Laboratory Evaluation of SARS-CoV-2 Specific T-Cell Immunity by ELISpot Interferon-γ Based Immunoassay

Cellular and humoral immune responses are fundamental for SARS-CoV-2 elimination, infection resolution, and protection against reinfection. Data on long-term SARS-CoV-2-specific T-cell responses are limited. We conducted this study to evaluate the presence of SARS-CoV-2 specific T lymphocytes using the ELISpot interferon-γ-based kit for outpatients with or without a history of SARS-CoV-2 infection. SARS-CoV-2 activated T-cell response was defined from peripheral blood mononuclear cells (PBMCs) of nine (n=9) outpatients- 6 women and 3 men, aged 32 to 73 years old, all from Varna city, Bulgaria. They were tested between November and December 2021. Eight of them – 88.9% were in contact with the COVID-19 virus from 1 to 20 months ago. The number of spots obtained provides a measure of the abundance of SARS-CoV-2 – sensitized effector T cells in the peripheral blood. A reactive T-cellular immune response was ob¬served 12 months after SARS-CoV-2 viral infection. In addition, IgG humoral immunity was analyzed and compared with the specific T-cell response in some participants. Compared with humoral immunity-re¬lated studies, those focusing on SARS-CoV-2-specific cellular immunity using the ElISpot immunoassay are relatively falling behind standardization. The SARS-CoV-2 specific ELISpot Interferon-γ immunoassay, described in our study, conducted with a small group of patients, can serve as an effective immunoassay to measure host T-cell responses and help further detailed understanding of pathogenetic mechanisms and persistence of cellular and humoral immunity against SARS-CoV-2.