Natalia Danilchenko

In this study, we aimed to analyze the antiviral susceptibility of clade 2.3.4.4b H5N1 and H5N5 influenza viruses detected in Russia during 2021–2022. During this period, we investigated 40 avian influenza outbreaks in wild and domestic birds, isolating 109 H5N1 and 9 H5N5 strains. Using a genetic approach, we analyzed the presence of markers associated with reduced susceptibility to baloxavir and M2 blockers, as well as markers of reduced inhibition by neuraminidase inhibitors (NAIs). Additionally, the isolated strains were tested in a functional assay to evaluate the inhibitory activity of oseltamivir, zanamivir, and peramivir against viral neuraminidase. None of the isolates harbored genetic markers of reduced susceptibility to M2 blockers and baloxavir or reduced inhibition by NAIs. Functional assay showed that the median IC₅₀ values of oseltamivir, zanamivir, and peramivir were 1.73, 0.49, and 0.16 nM for the H5N1 subtype, and 0.65, 1.13, and 0.12 nM for the H5N5 subtype, respectively. None of the tested strains demonstrated a ≥10-fold increase in NAI IC₅₀ values compared to the corresponding subtype medians, and were thus classified as having a normal level of inhibition. The median IC₅₀ values of the NAIs determined for the tested avian viruses were comparable to those of a susceptible seasonal A(H1N1)pdm09 strain, except for a slight reduction in oseltamivir activity against H5N1 viruses (4.3-fold) and zanamivir activity against H5N5 viruses (3.4-fold). Our study revealed a group of H5N1 viruses whose NA belonged to the ea5.1 genetic subclade, characterized by NA-Y253H and T452I amino acid substitutions, which exhibited a 28.8-fold decrease in oseltamivir IC₅₀ values compared to the subtype median. These strains were detected in the European and Ural regions of Russia between May 2022 and January 2023, with no subsequent detections in the available surveillance data. To the best of our knowledge, such strains have not been identified outside Russia.

INTRODUCTION. The highly pathogenic avian influenza virus subtype H5Nx is rapidly evolving and infecting various species of wild and domestic mammals, including cattle, highlighting its pandemic potential for humans. To combat the pandemic threat, it is essential to develop suitable vaccine platforms, including mRNA vaccines, the efficacy of which largely depends on the delivery system. This study evaluates the immunogenicity and protective efficacy of the mRNA-H5 vaccine, delivered via lipid nanoparticles (LNPs) and jet injection (JI). AIM. The aim of the study was to evaluate the immunogenic and protective properties of the experimental mRNA-H5 vaccine in a ferret model. MATERIALS AND METHODS. Ferrets were immunized twice with the mRNA-H5 vaccine at a dose of 30 μg formulated with LNPs and at a dose of 100 μg administered by JI. Sera from immunized ferrets were analyzed using an enzyme-linked immunosorbent assay (ELISA) against the recombinant HA/H5 protein, an enzyme-linked immunospot (ELISpot) assay using a pool of specific peptides, and a virus neutralization assay in MDCK-SIAT1 cell culture using the influenza virus strain A/turkey/Stavropol/320-01/2020 (H5N8). Immunized ferrets were intranasally challenged with 5 LD ₅₀ of the influenza virus strain A/dalmatian pelican/Kalmykia/ 330-10V/2023 (H5N1), and their status was recorded for 14 days after challenge. RESULTS. Using ELISA, it was established that specific antibody titers were determined in groups of animals immunized with the mRNA-H5 vaccine administered by JI or formulated with LNPs; the average titers in the groups were 1:180,000 and 1:4,000,000, respectively. Using the virus neutralization assay, sera from animals immunized with the mRNA-H5 vaccine administered by JI or formulated with LNPs had virus-neutralizing activity; the average 50% neutralizing titers were 1:250 and 1:1500, respectively. The ELISpot assay showed that in groups of ferrets immunized with the mRNA-H5 vaccine, specific cellular immunity was induced. Immunization with the mRNA-H5 vaccine provided 100% protection against mortality in ferrets challenged with 5 LD ₅₀ of the influenza virus strain A/dalmatian pelican/Kalmykia/330-10V/2023 (H5N1). CONCLUSIONS. This study demonstrated the effective induction of virus-specific humoral and cellular immune responses in ferrets immunized with the mRNA-H5 vaccine administered by JI or formulated with LNPs.

Background/Objectives: The development of a vaccine against highly pathogenic avian influenza viruses subtype A/H5 is an urgent task due to concerns about its pandemic potential. Methods: In this study, we have developed an experimental mRNA vaccine, mRNA-H5, encoding a modified hemagglutinin trimer of influenza virus A/turkey/Stavropol/320-01/2020 (H5N8). BALB/c mice were immunized with the mRNA-H5 vaccine using lipid nanoparticles (LNPs) and needle-free jet injection (JI). Subsequently, the immune response to vaccine was assessed using ELISA, microneutralization assay, and ICS methods, and a challenge study was conducted. Results: mRNA-H5 was shown to effectively stimulate specific humoral and T-cell immune responses. Moreover, mRNA-H5 delivered by LNPs and JI provided 100% protection of immunized mice against lethal challenge with homologous and heterologous strains of avian influenza virus (A/Astrakhan/3212/2020 (H5N8) and A/chicken/Magadan/14-7V/2022 (H5N1), respectively). Conclusions: The present results indicate that JI can be considered as an alternative to LNPs for mRNA delivery, and according to the literature, JI is safer than delivery using LNP. mRNA-H5 has potential as a vaccine against infection with highly pathogenic avian influenza A/H5 viruses with pandemic potential.

The development of a vaccine against highly pathogenic avian influenza A/H5 viruses is an urgent task due to concerns about its pandemic potential. Here, we have developed an experimental mRNA vaccine mRNA-H5, encoding a modified hemagglutinin trimer of influenza virus A/turkey/Stavropol/320-01/2020 (H5N8). Immunization of BALB/c mice with the obtained mRNA-H5 vaccine using lipid nanoparticles (LNPs) and needle-free jet injection (JI) has been shown to effectively stimulate specific humoral and T-cell immune responses. Moreover, mRNA-H5 delivered by LNPs and JI provided 100% protectivity of immunized mice against lethal challenge with homologous and heterologous strains of avian influenza virus (A/Astrakhan/3212/2020 (H5N8) and A/chicken/Magadan/14-7V/2022 (H5N1), respectively). The present results indicate that needle-free jet injection can be considered as an alternative to LNPs for mRNA delivery. mRNA-H5 is a promising candidate as a vaccine against highly pathogenic avian influenza A/H5 viruses with pandemic potential.

Tumor necrosis factor alpha (TNF-α) is a cytokine that is responsible for many processes associated with immune response and inflammation. It is involved in the development of an antiviral response to many virus infections. This factor was shown to be activated in influenza A virus infection, which enhances production of other cytokines. The overexpression of these cytokines can lead to a cytokine storm. To study the role of TNF-α in the development of pathologies associated with viral infection, we generated a Tnfa knockout mouse strain. We demonstrated that these mice were characterized by a significant increase in the number of viral genomes compared to that in the parental strain, but the amount of live virus did not differ. A histopathology of the lungs in the genetically modified animals was significantly lower in terms of interalveolar septal infiltration. The generated model may be used to further study pathological processes in viral infections.

Scientific relevance. The use of recombinant antigens in vaccine production is limited because vaccines based on such antigens tend to have low immunogenicity. However, a COVID-19 vaccine that combines recombinant SARS-CoV-2 spike glycoprotein as its antigen and virus-like immune-stimulating complexes (ISCOMs) as its adjuvant (Nuvaxovid) induces a protective virus-neutralising response. The State Research Center of Virology and Biotechnology “Vector” (hereinafter, Vector) has developed the ISCOM adjuvant Matrix-V, which plays a key role in inducing virus-neutralising antibodies. Studying Matrix-V will provide for the wide use of recombinant antigens combined with this adjuvant in the development and production of novel Russian vaccines.Aim. This study aimed to evaluate the humoral immune responses of experimental animals to intramuscular injections of a complex combining the recombinant Wuhan-type SARS-CoV-2 spike RBD antigen and the virus-like ISCOM adjuvant containing Quillaja saponaria saponins.Materials and methods. The Matrix-V ISCOM adjuvant was produced using Vector’s proprietary technology, which involves cross-flow filtration through Sartorius VivaFlow cassettes. To determine the saponin and residual detergent concentrations in Matrix-V, the authors conducted high-performance liquid chromatography. Having produced the recombinant SARS-CoV-2 RBD antigen, the authors used electron microscopy to analyse the ultrastructure of the ISCOM–antigen complex. In the study of the ISCOM–antigen complex, 25 female Balb/c mice (5 groups) and 15 male and female outbred guinea pigs (3 groups) received two intramuscular injections with a 14-day interval. Serum tests relied on virus neutralisation (VN) and enzyme-linked immunosorbent assay (ELISA) methods and used antigens of 8 SARS-CoV-2 variants (State Collection of Viruses and Rickettsia, Vector). The authors used Statistica 10 to analyse the results.Results. Two injections of the SARS-CoV-2 RBD antigen (mice: 7 μg, guinea pigs: 1 μg) alone did not induce statistically significant virus-neutralising antibody responses, as shown by the VN results. Two injections of the SARS-CoV-2 RBD antigen (mice: 7 μg, guinea pigs: 1 μg) adjuvanted with Matrix-V (25 μg) resulted in geometric mean antibody titres of 1:83–1:178 (mice) and 1:174–1:587 (guinea pigs) in the VN tests with the Wuhan variant. One injection of the antigen (1 μg or 7 μg) with Matrix-V (25 μg) induced antibodies only in individual cases, as demonstrated by the VN and/or ELISA results. The most intensive immune response was observed in ELISA tests with the Delta variant after two injections of the Ecto-S-Wuhan (1 μg) and Matrix-V (25 μg) complex. Immune responses did not differ between the group that received two injections of the Ecto-S-Wuhan antigen (1 μg) without the ISCOM adjuvant and the negative control group (titres below 1:100; p=0.95). Two injections of the SARS-CoV-2 RBD antigen (7 μg) without the ISCOM adjuvant induced antibodies in mice (titres between 1:248 and 1:1477).Conclusions. Two intramuscular injections of the complex containing the recombinant SARS-CoV-2 RBD antigen and the Matrix-V ISCOM adjuvant induce virus-neutralising antibodies. The approach proposed by the authors has the potential for use in the development of immunobiological medicinal products to prevent and treat a wide range of infectious diseases.

The WHO has developed a tool to assess the risk of newly emerging influenza viruses with pandemic potential (TIPRA). According to TIPRA, the main parameters for assessing the risk of human-to-human transmission of a novel influenza virus are its ability to bind to human cell receptors of the upper respiratory tract (URT) and transmit in model animals. The aim of this study was to quantify airborne transmission of human and animal influenza viruses in the ferret model. The transmission of influenza viruses was studied in the ferret model in an aerobiology chamber. Airborne particles concentration and fractional composition in the aerobiology chamber were measured using an aerosol particle counter and analytical aerosol filters. Viral load in ferret nasal washings and aerosol filters was determined by titration in MDCK cells and quantitative RT-PCR. Genetic analysis of influenza viruses was performed using virus genome sequences obtained by NGS. After intranasal infection, human and animal influenza viruses replicated in the cells of nasal mucosa in ferrets. The level of virus airborne particles contamination provided by infected animals depends on the infectious dose and differs significantly between influenza virus strains. The studied avian influenza viruses show insufficient transmission in the ferret model, while human and swine influenza viruses are highly transmitted in ferrets. We propose a quantitative model of airborne transmission of influenza virus from donor to recipient ferrets. Level of influenza virus transmission in the ferret model correlates with genetic markers of virus receptor specificity and the level of virus airborne particle contamination induced by donor ferrets.

In this study, we investigated the features of the infectious process by simulating co-infection with SARS-CoV-2 and human adenovirus type 5 (HAdV-5) or influenza A virus (IAV) in vitro and in vivo. The determination of infectious activity of viruses and digital PCR demonstrated that during simultaneous and sequential HAdV-5 followed by SARS-CoV-2 infection in vitro and in vivo, the HAdV-5 infection does not interfere with replication of SARS-CoV-2. The hamsters co-infected and mono-infected with SARS-CoV-2 exhibited nearly identical viral titers and viral loads of SARS-CoV-2 in the lungs. The hamsters and ferrets co-infected by SARS-CoV-2- and IAV demonstrated more pronounced clinical manifestations than mono-infected animals. Additionally, the lung histological data illustrate that HAdV-5 or IAV and SARS-CoV-2 co-infection induces more severe pathological changes in the lungs than mono-infection. The expression of several genes specific to interferon and cytokine signaling pathways in the lungs of co-infected hamsters was more upregulated compared to single infected with SARS-CoV-2 animals. Thus, co-infection with HAdV-5 or IAV and SARS-CoV-2 leads to more severe pulmonary disease in animals.

The COVID-19 pandemic has exacerbated the public’s need for effective vaccines. Consequently, significant financial support has been provided to developers of a number of innovative vaccines, including the vaccines with saponin-based adjuvants. In 2021, the World Health Organisation recommended Mosquirix, the first malaria vaccine, which contains a saponin adjuvant. An anti-covid vaccine by Novavax is in the approval phase. A promising approach to vaccine development is presented by the use of virus-like immune-stimulating complexes (ISCOMs) containing saponins and by the creation of combinations of ISCOMs with antigens. The aim of the study was to develop, produce and characterise virus-like immune-stimulating complexes based on saponins of Quillaja saponaria, as well as similar saponins of Russian-sourced Polemonium caeruleum. Materials and methods: The ISCOM adjuvants, Matrix-BQ and Matrix-BP, were produced using liquid chromatography and examined using electron microscopy. Balb/c mice were immunised intraperitoneally and intramuscularly with ISCOM-antigen preparations. Afterwards, the immunised animals were challenged with the influenza virus strain, A/California/4/2009(H1N1)pdm09, adapted and lethal to mice. The serum samples were examined using haemagglutination inhibition (HI) tests. Results: The authors produced the ISCOMs containing saponins of Quillaja saponaria and Polemonium caeruleum. After one intramuscular injection of either of the ISCOM-antigen preparations with 1 µg of each of A/Brisbane/02/2018 (H1N1) pdm09, A/Kansas/14/2017 (H3N2), and B/Phuket/3073/2013 haemagglutinin antigens (HAs), HI tests detected serum antibody titres to the corresponding antigens of ≥1:40. Two intramuscular injections of the ISCOM-antigen preparation containing 50 ng of each of the HAs and Matrix-BQ resulted in a protective response. In some animals, two intraperitoneal injections of ISCOM-antigen preparations resulted in the maximum antibody titre to the A/Kansas/14/2017 (H3N2) vaccine strain of 1:20,480. Two intramuscular injections of a test preparation containing 5 µg, 1 µg, 200 ng, or 50 ng of each of the HAs and Matrix-BQ or a control preparation containing 5 µg, 1 µg, or 200 ng of each of the HAs (commercially available vaccines) to the mice that were afterwards infected with the lethal influenza strain protected the experimental animals from death. Conclusions: The ISCOM-based preparations had high immunostimulatory activity in the mouse-model study. The presented results indicate the potential of further studies of ISCOM-based preparations in terms of both vaccine and immunotherapeutic development.