NUCLEATED ERYTHROCYTES IN MATERNAL BLOOD - QUANTITY AND QUALITY OF FETAL CELLS IN ENRICHED POPULATIONS

The discovery of nucleated erythrocytes in maternal circulation provid es a potential source for non-invasive prenatal diagnosis. We have eva luated the use of a three-stage procedure to determine the number of c ells that are of fetal rather than maternal origin. First, monoclonal antibodies specific for CD45 and CD14 were used in conjunction with a magnetic (MACS) column to deplete unwanted leukocytes from maternal bl ood. This was followed by a positive MACS enrichment for nucleated ery throcytes, using an anti-CD71 (transferrin receptor) monoclonal antibo dy. To discriminate between fetal nucleated erythrocytes and those of maternal origin, enriched fractions were simultaneously stained with a n anti-fetal haemoglobin (HbF) antibody and hybridized with probes spe cific for X and Y chromosomes. Samples were then subjected to blind an alysis along with negative control samples from non-pregnant volunteer s. Using this dual analysis, we were able to determine that less than one nucleated erythrocyte per mi of maternal blood was of fetal origin . Small numbers of these fetal cells were found in 87.5% of pregnancie s, ranging from 6 to 35 weeks gestational age. Comparison of HbF and X /Y probe data also suggests that the fetal cells are less suitable for fluorescence in-situ hybridization (FISH) analysis than similar prepa rations from other sources.