Patients with severe COVID-19 had increased serum levels of CXCR9 and CXCR10, which, along with the elevated count of both cellular (“unclassified” monocytes, CD38+HLA-DR+ T-cells and granzyme-B+/perforin+ T-cells) and serum (CXCL8, IL-6 and IL-10 levels) cues, allowed us to differentiate mild from severe disease [82]. The gene discussed is PRF1; the disease is COVID-19.