PROS1 and COVID-19: By using ExoTESTTM, a platform for exosome quantification and characterization (23–25), and commercial anti-SARS-CoV-2-S antibodies for the detection of the S protein, we found that the SARS-CoV-2-S protein or derived fragments were clearly present in exosomes of COVID-19 patients but not in those of HDs, as expected (Figure 1A).