Elevated Nucleoprotein-Induced Interferon-γ Release in COVID-19 Patients Detected in a SARS-CoV-2 Enzyme-Linked Immunosorbent Spot Assay

Background: A new coronavirus, SARS-CoV-2, has recently emerged to cause a human pandemic. Data on SARS-CoV-2 specific T-cell responses is scarce, but various studies suggest a suppressed T-cell mediated immunity in patients with COVID-19. Methods: The objective of the present study was to determine functional T-cell responses to SARS-CoV-2 antigens (mosaic surface protein and nucleoprotein), by using an enzyme-linked immunosorbent spot (ELISpot) interferon-γ release assay, in patients with RT-PCR confirmed COVID-19. T-cell immune responses were evaluated in patients with severe disease admitted to the intensive care unit (ICU), patients with moderate disease treated on the pulmonary ward and healthy volunteers. Findings: More than half of the 19 COVID-19 patients sampled at ≥14 days after the onset of symptoms showed a significant T-cell response against the nucleoprotein. A subgroup of nine (47%) of these 19 COVID-19 patients showed a delayed or reduced T-cell response against the nucleoprotein and showed significant lower reactivity against the mitogen control stimulant. Interpretation: As none of the healthy controls had more than nine IFN-γ spot forming cells specific for the SARS-CoV-2 nucleoprotein, 10 or more spots was determined to be indicative for COVID-19 disease. The SARS-CoV-2 nucleoprotein ELISpot of patient samples taken more than three weeks after the start of symptoms showed a high diagnostic sensitivity for COVID-19 disease. T-cell response in a subgroup of COVID-19 patients was suboptimal and supports previous studies in which patients with COVID-19 were associated with a suppressed T-cell mediated immunity. Funding Statement: N/A Declaration of Interests: The authors declare no conflict of interest. Ethics Approval Statement: The regional Medical Research Ethics Committees United approved the study (Nieuwegein, the Netherlands; MEC-U: NL73618.100.20).