We found that plasma exosomes from COVID-19 patients upon hospital admission significantly increased expression of IL-6, IL-8, and TNF-α in PBMCs gated for CD3+ lymphocytes, CD4+ T cells, CD8+ T cells, or CD14+ monocytes compared with plasma exosomes from the same patients later in their hospitalization or those from non-COVID donors (Fig. 2a,b, Supplementary Fig S2a). Here, CD8A is linked to COVID-19.