Presence of SARS-CoV-2-specific T cells before vaccination in the Mexican population

Area of Science:

• Immunology
• Virology
• Epidemiology

Background:

• The immune response to SARS-CoV-2 is crucial, but pre-vaccination T cell specificities in Mexico remained unevaluated.
• Understanding T cell responses is key to characterizing immunity against SARS-CoV-2.

Purpose of the Study:

• To determine the frequency and characteristics of T CD4+ and T CD8+ cells specific to SARS-CoV-2 spike (S) and nucleocapsid (N) proteins in an unvaccinated Mexican population.
• To analyze cytokine profiles and T cell activation/memory phenotypes.

Main Methods:

• Collected peripheral blood from 78 unvaccinated Mexican subjects.
• Assessed antibodies against S (RBD) and N proteins.
• Isolated peripheral blood mononuclear cells, stimulated with S or N peptides, and quantified cytokine levels (IL-1β, IL-4, IL-6, IL-10, IL-2, IL-8, TNF-α, IFN-γ, GM-CSF).
• Stained cells to evaluate activation and memory phenotypes.

Main Results:

• Differential activation frequency in CD4+ cells based on serological status, but not in CD8+ cells.
• Central memory T CD4+ cells were the predominantly activated population.
• S peptides induced a more pro-inflammatory cytokine response compared to N peptides.
• Only 10% of the population showed a consistent phenotype for nucleocapsid peptide response.

Conclusions:

• A significant T cell response to SARS-CoV-2 S and N proteins was observed in the unvaccinated Mexican cohort.
• This response likely resulted from prior infections with seasonal coronaviruses or undetected SARS-CoV-2 exposure.
• Findings highlight pre-existing immunity and T cell memory dynamics in the Mexican population prior to widespread vaccination.