Effects of a humanized ectopic niche (human ossicle or hOss) on human hematopoiesis

Human hematopoiesis takes place in the bone marrow (BM) where a multitude of interactions regulate differentiation and preservation of hematopoietic stem/progenitor cells (HSPC). Well-studied in mouse models, human BM microenvironment still contain unexplored features. Development of immune-deficient mouse models have considerably improved our knowledge of the molecular and cellular regulation of human HSPC, but remain limited by the numerous non-cross-reactive signals provided by the mouse BM to human HSPC. Here, we thoroughly characterized a humanized BM model, based on Mesenchymal stromal cells (MSC) and called human ossicles (hOss), and the different hematopoietic cell compartments generated 3 months post-transplant of human CD34+ cells using scRNA sequencing. Human CD34+ HSPCs from a cord blood source were injected intravenously into NSG mice. Mice were either hOss-bearing or hOss-free. Three months after HSPC injection, mice were sacrificed and mononuclear cells (MNC) that had engrafted into hOss and murine BM were pooled for each condition. In total, we had 1 sample of murine BM (mBM W/o hOss, and 2 samples of pooled ossicles (F/hOss and P-N/hOss). To enrich samples in CD34+ fraction, immunomagnetic sorting was performed. The CD34+ cell fraction was then used to prepare scRNA-seq libraries. F hOss: hematopoietic stem cells (HSC) derived from organoids of fetal origin P-N hOss: hematopoietic stem cells (HSC) derived from organoids of postnatal origin