Ex vivo expansion of haematopoietic progenitors on an endothelialized hydroxyapatite matrix.

Autologous haematopoietic progenitor cell (HPC) transplantation is increasingly used to restore haematopoiesis after high-dose chemotherapy treatments. The present study was designed to analyse the ability of hydroxyapatite (HAP) seeded with endothelial cells (EC) to support the proliferation and differentiation of CD34+ HPC in static culture conditions. HAP is endothelializable as assessed by scanning electron microscopy and time-course DNA synthesis analysis using tritiated thymidine incorporated in EC isolated from human umbilical vein cord. Short-term coculture experiments in which CD34+ cells isolated from human cord blood were seeded on endothelialized HAP, were performed. Results show that endothelialized HAP is permissive to CD34+ cell expansion with a maximum expansion obtained between days 7 and 14 of coculture in the presence of IL-1 and IL-3 when compared with other experiments omitting either EC or interleukins. From morphological analyses, the expanded cell population mainly belonged to the myelocytic lineage with 33% mature cells (polymorphonuclear neutrophils and monocytes) at day 14 of coculture. The immature HPC could remain trapped within HAP while giving rise to a more mature progeny that exit from HAP microenvironment.