The tetraspanin CD9 affords high-purity capture of all murine hematopoietic stem cells.

Prospective isolation is critical for understanding the cellular and molecular aspects of stem cell heterogeneity. Here, we identify the cell surface antigen CD9 as a positive marker that provides a simple alternative for hematopoietic stem cell isolation at high purity. Crucially, CD9 affords the capture of all hematopoietic stem cells in murine bone marrow in the absence of contaminating populations that lack authentic stem cell function. Using CD9 as a tool to subdivide hematopoietic stem-cell-containing populations, we provide evidence for heterogeneity at the cellular, functional, and molecular levels.