Tixagevimab Plus Cilgavimab Does Not Affect the Interpretation of Electrophoretic and Free Light Chain Assays.

OBJECTIVES: There is concern that the anti-severe acute respiratory syndrome coronavirus 2 therapeutic monoclonal antibodies, used as preexposure prophylaxis in patients with multiple myeloma, may appear as a detectable monoclonal protein by electrophoretic methods, resulting in misinterpretation or inability to measure therapeutic responses in some patients. In this pilot study, we characterize the effect of tixagevimab plus cilgavimab (Evusheld; T + C) on interpretation of serum protein electrophoresis (SPE), immunofixation electrophoresis (IFE), and serum free light chain (sFLC) assays. METHODS: We performed spiking experiments with T + C at serum maximum concentration following a 300-mg dose (1× Cmax) and at 10 times the concentration of Cmax (10× Cmax) with pooled serum samples. SPE and IFE technical procedures were performed on the SPIFE 3000, and sFLC and immunoglobulin G1 (IgG1) subtype quantitation was performed on the Optilite. RESULTS: T + C-associated interference was not visible as an M-spike in normogammaglobulinemic pooled samples. Hypogammaglobulemic pooled samples at 10× Cmax demonstrated an M-spike in SPE and immunoglobulin Gκ pattern in IFE. No increases were noted in the results of sFLC or IgG1 levels. CONCLUSIONS: This study indicates that T + C at pharmacologic Cmax is unlikely to interfere with SPE, IFE, sFLC, or IgG1 analyses when spiked into patient serum samples, but further evaluation of recently injected patients may be warranted.

COVID-19 mRNA Vaccines May Cause False Reactivity in Some Serologic Laboratory Tests, Including Rapid Plasma Reagin Tests.

OBJECTIVES: Acute viral infections and some vaccines have been shown to increase false positivity in serologic assays. We assessed if the messenger RNA coronavirus disease 2019 (COVID-19) vaccines could cause false reactivity in common serologic assays in a pilot longitudinal cohort. METHODS: Thirty-eight participants with sera available prevaccination, 2 weeks after each vaccine dose, and monthly thereafter for up to 5 months were tested for common infectious disease serologies and antiphospholipid syndrome (APS) serology markers on the BioPlex 2200, Sure-Vue rapid plasma reagin (RPR), and Macro-Vue RPR. Twenty-two participants received the Moderna vaccine and 16 received the Pfizer vaccine. RESULTS: Most assays had no change in reactivity over the course of the sample draws, including APS markers. Epstein-Barr virus immunoglobulin G (IgG), measles IgG, and rubella immunoglobulin M all had possible false reactivity in one to two participants. RPR tests demonstrated false reactivity, with baseline nonreactive participant samples becoming reactive following vaccination. There were more false reactive participants (7/38) in the BioPlex RPR than in the Sure-Vue (2/38) and Macro-Vue (1/38) tests. All falsely reactive RPR tests were in participants who received the Moderna vaccine. CONCLUSIONS: Serologic assays with results that do not fit the clinical picture following COVID-19 vaccination should be repeated. Effects of false reactivity can last more than 5 months in some assays. In particular, RPR is susceptible to false reactivity, and there is variability among assays. Larger longitudinal studies are needed to determine the incidence and window of false reactivity.

Multiplex assessment of SARS-CoV-2 antibodies improves assay sensitivity and correlation with neutralizing antibodies.

OBJECTIVES: Detection of antibodies to multiple SARS-CoV-2 antigens in a single assay could increase diagnostic accuracy, differentiate vaccination from natural disease, and aid in retrospective exposure determination. Correlation of binding antibody assessment in clinical assays with neutralizing antibodies is needed to better understand the humoral response to SARS-CoV-2 infection and establish of correlates of protection. METHODS: A cohort of 752 samples was used to assess specificity, sensitivity, and comparison to 6 other Conformitè Europëenne serologic assays for the BioRad SARS-CoV-2 IgG multiplex assay which measures receptor binding domain IgG (RBD), spike-S1 IgG (S1), spike-S2 IgG (S2), and nucleocapsid IgG (N). A subset of serial specimens from 14 patients was also tested for neutralizing antibodies (n = 61). RESULTS: Specificity for RBD and S1 IgG was 99.4% (n = 170) and 100% for S2 and N IgG (n = 170) in a cohort selected for probable interference. Overall assay concordance with other assays was >93% for IgG and total antibody assays and reached 100% sensitivity for clinical concordance at >14 days as a multiplex assay. RBD and S1 binding antibody positivity demonstrated 79-95% agreement with the presence of neutralizing antibodies. CONCLUSIONS: The BioRad SARS-CoV-2 IgG assay is comparable to existing assays, and achieved 100% sensitivity when all markers were included. The ability to measure antibodies against spike and nucleocapsid proteins simultaneously may be advantageous for complex clinical presentations, epidemiologic research, and in decisions regarding infection prevention strategies. Additional independent validations are needed to further determine binding antibody and neutralizing antibody correlations.

Differential Antibody Response to mRNA COVID-19 Vaccines in Healthy Subjects.

Knowledge about development and duration of virus-specific antibodies after COVID-19 vaccination is important for understanding how to limit the pandemic via vaccination in different populations and societies. However, the clinical utility of postvaccination testing of antibody response and selection of targeted SARS-CoV-2 antigen(s) has not been established. The results of such testing from clinical teams independent from vaccine manufacturers are also limited. Here, we report the initial results of an ongoing clinical study on evaluation of antibody response to four different SARS-CoV-2 antigens after first and second dose of Pfizer and Moderna mRNA vaccines and at later time points. We revealed a peak of antibody induction after the vaccine boosting dose with a gradual decline of antibody levels at later time. Anti-nucleocapsid antibody was not induced by spike protein-encoding vaccines and this may continue to serve as a marker of previous SARS-CoV-2 infection. No differences between the two vaccines in terms of antibody response were revealed. Age and gender dependencies were determined to be minimal within the healthy adult (but not aged) population. Our results suggest that postvaccination testing of antibody response is an important and feasible tool for following people after vaccination and selecting individuals who might require a third dose of vaccine at an earlier time point or persons who may not need a second dose due to previous SARS-CoV-2 infection. IMPORTANCE Now that authorized vaccines for COVID-19 have been widely used, it is important to understand how they induce antivirus antibodies, which antigens are targeted, how long antibodies circulate, and how personal health conditions and age may affect this humoral immunity. Here, we report induction and time course of multiple anti-SARS-CoV-2 antibody responses in healthy individuals immunized with Pfizer and Moderna mRNA vaccines. We also determined the age and gender dependence of the antibody response and compared antibody levels to responses seen in those who have recovered from COVID-19. Our results suggest the importance of screening for antibody response to multiple antigens after vaccination in order to reveal individuals who require early and late additional boosting and those who may not need second dose due to prior SARS-CoV-2 infection.

Antibody Responses After mRNA-Based COVID-19 Vaccination in Residential Older Adults: Implications for Reopening.

OBJECTIVE: COVID-19 disproportionately impacts residents in long-term care facilities. Our objective was to quantify the presence and magnitude of antibody response in vaccinated, older adult residents at assisted living, personal care, and independent living communities. DESIGN: A cross-sectional quality improvement study was conducted March 15 - April 1, 2021 in the greater Pittsburgh region. SETTING AND POPULATION: Participants were older adult residents at assisted living, personal care, and independent living communities, who received mRNA-based COVID-19 vaccine. Conditions that impair immune responses were exclusionary criteria. METHODS: Sera were collected to measure IgG anti-SARS-CoV-2 antibody level with reflex to total anti-SARS-CoV-2 immunoglobulin levels, and blinded evaluation of SARS-CoV-2 pseudovirus neutralization titers. Descriptive statistics, Pearson correlation coefficients, and multiple linear regression analysis evaluated relationships between factors potentially associated with antibody levels. Spearman correlations were calculated between antibody levels and neutralization titers. RESULTS: All participants (N = 70) had received two rounds of vaccination and were found to have antibodies with wide variation in relative levels. Antibody levels trended lower in males, advanced age, current use of steroids, and longer length of time from vaccination. Pseudovirus neutralization titer levels were strongly correlated (P < .001) with Beckman Coulter antibody levels [D614 G NT50, rs = 0.91; B.1.1.7 (UK) NT50, rs = 0.91]. CONCLUSIONS AND IMPLICATIONS: Higher functioning, healthier, residential older adults mounted detectable antibody responses when vaccinated with mRNA-based COVID-19 vaccines. Data suggests some degree of immunity is present during the immediate period following vaccination. However, protective effects remain to be determined in larger studies as clinical protection is afforded by ongoing adaptive immunity, which is known to be decreased in older adults. This study provides important preliminary results on level of population risk in older adult residents at assisted living, personal care, and independent living communities to inform reopening strategies, but are not likely to be translatable for residents in nursing homes.

A Cross-Sectional Study of SARS-CoV-2 Seroprevalence between Fall 2020 and February 2021 in Allegheny County, Western Pennsylvania, USA.

Seroprevalence studies are important for understanding the dynamics of local virus transmission and evaluating community immunity. To assess the seroprevalence for SARS-CoV-2 in Allegheny County, an urban/suburban county in Western PA, 393 human blood samples collected in Fall 2020 and February 2021 were examined for spike protein receptor-binding domain (RBD) and nucleocapsid protein (N) antibodies. All RBD-positive samples were evaluated for virus-specific neutralization activity. Our results showed a seroprevalence of 5.5% by RBD ELISA, 4.5% by N ELISA, and 2.5% for both in Fall 2020, which increased to 24.7% by RBD ELISA, 14.9% by N ELISA, and 12.9% for both in February 2021. Neutralization titer was significantly correlated with RBD titer but not with N titer. Using these two assays, we were able to distinguish infected from vaccinated individuals. In the February cohort, higher median income and white race were associated with serological findings consistent with vaccination. This study demonstrates a 4.5-fold increase in SARS-CoV-2 seroprevalence from Fall 2020 to February 2021 in Allegheny County, PA, due to increased incidence of both natural disease and vaccination. Future seroprevalence studies will need to include the effect of vaccination on assay results and incorporate non-vaccine antigens in serological assessments.

Rapid Detection of SARS-CoV-2 Antigens Using High-Purity Semiconducting Single-Walled Carbon Nanotube-Based Field-Effect Transistors.

Early diagnosis of SARS-CoV-2 infection is critical for facilitating proper containment procedures, and a rapid, sensitive antigen assay is a critical step in curbing the pandemic. In this work, we report the use of a high-purity semiconducting (sc) single-walled carbon nanotube (SWCNT)-based field-effect transistor (FET) decorated with specific binding chemistry to assess the presence of SARS-CoV-2 antigens in clinical nasopharyngeal samples. Our SWCNT FET sensors, with functionalization of the anti-SARS-CoV-2 spike protein antibody (SAb) and anti-nucleocapsid protein antibody, detected the S antigen (SAg) and N antigen (NAg), reaching a limit of detection of 0.55 fg/mL for SAg and 0.016 fg/mL for NAg in calibration samples. SAb-functionalized FET sensors also exhibited good sensing performance in discriminating positive and negative clinical samples, indicating a proof of principle for use as a rapid COVID-19 antigen diagnostic tool with high analytical sensitivity and specificity at low cost.

SARS-CoV-2 Serologic Immune Response in Exogenously Immunosuppressed Patients.

BACKGROUND: While it is presumed that immunosuppressed patients, such as solid organ transplant recipients on immunosuppression, are at greater risk from SARS-CoV-2 infection than the general population, the antibody response to infection in this patient population has not been studied. METHODS: In this report, we follow the anti-SARS-CoV-2 antibody levels in patients with COVID-19 who are undergoing exogenous immunosuppression. Specifically, we studied the antibody response of 3 solid organ transplant recipient patients, 3 patients who take daily inhaled fluticasone, and a patient on etanercept and daily inhaled fluticasone, and compared them to 5 patients not on exogenous immunosuppression. RESULTS: We found that the solid organ transplant patients on full immunosuppression are at risk of having a delayed antibody response and poor outcome. We did not find evidence that inhaled steroids or etanercept predispose patients to delayed immune response to SARS-CoV-2. CONCLUSION: The data presented here suggest that solid organ transplant recipients may be good candidates for early targeted intervention against SARS-CoV-2.

Variable Performance in 6 Commercial SARS-CoV-2 Antibody Assays May Affect Convalescent Plasma and Seroprevalence Screening.

OBJECTIVES: Serologic detection of prior severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is needed for definition of convalescent plasma donors, for confounding SARS-CoV-2 presentation, and for seroprevalence studies. Reliable serologic assays with independent validation are required. METHODS: Six SARS-CoV-2 antibody assays from Beckman Coulter, Euroimmun (IgG, IgA), Roche, and Siemens (Centaur, Vista) were assessed for specificity (n = 184), sensitivity (n = 154), and seroconversion in a defined cohort with clinical correlates and molecular SARS-CoV-2 results. RESULTS: Assay specificity was 99% or greater for all assays except the Euroimmun IgA (95%). Sensitivity at more than 21 days from symptom onset was 84%, 95%, 72%, 98%, 67%, and 96% for Beckman Coulter, Centaur, Vista, Roche, Euroimmun IgA, and Euroimmun IgG, respectively. Average day of seroconversion was similar between assays (8-10 d), with 2 patients not producing nucleocapsid antibodies during hospitalization. CONCLUSIONS: SARS-CoV-2 nucleocapsid antibodies may be less reliably produced early in disease than spike protein antibodies. Assessment of convalescent plasma donors at more than 30 days from symptom onset and seroprevalence studies should use assays with defined sensitivity at time points of interest because not all assays detected antibodies reliably at more than 30 days.

Evaluation of SARS-CoV-2 prototype serologic test in hospitalized patients.

OBJECTIVES: Humoral immune response to SARS-CoV-2 infection has been reported in several patient cohorts with results that vary by method and population studied due to the lack of reliable commercial assays available as the pandemic initially spread. We sought to clinically assess commercial prototype SARS-CoV-2 IgG and IgA assays for use in screening for prior infection and convalescent plasma donation. DESIGN AND METHODS: Prototype SARS-CoV-2 IgG and IgA assays from Euroimmun were assessed utilizing remnant specimens. Specificity testing used specimens in their convalescent window for the common coronaviruses and other infectious diseases known to be associated with increased non-specificity in serologic assays. Sensitivity testing utilized serial specimens from molecularly confirmed SARS-CoV-2 critically ill patients to assess seroconversion. Utilizing recombinant spike protein we also developed a competitive confirmation procedure to increase assay specificity. RESULTS: We determined specificity to be 97% and 81%, respectively, when indeterminate samples were considered positive and 99% and 86% when indeterminate samples were considered negative. We developed a new confirmation methodology to enhance the specificity of the assays with an anticipated specificity of 98% for IgA. Valuation of hospitalized COVID-19 patients determined median IgA seroconversion to be 8 days and IgG 10 days. Neither level nor timing of antibody response correlated with days on ventilation. End titer measurements indicate that validated improved assays may be capable of semi-quantitative measurement. CONCLUSIONS: We found these assays to be clinically acceptable for the high prevalence population tested, for instance, for convalescent plasma donation.