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The efficacy of SARS-CoV-2 mRNA-based vaccines in preventing COVID-19 disease has been extensively demonstrated; however, it is of uttermost importance to acquire knowledge on the persistence of immune-protection both in terms of levels of neutralizing antibodies and specialized memory cells. This can provide important scientific basis for decisions on the need of additional vaccine doses and on when these should be administered thus resulting in an improvement in vaccination schedules. Here, we briefly report the changes in antibody levels and cellular immunity following BNT162b2 administration. We show an important fall in anti S1-Spike antibodies in BNT162b2 vaccinated subjects overtime, paralleled by a contextual consolidation of specific spike (S) T-cells, mainly of the CD8+ compartment. Contrariwise, CD4+ S-specific response shows a considerable interindividual variability. These data suggest that the well-known antibody drop in vaccinated subjects is replaced by memory cell consolidation that can protect from severe adverse effects of SARS-CoV-2 infection.

Extracellular vesicles (EVs) play a crucial role in the intercellular crosstalk. Mesenchymal stem cell-derived EVs (MSC-EVs), displaying promising therapeutic roles, contribute to the strong rationale for developing EVs as an alternative therapeutic option. EV analysis still represents one of the major issues to be solved in order to translate the use of MSC-EV detection in clinical settings. Even if flow cytometry (FC) has been largely applied for EV studies, the lack of consensus on protocols for FC detection of EVs generated controversy. Standard FC procedures, based on scatter measurements, only allows the detection of the &ldquo, tip of the iceberg&rdquo, of all EVs. We applied an alternative FC approach based on the use of a trigger threshold on a fluorescence channel. The EV numbers obtained by the application of the fluorescence triggering resulted significantly higher in respect to them obtained from the same samples acquired by placing the threshold on the side scatter (SSC) channel. The analysis of EV concentrations carried out by three different standardized flow cytometers allowed us to achieve a high level of reproducibility (CV &lt, 20%). By applying the here-reported method highly reproducible results in terms of EV analysis and concentration measurements were obtained.