PMC10350526_01
Antibody generation after COVID-19 vaccination. (A) Neutralizing Ab titers; (B) IgG antibody against the Spike protein (S); (C) Total antibody (IgA, IgM, IgG), measured over time after three vaccine doses.
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Gating strategy for the analyzing antigen specific T cells has been shown in  Supplementary Figure 1A . S/Co= 207, S/Co= 1.3 and 1:20 before the booster to S/Co=1270, S/Co=15.5 and 1:360 one month after the booster respectively. She was still seropositive eight months after the booster dose with total, IgG and neutralizing antibodies level of S/Co= 2380, S/Co= 19.6 and 1:160 respectively ( Figures 1A-C ). A robust T-cell response was observed against hCoVs with four antigens from alpha-hCoV-NL63 and three out of four antigens of alpha-hCoV-229E were recognized, whereas a minimal reactivity was observed against both beta-hCoVs ( Figure S1 ). Table S1 ) and therefore represent only a minor portion of the overall T cell immunity against the full-length spike proteins. Total anti-spike T cell reactivity induced by vaccination ( Supplementary Figure 1 ), potentially reflecting the broad T cell immunity against SARS-CoV-2 which targets the full length of the immunodominant viral proteins, is more comprehensive.
Kinetics of T-Cell Response post SARS-CoV-2 mRNA vaccine. PBMCs from the subject collected at three different time points (189, 292, and 390 days post vaccination), were primed with the ancestral or omicron spike peptide library (S1 & S2), cultured for 14 days and tested against the indicated antigens. (A) Ancestral spike primed T cells were stimulated with S1 and S2 antigens from either ancestral or omicron spike followed by cytokine release assay. (B) Cytokine release assay of cultures primed with M and NP peptide and tested against cognate antigens post 14-day expansion. (C) Longitudinal T cell response against ancestral SARS-CoV2. (D) Omicron spike primed T cells were stimulated with S1 and S2 antigens from either ancestral or omicron spike followed by cytokine release assay. (E) Cross-reactivity of ancestral (Left) and omicron (Right) spike-specific T cells. (F) Percentage of cross-reactive cells among total reactive cells in both ancestral and omicron spike primed cultures.
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T-cell response against S1 and S2 peptide pool was observed after two doses of vaccination ( Figure 2A ), as previously documented in SCoV2 infected and/or exposed individuals who mounted a robust T cell response without seroconversion. Third vaccination dose further enhanced the reactivity against these antigens, with up to 17.7% and 24.5% of T cells recognizing S1 and S2 antigens respectively. The ancestral-spike specific T cells were able to mount a response against omicron variant, with similar reactivity to that of cognate antigens at each tested timepoint ( Figure 2A ). No response was elicited against NP antigens ( Figure 2B ). We observed reciprocal cross-reactivity with Omicron S1/S2-induced T cells showing potent reactivity against ancestral counterparts ( Figures 2D, E ) at each analyzed timepoint. Both cultures did not show statistically significant difference in % cross-reactive cells among total reactive T cells ( Figure 2F ).
Response of ancestral spike-specific T-cells against various SARS-CoV2 variants: (A) Gating strategy used for the analysis of antigen reactive T cells. (B) Ancestral spike primed T cells were expanded for 14 days and challenged with indicated peptide libraries of variants of SCoV2. Each variant library consisted of peptides spanning mutated regions only. Dot-plots shows antigen-specific CD4+ T cell response.
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Most of the variants that showed response against WT-epitope also showed response against mutant epitope, although to a lesser extent in some instances ( Figure 3 ).