ABSTRACT
Background: A simple, accurate and rapid whole blood-based T-cell test was previously developed to determine SARS-CoV- 2- specific T-cell immunity. Herein, the test was utilized to measure the magnitude of T-cell responses up to 6 months post-vaccination, assess the effects of vaccine boosters, and to elucidate any effect that Delta and Omicron variants may have on T-cell immunity. Method(s): Immunocompetent individuals (n = 44) were recruited to donate a blood sample between one-and six-months post-vaccination. Whole blood was stimulated overnight with peptides spanning immunodominant regions specific for ancestral SARS-CoV- 2. Blood plasma samples were analysed for IL-2 production via Luminex xMAP cytokine array, as this was previously demonstrated to be the most accurate biomarker for the test. Following booster vaccinations, 58 individuals donated a blood sample between one-and four-months post-booster and T-cell responses after overnight stimulations were assessed. Additionally, 30 samples were stimulated with peptides from the immunodominant regions of the Delta and Omicron SARS-CoV- 2 variants and IL-2 levels were compared. Result(s): A comparison of T-cell responses from samples donated up to one-month and six-months post-vaccination revealed no significant differences in the magnitude of IL-2 production (p = 0.9252), with near equivalent means. Booster vaccinations increased the magnitude of the T-cell response in 69% of individuals analysed, with the mean production of IL-2 rising from 77pg/ml six-months pre-booster to 141pg/ml 3-weeks post-booster. Analysis of the longevity of post-booster T-cell response demonstrated no significant differences in the magnitude of IL-2 (p = 0.8141) production, with near equivalent means at one-month and 4-months post-booster (119pg/ml and 111pg/ml, respectively). Finally, no significant differences in the magnitude of IL-2 were observed between samples stimulated with either ancestral, Delta or Omicron peptides, with the means of each group being highly comparable. Conclusion(s): Results from this rapid whole blood-based T-cell test indicate that T-cell immunity to multiple variants of SARS-CoV- 2 within immunocompetent cohorts does not wane significantly over time. However, booster vaccinations may be important for individuals who have lower levels of immunity following their first complete vaccination doses. This test could be a valuable tool in the assessment of SARS-CoV- 2 immunity in multiple cohorts of clinical vulnerable individuals.
ABSTRACT
Background: A simple, accurate and rapid whole blood-based T cell test was previously developed to determine SARS-CoV-2-specific T cell immunity. The test was established by comparing cytokine production from naturally infected convalescent donors with covid-19 negative donors. The data revealed IL-2 production to be the most indicative of prior SARS-CoV-2 infection. However, accurately identifying vaccine-induced SARS-CoV-2-specific T cell immunity via this method was still to be confirmed. Herein, we sort to address if this was possible. Method: A cohort of unvaccinated healthy individuals was recruited to donate a single blood sample for an overnight in vitro stimulation with peptides spanning immunodominant regions specific for SARS-CoV-2. Blood plasma samples were harvested and analysed for a broad panel of cytokines using ELISA for IFN-g and Luminex xMAP cytokine arrays for IL-2 and other TH1/TH2 cytokines. The same cohort were then asked to donate a second blood sample following SARS-CoV-2 vaccinations, and the same stimulations and analyses were performed. In addition, plasma anti-SARS-CoV-2 IgG levels were assessed in both pre-and post-vaccination samples by direct ELISA against the whole spike protein. Results: A multiplex cytokine array revealed IL-2 to be the most reliable biomarker in indicating a vaccine-induced SARS-CoV-2-specific T cell response, with 100% of post-vaccinated donors mounting a significant IL-2 response above a pre-determined cut off level for positivity of 19.91pg/ml. All donors demonstrated a considerable increase in magnitude of IL-2 responses from pre-vaccination to post-vaccination, with results ranging from ∼125% change to >36,000% change. In addition, IFN-g and plasma IgG ELISAs revealed both to be reliable biomarkers, with post-vaccination levels of each being significantly raised above pre-vaccination levels. However, the magnitude of these responses was not as greatly increased as those observed with IL-2, nor did they achieve an increase in 100% of donors assessed. Conclusion: This standardisable, rapid, and accurate T cell test approach can be utilised to make accurate and comparable assessments of vaccine-induced T cell immunity across multiple population cohorts. This could provide valuable insight into the extremely important question of how long vaccine-induced immunity may last, and aid decision making around if and when vaccine boosters should be administered.