ABSTRACT
Serological tests are essential for the control and management of COVID-19 pandemic, not only for current and historical diagnostics but especially for surveillance, epidemiological, and acquired immunity studies. Clinical COVID-19 serology is routinely performed by enzymatic or chemiluminescence immunoassays (i.e., ELISA or CLIA), which provide good sensitivities at the expense of relatively long turnaround times and specialized laboratory settings. Rapid serological tests, based on lateral flow assays, have also been developed and widely commercialized, but they suffer from limited reliability due to relatively low sensitivity and specificity. We have developed and validated a direct serological biosensor assay employing proprietary technology based on Surface Plasmon Resonance (SPR). The biosensor offers a rapid -less than 15 min- identification and quantification of SARS-CoV-2 antibodies directly in clinical samples, without the need of any signal amplification. The portable plasmonic biosensor device employs a custom-designed multi-antigen sensor biochip, combining the two main viral antigens (RBD peptide and N protein), for simultaneous detection of human antibodies targeting both antigens. The SPR serology assay reaches detection limits in the low ng mL-1 range employing polyclonal antibodies as standard, which are well below the commonly detected antibody levels in COVID-19 patients. The assay has also been implemented employing the first WHO approved anti-SARS-CoV-2 immunoglobulin standard. We have carried out a clinical validation with COVID-19 positive and negative samples (n=120) that demonstrates the excellent diagnostic sensitivity (99%) and specificity (100%). This positions our biosensor device as an accurate, robust, and easy-to-use diagnostics tool for rapid and reliable COVID-19 serology to be employed both at laboratory and decentralized settings for the management of COVID-19 patients and for the evaluation of immunological status during vaccination, treatment or in front of emerging variants.
Subject(s)
COVID-19ABSTRACT
Background: Clinical trials on the different vaccines to SARS-CoV-2 have demonstrated protection efficacy, but it is urgent to assess the levels of protection generated with real-world data, especially in individuals professionally exposed. Measuring T-cell responses may complement antibody tests currently in use as correlates of protection but there are not validated T-cell responses applicable to large number of samples. Objective: To assess the feasibility of using T-cell responses to SARS-CoV-2 S peptides by commercially available whole blood interferon-gamma release assays (IGRA) as a correlate of protection. Patients: Twenty health care workers before and after vaccination. Methods: Antibody test to SARS-CoV-2 N and S proteins in parallel with one IGRA assay and two detection techniques than can be automated. Results: IGRA test detected T-cell responses in naturally exposed and vaccinated HCW already after first vaccination dose. the correlation by the two detection methods, CLIA and ELISA, very high (R>0.9) and sensitivity and specificity ranged between 100 and 86% and 100-73% respectively. Even though there was a very high concordance between antibody and the IGRA assay in the ability to detect immune response to SARS-CoV-2 there was a relatively low quantitative correlation. In the small group primed by natural infection, one vaccine dose was sufficient to reach immune response plateau. IGRA was positive in one Ig (S) antibody negative vaccinated immunosuppressed HCW illustrating another advantage of the IGRA test. Conclusion: Whole blood IGRA tests amenable to automation, as the one here reported, constitute a promising additional tool for measuring the state of the immune response to SARS-CoV-2; they are applicable to large number of samples and may become valuable correlates of protection to COVID-19, particularly for vulnerable groups at risk of being re-exposed to infection, as are health care workers.