A niche in a dish: pericytes support HSC.

摘要

Cord bfood is an easily accessible source of HSCs for transplantations. However, the absolute number of HSCs per cord blood unit is generally too low to ensure rapid engraftment and immune reconstitution in adults after transplantation. The ability to expand cord blood ex vivo in a bioreactor would overcome this limitation; however, to date, this has proven difficult to achieve. The main reason for the difficulty? Once isolated from supportive niches in the bone marrow, HSC proliferation is accompanied by rapid differentiation into lineage-committed progenitors that have lost their long-term self-renewal potential and ability to regenerate the whole hematopoietic system after transplantation. Therefore, ex vivo expansion of genuine long-term reconstituting HSCs requires the prior identification of the missing factors from the niche, which is much harder than it sounds because (1) the bone marrow is encased in a hard, mineralized bone and is, consequently, not easy to access and process for cellular and molecular studies and (2) there is a lack of molecular markers for HSC-supportive niche cells.