Characterization of a Small Plaque Variant Derived from Genotype V Japanese Encephalitis Virus Clinical Isolate K15P38.

Genotype V (GV) Japanese encephalitis virus (JEV) has been predominantly reported in the Republic of Korea (ROK) since 2010. GV JEV exhibits higher virulence and distinct antigenicity compared to other genotypes, which results in reduced efficacy of existing vaccines. Research on GV JEV is essential to minimize its clinical impact, but the only available clinical strain in the ROK is K15P38, isolated from the cerebrospinal fluid of a patient in 2015. We obtained this virus from National Culture Collection for Pathogens (NCCP) and isolated a variant forming small plaques during our research. We identified that this variant has one amino acid substitution each in the PrM and NS5 proteins compared to the reported K15P38. Additionally, we confirmed that this virus exhibits delayed propagation in vitro and an attenuated phenotype in mice. The isolation of this variant is a critical reference for researchers intending to study K15P38 obtained from NCCP, and the mutations in the small plaque-forming virus are expected to be useful for studying the pathology of GV JEV.

Antiviral activity of pimecrolimus against dengue virus type 2 infection in vitro and in vivo.

Dengue virus (DENV) infection is a public health concern in several countries and is associated with severe diseases, such as dengue hemorrhagic fever and dengue shock syndrome. DENVs are transmitted to humans via the bites of infected Aedes mosquitoes, and no antiviral therapeutics are currently available. In this work, we aimed to identify antiviral drugs against DENV type 2 (DENV2) infections and selected pimecrolimus as a potential antiviral drug candidate. Pimecrolimus significantly inhibited DENV2-mediated cell death and replication in vitro. We also confirmed a decrease in the number of plaques formed as well as in the envelope protein levels of DENV2. The time-of-addition and course experiments revealed that pimecrolimus inhibited DENV2 infection during the early stages of the virus replication cycle. In an experimental mouse model, orally administered pimecrolimus alleviated body weight loss and lethality caused by DENV2 infection, which we used as readouts of the drug's antiviral potency. Furthermore, pimecrolimus significantly inhibited the DENV2 load and ameliorated focal necrosis in the liver and spleen. Taken together, our in vitro and in vivo findings suggest that pimecrolimus is a promising antiviral drug candidate for the treatment of DENV2 infection.

Characterization of genotype V Japanese encephalitis virus isolates from Republic of Korea.

Japanese encephalitis (JE), caused by the Japanese encephalitis virus (JEV) infection, continues to pose significant public health challenges worldwide despite efficient vaccines. The virus is classified into five genotypes, among which genotype V (GV) was not detected for a long period after its initial isolation in 1952, until reports emerged from China and the Republic of Korea (ROK) since 2009. The characteristics of the virus are crucial in estimating its potential epidemiological impact. However, characterization of GV JEVs has so far been limited to two strains: Muar, the original isolate, and XZ0934, isolated in China. Two additional ROK GV JEV isolates, NCCP 43279 and NCCP 43413, are currently available, but their characteristics have not been explored. Our phylogenetic analysis revealed that GV virus sequences from the ROK segregate into two clades. NCCP 43279 and NCCP 43413 belong to different clades and exhibit distinct in vitro phenotypes. NCCP 43279 forms larger plaques but demonstrates inefficient propagation in cell culture compared to NCCP 43413. In vivo, NCCP 43279 induces higher morbidity and mortality in mice than NCCP 43413. Notably, NCCP 43279 shows more severe blood-brain barrier damage, suggesting superior brain invasion capabilities. Consistent with its higher virulence, NCCP 43279 displays more pronounced histopathological and immunopathological outcomes. In conclusion, our study confirms that the two ROK isolates are not only classified into different clades but also exhibit distinct in vitro and in vivo characteristics.

Evaluating Z-FA-FMK, a host cathepsin L protease inhibitor, as a potent and broad-spectrum antiviral therapy against SARS-CoV-2 and related coronaviruses.

Even though the World Health Organization announced the end of the COVID-19 pandemic as a global public health emergency on May 5, 2023, SARS-CoV-2 continues to pose a significant health threat worldwide, resulting in substantial numbers of infections and fatalities. This study investigated the antiviral potential of Z-FA-FMK (FMK), a novel host cathepsin L protease inhibitor, against SARS-CoV-2 infection using both in vitro and in vivo models. In vitro assessments of FMK against a diverse set of SARS-CoV-2 strains, including the Wuhan-like strain and nine variants, demonstrated potent inhibition with EC50 values ranging from 0.55 to 2.41 µM, showcasing similar or superior efficacy compared to FDA-approved antivirals nirmatrelvir (NTV) and molnupiravir (MPV). In vivo experiments using orally administered FMK (25 mg/kg) in SARS-CoV-2-infected K18 hACE2 transgenic mice revealed improved survival rates of 60% and accelerated recovery compared to NTV and MPV treatments. Additionally, FMK displayed a longer half-life (17.26 ± 8.89 h) than NTV and MPV in the mouse model. Due to its host-targeting mechanism, FMK offers potential advantages such as reduced drug resistance and broad-spectrum antiviral activity against multiple coronaviruses. These findings indicate that FMK may serve as a promising candidate for further clinical evaluation in the fight against SARS-CoV-2.

Surveillance of avian influenza viruses from 2014 to 2018 in South Korea.

Surveillance of influenza A viruses (IAVs) among migratory waterfowl is a first step in understanding the ecology, biology, and pathogenicity of IAVs. As part of the nationwide surveillance effort for IAVs in fowl in South Korea, we collected environmental fecal samples in different migratory bird stopover sites in South Korea during the winter seasons within November 2014 through January 2018. We collected a total of 6758 fecal samples, 75 of which were positive for IAV (1.11% positivity). Prevalence of IAVs varied per site and per year. Based on sequencing, the most prevalent hemagglutinin (HA) subtypes were H1, H6, and H5, and the most prevalent neuraminidase (NA) subtypes were N1, N3, and N2. Phylogenetic analyses showed that the genes we isolated clustered with reported isolates collected from other locations along the East Asian-Australasian Flyway. All the H5 and H7 isolates collected in this study were of low pathogenicity. None of the N1 and N2 genes carried amino acid markers of resistance against NA inhibitors. The winter 2016-2017 subset were primarily borne by migratory geese (Anser spp.). These results suggest that majority of the IAVs circulating among migratory wild fowl in South Korea in 2014-2018 were of low pathogenicity.

Persistence of the neutralizing antibody response after SARS-CoV-2 infection.

OBJECTIVE: Neutralizing antibodies are among the factors used to measure an individual's immune status for the control of infectious diseases. We aimed to confirm the persistence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) neutralizing antibody levels in patients who had recovered from coronavirus disease 2019 (COVID-19). METHODS: Plasma donors in South Korea who had completely recovered from SARS-CoV-2 infection had follow-up testing to determine the persistence of neutralizing antibodies using a plaque-reduction neutralization test and ELISA. RESULTS: Of the 111 participants-aged 20-29 years, 37/111 (33.3%); 30-39 years, 17/111 (15.3%); 40-49 years, 23/111 (20.7%); 50-59 years, 21/111 (18.9%); 60-65 years, 13/111 (11.7%); male, 43/111 (38.7%); female, 68/111 (61.3%)-66.1% still had neutralizing antibodies approximately 9 months (range 255-302 days) after confirmation of the diagnosis. CONCLUSIONS: In this study we analysed the titre of neutralizing antibodies associated with predicting immune status in individuals with natural infection. Information about the persistence and change in levels of neutralizing antibodies against SARS-CoV-2 can be utilized to provide evidence for developing vaccination schedules for individuals with previous infection.

Surveillance of avian influenza viruses from 2009 to 2013 in South Korea.

Avian influenza viruses (AIVs) are carried by wild migratory waterfowl across migratory flyways. To determine the strains of circulating AIVs that may pose a risk to poultry and humans, regular surveillance studies must be performed. Here, we report the surveillance of circulating AIVs in South Korea during the winter seasons of 2009-2013. A total of 126 AIVs were isolated from 7942 fecal samples from wild migratory birds, with a total isolation rate of 1.59%. H1‒H7 and H9‒H11 hemagglutinin (HA) subtypes, and N1‒N3, N5, and N7‒N9 neuraminidase (NA) subtypes were successfully isolated, with H6 and N2 as the most predominant HA and NA subtypes, respectively. Sequence identity search showed that the HA and NA genes of the isolates were highly similar to those of low-pathogenicity influenza strains from the East Asian-Australasian flyway. No match was found for the HA genes of high-pathogenicity influenza strains. Thus, the AIV strains circulating in wild migratory birds from 2009 to 2013 in South Korea likely had low pathogenicity. Continuous surveillance studies such as this one must be performed to identify potential precursors of influenza viruses that may threaten animal and human health.

Inhibitory effects of aprotinin on influenza A and B viruses in vitro and in vivo.

Influenza viruses cause significant morbidity and mortality worldwide. Long-term or frequent use of approved anti-influenza agents has resulted in drug-resistant strains, thereby necessitating the discovery of new drugs. In this study, we found aprotinin, a serine protease inhibitor, as an anti-influenza candidate through screening of compound libraries. Aprotinin has been previously reported to show inhibitory effects on a few influenza A virus (IAV) subtypes (e.g., seasonal H1N1 and H3N2). However, because there were no reports of its inhibitory effects on the other types of influenza viruses, we investigated the inhibitory effects of aprotinin in vitro on a wide range of influenza viruses, including avian and oseltamivir-resistant influenza virus strains. Our cell-based assay showed that aprotinin had inhibitory effects on seasonal human IAVs (H1N1 and H3N2 subtypes), avian IAVs (H5N2, H6N5, and H9N2 subtypes), an oseltamivir-resistant IAV, and a currently circulating influenza B virus. We have also confirmed its activity in mice infected with a lethal dose of influenza virus, showing a significant increase in survival rate. Our findings suggest that aprotinin has the capacity to inhibit a wide range of influenza virus subtypes and should be considered for development as a therapeutic agent against influenza.

Characterization of a human monoclonal antibody generated from a B-cell specific for a prefusion-stabilized spike protein of Middle East respiratory syndrome coronavirus.

Middle East respiratory syndrome coronavirus (MERS-CoV) causes severe respiratory infection and continues to infect humans, thereby contributing to a high mortality rate (34.3% in 2019). In the absence of an available licensed vaccine and antiviral agent, therapeutic human antibodies have been suggested as candidates for treatment. In this study, human monoclonal antibodies were isolated by sorting B cells from patient's PBMC cells with prefusion stabilized spike (S) probes and a direct immunoglobulin cloning strategy. We identified six receptor-binding domain (RBD)-specific and five S1 (non-RBD)-specific antibodies, among which, only the RBD-specific antibodies showed high neutralizing potency (IC50 0.006-1.787 µg/ml) as well as high affinity to RBD. Notably, passive immunization using a highly potent antibody (KNIH90-F1) at a relatively low dose (2 mg/kg) completely protected transgenic mice expressing human DPP4 against MERS-CoV lethal challenge. These results suggested that human monoclonal antibodies isolated by using the rationally designed prefusion MERS-CoV S probe could be considered potential candidates for the development of therapeutic and/or prophylactic antiviral agents for MERS-CoV human infection.

Genetic Characterization of Japanese Encephalitis Virus Genotype 5 Isolated from Patient, South Korea, 2015.

We isolated Japanese encephalitis virus genotype 5 from human specimens in South Korea. Whole-genome analysis showed 90.4% identity with other genotype 5 viruses from humans. This virus had a unique insertion in the NS4A gene. However, the envelope protein contained Lys 84, which was specific to strains of genotype 5 viruses from South Korea.

Molecular and phylogenetic analyses of influenza B viruses isolated from pediatric inpatients in South Korea during the 2011-2012 winter season.

Influenza B virus remains a major cause of respiratory diseases worldwide. Because of limited epidemiological and genetic data, the local and global transmission patterns of influenza B virus are not fully understood. Here we report the molecular and phylogenetic characterization of 163 influenza B virus isolates from pediatric inpatients with influenza-like illness in the winter of 2011-2012 in South Korea. Analysis of haemagglutinin and neuraminidase genes of the influenza B isolates revealed that both B/Victoria (62 %) and B/Yamagata lineages (38 %) co-circulated during that influenza season, and a considerable number of the isolates carried several amino acid substitutions in the four major antigenic epitopes of their haemagglutinin protein.

Rapid virulence shift of an H5N2 avian influenza virus during a single passage in mice.

Influenza A viruses must undergo adaptation to acquire virulence in new host species. In mouse models, host adaptation for virulence is generally performed through 5 to 20 lung-to-lung passages. However, highly pathogenic avian influenza viruses (e.g., H5N1 and H7N7 subtypes) have been observed to acquire virulence in mice after only a few in vivo passages. In this study, a low-pathogenic avian influenza H5N2 virus, A/Aquatic Bird/Korea/CN2/2009, which was a prevalent subtype in South Korea in 2009, was serially passaged in mice to evaluate its potential to become highly pathogenic. Unexpectedly, the virus became highly pathogenic in mice after a single lung-to-lung passage, resulting in 100% lethality with a mean death time (MDT) of 6.1 days postinfection (DPI). Moreover, the pathogenicity gradually increased after subsequent in vivo passages with an MDT of 5.2 and 4.2 DPI after the second and third passage, respectively. Our molecular analysis revealed that two amino acid changes in the polymerase complex (a glutamate-to-lysine substitution at position 627 of PB2 and a threonine-to-isoleucine substitution at position 97 of PA) were associated with the increased pathogenicity; the PB2 E627K mutation was responsible for the initial virulence conversion (0 to 100% lethality), while the PA T97I mutation acted as an accessory for the increased virulence.

Nontoxic outer membrane vesicles efficiently increase the efficacy of an influenza vaccine in mice and ferrets.

In this study, we developed a further-modified outer membrane vesicle (fmOMV) from the ΔmsbB/ΔpagP mutant of Escherichia coli transformed with the plasmid, pLpxF, in order to use it as an adjuvant for pandemic H1N1 (pH1N1) influenza vaccine. We evaluated the efficacy of the pH1N1 influenza vaccine containing the fmOMV in animal models as compared to the commercial adjuvants, alum or AddaVaxTM. The fmOMV-adjuvanted pH1N1 influenza vaccine induced a significant increase in the humoral immunity; however, this effect was less than that of the AddaVaxTM. The fmOMV-adjuvanted vaccine displayed pronounced an enhanced protective efficacy with increased T cell immune response and reduced the viral load in the lungs of the infected mice after challenging them with a lethal dose of the homologous virus. Moreover, it resulted in a significantly higher cross-protection against heterologous virus challenge than that of the pH1N1 vaccine with alum or with no adjuvants. In ferrets, the fmOMV-adjuvanted vaccine elicited a superior antibody response based on the HI titer and efficiently protected the animals from the lethal viral challenges. Taken together, the nontoxic fmOMV could be a promising adjuvant for inducing robust T cell priming into the pH1N1 vaccine and might be broadly applicable to the development of preventive measures against influenza virus infection.

Poly-γ-glutamic acid/chitosan nanogel greatly enhances the efficacy and heterosubtypic cross-reactivity of H1N1 pandemic influenza vaccine.

In 2009, the global outbreak of an influenza pandemic emphasized the need for an effective vaccine adjuvant. In this study, we examined the efficacy of poly-γ-glutamic acid/chitosan (PC) nanogel as an adjuvant for the influenza vaccine. PC nanogel significantly enhanced antigen-specific cross-presentation and cytotoxic T lymphocyte (CTL) activity. Compared with alum, the protective efficacy of the pandemic H1N1 influenza (pH1N1) vaccine was substantially increased by PC nanogel, with increased hemagglutination-inhibition titers, CTL activity, and earlier virus clearance after homologous and heterosubtypic [A/Philippines/2/82 (H3N2)] virus challenges. However, CD8+ T cell-depleted mice displayed no protection against the heterosubtypic virus challenge after immunization with PC nanogel-adjuvanted pH1N1 vaccine. We also observed that using PC nanogel as a vaccine adjuvant had a dose-sparing effect and significantly enhanced the long-lasting protection of the pH1N1 vaccine. Together, these results suggest that PC nanogel is a promising vaccine adjuvant that could broadly prevent influenza virus infection.

Genetic Characterization of an Ancestral Strain of the Avian-Origin H3N2 Canine Influenza Virus Currently Circulating in East Asia.

H3N2 canine influenza virus emerged in South Korea in 2007 and subsequently spread to China and Thailand, causing epidemic or endemic respiratory diseases in dogs. Through intermammalian species transmission, the virus has also infected cats. However, no direct evidence of significant genetic evolution has been reported since its first emergence. Here, we describe in depth the genetic and molecular characteristics of the ancestral strain (i.e., the first virus isolate from South Korea) of the H3N2 canine influenza virus currently circulating in East Asia.

Polymer nanomicelles for efficient mucus delivery and antigen-specific high mucosal immunity.

Micelles for mucosal immunity: A mucosal vaccine system based on γ-PGA nanomicelles and viral antigens was synthesized. The intranasal administration of the vaccine system induces a high immune response both in the humoral and cellular immunity (see picture).

Bioderived polyelectrolyte nanogels for robust antigen loading and vaccine adjuvant effects.

An easy but robust strategy for the synthesis of bioderived polyelectrolyte nanogels for protein antigen loading and vaccine adjuvant systems that can improve both humoral (Th2) and cellular immunity (Th1) is presented. The synthesized polyelectrolyte nanogels promote the uptake of antigens into antigen-presenting cells and strongly induce ovalbumin-specific INF-γ producing cells, cytotoxic T cell activity, and antibody production.