In support of these results, concerning DDC, further analysis of the single cell gene expression data (RNA-sequencing) of Chua et al., derived from nasopharyngeal swabs of COVID-19 patients (available in Magellan COVID-19 Omics Explorer, https://digital.bihealth.org (accessed on 25 August 2022)), revealed that DDC is almost exclusively expressed in epithelial cells (secretory, ciliated and FOXN4) and not in immune cell populations [21]. This evidence concerns the gene FOXN4 and COVID-19.