Culturing human umbilical cord blood: a comparison of mononuclear vs CD34+ selected cells

We compared UCB mononuclear cells (MNC) with CD34+ selected cells in a serum-free static culture system. Cell number proliferation of MNCs was inferior to CD34+ selected cells. MNCs, however, showed a substantial increase from 0.94% CD34+ cells on day 0 to 5.8% on day 7, whereas in the CD34+ selected samples the CD34+ cell content declined continously from 62.2% on day 0 to 27.7% on day 7. The number of CFU-GM increased during culture of both cell fractions. Here, only the MNCs showed a substantial increase in clonogenicity on day 7 and day 14 to 11.1- and 4.1-fold input, respectively. This expansion of the CD34+ progenitor cell pool in the MNCs fraction was at least in part attributable to T cells, since the physical abrogation of T cells blocked this effect. Refeeding and reseeding of cells on day 7 had stimulating effects especially on the CD34+ cells, where cell number proliferation increased from 16.3-fold without to 58.1-fold on day 14. Also, we could find sporadic chromosomal aberrations in four of 100 metaphases examined after 7-20 days of ex vivo expansion. The significance of this observation needs to be clarified in a larger series.