Vaccinia virus strain NYVAC induces substantially lower and qualitatively different human antibody responses compared with strains Lister and Dryvax

Plaque reduction neutralization test for smallpox vaccines: Laboratory optimization and validation method for immunogenicity assessment

The eradication of smallpox, a historic triumph in global public health, was accomplished without a complete conception of the mechanisms underlying vaccine-induced protection. Contemporary concerns regarding potential bioterrorism threats and the possibility of smallpox reemergence have spurred research efforts toward developing third-generation vaccines capable of effectively neutralizing the variola virus. Clinical trials for a third-generation smallpox vaccine (KVAC103) are underway to obtain licensure. As a surrogate marker for efficacy, vaccinia virus (VACV) antibody levels can be assessed using the plaque reduction neutralization test (PRNT). In the current study, the PRNT methodology underwent comprehensive development, optimization, and validation in strict adherence to the guidelines for bioanalytical test methods. The VACV PRNT50 was optimized to include the working virus concentration (4 × 102 plaque-forming units/mL), virus-serum neutralization time (60 min), concentration of carboxymethylcellulose sodium salt overlay (1 %), and days of incubation post infection (3 days). Using human serum samples from individuals administered the second-generation smallpox vaccine (CJ-50300), the VACV PRNT50 (cut-off point, 22.58), based on the receiver-operating characteristic curve (area under the curve = 0.9859) and sensitivity and specificity assays, exhibited favorable outcomes, showing 93.75 % specificity (95 % confidence interval [CI], 71.67-99.68 %) and 93.55 % sensitivity (95 % CI, 79.28-98.85 %) against the VACV strain Western Reserve. The validation process encompassed crucial parameters, including intra-assay and inter-assay precision, robustness, dilution linearity, and the lower limit of quantification. The VACV PRNT50 exhibited high accuracy and 100 % intra-assay and inter-assay precision across various ND50 titers (high, middle, and low). Overall, the PRNT was validated as a reliable tool for measuring VACV-neutralizing antibodies and evaluating the effectiveness of new smallpox vaccinations in human serum samples.

Designing a smallpox B-cell and T-cell multi-epitope subunit vaccine using a comprehensive immunoinformatics approach

Smallpox is a highly contagious human disease caused by the variola virus. Although the disease was eliminated in 1979 due to its highly contagious nature and historical pathogenicity, with a mortality rate of up to 30%, this virus is an important candidate for biological weapons. Currently, vaccines are the critical measures to prevent this virus infection and spread. In this study, we designed a peptide vaccine using immunoinformatics tools, which have the potential to activate human immunity against variola virus infection efficiently. The design of peptides derives from vaccine-candidate proteins showing protective potential in vaccinia WR strains. Potential non-toxic and nonallergenic T-cell and B-cell binding and cytokine-inducing epitopes were then screened through a priority prediction using special linkers to connect B-cell epitopes and T-cell epitopes, and an appropriate adjuvant was added to the vaccine construction to enhance the immunogenicity of the peptide vaccine. The 3D structure display, docking, and free energy calculation analysis indicate that the binding affinity between the vaccine peptide and Toll-like receptor 3 is high, and the vaccine receptor complex is highly stable. Notably, the vaccine we designed is obtained from the protective protein of the vaccinia and combined with preventive measures to avoid side effects. This vaccine is highly likely to produce an effective and safe immune response against the variola virus infection in the body.

IMPORTANCE

In this work, we designed a vaccine with a cluster of multiple T-cell/B-cell epitopes, which should be effective in inducing systematic immune responses against variola virus infection. Besides, this work also provides a reference in vaccine design for preventing monkeypox virus infection, which is currently prevalent.

Rendezvous with Vaccinia Virus in the Post-smallpox Era: R&D Advances

Smallpox was eradicated in less than 200 years after Edward Jenner's practice of cowpox variolation in 1796. The forty-three years of us living free of smallpox, beginning in 1979, never truly separated us from poxviruses. The recent outbreak of monkeypox in May 2022 might well warn us of the necessity of keeping up both the scientific research and public awareness of poxviruses. One of them in particular, the vaccinia virus (VACV), has been extensively studied as a vector given its broad host range, extraordinary thermal stability, and exceptional immunogenicity. Unceasing fundamental biological research on VACV provides us with a better understanding of its genetic elements, involvement in cellular signaling pathways, and modulation of host immune responses. This enables the rational design of safer and more efficacious next-generation vectors. To address the new technological advancement within the past decade in VACV research, this review covers the studies of viral immunomodulatory genes, modifications in commonly used vectors, novel mechanisms for rapid generation and purification of recombinant virus, and several other innovative approaches to studying its biology.

Vaccines against monkeypox

The monkeypox virus is a virus that has 90% genomic homology with the human (smallpox), but it is naturally transmitted between different wild animal reservoirs and is considered a zoonosis. Throughout the 20th century, different vaccines based on the vaccinia poxvirus were developed and used for vaccination against smallpox. After the eradication of smallpox, these vaccines were no longer used. Current vaccines against monkeypox virus are classified by the WHO as replicative (ACAM2000), minimally replicative (LC16m8) and non-replicative (MVA-BN), the latter being the one currently used. The 2022 extra-African monkeypox virus epidemic has highlighted the lack of vaccines with proven efficacy and low reactogenicity. It is considered that the use of this vaccine in the current outbreak may play a role in the prevention or attenuation of the disease as pre-exposure prophylaxis in close contacts of confirmed cases.

Vaccines against monkeypox

The monkeypox virus is a virus that has 90% genomic homology with the human (smallpox), but it is naturally transmitted between different wild animal reservoirs and is considered a zoonosis. Throughout the 20th century, different vaccines based on the vaccinia poxvirus were developed and used for vaccination against smallpox. After the eradication of smallpox, these vaccines were no longer used. Current vaccines against monkeypox virus are classified by the WHO as replicative (ACAM2000), minimally replicative (LC16m8) and non-replicative (MVA-BN), the latter being the one currently used. The 2022 extra-African monkeypox virus epidemic has highlighted the lack of vaccines with proven efficacy and low reactogenicity. It is considered that the use of this vaccine in the current outbreak may play a role in the prevention or attenuation of the disease as pre-exposure prophylaxis in close contacts of confirmed cases.

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.

Smallpox, Monkeypox and Other Human Orthopoxvirus Infections

Considering that vaccination against smallpox with live vaccinia virus led to serious adverse effects in some cases, the WHO, after declaration of the global eradication of smallpox in 1980, strongly recommended to discontinue the vaccination in all countries. This led to the loss of immunity against not only smallpox but also other zoonotic orthopoxvirus infections in humans over the past years. An increasing number of human infections with zoonotic orthopoxviruses and, first of all, monkeypox, force us to reconsider a possible re-emergence of smallpox or a similar disease as a result of natural evolution of these viruses. The review contains a brief analysis of the results of studies on genomic organization and evolution of human pathogenic orthopoxviruses, development of modern methods for diagnosis, vaccination, and chemotherapy of smallpox, monkeypox, and other zoonotic human orthopoxvirus infections.

Monkeypox: disease epidemiology, host immunity and clinical interventions

Monkeypox virus (MPXV), which causes disease in humans, has for many years been restricted to the African continent, with only a handful of sporadic cases in other parts of the world. However, unprecedented outbreaks of monkeypox in non-endemic regions have recently taken the world by surprise. In less than 4 months, the number of detected MPXV infections has soared to more than 48,000 cases, recording a total of 13 deaths. In this Review, we discuss the clinical, epidemiological and immunological features of MPXV infections. We also highlight important research questions and new opportunities to tackle the ongoing monkeypox outbreak.

[We should be prepared to smallpox re-emergence.]

The review contains a brief analysis of the results of investigations conducted during 40 years after smallpox eradication and directed to study genomic organization and evolution of variola virus (VARV) and development of modern diagnostics, vaccines and chemotherapies of smallpox and other zoonotic orthopoxviral infections of humans. Taking into account that smallpox vaccination in several cases had adverse side effects, WHO recommended ceasing this vaccination after 1980 in all countries of the world. The result of this decision is that the mankind lost the collective immunity not only to smallpox, but also to other zoonotic orthopoxvirus infections. The ever more frequently recorded human cases of zoonotic orthopoxvirus infections force to renew consideration of the problem of possible smallpox reemergence resulting from natural evolution of these viruses. Analysis of the available archive data on smallpox epidemics, the history of ancient civilizations, and the newest data on the evolutionary relationship of orthopoxviruses has allowed us to hypothesize that VARV could have repeatedly reemerged via evolutionary changes in a zoonotic ancestor virus and then disappeared because of insufficient population size of isolated ancient civilizations. Only the historically last smallpox pandemic continued for a long time and was contained and stopped in the 20th century thanks to the joint efforts of medics and scientists from many countries under the aegis of WHO. Thus, there is no fundamental prohibition on potential reemergence of smallpox or a similar human disease in future in the course of natural evolution of the currently existing zoonotic orthopoxviruses. Correspondingly, it is of the utmost importance to develop and widely adopt state-of-the-art methods for efficient and rapid species-specific diagnosis of all orthopoxvirus species pathogenic for humans, VARV included. It is also most important to develop new safe methods for prevention and therapy of human orthopoxvirus infections.

Modulating Vaccinia Virus Immunomodulators to Improve Immunological Memory

The increasing frequency of monkeypox virus infections, new outbreaks of other zoonotic orthopoxviruses and concern about the re-emergence of smallpox have prompted research into developing antiviral drugs and better vaccines against these viruses. This article considers the genetic engineering of vaccinia virus (VACV) to enhance vaccine immunogenicity and safety. The virulence, immunogenicity and protective efficacy of VACV strains engineered to lack specific immunomodulatory or host range proteins are described. The ultimate goal is to develop safer and more immunogenic VACV vaccines that induce long-lasting immunological memory.

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.

40 Years without Smallpox

The last case of natural smallpox was recorded in October, 1977. It took humanity almost 20 years to achieve that feat after the World Health Organization had approved the global smallpox eradication program. Vaccination against smallpox was abolished, and, during the past 40 years, the human population has managed to lose immunity not only to smallpox, but to other zoonotic orthopoxvirus infections as well. As a result, multiple outbreaks of orthopoxvirus infections in humans in several continents have been reported over the past decades. The threat of smallpox reemergence as a result of evolutionary transformations of these zoonotic orthopoxviruses exists. Modern techniques for the diagnostics, prevention, and therapy of smallpox and other orthopoxvirus infections are being developed today.

Are We Prepared in Case of a Possible Smallpox-Like Disease Emergence?

Smallpox was the first human disease to be eradicated, through a concerted vaccination campaign led by the World Health Organization. Since its eradication, routine vaccination against smallpox has ceased, leaving the world population susceptible to disease caused by orthopoxviruses. In recent decades, reports of human disease from zoonotic orthopoxviruses have increased. Furthermore, multiple reports of newly identified poxviruses capable of causing human disease have occurred. These facts raise concerns regarding both the opportunity for these zoonotic orthopoxviruses to evolve and become a more severe public health issue, as well as the risk of Variola virus (the causative agent of smallpox) to be utilized as a bioterrorist weapon. The eradication of smallpox occurred prior to the development of the majority of modern virological and molecular biological techniques. Therefore, there is a considerable amount that is not understood regarding how this solely human pathogen interacts with its host. This paper briefly recounts the history and current status of diagnostic tools, vaccines, and anti-viral therapeutics for treatment of smallpox disease. The authors discuss the importance of further research to prepare the global community should a smallpox-like virus emerge.

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.

Virus-vectored influenza virus vaccines

Despite the availability of an inactivated vaccine that has been licensed for >50 years, the influenza virus continues to cause morbidity and mortality worldwide. Constant evolution of circulating influenza virus strains and the emergence of new strains diminishes the effectiveness of annual vaccines that rely on a match with circulating influenza strains. Thus, there is a continued need for new, efficacious vaccines conferring cross-clade protection to avoid the need for biannual reformulation of seasonal influenza vaccines. Recombinant virus-vectored vaccines are an appealing alternative to classical inactivated vaccines because virus vectors enable native expression of influenza antigens, even from virulent influenza viruses, while expressed in the context of the vector that can improve immunogenicity. In addition, a vectored vaccine often enables delivery of the vaccine to sites of inductive immunity such as the respiratory tract enabling protection from influenza virus infection. Moreover, the ability to readily manipulate virus vectors to produce novel influenza vaccines may provide the quickest path toward a universal vaccine protecting against all influenza viruses. This review will discuss experimental virus-vectored vaccines for use in humans, comparing them to licensed vaccines and the hurdles faced for licensure of these next-generation influenza virus vaccines.

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.

Understanding the immune response to seasonal influenza vaccination in older adults: a systems biology approach

Annual vaccination against seasonal influenza is recommended to decrease disease-related mortality and morbidity. However, one population that responds suboptimally to influenza vaccine is adults over the age of 65 years. The natural aging process is associated with a complex deterioration of multiple components of the host immune system. Research into this phenomenon, known as immunosenescence, has shown that aging alters both the innate and adaptive branches of the immune system. The intricate mechanisms involved in immune response to influenza vaccine, and how these responses are altered with age, have led us to adopt a more encompassing systems biology approach to understand exactly why the response to vaccination diminishes with age. Here, the authors review what changes occur with immunosenescence, and some immunogenetic factors that influence response, and outline the systems biology approach to understand the immune response to seasonal influenza vaccination in older adults.

Humoral immunity to smallpox vaccines and monkeypox virus challenge: proteomic assessment and clinical correlations

Despite the eradication of smallpox, orthopoxviruses (OPV) remain public health concerns. Efforts to develop new therapeutics and vaccines for smallpox continue through their evaluation in animal models despite limited understanding of the specific correlates of protective immunity. Recent monkeypox virus challenge studies have established the black-tailed prairie dog (Cynomys ludovicianus) as a model of human systemic OPV infections. In this study, we assess the induction of humoral immunity in humans and prairie dogs receiving Dryvax, Acam2000, or Imvamune vaccine and characterize the proteomic profile of immune recognition using enzyme-linked immunosorbent assays (ELISA), neutralization assays, and protein microarrays. We confirm anticipated similarities of antigenic protein targets of smallpox vaccine-induced responses in humans and prairie dogs and identify several differences. Subsequent monkeypox virus intranasal infection of vaccinated prairie dogs resulted in a significant boost in humoral immunity characterized by a shift in reactivity of increased intensity to a broader range of OPV proteins. This work provides evidence of similarities between the vaccine responses in prairie dogs and humans that enhance the value of the prairie dog model system as an OPV vaccination model and offers novel findings that form a framework for examining the humoral immune response induced by systemic orthopoxvirus infection.

Targeting 4-1BB (CD137) to enhance CD8 T cell responses with poxviruses and viral antigens

Attenuated vaccinia virus (VACV) vectors are considered prime vaccine candidates for use in immunotherapy of infectious disease. In spite of this, recent data show that the level of attenuation may hamper the efficient generation of protective CD8 T cells. This suggests that additional adjuvant-like activities may need to be combined with attenuated VACV for optimal vaccination. Stimulatory reagents to the TNFR family molecule 4-1BB (CD137) may represent such an adjuvant for vaccination. Previous murine studies have found that 4-1BB can participate in optimal priming of effector and memory CD8 T cells in response to several virus infections, and concordantly direct stimulation of 4-1BB with agonist reagents effectively boosts the CD8 T cell response against those viruses. In contrast, we recently reported that 4-1BB plays no role in the response to a virulent strain of VACV, questioning whether agonists of 4-1BB will be useful adjuvants for vaccination with VACV vectors. Here we show that agonist anti-4-1BB strongly enhanced the primary viral-specific effector CD8 T cell response during infection with live virulent VACV and attenuated VACV, and during immunization with VACV peptides given in IFA. However, accumulation of memory CD8 T cells was enhanced only following infection with virulent VACV or with peptide vaccination, but not with attenuated VACV, correlating in part with more transient expression of 4-1BB on CD8 T cells with attenuated virus. Our data therefore suggest that 4-1BB may be a promising candidate for targeting as an adjuvant for short-term enhancement of CD8 T cell responses with VACV vaccine strategies, but additional receptors may need to be engaged with 4-1BB to allow long-term CD8 T cell immunity with attenuated VACV vectors.

A vaccinia virus renaissance: new vaccine and immunotherapeutic uses after smallpox eradication

In 1796, Edward Jenner introduced the concept of vaccination with cowpox virus, an Orthopoxvirus within the family Poxviridae that elicits cross protective immunity against related orthopoxviruses, including smallpox virus (variola virus). Over time, vaccinia virus (VACV) replaced cowpox virus as the smallpox vaccine, and vaccination efforts eventually led to the successful global eradication of smallpox in 1979. VACV has many characteristics that make it an excellent vaccine and that were crucial for the successful eradication of smallpox, including (1) its exceptional thermal stability (a very important but uncommon characteristic in live vaccines), (2) its ability to elicit strong humoral and cell-mediated immune responses, (3) the fact that it is easy to propagate, and (4) that it is not oncogenic, given that VACV replication occurs exclusively within the host cell cytoplasm and there is no evidence that the viral genome integrates into the host genome. Since the eradication of smallpox, VACV has experienced a renaissance of interest as a viral vector for the development of recombinant vaccines, immunotherapies, and oncolytic therapies, as well as the development of next-generation smallpox vaccines. This revival is mainly due to the successful use and extensive characterization of VACV as a vaccine during the smallpox eradication campaign, along with the ability to genetically manipulate its large dsDNA genome while retaining infectivity and immunogenicity, its wide mammalian host range, and its natural tropism for tumor cells that allows its use as an oncolytic vector. This review provides an overview of new uses of VACV that are currently being explored for the development of vaccines, immunotherapeutics, and oncolytic virotherapies.

Safety and immunogenicity of LC16m8, an attenuated smallpox vaccine in vaccinia-naive adults

INTRODUCTION

LC16m8 is an attenuated cell culture-adapted Lister vaccinia smallpox vaccine missing the B5R protein and licensed for use in Japan.

METHODS

We conducted a phase I/II clinical trial that compared the safety and immunogenicity of LC16m8 with Dryvax in vaccinia-naive participants. Adverse events were assessed, as were electrocardiography and laboratory testing for cardiotoxicity and viral culturing of the vaccination sites. Neutralization titers to vaccinia, monkeypox, and variola major were assessed and cell-mediated immune responses were measured by interferon (IFN)-γ enzyme-linked immunosorbent spot and lymphoproliferation assays.

RESULTS

Local and systemic reactions after vaccination with LC16m8 were similar to those reported after Dryvax. No clinically significant abnormalities consistent with cardiac toxicity were seen for either vaccine. Both vaccines achieved antivaccinia, antivariola, and antimonkeypox neutralizing antibody titers >1:40, although the mean plaque reduction neutralization titer of LC16m8 at day 30 after vaccination was significantly lower than Dryvax for anti-NYCBH vaccinia (P < .01), antimonkeypox (P < .001), and antivariola (P < .001). LC16m8 produced robust cellular immune responses that trended higher than Dryvax for lymphoproliferation (P = .06), but lower for IFN-γ ELISPOT (P = .02).

CONCLUSIONS

LC16m8 generates neutralizing antibody titers to multiple poxviruses, including vaccinia, monkeypox, and variola major, and broad T-cell responses, indicating that LC16m8 may have efficacy in protecting individuals from smallpox. Clinical Trials Registration. NCT00103584.

Serological responses in humans to the smallpox vaccine LC16m8

In response to potential bioterrorism with smallpox, members of the Japanese Self-Defense Forces were vaccinated with vaccinia virus (VACV) strain LC16m8, an attenuated smallpox vaccine derived from VACV strain Lister. The serological response induced by LC16m8 to four virion-surface proteins and the intracellular mature virus (IMV) and extracellular enveloped virus (EEV) was investigated. LC16m8 induced antibody response against the IMV protein A27 and the EEV protein A56. LC16m8 also induced IMV-neutralizing antibodies, but unlike the VACV strain Lister, did not induce either EEV-neutralizing antibody or antibody to EEV protein B5, except after revaccination. Given that B5 is the only target for EEV-neutralizing antibody and that neutralization of both IMV and EEV give optimal protection against orthopoxvirus challenge, these data suggest that immunity induced by LC16m8 might be less potent than that deriving from strain Lister. This potential disadvantage should be balanced against the advantage of the greater safety of LC16m8.

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

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

The TNFR family members OX40 and CD27 link viral virulence to protective T cell vaccines in mice

Induction of CD8+ T cell immunity is a key characteristic of an effective vaccine. For safety reasons, human vaccination strategies largely use attenuated nonreplicating or weakly replicating poxvirus-based vectors, but these often elicit poor CD8+ T cell immunity and might not result in optimal protection. Recent studies have suggested that virulence is directly linked to immunogenicity, but the molecular mechanisms underlying optimal CD8+ T cell responses remain to be defined. Here, using natural and recombinant vaccinia virus (VACV) strains, we have shown in mice that VACV strains of differing virulence induce distinct levels of T cell memory because of the differential use of TNF receptor (TNFR) family costimulatory receptors. With strongly replicating (i.e., virulent) VACV, the TNFR family costimulatory receptors OX40 (also known as CD134) and CD27 were engaged and promoted the generation of high numbers of memory CD8+ T cells, which protected against a lethal virus challenge in the absence of other mechanisms, including antibody and help from CD4+ T cells. In contrast, weakly replicating (i.e., low-virulence) VACV strains were poor at eliciting protective CD8+ T cell memory, as only the Ig family costimulatory receptor CD28 was engaged, and not OX40 or CD27. Our results suggest that the virulence of a virus dictates costimulatory receptor usage to determine the level of protective CD8+ T cell immunity.

Smallpox vaccine with integrated IL-15 demonstrates enhanced in vivo viral clearance in immunodeficient mice and confers long term protection against a lethal monkeypox challenge in cynomolgus monkeys

Despite the eradication of smallpox, there is heightened concern that it could be reintroduced as a result of intentional release of Variola major virus through an act of bioterrorism. The live vaccine that was pivotal in the eradication of smallpox though considered a gold standard for its efficacy still retains sufficient residual virulence that can cause life-threatening sequelae especially in immune deficient individuals. Therefore, a safer smallpox vaccine that can match the efficacy of first generation vaccines is urgently needed. We previously reported that the integration of human IL-15 cytokine into the genome of Wyeth strain of vaccinia (Wyeth/IL-15), the same strain as the licensed vaccine, generates a vaccine with superior immunogenicity and efficacy in a mouse model. We now demonstrate that Wyeth/IL-15 is non-lethal to athymic nude mice when administered intravenously at a dose of 10(7) plaque forming units and it undergoes enhanced in vivo clearance in these immune deficient mice. Furthermore, a majority of cynomolgus monkeys vaccinated with vaccinia viruses with integrated IL-15, when challenged 3 years later with a lethal dose of monkeypox virus displayed milder clinical manifestations with complete recovery supporting the utility of Wyeth/IL-15 for contemporary populations as a safer and efficacious smallpox vaccine.

Third-generation smallpox vaccines: challenges in the absence of clinical smallpox

Smallpox, a disease caused by variola virus, is estimated to have killed hundreds of millions to billions of people before it was certified as eradicated in 1980. However, there has been renewed interest in smallpox vaccine development due in part to zoonotic poxvirus infections and the possibility of a re-emergence of smallpox, as well as the fact that first-generation smallpox vaccines are associated with relatively rare, but severe, adverse reactions in some vaccinees. An understanding of the immune mechanisms of vaccine protection and the use of suitable animal models for vaccine efficacy assessment are paramount to the development of safer and effective smallpox vaccines. This article focuses on studies aimed at understanding the immune responses elicited by vaccinia virus and the various animal models that can be used to evaluate smallpox vaccine efficacy. Harnessing this information is necessary to assess the effectiveness and potential usefulness of new-generation smallpox vaccines.

Introduction of the six major genomic deletions of modified vaccinia virus Ankara (MVA) into the parental vaccinia virus is not sufficient to reproduce an MVA-like phenotype in cell culture and in mice

Modified vaccinia virus Ankara (MVA) has a highly restricted host range in cell culture and is apathogenic in vivo. MVA was derived from the parental chorioallantois vaccinia virus Ankara (CVA) by more than 570 passages in chicken embryo fibroblast (CEF) cells. During CEF cell passaging, six major deletions comprising 24,668 nucleotides occurred in the CVA genome. We have cloned both the MVA and the parental CVA genome as bacterial artificial chromosomes (BACs) and have sequentially introduced the six major MVA deletions into the cloned CVA genome. Reconstituted mutant CVA viruses containing up to six major MVA deletions showed no detectable replication restriction in 12 of 14 mammalian cell lines tested; the exceptions were rabbit cell lines RK13 and SIRC. In mice, CVA mutants with up to three deletions showed slightly enhanced virulence, suggesting that gene deletion in replicating vaccinia virus (VACV) can result in gain of fitness in vivo. CVA mutants containing five or all six deletions were still pathogenic, with a moderate degree of attenuation. Deletion V was mainly responsible for the attenuated phenotype of these mutants. In conclusion, loss or truncation of all 31 open reading frames in the six major deletions is not sufficient to reproduce the specific MVA phenotype of strong attenuation and highly restricted host range. Mutations in viral genes outside or in association with the six major deletions appear to contribute significantly to this phenotype. Host range restriction and avirulence of MVA are most likely a cooperative effect of gene deletions and mutations involving the major deletions.

Safety and immunogenicity of modified vaccinia Ankara (ACAM3000): effect of dose and route of administration

BACKGROUND

We conducted a clinical trial of the safety and immunogenicity of modified vaccinia Ankara (MVA) to examine the effects of dose and route of administration.

METHODS

Seventy-two healthy, vaccinia virus-naive subjects received 1 of 6 regimens of MVA (ACAM3000) or placebo consisting of 2 administrations given 1 month apart.

RESULTS

MVA was generally well tolerated at all dose levels and by all routes. More pronounced local reactogenicity was seen with the intradermal and subcutaneous routes than with intramuscular administration. Binding antibodies to whole virus and neutralizing antibodies to the intracellular mature virion and extracellular enveloped virion forms of vaccinia virus were elicited by all routes of MVA administration and were greater for the higher dose by each route. Similar levels of neutralizing antibodies were seen at a 10-fold-lower dose given intradermally (1 x 10(7) median tissue culture infective doses [TCID(50)]), compared with responses after 1 x 10(8) TCID(50) given intramuscularly or subcutaneously. T cell immune responses to vaccinia virus were detected by an interferon gamma enzyme-linked immunospot assay but had no clear relationship to dose or route.

CONCLUSIONS

These data suggest that intradermal immunization with MVA provides a dose-sparing effect by eliciting antibody responses similar in magnitude and kinetics to those elicited by the intramuscular or subcutaneous routes but at a 10-fold-lower dose.

Uncovering the interplay between CD8, CD4 and antibody responses to complex pathogens

Vaccinia virus (VACV) was used as the vaccine strain to eradicate smallpox. VACV is still administered to healthcare workers or researchers who are at risk of contracting the virus, and to military personnel. Thus, VACV represents a weapon against outbreaks, both natural (e.g., monkeypox) or man-made (bioterror). This virus is also used as a vector for experimental vaccine development (cancer/infectious disease). As a prototypic poxvirus, VACV is a model system for studying host-pathogen interactions. Until recently, little was known about the targets of host immune responses, which was likely owing to VACVs large genome (>200 open reading frames). However, the last few years have witnessed an explosion of data, and VACV has quickly become a useful model to study adaptive immune responses. This review summarizes and highlights key findings based on identification of VACV antigens targeted by the immune system (CD4, CD8 and antibodies) and the complex interplay between responses.

Viruses as vaccine vectors for infectious diseases and cancer

Recent developments in the use of viruses as vaccine vectors have been facilitated by a better understanding of viral biology. Advances occur as we gain greater insight into the interrelationship of viruses and the immune system. Viral-vector vaccines remain the best means to induce cellular immunity and are now showing promise for the induction of strong humoral responses. The potential benefits for global health that are offered by this field reflect the scope and utility of viruses as vaccine vectors for human and veterinary applications, with targets ranging from certain types of cancer to a vast array of infectious diseases.

Smallpox vaccines for biodefense

Few diseases can match the enormous impact that smallpox has had on mankind. Its influence can be seen in the earliest recorded histories of ancient civilizations in Egypt and Mesopotamia. With fatality rates up to 30%, smallpox left its survivors with extensive scarring and other serious sequelae. It is estimated that smallpox killed 500 million people in the 19th and 20th centuries. Given the ongoing concerns regarding the use of variola as a biological weapon, this review will focus on the licensed vaccines as well as current research into next-generation vaccines to protect against smallpox and other poxviruses.

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.