The dysregulated functional phenotype observed in patients who recovered from COVID-19 may be at least partially linked to the abnormal systemic cytokine levels characterizing a cytokine storm, since PBMCs isolated from healthy controls and exposed to recombinant IL-1β, IL-6, or IP-10 are subject to altered expression of LAG3 and 2B4, while antibody-mediated blockade of different cytokines — including IL-1β, IL-1RA, IL-6, IL-8, and IP-10 — promotes reversal of the COVID-19 serum–induced increase in exhaustion and costimulatory markers observed in both CD4+ and CD8+ T cells. Here, LAG3 is linked to COVID-19.