library_construction_protocol: Peripheral blood mononuclear cells (PBMC) of different donors were isolated by the standard density-gradient centrifugation and cryopreserved until the day of use.  The CD19+ cell fraction was enriched from PBMCs by positive selection with CD19 magnetic microbeads (Miltenyi Biotech) and subsequently stained on ice for 20 min with the following fluorochrome-labeled mouse monoclonal antibodies: CD20 (clone 2H7, BioLegend) and APC mouse anti-human IgG (Clone: G18-145 BD Pharmingen). Cells were sorted to over 99% purity on a FACSAria III (BD). FACS-sorted cells were collected in 6 μl FCS in Eppendorf tubes that were pre-coated overnight with 2% BSA. Single-cell suspensions with 1 × 105 cells/mL in PBS were prepared. Then, the suspensions were loaded onto microfluidic devices, and scRNA-seq libraries were constructed according to the Singleron GEXSCOPE protocol in the GEXSCOPE Single-Cell RNA Library Kit (Singleron Biotechnologies) (Dura B. et al. scFTD-seq: freeze-thaw lysis based, portable approach toward highly distributed single-cell 3′ mRNA profiling. Nucleic Acids Res. 2019).  Individual libraries were diluted to 4 nM and pooled for sequencing. Pools were sequenced on an Illumina HiSeq X with 150 bp paired-end reads