Resumen de Expansion and differentiation of human hematopoietic stem cells: role of niche components
Hematopoietic stem cells (HSCs) that reside in the bone marrow (BM) are cells that can self-renew and give rise to proliferative progenitors that differentiate into the various blood lineages. A variety of signals from the bone marrow microenvironment guarantee preservation of the hallmarks of hematopoietic stem cells. Notch signaling is thought to play a role in the BM niche by maintaining HSC without inducing differentiation. So manipulating that pathway constitutes a useful tool to expand HSCs for transplantation as a final objective. Working with human cord blood (CB) progenitors, we have demonstrated that Notch signal DL1, may contribute to preserve the multilineage condition of the CD34+CD38-CD45RA-CD90+ population hematopoietic progenitors, in part by retaining T cell potential. This immature phenotype constitutes the fingerprint of Notch activation in human hematopoiesis. We have also shown that Notch pathway exerts regulatory effects on expansion properties of CD90/CD45RA subsets: allowing selectively CD34+CD38-CD45RA-CD90+ expansion in vitro, favouring self-renewal divisions and blocking selectively differentiation of CD45RA- cells into CD45RA+ subsets.
Different approaches can be used to expand hematopoietic progenitors.The number of CD34+CD38-CD45RA-CD90+ obtained at the end of co-cultures (both in OP9 or OP9-DL1) conditions was not very high. Thus, In the second part of our project after defining systems properties, we tried to expand that CD34+CD38-CD45RA-CD90+ subset, by adding proteins previously reported to regulate homeostasis in different hematopoietic compartments. Galectin1 has been reported as a stimulator for committed hematopoietic progenitor cell growth both in mice and humans. IFN¿ that has been proposed to promote the exit of HSCs out of the dormant stage. Although we were not able to improve significantly absolute numbers of CD34+CD38-CD45RA-CD90+ at the end of the co-culture whit neither GAL1 nor IFN¿, we have defined a biological effect of IFN¿ on homeostasis of CD45RA/CD90 CB hematopoietic progenitors accelerating its differentiation.
CB is not the only source of hematopoietic cells useful for stem cell transplantantion. Progenitor cells mobilized into the circulation by cytokine exposure or by chemotherapy are also a highly accessible resource for transplantation. Given the characteristics of the CD34+CD38-CD45RA-CD90+ CB population, we began to study the properties of the same in mobilised peripheral blood progenitor cells (PBPC). Previously, functional studies with PBPC has been shown to be enriched for clonogenic cells and for LTC-IC but there is both clinical and experimental evidences that long term reconstitution in CB has been more successful than in PBPC patients transplanted. We have observed a lower proportion of CD34+CD38-CD45RA-CD90+ population phenotype in frozen PBPC compared with the same population in CB. In addition, we have tested their capacity to give rise to all mature blood lineages in vitro. That PBPC population is able to differentiate to myeloid cells, as wells as Natural Killer cells and B cells, but surprisingly these progenitor cells failed to generate T cells in OP9-DL1 systems (compare with frozen CB control). A different initial protein profile was observed related to CD7 between the two sources of hematopoietic progenitors. Phenotypical and functional differences between the two sources of progentiors tested, could be responsible of experimental and clinical differences observed related to quantity and long term capability of progenitor cells pertaining to both sources. These differences could be a consequence of disctint niches in vitro.
