Comprehensive analysis of nasal IgA antibodies induced by intranasal administration of the SARS-CoV-2 spike protein (preprint)

Intranasal vaccination is an attractive strategy for preventing COVID-19 disease as it stimulates the production of multimeric secretory immunoglobulin A (IgAs), the predominant antibody isotype in the mucosal immune system, at the target site of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) entry. Currently, the evaluation of intranasal vaccine efficacy is based on the measurement of polyclonal antibody titers in nasal lavage fluid. However, how individual multimeric secretory IgA protects the mucosa from SARS-CoV-2 infection remains to be elucidated. To understand the precise contribution and molecular nature of multimeric secretory IgAs induced by intranasal vaccines, we developed 99 monoclonal IgAs from nasal mucosa and 114 monoclonal IgAs or IgGs from nonmucosal tissues of mice that were intranasally immunized with the SARS-CoV-2 spike protein. The nonmucosal IgAs exhibited shared origins and both common and unique somatic mutations with the related nasal IgA clones, indicating that the antigen-specific plasma cells in the nonmucosal tissues originated from B cells stimulated at the nasal mucosa. Comparing the spike protein binding reactivity, angiotensin-converting enzyme-2-blocking and SARS-CoV-2 virus neutralization of monomeric and multimeric IgA pairs recognizing different epitopes showed that even nonneutralizing monomeric IgA, which represents 70% of the nasal IgA repertoire, can protect against SARS-CoV-2 infection when expressed as multimeric secretory IgAs. Our investigation is the first to demonstrate the function of nasal IgAs at the monoclonal level, showing that nasal immunization can provide effective immunity against SARS-CoV-2 by inducing multimeric secretory IgAs at the target site of virus infection.

Evaluation of SARS-CoV-2 isolation in cell culture from nasal/nasopharyngeal swabs or saliva specimens of patients with COVID-19 (preprint)

It has been revealed that SARS-CoV-2 can be efficiently isolated from clinical specimens such as nasal/nasopharyngeal swabs or saliva in cultured cells. In this study, we examined the efficiency of viral isolation including SARS-CoV-2 mutant strains between nasal/nasopharyngeal swab or saliva specimens. Furthermore, we also examined the comparison of viral isolation rates by sample species using simulated specimens for COVID-19. As a result, it was found that the isolation efficiency of SARS-CoV-2 in the saliva specimens was significantly lower than that in the nasal/nasopharyngeal swab specimens. In order to determine which component of saliva is responsible for the lower isolation rate of saliva specimens, we tested the abilities of lactoferrin, amylase, cathelicidin, and mucin, which are considered to be abundant in saliva, to inhibit the infection of SARS-CoV-2 pseudotyped viruses (SARS-CoV-2pv). Lactoferrin and amylase were found to inhibit SARS-CoV-2pv infection. In conclusion, even if the same number of viral genome copies was detected by the real-time RT-PCR test, infection of SARS-CoV-2 present in saliva is thought to be inhibited by inhibitory factors such as lactoferrin and amylase, compared to nasal/nasopharyngeal swab specimens.

Neutralizing antibody levels and epidemiological information of patients with breakthrough COVID-19 infection in Toyama, Japan (preprint)

Breakthrough infection (BI) after coronavirus disease 2019 (COVID-19) vaccination has exploded owing to the emergence of various SARS-CoV-2 variants and has become a major problem at present. In this study, we analyzed the epidemiological information and possession status of neutralizing antibodies in patients with BI using SARS-CoV-2 pseudotyped viruses (SARS-CoV-2pv). Analysis of 44 specimens diagnosed with COVID-19 after two or more vaccinations showed high inhibition of infection by 90% or more against the Wuhan strain and the Alpha and Delta variants of pseudotyped viruses in 40 specimens. In contrast, almost no neutralizing activity was observed against the Omicron BA.1 variant. Many cases without neutralizing activity or BI were immunosuppressed individuals. The results of this study show that BI occurs even when there are sufficient neutralizing antibodies in the blood due to exposure to close contacts at the time of infection. Thus, even after vaccination, sufficient precautions must be taken to prevent infection.

Evaluation of SARS-CoV-2 isolation in cell culture from nasal/nasopharyngeal swabs or saliva specimens of patients with COVID-19 (preprint)

It has been revealed that SARS-CoV-2 can be efficiently isolated from clinical specimens such as nasal/nasopharyngeal swabs or saliva in cultured cells. In this study, we examined the efficiency of viral isolation including SARS-CoV-2 mutant strains between nasal/nasopharyngeal swab or saliva specimens. Furthermore, we also examined the comparison of viral isolation rates by sample species using simulated specimens for COVID-19. As a result, it was found that the isolation efficiency of SARS-CoV-2 in the saliva specimens was significantly lower than that in the nasal/nasopharyngeal swab specimens. In order to determine which component of saliva is responsible for the lower isolation rate of saliva specimens, we tested the abilities of lactoferrin, amylase, cathelicidin, and mucin, which are considered to be abundant in saliva, to inhibit the infection of SARS-CoV-2 pseudotyped viruses (SARS-CoV-2pv). Lactoferrin and amylase were found to inhibit SARS-CoV-2pv infection. In conclusion, even if the same number of viral genome copies was detected by the real-time RT-PCR test, infection of SARS-CoV-2 present in saliva is thought to be inhibited by inhibitory factors such as lactoferrin and amylase, compared to nasal/nasopharyngeal swab specimens.

Efficacy of the wild-type/Omicron BA.1 bivalent vaccine as the second booster dose against Omicron BA.2 and BA.5 (preprint)

Introduction In addition to the original monovalent vaccines available for SARS-CoV-2, bivalent vaccines covering wild-type (WT) and Omicron BA.1 are also available. However, there is a lack of real-world data on the effectiveness of bivalent vaccines as second boosters on the dominant Omicron sublineages, including BA.2 and BA.5. Methods This prospective longitudinal cohort study was conducted at Toyama University Hospital, a tertiary medical center in Japan. Participants (n = 565) who received the first booster vaccination were followed up until 2 weeks after the second booster dose of the monovalent mRNA-1273 (WT group, n = 168) and bivalent BNT162b2 (WT+BA.1 group, n = 23) vaccines. Participants with previous SARS-CoV-2 infections were excluded from the study. Anti-receptor-binding domain (RBD) antibody levels and neutralizing activity were measured. Vaccine-related symptoms were also assessed using a questionnaire after the second booster dose. Results The anti-RBD antibody levels after the second booster dose in the WT and WT+BA.1 group were similar (median [inter quartile], 26262.0 [16951.0-38137.0] U/mL vs. 24840.0 [14828.0-41460.0] U/mL, respectively). Although the neutralization activity of the pooled sera of the WT+BA.1 group was the lowest against BA.5, the activities against BA.2 and BA.5 were higher than those of the WT group in both pseudotyped and live virus assays. Vaccine-related symptoms, including systemic and local symptoms, were strongly correlated with anti-RBD antibody levels and neutralizing titers with significant differences. Conclusion The second booster dose of the bivalent (WT/Omicron BA.1) vaccine induced higher neutralizing activity against BA.2 and BA.5 than that of the original monovalent vaccine.

Activation of SARS-CoV-2 by trypsin-like proteases in the clinical specimens of patients with COVID-19 (preprint)

SARS-CoV-2 enters host cells through the angiotensin converting enzyme 2 (ACE2) receptor and/or transmembrane protease, serine 2 (TMPRSS2). Serine proteases, such as TMPRSS2 and trypsin, promote viral entry. In this study, we investigated whether proteases increased SARS-CoV-2 infectivity using pseudotyped viruses and clinical specimens from patients with COVID-19. First, we investigated how trypsin increased infectivity using the pseudotyped virus. Our findings revealed that trypsin increased infectivity after the virus was adsorbed on the cells, but no increase in infectivity was observed when the virus was treated with trypsin. We examined the effect of trypsin on SARS-CoV-2 infection in clinical specimens and found that the infectivity of the SARS-CoV-2 delta variant increased 36,000-fold after trypsin treatment. By contrast, the infectivity of SARS-CoV-2 omicron variant increased to less than 20-fold in the clinical specimens. Finally, infectivity of clinical specimens containing culture supernatants of Fusobacterium necrophorum was increased from several- to 10-fold. Because SARS-CoV-2 infectivity increases in the oral cavity, which may contain anaerobic bacteria, keeping the oral cavities clean may help prevent SARS-CoV-2 infection.

Effectiveness of the third dose of BNT162b2 vaccine on neutralizing Omicron variant in the Japanese population (preprint)

IntroductionThe vaccine against SARS-CoV-2 provides humoral immunity to fight COVID-19; however, the acquired immunity gradually declines. Booster vaccination restores reduced humoral immunity; however, its effect on newly emerging variants, such as the Omicron variant, is a concern. As the waves of COVID-19 cases and vaccine programs differ between countries, it is necessary to know the domestic effect of the booster. MethodsSerum samples were obtained from healthcare workers (20-69 years old) in the Pfizer BNT162b2 vaccine program at the Toyama University Hospital 6 months after the second dose (6mA2D, n = 648) and 2 weeks after the third dose (2wA3D, n = 565). The anti-SARS-CoV-2 antibody level was measured, and neutralization against the wild-type and variants (Delta and Omicron) was evaluated using pseudotyped viruses. Data on booster-related events were collected using questionnaires. ResultsThe median anti-SARS-CoV-2 antibody was >30.9-fold elevated after the booster (6mA2D, 710.0 U/mL [interquartile range (IQR): 443.0-1068.0 U/mL]; 2wA3D, 21927 U/mL [IQR: 15321.0->25000.0 U/mL]). Median neutralizing activity using 100-fold sera against wild-type-, Delta-, and Omicron-derived variants was elevated from 84.6%, 36.2%, and 31.2% at 6mA2D to >99.9%, 99.1%, and 94.6% at 2wA3D, respectively. The anti-SARS-CoV-2 antibody levels were significantly elevated in individuals with fever [≥]37.5 {degrees}C, general fatigue, and myalgia, local swelling, and local hardness. ConclusionThe booster effect, especially against the Omicron variant, was observed in the Japanese population. These findings contribute to the precise understanding of the efficacy and side effects of the booster and the promotion of vaccine campaigns.

A novel hamster model of SARS-CoV-2 respiratory infection using a pseudotyped virus (preprint)

BackgroundSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a biosafety level (BSL)-3 pathogen; therefore, its research environment is strictly limited. Pseudotyped viruses that mimic SARS-CoV-2 have been widely used for in vitro evaluation because they are available in BSL-2 containment laboratories; however, in vivo application is inadequate. Therefore, animal models that can be instigated with animal BSL-2 will increase opportunities for in vivo evaluations. MethodsHamsters (6-to 10-week-old males) were intratracheally inoculated with luciferase-expressing vesicular stomatitis virus (VSV)-based SARS-CoV-2 pseudotyped virus. The lungs were harvested 24 h after inoculation, and luminescence was measured using an in vivo imaging system. ResultsLung luminescence after inoculation with the SARS-CoV-2 pseudotyped virus increased in a dose-dependent manner. VSV-G (envelope [G]) pseudotyped virus also induced luminescence; however, a 100-fold concentration was required to reach a level similar to that of the SARS-CoV-2 pseudotyped virus. ConclusionsThe SARS-CoV-2 pseudotyped virus is applicable to SARS-CoV-2 respiratory infections in a hamster model. Because of the single-round infectious virus, the model can be used to study the steps from viral binding to entry, which will be useful for future research regarding SARS-CoV-2 entry without using live SARS-CoV-2 or transgenic animals.

Functional and quantitative evaluation of BNT162b2 SARS-CoV-2 vaccine-induced immunity (preprint)

Objectives Vaccines against severe acute respiratory syndrome coronavirus-2 have been introduced. To investigate whether the vaccine provides protective immunity effectively, the amount and function of vaccine-induced antibodies were evaluated. Methods Sera from 13-17 days after the second dose of the Pfizer BNT162b2 vaccine were collected from healthcare workers at the University of Toyama (n=740). Antibody levels were quantitatively measured by the anti-receptor binding domain antibody test (anti-RBD test), and neutralising activity against pseudotyped viruses displaying wild-type (WT) and mutant spike proteins (B.1.1.7- and B.1.351-derived variants) were assayed using a high-throughput chemiluminescent reduction neutralising test (htCRNT). Basic clinical characteristics were obtained from questionnaires. Results Antibodies were confirmed in all participants in both the anti-RBD test (median 2112 U/mL, interquartile range [IQR] 1275-3390 U/mL) and the htCRNT against WT (median % inhibition >99.9, IQR >99.9 to >99.9). For randomly selected sera (n=61), 100.0% were positive for htCRNT against the B.1.1.7- and B.1.351-derived variants. Among those who answered the questionnaire (n=237), the values of the anti-RBD test were negatively correlated with age for females (p<0.01; r = -0.31, 95% confidence interval -0.45 to -0.16). Systemic symptoms after vaccination were related to higher values of the anti-RBD test (median 2425, IQR 1450 - 3933 vs. median 1347, IQR 818 - 2125 for no symptoms; p<0.01). Conclusions The BNT162b2 vaccine produced sufficient antibodies in terms of quality and quantity which could neutralise emerging variants. Antibody induction can be affected by age and sex but will still be at a sufficient level.

Correlation of the commercial anti-SARS-CoV-2 receptor binding domain antibody test with the chemiluminescent reduction neutralizing test and possible detection of antibodies to emerging variants (preprint)

Background Serological tests are beneficial for recognizing the immune response against SARS-CoV-2. To identify protective immunity, optimization of the chemiluminescent reduction neutralizing test (CRNT), using pseudotyped SARS-CoV-2, is critical. Whether commercial antibody tests are comparably accurate is unknown. Methods Serum samples collected before variants were locally found were obtained from confirmed COVID-19 patients (n = 74), confirmed non-COVID-19 individuals (n = 179), and unscreened individuals (suspected healthy individuals, n = 229). The convalescent phase was defined as the period after day 10 from disease onset. The CRNT against pseudotyped viruses displaying the wild-type spike protein and a commercially available anti-receptor binding domain (RBD) antibody test were assayed. The CRNT was also assayed, using South African (SA) and United Kingdom (UK)-derived variants. Results The CRNT (cut off value, 50% inhibition) and the anti-RBD antibody test (cut off value, 0.8 U/mL) concurred regarding symptomatic COVID-19 patients in the convalescent phase and clearly differentiated between patients and suspected healthy individuals (sensitivity; 95.8% and 100%, specificity; 99.1% and 100%, respectively). Anti-RBD antibody test results correlated with neutralizing titer (r = 0.47, 95% CI 0.20-0.68). Compared with the wild-type, CRNT reduction was observed for the SA and UK-derived variants. Of the samples with [≥]100 U/mL by the anti-RBD antibody test, 77.8% and 88.9% showed [≥]50% neutralization against the UK and the SA variants, respectively. Conclusion The CRNT and commercial anti-RBD antibody test effectively classified convalescent COVID-19 patients. The strong positive results using the commercial antibody test can reflect neutralizing activity against emerging variants.