library_construction_protocol: To identify HSC, fresh BM samples were enriched over Lymphoprep™ (Ficoll with a density of 1.077 g/l). Cells of the mononuclear layer were collected and washed once with sample medium (phosphate-buffered saline supplemented with 2 mM EDTA and 2% serum). Cells were stained for 1 h on ice using the fluorescence-conjugated antibodies, CD34-FITC, CD38-ReCy7, CD90-PrcpCy5.5, and CD45RA-APC, and biotinylated lineage-antibodies, including anti-hCD3, hCD19, Mac1, and Ter119. After washing, DAPI and streptavidin, Pacific Blue™ conjugate were added, and HSC were sorted by FACS by immunophenotype Lin-CD34+, CD38-, CD90+, CD45RA-, CD49f. The population of HSC was then re-sorted as single cells into a 384-plate, using the same HSC gates. Each well of the plate contained Smart-Seq2 lysis-and-storage buffer. We estimated the FACS drop volume at roughly 0.001 µl (using a 70-µm nozzle). Plates were frozen to -80°C. Processing of samples, library preparation, and sequencing were carried out at the INCPM facility (Rehovot, Israel). Sequencing of 1,150 cells was performed according to the Smart-seq2 protocol.