Prediction models for neutralization activity against emerging SARS-CoV-2 variants: A cross-sectional study.

Objective: Despite extensive vaccination campaigns to combat the coronavirus disease (COVID-19) pandemic, variants of concern, particularly the Omicron variant (B.1.1.529 or BA.1), may escape the antibodies elicited by vaccination against SARS-CoV-2. Therefore, this study aimed to evaluate 50% neutralizing activity (NT50) against SARS-CoV-2 D614G, Delta, Omicron BA.1, and Omicron BA.2 and to develop prediction models to predict the risk of infection in a general population in Japan. Methods: We used a random 10% of samples from 1,277 participants in a population-based cross-sectional survey conducted in January and February 2022 in Yokohama City, the most populous municipality in Japan. We measured NT50 against D614G as a reference and three variants (Delta, Omicron BA.1, and BA.2) and immunoglobulin G against SARS-CoV-2 spike protein (SP-IgG). Results: Among 123 participants aged 20-74, 93% had received two doses of SARS-CoV-2 vaccine. The geometric means (95% confidence intervals) of NT50 were 65.5 (51.8-82.8) for D614G, 34.3 (27.1-43.4) for Delta, 14.9 (12.2-18.0) for Omicron BA.1, and 12.9 (11.3-14.7) for Omicron BA.2. The prediction model with SP-IgG titers for Omicron BA.1 performed better than the model for Omicron BA.2 (bias-corrected R 2 with bootstrapping: 0.721 vs. 0.588). The models also performed better for BA.1 than for BA.2 (R 2 = 0.850 vs. 0.150) in a validation study with 20 independent samples. Conclusion: In a general Japanese population with 93% of the population vaccinated with two doses of SARS-CoV-2 vaccine, neutralizing activity against Omicron BA.1 and BA.2 were substantially lower than those against D614G or the Delta variant. The prediction models for Omicron BA.1 and BA.2 showed moderate predictive ability and the model for BA.1 performed well in validation data.

Enhancement of Humoral and Cellular Immunity Against Severe Acute Respiratory Syndrome Coronavirus 2 by a Third Dose of BNT162b2 Vaccine in Japanese Healthcare Workers.

The Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has raised concerns regarding vaccine effectiveness. We investigated humoral and cellular immune responses against SARS-CoV-2 in healthcare workers before and after a third (booster) dose of the BNT162b2 messenger RNA vaccine. It significantly enhanced both humoral and cellular immunity in previously uninfected individuals. However, cellular immunity was not enhanced in previously infected persons, suggesting that 3 antigenic stimuli by vaccination or natural infection reached a plateau of cellular immunity. Even with reinforced immunity to SARS-CoV-2, we confirmed several postbooster breakthrough cases caused by the Omicron variant.

Vaccine-induced humoral response against SARS-CoV-2 dramatically declined but cellular immunity possibly remained at 6 months post BNT162b2 vaccination.

To evaluate vaccine-induced humoral and cell-mediated immunity at 6 months after completion of two doses of BNT162b2 vaccination, immunoglobulin G against SARS-CoV-2 spike protein (SP IgG), 50% neutralizing antibody (NT50), and spot-forming cell (SFC) counts were evaluated by interferon-γ releasing ELISpot assay of 98 healthy subjects (median age, 43 years). The geometric mean titers of SP IgG and NT50 decreased from 95.2 (95% confidence interval (CI) 79.8-113.4) to 5.7 (95% CI 4.9-6.7) and from 680.4 (588.0-787.2) to 130.4 (95% CI 104.2-163.1), respectively, at 3 weeks and 6 months after the vaccination. SP IgG titer was negatively correlated with age and alcohol consumption. Spot-forming cell counts at 6 months did not correlate with age, gender, and other parameters of the patients. SP IgG, NT50, and SFC titers were elevated in the breakthrough infected subjects. Although the levels of vaccine-induced antibodies dramatically declined at 6 months after vaccination, a certain degree of cellular immunity was observed irrespective of the age.

Persistence of Robust Humoral Immune Response in Coronavirus Disease 2019 Convalescent Individuals Over 12 Months After Infection.

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection elicits varying degrees of protective immunity conferred by neutralizing antibodies (nAbs). In this study, we report the persistence of nAb responses over 12 months after infection despite their decreasing trend noticed from 6 months. METHODS: The study included sera from 497 individuals who had been infected with SARS-CoV-2 between January and August 2020. Samples were collected at 6 and 12 months after onset. The titers of immunoglobulin (Ig)G to the viral nucleocapsid protein (NP) and receptor-binding domain (RBD) of the spike protein were measured by chemiluminescence enzyme immunoassay. The nAb titer was determined using lentivirus-based pseudovirus or authentic virus. RESULTS: Antibody titers of NP-IgG, RBD-IgG, and nAbs were higher in severe and moderate cases than in mild cases at 12 months after onset. Although the nAb levels were likely to confer adequate protection against wild-type viral infection, the neutralization activity to recently circulating variants in some of the mild cases (~30%) was undermined, implying the susceptibility to reinfection with the variants of concerns (VOCs). CONCLUSIONS: Coronavirus disease 2019 convalescent individuals have robust humoral immunity even at 12 months after infection albeit that the medical history and background of patients could affect the function and dynamics of antibody response to the VOCs.

Antibody titers against the Alpha, Beta, Gamma, and Delta variants of SARS-CoV-2 induced by BNT162b2 vaccination measured using automated chemiluminescent enzyme immunoassay.

BACKGROUND: Levels of 50% neutralizing titer (NT50) reflect the a vaccine-induced humoral immunity after the vaccination against the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Measurements of NT50 are difficult to implement in large quantities. A high-throughput laboratory test is expected for determining the level of herd immunity against SARS-CoV-2. METHODS: We analyzed samples from 168 Japanese healthcare workers who had completed two doses of the BNT162b2 vaccine. We analyzed immunoglobulin G (IgG) index values against spike protein (SP) using automated chemiluminescent enzyme immunoassay system AIA-CL and analyzed the background factors affecting antibody titer. SP IgG index was compared with 50% neutralization titers. RESULTS: The median SP IgG index values of the subjects (mean age = 43 years; 75% female) were 0.1, 1.35, 60.80, and 97.35 before and at 2, 4, and 6 weeks after the first dose, respectively. At 4 and 6 weeks after the first dose, SP IgG titers were found to have positive correlation with NT50 titer (r = 0.7535 in 4 weeks; r = 0.4376 in 6 weeks). Proportions of the SP IgG index values against the Alpha, Beta, Gamma, and Delta variants compared with the original strain were 2.029, 0.544, 1.017, and 0.6096 respectively. Older age was associated with lower SP IgG titer index 6 weeks after the first dose. CONCLUSIONS: SP IgG index values were rised at 3 weeks after two doses of BNT162b2 vaccination and have positive correlation with NT50. SP IgG index values were lower in the older individuals and against Beta and Delta strain.

Sustained Neutralizing Antibodies 6 Months Following Infection in 376 Japanese COVID-19 Survivors.

Objective: There is scarce evidence regarding the long-term persistence of neutralizing antibodies among coronavirus disease 2019 (COVID-19) survivors. This study determined neutralizing antibody titers (NT50) and antibodies against spike protein (SP) or nucleocapsid protein (NP) antigens approximately 6 months after the diagnosis of COVID-19. Methods: COVID-19 survivors in Japan were recruited. Serum samples and data related to patients' characteristics and COVID-19 history were collected. NT50 and titers of antibodies against NP and SP antigens were measured at 20-32 weeks after the first positive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) test results. Factors associated with NT50 were identified using the multivariable linear regression and the correlations among NT50 and titers of immunoglobulin G (IgG) and total immunoglobulins (Igs) against NP and SP were assessed by Spearman's correlation. Results: Among 376 participants (median [range] days after testing positive for SARS-CoV-2, 180 (147-224); median [range] years of age, 50 (20-78); 188 [50%] male), most tested positive for NT50 (n = 367, 98%), SP-IgG (n = 344, 91%), SP-total Ig (n = 369, 98%), NP-IgG (n = 314, 84%), and NP-total Ig (n = 365, 97%). Regression analysis indicated that higher BMI, fever, and the requirement of mechanical ventilation or extracorporeal membrane oxygenation were significantly associated with higher NT50. Anti-SP antibodies correlated moderately with NT50 (Spearman's correlation: 0.63 for SP IgG; 0.57 for SP-total Ig), while the correlation was weak for anti-NP antibodies (0.37 for NP IgG; 0.32 for NP-total Ig). Conclusions: Most COVID-19 survivors had sustained neutralizing antibodies and tested positive for SP-total Ig and NP-total Ig approximately 6 months after infection.

Tissue factor pathway inhibitor­2 is specifically expressed in ovarian clear cell carcinoma tissues in the nucleus, cytoplasm and extracellular matrix.

Tissue factor pathway inhibitor­2 (TFPI­2) is a promising candidate as a serum biomarker of ovarian clear cell carcinoma (OCCC), a lethal histological subtype of epithelial ovarian cancer (EOC). TFPI­2 is a secreted serine protease inhibitor that suppresses cancer progression through the inhibition of matrix protease activities. Previous studies have also identified TFPI­2 in the nucleus, and a possible function of nuclear TFPI­2 as a transcriptional repressor of matrix metalloproteinase­2 (MMP­2) was recently demonstrated. We are currently establishing TFPI­2 as a serum biomarker for OCCC patients; however, TFPI­2 expression in OCCC tissues has not been previously investigated. In the present study, we examined TFPI­2 expression and its localization in 11 OCCC cell lines by western blotting and enzyme­linked immune assay. Four cell lines expressed TFPI­2 in the nucleus, cytoplasm and culture plate-attached extracellular fraction, while four other cell lines expressed TFPI­2 only in the extracellular fraction. In the remaining three cell lines, TFPI­2 was not identified in any fraction. The amount of secreted soluble TFPI­2 showed similar trends to that of the plate­attached fraction. We next investigated the expression levels and distribution of TFPI­2 in surgically resected EOC tissues by immunohistochemistry. In 52 of the 77 (67.5%) OCCC tumors, TFPI­2 expression was detected in at least one of the nuclear, cytoplasmic and extracellular matrix fractions. In contrast, we did not identify TFPI­2 in the other EOC subtypes (n=65). TFPI­2­positive expression distinguished CCC from the other EOC tissues with a sensitivity of 67.5% and specificity of 100%. Although the inherent tumor suppressor function, statistical analyses failed to demonstrate correlations between TFPI­2 expression and clinical parameters, including 5­year overall survival, except for the patient age. In conclusion, we identified TFPI­2 expression in the nucleus, cytoplasm and extracellular matrix in OCCC tissues. The high specificity of TFPI­2 may support its use for diagnosis of OCCC in combination with existing markers.

Development of an Automated Chemiluminescence Assay System for Quantitative Measurement of Multiple Anti-SARS-CoV-2 Antibodies.

OBJECTIVES: Serological tests for COVID-19 have been instrumental in studying the epidemiology of the disease. However, the performance of the currently available tests is plagued by the problem of variability. We have developed a high-throughput serological test capable of simultaneously detecting total immunoglobulins (Ig) and immunoglobulin G (IgG) against nucleocapsid protein (NP) and spike protein (SP) and report its performance in detecting COVID-19 in clinical samples. METHODS: We designed and prepared reagents for measuring NP-IgG, NP-Total Ig, SP-IgG, and SP-Total Ig (using N-terminally truncated NP (ΔN-NP) or receptor-binding domain (RBD) antigen) dedicated automated chemiluminescent enzyme immunoassay analyzer AIA-CL1200. After determining the basal thresholds based on 17 sera obtained from confirmed COVID-19 patients and 600 negative sera, the clinical validity of the assay was evaluated using independent 202 positive samples and 1,000 negative samples from healthy donors. RESULTS: All of the four test parameters showed 100% specificity individually (1,000/1,000; 95%CI, 99.63-100). The sensitivity of the assay increased proportionally to the elapsed time from symptoms onset, and all the tests achieved 100% sensitivity (153/153; 95%CI, 97.63-100) after 13 days from symptoms onset. NP-Total Ig was the earliest to attain maximal sensitivity among the other antibodies tested. CONCLUSION: Our newly developed serological testing exhibited 100% sensitivity and specificity after 13 days from symptoms onset. Hence, it could be used as a reliable method for accurate detection of COVID-19 patients and to evaluate seroprevalence and possibly for surrogate assessment of herd immunity.

Clinical Significance of Tissue Factor Pathway Inhibitor 2, a Serum Biomarker Candidate for Ovarian Clear Cell Carcinoma.

BACKGROUND: There is currently no reliable serum biomarker for ovarian clear cell carcinoma (CCC), a highly lethal histological subtype of epithelial ovarian cancer (EOC). Previously, using a proteome-based approach, we identified tissue factor pathway inhibitor 2 (TFPI2) as a candidate serum biomarker for CCC. In this study, we sought to evaluate the clinical diagnostic performance of TFPI2 in preoperative prediction of CCC. METHODS: Serum TFPI2 levels were measured in serum samples from a retrospective training set consisting of patients with benign and borderline ovarian tumors, EOC subtypes, and uterine diseases. Via receiver operating characteristic (ROC) analyses, we compared the diagnostic performance of TFPI2 with that of CA125 in discrimination of patients with ovarian CCC from other patient groups. The observed diagnostic performances were examined in a prospective validation set. RESULTS: The 268-patient training set included 29 patients with ovarian CCC. Unlike CA125, which was also elevated in patients with endometriosis and several EOC subtypes, serum TFPI2 levels were specifically elevated only in ovarian CCC patients, consistent with the mRNA expression pattern in tumor tissues. The area under the ROC curve (AUC) of serum TFPI2 was obviously higher than that of CA125 for discrimination of CCC from other ovarian diseases (AUC = 0.891 versus 0.595). Applying a cut-off value of 280 pg/mL, TFPI2 could distinguish early-stage (FIGO I and II) CCC from endometriosis with 72.2% sensitivity, 93.3% specificity, and 88.8% accuracy. Similar results were confirmed in an independent 156-patient prospective validation set. CONCLUSIONS: TFPI2 is a useful serum biomarker for preoperative clinical diagnosis of CCC.

Secretome-based identification of TFPI2, a novel serum biomarker for detection of ovarian clear cell adenocarcinoma.

Of all of the epithelial ovarian cancers (EOC), clear cell adenocarcinoma (CCA) has the worst clinical prognosis. Furthermore, the conventional EOC biomarker CA125 is more often negative in CCA than in other subtypes of EOC. This study sought to discover a new diagnostic biomarker that would allow more reliable detection of CCA. Using mass spectrometry, we compared proteins in conditioned media from cell lines derived from CCA and other types of EOC. We identified 30 extracellular or released proteins specifically present in CCA-derived cell lines. Bioinformatics analyses identified a serine protease inhibitor, tissue factor pathway inhibitor 2 (TFPI2), as a potential biomarker for CCA. Real time RT-PCR and Western blot analyses revealed that TFPI2 was exclusively expressed in CCA-derived cell lines and tissues. For clinical validation, we measured levels of TFPI2 and CA125 in a set of sera from 30 healthy women, 30 patients with endometriosis, and 50 patients with CCA, using an automated enzyme-linked immunosorbent assay systems. Serum levels of TFPI2 were significantly elevated in CCA patients, even those with normal CA125 levels. In terms of area under the receiver operating characteristic curve (AUC), TFPI2 was superior to CA125 in discriminating CCA patients from healthy women (AUC 0.97 for TFPI2 versus AUC 0.80 for CA125), or from patients with endometriosis (AUC 0.93 for TFPI2 versus 0.80 for CA125). This is the first evidence for TFPI2 as a serum biomarker of CCA. We propose that this biomarker may be useful for detection of CCA and for monitoring the transformation from endometriosis into CCA.