The nasal cavity is the primary entry site for respiratory viruses, including SARS-CoV-2, and represents a critical frontline of immune defence. We have previously shown that mucosal-resident virus-specific CD8⁺ T cells are induced in the human nasal cavity following primary respiratory infection1 and likely contribute to protection against subsequent viral re-infections. However, longitudinal tracking over nine months suggested that the temporal kinetics and persistence of these responses in the nasal mucosa are associated with repeated viral exposure: influenza- and common cold coronavirus–specific T-cell responses persisted, whereas SARS-CoV-2–specific responses declined below the limit of detection within six months2.
Understanding the kinetics of virus-specific CD8⁺ T-cell induction and contraction following viral challenge is therefore important for respiratory virus management and vaccine development. In prior studies, virus-specific T cells in the nasal cavity were detected using nasal swabs followed by ELISpot or activation-induced marker (AIM) assays3. However, the complexity of these assays and the limited lymphocyte numbers obtained by nasal sampling restrict their broader application. Here, we evaluated a simple and rapid virus-specific nasal T-cell cytokine release assay (CRA), based on stimulation of nasal cells with peptide pools spanning SARS-CoV-2 and influenza A virus proteins, followed by quantification of IFN-γ and CXCL10. Parallel analyses using IFN-γ ELISpot, AIM, and CRA demonstrated that the CRA reliably captures virus-specific nasal T-cell responses, with combined IFN-γ and CXCL10 measurement improving assay sensitivity.
We next applied this rapid CRA to freshly collected nasal samples from healthy volunteers (n = 19) participating in a controlled human infection model (CHIM) study with SARS-CoV-2 Delta. Although only 2/19 participants developed productive infection, defined by ≥2 positive qPCR results, all participants showed rapid recruitment of lymphocytes to the nasal cavity as early as day 1 post-challenge. In contrast to natural primary infection—where SARS-CoV-2–specific nasal T cells were detectable in the majority of individuals and persisted for several months—the kinetics of the SARS-CoV-2–specific T-cell response following experimental challenge were characterised by a brief and modest expansion, returning to baseline or below the limit of detection within days in nearly all participants. These findings suggest fundamental differences in nasal T-cell dynamics between natural infection and controlled viral challenge, and/or between primary and secondary infections, with implications for the interpretation of mucosal immunity in CHIM studies.