Fig. 1. Study design summary.

Blood samples were collected from healthy controls and from severely ill patients with COVID-19 at the time of hospitalization (d0) and at follow-ups (days 5 and 15) during their stay in the critical care unit. PBMCs were isolated from the blood and captured for single-cell RNA sequencing (scRNA-seq). CD14⁺ monocytes were also enriched from PBMCs for epigenetic analyses: chromatin accessibility by assay for transposase-accessible chromatin sequencing (ATAC-seq) and DNA methylation by whole-genome bisulfite sequencing (WGBS).