This was primarily characterized by increased expression of CXCR4, the chemokine receptor for CXCL12, and a resulting shift in the frequency of clusters from CXCR4lo naïve to CXCR4hi naïve in moderate, severe, and critical COVID-19 patients and then returned to CXCR4lo naïve in the follow-up samples (Fig. 2 B–D). This evidence concerns the gene CXCL12 and COVID-19.