Combined assessment of S- and N-specific IL-2 and IL-13 secretion and CD69 neo-expression for discrimination of post-infection and post-vaccination cellular SARS-CoV-2-specific immune response

Background: Antibody-based tests are available for measuring SARS-CoV-2-specific immune responses but fast T-cell assays remain scarce. Robust T cell-based tests are needed to differentiate specific cellular immune responses after infection from those after vaccination.

Methods: One hundred seventeen individuals (COVID-19 convalescent patients: n = 40; SARS-CoV-2 vaccinees: n = 41; healthy controls: n = 36) were evaluated for SARS-CoV-2-specific cellular immune responses (proliferation, Th1, Th2, Th17, and inflammatory cytokines, activation-induced marker [AIM] expression) by incubating purified peripheral blood mononuclear cells (PBMC) or whole blood (WB) with SARS-CoV-2 peptides (S, N, or M), vaccine antigens (tetanus toxoid, tick borne encephalitis virus) or polyclonal stimuli (Staphylococcal enterotoxin, phytohemagglutinin).

Results: N-peptide mix stimulation of WB identified the combination of IL-2 and IL-13 secretion as superior to IFN-γ secretion to discriminate between COVID-19-convalescent patients and healthy controls (p < .0001). Comparable results were obtained with M- or S-peptides, the latter almost comparably recalled IL-2, IFN-γ, and IL-13 responses in WB of vaccinees. Analysis 10 months as opposed to 10 weeks after COVID-19, but not allergic disease status, positively correlated with IL-13 recall responses. WB cytokine responses correlated with cytokine and proliferation responses of PBMC. Antigen-induced neo-expression of the C-type lectin CD69 on CD4⁺ (p < .0001) and CD8⁺ (p = .0002) T cells informed best about the SARS-CoV-2 exposure status with additional benefit coming from CD25 upregulation.

Conclusion: Along with N- and S-peptide-induced IL-2 and CD69 neo-expression, we suggest to include the type 2 cytokine IL-13 as T-cellular recall marker for SARS-CoV-2 specific T-cellular immune responses after infection and vaccination.