Stanford University scientists have identified a single marker that is only expressed in hematopoietic stem cells of the bone marrow.
Grounded in over a half of a century of research, the study of hematopoietic stem cells (HSCs) is one of the most exciting and rapidly advancing fields in medicine today. HSCs have great potential because of two cardinal properties: multipotency, defined as the ability to differentiate into all blood cell lineages, and long-term self-renewal, defined by the inexhaustible ability to produce daughter cells functionally identical to the parent upon cell division. Thus, HSC transplants have been routinely used to treat patients with malignant and non-malignant disorders of the blood and immune system.
In order to generate an inexhaustible source of cells for use in regenerative medicine, methods for identification and isolation of blood stem cells are necessary. Current strategies rely on multi-parameter flow cytometric isolation of cells based on expression of specific cell-surface markers. Although considerable progress has been made in identification of HSC markers, markers that distinguish the most primitive blood stem cell from other hematopoietic progenitor populations have yet to be discovered.
Recently, researchers at Stanford University reported the discovery of a marker that distinguishes between short-term and long-term HSCs . Since the bone marrow is one of the primary sources of HSCs, the authors compared microarray gene expression assays among various populations in mouse bone marrow. Starting with a list of over 100 genes, they eliminated genes expressed in non-hematopoietic populations, thereby narrowing down to 45 candidate genes. From these, three genes were highly expressed in HSC populations. Only one gene was completely off in some cells and on in others: homeobox B5(Hoxb5).
To confirm that Hoxb5 was only expressed in long-term HSCs and not in short-term HSCs, they engrafted Hoxb5+ HSCs into lethally irradiated mouse recipients and examined reconstitution of all blood cell types. Indeed, Hoxb5+ HSCs exhibited long-term reconstitution capacity in primary and secondary recipients. In addition, imaging studies revealed that Hoxb5+ HSCs reside in the perivascular space of the bone marrow. Further studies on this HSC niche may provide more insights on how to culture long-term HSCs outside of the body, which is a current limitation in the field of regenerative medicine.
HemaCare is excited to contribute to stem cell research by providing various high-quality cell products derived from bone marrow, including CD34+ cells. For more information or to place an order, call (877) 397-3087.
 Chen, J. Y. et al. Hoxb5 marks long-term haematopoietic stem cells and reveals a homogenous perivascular niche. Nature 530, 223-227, doi:10.1038/nature16943 (2016).