Introduction
Understanding the longevity of the adaptive immune response to
SARS-CoV-2 is critical for devising public health policies to prevent
reinfection. The ability to accurately measure the protective endurance
of both memory B and T cells is fundamental to this understanding.
Concerns about rapidly waning antibody levels post viral clearance have
been raised 1. However, T cell responses may be more
robust and longer lived 2. Initial studies revealed
that virus-specific T cell responses developed in nearly all individuals
with confirmed SARS-CoV-2 infection 3-6, with
responses persisting for at least six months post-infection7, 8. Once vaccination programmes were established,
vaccine-induced T cell responses could be investigated. Early studies
demonstrated that SARS-CoV-2 vaccines were efficient at generating
broad, protective T cell responses 9-12. Little is
known about the longevity of these responses and simple methods for
accurately screening viral specific T cell responses at a population
level are needed to assess long term vaccine efficacy. Traditional
methods of measuring T cell responses are time consuming, difficult to
standardise, and require specialised equipment and technical knowledge.
Moreover, current commercial tests, such as ELISpot, solely measure T
cell production of interferon-gamma (IFN-γ), although other cytokines
may provide better indication of anti-viral responses7. Simple, ‘rapid’ tests using whole blood, similar to
those routinely used for diagnosis of tuberculosis provide an
alternative approach to measure viral specific T cell responses13-15. Here, we adapted and optimised an in
vitro whole blood stimulation assay to determine the most accurate
biomarkers for identifying the presence of SARS-CoV-2-specific T cells
in naturally infected individuals and in two cohorts of individuals pre-
and post-vaccination. The high specificity and sensitivity of the test
distinguishes individuals with either natural and/or vaccine induced T
cell immunity from those individuals with no immunity to SARS-CoV-2.