Rapid cytokine release assay in whole blood determines longitudinal T-cell responses against ancestral, Delta, and Omicron SARS CoV-2 variants

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.