Apoptosis in fetal nucleated erythrocytes circulating in maternal blood

Case Report: Challenges of Non-Invasive Prenatal Testing (NIPT): A Case Report of Confined Placental Mosaicism and Clinical Considerations

Since the introduction of cell-free (cf) DNA analysis, Non-Invasive Prenatal Testing (NIPT) underwent a deep revolution. Pregnancies at high risk for common fetal aneuploidies can now be easily identified through the analysis of chromosome-derived components found in maternal circulation, with the highest sensitivity and specificity currently available. Consequently, the last decade has witnessed a widespread growth in cfDNA-based NIPT use, enough to be often considered an alternative method to other screening modalities. Nevertheless, the use of NIPT in clinical practice is still not devoid of discordant results. Hereby, we report a case of confined placental mosaicism (CPM) in which a NIPT false-positive result for trisomy 13 required not only amniocentesis but also cordocentesis, to rule out the fetal aneuploidy, with the additional support of molecular cytogenetics on placental DNA at delivery. Relevant aspects allowing for precision genetic diagnosis and counselling, including the number of analysed metaphases on the different fetal cells compartments and a repeated multidisciplinary evaluation, are discussed.

Isolation and characterization of fetal nucleated red blood cells from maternal blood as a target for single cell sequencing-based non-invasive genetic testing

PURPOSE

Although non-invasive prenatal testing (NIPT) based on cell-free DNA (cfDNA) in maternal plasma has been prevailing worldwide, low levels of fetal DNA fraction may lead to false-negative results. Since fetal cells in maternal blood provide a pure source of fetal genomic DNA, we aimed to establish a workflow to isolate and sequence fetal nucleated red blood cells (fNRBCs) individually as a target for NIPT.

METHODS

Using male-bearing pregnancy cases, we isolated fNRBCs individually from maternal blood by FACS, and obtained their genomic sequence data through PCR screening with a Y-chromosome marker and whole-genome amplification (WGA)-based whole-genome sequencing.

RESULTS

The PCR and WGA efficiencies of fNRBC candidates were consistently lower than those of control cells. Sequencing data analyses revealed that although the majority of the fNRBC candidates were confirmed to be of fetal origin, many of the WGA-based genomic libraries from fNRBCs were considered to have been amplified from a portion of genomic DNA.

CONCLUSIONS

We established a workflow to isolate and sequence fNRBCs individually. However, our results demonstrated that, to make cell-based NIPT targeting fNRBCs feasible, cell isolation procedures need to be further refined such that the nuclei of fNRBCs are kept intact.

Fetomaternal microchimerism and genetic diagnosis: On the origins of fetal cells and cell-free fetal DNA in the pregnant woman

During pregnancy several types of fetal cells and fetal stem cells, including pregnancy-associated progenitor cells (PAPCs), traffic into the maternal circulation. Whereas they also migrate to various maternal organs and adopt the phenotype of the target tissues to contribute to regenerative processes, fetal cells also play a role in the pathogenesis of maternal diseases. In addition, cell-free fetal DNA (cffDNA) is detectable in the plasma of pregnant women. Together they constitute the well-known phenomenon of fetomaternal microchimerism, which inspired the concept of non-invasive prenatal testing (NIPT) using maternal blood. An in-depth knowledge concerning the origins of these fetal cells and cffDNA allows a more comprehensive understanding of the biological relevance of fetomaternal microchimerism and has implications for the ongoing expansion of resultant clinical applications.

Direct Assessment of Single-Cell DNA Using Crudely Purified Live Cells: A Proof of Concept for Noninvasive Prenatal Definitive Diagnosis

Noninvasive testing techniques are often used for fetal diagnosis of genetic abnormalities but are limited by certain characteristics, including noninformative results. Thus, novel methods of noninvasive definitive diagnosis of fetal genetic abnormalities are needed. The aim of this study was to develop a single-cell DNA analysis method with high sensitivity and specificity that enables direct extraction of genetic information from live fetal cells in a crude mixture for simultaneous evaluation. Genomic DNA from circulating fetal CD45^-CD14^- cells, an extremely rare cell type, extracted from 10-mL samples of maternal peripheral blood, was extracted using a single-cell-based droplet digital (sc-dd) PCR system with a modified amount of polymerase. A hexachloro-6-carboxyfluorescein-labeled RPP30 probe was used as an internal control and a 6-carboxyfluorescein-labeled SRY probe as a target. The results indicated that no droplets generated with samples from pregnant women carrying female fetuses were positive for both probe signals, whereas droplets prepared with samples from pregnant women carrying male fetuses were positive for both probe signals. The latter was considered a direct assessment of genetic information from single circulating male fetal cells. Thus, the modified sc-ddPCR system allows the detection of genetic information from rare target cells in a crudely purified cell population. This research also serves as a proof of concept for noninvasive prenatal definitive diagnosis.

The Level of Free Fetal DNA as Precise Noninvasive Marker for Chromosomal Aneuploidies: First Results from BALTIC Region

Background and objectives: Noninvasive prenatal testing (NIPT), which has been introduced clinically since 2011, uses the circulating cell-free fetal DNA in the maternal blood to evaluate the risk of a chromosomal anomaly. The aim of this study was to examine the effectiveness of NIPT using a single nucleotide polymorphism method. Materials and Methods: A retrospective study was conducted between 2013 and 2019. The Natera Panorama test was used to analyze the risk of trisomies 21, 18, 13, X monosomy, trisomy, and other sex chromosome abnormalities. A positive result of NIPT for aneuploidy was confirmed by invasive testing. Results: 850 women with a singleton pregnancy participated in the study. The median fetal fraction was 9.0%. The fetal fraction was lower in the no-call group (3.1%) compared with the group that received a call (9.1%) (p < 0.001). A positive correlation was determined between the gestational age and the fetal fraction (r = 0.180, p < 0.001). The overall positive predictive value (PPV) of NIPT for trisomy 21 (n = 9), trisomy 18 (n = 3) and XYY syndrome (n = 1) was 100%. Conclusions: The results of present study showed 100% PPV effectiveness of NIPT Panorama test detecting trisomies of 21 and 18 chromosomes, as well as XYY syndrome in the studied cohort. Therefore, NIPT due to its high PPV, significantly reduces the need for invasive testing, thereby reducing the risk of miscarriage and stillbirth.

Discordant fetal sex on NIPT and ultrasound

Prenatal diagnosis of sex discordance is a relatively new phenomenon. Prior to cell-free DNA testing, the diagnosis of a disorder of sexual differentiation was serendipitous, either through identification of ambiguous genitalia at the midtrimester morphology ultrasound or discovery of genotype-phenotype discordance in cases where preimplantation genetic diagnosis or invasive prenatal testing had occurred. The widespread integration of cfDNA testing into modern antenatal screening has made sex chromosome assessment possible from 10 weeks of gestation, and discordant fetal sex is now more commonly diagnosed prenatally, with a prevalence of approximately 1 in 1500-2000 pregnancies. Early detection of phenotype-genotype sex discordance is important as it may indicate an underlying genetic, chromosomal or biochemical condition and it also allows for time-critical postnatal treatment. The aim of this article is to review cfDNA and ultrasound diagnosis of fetal sex, identify possible causes of phenotype-genotype discordance and provide a systematic approach for clinicians when counseling and managing couples in this circumstance.

Comparison between paramagnetic and CD71 magnetic activated cell sorting of fetal nucleated red blood cells from the maternal blood

Background

Fetal nucleated red blood cells (NRBC) from maternal circulation are rare events but can be enriched and used to evaluate the genetics of the fetus. We compared two simplified selection methods of the fetal cells from the maternal blood.

Methods

We isolated fetal cells from maternal blood through double‐density gradient centrifugation followed either by magnetic cell selection, based on the paramagnetic proprieties of the NRBC hemoglobin, converted to methemoglobin, or by a positive magnetic‐activated cell sorting (MACS) enrichment, using anti‐CD71 monoclonal antibodies. Finally, the cells were identified through fluorescence in situ hybridization (FISH) with specific chromosome X and Y probes.

Results

We processed 10 mL of peripheral blood samples from 27 pregnant women with singleton normal male fetuses. Hemoglobin‐based enrichment isolated significantly more NRBCs: 29.7 × 10⁴ cells than anti‐CD71 MACS: 10.1 × 10⁴ cells (P < .001). The FISH analysis found at least one XY cell in 81.5% and 61.5% of cases, respectively, for paramagnetic and anti‐CD71 selection. Also, the average number of XY cells identified through paramagnetic selection was 5.09 ± 2.5, significantly higher than those observed through CD71 sorting: 3.38 ± 1.7 cells (average ± SE) (P = .03).

Conclusion

The combination of density gradient centrifugation with paramagnetic selection has the advantage of simplicity and achieves a minimal manipulation and treatment of cells. It yields an increased number of NRBCs and FISH confirmed fetal cells, compared to the anti‐CD71 sorting.

Cell-Free Fetal DNA Increases Prior to Labor at Term and in a Subset of Preterm Births

Cell-free fetal DNA in the maternal circulation has been associated with the onset of labor at term. Moreover, clinical studies have suggested that cell-free fetal DNA has value to predict pregnancy complications such as spontaneous preterm labor leading to preterm birth. However, a mechanistic link between cell-free fetal DNA and preterm labor and birth has not been established. Herein, using an allogeneic mouse model in which a paternal green fluorescent protein (GFP) can be tracked in the fetuses, we established that cell-free fetal DNA (Egfp) concentrations were higher in late gestation compared to mid-pregnancy and were maintained at increased levels during the onset of labor at term, followed by a rapid decrease after birth. A positive correlation between cell-free fetal DNA concentrations and the number of GFP-positive pups was also observed. The increase in cell-free fetal DNA concentrations prior to labor at term was not linked to a surge in any specific cytokine/chemokine; yet, specific chemokines (i.e., CCL2, CCL7, and CXCL2) increased as gestation progressed and maintained elevated levels in the postpartum period. In addition, cell-free fetal DNA concentrations increased prior to systemic inflammation-induced preterm birth, which was associated with a strong cytokine response in the maternal circulation. However, cell-free fetal DNA concentrations were not increased prior to intra-amniotic inflammation-induced preterm birth, but in this model, a mild inflammatory response was observed in the maternal circulation. Collectively, these findings suggest that an elevation in cell-free fetal DNA concentrations in the maternal circulation precedes the physiological process of labor at term and the pathological process of preterm labor linked with systemic inflammation, but not that associated with intra-amniotic inflammation.

Non-invasive Prenatal Testing Using Fetal DNA

Non-invasive prenatal diagnosis (NIPD) is based on fetal DNA analysis starting from a simple peripheral blood sample, thus avoiding risks associated with conventional invasive techniques. During pregnancy, the fetal DNA increases to approximately 3-13% of the total circulating free DNA in maternal plasma. The very low amount of circulating cell-free fetal DNA (ccffDNA) in maternal plasma is a crucial issue, and requires specific and optimized techniques for ccffDNA purification from maternal plasma. In addition, highly sensitive detection approaches are required. In recent years, advanced ccffDNA investigation approaches have allowed the application of non-invasive prenatal testing (NIPT) to determine fetal sex, fetal rhesus D (RhD) genotyping, aneuploidies, micro-deletions and the detection of paternally inherited monogenic disorders. Finally, complex and innovative technologies such as digital polymerase chain reaction (dPCR) and next-generation sequencing (NGS) (exhibiting higher sensitivity and/or the capability to read the entire fetal genome from maternal plasma DNA) are expected to allow the detection, in the near future, of maternally inherited mutations that cause genetic diseases. The aim of this review is to introduce the principal ccffDNA characteristics and their applications as the basis of current and novel NIPT.

A Forward Look At Noninvasive Prenatal Testing

Genomic abnormalities are a leading cause of birth defects and pregnancy complications, including in utero growth retardation and risk of miscarriage. Traditional invasive methods detecting such genomic abnormalities pose a relative risk to mother and unborn fetus. Non-invasive prenatal testing (NIPT) is a method that determines the genomic status of a fetus in utero by analyzing circulating fetal DNA in maternal plasma or serum. This review comes at a time when more and more physicians and hospitals might be using NIPT; there is great potential in extending this technology to other diagnostic applications. We discuss here the most current advances in diagnostic NIPT, its applications and limitations, as well as the development of future technology and possible clinical applications.

Validation of a DNA methylation reference panel for the estimation of nucleated cells types in cord blood

Cord blood is widely used as surrogate tissue in epigenome-wide association studies of prenatal conditions. Cell type composition variation across samples can be an important confounder of epigenome-wide association studies in blood that constitute a mixture of cells. We evaluated a newly developed cord blood reference panel to impute cell type composition from DNA methylation levels, including nucleated red blood cells (nRBCs). We estimated cell type composition from 154 unique cord blood samples with available DNA methylation data as well as direct measurements of nucleated cell types. We observed high correlations between the estimated and measured composition for nRBCs (r = 0.92, R² = 0.85), lymphocytes (r = 0.77, R² = 0.58), and granulocytes (r = 0.72, R² = 0.52), and a moderate correlation for monocytes (r = 0.51, R² = 0.25) as well as relatively low root mean square errors from the residuals ranging from 1.4 to 5.4%. These results validate the use of the cord blood reference panel and highlight its utility and limitations for epidemiological studies.

The Effect of the Elapsed Time Between Blood Draw and Processing on the Recovery of Fetal Cells From Maternal Blood

OBJECTIVE

To test the hypothesis that a delay in initial fetal cell enrichment processing of maternal blood samples (defined as the time between blood draw and the initial density gradient centrifugation step) compromises the ability to recover fetal cells, we performed a randomized comparison of immediate (within 4 hours of draw) versus delayed (between 18-24 hours of draw) processing.

METHODS

Four centers participated: two centers utilized flow cytometry (FLOW), and two centers utilized magnetic-activated cell sorting (MACS) techniques. Each center collected 34 samples. The outcome was the percentage of gamma positive (gamma(+)) cells for FLOW or the number of nucleated red blood cells (NRBCs) for MACS, found in the final enriched cell population. Both outcomes reflect cell properties that are potentially fetal in origin, thus making them representative of the ability to recover fetal cells.

RESULTS

Our results did not support our hypothesis that delay in processing compromises fetal cell recovery. Instead, in MACS processing, we observed an increase in recovered NRBCs when blood sample processing was delayed compared with immediate processing. There was no significant difference in gamma(+) cells with FLOW.

CONCLUSION

Time-related changes in the density of target cells, perhaps associated with their progress towards apoptosis during the delay period, may result in increased intact fetal cells with the study methods utilized.

Does Formaldehyde Increase Cell Free DNA in Maternal Plasma Specimens?

BACKGROUND

There have been conflicting observations reported in the literature regarding the effects of formaldehyde in the recovery of cell free fetal DNA (CFF DNA) from maternal plasma. The aim of the present study was to assess the effect of formaldehyde treatment on circulating cell free DNA.

METHODS

We conducted this study using blood specimens collected from 11 pregnant women, each of whom was carrying a male fetus. DYS14 and HBB real time assays were performed to quantify fetal and total circulating cell free DNA from formaldehyde treated and untreated maternal plasma specimens, respectively.

RESULTS

The concentration of total circulating cell free DNA in formaldehyde-treated maternal plasma was reduced, compared with untreated maternal plasma (n = 11; P = .02). The percentage of CFF DNA between formaldehyde-treated and untreated maternal plasma specimens did not differ significantly (n = 11; P = .15).

CONCLUSION

Addition of formaldehyde does not significantly enhance the proportion of cell free fetal DNA when blood specimens are processed without delay.

Non-invasive prenatal diagnosis of aneuploidies: new technologies and clinical applications

Non-invasive prenatal diagnosis (NIPD) has substantial medical importance as it targets the development of safer and more effective methods to avoid the risk of fetal loss associated with currently used invasive methods. Several approaches have been demonstrated as being proof-of concept for NIPD of chromosomal aneuploidies. These approaches include cell-based and cell-free detection methods, involving the investigation of fetal cells in the maternal circulation, formaldehyde treatment of maternal plasma, DNA methylation studies using sodium bisulfite or restriction enzymes, protein-based studies, identification of fetal-specific mRNAs and digital polymerase chain reaction (PCR) approaches, and recently next-generation sequencing and methylated DNA immunoprecipitation real-time quantitative PCR-based approaches. Although all these NIPD methods have both advantages and limitations, some are moving closer to clinical implementation. Biotechnology companies dedicated to the development of NIPD tests such as the sequencing- or methylation-based approaches are finalizing large clinical trials. It is expected that these new technologies will facilitate safer, more sensitive and accurate prenatal diagnostic tests in the near future. In this review, we highlight the most recent advances in methods for NIPD of aneuploidies, and we discuss their future implications in clinical practice.

Tracking fetal development through molecular analysis of maternal biofluids

Current monitoring of fetal development includes fetal ultrasonography, chorionic villus sampling or amniocentesis for chromosome analysis, and maternal serum biochemical screening for analytes associated with aneuploidy and open neural tube defects. Over the last 15 years, significant advances in noninvasive prenatal diagnosis (NIPD) via cell-free fetal (cff) nucleic acids in maternal plasma have resulted in the ability to determine fetal sex, RhD genotype, and aneuploidy. Cff nucleic acids in the maternal circulation originate primarily from the placenta. This contrasts with cff nucleic acids in amniotic fluid, which derive from the fetus, and are present in significantly higher concentrations than in maternal blood. The fetal origin of cff nucleic acids in the amniotic fluid permits the acquisition of real-time information about fetal development and gene expression. This review seeks to provide a comprehensive summary of the molecular analysis of cff nucleic acids in maternal biofluids to elucidate mechanisms of fetal development, physiology, and pathology. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.

Prenatal diagnosis: update on invasive versus noninvasive fetal diagnostic testing from maternal blood

The modern obstetrics care includes noninvasive prenatal diagnosis testing such as first trimester screening performed between 11 and 14 weeks' gestation and second trimester screening performed between 15 and 20 weeks. In these screening tests, biochemical markers are measured in the maternal blood with or without ultrasound for fetal nuchal translucency with reported accuracy of up to 90%. Invasive procedures, including amniocentesis or chorionic villi sampling, are used to achieve over 99% accuracy. During these procedures direct fetal material is examined and, therefore, these tests are highly accurate with the caveat of a small risk for pregnancy loss. Much research now focuses on other noninvasive highly accurate and risk-free tests that will identify fetal material in the maternal blood. Fetal cells and fetal DNA/RNA provide fetal information but are hard to find in an overwhelming background of maternal cells and in the absence of specific fetal cell markers. The most experience has been accumulated with fetal rhesus and fetal sex determination from maternal blood, with an accuracy of up to 100% by using gene sequences that are absent from maternal blood. Although not clinically applicable yet, fetal cells, fetal DNA/RNA and fetal proteomics in combination with cutting edge technology are described to prenatally diagnose aneuploidies and single-gene disorders.

Circulating nucleic acids in plasma/serum

Since the discovery of circulating nucleic acids in plasma in 1948, many diagnostic applications have emerged. For example, diagnostic and prognostic potentials of circulating tumour-derived DNA have been demonstrated for many types of cancer. The parallel development of fetal-derived DNA detection in maternal plasma has opened up the possibility of non-invasive prenatal diagnosis and monitoring of many pregnancy-associated disorders. In this regard, non-invasive fetal rhesus blood group genotyping has already been translated to clinical practice. Other applications of circulating DNA in traumatology and transplant monitoring have also been reported. The more recent discoveries of circulating tumour-derived RNA and fetal-derived RNA have proven to be equally important as their DNA counterparts. Successful prenatal diagnosis of Down's syndrome by fetal RNA analysis has recently been reported. However, the definite origin and release mechanisms of circulating nucleic acids have remained incompletely understood, with cell death being suggested to be associated with such nucleic acid release. Pre-analytical standardisation will become increasingly relevant when comparing data from different laboratories. In conclusion, studies of circulating nucleic acids have promised exciting developments in molecular diagnostics in the years to come.

Identification of nucleated red blood cells in maternal circulation: a second step in screening for fetal aneuploidies and pregnancy complications

BACKGROUND

Identification of fetal nucleated red blood cells (NRBCs) in maternal circulation can facilitate non-invasive prenatal diagnosis, but technical difficulties still exist. An increase in the number of circulating NRBCs, however, could indicate fetal aneuploidies or pregnancy complications.

MATERIALS AND METHODS

The number of NRBCs was determined from 20 mL peripheral blood in 351 women in the second trimester of pregnancy after isolation by magnetic cell sorting (MACS) with anti-CD71 antibody and identification with May-Grunwald/Giemsa staining.

RESULTS

An average of eight NRBCs (range 1-12) were identified among 282 women with chromosomally normal fetuses. In cases known to carry aneuploid fetuses the mean number was 35 (range 7-113), but when the fetus had trisomy 21 (n = 17) an average of 71 NRBCs were identified. Among 26 carriers of beta-thalassemia, 42 NRBCs (range 22-158) were isolated. In pregnancies with abnormal Doppler findings in both uterine arteries (n = 20), 15 NRBCs (range 2-75) were isolated.

CONCLUSION

Determining the number of NRBCs in maternal circulation could represent an additional screening step for fetal aneuploidies, as long as the anemic status of the mother is taken into consideration. However, more cases with abnormal Doppler results must be investigated before this test is used for in the prediction of pregnancy complications.

Prenatal diagnosis using cell-free nucleic acids in maternal body fluids: A decade of progress

The ability to detect cell-free fetal nucleic acids in pregnant women has greatly evolved over the past decade. Dozens of papers have explored the biology, kinetics, and clinical significance of both cell-free fetal DNA and mRNA in the maternal circulation. As a result, our overall understanding of fetal nucleic acid trafficking has expanded. To date, two applications, gender determination and fetal RhD status, have translated into clinical medicine. However, with advanced molecular techniques such as mass spectrometry, real-time quantitative polymerase chain reaction, and gene expression arrays, the ease with which fetal genes can be detected within the mother has greatly improved. Newly identified placental and fetal mRNA transcripts as well as an epigenetically modified placental DNA marker, maspin, have universal applicability. Global expression analyses of fetal mRNA in both amniotic fluid and blood provide new insights into fetal development and pathology. Prenatal diagnosis is poised to evolve from detection of aneuploidy to detection of deviation from normal development, which should provide novel opportunities for fetal treatment.

Two-way trafficking of Annexin V positive cells between mother and fetus: determination of apoptosis at delivery

OBJECTIVES

The aim of this study was to quantitate apoptosis in maternal circulation and umbilical cord blood (UCB) at delivery. The proportion of fetal cells in maternal blood as well as that of maternal cells in UCB was also determined.

MATERIAL AND METHODS

Three milliliters of peripheral blood was collected from nine women during labor. Five women delivered males and four delivered females. Immediately after delivery, 3 mL UCB was collected. Ten microliters was used to quantitate apoptosis by the ethidium bromide assay (EthBr) and from the remaining blood, Annexin V positive cells were isolated by MACS.

RESULTS

The Median apoptosis rate in maternal samples was 25% (19-34) and in UCB 20% (16-28). Annexin V positive cells were present in all samples analyzed. As shown by Fluorescence in situ hybridization (FISH) in maternal samples, cells with an XY hybridization pattern were identified in cases with male newborns in a median concentration of 1.7% (1.6-2.1). On the corresponding UCB, a median of 1.2% (0.8-1.6) XX cells were detected.

CONCLUSION

The study demonstrates the existence of a bidirectional transfer of fetal and maternal cells under apoptosis across the placenta and provides useful information regarding use of UCB for transplantation.

Enrichment of NRBC in maternal blood: a more feasible method for noninvasive prenatal diagnosis

OBJECTIVE

To assess the efficiency and reliability of the separation of fetal nucleated red blood cells (NRBCs) using the galactose-specific lectin method, we counted the number of NRBCs in the blood of pregnant women at various gestational ages, as well as after amniocentesis and termination.

METHOD

Peripheral blood samples were obtained from (1) 22 singleton pregnant women (between 9 and 34 weeks of gestation) and from 23 women who underwent termination (between 6 and 19 weeks of gestation). To determine whether amniocentesis influences numbers of NRBCs, five samples were obtained (2) before and after the procedure. NRBC enrichment was initially performed using density gradients and subsequently using galactose-specific lectin. The cells were then stained with May-Gruenwald Giemsa (MGG) and counted under a light microscope.

RESULTS

NRBCs were found in all samples, ranging from 1 to 82 (median = 12.5 cells/sample). The multiples of the median (MoM) conversion of the number of cells revealed a raise of 1.66-fold (0.12-6.64) in post-termination samples compared with the control value of 1.00 MoM (0.11-6.92; p = 0.036). The postamniocentesis increase was, instead, 1.11-fold (0.17-4.02), which did not reach statistical significance.

CONCLUSION

All blood samples tested contained NRBCs. Samples obtained after termination yielded more cells than those obtained from women whose pregnancies were going on normally. The number of NRBCs in post-termination samples after MoM conversion differed significantly from those in controls. Although separation of NRBCs was not feasible due to extremely low numbers, our results indicated that NRBCs are detectable in all blood samples from normal pregnant women.

Clinical Potential for Noninvasive Prenatal Diagnosis Through Detection of Fetal Cells in Maternal Blood

Fetal cells circulate in maternal blood and are considered a suitable means by which to detect fetal genetic and chromosomal abnormalities. This approach has the advantage of being noninvasive. Since the early 1990s, nucleated erythrocytes (NRBCs) have been considered good target cells for a number of techniques, including fluorescence-activated cell sorting and magnetic cell sorting, using antibodies such as anti-transferrin receptor and anti-gamma-hemoglobin antibodies, followed by analysis with fluorescence in situ hybridization or polymerase chain reaction. In the late 1990s, the National Institute of Child Health and Human Development Fetal Cell Isolation Study assessed the reliability of noninvasive prenatal diagnosis of fetal aneuploidy using NRBCs isolated from maternal circulation. This study revealed the limitations of NRBC separation using antibodies specific for NRBC antigens. A more recent study has demonstrated the efficiency and success of recovery of NRBCs using a galactose-specific lectin, based on the observation that erythroid precursor cells have a large quantity of galactose molecules on their cell surface. Thus, recent advances in this field enhance the feasibility of this diagnostic method. This review article focuses on various methods of detection of fetal cells within the maternal circulation, as well as the status of previous and current studies and the prospective view for noninvasive prenatal diagnosis using fetal cells from the maternal circulation.

Quantification of all fetal nucleated cells in maternal blood in different cases of aneuploidies

We quantified all fetal nucleated cells (FNCs) per unit volume of maternal blood in different aneuploid pregnancies using molecular cytogenetic techniques. Seven cases of male trisomy 18, two triploidies (69,XXX), two 47,XXX, one 47,XXY, one 47,XYY, one male trisomy 13, and one case of 47,XY,r(22),+r(22) were analyzed. Whole blood samples were obtained from 15 women between 17 and 29 gestational weeks and harvested without using fetal cell enrichment procedures. Fluorescence in situ hybridization and primed in situ labeling were performed to identify the FNCs. All slides were manually scanned to quantify those cells. We have identified 4-20 FNCs/ml of maternal blood in the cases of trisomy 18; 10 and 25 FNCs/ml in the two cases of triploidy; 16 and 14 FNCs/ml, respectively, in the two X trisomies; 19 FNCs/ml in the 47,XXY; 26 FNCs/ml in the 47,XYY; nine FNCs/ml in the trisomy 13; and 10 FNCs/ml in the case of r(22). To detect all FNCs in all aneuploid pregnancies, we have used a very simple method that minimizes the manipulation steps to avoid losing fetal cells. The number of FNCs identified in aneuploid pregnancies was 2-5 times higher than in normal pregnancies. This higher number of FNCs will favor the design of a non-invasive pre-natal test.

Cell-free foetal DNA in maternal plasma does not appear to be derived from the rich pool of cell-free foetal DNA in amniotic fluid

BACKGROUND

Large quantities of cell-free foetal DNA have been detected in amniotic fluid, and it has been proposed that this material may contribute to the pool of cell-free foetal DNA in maternal plasma.

METHODS

Twelve maternal blood samples were obtained from pregnant women about to undergo an amniocentesis. Cell-free DNA was extracted from the maternal plasma samples and the matched amniotic fluid samples. The amount of cell-free foetal DNA was quantified by real-time PCR assays for the SRY and RHD genes.

RESULTS

Amniotic fluid was found to contain vast quantities of cell-free DNA (median concentration = 3,978 copies/ml amniotic fluid). The concentration of cell-free foetal DNA in maternal plasma was much lower (median concentration = 96.6 copies/ml maternal plasma). No significant correlation could, however, be determined between these two pools of cell-free foetal DNA.

CONCLUSIONS

Our data confirm that amniotic fluid contains prodigious quantities of cell-free foetal DNA, but as no relationship exists between this material and that in the maternal circulation, it is unlikely that the amnion contributes to the presence of cell-free foetal DNA in maternal plasma.

Quantitative analysis of cellular fetal hemoglobin gamma chain messenger RNA (HbF-gamma mRNA) in maternal peripheral blood

OBJECTIVE

Fetal cells cross the feto-maternal barrier and circulate in maternal peripheral blood; thus, this study aimed to show the relationship between clinical evidence in pregnancy and qualitative feto-maternal barrier changes.

METHODS

The expression of fetal hemoglobin gamma chain messenger RNA (HbF-gamma mRNA) was measured by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) in maternal peripheral blood.

RESULTS

HbF-gamma mRNA was detected in all pregnant women after 5 weeks of gestation. In normal pregnancy, there were two peaks at 10 and 40 weeks, and a significant increase 4 weeks prior to the onset of labor. In intrauterine growth restriction (IUGR), preterm delivery and placenta previa, the HbF-gamma mRNA expression was significantly higher than in normal pregnancies.

CONCLUSION

The expression of HbF-gamma mRNA relative to that of beta-actin mRNA is thought to reflect the real-time leakage of fetal cells into maternal blood.

Quantification of fetal nucleated cells in maternal blood of pregnant women with a male trisomy 21 fetus using molecular cytogenetic techniques

BACKGROUND

Prenatal diagnosis of trisomy 21 is based on fetal karyotyping generally obtained using invasive methods. During pregnancy, the circulating fetal cells in maternal blood constitute a potential source for development of a noninvasive prenatal diagnosis. The objective of this study was the identification and quantification of all fetal nucleated cells per unit volume of peripheral blood of pregnant women carrying male fetuses with trisomy 21 using molecular cytogenetic techniques.

METHODS

Peripheral blood samples were obtained from 16 women carrying male fetuses with trisomy 21. We used a simple and rapid method of harvesting blood without recourse to any enrichment procedures or cell-separation techniques. To evaluate the potential of this method, 16 specimens were analyzed by molecular cytogenetic techniques such as fluorescence in situ hybridization (FISH) and primed in situ labeling (PRINS) using specific probes to chromosomes X, Y and 21.

RESULTS

The number of fetal cells varied between 6 and 32 per mL of maternal blood. This number is 3-5 times higher than that from normal pregnancies.

CONCLUSIONS

Our current results are in agreement with the results previously reported by other groups showing that the number of fetal cells in maternal blood in trisomic 21 pregnancies is higher than in normal pregnancies. This high number of fetal cells is regarded as an advantage for the development of a noninvasive prenatal diagnostic test.

Simultaneous demonstration of clonal chromosome abnormalities and apoptosis in individual marrow cells in myelodysplastic syndrome

Bone marrow samples from 18 patients with myelodysplastic syndrome (MDS) with clonal cytogenetic abnormalities were characterized by combining fluorescence in situ hybridization (FISH) with in situ end-labeling (ISEL) or with annexin V staining and flow cytometry (AV/FLOW) to determine the clonal nature of hematopoietic cells undergoing apoptosis in marrow cells. Apoptosis occurred in both normal and clonal cells. However, the proportion of clonal cells identified by FISH among apoptotic cells was lower than the proportion among nonclonal cells in 17 of 18 patients, regardless of whether ISEL or AV/ FLOW was used to identify apoptosis. This technique allows us to identify simultaneously clonality (as determined by FISH) and apoptosis in individual cells and shows that although apoptosis occurs predominantly in residual normal (FISH-negative) cells, a proportion of clonal precursors in MDS marrow also die from programmed cell death. Such a mechanism may be responsible for the generally slow expansion of the clone in MDS.

Fetal Cell-Free Nucleic Acids in the Maternal Circulation: New Clinical Applications

Six years after the demonstration of the presence of cell-free fetal nucleic acids in maternal plasma, perinatal clinical applications continue to expand. The focus of this article is on advances that have occurred since the CNAPS II conference held in Hong Kong in 2001. Circulating fetal DNA levels (fDNA) are elevated in pregnancies complicated by fetal trisomies 13 and 21 but not 18. Measurement of fDNA levels improves the performance of the current standard maternal serum screen, by increasing the detection of Down syndrome cases by 5% with no increase in the false-positive rate. fDNA levels are elevated in women who have developed clinical symptoms of preeclampsia, but they are also elevated by the early second trimester in women who will eventually develop preeclampsia. fDNA and mRNA gamma globin measurement may have clinical utility as markers for fetomaternal hemorrhage in the late first trimester. Cell-free fetal DNA levels are quite high in the amniotic fluid, permitting fetal genomic isolation and analysis using comparative genomic hybridization techniques. Fetal DNA crosses the blood-brain barrier and is detectable in maternal cerebrospinal fluid in a subset of pregnant women. The biological implications of this are currently unknown. Review of the literature suggests that the placenta is the predominant source of the circulating fetal nucleic acids. However, detection of gamma globin mRNA sequences in the plasma of pregnant women suggests that fetal blood cells also contribute to the pool of nucleic acids. Widespread incorporation of fetal nucleic acid measurement into routine prenatal care depends on the identification of a readily accessible gender-independent fetal marker.

Examination of fetal cells and cell-free fetal DNA in maternal blood for fetal gender determination

BACKGROUND

To assess applicability of noninvasive methods for prenatal sex determination, both intact fetal cells and cell-free DNA from maternal blood were studied.

METHODS

Maternal peripheral blood samples were obtained from 41 women carrying chromosomally normal fetuses and from 3 women with aneuploid fetuses (47,XX,+18; 47,XY,+18 and 47,XY,+21) at 9-22 weeks of gestation. DNA was extracted from the plasma fraction and analyzed by the nested polymerase chain reaction (PCR) using Y chromosome specific primers. After fetal cells were enriched by MACS, fluorescence in situ hybridization (FISH) with chromosome X and Y specific probes was performed to detect XY cells.

RESULTS

Although Y-chromosome-specific DNA was detected by PCR analysis in all maternal plasma samples with male fetuses, 26% women bearing female fetuses also gave positive results. By FISH analysis, XY cells were detected in not only 58% of women bearing male fetuses, but also 13% of their counterpoints with female fetuses.

CONCLUSIONS

Our findings suggested that consistent results for fetal gender using PCR or FISH cannot be obtained with intact fetal cells and cell-free DNA present in maternal blood and plasma at 9-22 weeks of gestation, despite their apparent abundant presence.

Circulating Fetal DNA: Its Origin and Diagnostic Potential—A Review

OBJECTIVE

In contrast to the traditional teaching that the placenta forms an impermeable barrier, multiple studies show that both intact fetal cells and cell-free nucleic acids circulate freely in maternal blood. Complications of pregnancy, such as pre-eclampsia, or fetal cytogenetic abnormalities, such as trisomy 21, increase transfusion of both intact fetal cells and cell-free fetal nucleic acids into the maternal circulation. The objective of our research is to show that abnormal feto-maternal trafficking of nucleic acids is associated with fetal and placental pathology, and that these observations may lead to novel non-invasive diagnostic and screening tests.

METHODS

Real-time quantitative PCR amplification of DYS1 is used to measure the levels of male fetal DNA in case-control sets of serum or plasma taken from pregnant women. In our laboratory, we use DYS1, a Y-chromosome specific gene, as a uniquely fetal DNA marker for the development of gestation-specific normal values and theoretical models.

RESULTS

Women carrying fetuses with trisomies 21 or 13 (but not 18) have increased levels of fetal DNA in their fresh or archived serum and/or plasma samples. Women destined to develop pre-eclampsia have a characteristic bi-phasic elevation of cell-free fetal DNA that precedes clinical symptoms. Data obtained from a variety of clinical scenarios suggest that the placenta is the predominant source of the circulating fetal nucleic acids, although apoptotic haematopoietic cells may contribute to the pool as well.

CONCLUSIONS

Fetal cell-free DNA is elevated in a number of conditions associated with placental pathology. Widespread clinical implementation of fetal DNA as a screening tool awaits discovery of a reliable gender-independent marker, which may be DNA polymorphisms, epigenetic markers, or mRNA. Fetal cell-free nucleic acids have potential for non-invasive monitoring of placental pathology.

On the evolution of erythrocyte programmed cell death: apoptosis of Rana esculenta nucleated red blood cells involves cysteine proteinase activation and mitochondrion permeabilization

Batracian Rana esculenta erythrocytes cell death induced by either calcium influx, or staurosporine, involves typical apoptotic phenotype. Our data reveal: (i) a drastic modification of the cell morphology with loss of the ellipsoidal form as assessed by phase contrast microscopy and scanning electron microscopy; (ii) an exposure of the phosphatidylserine residues in the outer leaflet of the cell membrane; (iii) a caspase-3-like activity; (iv) a mitochondrial membrane potential (Delta Psi m) loss; and (v) a chromatin condensation and fragmentation. Erythrocyte chromatin condensation and fragmentation are prevented by caspase and calpain peptide inhibitors. These inhibitors also prevent Delta Psi m loss supporting the idea that mitochondria is a central sensor for Rana erythrocytes cell death. Our observations highlight the conservation of the programmed cell death machinery in erythrocytes across kingdom.

Analysis of Fetal Blood Cells in the Maternal Circulation: Challenges, Ongoing Efforts, and Potential Solutions

The invasive procedures amniocentesis and chorionic villus sampling (CVS) are routinely applied in pregnancies at risk for fetal abnormalities and the results obtained are the gold standard for prenatal diagnosis. Because these methods of fetal cell procurement involve a 0.5-2% risk for fetal loss, they are recommended mainly in cases at high risk for fetal genetic or cytogenetic abnormalities. The development of a reproducible, reliable, noninvasive method based on retrieval of rare fetal cells from the maternal circulation will render testing feasible for the general population. Despite intensive investigation, a satisfactory, clinically acceptable method has not yet emerged. Several cell types have been targeted to this end, mostly nucleated red blood cells (NRBC), CD34+ hematopoietic progenitors, and trophoblasts. Although these cell types have been unequivocally proven to be present in the maternal circulation, each bears a significant disadvantage, rendering their application in clinical testing currently impossible: NRBC cannot be expanded in culture, thereby ruling out metaphase chromosome analysis, an essential component of prenatal diagnosis. CD34+ cells do posses the potential for in vitro proliferation, however, they have been found to persist in the maternal circulation after delivery, thereby complicating diagnosis in consecutive pregnancies. Trophoblasts are not consistently detected in the maternal circulation. Moreover, due to the lack of a definitive fetal cell marker and a reliable sorting method, foolproof fetal cell identification of any of these cell types is not possible. This report outlines the obstacles that impede development of a method for noninvasive fetal cell sampling for prenatal genetic diagnosis, along with a description of our efforts to analyze simultaneously two fetal blood cell types, NRBC and CD34+ cells in maternal blood during pregnancy, and the problems encountered. This work and that of others lead us to suggest potential future directions to help develop this important technique.

Studies on the isolation and identification of fetal nucleated red blood cells in the circulation of pregnant women before and after chorion villus sampling

OBJECTIVE

To investigate the feasibility of various molecular forms of hemoglobin as markers for fetal nucleated red blood cells (NRBCs).

METHODS

The presence of epsilon and gamma globin positive NRBCs was investigated in pure fetal blood and in blood from pregnant women before and after chorion biopsy. Maternal samples were enriched for NRBCs by various conventional methods, including limited enrichment by only positive CD71 selection or single density gradient. We searched for fetal cells on slides by automated scanning. Fetal cells were defined by (1) the presence of epsilon or gamma globin and (2) simultaneously by the presence of a Y chromosome signal.

RESULTS

18 of 25 gamma globin positive cells identified in blood samples after chorion biopsy were chromosome Y signal positive, and 1 cell had two X chromosome signals. 263 of 339 epsilon globin positive cells identified in blood samples after chorion biopsy were hybridized with X and Y chromosome probes. None had two X signals, and 249 were Y positive. In blood samples before chorion biopsy, only 1 epsilon globin positive fetal NRBC and no epsilon globin positive maternal NRBCs were found.

CONCLUSIONS

Epsilon globin may be specific for fetal NRBCs. Only 1 epsilon globin positive fetal cell was identified in 1 of 12 blood samples before chorion biopsy, representing a total of 182 ml of maternal blood. This suggests that most fetal cells found in maternal blood by fluorescence in situ hybridization methods may not be NRBCs.

Evaluation of bidirectional transfer of plasma DNA through placenta

To clarify the origin of cell-free fetal DNA in maternal plasma, we analyzed bidirectional transfer of plasma DNA between fetus and mother. We analyzed maternal and fetal plasma DNA obtained from 15 pregnant women at the time of Cesarean section. The subjects were five patients with preeclampsia and 10 gestational-age-matched normal controls. DNA was extracted from 1.5-ml plasma samples and the cellular fraction of maternal and umbilical blood. Seven polymorphic marker genes were analyzed. The relative concentration of fetal DNA in maternal plasma and maternal DNA in cord blood were evaluated. The relative concentration of maternal DNA in fetal circulation (median, 0.9%; range, 0.2-8.4%) was significantly lower than that of fetal DNA in maternal blood (14.3%, 2.3-64%), with P=0.007. The relative concentration of maternal DNA in fetal blood was not affected by preeclampsia. These findings indicate that cell-free DNA is unequally transferred through the placenta. The structural characteristics of the placenta suggest that the majority of cell-free fetal DNA in maternal plasma is derived from villous trophoblasts.

Intact fetal cell isolation from maternal blood: improved isolation using a simple whole blood progenitor cell enrichment approach (RosetteSep)

Isolation and analysis of intact fetal cells in maternal blood is an attractive method of non-invasive prenatal diagnosis; however, detection levels are not optimal. The poor sensitivity and inconsistent recovery of fetal cells is compounded by small numbers of circulating fetal cells and loss of fetal cells during enrichment procedures. Optimizing selection criteria by utilizing less complicated methods for target cell enrichment is essential. We report here salutary results using a simple density-based depletion method that requires neither MACS (magnetic-activated cell sorting) nor flow cytometric separation for enrichment of progenitor cells. Maternal blood samples (n = 81) were obtained from women prior to invasive prenatal genetic diagnostic procedures and processed randomly within 24 h using one of two density-based enrichment methods. For progenitor cell enrichment, samples (n = 49) were labeled with a RosetteSep progenitor antibody cocktail to remove unwanted mature T-cells, B-cells, granulocytes, natural killer cells, neutrophils and myelomonocytic cells. For CD45-negative cell enrichment, samples (n = 14) were labeled with RosetteSep CD45 antibody to remove unwanted maternal white cells. The desired cellular fraction was collected and analyzed by either fluorescent in situ hybridization (FISH) or real-time PCR for the presence of intact fetal cells and to quantify Y-chromosome-specific DYS1 sequences, respectively. Overall, FISH and real-time PCR correct detection rates for the progenitor cell enrichment approach were 53% and 89% with 3% (1 out of 30 cases) and 0% false-positive detection, respectively. Fetal sequences were detected in the range from 0.067 to 1.167 genome equivalents per milliliter of blood. No fetal cells were detected using the CD45-negative enrichment method. Flow cytometric analysis of cord blood showed that a unique myeloid population of cells was recovered using RosetteSep trade mark progenitor enrichment compared with the CD45-negative enrichment method. Sensitivity of the RosetteSep progenitor enrichment approach for detection of fetal cells in this pilot study shows great promise with recovery of cells that are suitable for FISH and automated microscope scanning. This simple and rapid method may also allow expansion in culture and characterization of the fetal cell type(s) that circulate in maternal blood, hence, greatly improving reliability of non-invasive prenatal diagnosis.

Quantitative analysis of male fetal DNA in maternal serum of gravid rhesus monkeys (Macaca mulatta)

The isolation of human fetal DNA from the maternal circulation has provided a source of fetal material for prenatal diagnosis. The objective of this study was to investigate whether a similar pattern could be observed in the maternal circulation of male-bearing gravid rhesus monkeys. A real-time PCR TaqMan system for the rhesus Y-chromosome sex determining region was used to determine fetal sex and to quantify fetal DNA concentrations. Results in 14 healthy pregnancies indicated that fetal male DNA could be routinely detected in maternal serum by 50 d of gestation (late first trimester; term 165 +/- 10 d). Fetal DNA concentrations increased with advancing gestation, reaching a mean of 341 genome equivalents/mL of serum (range 11-1570 copies/mL) in the last trimester of gestation, similar to findings in humans. The fetal DNA concentration corresponded to 2.7% of the total maternal serum DNA in the third trimester. Similar to findings in humans, male fetal DNA sequences were not detected postpartum (through 4 wk postpartum) or in animals with a previous history of delivering male offspring. These data indicate that fetal male DNA is present in the maternal circulation of gravid rhesus monkeys comparable to findings in humans and further support the use of this nonhuman primate species as a model to investigate fetomaternal cell trafficking and microchimerism.

Limited expression of Fas and Fas ligand in fetal nucleated erythrocytes isolated from first trimester maternal blood

OBJECTIVE

Intact fetal cells isolated from maternal blood can be used for non-invasive gender determination and genetic diagnosis. Recent studies demonstrating a large amount of cell-free fetal DNA in maternal plasma suggest that the circulating fetal DNA may result from fetal cells undergoing apoptosis. In the present study we evaluated the potential role of Fas and Fas ligand (FasL) cell surface expression with respect to apoptosis induction in fetal cells isolated from maternal blood.

METHODS

We flow sorted candidate fetal cells that were gamma chain-positive and Fas- or FasL-positive or -negative, and subsequently analysed them by fluorescence in situ hybridization (FISH) analysis using X and Y chromosome-specific probes.

RESULTS

Among all gamma hemoglobin-positive cells, there was a significant difference in the percent of cells expressing Fas versus FasL (4.4 and 12.3, respectively). We found no significant correlation between the total number of fetal nucleated red blood cells (NRBCs) and gestational age or the presence of Fas- and FasL-positive cells. From approximately 7 ml of maternal peripheral blood, most of the confirmed fetal (XY) cells were found in the Fas- and FasL-negative sorted population; the average numbers were 12.8 and 15.7, respectively.

CONCLUSION

We conclude that fetal NRBCs express FasL more than Fas, although most fetal NRBCs in first trimester maternal blood samples do not express Fas or FasL. This suggests the absence of a functional Fas/FasL apoptotic system in fetal NRBCs, and that programmed cell death in these cells, which may lead to circulating fetal DNA in maternal plasma, probably occurs by another pathway.