Measurement of IFN-γ and IL-2 for the assessment of the cellular immunity against SARS-CoV-2.

The study of specific T-cell responses against SARS-CoV-2 is important for understanding long-term immunity and infection management. The aim of this study was to assess the dual IFN-γ and IL-2 detection, using a SARS-CoV-2 specific fluorescence ELISPOT, in patients undergoing acute disease, during convalescence, and after vaccination. We also evaluated humoral response and compared with T-cells with the aim of correlating both types of responses, and increase the number of specific response detection. Blood samples were drawn from acute COVID-19 patients and convalescent individuals classified according to disease severity; and from unvaccinated and vaccinated uninfected individuals. IgGs against Spike and nucleocapsid, IgMs against nucleocapsid, and neutralizing antibodies were also analyzed. Our results show that IFN-γ in combination with IL-2 increases response detection in acute and convalescent individuals (p = 0.023). In addition, IFN-γ detection can be a useful biomarker for monitoring severe acute patients, as our results indicate that those individuals with a poor outcome have lower levels of this cytokine. In some cases, the lack of cellular immunity is compensated by antibodies, confirming the role of both types of immune responses in infection, and confirming that their dual detection can increase the number of specific response detections. In summary, IFN-γ/IL-2 dual detection is promising for characterizing and assessing the immunization status, and helping in the patient management.

Measuring T-Cell Responses against SARS-CoV-2 Is of Utility for Disease and Vaccination Management.

The measurement of specific T-cell responses can be a useful tool for COVID-19 diagnostics and clinical management. In this study, we evaluated the IFN-γ T-cell response against the main SARS-CoV-2 antigens (spike, nucleocapsid and membrane) in acute and convalescent individuals classified according to severity, and in vaccinated and unvaccinated controls. IgG against spike and nucleocapsid were also measured. Spike antigen triggered the highest number of T-cell responses. Acute patients showed a low percentage of positive responses when compared to convalescent (71.6% vs. 91.7%, respectively), but increased during hospitalization and with severity. Some convalescent patients showed an IFN-γ T-cell response more than 200 days after diagnosis. Only half of the vaccinated individuals displayed an IFN-γ T-cell response after the second dose. IgG response was found in a higher percentage of individuals compared to IFN-γ T-cell responses, and moderate correlations between both responses were seen. However, in some acute COVID-19 patients specific T-cell response was detected, but not IgG production. We found that the chances of an IFN-γ T-cell response against SARS-CoV-2 is low during acute phase, but may increase over time, and that only half of the vaccinated individuals had an IFN-γ T-cell response after the second dose.