Shared modes of protection against poxvirus infection by attenuated and conventional smallpox vaccine viruses

Immune responses associated with mpox viral clearance in men with and without HIV in Spain: a multisite, observational, prospective cohort study

BACKGROUND

Since the emergence of the global mpox outbreak in May, 2022, more than 90 000 cases have been diagnosed across 110 countries, disproportionately affecting people with HIV. The durability of mpox-specific immunity is unclear and reinfections have been reported. We aimed to compare mpox immune responses up to 6 months after diagnosis in participants with and without HIV and assess their effect on disease severity and viral clearance dynamics.

METHODS

This study was embedded within a prospective, observational, multicentre cohort study of viral clearance dynamics among people with mpox in Spain (MoViE). We included women and men aged 18 years or older, who had signs of mpox, and reported having symptom onset within the previous 10 days at the moment of mpox diagnosis from three sex clinics of the Barcelona metropolitan area. Samples from skin ulcers were collected weekly to estimate the time to clear monkeypox virus (MPXV) from skin lesions. Blood samples were taken at diagnosis, 29, 91, and 182 days later for immune analysis. This included quantifying IgG and IgA against three mpox antigens by ELISA, evaluating in-vitro neutralisation, and characterising mpox-specific T-cell responses using interferon γ detecting enzyme-linked immunospot (ELISpot) assay and multiparametric flow cytometry.

FINDINGS

Of the 77 originally enrolled participants, we included 33 participants recruited between July 19, and Oct 6, 2022. Participants without HIV (19 [58%] participants) and participants with HIV (14 [42%] participants) had similar clinical severity and time to MPXV clearance in skin lesions. Participants with HIV had a CD4+ T-cell count median of 777 cells per μL (IQR 484-1533), and 11 (78%) of 14 were virally suppressed on antiretroviral therapy. Nine (27%) of 33 participants were age 49 years or older. 15 (45%) of 33 participants were originally from Spain, and all participants were men. Early humoral responses, particularly concentrations and breadth of IgG and IgA, were associated with milder disease and faster viral clearance. Orthopoxvirus-specific T cells count was also positively correlated with MPXV clearance. Antibody titres declined more rapidly in participants with HIV, but T-cell responses against MPXV were sustained up to day 182 after diagnosis, regardless of HIV status.

INTERPRETATION

Higher breadth and magnitude of B-cell and T-cell responses are important in facilitating local viral clearance, limiting mpox dissemination, and reducing disease severity in individuals with preserved immune system. Antibodies appear to contribute to early viral control and T-cell responses are sustained over time, which might contribute to milder presentations during reinfection.

FUNDING

Fundació Lluita contra les Infeccions, IrsiCaixa, and Consorcio Centro de Investigación Biomédica en Red, Instituto de Salud Carlos III, Ministerio de Ciencia, Innovación e Universidades.

Long-lasting humoral and cellular memory immunity to vaccinia virus Tiantan provides pre-existing immunity against mpox virus in Chinese population

Investigating immune memory to vaccinia virus and pre-existing immunity to mpox virus (MPXV) among the population is crucial for the global response to this ongoing mpox epidemic. Blood was sampled from vaccinees inoculated with vaccinia virus Tiantan (VTT) strain born before 1981 and unvaccinated control subjects born since 1982. After at least 40 years of the inoculation, 60% or 5% VTT vaccinees possess neutralizing antibodies (NAbs) to VTT or MPXV, with at least 50% having T cell memory to VTT protein antigens. Notably, 46.7% vaccinees show pre-existing T cell responses to MPXV. Broad pre-existing CD8+ T cell reactivities to MPXV are detected not only against conserved epitopes but also against variant epitopes between VTT and MPXV. Persistent NAbs and T cell memory to VTT among vaccinees, along with pre-existing T cells to MPXV among both vaccinees and the unvaccinated population, indicate a particular immune barrier to mpox.

Characterizing the acute antibody response of monkeypox and MVA-BN vaccine following an Australian outbreak

In response to the emergence of the monkeypox virus (MPXV) in Australia in May 2022, we developed and evaluated indirect immunofluorescence assays (IFA) for MPXV and Vaccinia virus (VACV) IgG and IgM antibodies using serum samples from patients with nucleic acid amplification test (NAAT)-confirmed mpox and uninfected unvaccinated controls. Additionally, 47 healthcare workers receiving two doses of the third-generation smallpox vaccine Modified Vaccinia Ankara-Bavarian Nordic (MVA-BN) undertook serial serum collection to describe the serological response to vaccination. MPXV antibodies were detected in 16/18 individuals with NAAT-confirmed mpox (sensitivity 0.89, specificity 1.00), and VACV antibodies were detected in 28/29 individuals who received two doses of MVA-BN vaccine (sensitivity 0.97, specificity 1.00). Detectable antibody in subjects historically vaccinated with early-generation vaccines against smallpox was found in 7/7 subjects, at a median of 48 years following vaccination. MPXV NAAT-positive patients with serum samples collected within the first 14 days after rash onset had detectable IgG and IgM in 9/12 and 5/12 of patients, respectively, with maintenance of IgG and disappearance of IgM titers after 60 days. While specificity was high when testing unvaccinated and uninfected subjects, significant cross-reactivity between MPXV and VACV antibodies was observed.

Construction of a recombinant vaccine expressing Nipah virus glycoprotein using the replicative and highly attenuated vaccinia virus strain LC16m8

Nipah virus (NiV) is a highly pathogenic zoonotic virus that causes severe encephalitis and respiratory diseases and has a high mortality rate in humans (>40%). Epidemiological studies on various fruit bat species, which are natural reservoirs of the virus, have shown that NiV is widely distributed throughout Southeast Asia. Therefore, there is an urgent need to develop effective NiV vaccines. In this study, we generated recombinant vaccinia viruses expressing the NiV glycoprotein (G) or fusion (F) protein using the LC16m8 strain, and examined their antigenicity and ability to induce immunity. Neutralizing antibodies against NiV were successfully induced in hamsters inoculated with LC16m8 expressing NiV G or F, and the antibody titers were higher than those induced by other vaccinia virus vectors previously reported to prevent lethal NiV infection. These findings indicate that the LC16m8-based vaccine format has superior features as a proliferative vaccine compared with other poxvirus-based vaccines. Moreover, the data collected over the course of antibody elevation during three rounds of vaccination in hamsters provide an important basis for the clinical use of vaccinia virus-based vaccines against NiV disease. Trial Registration: NCT05398796.

Cross-reactive antibody response to Monkeypox virus surface proteins in a small proportion of individuals with and without Chinese smallpox vaccination history

BACKGROUND

After the eradication of smallpox in China in 1979, vaccination with the vaccinia virus (VACV) Tiantan strain for the general population was stopped in 1980. As the monkeypox virus (MPXV) is rapidly spreading in the world, we would like to investigate whether the individuals with historic VACV Tiantan strain vaccination, even after more than 40 years, could still provide ELISA reactivity and neutralizing protection; and whether the unvaccinated individuals have no antibody reactivity against MPXV at all.

RESULTS

We established serologic ELISA to measure the serum anti-MPXV titer by using immunodominant MPXV surface proteins, A35R, B6R, A29L, and M1R. A small proportion of individuals (born before 1980) with historic VACV Tiantan strain vaccination exhibited serum ELISA cross-reactivity against these MPXV surface proteins. Consistently, these donors also showed ELISA seropositivity and serum neutralization against VACV Tiantan strain. However, surprisingly, some unvaccinated young adults (born after 1980) also showed potent serum ELISA activity against MPXV proteins, possibly due to their past infection by some self-limiting Orthopoxvirus (OPXV).

CONCLUSIONS

We report the serum ELISA cross-reactivity against MPXV surface protein in a small proportion of individuals both with and without VACV Tiantan strain vaccination history. Combined with our serum neutralization assay against VACV and the recent literature about mice vaccinated with VACV Tiantan strain, our study confirmed the anti-MPXV cross-reactivity and cross-neutralization of smallpox vaccine using VACV Tiantan strain. Therefore, it is necessary to restart the smallpox vaccination program in high risk populations.

Smallpox vaccination in a mouse model

The monkeypox epidemic, which became unusually widespread among humans in 2022, has brought awareness about the necessity of smallpox vaccination of patients in the risk groups. The modern smallpox vaccine variants are introduced either intramuscularly or by skin scarification. Intramuscular vaccination cannot elicit an active immune response, since tissues at the vaccination site are immunologically poor. Skin has evolved into an immunologically important organ in mammals; therefore, intradermal delivery of a vaccine can ensure reliable protective immunity. Historically, vaccine inoculation into scarified skin (the s.s. route) was the first immunization method. However, it does not allow accurate vaccine dosing, and high-dose vaccines need to be used to successfully complete this procedure. Intradermal (i.d.) vaccine injection, especially low-dose one, can be an alternative to the s.s. route. This study aimed to compare the s.s. and i.d. smallpox immunization routes in a mouse model when using prototypic second- and fourth-generation low-dose vaccines (104 pfu). Experiments were conducted using BALB/c mice; the LIVP or LIVP-GFP strains of the vaccinia virus (VACV) were administered into the tail skin via the s.s. or i.d. routes. After vaccination (7, 14, 21, 28, 42, and 56 days post inoculation (dpi)), blood samples were collected from the retro-orbital venous sinus; titers of VACV-specific IgM and IgG in the resulting sera were determined by ELISA. Both VACV strains caused more profound antibody production when injected via the i.d. route compared to s.s. inoculation. In order to assess the level of the elicited protective immunity, mice were intranasally infected with a highly lethal dose of the cowpox virus on 62 dpi. The results demonstrated that i.d. injection ensures a stronger protective immunity in mice compared to s.s. inoculation for both VACV variants.

Effect of the ati Gene Deletion on the Pathogenicity and Immunogenicity of the Vaccinia Virus

Among the nonvirion proteins of the vaccinia virus (VACV), a 94-kDa long protein is most abundantly present; the protein is a truncated form of the 150-kDa A-type inclusion (ATI) protein of the cowpox virus encoded by the ati gene. This VACV protein does not form intracellular ATIs, being as it is a major immunogen upon infection/immunization of humans or animals with the VACV. Antibodies specific to this protein are not virus-neutralizing. The present study focused on the effect of the production of this nonstructural major immunogenic VACV protein on the manifestation of pathogenicity and immunogenicity of the virus in the BALB/c mouse model of infection. In order to introduce a targeted deletion into the VACV LIVP genome, the recombinant integration/deletion plasmid pΔati was constructed and further used to generate the recombinant virus LIVPΔati. The pathogenicity of the VACV LIVP and LIVPΔati strains was studied in 3-week-old mice. The mice were intranasally infected with the viruses at a dose of 107 pfu; 50% of the animals infected with the parent LIVP strain died, while infection with the LIVPΔati strain led to the death of only 20% of the mice. Intradermal vaccination of mice aged 6- weeks with the LIVPΔati virus statistically significantly increased the production of VACV-specific IgG, compared to that after intradermal vaccination with VACV LIVP. Meanwhile, no differences were noted in the cell-mediated immune response to the vaccination of mice with VACV LIVP or LIVPΔati, which was assessed by ELISpot according to the number of splenocytes producing IFN-γ in response to stimulation with virus-specific peptides. Intranasal infection of mice with lethal doses of the cowpox virus or the ectromelia virus on day 60 post-immunization with the studied VACV variants demonstrated that the mutant LIVPΔati elicits a stronger protective response compared to the parent LIVP.

A Monoclonal Antibody Produced in Glycoengineered Plants Potently Neutralizes Monkeypox Virus

The 2022 global outbreaks of monkeypox virus (MPXV) and increased human-to-human transmission calls for the urgent development of countermeasures to protect people who cannot benefit from vaccination. Here, we describe the development of glycovariants of 7D11, a neutralizing monoclonal IgG antibody (mAb) directed against the L1 transmembrane protein of the related vaccinia virus, in a plant-based system as a potential therapeutic against the current MPVX outbreak. Our results indicated that 7D11 mAb quickly accumulates to high levels within a week after gene introduction to plants. Plant-produced 7D11 mAb assembled correctly into the tetrameric IgG structure and can be easily purified to homogeneity. 7D11 mAb exhibited a largely homogeneous N-glycosylation profile, with or without plant-specific xylose and fucose residues, depending on the expression host, namely wild-type or glycoengineered plants. Plant-made 7D11 retained specific binding to its antigen and displayed a strong neutralization activity against MPXV, as least as potent as the reported activity against vaccinia virus. Our study highlights the utility of anti-L1 mAbs as MPXV therapeutics, and the use of glycoengineered plants to develop mAb glycovariants for potentially enhancing the efficacy of mAbs to combat ever-emerging/re-emerging viral diseases.

Human monkeypox (hMPXV) re-emergence: Host immunity status and current vaccines landscape

Monkeypox virus is a member of the Orthopoxvirus genus and the Poxviridae family. Orthopoxviruses are among the most intricate animal viruses. The pathogenicity of human monkeypox infection has been emphasized in response to its recent emergence in non-endemic countries and the threat of bioterrorism. It is always necessary to take appropriate precautions in exposure to emerging or re-emerging infections. Here, we focus on the current state of the human monkeypox infection outbreak, research & development of immune responses, and clinical interventions to prevent and treat the human monkeypox virus and other human poxviruses.

Mpox diagnostics: Review of current and emerging technologies

Mpox is a zoonotic disease caused by monkeypox virus (MPXV) from the Orthopoxvirus genus. Unprecedented transmission events have led to more than 70 000 cases reported worldwide by October 2022. The change in mpox epidemiology has raised concerns of its ability to establish endemicity beyond its traditional geographical locations. In this review, we discuss the current understanding of mpox virology and viral dynamics that are relevant to mpox diagnostics. A synopsis of the traditional and emerging laboratory technologies useful for MPXV detection and in guiding "elimination" strategies is outlined in this review. Importantly, development in MPXV genomics has rapidly advanced our understanding of the role of viral evolution and adaptation in the current outbreak.

Comparison of the Effectiveness of Transepidemal and Intradermal Immunization of Mice with the Vacinia Virus

The spread of the monkeypox virus infection among humans in many countries outside of Africa, which started in 2022, is now drawing the attention of the medical and scientific communities to the fact that immunization against this infection is sorely needed. According to current guidelines, immunization of people with the first-generation smallpox vaccine based on the vaccinia virus (VACV) LIVP strain, which is licensed in Russia, should be performed via transepidermal inoculation (skin scarification, s.s.). However, the long past experience of using this vaccination technique suggests that it does not ensure virus inoculation into patients' skin with enough reliability. The procedure of intradermal (i.d.) injection of a vaccine can be an alternative to s.s. inoculation. The effectiveness of i.d. vaccination can depend on the virus injection site on the body. Therefore, the aim of this study was to compare the development of the humoral and cellular immune responses in BALB/c mice immunized with the LIVP VACV strain, which was administered either by s.s. inoculation or i.d. injection into the same tail region of the animal. A virus dose of 105 pfu was used in both cases. ELISA of serum samples revealed no significant difference in the dynamics and level of production of VACV-specific IgM and IgG after i.d. or s.s. vaccination. A ELISpot analysis of splenocytes from the vaccinated mice showed that i.d. administration of VACV LIVP to mice induces a significantly greater T-cell immune response compared to s.s. inoculation. In order to assess the protective potency, on day 45 post immunization, mice were intranasally infected with lethal doses of either the cowpox virus (CPXV) or the ectromelia virus (ECTV), which is evolutionarily distant from the VACV and CPXV. Both vaccination techniques ensured complete protection of mice against infection with the CPXV. However, when mice were infected with a highly virulent strain of ECTV, 50% survived in the i.d. immunized group, whereas only 17% survived in the s.s. immunized group. It appears, therefore, that i.d. injection of the VACV can elicit a more potent protective immunity against orthopoxviruses compared to the conventional s.s. technique.

Protective Human Anti-Poxvirus Monoclonal Antibodies Are Generated from Rare Memory B Cells Isolated by Multicolor Antigen Tetramers

Smallpox, an epidemic disease caused by Orthopoxvirus variola, was eradicated worldwide through immunization. The immunization against smallpox was discontinued in 1980. However, incidences of monkeypox virus infection in humans have occurred sporadically, and there is also great fear that engineered forms of poxvirus could be used as biological weapons. Therefore, monoclonal antibodies against poxvirus are urgently needed for the detection and treatment of poxvirus infection. The vaccinia virus’ extracellular envelope protein A33 is a potential candidate for a subunit vaccine. We used multi-fluorescence-labeled tetrameric A33 antigen to identify rare poxvirus-specific memory B cells from the PBMC of volunteers with vaccinia virus immunization more than 40 years ago. Despite extremely low frequencies of the poxvirus-specific memory B cells, we successfully sorted A33 tetramer-labeled single memory B cells and reconstructed the antibodies with the single-cell RT-PCR of the B-cell receptor. Among the monoclonal antibodies, one clone H2 exhibited high specificity and affinity with A33. H2 efficiently inhibited viral infection and spread in cells. Passive immunotherapy of H2 in mice protected mice from lethal infection when administered either prophylactically or therapeutically. These results suggest the potential of anti-A33 human-antibody-based detection and therapeutics for poxvirus infection.

Enhancing the Immunogenicity of Vaccinia Virus

The conventional live smallpox vaccine based on the vaccinia virus (VACV) cannot be widely used today because it is highly reactogenic. Therefore, there is a demand for designing VACV variants possessing enhanced immunogenicity, making it possible to reduce the vaccine dose and, therefore, significantly eliminate the pathogenic effect of the VACV on the body. In this study, we analyzed the development of the humoral and T cell-mediated immune responses elicited by immunizing mice with low-dose VACV variants carrying the mutant A34R gene (which increases production of extracellular virions) or the deleted A35R gene (whose protein product inhibits antigen presentation by the major histocompatibility complex class II). The VACV LIVP strain, which is used as a smallpox vaccine in Russia, and its recombinant variants LIVP-A34R*, LIVP-dA35R, and LIVP-A34R*-dA35R, were compared upon intradermal immunization of BALB/c mice at a dose of 10⁴ pfu/animal. The strongest T cell-mediated immunity was detected in mice infected with the LIVP-A34R*-dA35R virus. The parental LIVP strain induced a significantly lower antibody level compared to the strains carrying the modified A34R and A35R genes. Simultaneous modification of the A34R gene and deletion of the A35R gene in VACV LIVP synergistically enhanced the immunogenic properties of the LIVP-A34R*-dA35R virus.

[Mutations in the A34R gene increase the immunogenicity of vaccinia virus]

Самым простым и надежным способом защиты от вирусных инфекций является вакцинопрофилактика. При этом наибольшей протективной эффективностью обладают живые вакцины, в основе которых используют слабовирулентные для человека вирусы, близкородственные патогенным, или аттенуированные (ослабленные за счет мутаций/делеций в вирусном геноме) варианты патогенного для человека вируса. Вакцинация против оспы с использованием живого вируса осповакцины (vaccinia virus, VACV), близкородственного вирусу натуральной оспы, сыграла важнейшую роль в успехе программы глобальной ликвидации оспы, которая осуществлялась под эгидой Всемирной организации здравоохранения. Прекращение после 1980 г. противооспенной вакцинации привело к тому, что огромная часть населения Земли в настоящее время не имеет иммунитета не только к оспе, но и любым другим зоонозным ортопоксвирусным инфекциям. Это создает возможность циркуляции зоонозных ортопоксвирусов в человеческой популяции и, как следствие, приводит к изменению экологии и круга чувствительных хозяев для разных видов ортопоксвирусов. При этом использование классической живой вакцины на основе VACV для защиты от этих инфекций в настоящее время не приемлемо, так как она может обусловливать тяжелые побочные реакции. В связи с этим все более актуальной становится разработка новых безопасных вакцин против ортопоксвирусных инфекций человека и животных. Аттенуация (ослабление вирулентности) VACV достигается в результате направленной инактивации определенных генов вируса и обычно приводит к уменьшению эффективности размножения VACV in vivo. Следствием этого может быть снижение иммунного ответа при введении аттенуированного вируса пациентам в стандартных дозах. Часто используемым для встройки/инактивации в геноме VACV является ген тимидинкиназы, нарушение которого приводит к аттенуации вируса. В данной работе изучено, как введение двух точечных мутаций в ген A34R аттенуированного штамма LIVP-GFP (ТК-), увеличивающих выход внеклеточных оболочечных вирионов (EEV), влияет на свойства пато- и иммуногенности варианта VACV LIVP-GFP-A34R при интраназальном заражении лабораторных мышей. Показано, что увеличение продукции EEV рекомбинантным штаммом VACV LIVP-GFP-A34R не меняет аттенуированный фенотип, характерный для родительского штамма LIVP-GFP, но приводит к существенно большей продукции VACV-специфичных антител. Ключевые слова: вирус осповакцины; направленные мутации; аттенуация; иммуногенность.

Optimization of translation enhancing element use to increase protein expression in a vaccinia virus system

Since the successful use of vaccinia virus (VACV) in the immunization strategies to eliminate smallpox, research has been focused on the development of recombinant VACV strains expressing proteins from various pathogens. Attempts at decreasing the side effects associated with exposure to recombinant, wild-type viral strains have led to the development of attenuated viruses. Yet while these attenuated VACV's have improved safety profiles compared to unmodified strains, their clinical use has been hindered due to efficacy issues in stimulating a host immune response. This deficiency has largely been attributed to decreased production of the target protein for immunization. Efforts to increase protein production from attenuated VACV strains has largely centered around modulation of viral factors, while manipulation of the translation of viral mRNAs has been largely unexplored. In this study we evaluate the use of translation enhancing element hTEE-658 to increase recombinant protein production in an attenuated VACV system. Optimization of the use of this motif is also attempted by combining it with strategies that have demonstrated effectiveness in previous research. We show that extension of the 5' leader sequence containing hTEE-658 does not improve motif function, nor does the combination with other known translation enhancing elements. However, the sole use of hTEE-658 in an attenuated VACV system is shown to increase protein expression levels beyond those of a standard viral promoter when used with a wild-type virus. Taken together these results highlight the potential for hTEE-658 to improve the effectiveness of attenuated VACV vaccine candidates and give insights into the optimal sequence context for its use in vaccine design.

Adaptive Immune Response to Vaccinia Virus LIVP Infection of BALB/c Mice and Protection against Lethal Reinfection with Cowpox Virus

Mass vaccination has played a critical role in the global eradication of smallpox. Various vaccinia virus (VACV) strains, whose origin has not been clearly documented in most cases, have been used as live vaccines in different countries. These VACV strains differed in pathogenicity towards various laboratory animals and in reactogenicity exhibited upon vaccination of humans. In this work, we studied the development of humoral and cellular immune responses in BALB/c mice inoculated intranasally (i.n.) or intradermally (i.d.) with the VACV LIVP strain at a dose of 10⁵ PFU/mouse, which was used in Russia as the first generation smallpox vaccine. Active synthesis of VACV-specific IgM in the mice occurred on day 7 after inoculation, reached a maximum on day 14, and decreased by day 29. Synthesis of virus-specific IgG was detected only from day 14, and the level increased significantly by day 29 after infection of the mice. Immunization (i.n.) resulted in significantly higher production of VACV-specific antibodies compared to that upon i.d. inoculation of LIVP. There were no significant differences in the levels of the T cell response in mice after i.n. or i.d. VACV administration at any time point. The maximum level of VACV-specific T-cells was detected on day 14. By day 29 of the experiment, the level of VACV-specific T-lymphocytes in the spleen of mice significantly decreased for both immunization procedures. On day 30 after immunization with LIVP, mice were infected with the cowpox virus at a dose of 46 LD₅₀. The i.n. immunized mice were resistant to this infection, while 33% of i.d. immunized mice died. Our findings indicate that the level of the humoral immune response to vaccination may play a decisive role in protection of animals from orthopoxvirus reinfection.

Capripoxvirus Infections in Ruminants: A Review

Lumpy skin disease, sheeppox, and goatpox are notifiable diseases of cattle, sheep, and goats, respectively, caused by viruses of the Capripoxvirus genus. They are responsible for both direct and indirect financial losses. These losses arise through animal mortality, morbidity cost of vaccinations, and constraints to animals and animal products' trade. Control and eradication of capripoxviruses depend on early detection of outbreaks, vector control, strict animal movement, and vaccination which remains the most effective means of control. To date, live attenuated vaccines are widely used; however, conferred protection remains controversial. Many vaccines have been associated with adverse reactions and incomplete protection in sheep, goats, and cattle. Many combination- and recombinant-based vaccines have also been developed. Here, we review capripoxvirus infections and the immunity conferred against capripoxviruses by their respective vaccines for each ruminant species. We also review their related cross protection to heterologous infections.

Vaccine Development for Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS), which is caused by SFTS virus (SFTSV), is a tick-borne emerging zoonosis with a high case-fatality rate. At present, there is no approved SFTS vaccine, although the development of a vaccine would be one of the best strategies for preventing SFTS. This article focused on studies aimed at establishing small animal models of SFTS that are indispensable for evaluating vaccine candidates, developing these vaccine candidates, and establishing more practical animal models for evaluation. Innate immune-deficient mouse models, a hamster model, an immunocompetent ferret model and a cat model have been developed for SFTS. Several vaccine candidates for SFTS have been developed, and their efficacy has been confirmed using these animal models. The candidates consist of live-attenuated virus-based, viral vector-based, or DNA-based vaccines. SFTS vaccines are expected to be used for humans and companion dogs and cats. Hence for practical use, the vaccine candidates should be evaluated for efficacy using not only nonhuman primates but also dogs and cats. There is no practical nonhuman primate model of SFTS; however, the cat model is available to evaluate the efficacy of these candidate SFTS vaccines on domesticated animals.

A highly attenuated vaccinia virus strain LC16m8-based vaccine for severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) caused by a species Dabie bandavirus (formerly SFTS virus [SFTSV]) is an emerging hemorrhagic infectious disease with a high case-fatality rate. One of the best strategies for preventing SFTS is to develop a vaccine, which is expected to induce both humoral and cellular immunity. We applied a highly attenuated but still immunogenic vaccinia virus strain LC16m8 (m8) as a recombinant vaccine for SFTS. Recombinant m8s expressing SFTSV nucleoprotein (m8-N), envelope glycoprotein precursor (m8-GPC), and both N and GPC (m8-N+GPC) in the infected cells were generated. Both m8-GPC- and m8-N+GPC-infected cells were confirmed to produce SFTSV-like-particles (VLP) in vitro, and the N was incorporated in the VLP produced by the infection of cells with m8-N+GPC. Specific antibodies to SFTSV were induced in mice inoculated with each of the recombinant m8s, and the mice were fully protected from lethal challenge with SFTSV at both 10³ TCID₅₀ and 10⁵ TCID₅₀. In mice that had been immunized with vaccinia virus strain Lister in advance of m8-based SFTSV vaccine inoculation, protective immunity against the SFTSV challenge was also conferred. The pathological analysis revealed that mice immunized with m8-GPC or m8-N+GPC did not show any histopathological changes without any viral antigen-positive cells, whereas the control mice showed focal necrosis with inflammatory infiltration with SFTSV antigen-positive cells in tissues after SFTSV challenge. The passive serum transfer experiments revealed that sera collected from mice inoculated with m8-GPC or m8-N+GPC but not with m8-N conferred protective immunity against lethal SFTSV challenge in naïve mice. On the other hand, the depletion of CD8-positive cells in vivo did not abrogate the protective immunity conferred by m8-based SFTSV vaccines. Based on these results, the recombinant m8-GPC and m8-N+GPC were considered promising vaccine candidates for SFTS.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging viral hemorrhagic fever with a high case-fatality rate (approximately 5% to >40%). Indigenous SFTS has been reported in China, Japan, South Korea, and Vietnam. Thus, the development of an effective vaccine for SFTS is urgently needed. Vaccinia virus (VAC) was previously used as a vaccine for smallpox. Unfortunately, after these strains, the so-called second generation of VAC used during the eradication campaign was associated with severe adverse events, and the third generation of VAC strains such as LC16m8 (m8) and modified vaccinia Ankara (MVA) was established. m8 is confirmed to be highly attenuated while still maintaining immunogenicity. m8 is licensed for use in healthy people in Japan. At the present time, approximately 100,000 people have undergone vaccination with m8 without experiencing any severe postvaccine complications. At present, third-generation VAC strains are attractive for a recombinant vaccine vector, especially for viral hemorrhagic infectious diseases, such as Ebola virus disease, Lassa fever, Crimean-Congo hemorrhagic fever, and SFTS. We investigated the practicality of an m8-based recombinant vaccine for SFTS as well as other promising recombinant VAC-based vaccines for viral hemorrhagic infectious diseases.

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

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

Genes that Control Vaccinia Virus Immunogenicity

The live smallpox vaccine was a historical first and highly effective vaccine. However, along with high immunogenicity, the vaccinia virus (VACV) caused serious side effects in vaccinees, sometimes with lethal outcomes. Therefore, after global eradication of smallpox, VACV vaccination was stopped. For this reason, most of the human population worldwide lacks specific immunity against not only smallpox, but also other zoonotic orthopoxviruses. Outbreaks of diseases caused by these viruses have increasingly occurred in humans on different continents. However, use of the classical live VACV vaccine for prevention against these diseases is unacceptable because of potential serious side effects, especially in individuals with suppressed immunity or immunodeficiency (e.g., HIV-infected patients). Therefore, highly attenuated VACV variants that preserve their immunogenicity are needed. This review discusses current ideas about the development of a humoral and cellular immune response to orthopoxvirus infection/vaccination and describes genetic engineering approaches that could be utilized to generate safe and highly immunogenic live VACV vaccines.

Evidence of vaccinia dissemination despite lack of major reaction following smallpox vaccination

Following vaccinia vaccination, vesicle formation at the site occurs in 95% of primary vaccinees and is thought to indicate virus replication and vaccine efficacy. Little is known about virus replication and immune response in those who do not develop a vesicle. We used PCR to detect vaccinia in various sites following receipt of the smallpox vaccine in those with and without vesicle formation. Among 80 participants, 74 developed and 6 failed to develop a vesicle. Vaccinia DNA was detected in the blood, in the oropharynx, on the dressing, and on the hands of 5%, 11%, 4%, and 0% of those with vesicle formation and of 33%, 17%, 0%, and 17% of those without vesicle formation, respectively (p > 0.05 for each site). The detection of systemic vaccinia DNA in vaccinees without vesicle formation challenges the current understanding that lack of vesicle formation indicates lack of virus replication, the prerequisite to immune response.

Enhanced Efficacy of Vaccination With Vaccinia Virus in Old vs. Young Mice

Immunosenescence is believed to be responsible for poor vaccine efficacy in the elderly. To overcome this difficulty, research into vaccination strategies and the mechanisms of immune responses to vaccination is required. By analyzing the innate and adaptive immune responses to vaccination with vaccinia virus (VACV) in mice of different age groups, we found that immune cell recruitment, production of cytokines/chemokines and control of viral replication at the site of intradermal vaccination were preserved in aged mice and were comparable with younger groups. Analysis of cervical draining lymph nodes (dLN) collected after vaccination showed that numbers of germinal center B cells and follicular T helper cells were similar across different age groups. The number of VACV-specific CD8 T cells in the spleen and the levels of serum neutralizing antibodies 1 month after vaccination were also comparable across all age groups. However, following intranasal challenge of vaccinated mice, body weight loss was lower and virus was cleared more rapidly in aged mice than in younger animals. In conclusion, vaccination with VACV can induce an effective immune response and stronger protection in elderly animals. Thus, the development of recombinant VACV-based vaccines against different infectious diseases should be considered as a strategy for improving vaccine immunogenicity and efficacy in the elderly.

Simple, Rapid Preparation of Poxvirus DNA for PCR Cloning and Analysis

This chapter describes the simple, rapid, and inexpensive preparation of template DNA from poxvirus-infected cells, plaques, or crude virus stocks for PCR amplification. This technique is reliable and robust and only requires centrifugation, detergent, and protease treatment. The resulting DNA template preparation is suitable for PCR amplification for screening viruses, cloning, transfection, and DNA sequencing.

T Lymphocytes as Measurable Targets of Protection and Vaccination Against Viral Disorders

Continuous epidemiological surveillance of existing and emerging viruses and their associated disorders is gaining importance in light of their abilities to cause unpredictable outbreaks as a result of increased travel and vaccination choices by steadily growing and aging populations. Close surveillance of outbreaks and herd immunity are also at the forefront, even in industrialized countries, where previously eradicated viruses are now at risk of re-emergence due to instances of strain recombination, contractions in viral vector geographies, and from their potential use as agents of bioterrorism. There is a great need for the rational design of current and future vaccines targeting viruses, with a strong focus on vaccine targeting of adaptive immune effector memory T cells as the gold standard of immunity conferring long-lived protection against a wide variety of pathogens and malignancies. Here, we review viruses that have historically caused large outbreaks and severe lethal disorders, including respiratory, gastric, skin, hepatic, neurologic, and hemorrhagic fevers. To observe trends in vaccinology against these viral disorders, we describe viral genetic, replication, transmission, and tropism, host-immune evasion strategies, and the epidemiology and health risks of their associated syndromes. We focus on immunity generated against both natural infection and vaccination, where a steady shift in conferred vaccination immunogenicity is observed from quantifying activated and proliferating, long-lived effector memory T cell subsets, as the prominent biomarkers of long-term immunity against viruses and their associated disorders causing high morbidity and mortality rates.

Characterization of murine antibody responses to vaccinia virus envelope protein A14 reveals an immunodominant antigen lacking of effective neutralization targets

Vaccinia virus (VACV) A14 is a major envelope protein and a dominant antibody target in the smallpox vaccine. However, the role of anti-A14 antibodies in immunity against orthopoxviruses is unclear. Here, we characterized 22 A14 monoclonal antibodies (mAb) from two mice immunized with VACV. Epitope mapping showed that 21 mAbs targeted the C-terminal hydrophilic region, while one mAb recognized the middle region predicted to be across the viral envelope from the C-terminus. However, none of the mAbs bound to virions in studies with electron microscopy. Interestingly, some mAbs showed low VACV neutralization activities in the presence of complement and provided protection to SCID mice challenged with VACV ACAM2000. Our data showed that, although A14 is an immunodominant antigen in smallpox vaccine, its B cell epitopes are either enclosed within the virions or are inaccessible on virion surface. Anti-A14 antibodies, however, could contribute to protection against VACV through a complement-dependent pathway.

A Novel System for Constructing a Recombinant Highly-Attenuated Vaccinia Virus Strain (LC16m8) Expressing Foreign Genes and Its Application for the Generation of LC16m8-Based Vaccines against Herpes Simplex Virus 2

A novel system was developed for generating highly attenuated vaccinia virus LC16m8 (m8, third-generation smallpox vaccine) that expresses foreign genes. The innovations in this system are its excisable selection marker, specificity of the integration site of a gene of interest, and easy identification of clones with a fluorescent signal. Using this system, recombinant m8s, which expressed herpes simplex virus 2 (HSV-2) glycoprotein B (gB)-, gD-, or both gB and gD (gB + gD), were generated, and their efficacy was evaluated. First, the induction of a specific IgG against these HSV-2 glycoproteins in mice infected with one of these recombinant m8s was confirmed by an immunofluorescent assay. Next, mice preinfected with one of the recombinant m8s were infected with HSV-2 at a lethal dose to examine the vaccine efficacy. The fatality rate among the mice preinfected with either the recombinant gB + gD- or gD-expressing m8 significantly decreased in comparison with the control. The survival rate in male and female mice preinfected with either the recombinant gB + gD- or gD-expressing m8 increased to 100% and 60%, respectively, while most of the control mice died. In summary, this new system may be applicable to creation of a novel m8-based vaccine.

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.

Development of improved therapeutic mesothelin-based vaccines for pancreatic cancer

Pancreatic cancer is the 5^th leading cause of cancer deaths, and there are no effective treatments. We developed a poxvirus platform vaccine with improved immunogenicity and inserted the mesothelin gene to create an anti-mesothelin cancer vaccine. Mesothelin expression is mostly restricted to tumors in adult mammals and thus may be a good target for cancer treatment. We show here that the modified vaccinia virus Ankara (MVA) virus expressing mesothelin and the enhanced MVA virus missing the immunosuppressive A35 gene and expressing mesothelin were both safe in mice and were able to induce IFN-gamma secreting T cells in response to mesothelin expressing tumor cells. In addition, the MVA virus has oncolytic properties in vitro as it can replicate in and kill Panc02 pancreatic adenocarcinoma cell line tumor cells, even though it is unable to replicate in most mammalian cells. Deletion of the A35 gene in MVA improved T cell responses as expected. However, we were unable to demonstrate inhibition of Panc02 tumor growth in immunocompetent mice with pre-vaccination of mice, boosts, or even intratumoral injections of the recombinant viruses. Vaccine efficacy may be limited by shedding of mesothelin from tumor cells thus creating a protective screen from the immune system.

Construction and characterization of bacterial artificial chromosomes harboring the full-length genome of a highly attenuated vaccinia virus LC16m8

LC16m8 (m8), a highly attenuated vaccinia virus (VAC) strain, was developed as a smallpox vaccine, and its safety and immunogenicity have been confirmed. Here, we aimed to develop a system that recovers infectious m8 from a bacterial artificial chromosome (BAC) that retains the full-length viral genomic DNA (m8-BAC system). The infectious virus was successfully recovered from a VAC-BAC plasmid, named pLC16m8-BAC. Furthermore, the bacterial replicon-free virus was generated by intramolecular homologous recombination and was successfully recovered from a modified VAC-BAC plasmid, named pLC16m8.8S-BAC. Also, the growth of the recovered virus was indistinguishable from that of authentic m8. The full genome sequence of the plasmid, which harbors identical inverted terminal repeats (ITR) to that of authentic m8, was determined by long-read next-generation sequencing (NGS). The ITR contains x 18 to 32 of the 70 and x 30 to 45 of 54 base pair tandem repeats, and the number of tandem repeats was different between the ITR left and right. Since the virus recovered from pLC16m8.8S-BAC was expected to retain the identical viral genome to that of m8, including the ITR, a reference-based alignment following a short-read NGS was performed to validate the sequence of the recovered virus. Based on the pattern of coverage depth in the ITR, no remarkable differences were observed between the virus and m8, and the other region was confirmed to be identical as well. In summary, this new system can recover the virus, which is geno- and phenotypically indistinguishable from authentic m8.

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.

Characterizing the effects of insertion of a 5.2 kb region of a VACV genome, which contains known immune evasion genes, on MVA immunogenicity

Modified Vaccinia virus Ankara (MVA) is an attenuated Vaccinia virus (VACV) that is a popular vaccine vector candidate against many different pathogens. Its replication-restricted nature makes it a safe vaccine. However, higher doses or multiple boosts of MVA are necessary to elicit an immune response similar to wild-type VACV. Multiple strategies have been used to create modified MVA viruses that remain safe, but have increased immunogenicity. For example, one common strategy is to delete MVA immunomodulatory proteins in hopes of increasing the host immune response. Here, we take the opposite approach and examine, for the first time, how re-introduction of a 5.2 kb region of VACV DNA (that codes for multiple immunomodulatory proteins) into MVA alters viral immunogenicity. Since antigen presenting cells (APCs) are critical connectors between the innate and adaptive immune system, we examined the effect of MVA/5.2 kb infection in these cells in vitro. MVA/5.2 kb infection decreased virus-induced apoptosis and virus-induced NF-κB activation. MVA.5.2 kb infection decreased TNF production. However, MVA/5.2 kb infection did not alter APC maturation or IL-6 and IL-8 production in vitro. We further explored MVA/5.2 kb immunogenicity in vivo. VACV-specific CD8⁺ T cells were decreased after in vivo infection with MVA/5.2 kb versus MVA, suggesting that the MVA/5.2 kb construct is less immunogenic than MVA. These results demonstrate the limitations of in vitro studies for predicting the effects of genetic manipulation of MVA on immunogenicity. Although MVA/5.2 kb did not enhance MVA's immunogenicity, this study examined an unexplored strategy for optimizing MVA, and the insight gained from these results can help direct how to modify MVA in the future.

Poxvirus Safety Analysis in the Pregnant Mouse Model, Vaccinia, and Raccoonpox Viruses

Poxviruses cause many diseases in humans and animals worldwide, and there is a need for vaccines with improved safety and good efficacy. In addition, poxvirus vectors are widely used as recombinant vaccines for various infectious diseases and as recombinant and oncolytic vaccines for cancer. One concern with poxvirus vaccine vectors is that some poxviruses can infect a developing fetus and cause fetal loss or congenital disease. This can be an issue both for patients receiving a vaccine and for pregnant health care providers, including doctors, nurses, and veterinarians, who might receive accidental exposure to the poxvirus by injection or during patient care. We describe here a method for analyzing the safety of virus exposure in pregnant mammals using a mouse model testing vaccinia, canarypox, and raccoonpox virus vectors.

Cross-Neutralizing and Protective Human Antibody Specificities to Poxvirus Infections

Monkeypox (MPXV) and cowpox (CPXV) are emerging agents that cause severe human infections on an intermittent basis, and variola virus (VARV) has potential for use as an agent of bioterror. Vaccinia immune globulin (VIG) has been used therapeutically to treat severe orthopoxvirus infections but is in short supply. We generated a large panel of orthopoxvirus-specific human monoclonal antibodies (Abs) from immune subjects to investigate the molecular basis of broadly neutralizing antibody responses for diverse orthopoxviruses. Detailed analysis revealed the principal neutralizing antibody specificities that are cross-reactive for VACV, CPXV, MPXV, and VARV and that are determinants of protection in murine challenge models. Optimal protection following respiratory or systemic infection required a mixture of Abs that targeted several membrane proteins, including proteins on enveloped and mature virion forms of virus. This work reveals orthopoxvirus targets for human Abs that mediate cross-protective immunity and identifies new candidate Ab therapeutic mixtures to replace VIG.

Use of functional genomics to understand replication deficient poxvirus-host interactions

High-throughput genomics technologies are currently being used to study a wide variety of viral infections, providing insight into which cellular genes and pathways are regulated after infection, and how these changes are related, or not, to efficient elimination of the pathogen. This article will focus on how gene expression studies of infections with non-replicative poxviruses currently used as vaccine vectors provide a global perspective of the molecular events associated with the viral infection in human cells. These high-throughput genomics approaches have the potential to lead to the identification of specific new properties of the viral vector or novel cellular targets that may aid in the development of more effective pox-derived vaccines and antivirals.

Highly immunogenic variant of attenuated vaccinia virus

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

Freeze-dried live attenuated smallpox vaccine prepared in cell culture "LC16-KAKETSUKEN": Post-marketing surveillance study on safety and efficacy compliant with Good Clinical Practice

BACKGROUND

In Japan, production of smallpox vaccine LC16m8 (named LC16-KAKETSUKEN) was restarted and was determined to be maintained as a national stockpile in March 2002.

OBJECTIVE

To conduct a post-marketing surveillance study of the vaccination of freeze-dried live attenuated smallpox vaccine prepared in cell culture LC16-KAKETSUKEN using attenuated vaccinia strain LC16m8. The study complied with Good Clinical Practice, focusing on a comparison between primary vaccinees and re-vaccinees.

METHOD

268 personnel (261 males and 7 females) of the Japan Ground Self-Defense Force were inoculated with LC16-KAKETSUKEN and thereafter adverse events and efficacy were evaluated.

RESULTS

Among 268 vaccinee participants, the following vaccinees showed adverse events, none serious: 53 of 196 primary vaccinees (without previous smallpox vaccination), 4 of 71 re-vaccinees (with previous smallpox vaccination) and 1 vaccinee with unknown previous vaccination history. A breakdown of adverse events observed in this study (total 268 vaccinees) showed the following minor or mild adverse events: 52 (19.4%) swelling of axillary lymph node, 4 (1.5%) fever, 2 (0.7%) fatigue, 1 (0.4%) of rash, 14 (5.2%) erythema at the inoculation site, 1 (0.4%) swelling at the inoculation site and 1 (0.4%) autoinoculation. The incidence of adverse events for primary vaccinees (53/196; 27.0%) was significantly higher than for re-vaccinees (4/71; 5.6%). However, the proportion of vaccine take was significantly higher for primary vaccinees (185/196; 94.4%) than for re-vaccinees (58/71; 81.7%). Although the proportion of vaccine take of re-vaccinees was significantly lower than for primary vaccinees due to preexisting immunity by previous vaccination, no significant difference was found in neutralizing antibody titers between primary vaccinees and re-vaccinees at 1, 4 and 7 months after LC16-KAKETSUKEN vaccination.

CONCLUSION

The present post-marketing surveillance study compliant with Good Clinical Practice demonstrated the efficacy and safety of the smallpox vaccine LC16-KAKETSUKEN in an adult population. LC16-KAKETSUKEN is the sole currently available licensed smallpox vaccine for both adult and pediatric populations.

Genomic Analysis, Phenotype, and Virulence of the Historical Brazilian Smallpox Vaccine Strain IOC: Implications for the Origins and Evolutionary Relationships of Vaccinia Virus

Smallpox was declared eradicated in 1980 after an intensive vaccination program using different strains of vaccinia virus (VACV; Poxviridae). VACV strain IOC (VACV-IOC) was the seed strain of the smallpox vaccine manufactured by the major vaccine producer in Brazil during the smallpox eradication program. However, little is known about the biological and immunological features as well as the phylogenetic relationships of this first-generation vaccine. In this work, we present a comprehensive characterization of two clones of VACV-IOC. Both clones had low virulence in infected mice and induced a protective immune response against a lethal infection comparable to the response of the licensed vaccine ACAM2000 and the parental strain VACV-IOC. Full-genome sequencing revealed the presence of several fragmented virulence genes that probably are nonfunctional, e.g., F1L, B13R, C10L, K3L, and C3L. Most notably, phylogenetic inference supported by the structural analysis of the genome ends provides evidence of a novel, independent cluster in VACV phylogeny formed by VACV-IOC, the Brazilian field strains Cantagalo (CTGV) and Serro 2 viruses, and horsepox virus, a VACV-like virus supposedly related to an ancestor of the VACV lineage. Our data strongly support the hypothesis that CTGV-like viruses represent feral VACV that evolved in parallel with VACV-IOC after splitting from a most recent common ancestor, probably an ancient smallpox vaccine strain related to horsepox virus. Our data, together with an interesting historical investigation, revisit the origins of VACV and propose new evolutionary relationships between ancient and extant VACV strains, mainly horsepox virus, VACV-IOC/CTGV-like viruses, and Dryvax strain.

IMPORTANCE

First-generation vaccines used to eradicate smallpox had rates of adverse effects that are not acceptable by current health care standards. Moreover, these vaccines are genetically heterogeneous and consist of a pool of quasispecies of VACV. Therefore, the search for new-generation smallpox vaccines that combine low pathogenicity, immune protection, and genetic homogeneity is extremely important. In addition, the phylogenetic relationships and origins of VACV strains are quite nebulous. We show the characterization of two clones of VACV-IOC, a unique smallpox vaccine strain that contributed to smallpox eradication in Brazil. The immunogenicity and reduced virulence make the IOC clones good options for alternative second-generation smallpox vaccines. More importantly, this study reveals the phylogenetic relationship between VACV-IOC, feral VACV established in nature, and the ancestor-like horsepox virus. Our data expand the discussion on the origins and evolutionary connections of VACV lineages.

Cytokine production associated with smallpox vaccine responses

Smallpox was eradicated 34 years ago due to the success of the smallpox vaccine; yet, the vaccine continues to be studied because of its importance in responding to potential biological warfare and the adverse events associated with current smallpox vaccines. Interindividual variations in vaccine response are observed and are, in part, due to genetic variation. In some cases, these varying responses lead to adverse events, which occur at a relatively high rate for the smallpox vaccine compared with other vaccines. Here, we aim to summarize the cytokine responses associated with smallpox vaccine response to date. Along with a description of each of these cytokines, we describe the genetic and adverse event data associated with cytokine responses to smallpox vaccination.

Vaccinia virus strain LC16m8 defective in the B5R gene keeps strong protection comparable to its parental strain Lister in immunodeficient mice

BACKGROUND

Attenuated vaccinia virus strain, LC16m8, defective in the B5R envelope protein gene, is used as a stockpile smallpox vaccine strain in Japan against bioterrorism: the defect in the B5R gene mainly contributes to its highly attenuated properties.

METHODS

The protective activity of LC16m8 vaccine against challenge with a lethal dose of vaccinia Western Reserve strain was assessed in wild-type and immunodeficient mice lacking CD4, MHC class I, MHC class II or MHC class I and II antigens.

RESULTS

The immunization with LC16m8 induced strong protective activity comparable to that of its parent strain, Lister (Elstree) strain, in wild-type mice from 2 days to 1 year after vaccination, as well as in immunodeficient mice at 2 or 3 weeks after vaccination. These results implicated that the defect in the B5R gene hardly affected the potential activity of LC16m8 to induce innate, cell-mediated and humoral immunity, and that LC16m8 could be effective in immunodeficient patients.

CONCLUSION

LC16m8 with truncated B5 protein has an activity to induce immunity, such as innate immunity and subsequent cell-mediated and humoral immunity almost completely comparable to the activity of its parental strain Lister.

Genome sequence and comparative virulence of raccoonpox virus: the first North American poxvirus sequence

We report here the complete genome sequence of raccoonpox virus (RCNV), a naturally occurring North American poxvirus. This is the first such North American sequence to the best of our knowledge, and the data showed that RCNV forms a new phylogenetic branch between orthopoxviruses and Yoka poxvirus. RCNV shared overall similarity in genome organization with orthopoxviruses, and the proteins in the central conserved region shared approximately 90  % amino acid identity with orthopoxviruses. RCNV proteins shared approximately 81  % amino acid identity with Yokapox virus proteins. RCNV is missing 10 genes normally conserved in orthopoxviruses, most of which are implicated in virulence. These gene deletions may explain the attenuated phenotype of RCNV in mammals. RCNV contained one unique genome region containing approximately 1 kb of DNA sequence that is not present in any reported poxvirus. It contained a unique ORF predicted to encode a protein with a transmembrane domain. RCNV replicates well in mammalian cells, is naturally attenuated and has been shown to be effective as a vaccine vector platform, so we further tested its safety. We showed here that RCNV is substantially more attenuated than even the highly attenuated VACV-A35Del mutant virus in pregnant, nude and severe combined immunodeficient (SCID) mouse models. RCNV was much safer in pregnant mice and was cleared rapidly from tissues, even in immunocompromised animals, whereas the VACV-A35Del mutant retains virulence and persists in tissues. Thus, RCNV is expected to be a superior vaccine vector for infectious diseases and cancer due to its excellent safety profile, reported vaccine efficacy and ability to replicate in mammalian cells.

Vaccine-induced protection against orthopoxvirus infection is mediated through the combined functions of CD4 T cell-dependent antibody and CD8 T cell responses

Antibody production by B cells in the absence of CD4 T cell help has been shown to be necessary and sufficient for protection against secondary orthopoxvirus (OPV) infections. This conclusion is based on short-term depletion of leukocyte subsets in vaccinated animals, in addition to passive transfer of immune serum to naive hosts that are subsequently protected from lethal orthopoxvirus infection. Here, we show that CD4 T cell help is necessary for neutralizing antibody production and virus control during a secondary ectromelia virus (ECTV) infection. A crucial role for CD4 T cells was revealed when depletion of this subset was extended beyond the acute phase of infection. Sustained depletion of CD4 T cells over several weeks in vaccinated animals during a secondary infection resulted in gradual diminution of B cell responses, including neutralizing antibody, contemporaneous with a corresponding increase in the viral load. Long-term elimination of CD8 T cells alone delayed virus clearance, but prolonged depletion of both CD4 and CD8 T cells resulted in death associated with uncontrolled virus replication. In the absence of CD4 T cells, perforin- and granzyme A- and B-dependent effector functions of CD8 T cells became critical. Our data therefore show that both CD4 T cell help for antibody production and CD8 T cell effector function are critical for protection against secondary OPV infection. These results are consistent with the notion that the effectiveness of the smallpox vaccine is related to its capacity to induce both B and T cell memory.

IMPORTANCE

Smallpox eradication through vaccination is one of the most successful public health endeavors of modern medicine. The use of various orthopoxvirus (OPV) models to elucidate correlates of vaccine-induced protective immunity showed that antibody is critical for protection against secondary infection, whereas the role of T cells is unclear. Short-term leukocyte subset depletion in vaccinated animals or transfer of immune serum to naive, immunocompetent hosts indicates that antibody alone is necessary and sufficient for protection. We show here that long-term depletion of CD4 T cells over several weeks in vaccinated animals during secondary OPV challenge reveals an important role for CD4 T cell-dependent antibody responses in effective virus control. Prolonged elimination of CD8 T cells alone delayed virus clearance, but depletion of both T cell subsets resulted in death associated with uncontrolled virus replication. Thus, vaccinated individuals who subsequently acquire T cell deficiencies may not be protected against secondary OPV infection.

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

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

Safety of attenuated smallpox vaccine LC16m8 in immunodeficient mice

Freeze-dried live attenuated smallpox vaccine LC16m8 prepared in cell culture has been the sole smallpox vaccine licensed in Japan since 1975 and was recently recommended as a WHO stockpile vaccine. We evaluated the safety of recently remanufactured lots of LC16m8 using a series of immunodeficient mouse models. These models included suckling mice, severe combined immunodeficiency disease (SCID) mice, and wild-type mice treated with cyclosporine. LC16m8 showed extremely low virulence in each of the three mouse models compared with that of its parental strains, Lister and LC16mO. These results provide further evidence that LC16m8 is one of the safest replication-competent smallpox vaccines in the world and may be considered for use in immunodeficient patients.

T cell inactivation by poxviral B22 family proteins increases viral virulence

Infections with monkeypox, cowpox and weaponized variola virus remain a threat to the increasingly unvaccinated human population, but little is known about their mechanisms of virulence and immune evasion. We now demonstrate that B22 proteins, encoded by the largest genes of these viruses, render human T cells unresponsive to stimulation of the T cell receptor by MHC-dependent antigen presentation or by MHC-independent stimulation. In contrast, stimuli that bypass TCR-signaling are not inhibited. In a non-human primate model of monkeypox, virus lacking the B22R homologue (MPXVΔ197) caused only mild disease with lower viremia and cutaneous pox lesions compared to wild type MPXV which caused high viremia, morbidity and mortality. Since MPXVΔ197-infected animals displayed accelerated T cell responses and less T cell dysregulation than MPXV US2003, we conclude that B22 family proteins cause viral virulence by suppressing T cell control of viral dissemination.

Differential induction of apoptosis, interferon signaling, and phagocytosis in macrophages infected with a panel of attenuated and nonattenuated poxviruses

Due to the essential role macrophages play in antiviral immunity, it is important to understand the intracellular and molecular processes that occur in macrophages following infection with various strains of vaccinia virus, particularly those used as vaccine vectors. Similarities as well as differences were found in macrophages infected with different poxvirus strains, particularly at the level of virus-induced apoptosis and the expression of immunomodulatory genes, as determined by microarray analyses. Interestingly, the attenuated modified vaccinia Ankara virus (MVA) was particularly efficient in triggering apoptosis and beta interferon (IFN-β) secretion and in inducing changes in the expression of genes associated with increased activation of innate immunity, setting it apart from the other five vaccinia virus strains tested. Taken together, these results increase our understanding of how these viruses interact with human macrophages, at the cellular and molecular levels, and suggest mechanisms that may underlie their utility as recombinant vaccine vectors.

IMPORTANCE

Our studies clearly demonstrate that there are substantial biological differences in the patterns of cellular gene expression between macrophages infected with different poxvirus strains and that these changes are due specifically to infection with the distinct viruses. For example, a clear induction in IFN-β mRNA was observed after infection with MVA but not with other poxviruses. Importantly, antiviral bioassays confirmed that MVA-infected macrophages secreted a high level of biologically active type I IFN. Similarly, the phagocytic capacity of macrophages was also specifically increased after infection with MVA. Although the main scope of this study was not to test the vaccine potential of MVA as there are several groups in the field working extensively on this aspect, the characteristics/phenotypes we observed at the in vitro level clearly highlight the inherent advantages that MVA possesses in comparison to other poxvirus strains.

Genetic Adjuvantation of Recombinant MVA with CD40L Potentiates CD8 T Cell Mediated Immunity

Modified vaccinia Ankara (MVA) is a safe and promising viral vaccine vector that is currently investigated in several clinical and pre-clinical trials. In contrast to inactivated or sub-unit vaccines, MVA is able to induce strong humoral as well as cellular immune responses. In order to further improve its CD8 T cell inducing capacity, we genetically adjuvanted MVA with the coding sequence of murine CD40L, a member of the tumor necrosis factor superfamily. Immunization of mice with this new vector led to strongly enhanced primary and memory CD8 T cell responses. Concordant with the enhanced CD8 T cell response, we could detect stronger activation of dendritic cells and higher systemic levels of innate cytokines (including IL-12p70) early after immunization. Interestingly, acquisition of memory characteristics (i.e., IL-7R expression) was accelerated after immunization with MVA-CD40L in comparison to non-adjuvanted MVA. Furthermore, the generated cytotoxic T-lymphocytes (CTLs) also showed improved functionality as demonstrated by intracellular cytokine staining and in vivo killing activity. Importantly, the superior CTL response after a single MVA-CD40L immunization was able to protect B cell deficient mice against a fatal infection with ectromelia virus. Taken together, we show that genetic adjuvantation of MVA can change strength, quality, and functionality of innate and adaptive immune responses. These data should facilitate a rational vaccine design with a focus on rapid induction of large numbers of CD8 T cells able to protect against specific diseases.

Genomic sequence and virulence of clonal isolates of vaccinia virus Tiantan, the Chinese smallpox vaccine strain

Despite the worldwide eradication of smallpox in 1979, the potential bioterrorism threat from variola virus and the ongoing use of vaccinia virus (VACV) as a vector for vaccine development argue for continued research on VACV. In China, the VACV Tiantan strain (TT) was used in the smallpox eradication campaign. Its progeny strain is currently being used to develop a human immunodeficiency virus (HIV) vaccine. Here we sequenced the full genomes of five TT clones isolated by plaque purification from the TT (752-1) viral stock. Phylogenetic analysis with other commonly used VACV strains showed that TT (752-1) and its clones clustered and exhibited higher sequence diversity than that found in Dryvax clones. The ∼190 kbp genomes of TT appeared to encode 273 open reading frames (ORFs). ORFs located in the middle of the genome were more conserved than those located at the two termini, where many virulence and immunomodulation associated genes reside. Several patterns of nucleotide changes including point mutations, insertions and deletions were identified. The polymorphisms in seven virulence-associated proteins and six immunomodulation-related proteins were analyzed. We also investigated the neuro- and skin- virulence of TT clones in mice and rabbits, respectively. The TT clones exhibited significantly less virulence than the New York City Board of Health (NYCBH) strain, as evidenced by less extensive weight loss and morbidity in mice as well as produced smaller skin lesions and lower incidence of putrescence in rabbits. The complete genome sequences, ORF annotations, and phenotypic diversity yielded from this study aid our understanding of the Chinese historic TT strain and are useful for HIV vaccine projects employing TT as a vector.

L1R, A27L, A33R and B5R vaccinia virus genes expressed by fowlpox recombinants as putative novel orthopoxvirus vaccines

Background

The traditional smallpox vaccine, administered by scarification, was discontinued in the general population from 1980, because of the absence of new smallpox cases. However, the development of an effective prophylactic vaccine against smallpox is still necessary, to protect from the threat of deliberate release of the variola virus for bioterrorism and from new zoonotic infections, and to improve the safety of the traditional vaccine. Preventive vaccination still remains the most effective control and new vectors have been developed to generate recombinant vaccines against smallpox that induce the same immunogenicity as the traditional one. As protective antibodies are mainly directed against the surface proteins of the two infectious forms of vaccinia, the intracellular mature virions and the extracellular virions, combined proteins from these viral forms can be used to better elicit a complete and protective immunity.

Methods

Four novel viral recombinants were constructed based on the fowlpox genetic background, which independently express the vaccinia virus L1 and A27 proteins present on the mature virions, and the A33 and B5 proteins present on the extracellular virions. The correct expression of the transgenes was determined by RT-PCR, Western blotting, and immunofluorescence.

Results and conclusions

Using immunoprecipitation and Western blotting, the ability of the proteins expressed by the four novel FP_L1R, FP_A27L, FP_A33R and FP_B5R recombinants to be recognized by VV-specific hyperimmune mouse sera was demonstrated. By neutralisation assays, recombinant virus particles released by infected chick embryo fibroblasts were shown not be recognised by hyperimmune sera. This thus demonstrates that the L1R, A27L, A33R and B5R gene products are not inserted into the new viral progeny. Fowlpox virus replicates only in avian species, but it is permissive for entry and transgene expression in mammalian cells, while being immunologically non–cross-reactive with vaccinia virus. These recombinants might therefore represent safer and more promising immunogens that can circumvent neutralisation by vector-generated immunity in smallpox-vaccine-experienced humans.