library_construction_protocol: Peripheral blood mononuclear cells (PBMC) were isolated according to manufacturer's protocol and stored in liquid nitrogen. For single-cell RNA sequencing (scRNA-seq) analyses, PBMCs from healthy donors (n = 3) were stained by fluorescence-activated cell sorting (FACS) using fluorochrome-labeled monoclonal anti-human antibodies (Table S8). Viable CD19+ B cells were sorted using the FACSAriaTM Fusion cell sorter (BD Biosciences) in 5 ml pure fetal calf serum (FCS). Cells were washed and resuspended in RPMI with 10% FCS, to continue single-cell processing. Single-cell samples were loaded on a 10xGenomics Next GEM K chip to aim for a final recovery of 10000 cells. Final 5' gene expression (5' GEX) libraries, were generated according to the Chromium Next GEM Single cell 5' kit (v2 chemistry, dual index) User Guide (CG000330, 10x Genomics). Libraries were sequenced on a NovaSeq 6000 platform (Illumina), paired-end mode with a 28-10-10-90 cycle setting, with a sequencing depth of around 25000 reads/cell.