Ex vivo expansion of human umbilical cord blood does not lead to co-expansion of contaminating maternal mononuclear cells

Abstract

One of the main limiting factors for increased use of human umbilical cord blood (UCB) in adult allogeneic transplantation is the small number of progenitor cells that can be collected and infused. Ex vivo expansion of UCB might help to overcome this limitation. Whether an expansion of UCB cells will also lead to co-expansion of contaminating maternal cells, and thus may alter graft characteristics and lead to an increased incidence of GVHD, has not been looked at so far. We initiated cultures with UCB mononuclear cells (MNC) in a standard medium containing stem cell factor (SCF), flt-3L, Il-3, IL-6, EPO and G-CSF. To address the question of contaminating maternal cells we performed interphase FISH analysis of the X and Y chromosome simultaneously. Male (XY) cord blood samples were investigated for maternal (XX) cells at day 0 and at several time points during culture. We could not detect maternal cells in any of the nine samples studied when cultures were started at day 0. Culturing did not expand previously undetected maternal cells into a range that could be seen with FISH technology, as all samples remained negative for maternal cells throughout culture periods of 14 days. We then artificially contaminated male UCB with maternal mononuclear cells at concentrations of 5 and 15% at day 0. After 14 days, maternal MNC were still detectable, but the percentage was reduced to 1.7% and 6%, respectively. During culturing of CD34⁺-selected UCB the content of maternal cells also declined from a mean of 1.6% after contamination to 0.4% on day 7. Taken together we could show that maternal cells co-cultured with UCB do not co-expand and thus do not interfere with ex vivo expansion of UCB for adult allogeneic transplantation.