Enrichment of foetal cells from the blood of pregnant women by fluorescence activated cell sorting
Consensus is that foetal cell recovery could be instrumental in detecting foetal aneuploidy and selected Mendelian disorders and traits. There have been many attempts to develop a reliable method for foetal cell isolation from maternal blood samples. The general lack of success is due, to a large extent, to the low frequency of foetal cells in maternal blood; the most common estimates being in the order of one foetal cell per milliliter of maternal blood. The candidate foetal cells available for subsequent enrichment and diagnostic purposes are: trophoblasts, lymphocyctes and granulocytes, and nucleated red blood cells. All of the previously published studies attempting foetal cell enrichment have targeted a specific cell type. We have developed a technique for the enrichment of foetal cells by fluorescence activated cell sorting, based upon monoclonal antibody labeling of polymorphic cell surface markers, in particular the HLA group of surface antigens. The method relies upon the fact that the foetus inherits one, but not both alleles of these polymorphic antigens from the mother and is more effective due to its ability to capture all foetal cell types. The enrichment procedure is one of negative selection and does not rely upon knowledge of the paternal HLA type. Using this approach we have been able to achieve an enrichment of approximately 10,000 - fold, to one male cell per 50,000 female cells, which is not quite sufficient for reliable aneuploidy detection. However, automated scanning microscopy of XY-FISH labels confirmed the presence of male cells in approximately 50% of samples. Blood samples were obtained from patients at weeks 8-10 of pregnancy. Current efforts are aimed at reducing maternal cell contamination and maximizing foetal cell recovery.