Induction of an immune responseby a nonreplicating adenoviruses-based formulation versusa commercial pseudo-SARS-CoV-2 vaccine

Screening for effective vaccines requires broad studies on their immunogenicity <i>in vitro</i> and <i>ex vivo</i> . We used a PBMC-based system to assess changes in CD4⁺ T cells, CD8⁺ T cells, and CD19⁺ B cells upon stimulation with different combinations of antigens and adjuvants. We studied the activation mechanism using flow cytometry and two different adenoviral adjuvants characterized by the presence or absence of costimulatory ligands for the ICOS and CD40 receptors. Our studies identified the cellular targets and molecular mechanisms driving ongoing switched-antibody diversification. Class-switched memory B cells were the main precursor cells (95.03% ± 0.38 vs. mock 82.33% ± 0.45, <i>P</i> < 0.05) after treatment with the immunogenic formula: adenovirus armed (MIX1) or not (MIX2) with the ICOS and CD40 ligand, the recombinant receptor binding domain (rRBD), and Lentifect™ SARS-CoV-2 spike-pseudotyped lentivirus (GeneCopoeia, USA). Bcell class-switching towards the IgG⁺IgM⁺- positive phenotypes was noted (~50-fold increase vs. mock, <i>P</i> < 0.05). A significant increase was observed in the CD8⁺T_EM population of the MIX1 (~2-fold, <i>P</i> < 0.05) and MIX2 (~4.7-fold, <i>P</i> < 0.05) treated samples. CD8⁺T_EMRA increased when PBMCs were treated with MIX2 (9.63% ± 0.90, <i>P</i> < 0.05) vs. mock (2.63% ± 1.96). Class-switched memory B cells were the dominant antigen-specific cells in primary reactions. We indicated a correlation between the protection offered by vaccine regimens and their ability to induce high frequencies of multifunctional T cells.