Recent Developments in SARS-CoV-2 Neutralizing Antibody Detection Methods.

The ongoing Coronavirus disease 19 pandemic has likely changed the world in ways not seen in the past. Neutralizing antibody (NAb) assays play an important role in the management of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) outbreak. Using these tools, we can assess the presence and duration of antibody-mediated protection in naturally infected individuals, screen convalescent plasma preparations for donation, test the efficacy of immunotherapy, and analyze NAb titers and persistence after vaccination to predict vaccine-induced protective effects. This review briefly summarizes the various methods used for the detection of SARS-CoV-2 NAbs and compares their advantages and disadvantages to facilitate their development and clinical application.

Anti-SARS-CoV-2 IgG responses are powerful predicting signatures for the outcome of COVID-19 patients.

Introduction: The COVID-19 global pandemic is far from ending. There is an urgent need to identify applicable biomarkers for early predicting the outcome of COVID-19. Growing evidences have revealed that SARS-CoV-2 specific antibodies evolved with disease progression and severity in COIVD-19 patients. Objectives: We assumed that antibodies may serve as biomarkers for predicting the clinical outcome of hospitalized COVID-19 patients on admission. Methods: By taking advantage of a newly developed SARS-CoV-2 proteome microarray, we surveyed IgG responses against 20 proteins of SARS-CoV-2 in 1034 hospitalized COVID-19 patients on admission and followed till 66 days. The microarray results were further correlated with clinical information, laboratory test results and patient outcomes. Cox proportional hazards model was used to explore the association between SARS-CoV-2 specific antibodies and COVID-19 mortality. Results: Nonsurvivors (n = 955) induced higher levels of IgG responses against most of non-structural proteins than survivors (n = 79) on admission. In particular, the magnitude of IgG antibodies against 8 non-structural proteins (NSP1, NSP4, NSP7, NSP8, NSP9, NSP10, RdRp, and NSP14) and 2 accessory proteins (ORF3b and ORF9b) possessed significant predictive power for patient death, even after further adjustments for demographics, comorbidities, and common laboratory biomarkers for disease severity (all with p trend < 0.05). Additionally, IgG responses to all of these 10 non-structural/accessory proteins were also associated with the severity of disease, and differential kinetics and serum positive rate of these IgG responses were confirmed in COVID-19 patients of varying severities within 20 days after symptoms onset. The area under curves (AUCs) for these IgG responses, determined by computational cross-validations, were between 0.62 and 0.71. Conclusions: Our findings might have important implications for improving clinical management of COVID-19 patients.

Human IgM and IgG Responses to an Inactivated SARS-CoV-2 Vaccine.

OBJECTIVE: The ongoing COVID-19 pandemic warrants accelerated efforts to test vaccine candidates. To explore the influencing factors on vaccine-induced effects, antibody responses to an inactivated SARS-CoV-2 vaccine in healthy individuals who were not previously infected by COVID-19 were assessed. METHODS: All subjects aged 18-60 years who did not have SARS-CoV-2 infection at the time of screening from June 19, 2021, to July 02, 2021, were approached for inclusion. All participants received two doses of inactivated SARS-CoV-2 vaccine. Serum IgM and IgG antibodies were detected using a commercial kit after the second dose of vaccination. A positive result was defined as 10 AU/mL or more and a negative result as less than 10 AU/mL. This retrospective study included 97 infection-naïve individuals (mean age 35.6 years; 37.1% male, 62.9% female). RESULTS: The seropositive rates of IgM and IgG antibody responses elicited after the second dose of inactivated SARS-CoV-2 vaccine were 3.1% and 74.2%, respectively. IgG antibody levels were significantly higher than IgM levels (P<0.0001). Sex had no effect on IgM and IgG antibody response after the second dose. The mean anti-IgG level in older persons (⩾42 years) was significantly lower than that of younger recipients. There was a significantly lower antibody level at > 42 days compared to that at 0-20 days (P<0.05) and 21-31 days (P<0.05) after the second dose. CONCLUSION: IgG antibody response could be induced by inactivated SARS-CoV-2 vaccine in healthy individuals (>18 years), which can be influenced by age and detection time after the second dose of vaccination.

Systematic profiling of SARS-CoV-2-specific IgG responses elicited by an inactivated virus vaccine identifies peptides and proteins for predicting vaccination efficacy.

One of the best ways to control COVID-19 is vaccination. Among the various SARS-CoV-2 vaccines, inactivated virus vaccines have been widely applied in China and many other countries. To understand the underlying protective mechanism of these vaccines, it is necessary to systematically analyze the humoral responses that are triggered. By utilizing a SARS-CoV-2 microarray with 21 proteins and 197 peptides that fully cover the spike protein, antibody response profiles of 59 serum samples collected from 32 volunteers immunized with the inactivated virus vaccine BBIBP-CorV were generated. For this set of samples, the microarray results correlated with the neutralization titers of the authentic virus, and two peptides (S1-5 and S2-22) were identified as potential biomarkers for assessing the effectiveness of vaccination. Moreover, by comparing immunized volunteers to convalescent and hospitalized COVID-19 patients, the N protein, NSP7, and S2-78 were identified as potential biomarkers for differentiating COVID-19 patients from individuals vaccinated with the inactivated SARS-CoV-2 vaccine. The comprehensive profile of humoral responses against the inactivated SARS-CoV-2 vaccine will facilitate a deeper understanding of the vaccine and provide potential biomarkers for inactivated virus vaccine-related applications.

Antibody dynamics to SARS-CoV-2 in asymptomatic COVID-19 infections.

BACKGROUND: The missing asymptomatic COVID-19 infections have been overlooked because of the imperfect sensitivity of the nucleic acid testing (NAT). Globally understanding the humoral immunity in asymptomatic carriers will provide scientific knowledge for developing serological tests, improving early identification, and implementing more rational control strategies against the pandemic. MEASURE: Utilizing both NAT and commercial kits for serum IgM and IgG antibodies, we extensively screened 11 766 epidemiologically suspected individuals on enrollment and 63 asymptomatic individuals were detected and recruited. Sixty-three healthy individuals and 51 mild patients without any preexisting conditions were set as controls. Serum IgM and IgG profiles were further probed using a SARS-CoV-2 proteome microarray, and neutralizing antibody was detected by a pseudotyped virus neutralization assay system. The dynamics of antibodies were analyzed with exposure time or symptoms onset. RESULTS: A combination test of NAT and serological testing for IgM antibody discovered 55.5% of the total of 63 asymptomatic infections, which significantly raises the detection sensitivity when compared with the NAT alone (19%). Serum proteome microarray analysis demonstrated that asymptomatics mainly produced IgM and IgG antibodies against S1 and N proteins out of 20 proteins of SARS-CoV-2. Different from strong and persistent N-specific antibodies, S1-specific IgM responses, which evolved in asymptomatic individuals as early as the seventh day after exposure, peaked on days from 17 days to 25 days, and then disappeared in two months, might be used as an early diagnostic biomarker. 11.8% (6/51) mild patients and 38.1% (24/63) asymptomatic individuals did not produce neutralizing antibody. In particular, neutralizing antibody in asymptomatics gradually vanished in two months. CONCLUSION: Our findings might have important implications for the definition of asymptomatic COVID-19 infections, diagnosis, serological survey, public health, and immunization strategies.