Systemic profiling of immune responses in healthy adults vaccinated with an RBD-targeting COVID-19 mRNA vaccine

Coronavirus disease 2019 (COVID-19) messenger RNA (mRNA) vaccines have succeeded unprecedentedly due to high protection efficacy and robust immune responses. However, systematic and longitudinal profiling of immune responses in mRNA vaccine recipients remains limited. Here, a cohort of ten healthy volunteers who received two doses of ARCoV, a non-modified mRNA vaccine, were enrolled. Peripheral blood samples were collected and analyzed using Olink technology, antibody detection, intracellular cytokine staining, single-cell sequencing, and T cell receptor (TCR) sequencing. ARCoV vaccination induced potent humoral and cellular immune responses, as well as elevated cytokines including C-X-C motif chemokine ligand 10 (CXCL10) and interferon-gamma (IFN-γ). Single-cell sequencing revealed that ARCoV immunization induced an increased relative abundance of interferon-activated T cells, proliferative T cells, and naïve T cells. Monocytes and dendritic cells exhibited activation of the innate immune response, downregulation of hypoxia and glycolysis pathways, and a transient decrease in their proportions. Integrative analysis of single-cell RNA and TCR sequencing identified clonal expansion of effector T cells and killer cell immunoglobulin-like receptor (KIR)-expressing natural killer-like cells after the second dose. These findings deepen our understanding of the immune dynamics following mRNA vaccination and offer valuable insights for designing next-generation vaccines. This study was registered at the Chinese Clinical Trial Registry (ChiCTR2100049104).