Smallpox vaccine: problems and prospects

Prevention of monkeypox with vaccines: a rapid review

The largest outbreak of monkeypox in history began in May, 2022, and has rapidly spread across the globe ever since. The purpose of this Review is to briefly describe human immune responses to orthopoxviruses; provide an overview of the vaccines available to combat this outbreak; and discuss the various clinical data and animal studies evaluating protective immunity to monkeypox elicited by vaccinia virus-based smallpox vaccines, address ongoing concerns regarding the outbreak, and provide suggestions for the appropriate use of vaccines as an outbreak control measure. Data showing clinical effectiveness (~85%) of smallpox vaccines against monkeypox come from surveillance studies conducted in central Africa in the 1980s and later during outbreaks in the same area. These data are supported by a large number of animal studies (primarily in non-human primates) with live virus challenge by various inoculation routes. These studies uniformly showed a high degree of protection and immunity against monkeypox virus following vaccination with various smallpox vaccines. Smallpox vaccines represent an effective countermeasure that can be used to control monkeypox outbreaks. However, smallpox vaccines do cause side-effects and the replication-competent, second-generation vaccines have contraindications. Third-generation vaccines, although safer for use in immunocompromised populations, require two doses, which is an impediment to rapid outbreak response. Lessons learned from the COVID-19 pandemic should be used to inform our collective response to this monkeypox outbreak and to future outbreaks.

Primary Human B Cells at Different Differentiation and Maturation Stages Exhibit Distinct Susceptibilities to Vaccinia Virus Binding and Infection

Vaccinia virus (VACV), the prototypical member of the poxvirus family, was used as a live-virus vaccine to eradicate smallpox worldwide and has recently received considerable attention because of its potential as a prominent vector for the development of vaccines against infectious diseases and as an oncolytic virus for cancer therapy. Studies have demonstrated that VACV exhibits an extremely strong bias for binding to and infection of primary human antigen-presenting cells (APCs), including monocytes, macrophages, and dendritic cells. However, very few studies have assessed the interactions of VACV with primary human B cells, a main type of professional APCs. In this study, we evaluated the susceptibility of primary human peripheral B cells at various differentiation and maturation stages to VACV binding, infection, and replication. We found that plasmablasts were resistant to VACV binding, while other B subsets, including transitional, mature naive, memory, and plasma cells, were highly susceptible to VACV binding. VACV binding preference was likely associated with differential expression of chemokine receptors, particularly CXCR5. Infection studies showed that plasmablast, plasma, transitional, and mature naive B cells were resistant to VACV infection, while memory B cells were preferentially infected. VACV infection in ex vivo B cells was abortive, which occurred at the stage of late viral gene expression. In contrast, activated B cells were permissive to productive VACV infection. Thus, primary human B cells at different differentiation stages exhibit distinct susceptibilities to VACV binding and infection, and the infections are abortive and productive in ex vivo and activated B cells, respectively.IMPORTANCE Our results provide critical information to the field of poxvirus binding and infection tropism. We demonstrate that VACV preferentially infects memory B cells that play an important role in a rapid and vigorous antibody-mediated immune response upon reinfection by a pathogen. Additionally, this work highlights the potential of B cells as natural cellular models to identify VACV receptors or dissect the molecular mechanisms underlying key steps of the VACV life cycle, such as binding, penetration, entry, and replication in primary human cells. The understanding of VACV biology in human primary cells is essential for the development of a safe and effective live-virus vector for oncolytic virus therapy and vaccines against smallpox, other pathogens, and cancer.

Combinatorial Approach of Antigen Delivery Using M Cell-Homing Peptide and Mucoadhesive Vehicle to Enhance the Efficacy of Oral Vaccine

Orally ingested pathogens or antigens are taken up by microfold cells (M cells) in Peyer's patches of intestine to initiate protective immunity against infections. However, the uptake of orally delivered protein antigens through M cells is very low due to lack of specificity of proteins toward M cells and degradation of proteins in the harsh environment of gastrointestinal (GI) tract. To overcome these limitations, here we developed a pH-sensitive and mucoadhesive vehicle of thiolated eudragit (TE) microparticles to transport an M cell-targeting peptide-fused model protein antigen. Particularly, TE prolonged the particles transit time through the GI tract and predominantly released the proteins in ileum where M cells are abundant. Thus, oral delivery of TE microparticulate antigens exhibited high transcytosis of antigens through M cells resulting in strong protective sIgA as well as systemic IgG antibody responses. Importantly, the delivery system not only induced CD4(+) T cell immune responses but also generated strong CD8(+) T cell responses with enhanced production of IFN-γ in spleen. Given that M cells are considered a promising target for oral vaccination, this study could provide a new combinatorial method for the development of M-cell-targeted mucosal vaccines.

Adversomics: a new paradigm for vaccine safety and design

Despite the enormous population benefits of routine vaccination, vaccine adverse events (AEs) and reactions, whether real or perceived, have posed one of the greatest barriers to vaccine acceptance--and thus to infectious disease prevention--worldwide. A truly integrated clinical, translational, and basic science approach is required to understand the mechanisms behind vaccine AEs, predict them, and then apply this knowledge to new vaccine design approaches that decrease, or avoid, these events. The term 'adversomics' was first introduced in 2009 and refers to the study of vaccine adverse reactions using immunogenomics and systems biology approaches. In this review, we present the current state of adversomics research, review known associations and mechanisms of vaccine AEs/reactions, and outline a plan for the further development of this emerging research field.

Discovery of naturally processed and HLA-presented class I peptides from vaccinia virus infection using mass spectrometry for vaccine development

An important approach for developing a safer smallpox vaccine is to identify naturally processed immunogenic vaccinia-derived peptides rather than live whole vaccinia virus. We used two-dimensional liquid chromatography coupled to mass spectrometry to identify 116 vaccinia peptides, encoded by 61 open reading frames, from a B-cell line (homozygous for HLA class I A*0201, B*1501, and C*03) after infection with vaccinia virus (Dryvax). Importantly, 68 of these peptides are conserved in variola, providing insight into the peptides that induce protection against smallpox. Twenty-one of these 68 conserved peptides were 11 amino acids long or longer, outside of the range of most predictive algorithms. Thus, direct identification of naturally processed and presented HLA peptides gives important information not provided by current computational methods for identifying potential vaccinia epitopes.

Statistical approach to estimate vaccinia-specific neutralizing antibody titers using a high-throughput assay

Because of the bioterrorism threat posed by agents such as variola virus, considerable time, resources, and effort have been devoted to biodefense preparation. One avenue of this research has been the development of rapid, sensitive, high-throughput assays to validate immune responses to poxviruses. Here we describe the adaptation of a beta-galactosidase reporter-based vaccinia virus neutralization assay to large-scale use in a study that included over 1,000 subjects. We also describe the statistical methods involved in analyzing the large quantity of data generated. The assay and its associated methods should prove useful tools in monitoring immune responses to next-generation smallpox vaccines, studying poxvirus immunity, and evaluating therapeutic agents such as vaccinia virus immune globulin.

Coadministration of cidofovir and smallpox vaccine reduced vaccination side effects but interfered with vaccine-elicited immune responses and immunity to monkeypox

While the smallpox vaccine, Dryvax or Dryvax-derived ACAM2000, holds potential for public immunization against the spread of smallpox by bioterror, there is serious concern about Dryvax-mediated side effects. Here, we report that a single-dose vaccination regimen comprised of Dryvax and an antiviral agent, cidofovir, could reduce vaccinia viral loads after vaccination and significantly control Dryvax vaccination side effects. However, coadministration of cidofovir and Dryvax also reduced vaccine-elicited immune responses of antibody and T effector cells despite the fact that the reduced priming could be boosted as a recall response after monkeypox virus challenge. Evaluations of four different aspects of vaccine efficacy showed that coadministration of cidofovir and Dryvax compromised the Dryvax-induced immunity against monkeypox, although the covaccinated monkeys exhibited measurable protection against monkeypox compared to that of naïve controls. Thus, the single-dose coadministration of cidofovir and Dryvax effectively controlled vaccination side effects but significantly compromised vaccine-elicited immune responses and vaccine-induced immunity to monkeypox.

ACAM2000: a newly licensed cell culture-based live vaccinia smallpox vaccine

BACKGROUND

Due to concern over i) expiration of currently available calf-lymph vaccine (Dryvax); ii) calf lymph as a vaccine (bovine spongiform encephalopathy [BSE], other possible contaminations and animal welfare); and iii) use of variola as a weapon for bioterrorism, a new and safer vaccinia-based smallpox vaccine derived from new cell culture-based technology was proposed. Federally funded work by Acambis, Inc. resulted in FDA approval for ACAM2000 in August 2007.

OBJECTIVES

This paper describes the development from conception to FDA approval of the new vaccinia cell cultured-based smallpox vaccine ACAM2000.

METHODS

Data were compiled from available public reports.

RESULTS/CONCLUSIONS

The studies with ACAM2000 indicate that it closely matches the safety of Dryvax in both non-clinical and clinical trials. ACAM2000 met two of the four primary surrogate efficacy end point criteria established for the Phase III clinical trials. Concern over the incidence of myopericarditis with ACAM2000 and Dryvax exists. So far the cardiac events seem to be self-limited. There are no pediatric safety data for ACAM2000. Overall, clinical trial results were sufficient to convince the FDA that ACAM2000 is a suitable replacement for Dryvax in the event of bioterrorism involving variola (smallpox).

T-Cell epitope discovery for variola and vaccinia viruses

Variola major, the causative agent of smallpox, afflicted mankind throughout history until the worldwide World Health Organisation WHO vaccination campaign successfully eradicated the disease. Unfortunately, recent concerns about bioterrorism have renewed scientific interest in this virus. One essential component of our biodefense and preparedness efforts is an understanding of poxvirus immunity. To this end a number of laboratories have sought to discover T- and B-Cell epitopes from select agents such as variola virus. This review focuses on the efforts to identify CD8(+) T-Cell epitopes from poxviruses as a means to develop new vaccines and therapeutics. A wide variety of techniques have been employed by several research groups to provide complementary information regarding cellular immune responses to poxviruses. In the last several years well over 100 T-Cell epitopes have been identified and the work rapidly continues. The information gleaned from these studies will not only give us a greater understanding of immunity to variola virus and other viruses, but also provide a foundation for next generation vaccines and additional tools with which to study host-pathogen interactions.

Particulate delivery systems for biodefense subunit vaccines

Expanding identification of potentially protective subunit antigens and correlates of protection has provided a basis for the introduction of safer vaccines. Despite encouraging results in animal models, the significant potential of particulate delivery systems in vaccine design has not yet translated into effective vaccines available for use in humans. This review article will focus on the current status of the development of particulate vaccines, mainly liposomes and bio-degradable polymers, against potential agents for biowarfare: plague, anthrax, botulinum, and smallpox; and filoviruses: Marburg and Ebola.

Rethinking smallpox

The potential consequences of a competently executed smallpox attack have not been adequately considered by policy makers. The possibility of release of an aerosolized and/or bioengineered virus must be anticipated and planned for. The transmission and infectivity of variola virus are examined. Arguments for and against pre-event vaccination are offered. The likely morbidity and mortality that would ensue from implementation of a mass pre-event vaccination program, within reasonable boundaries, are known. The extent of contagion that could result from an aerosolized release of virus is unknown and may have been underestimated. Pre-event vaccination of first responders is urged, and voluntary vaccination programs should be offered to the public. Two defenses against a vaccine-resistant, engineered variola virus are proposed for consideration. Methisazone, an overlooked drug, is reported to be effective for prophylaxis only. The extent of reduction in the incidence of smallpox with use of this agent is uncertain. It is useless for treatment of clinical smallpox. N-100 respirators (face masks) worn by uninfected members of the public may prevent transmission of the virus.

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