Haematopoietic stem cells (HS cells) are the body's blood bank, giving rise to all types of blood cell including leukocytes and erythrocytes. Each time an HS cell produces a mature blood cell, it also produces a replica of itself, which continues to function as an "immortal" inexhaustible stem cell. This way, our supply of HS cells - a rare cell population lodging mainly in the adult bone marrow - is never used up.

These qualities make HS cells important clinical targets: bone marrow transplants - which help to restore the blood system of patients treated with chemo- and irradiation therapy - depend on the HS cells contained in transplants. But the availability of suitable donors for bone marrow transplantations is limited - leading researchers to look for ways to generate HS cells in the lab.

This is something my lab has been working on for some time.  We are particularly interested in the AGM region in the developing embryo - an area surrounding the embryonic dorsal aorta where HS cells first emerge (Medvinsky and Dzierzak 1996), and which can generate HS cells when cultured as a whole organ. Scientists have been trying to establish which mechanisms the AGM region uses to generate HS cells, but until recently lacked an efficient system to investigate this.

Last month, we published a new method to expand and track HS cells (Taoudi et al. 2008). The culture conditions we developed yielded a dramatic enhancement of HS cell generation.  We also found that re-aggregation of the AGM region after cell dissociation restores the capacity of the AGM region to generate HS cells in culture. The combination of these two approaches provided access to individual cell populations in the AGM region, and made it possible to perform efficient analysis.

An important implication for this development is that exogenous cells can be integrated into this culture and their potential to generate HS cells under the influence of the inductive AGM microenvironment explored. Interestingly, another paper in the same issue of Cell Stem Cell showed that haematopoietic production was significantly induced by co-culture with the AGM region (Ledran et al. 2008). The future will show whether these approaches will lead to development of new clinically relevant protocols for generating HS cells in culture.