Detection of IFNγ-Secreting CD4+ and CD8+ Memory T Cells in COVID-19 Convalescents after Stimulation of Peripheral Blood Mononuclear Cells with Live SARS-CoV-2

Abstract

Background: New coronavirus SARS-CoV-2, a causative agent of the COVID-19 pandemic, has been circulating among humans since November 2019. Multiple studies have assessed the qualitative and quantitative characteristics of virus-specific immunity in COVID-19 convalescents, however, some aspects of the development of memory T-cell responses after natural SARS-CoV-2 infection remain uncovered. Methods: In most of published studies T-cell immunity to the new coronavirus is assessed using peptides corresponding to SARS-CoV-1 or SARS-CoV-2 T-cell epitopes, or with peptide pools covering various parts of the viral proteins. Here, we determined the level of CD4+ and CD8+ memory T-cell responses in COVID-19 convalescents by stimulating PBMCs collected 1 to 6 months after recovery with sucrose gradient-purified live SARS-CoV-2. IFNγ production by the central and effector memory helper and cytotoxic T cells was assessed by intracellular cytokine staining assay and flow cytometry. Results: Stimulation of PBMCs with live SARS-CoV-2 revealed IFNγ-producing T-helper effector memory cells with CD4+CD45RA−CCR7− phenotype, which persisted in circulation for up to 6 month after COVID-19. In contrast, SARS-CoV-2-specific IFNγ-secreting cytotoxic effector memory T cells were found at significant levels only shortly after the disease, but rapidly decreased over time. Conclusion: The stimulation of immune cells with live SARS-CoV-2 revealed a rapid decline in the pool of effector memory CD8+, but not CD4+, T cells after recovery from COVID-19. These data provide additional information on the development and persistence of cellular immune responses after natural infection, and can inform further development of T cell-based SARS-CoV-2 vaccines.

Progress and Challenges Toward Generation and Maintenance of Long-Lived Memory T Lymphocyte Responses During COVID-19

“…IFN-g ELISPOT analysis revealed the presence of predominant antigen-specific CD4 + T cells with robust IL-2 expression (68). However, CD8 + response was found to be half as compared to the CD4 + T cell response which is mostly seen against non-spike proteins (68,69). The level of T cell response can be strongly correlated with the magnitude of peak antibody level specific against spike and RBD (68).…”

Decline of Humoral and Cellular Immune Responses Against SARS-CoV-2 6 Months After Full BNT162b2 Vaccination in Hospital Healthcare Workers

“…Data on cell-mediated immunity against SARS-CoV-2 are more subject to debate. Several reports suggested a decline in anti-spike specific CD4+ immune response after a few months ( 14 , 15 ) whereas, in recent reports, cell memory responses were observed to be relatively stable over 8 months following natural infection with SARS-CoV-2 ( 16 – 19 ). Clinical factors related to medical history and acute infection could be associated with variability in T-cell responses over time ( 19 ).…”

T cell response to intact SARS-CoV-2 includes coronavirus cross-reactive and variant-specific components

“…In the present report, we leveraged the ability of moDC to cross-present whole viral antigen to CD8 T cells, and to present viral antigen to CD4 T cells, in order to enrich polyclonal SARS-CoV-2–specific T cells. Similar studies are rare; in one report, live virus induced subtle IFN-γ expression in convalescent T cells, but confirmation of virus specificity was not documented ( 38 ). Using established ( 25 , 30 , 39 – 42 ) readout methods, TCL created after whole virus or simpler antigen stimulation were used to study the breadth and specificity of the T cell response, reactivity to virus-infected cells, and recognition of sCoV and SARS-CoV-2 variants.…”