Are fetal cells in maternal plasma really there? We think they are

Bovine foetal sex determination-Different DNA extraction and amplification approaches for efficient livestock production

Foetal sex determination using polymerase chain reaction (PCR) in mammals is based on the amplification of gender-specific foetal DNA sequences circulating in maternal blood. The bovine synepitheliochorial placenta does not allow a direct contact between the trophoblast and the maternal blood, resulting in difficult passage of foetal DNA and, consequently, its very small amounts in maternal bloodstream. Circulating cell-free foetal DNA (ccffDNA) encompasses short nucleotide fragments (300-600 bp) in maternal circulation. The aim of this study was to assess this non-invasive method in accurate prenatal sexing in early and late gestational periods in comparison with ultrasound diagnostics. As various DNA isolation and amplification methods were tested, their success in obtaining reliable results was evaluated. Two groups were tested, each consisting of 20 pregnant cows. Blood of a bull and a non-pregnant heifer was the controls. Extraction of foetal DNA was accomplished by three different methods: using tubes with silicone membranes, a single-tube extraction without silicone membranes and phenol-chloroform extraction. Following each extraction method, foetal DNA was amplified using PCR and real-time PCR with both bAML and TSPY primers in a separate reaction. Positive results were obtained only after amplification of foetal DNA extracted with a single-tube extraction kit. In comparison with ultrasound examination results and foetal gender recorded at birth, the sensitivity of the PCR test was 90% in Group I, but the technique failed to detect male foetuses in Group II. The real-time PCR test sensitivity in Group I was 90% and in Group II 91.6%.

Fetal Cell Based Prenatal Diagnosis: Perspectives on the Present and Future

The ability to capture and analyze fetal cells from maternal circulation or other sources during pregnancy has been a goal of prenatal diagnostics for over thirty years. The vision of replacing invasive prenatal diagnostic procedures with the prospect of having the entire fetal genome in hand non-invasively for chromosomal and molecular studies for both clinical and research use has brought many investigators and innovations into the effort. While the object of this desire, however, has remained elusive, the aspiration for this approach to non-invasive prenatal diagnosis remains and the inquiry has continued. With the advent of screening by cell-free DNA analysis, the standards for fetal cell based prenatal diagnostics have been sharpened. Relevant aspects of the history and the current status of investigations to meet the goal of having an accessible and reliable strategy for capturing and analyzing fetal cells during pregnancy are reviewed.

Direct quantification of fetal cells in maternal blood by real-time PCR

BACKGROUND

Fetal cells in maternal blood still present an enticing alternative for the development of a safe and efficacious non-invasive method for prenatal diagnosis. However, most enrichment methods are very tedious and have failed to realise this long sought after goal. We developed a simple, robust TaqMan real-time PCR assay to directly quantify male fetal cells in maternal blood using the multi-copy DYS14, without the need for any additional enrichment procedure.

METHODS

The sensitivity of the DYS14 assay was evaluated by using female genomic DNA spiked with male DNA or male cells. The specificity of the DYS14 assay was evaluated by examining 40 adult blood samples and 44 maternal blood samples from pregnant women with known fetal gender. Direct quantification of fetal cells in maternal blood was performed in 14 of the maternal blood samples by the DYS14 assay. The results were compared to those by SRY assay.

RESULTS

The sensitivity of DYS14 PCR assay was found to be higher than that of SRY assay for the detection of fetal cells. The number of fetal cells in maternal blood did not exceed 2/mL blood. The presence of cell-free fetal DNA in maternal blood could lead to erroneous quantification of fetal cell DNA. The number of fetal cells detected in blood cell pellets, which had been unwashed to remove the cell-free fetal DNA, was indeed significantly higher than those in extensively washed samples.

CONCLUSIONS

We quantified the fetal cells in maternal blood without fetal cell enrichment procedures by TaqMan real-time PCR for a multi-copy DYS14 locus. Our assay is sensitive and also suitable for automation, and may be a useful tool for the determination of fetal-maternal cell trafficking, such as microchimerism.

Cell-free fetal DNA in maternal blood: kinetics, source and structure

The kinetics and structure of cell-free fetal DNA in maternal plasma is currently under investigation. Plasma fetal DNA seems quite stable albeit cleared rapidly following birth, suggesting continuous fetal DNA release into the maternal circulation during pregnancy. However, to understand better the kinetics of circulating DNA, studies to determine the biological (structural) form in which fetal and maternal DNA exist and the mechanisms underlying variation in plasma are warranted to ensure quantitative diagnostic reliability. It is likely that circulating fetal DNA is released from fetal and/or placental cells undergoing apoptosis. Thus, the majority of fetal DNA is proposed to circulate in membrane-bound vesicles (apoptotic bodies). This review summarizes the latest reports in this field.