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.
ABSTRACT
The heterogeneous disease course of COVID-19 is unpredictable, ranging from mild self-limiting symptoms to cytokine storms, acute respiratory distress syndrome (ARDS), multi-organ failure and death. Identification of high-risk cases will enable appropriate intervention and escalation. This study investigates the routine laboratory tests and cytokines implicated in COVID-19 for their potential application as biomarkers of disease severity, respiratory failure and need of higher-level care. From analysis of 203 samples, CRP, IL-6, IL-10 and LDH were most strongly correlated with the WHO ordinal scale of illness severity, the fraction of inspired oxygen delivery, radiological evidence of ARDS and level of respiratory support (p ≤ 0.001). IL-6 levels of ≥3.27 pg/ml provide a sensitivity of 0.87 and specificity of 0.64 for a requirement of ventilation, and a CRP of ≥37 mg/l of 0.91 and 0.66. Reliable stratification of high-risk cases has significant implications on patient triage, resource management and potentially the initiation of novel therapies in severe patients.