FACS-Based Assessment of Human Hematopoietic Stem and Progenitor Cells.

The existing heterogeneity of the human hematopoietic stem cell (HSC) compartment imposes significant challenges in understanding their physiology and molecular constitution. The hematopoietic system is hierarchically organized, with HSCs at the apex, responsible for maintaining homeostasis by ensuring a life-long supply of blood cells. HSCs are highly potent but rare, making their pure isolation challenging. To address this, flow-cytometry-based methods are commonly used to isolate HSCs, bridging the gap between surface marker expression and understanding their functional and molecular properties. However, detailed methodology papers providing practical guidance for the prospective isolation of distinct human hematopoietic stem and progenitor cell (HSPC) populations are rare, hindering reproducible applications across different research groups. Here, we present a comprehensive protocol for isolating multipotent long-term repopulating HSCs (LT-HSCs) and define multipotent progenitor populations (MPPs) from human mobilized peripheral blood (mPB) after leukapheresis using fluorescence-activated cell sorting (FACS). By highlighting the workflow, outlining critical considerations and emphasizing recent advancements in the field, we provide an extensive overview of FACS-based human HSC isolation. This facilitates the enrichment of these rare cells for downstream analysis and enables researchers to improve our understanding of the heterogeneity within the HSC compartment.