In a cohort study of severe COVID-19 patients (n = 9) it was shown that their BAL contained a clonal expansion of a sub-population of memory Th17 cells that increase the secretion of several pro-inflammatory mediators, such as IL-17A and granulocyte–macrophage colony-stimulating factor (GM-CSF) [121]. The gene discussed is IL17A; the disease is COVID-19.