Immunogenicity and Safety of Half-Dose Heterologous mRNA-1273 Booster Vaccination for Adults Primed with the CoronaVac® and ChAdOx1-S Vaccines for SARS-CoV-2.

Coronavirus disease 2019 (COVID-19) has been extensively researched, particularly with regard to COVID-19 vaccines. However, issues with logistics and availability might cause delays in vaccination programs. Thus, the efficacy and safety of half-dose heterologous mRNA should be explored. This was an open-label observational study to evaluate the immunogenicity and safety of half-dose mRNA-1273 as a booster vaccine among adults aged >18 years who underwent a complete primary SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) vaccination regimen with CoronaVac® and ChAdOx1-S. Adverse events (AEs), seropositivity rate, seroconversion, geometric mean titer (GMT) of SARS-CoV-2 antibodies, neutralizing antibodies, and T cells (CD4+ and CD8+) specific for SARS-CoV-2 were analyzed. Two hundred subjects were included in the final analysis, with 100 subjects in each priming vaccine group. Most of the AEs were mild, with systemic manifestations occurring between 1 and 7 days following vaccination. A significant difference was observed in the GMT and seropositivity rate following booster dose administration between the two groups. CD8+/CD3+, IFN (interferon)-producing CD8+, and TNF (tumor necrosis factor)-producing CD8+ cells showed significant increases in both groups. The administration of the half-dose mRNA-1273 booster is safe and effective in increasing protection against SARS-CoV-2 infection.

Human immune responses elicited by an intranasal inactivated H5 influenza vaccine.

Intranasally administered influenza vaccines could be more effective than injected vaccines, because intranasal vaccination can induce virus-specific immunoglobulin A (IgA) antibodies in the upper respiratory tract, which is the initial site of infection. In this study, immune responses elicited by an intranasal inactivated vaccine of influenza A(H5N1) virus were evaluated in healthy individuals naive for influenza A(H5N1) virus. Three doses of intranasal inactivated whole-virion H5 influenza vaccine induced strong neutralizing nasal IgA and serum IgG antibodies. In addition, a mucoadhesive excipient, carboxy vinyl polymer, had a notable impact on the induction of nasal IgA antibody responses but not on serum IgG antibody responses. The nasal hemagglutinin (HA)-specific IgA antibody responses clearly correlated with mucosal neutralizing antibody responses, indicating that measurement of nasal HA-specific IgA titers could be used as a surrogate for the mucosal antibody response. Furthermore, increased numbers of plasma cells and vaccine antigen-specific Th cells in the peripheral blood were observed after vaccination, suggesting that peripheral blood biomarkers may also be used to evaluate the intranasal vaccine-induced immune response. However, peripheral blood immune cell responses correlated with neutralizing antibody titers in serum samples but not in nasal wash samples. Thus, analysis of the peripheral blood immune response could be a surrogate for the systemic immune response to intranasal vaccination but not for the mucosal immune response. The current study suggests the clinical potential of intranasal inactivated vaccines against influenza A(H5N1) viruses and highlights the need to develop novel means to evaluate intranasal vaccine-induced mucosal immune responses.

IgA tetramerization improves target breadth but not peak potency of functionality of anti-influenza virus broadly neutralizing antibody.

Mucosal immunoglobulins comprise mainly secretory IgA antibodies (SIgAs), which are the major contributor to pathogen-specific immune responses in mucosal tissues. These SIgAs are highly heterogeneous in terms of their quaternary structure. A recent report shows that the polymerization status of SIgA defines their functionality in the human upper respiratory mucosa. Higher order polymerization of SIgA (i.e., tetramers) leads to a marked increase in neutralizing activity against influenza viruses. However, the precise molecular mechanisms underlying the effects of SIgA polymerization remain elusive. Here, we developed a method for generating recombinant tetrameric monoclonal SIgAs. We then compared the anti-viral activities of these tetrameric SIgAs, which possessed variable regions identical to that of a broadly neutralizing anti-influenza antibody F045-092 against influenza A viruses, with that of monomeric IgG or IgA. The tetrameric SIgA showed anti-viral inhibitory activity superior to that of other forms only when the antibody exhibits low-affinity binding to the target. By contrast, SIgA tetramerization did not substantially modify anti-viral activity against targets with high-affinity binding. Taken together, the data suggest that tetramerization of SIgA improved target breadth, but not peak potency of antiviral functions of the broadly neutralizing anti-influenza antibody. This phenomenon presumably represents one of the mechanisms by which SIgAs present in human respiratory mucosa prevent infection by antigen-drifted influenza viruses. Understanding the mechanisms involved in cross neutralization of viruses by SIgAs might facilitate the development of vaccine strategies against viral infection of mucosal tissues.

Relationship of the quaternary structure of human secretory IgA to neutralization of influenza virus.

Secretory IgA (S-IgA) antibodies, the major contributors to humoral mucosal immunity to influenza virus infection, are polymeric Igs present in many external secretions. In the present study, the quaternary structures of human S-IgA induced in nasal mucosa after administration of intranasal inactivated influenza vaccines were characterized in relation to neutralization potency against influenza A viruses. Human nasal IgA antibodies have been shown to contain at least five quaternary structures. Direct and real-time visualization of S-IgA using high-speed atomic force microscopy (AFM) demonstrated that trimeric and tetrameric S-IgA had six and eight antigen-binding sites, respectively, and that these structures exhibited large-scale asynchronous conformational changes while capturing influenza HA antigens in solution. Furthermore, trimeric, tetrameric, and larger polymeric structures, which are minor fractions in human nasal IgA, displayed increased neutralizing potency against influenza A viruses compared with dimeric S-IgA, suggesting that the larger polymeric than dimeric forms of S-IgA play some important roles in protection against influenza A virus infection in the human upper respiratory tract.