Enhancing cross-protection against influenza by heterologous sequential immunization with mRNA LNP and protein nanoparticle vaccines.

Enhancing influenza vaccine cross-protection is imperative to alleviate the significant public health burden of influenza. Heterologous sequential immunization may synergize diverse vaccine formulations and routes to improve vaccine potency and breadth. Here we investigate the effects of immunization strategies on the generation of cross-protective immune responses in female Balb/c mice, utilizing mRNA lipid nanoparticle (LNP) and protein-based PHC nanoparticle vaccines targeting influenza hemagglutinin. Our findings emphasize the crucial role of priming vaccination in shaping Th bias and immunodominance hierarchies. mRNA LNP prime favors Th1-leaning responses, while PHC prime elicits Th2-skewing responses. We demonstrate that cellular and mucosal immune responses are pivotal correlates of cross-protection against influenza. Notably, intranasal PHC immunization outperforms its intramuscular counterpart in inducing mucosal immunity and conferring cross-protection. Sequential mRNA LNP prime and intranasal PHC boost demonstrate optimal cross-protection against antigenically drifted and shifted influenza strains. Our study offers valuable insights into tailoring immunization strategies to optimize influenza vaccine effectiveness.

A synthetic TLR4 agonist significantly increases humoral immune responses and the protective ability of an MDCK-cell-derived inactivated H7N9 vaccine in mice.

Antigenically divergent H7N9 viruses pose a potential threat to public health, with the poor immunogenicity of candidate H7N9 vaccines demonstrated in clinical trials underscoring the urgent need for more-effective H7N9 vaccines. In the present study, mice were immunized with various doses of a suspended-MDCK-cell-derived inactivated H7N9 vaccine, which was based on a low-pathogenic H7N9 virus, to assess cross-reactive immunity and cross-protection against antigenically divergent H7N9 viruses. We found that the CRX-527 adjuvant, a synthetic TLR4 agonist, significantly enhanced the humoral immune responses of the suspended-MDCK-cell-derived H7N9 vaccine, with significant antigen-sparing and immune-enhancing effects, including robust virus-specific IgG, hemagglutination-inhibiting (HI), neuraminidase-inhibiting (NI), and virus-neutralizing (VN) antibody responses, which are crucial for protection against influenza virus infection. Moreover, the CRX-527-adjuvanted H7N9 vaccine also elicited cross-protective immunity and cross-protection against a highly pathogenic H7N9 virus with a single vaccination. Notably, NI and VN antibodies might play an important role in cross-protection against lethal influenza virus infections. This study showed that a synthetic TLR4 agonist adjuvant has a potent immunopotentiating effect, which might be considered worth further development as a means of increasing vaccine effectiveness.

Protection against the H1N1 influenza virus using self-assembled nanoparticles formed by lumazine synthase and bearing the M2e peptide.

There is an urgent need for influenza vaccines that offer broad cross-protection. The highly conserved ectodomain of the influenza matrix protein 2 (M2e) is a promising candidate; however, its low immunogenicity can be addressed. In this study, we developed influenza vaccines using the Lumazine synthase (LS) platform. The primary objective of this study was to determine the protective potential of M2e proteins expressed on Lumazine synthase (LS) nanoparticles. M2e-LS proteins, produced through the E. coli system, spontaneously assemble into nanoparticles. The study investigated the efficacy of the M2e-LS nanoparticle vaccine in mice. Mice immunized with M2e-LS nanoparticles exhibited significantly higher levels of intracellular cytokines than those receiving soluble M2e proteins. The M2e-LS protein exhibited robust immunogenicity and provided 100% protection against cross-clade influenza.

4CMenB journey to the 10-year anniversary and beyond.

The 4-component meningococcal serogroup B (MenB) vaccine, 4CMenB, the first broadly protective, protein-based MenB vaccine to be licensed, is now registered in more than 50 countries worldwide. Real-world evidence (RWE) from the last decade confirms its effectiveness and impact, with infant immunization programs showing vaccine effectiveness of 71-95% against invasive MenB disease and cross-protection against non-B serogroups, including a 69% decrease in serogroup W cases in 4CMenB-eligible cohorts in England. RWE from different countries also demonstrates the potential for additional moderate protection against gonorrhea in adolescents. The real-world safety profile of 4CMenB is consistent with prelicensure reports. Use of the endogenous complement human serum bactericidal antibody (enc-hSBA) assay against 110 MenB strains may enable assessment of the immunological effectiveness of multicomponent MenB vaccines in clinical trial settings. Equitable access to 4CMenB vaccination is required to better protect all age groups, including older adults, and vulnerable groups through comprehensive immunization policies.

Invasive meningococcal disease, caused by the bacterium Neisseria meningitidis(meningococcus), is rare but often devastating and can be deadly. Effective vaccines are available, including vaccines against meningococcal serogroup B disease. In 2013, the 4-component meningococcal serogroup B vaccine, 4CMenB, became the first broadly protective, protein-based vaccine against serogroup B to be licensed, with the second (bivalent vaccine, MenB-FHbp) licensed the following year. 4CMenB is now registered in more than 50 countries, in the majority, for infants and all age groups. In the US, it is approved for individuals aged 10­25 years. Evidence from immunization programs in the last decade, comparing vaccinated and unvaccinated individuals and the same population before and after vaccination, confirms the effectiveness and positive impact of 4CMenB against serogroup B disease. This also demonstrates that 4CMenB can provide protection against invasive diseases caused by other meningococcal serogroups. Furthermore, N. meningitidis is closely related to the bacterium that causes gonorrhea, N. gonorrhoeae, and emerging real-world evidence suggests that 4CMenB provides additional moderate protection against gonococcal disease. The safety of 4CMenB when given to large numbers of infants, children, adolescents, and adults is consistent with the 4CMenB safety profile reported before licensure.For the future, it would be beneficial to address differences among national guidelines for the recommended administration of 4CMenB, particularly where there is supportive epidemiological evidence but no equitable access to vaccination. New assays for assessing the potential effectiveness of meningococcal serogroup B vaccines in clinical trials are also required because serogroup B strains circulating in the population are extremely diverse across different countries.

An inactivated SARS-CoV-2 vaccine based on a Vero cell culture-adapted high-titer virus confers cross-protection in small animals.

Rapidly waning immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) requires continued global access to affordable vaccines. Globally, inactivated SARS-CoV-2 vaccines have been widely used during the SARS-CoV-2 pandemic. In this proof-of-concept study we adapted an original-D614G SARS-CoV-2 virus to Vero cell culture as a strategy to enhance inactivated vaccine manufacturing productivity. A passage 60 (P60) virus showed enhanced fitness and 50-fold increased virus yield in a bioreactor compared to the original-D614G virus. It further remained susceptible to neutralization by plasma from SARS-CoV-2 vaccinated and convalescent individuals, suggesting exposure of relevant epitopes. Monovalent inactivated P60 and bivalent inactivated P60/omicron BA.1 vaccines induced neutralizing responses against original-D614G and BA.1 viruses in mice and hamsters, demonstrating that the P60 virus is a suitable vaccine antigen. Antibodies further cross-neutralized delta and BA.5 viruses. Importantly, the inactivated P60 vaccine protected hamsters against disease upon challenge with original-D614G or BA.1 virus, with minimal lung pathology and lower virus loads in the upper and lower airways. Antigenicity of the P60 virus was thus retained compared to the original virus despite the acquisition of cell culture adaptive mutations. Consequently, cell culture adaptation may be a useful approach to increase yields in inactivated vaccine antigen production.

Evaluation of monkeypox- and vaccinia-virus neutralizing antibodies before and after smallpox vaccination: A sero-epidemiological study.

Since May 2022, several countries outside of Africa experienced multiple clusters of monkeypox virus (MPXV)-associated disease. In the present study, anti-MPXV and anti-vaccinia virus (VACV) neutralizing antibody responses were evaluated in two cohorts of subjects from the general Italian population (one half born before the WHO-recommended end of smallpox vaccination in 1980, the other half born after). Higher titers (either against MPXV or VACV) were observed in the cohort of individuals born before the interruption of VACV vaccination. An association between VACV and MPXV antibody levels was observed, suggesting that the smallpox vaccination may confer some degree of cross-protection against MPXV infection. Results from this study highlight low levels of immunity toward the assessed Orthopoxviruses, especially in young adults, advocating the introduction of a VACV- or MPXV-specific vaccine in case of resurgence of monkeypox disease outbreaks.

Mechanisms of Flavivirus Cross-Protection against Yellow Fever in a Mouse Model.

The complete lack of yellow fever virus (YFV) in Asia, and the lack of urban YFV transmission in South America, despite the abundance of the peridomestic mosquito vector Aedes (Stegomyia.) aegypti is an enigma. An immunologically naïve population of over 2 billion resides in Asia, with most regions infested with the urban YF vector. One hypothesis for the lack of Asian YF, and absence of urban YF in the Americas for over 80 years, is that prior immunity to related flaviviruses like dengue (DENV) or Zika virus (ZIKV) modulates YFV infection and transmission dynamics. Here we utilized an interferon α/ß receptor knock-out mouse model to determine the role of pre-existing dengue-2 (DENV-2) and Zika virus (ZIKV) immunity in YF virus infection, and to determine mechanisms of cross-protection. We utilized African and Brazilian YF strains and found that DENV-2 and ZIKV immunity significantly suppresses YFV viremia in mice, but may or may not protect relative to disease outcomes. Cross-protection appears to be mediated mainly by humoral immune responses. These studies underscore the importance of re-assessing the risks associated with YF outbreak while accounting for prior immunity from flaviviruses that are endemic.

Does Prior Respiratory Viral Infection Provide Cross-Protection Against Subsequent Respiratory Viral Infections? A Systematic Review and Meta-Analysis.

The epidemiology of different respiratory viral infections is believed to be affected by prior viral infections in addition to seasonal effects. This PROSPERO-registered systematic review identified 7388 studies, of which six met our criteria to answer the question specifically. The purpose of this review was to compare the prevalence of sequential viral infections in those with previously documented positive versus negative swabs. The pooled prevalence of sequential viral infections over varying periods from 30-1000 days of follow-up was higher following a negative respiratory viral swab at 0.15 than following a positive swab at 0.08, indicating the potential protective effects of prior respiratory viral infections. However, significant heterogeneity and publication biases were noted. There is some evidence, albeit of low quality, of a possible protective effect of an initial viral infection against subsequent infections by a different virus, which is possibly due to broad, nonspecific innate immunity. Future prospective studies are needed to validate our findings.

Conservation of HLA Spike Protein Epitopes Supports T Cell Cross-Protection in SARS-CoV-2 Vaccinated Individuals against the Potentially Zoonotic Coronavirus Khosta-2.

Heterologous vaccines, which induce immunity against several related pathogens, can be a very useful and rapid way to deal with new pandemics. In this study, the potential impact of licensed COVID-19 vaccines on cytotoxic and helper cell immune responses against Khosta-2, a novel sarbecovirus that productively infects human cells, was analyzed for the 567 and 41 most common HLA class I and II alleles, respectively. Computational predictions indicated that most of these 608 alleles, covering more than 90% of the human population, contain sufficient fully conserved T-cell epitopes between the Khosta-2 and SARS-CoV-2 spike-in proteins. Ninety percent of these fully conserved peptides for class I and 93% for class II HLA molecules were verified as epitopes recognized by CD8+ or CD4+ T lymphocytes, respectively. These results show a very high correlation between bioinformatic prediction and experimental assays, which strongly validates this study. This immunoinformatics analysis allowed a broader assessment of the alleles that recognize these peptides, a global approach at the population level that is not possible with experimental assays. In summary, these findings suggest that both cytotoxic and helper cell immune protection elicited by currently licensed COVID-19 vaccines should be effective against Khosta-2 virus infection. Finally, by being rapidly adaptable to future coronavirus pandemics, this study has potential public health implications.

A speed limit on serial strain replacement from original antigenic sin.

Many pathogens evolve to escape immunity, yet it remains difficult to predict whether immune pressure will lead to diversification, serial replacement of one variant by another, or more complex patterns. Pathogen strain dynamics are mediated by cross-protective immunity, whereby exposure to one strain partially protects against infection by antigenically diverged strains. There is growing evidence that this protection is influenced by early exposures, a phenomenon referred to as original antigenic sin (OAS) or imprinting. In this paper, we derive constraints on the emergence of the pattern of successive strain replacements demonstrated by influenza, SARS-CoV-2, seasonal coronaviruses, and other pathogens. We find that OAS implies that the limited diversity found with successive strain replacement can only be maintained if [Formula: see text] is less than a threshold set by the characteristic antigenic distances for cross-protection and for the creation of new immune memory. This bound implies a "speed limit" on the evolution of new strains and a minimum variance of the distribution of infecting strains in antigenic space at any time. To carry out this analysis, we develop a theoretical model of pathogen evolution in antigenic space that implements OAS by decoupling the antigenic distances required for protection from infection and strain-specific memory creation. Our results demonstrate that OAS can play an integral role in the emergence of strain structure from host immune dynamics, preventing highly transmissible pathogens from maintaining serial strain replacement without diversification.

Evidence for immune priming specificity and cross-protection against sympatric and allopatric Vibrio splendidus strains in the oyster Magalana (Crassostrea) gigas.

Infections with pathogenic Vibrio strains are associated with high summer mortalities of Pacific oysters Magalana (Crassostrea) gigas, affecting production worldwide. This raises the question of how M. gigas cultures can be protected against deadly Vibro infection. There is increasing experimental evidence of immune priming in invertebrates, where previous exposure to a low pathogen load boosts the immune response upon secondary exposure. Priming responses, however, appear to vary in their specificity across host and parasite taxa. To test priming specificity in the Vibrio - M. gigas system, we used two closely related Vibrio splendidus strains with differing degrees of virulence towards M. gigas. These V. splendidus strains were either isolated in the same location as the oysters (sympatric, opening up the potential for co-evolution) or in a different location (allopatric). We extracted cell-free haemolymph plasma from infected and control oysters to test the influence of humoral immune effectors on bacterial growth in vitro. While addition of haemolypmph plasma in general promoted growth of both strains, priming by an exposure to a sublethal dose of bacterial cells lead to inhibitory effects against a subsequent challenge with a potentially lethal dose in vitro. Inhibitory effects and immune priming was strongest when oysters had been primed with the sympatric Vibrio strain, but inhibitory effects were seen both when challenged with the sympatric as well as against allopatric V. splendidus, suggesting some degree of cross protection. The stronger immune priming against the sympatric strain suggests that priming could be more efficient against matching local strains potentially adding a component of local adaptation or co-evolution to immune priming in oysters. These in vitro results, however, were not reflected in the in vivo infection data, where we saw increased bacterial loads following an initial challenge. This discrepancy might suggests that that it is the humoral part of the oyster immune system that produces the priming effects seen in our in vitro experiments.

Smallpox vaccination campaigns resulted in age-associated population cross-immunity against monkeypox virus.

Increased human-to-human transmission of monkeypox virus (MPXV) is cause for concern, and antibodies directed against vaccinia virus (VACV) are known to confer cross-protection against Mpox. We used 430 serum samples derived from the Scottish patient population to investigate antibody-mediated cross-neutralization against MPXV. By combining electrochemiluminescence immunoassays with live-virus neutralization assays, we show that people born when smallpox vaccination was routinely offered in the United Kingdom have increased levels of antibodies that cross-neutralize MPXV. Our results suggest that age is a risk factor of Mpox infection, and people born after 1971 are at higher risk of infection upon exposure.

A full-length glycoprotein mRNA vaccine confers complete protection against severe fever with thrombocytopenia syndrome virus, with broad-spectrum protective effects against bandaviruses.

Highly pathogenic viruses from family Phenuiviridae, which are mainly transmitted by arthropods, have intermittently sparked epidemics worldwide. In particular, tick-borne bandaviruses, such as severe fever with thrombocytopenia syndrome virus (SFTSV), continue to spread in mountainous areas, resulting in an average mortality rate as high as 10.5%, highlighting the urgency and importance of vaccine development. Here, an mRNA vaccine developed based on the full-length SFTSV glycoprotein, containing both the receptor-binding domain and the fusion domain, was shown to confer complete protection against SFTSV at a very low dose by triggering a type 1 helper T cell-biased cellular immune response in rodents. Moreover, the vaccine candidate elicited long-term immunity and protection against SFTSV for at least 5 months. Notably, it provided complete cross-protection against other bandaviruses, such as the Heartland virus and Guertu virus, in lethal challenge models. Further research revealed that the conserved epitopes among bandaviruses within the full-length SFTSV glycoprotein may facilitate broad-spectrum protection mediated by the cellular immune response. Collectively, these findings demonstrate that the full-length SFTSV glycoprotein mRNA vaccine is a promising vaccine candidate for SFTSV and other bandaviruses, and provide guidance for the development of broad-spectrum vaccines from conserved antigens and epitopes. IMPORTANCE: Tick-borne bandaviruses, such as SFTSV and Heartland virus, sporadically trigger outbreaks in addition to influenza viruses and coronaviruses, yet there are no specific vaccines or therapeutics against them. mRNA vaccine technology has advantages in terms of enabling in situ expression and triggering cellular immunity, thus offering new solutions for vaccine development against intractable viruses, such as bandaviruses. In this study, we developed a novel vaccine candidate for SFTSV by employing mRNA vaccination technology and using a full-length glycoprotein as an antigen target. This candidate vaccine confers complete and durable protection against SFTSV at a notably low dose while also providing cross-protection against Heartland virus and Guertu virus. This study highlights the prospective value of full-length SFTSV-glycoprotein-based mRNA vaccines and suggests a potential strategy for broad-spectrum bandavirus vaccines.

A combination influenza mRNA vaccine candidate provided broad protection against diverse influenza virus challenge.

Influenza viruses present a significant threat to global health. The production of a universal vaccine is considered essential due to the ineffectiveness of current seasonal influenza vaccines against mutant strains. mRNA technology offers new prospects in vaccinology, with various candidates for different infectious diseases currently in development and testing phases. In this study, we encapsulated a universal influenza mRNA vaccine. The vaccine encoded influenza hemagglutinin (HA), nucleoprotein (NP), and three tandem repeats of matrix protein 2 (3M2e). Twice-vaccinated mice exhibited strong humoral and cell-mediated immune responses in vivo. Notably, these immune responses led to a significant reduction in viral load of the lungs in challenged mice, and also conferred protection against future wild-type H1N1, H3N2, or H5N1 influenza virus challenges. Our findings suggest that this mRNA-universal vaccine strategy for influenza virus may be instrumental in mitigating the impact of future influenza pandemics.

Dimethyl-Dioctadecyl-Ammonium Bromide/Poly(lactic acid) Nanoadjuvant Enhances the Immunity and Cross-Protection of an NM2e-Based Universal Influenza Vaccine.

For most frequent respiratory viruses, there is an urgent need for a universal influenza vaccine to provide cross-protection against intra- and heterosubtypes. We previously developed an Escherichia coli fusion protein expressed extracellular domain of matrix 2 (M2e) and nucleoprotein, named NM2e, and then combined it with an aluminum adjuvant, forming a universal vaccine. Although NM2e has demonstrated a protective effect against the influenza virus in mice to some extent, further improvement is still needed for the induction of immune responses ensuring adequate cross-protection against influenza. Herein, we fabricated a cationic solid lipid nanoadjuvant using poly(lactic acid) (PLA) and dimethyl-dioctadecyl-ammonium bromide (DDAB) and loaded NM2e to generate an NM2e@DDAB/PLA nanovaccine (Nv). In vitro experiments suggested that bone marrow-derived dendritic cells incubated with Nv exhibited ∼4-fold higher antigen (Ag) uptake than NM2e at 16 h along with efficient activation by NM2e@DDAB/PLA Nv. In vivo experiments revealed that Ag of the Nv group stayed in lymph nodes (LNs) for more than 14 days after initial immunization and DCs in LNs were evidently activated and matured. Furthermore, the Nv primed T and B cells for robust humoral and cellular immune responses after immunization. It also induced a ratio of IgG2a/IgG1 higher than that of NM2e to a considerable extent. Moreover, NM2e@DDAB/PLA Nv quickly restored body weight and improved survival of homo- and heterosubtype influenza challenged mice, and the cross-protection efficiency was over 90%. Collectively, our study demonstrated that NM2e@DDAB/PLA Nv could offer notable protection against homo- and heterosubtype influenza virus challenges, offering the potential for the development of a universal influenza vaccine.

Cross-protective efficacy and safety of an adenovirus-based universal influenza vaccine expressing nucleoprotein, hemagglutinin, and the ectodomain of matrix protein 2.

It is necessary to develop universal vaccines that act broadly and continuously to combat regular seasonal epidemics of influenza and rare pandemics. The aim of this study was to find the optimal dose regimen for the efficacy and safety of a mixture of previously developed recombinant adenovirus-based vaccines that expressed influenza nucleoprotein, hemagglutinin, and ectodomain of matrix protein 2 (rAd/NP and rAd/HA-M2e). The vaccine efficacy and safety were measured in the immunized mice with the mixture of rAd/NP and rAd/HA-M2e intranasally or intramuscularly. The minimum dose that would be efficacious in a single intranasal administration of the vaccine mixture and cross-protective efficacy against various influenza strains were examined. In addition, the immune responses that may affect the cross-protective efficacy were measured. We found that intranasal administration is an optimal route for 107 pfu of vaccine mixture, which is effective against pre-existing immunity against adenovirus. In a study to find the minimum dose with vaccine efficacy, the 106 pfu of vaccine mixture showed higher antibody titers to the nucleoprotein than did the same dose of rAd/NP alone in the serum of immunized mice. The 106 pfu of vaccine mixture overcame the morbidity and mortality of mice against the lethal dose of pH1N1, H3N2, and H5N1 influenza infections. No noticeable side effects were observed in single and repeated toxicity studies. We found that the mucosal administration of adenovirus-based universal influenza vaccine has both efficacy and safety, and can provide cross-protection against various influenza infections even at doses lower than those previously known to be effective.

Cross-protection against influenza viruses by chimeric M2e-H3 stalk protein or multi-subtype neuraminidase plus M2e virus-like particle vaccine in ferrets.

Current influenza vaccine is not effective in providing cross-protection against variants. We evaluated the immunogenicity and efficacy of multi-subtype neuraminidase (NA) and M2 ectodomain virus-like particle (m-cNA-M2e VLP) and chimeric M2e-H3 stalk protein vaccines (M2e-H3 stalk) in ferrets. Our results showed that ferrets with recombinant m-cNA-M2e VLP or M2e-H3 stalk vaccination induced multi-vaccine antigen specific IgG antibodies (M2e, H3 stalk, NA), NA inhibition, antibody-secreting cells, and IFN-γ secreting cell responses. Ferrets immunized with either m-cNA-M2e VLP or M2e-H3 stalk vaccine were protected from H1N1 and H3N2 influenza viruses by lowering viral titers in nasal washes, trachea, and lungs after challenge. Vaccinated ferret antisera conferred broad humoral immunity in naïve mice. Our findings provide evidence that immunity to M2e and HA-stalk or M2e plus multi-subtype NA proteins induces cross-protection in ferrets.

Supplementation of seasonal vaccine with multi-subtype neuraminidase and M2 ectodomain virus-like particle improves protection against homologous and heterologous influenza viruses in aged mice.

The conventional inactivated split seasonal influenza vaccine offers low efficacy, particularly in the elderly and against antigenic variants. Here, to improve the efficacy of seasonal vaccination for the elderly population, we tested whether supplementing seasonal bivalent (H1N1 + H3N2) split (S) vaccine with M2 ectodomain repeat and multi-subtype consensus neuraminidase (NA) proteins (N1 NA + N2 NA + flu B NA) on a virus-like particle (NA-M2e) would induce enhanced cross-protection against different influenza viruses in aged mice. Immunization with split vaccine plus NA-M2e (S + NA-M2e) increased vaccine-specific IgG antibodies towards T-helper type 1 responses and hemagglutination inhibition titers. Aged mice with NA-M2e supplemented vaccination were protected against homologous and heterologous viruses at higher efficacies, as evidenced by preventing weight loss, lowering lung viral loads, inducing broadly cross-protective humoral immunity, and IFN-γ+ CD4 and CD8 T cell responses than those with seasonal vaccine. Overall, this study supports a new strategy of NA-M2e supplemented vaccination to enhance protection against homologous and antigenically different viruses in the elderly.

Development and Application of Attenuated Plant Viruses as Biological Control Agents in Japan.

In 1929, it was reported that yellowing symptoms caused by a tobacco mosaic virus (TMV) yellow mosaic isolate were suppressed in tobacco plants that were systemically infected with a TMV light green isolate. Similar to vaccination, the phenomenon of cross-protection involves a whole plant being infected with an attenuated virus and involves the same or a closely related virus species. Therefore, attenuated viruses function as biological control agents. In Japan, many studies have been performed on cross-protection. For example, the tomato mosaic virus (ToMV)-L11A strain is an attenuated isolate developed by researchers and shows high control efficiency against wild-type ToMV in commercial tomato crops. Recently, an attenuated isolate of zucchini yellow mosaic virus (ZYMV)-2002 was developed and registered as a biological pesticide to control cucumber mosaic disease. In addition, attenuated isolates of pepper mild mottle virus (PMMoV), cucumber mosaic virus (CMV), tobacco mild green mosaic virus (TMGMV), melon yellow spot virus (MYSV), and watermelon mosaic virus (WMV) have been developed in Japan. These attenuated viruses, sometimes called plant vaccines, can be used not only as single vaccines but also as multiple vaccines. In this review, we provide an overview of studies on attenuated plant viruses developed in Japan. We also discuss the application of the attenuated strains, including the production of vaccinated seedlings.

Japanese encephalitis virus E protein domain III immunization mediates cross-protection against Zika virus in mice via antibodies and CD8+T cells.

Zika virus (ZIKV) and Japanese encephalitis virus (JEV) are antigenically related flaviviruses that co-circulate in many countries/territories. The interaction between the two viruses needs to be determined. Recent findings by ourselves and other labs showed that JEV-elicited antibodies (Abs) and CD8+T cells exacerbate and protect against subsequent ZIKV infection, respectively. However, the impact of JEV envelope (E) protein domain III (EDIII)-induced immune responses on ZIKV infection is unclear. We show here that sera from JEV-EDIII-vaccinated mice cross-react with ZIKV-EDIII in vitro, and transfer of the same sera to mice significantly decreases death upon lethal ZIKV infection at a dose-dependent manner. Maternally acquired anti-JEV-EDIII Abs also significantly reduce the mortality of neonatal mice born to JEV-EDIII-immune mothers post ZIKV challenge. Similarly, transfer of ZIKV-EDIII-reactive IgG purified from JEV-vaccinated humans increases the survival of ZIKV-infected mice. Notably, transfer of an extremely low volume of JEV-EDIII-immune sera or ZIKV-EDIII-reactive IgG does not mediate the Ab-mediated enhancement (ADE) of ZIKV infection. Similarly, transfer of JEV-EDIII-elicited CD8+T cells protects recipient mice against ZIKV challenge. These results demonstrate that JEV-EDIII-induced immune components including Abs and T cells have protective roles in ZIKV infection, suggesting EDIII is a promising immunogen for developing effective and safety JEV vaccine.