CXCR4 and COVID-19: Immature myeloid subsets and bronchoalveolar cells of critically-ill COVID-19 patients have been found to express HIF1alpha, a critical regulator of the differentiation and function of MDSCs, and transcriptional targets related to inflammation (CXCL8, CXCR1, CXCR2, and CXCR4); virus sensing, (TLRs); and metabolism (SLC2A3, PFKFB3, PGK1, GAPDH and SOD2) (64).