Haematotoxicity testing in vitro using human cord blood haemopoietic cells

Exposure to benzene and lead results in human and experimental animals in myelotoxicity. Haemopoietic progenitor cells are considered the target cells for these effects. Currently, experimental animals are in widespread use to predict haematotoxicity. In vitro techniques allow use of human cells. This will highly improve the predictive power of myelotoxicity testing compared with experiments on syngeneic animals (mainly rat and mouse). Furthermore the number of animals required for product development and approval will be reduced. In vitro assays for studying haemopoietic progenitor cells are well developed. We examined the effect of two benzene metabolites and lead nitrate on the in vitro growth potential of human haemopoietic progenitor cells derived from human cord blood. The effects of lead nitrate and benzene metabolites such as catechol and hydroquinone on colony formation of cord blood haemopoietic progenitors were investigated in semi-solid (agar) assays (CFU-GM = Colony Forming Unit of granulocytes and/or macrophages). Toxic agents were added as single agents at the start of the cultures. Cells were exposed during the 14-day culture period. The in vitro exposure of the haemopoietic cells resulted in a dose-dependent depression of the CFU-GM numbers. The dose that caused a 50% decrease in colony formation (IC(50)) was 5 mum for catechol and 20 mum for hydroquinone. An interindividual variability was seen in the response to Pb exposure. In some cord blood samples Pb inhibited colony growth only at higher doses (IC(50) > 100 mum). In a large number of samples, haemopoietic cells were affected at much lower concentrations of Pb exposure (IC(50) < 10 mum). Effects in vitro are seen at concentration levels that are found in human blood in situ.