The CD34(+)CD38(neg) population is significantly increased in haemopoietic cell expansion cultures in serum-free compared to serum-replete conditions: dissociation of phenotype and function.

Expansion of haemopoietic stem cells is proposed to combat graft failure in adult recipients following cord blood (CB) transplantation. Cultures are traditionally performed in medium containing FCS, but to transfer expansion to the clinic, 'good manufacturing practice' (GMP) standards are required. This study evaluated expansion cultures in culture bags and serum-free (SF) conditions, to comply with GMP, by analysing sub-populations of CD34(+) cells, colony-forming cells (CFC) and long-term culture initiating cells (LTC-IC). CD34(+)cell analysis has previously been used to measure clonogenic capacity and the CD34(+)CD38(neg) surface phenotype to measure primitive cell numbers. In this study, comparison of expansion in serum-replete medium with that in SF conditions demonstrated a lack of expression of CD38 on CD34(+) cells in the absence of serum. These findings must be considered in clinical studies using in vitro expansion in SF conditions, and the CD34(+)CD38(neg) phenotype should not be used to confirm maintenance, or expansion, of primitive progenitor cells.