Ex vivo expansion of enriched CD34⁺ cells from neonatal blood in the presence of thrombopoietin, a comparison with cord blood and bone marrow

Abstract

Neonatal blood (NB) contains substantial numbers of stem and progenitor cells which decline rapidly after birth. Using a combination of cord blood (CB) and NB, we performed a successful, sibling transplant for a thalassaemia patient, leading to the proposal that NB could be used as an adjunct to CB for transplantation. This study was aimed at addressing the feasibility of expanding NB and thus minimizing the volume needed from a NB collection. In the presence of early acting cytokines interleukin-1β (IL-1β), IL-3, IL-6, stem cell factor (SCF), flt-3 ligand with and without thrombopoietin (Tpo), we compared the expansion capacity of CD34⁺ enriched cells from CB, NB and bone marrow (BM). Flow cytometry and colony-forming unit (CFU) analyses show that Tpo significantly increased the expansion of CD34⁺ cells from CB and NB to early and committed progenitors. No significant difference was observed between the expansion of CB and NB at 7, 14 or 21 days of culture in terms of CFU, CD34⁺ and CD61⁺ cell subsets. The expansion capacity of BM was significantly lower than that of NB or CB, possibly related to the low proportion of CD34⁺CD38⁻ cells observed at day 0. There was a relatively rapid expansion of NB which was evident at day 7 whilst the expansion of CB and BM remained low, suggesting a speedy maturation process in the postnatal infant. The expanded cells, being heterogeneous in their morphology and cell surface marker expression, were mostly of the myeloid lineage (CD45⁺, CD33⁺ and HLA-DR⁺). Our results showed that the expansion capacity of NB is comparable to that of CB and if transplanted, the expanded products of NB might contribute to the engraftment kinetics of the neutrophil and megakaryocyte lineage.