R-specific mAb, B7C9, were identified. They exhibited varying antiviral efficacy against vaccinia virus (VACV) in vitro and in vivo. A cocktail comprising M1H11 and M3B2 demonstrated a superior protective effect in vivo. A bsAb, Bis-M1M3, was engineered by conjugating the fragment crystallizable (Fc) region of the human-mouse chimeric engineered M1H11 with the single-chain fragment variable (scFv) of M3B2. In mice challenged with MPXV, Bis-M1M3 showed a notable protective effects. Analysis of neutralization mechanism showed that these mAbs and Bis-M1M3 exerted virus-neutralizing effects before the virus infects cells. In vivo pharmacokinetic experiments showed that Bis-M1M3 has a long half-life in rhesus macaques. This study provides crucial insights for further research on broad-spectrum antiviral drugs against MPXV and other orthopoxviruses.

Host immune responses against African swine fever virus: Insights and challenges for vaccine development

The African swine fever virus (ASFV) poses a serious threat to global swine populations, underscoring the urgent need for effective preventive strategies. This comprehensive review investigates the intricate interplay between innate, cellular, and humoral immunity against ASFV, with a focus on their relevance to vaccine development. By delving into immunopathogenesis and immunological challenges, this review article aims to provide a holistic perspective on the complexities of ASFV infections and immune evasion. Key findings underscore the critical role of innate immune recognition in shaping subsequent adaptive immune defenses, potential protective antigens, and the multifaceted nature of ASFV-specific antibodies and cytotoxic T-cell responses. Despite advancements, the unique attributes of ASFV present hurdles in the development of a successful vaccine. In conclusion, this review examines the current state of ASFV immune responses and offers insights into future research directions, fostering the development of effective interventions against this devastating pathogen.

Preclinical and clinical trials of oncolytic vaccinia virus in cancer immunotherapy: a comprehensive review

Oncolytic virotherapy has emerged as a promising treatment for human cancers owing to an ability to elicit curative effects via systemic administration. Tumor cells often create an unfavorable immunosuppressive microenvironment that degrade viral structures and impede viral replication; however, recent studies have established that viruses altered via genetic modifications can serve as effective oncolytic agents to combat hostile tumor environments. Specifically, oncolytic vaccinia virus (OVV) has gained popularity owing to its safety, potential for systemic delivery, and large gene insertion capacity. This review highlights current research on the use of engineered mutated viruses and gene-armed OVVs to reverse the tumor microenvironment and enhance antitumor activity in vitro and in vivo, and provides an overview of ongoing clinical trials and combination therapies. In addition, we discuss the potential benefits and drawbacks of OVV as a cancer therapy, and explore different perspectives in this field.

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.

Zebrafish-based platform for emerging bio-contaminants and virus inactivation research

Emerging bio-contaminants such as viruses have affected health and environment settings of every country. Viruses are the minuscule entities resulting in severe contagious diseases like SARS, MERS, Ebola, and avian influenza. Recent epidemic like the SARS-CoV-2, the virus has undergone mutations strengthen them and allowing to escape from the remedies. Comprehensive knowledge of viruses is essential for the development of targeted therapeutic and vaccination treatments. Animal models mimicking human biology like non-human primates, rats, mice, and rabbits offer competitive advantage to assess risk of viral infections, chemical toxins, nanoparticles, and microbes. However, their economic maintenance has always been an issue. Furthermore, the redundancy of experimental results due to aforementioned aspects is also in examine. Hence, exploration for the alternative animal models is crucial for risk assessments. The current review examines zebrafish traits and explores the possibilities to monitor emerging bio-contaminants. Additionally, a comprehensive picture of the bio contaminant and virus particle invasion and abatement mechanisms in zebrafish and human cells is presented. Moreover, a zebrafish model to investigate the emerging viruses such as coronaviridae and poxviridae has been suggested.

Monkeypox outbreak 2022: What we know so far and its potential drug targets and management strategies

Monkeypox is a rare zoonotic disease caused by infection with the monkeypox virus. The disease can result in flu-like symptoms, fever, and a persistent rash. The disease is currently spreading throughout the world and prevention and treatment efforts are being intensified. Although there is no treatment that has been specifically approved for monkeypox virus infection, infected patients may benefit from using certain antiviral medications that are typically prescribed for the treatment of smallpox. The drugs are tecovirimat, brincidofovir, and cidofovir, all of which are currently in short supply due to the spread of the monkeypox virus. Resistance is also a concern, as widespread replication of the monkeypox virus can lead to mutations that produce monkeypox viruses that are resistant to the currently available treatments. This article discusses monkeypox disease, potential drug targets, and management strategies to overcome monkeypox disease. With the discovery of new drugs, it is hoped that the problem of insufficient drugs will be resolved, and it is not anticipated that drug resistance will become a major issue in the near future.

African Swine Fever Vaccinology: The Biological Challenges from Immunological Perspectives

African swine fever virus (ASFV), a nucleocytoplasmic large DNA virus (NCLDV), causes African swine fever (ASF), an acute hemorrhagic disease with mortality rates up to 100% in domestic pigs. ASF is currently epidemic or endemic in many countries and threatening the global swine industry. Extensive ASF vaccine research has been conducted since the 1920s. Like inactivated viruses of other NCLDVs, such as vaccinia virus, inactivated ASFV vaccine candidates did not induce protective immunity. However, inactivated lumpy skin disease virus (poxvirus) vaccines are protective in cattle. Unlike some experimental poxvirus subunit vaccines that induced protection, ASF subunit vaccine candidates implemented with various platforms containing several ASFV structural genes or proteins failed to protect pigs effectively. Only some live attenuated viruses (LAVs) are able to protect pigs with high degrees of efficacy. There are currently several LAV ASF vaccine candidates. Only one commercial LAV vaccine is approved for use in Vietnam. LAVs, as ASF vaccines, have not yet been widely tested. Reports thus far show that the onset and duration of protection induced by the LAVs are late and short, respectively, compared to LAV vaccines for other diseases. In this review, the biological challenges in the development of ASF vaccines, especially subunit platforms, are discussed from immunological perspectives based on several unusual ASFV characteristics shared with HIV and poxviruses. These characteristics, including multiple distinct infectious virions, extremely high glycosylation and low antigen surface density of envelope proteins, immune evasion, and possible apoptotic mimicry, could pose enormous challenges to the development of ASF vaccines, especially subunit platforms designed to induce humoral immunity.

Serum Neutralizing and Enhancing Effects on African Swine Fever Virus Infectivity in Adherent Pig PBMC

African swine fever virus (ASFV) causes hemorrhagic fever with mortality rates of up to 100% in domestic pigs. Currently, there are no commercial vaccines for the disease. Only some live-attenuated viruses have been able to protect pigs from ASFV infection. The immune mechanisms involved in the protection are unclear. Immune sera can neutralize ASFV but incompletely. The mechanisms involved are not fully understood. Currently, there is no standardized protocol for ASFV neutralization assays. In this study, a flow cytometry-based ASFV neutralization assay was developed and tested in pig adherent PBMC using a virulent ASFV containing a fluorescent protein gene as a substrate for neutralization. As with previous studies, the percentage of infected macrophages was approximately five time higher than that of infected monocytes, and nearly all infected cells displayed no staining with anti-CD16 antibodies. Sera from naïve pigs and pigs immunized with a live-attenuated ASFV and fully protected against parental virus were used in the assay. The sera displayed incomplete neutralization with MOI-dependent neutralizing efficacies. Extracellular, but not intracellular, virions suspended in naïve serum were more infectious than those in the culture medium, as reported for some enveloped viruses, suggesting a novel mechanism of ASFV infection in macrophages. Both the intracellular and extracellular virions could not be completely neutralized.

Proteomic assessment of humoral immune responses in smallpox vaccine recipients

The availability of effective smallpox vaccines was a critical element of the successful eradication of smallpox in 1980. Antibody responses play a primary role in protective immunity and neutralizing antibody is an established correlate of protection against smallpox. In this study we used a poxvirus proteome array to assess the antibody response to individual viral proteins in a cohort of 1,037 smallpox vaccine recipients. Several statistically significant differences were observed in the antibody response to immunodominant proteins between men and women, including B5R-a major target of neutralizing antibody in vaccinia immune globulin, and the membrane proteins D8L and A27L, both of which have been used as vaccine antigens providing protection in animal models. We also noted differences across racial/ethnic groups. In this cohort, which consisted of both ACAM2000 and Dryvax recipients, we noted minute differences in the antibody responses to a restricted number of viral proteins, providing additional support for the use of ACAM2000 as a replacement smallpox vaccine. Furthermore, our data indicate that poxvirus proteome microarrays can be valuable for screening and monitoring smallpox vaccine-induced humoral immune responses in large-scale serologic surveillance studies and prove useful in the guidance of developing novel smallpox candidate vaccines.

Characterisation of an Anti-Vaccinia Virus F13 Single Chain Fragment Variable from a Human Anti-Vaccinia Virus-Specific Recombinant Immunoglobulin Library

Vaccinia virus (VACV) belongs to the genus Orthopoxvirus of the family Poxviridae. There are four different forms of infectious virus particles: intracellular mature virus (IMV), intracellular en-veloped virus (IEV), cell-associated enveloped virus (CEV) and extracellular enveloped virus (EEV). The F13 protein occupies the inner side of the CEV- and EEV-membranes and the outer side of the IEV-membranes. It plays an important role in wrapping progress and EEV production. We constructed a human single-chain fragment variable (scFv) library with a diversity of ≥4 × 108 independent colonies using peripheral blood from four vaccinated donors. One anti-F13 scFv was isolated and characterised after three rounds of panning. In Western blotting assays, the scFv 3E2 reacted with the recombinant F13VACV protein with a reduction of binding under denatured and reduced conditions. Two antigenic binding sites (139-GSIHTIKTLGVYSDY-153 and 169-AFNSAKNSWLNL-188) of scFv 3E2 were mapped using a cellulose membrane encompassing 372 15-mere peptides with 12 overlaps covering the whole F13 protein. No neutralisation capa-bilities were observed either in the presence or absence of complement. In conclusion, the con-struction of recombinant immunoglobulin libraries is a promising strategy to isolate specific scFvs to enable the study of the host-pathogen interaction.

An increase in glycoprotein concentration on extracellular virions dramatically alters vaccinia virus infectivity and pathogenesis without impacting immunogenicity

The extracellular virion (EV) form of Orthopoxviruses is required for cell-to-cell spread and pathogenesis, and is the target of neutralizing antibodies in the protective immune response. EV have a double envelope that contains several unique proteins that are involved in its intracellular envelopment and/or subsequent infectivity. One of these, F13, is involved in both EV formation and infectivity. Here, we report that replacement of vaccinia virus F13L with the molluscum contagiosum virus homolog, MC021L, results in the production of EV particles with significantly increased levels of EV glycoproteins, which correlate with a small plaque phenotype. Using a novel fluorescence-activated virion sorting assay to isolate EV populations based on glycoprotein content we determine that EV containing either higher or lower levels of glycoproteins are less infectious, suggesting that there is an optimal concentration of glycoproteins in the outer envelope that is required for maximal infectivity of EV. This optimal glycoprotein concentration was required for lethality and induction of pathology in a cutaneous model of animal infection, but was not required for induction of a protective immune response. Therefore, our results demonstrate that there is a sensitive balance between glycoprotein incorporation, infectivity, and pathogenesis, and that manipulation of EV glycoprotein levels can produce vaccine vectors in which pathologic side effects are attenuated without a marked diminution in induction of protective immunity.

Short-term and longer-term protective immune responses generated by subunit vaccination with smallpox A33, B5, L1 or A27 proteins adjuvanted with aluminum hydroxide and CpG in mice challenged with vaccinia virus

Smallpox, a contagious and deadly disease caused by variola virus, was eradicated by a strategy that included vaccination with vaccinia virus, a live-virus vaccine. Because the threat of bioterrorism with smallpox persists and infections with zoonotic poxvirus infections like monkeypox continue, and there may be a time when an alternative vaccine platform is needed, recombinant-subunit vaccine strategies for poxviruses have been pursued. Our prior work focused on understanding the immune responses generated to vaccine-formulations containing the virus protein L1. In this work, we examine vaccine-formulations with additional key protein targets: A33 and B5 (components of the extracellular virus) and another protein on the mature virus (A27) adjuvanted with aluminum hydroxide (AH) with and without CpG- oligonucleotide. Each vaccine was formulated to allow either adsorption or non-adsorption of the protein (and CpG) to AH. Mice given a prime and single boost produced long-lasting antibody responses. A second boost (given ~5-months after the first) further increased antibody titers. Similar to our prior findings with L1 vaccine-formulations, the most protective A33 vaccine-formulations included CpG, resulted in the generation of IgG2a-antibody responses. Unlike the prior findings with L1 (where formulations that adsorbed both the protein and the CpG to AH resulted in 100% survival after challenge and minimal weight loss), the AH-adsorption status of A33 and CpG did not play as important a role, since both AH-adsorbed and non-adsorbed groups lost weight after challenge and had similar survival. Vaccination with B5-formulations gave different results. While CpG-containing formulations were the only ones that generated IgG2a-antibody responses, the vaccine-formulation that adsorbed B5 to AH (without CpG) was as equally effective in protecting mice after challenge. These results indicate that the mechanism of how antibodies against A33 and B5 protect differ. The data also show the complexity of designing optimized vaccine-formulations containing multiple adjuvants and recombinant protein-based antigens.

Engineering vaccinia virus as an immunotherapeutic battleship to overcome tumor heterogeneity

INTRODUCTION

Immunotherapy is a rapidly evolving area of cancer therapeutics aimed at driving a systemic immune response to fight cancer. Oncolytic viruses (OVs) are at the cutting-edge of innovation in the immunotherapy field. Successful OV platforms must be effective in reshaping the tumor microenvironment and controlling tumor burden, but also be highly specific to avoid off-target side effects. Large DNA viruses, like vaccinia virus (VACV), have a large coding capacity, enabling the encoding of multiple immunostimulatory transgenes to reshape the tumor immune microenvironment. VACV-based OVs have shown promising results in both pre-clinical and clinical studies, including safe and efficient intravenous delivery to metastatic tumors.

AREA COVERED

This review summarizes attenuation strategies to generate a recombinant VACV with optimal tumor selectivity and immunogenicity. In addition, we discuss immunomodulatory transgenes that have been introduced into VACV and summarize their effectiveness in controlling tumor burden.

EXPERT OPINION

VACV encodes several immunomodulatory genes which aid the virus in overcoming innate and adaptive immune responses. Strategic deletion of these virulence factors will enable an optimal balance between viral persistence and immunogenicity, robust tumor-specific expression of payloads and promotion of a systemic anti-cancer immune response. Rational selection of therapeutic transgenes will maximize the efficacy of OVs and their synergy in combinatorial immunotherapy schemes.

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.

Partial Deletion of Glycoprotein B5R Enhances Vaccinia Virus Neutralization Escape while Preserving Oncolytic Function

Vaccinia virus (VV) has been utilized in oncolytic virotherapy, but it risks a host antiviral immune response. VV has an extracellular enveloped virus (EEV) form consisting of a normal virion covered with a host-derived outer membrane that enables its spread via circulation while evading host immune mechanisms. However, the immune resistance of EEV is only partial, owing to expression of the surface protein B5R, which has four short consensus repeat (SCR) domains that are targeted by host immune factors. To engineer a more effective virus for oncolytic virotherapy, we developed an enhanced immune-evading oncolytic VV by removing the SCRs from the attenuated strain LC16mO. Although deletion of only the SCRs preserved viral replication, progeny production, and oncolytic activity, deletion of whole B5R led to attenuation of the virus. Importantly, SCR-deleted EEV had higher neutralization resistance than did B5R-wild-type EEV against VV-immunized animal serum; moreover, it retained oncolytic function, thereby prolonging the survival of tumor-bearing mice treated with anti-VV antibody. These results demonstrate that partial SCR deletion increases neutralization escape without affecting the oncolytic potency of VV, making it useful for the treatment of tumors under the anti-virus antibody existence.

Immunoproteomics Methods and Techniques

The varied landscape of the adaptive immune response is determined by the peptides presented by immune cells, derived from viral or microbial pathogens or cancerous cells. The study of immune biomarkers or antigens is not new, and classical methods such as agglutination, enzyme-linked immunosorbent assay, or Western blotting have been used for many years to study the immune response to vaccination or disease. However, in many of these traditional techniques, protein or peptide identification has often been the bottleneck. Recent progress in genomics and mass spectrometry have led to many of the rapid advances in proteomics approaches. Immunoproteomics describes a rapidly growing collection of approaches that have the common goal of identifying and measuring antigenic peptides or proteins. This includes gel-based, array-based, mass spectrometry-based, DNA-based, or in silico approaches. Immunoproteomics is yielding an understanding of disease and disease progression, vaccine candidates, and biomarkers. This review gives an overview of immunoproteomics and closely related technologies that are used to define the full set of protein antigens targeted by the immune system during disease.

Therapeutic Antibodies for Biodefense

Diseases can be caused naturally by biological agents such as bacteria, viruses and toxins (natural risk). However, such biological agents can be intentionally disseminated in the environment by a State (military context) or terrorists to cause diseases in a population or livestock, to destabilize a nation by creating a climate of terror, destabilizing the economy and undermining institutions. Biological agents can be classified according to the severity of illness they cause, its mortality and how easily the agent can be spread. The Centers for Diseases Control and Prevention (CDC) classify biological agents in three categories (A, B and C); Category A consists of the six pathogens most suitable for use as bioweapons (Bacillus anthracis, Yersinia pestis, Francisella tularensis, botulinum neurotoxins, smallpox and viral hemorrhagic fevers). Antibodies represent a perfect biomedical countermeasure as they present both prophylactic and therapeutic properties, act fast and are highly specific to the target. This review focuses on the main biological agents that could be used as bioweapons, the history of biowarfare and antibodies that have been developed to neutralize these agents.

Multiplexed Fc array for evaluation of antigen-specific antibody effector profiles

Antibodies are widely considered to be a frequent primary and often mechanistic correlate of protection of approved vaccines; thus evaluating the antibody response is of critical importance in attempting to understand and predict the efficacy of novel vaccine candidates. Historically, antibody responses have been analyzed by determining the titer of the humoral response using measurements such as an ELISA, neutralization, or agglutination assays. In the simplest case, sufficiently high titers of antibody against vaccine antigen(s) are sufficient to predict protection. However, antibody titer provides only a partial measure of antibody function, which is dependent on both the variable region (Fv) to bind the antigen target, and the constant region (Fc) to elicit an effector response from the innate arm of the immune system. In the case of some diseases, such as HIV, for which an effective vaccine has proven elusive, antibody effector function has been shown to be an important driver of monoclonal antibody therapy outcomes, of viral control in infected patients, and of vaccine-mediated protection in preclinical and clinical studies. We sought to establish a platform for the evaluation of the Fc domain characteristics of antigen-specific antibodies present in polyclonal samples in order to better develop insights into Fc receptor-mediated antibody effector activity, more fully understand how antibody responses may differ in association with disease progression and between subject groups, and differentiate protective from non-protective responses. To this end we have developed a high throughput biophysical platform capable of simultaneously evaluating many dimensions of the antibody effector response.

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High-throughput array-based characterization platform for polyclonal antibodies.

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Development of a biophysical proxy for antibody effector function.

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Antigen and Fc receptor recognition characteristics are captured.

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Enables systematic serologic studies of NHP and human antibody samples.

Modulating Antibody Functionality in Infectious Disease and Vaccination

Induction of pathogen-specific binding antibodies has long been considered a signature of protective immunity following vaccination and infection. The humoral immune response is a complex network of antibodies that target different specificities and drive different functions, collectively acting to limit and clear infection either directly, via pathogen neutralization, or indirectly, via pathogen clearance by the innate immune system. Emerging data suggest that not all antibody responses are equal, and qualitative features of antibodies may be key to defining protective immune profiles. Here, we review the most recent advances in our understanding of protective functional antibody responses in natural infection, vaccination, and monoclonal antibody therapeutics. Moreover, we highlight opportunities to augment or modulate antibody-mediated protection through enhancement of antibody functionality.

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.

Structural and Functional Characterization of Anti-A33 Antibodies Reveal a Potent Cross-Species Orthopoxviruses Neutralizer

Vaccinia virus A33 is an extracellular enveloped virus (EEV)-specific type II membrane glycoprotein that is essential for efficient EEV formation and long-range viral spread within the host. A33 is a target for neutralizing antibody responses against EEV. In this study, we produced seven murine anti-A33 monoclonal antibodies (MAbs) by immunizing mice with live VACV, followed by boosting with the soluble A33 homodimeric ectodomain. Five A33 specific MAbs were capable of neutralizing EEV in the presence of complement. All MAbs bind to conformational epitopes on A33 but not to linear peptides. To identify the epitopes, we have adetermined the crystal structures of three representative neutralizing MAbs in complex with A33. We have further determined the binding kinetics for each of the three antibodies to wild-type A33, as well as to engineered A33 that contained single alanine substitutions within the epitopes of the three crystallized antibodies. While the Fab of both MAbs A2C7 and A20G2 binds to a single A33 subunit, the Fab from MAb A27D7 binds to both A33 subunits simultaneously. A27D7 binding is resistant to single alanine substitutions within the A33 epitope. A27D7 also demonstrated high-affinity binding with recombinant A33 protein that mimics other orthopoxvirus strains in the A27D7 epitope, such as ectromelia, monkeypox, and cowpox virus, suggesting that A27D7 is a potent cross-neutralizer. Finally, we confirmed that A27D7 protects mice against a lethal challenge with ectromelia virus.

Microscale purification of antigen-specific antibodies

Glycosylation of the Fc domain is an important driver of antibody effector function. While assessment of antibody glycoform compositions observed across total plasma IgG has identified differences associated with a variety of clinical conditions, in many cases it is the glycosylation state of only antibodies against a specific antigen or set of antigens that may be of interest, for example, in defining the potential effector function of antibodies produced during disease or after vaccination. Historically, glycoprofiling such antigen-specific antibodies in clinical samples has been challenging due to their low prevalence, the high sample requirement for most methods of glycan determination, and the lack of high-throughput purification methods. New methods of glycoprofiling with lower sample requirements and higher throughput have motivated the development of microscale and automatable methods for purification of antigen-specific antibodies from polyclonal sources such as clinical serum samples. In this work, we present a robot-compatible 96-well plate-based method for purification of antigen-specific antibodies, suitable for such population level glycosylation screening. We demonstrate the utility of this method across multiple antibody sources, using both purified plasma IgG and plasma, and across multiple different antigen types, with enrichment factors greater than 1000-fold observed. Using an on-column IdeS protease treatment, we further describe staged release of Fc and Fab domains, allowing for glycoprofiling of each domain.

Safety and Immunogenicity of Modified Vaccinia Ankara-Bavarian Nordic Smallpox Vaccine in Vaccinia-Naive and Experienced Human Immunodeficiency Virus-Infected Individuals: An Open-Label, Controlled Clinical Phase II Trial

Background.  First- and second-generation smallpox vaccines are contraindicated in individuals infected with human immunodeficiency virus (HIV). A new smallpox vaccine is needed to protect this population in the context of biodefense preparedness. The focus of this study was to compare the safety and immunogenicity of a replication-deficient, highly attenuated smallpox vaccine modified vaccinia Ankara (MVA) in HIV-infected and healthy subjects. Methods.  An open-label, controlled Phase II trial was conducted at 36 centers in the United States and Puerto Rico for HIV-infected and healthy subjects. Subjects received 2 doses of MVA administered 4 weeks apart. Safety was evaluated by assessment of adverse events, focused physical exams, electrocardiogram recordings, and safety laboratories. Immune responses were assessed using enzyme-linked immunosorbent assay (ELISA) and a plaque reduction neutralization test (PRNT). Results.  Five hundred seventy-nine subjects were vaccinated at least once and had data available for analysis. Rates of ELISA seropositivity were comparably high in vaccinia-naive healthy and HIV-infected subjects, whereas PRNT seropositivity rates were higher in healthy compared with HIV-infected subjects. Modified vaccinia Ankara was safe and well tolerated with no adverse impact on viral load or CD4 counts. There were no cases of myo-/pericarditis reported. Conclusions.  Modified vaccinia Ankara was safe and immunogenic in subjects infected with HIV and represents a promising smallpox vaccine candidate for use in immunocompromised populations.

T cell antigen discovery using soluble vaccinia proteome reveals recognition of antigens with both virion and nonvirion association

Vaccinia virus (VACV) is a useful model system for understanding the immune response to a complex pathogen. Proteome-wide Ab profiling studies reveal the humoral response to be strongly biased toward virion-associated Ags, and several membrane proteins induce Ab-mediated protection against VACV challenge in mice. Some studies have indicated that the CD4 response is also skewed toward proteins with virion association, whereas the CD8 response is more biased toward proteins with early expression. In this study, we have leveraged a VACV strain Western Reserve (VACV-WR) plasmid expression library, produced previously for proteome microarrays for Ab profiling, to make a solubilized full VACV-WR proteome for T cell Ag profiling. Splenocytes from VACV-WR-infected mice were assayed without prior expansion against the soluble proteome in assays for Th1 and Th2 signature cytokines. The response to infection was polarized toward a Th1 response, with the distribution of reactive T cell Ags comprising both early and late VACV proteins. Interestingly, the proportions of different functional subsets were similar to that present in the whole proteome. In contrast, the targets of Abs from the same mice were enriched for membrane and other virion components, as described previously. We conclude that a "nonbiasing" approach to T cell Ag discovery reveals a T cell Ag profile in VACV that is broader and less skewed to virion association than the Ab profile. The T cell Ag mapping method developed in the present study should be applicable to other organisms where expressible "ORFeome" libraries are also available, and it is readily scalable for larger pathogens.

Human antibody responses to the polyclonal Dryvax vaccine for smallpox prevention can be distinguished from responses to the monoclonal replacement vaccine ACAM2000

Dryvax (Wyeth Laboratories, Inc., Marietta, PA) is representative of the vaccinia virus preparations that were previously used for preventing smallpox. While Dryvax was highly effective, the national supply stocks were depleted, and there were manufacturing concerns regarding sterility and the clonal heterogeneity of the vaccine. ACAM2000 (Acambis, Inc./Sanofi-Pasteur Biologics Co., Cambridge, MA), a single-plaque-purified vaccinia virus derivative of Dryvax, recently replaced the polyclonal smallpox vaccine for use in the United States. A substantial amount of sequence heterogeneity exists within the polyclonal proteome of Dryvax, including proteins that are missing from ACAM2000. Reasoning that a detailed comparison of antibody responses to the polyclonal and monoclonal vaccines may be useful for identifying unique properties of each antibody response, we utilized a protein microarray comprised of approximately 94% of the vaccinia poxvirus proteome (245 proteins) to measure protein-specific antibody responses of 71 individuals receiving a single vaccination with ACAM2000 or Dryvax. We observed robust antibody responses to 21 poxvirus proteins in vaccinated individuals, including 11 proteins that distinguished Dryvax responses from ACAM2000. Analysis of protein sequences from Dryvax clones revealed amino acid level differences in these 11 antigenic proteins and suggested that sequence variation and clonal heterogeneity may contribute to the observed differences between Dryvax and ACAM2000 antibody responses.

Immunoproteomics: current technology and applications

The varied landscape of the adaptive immune response is determined by the peptides presented by immune cells, derived from viral or microbial pathogens or cancerous cells. The study of immune biomarkers or antigens is not new and classical methods such as agglutination, enzyme-linked immunosorbent assay, or Western blotting have been used for many years to study the immune response to vaccination or disease. However, in many of these traditional techniques, protein or peptide identification has often been the bottleneck. Recent advances in genomics and proteomics, has led to many of the rapid advances in proteomics approaches. Immunoproteomics describes a rapidly growing collection of approaches that have the common goal of identifying and measuring antigenic peptides or proteins. This includes gel based, array based, mass spectrometry, DNA based, or in silico approaches. Immunoproteomics is yielding an understanding of disease and disease progression, vaccine candidates, and biomarkers. This review gives an overview of immunoproteomics and closely related technologies that are used to define the full set of antigens targeted by the immune system during disease.