XCR1 and respiratory failure: Finally, the Solute Carrier Family 6 Member 20 (SLC6A20), Leucine zipper transcription factor like 1 (LZTFL1), C-C chemokine receptor type 9 (CCR9), FYVE and Coiled-Coil Domain Autophagy Adaptor 1 (FYCO1), C-X-C Motif Chemokine Receptor 6 (CXCR6), and X-C Motif Chemokine Receptor 1 (XCR1) are genes highly expressed in human lung cells, and polymorphisms have been related to the increased risk of respiratory failure and ARDS in severe COVID-19 cases [53,54] (Table 1).