Using single-cell transcriptomics, a study by Kalfaoglu et al. [12] demonstrated that CD4+ T cells from severe COVID-19 patients differentially expressed activation-induced genes, such as a higher expression of JUN and MKI67 as compared to CD4+ T cells from moderate COVID-19 patients, indicative of a substantially high immune activation status in severe COVID-19 patients. The gene discussed is JUN; the disease is COVID-19.