Early-acting hematopoietic growth factors: biology and clinical experience

Gene expression profiles and cytokine environments determine the in vitro proliferation and expansion capacities of human hematopoietic stem and progenitor cells

OBJECTIVE

The interplay between intrinsic and extrinsic elements involved in the physiology of hematopoietic cells is not completely understood. In the present study, we analyzed the transcriptional profiles of human cord blood-derived hematopoietic stem cells (HSCs), as well as myeloid (MPCs) and erythroid (EPCs) progenitors, and assessed their proliferation and expansion kinetics in vitro.

METHODS

All cell populations were obtained by cell-sorting, and were cultured in liquid cultures supplemented with different cytokine combinations. Their gene expression profiles were determined by RNA microarrays right after cell-sorting, before culture.

RESULTS

HSCs showed the highest proliferation and expansion capacities in culture, and were found to be more closely related, in transcriptional terms, to MPCs than to EPCs. This correlated with the fact that after 30 days, only cultures initiated with HSCs and MPCs were sustained. Expression of cell cycle and cell division-related genes was enriched in EPCs. Such cells showed significantly higher proliferation than MPCs, however, their expansion potential was reduced, so that cultures initiated with EPCs declined after 15 days and became exhausted by day 30. Proliferation and expansion of HSCs and EPCs were higher in the presence of a cytokine combination that favors erythropoiesis, whereas the growth of MPCs was higher under a cytokine combination that favors myelopoiesis.

CONCLUSION

This study shows a correlation between the transcriptional profiles of HSCs, MPCs, and EPCs, and their respective in vitro growth under particular culture conditions. These results may be relevant in the development of ex vivo systems for the expansion of hematopoietic cells for clinical application.

Human cord blood hematopoietic cells acquire neural features when cultured in the presence of neurogenic cytokines

In vitro growth of hematopoietic cells depends on the presence of hematopoietic cytokines. To date, it is unclear if these cells would be able to respond to non-hematopoietic cytokines. In the present study, we have explored this by culturing human hematopoietic cells in presence of neurogenic cytokines. Lineage-negative (Lin^-) umbilical cord blood (UCB)-derived cells -enriched for hematopoietic stem and progenitor cells- were cultured in presence of different combinations of hematopoietic cytokines, neurotrophins, epidermal growth factor, fibroblast growth factor, and neurogenic culture media, in a 3-phase culture system. A proportion (1-22%) of Lin^- UCB hematopoietic cells normally express neural markers and are capable of responding to neural cytokines. Neural cytokines did not have effects on hematopoietic cell proliferation; however, we observed generation of neural-like cells, assessed by morphology, and a significant increase in the proportion of cells expressing neural markers. Such neural-like cells, however, retained expression of hematopoietic markers. It seems that under our culture conditions, no actual transdifferentiation of hematopoietic cells into neural cells occurred; instead, the cells generated in culture seem to be hematopoietic cells that acquired neural features upon contact with neurogenic factors. The identity of UCB cells that acquired a neural phenotype is still unclear.