Fetal cells in the maternal circulation: feasibility for prenatal diagnosis

Quantitative analysis of intact fetal cells in maternal plasma by real-time PCR

OBJECTIVE

Fetal genetic materials in maternal circulation might be potentially used for non-invasive prenatal diagnosis (NIPD). In this study, we quantitatively analysed the intact fetal cells existing in maternal plasma, which would be a special method of NIPD.

STUDY DESIGN

Eleven samples from preeclamptic patients, two samples from patients with RhD incompatibilities, and 30 samples from normal pregnancies as controls were collected. The intact cells in the plasma fraction were separated by centrifugation at high speed. The intact cell pellets were washed with PBS to remove any cell-free DNA.

RESULTS

We were able to detect intact fetal cells in 3 out of 11 preeclamptic plasma samples from women carrying male fetuses, and from both plasma samples of RhD incompatibility affected pregnancies. However, intact fetal cells were not detected in all the 16 normal pregnancies with a male fetus, although cell-free fetal DNA was detected in all these cases.

CONCLUSIONS

Intact fetal cells might be present in maternal plasma. However, the rarity of these cells limits their use for reliable, non-invasive prenatal diagnosis. The detection of such cells was successful in some preeclamptic and RhD incompatibility samples, not in the normal controls. Therefore, as opposed to free fetal DNA in maternal blood the use of intact fetal cells does not provide a reliable mode for NIPD.

Placenta Accreta: A Review of Current Advances in Prenatal Diagnosis

Placenta accreta is a life-threatening obstetrical condition requiring a multidisciplinary approach. Despite identified obstetrical risk factors, the diagnosis is often made at the time of delivery. Recent advances in biology could allow a prenatal screening of placenta accreta with the identification of biological markers in maternal blood including cell-free fetal DNA, placental mRNA, and DNA microarray. These promising technologies can detect the presence of anomalies and should play a future role in developing a better understanding of placental invasion. Ultrasound imaging is popular due to its low cost and accessibility and widely used for the screening of placenta location and potential abnormal development. This exam is associated with high sensitivity and specificity for diagnosis of placenta accreta when specific defined criteria are used for the diagnosis. A placental MRI provides a morphological description, as well as recently demonstrated topographical information that optimizes diagnosis and surgical management. The screening of placenta accreta should be improved with the use of a combination of these diagnostic techniques and benefit high-risk populations with a reduction in morbidity.

Detection of Y STR markers of male fetal dna in maternal circulation

BACKGROUND:

Circulating fetal cells and cell free DNA in the maternal blood has been shown to help in prenatal diagnosis of genetic disorders without relying on invasive procedures leading to significant risk of pregnancy loss.

AIM:

The current study was undertaken to detect the male fetal population using Y STR markers DYS 19, DYS 385 and DYS 392 and also to study the extent of persistence of fetal DNA in the mother following delivery.

MATERIALS AND METHODS:

Blinded study was conducted on 50 mothers delivering male and female babies. Cellular and cell free DNA was extracted from maternal and fetal cord blood and amplified for Y STR markers by PCR.

RESULTS:

The amplification sensitivity of Y specific STR, DYS19 was 100% (22/22) in the male fetal DNA samples. The incidence of other STRs, i.e., DYS385 and DYS392 were 91% (20/22) each. Analysis of results revealed that thirteen of the twenty six women had detectable male fetal DNA at the time of delivery. However fetal DNA was not detectable twenty four hours after delivery.

CONCLUSION:

Preliminary results show that the separation of fetal cell-free DNA in the maternal circulation is a good low-cost approach for the future development of novel strategies to provide non-invasive techniques for early prenatal diagnosis.

Feto-maternal cell trafficking: a transfer of pregnancy associated progenitor cells

The embryonic and fetal development in the maternal uterine environment implies that different population of fetal progenitors must be in close contact to the maternal tissues. Accordingly, fetal mesenchymal and hematopoietic stem and progenitor cells have been described in the placenta and the fetal blood. Seeding in the maternal circulation, fetal progenitor cells can be detected in the circulation of pregnant women during most pregnancies. Decades after delivery, fetal CD34+ or mesenchymal stem cells are still detectable in maternal circulation or bone marrow. Recent studies point to the possibility for fetal progenitor cells persisting after pregnancy to home to maternal injured tissue and to adopt various phenotypes. Fetal cells in various maternal tissues can express epithelial, hepatocytic, hematopoietic, renal, cardiomyocytic, glial, or neuronal markers in human as well as mouse models. This apparent multipotency has been attributed to a fetal population of stem/progenitor cells acquired by the mother during pregnancy, named the pregnancy-associated progenitor cells. We will discuss the possible origins of this cell population and review the most recent data suggesting that these fetal microchimeric cells may participate in maternal tissue regeneration processes.

Maternal neoangiogenesis during pregnancy partly derives from fetal endothelial progenitor cells

Fetal progenitor cells enter the maternal circulation during pregnancy and can persist for decades. We aimed to determine the role of these cells in tissue inflammation during pregnancy. WT female mice were mated to males transgenic for the EGFP (ubiquitous) or the luciferase gene controlled by the VEGF receptor 2 (VEGFR2; V-Luc) promoter. A contact hypersensitivity reaction was triggered during such pregnancies. Fetal cells were tracked by using real-time quantitative amplification of the transgene (real-time PCR), Y chromosome in situ hybridization (FISH), immunofluorescence or in vivo bioluminescence imaging. Real-time PCR disclosed fetal cells in the inflamed areas in all tested mice (17/17) with higher frequency and numbers in the inflamed compared with the control areas (P = 0.01). Double labeling demonstrated CD31+ EGFP+ fetal cells organized as blood vessels. In WT pregnant mice bearing V-Luc fetuses, a specific luciferase activity signal could be detected at the hypersensitivity site only, demonstrating the elective presence of VEGFR2-expressing fetal cells. In conclusion, using various techniques, we found the presence of fetal endothelial cells lining blood vessels in maternal sites of inflammation. These results imply that fetal endothelial progenitor cells are acquired by the mother and participate in maternal angiogenesis during pregnancy.

Spot Counting to Locate Fetal Cells in Maternal Blood and Tissue: A Comparison of Manual and Automated Microscopy

BACKGROUND

Fetal cell detection in maternal tissue requires an accurate, efficient, and reproducible microscopy method. Our objective was to compare manual scoring to a commercially available automated scanning system for the detection of chromosome signals by fluorescence in situ hybridization (FISH).

METHODS

X and Y chromosome FISH signals were detected on slides of calibrated mixtures of blood, paraffin-embedded liver sections, and post-termination blood. For manual scoring (400x magnification), the number of cells located and duration of scoring were recorded. For automated scanning using the Metasystems Metafer3/Metafer4 Scanning System (200x magnification), duration of scanning, number of gallery images generated, duration of manual review of gallery images, and number of confirmed fetal cells were recorded.

RESULTS

From all slides the number of target fetal cells located by manual and automated microscopy was highly correlated (r = 0.90). However, automated scanning required on average 4-fold more time than manual scoring (P < 0.0001), with an average automated scanning time of 9.7 h per slide compared with 2.4 h per slide when scored manually.

CONCLUSIONS

In general, the accuracy of automated and manual microscopy is comparable, although manual scoring is more efficient because of the level of magnification necessary for automated scanning of cells, and a large number of gallery images generated by automated scanning that must then be reviewed manually. This suggests that when rapid analysis is required (i.e., clinical situations), manual microscopy is preferable. In contrast, automated scanning may have advantages over manual microscopy when time constraints are less imposed (i.e., research situations).

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.

Antibodies to Trophoblast Antigens HLA-G, Placenta Growth Factor, and NeuroD2 Do Not Improve Detection of Circulating Trophoblast Cells in Maternal Blood

OBJECTIVES

Non-invasive prenatal diagnosis using circulating fetal trophoblast cells has been challenging due to lack of a reproducible trophoblast-specific antibody. We investigated the use of three trophoblast cell-specific antibodies, HLA-G, placenta growth factor, and neuroD2, for the isolation of trophoblast cells from the maternal circulation.

METHODS

Trophoblast cells were isolated by density centrifugation from maternal blood samples (gestational age 10-20 weeks, n = 9). All women were carrying a male fetus. Following immunocytochemical staining with the trophoblast-specific antibodies, fluorescent in situ hybridization was performed, to verify whether any stained cells were indeed fetal.

RESULTS

The HLA-G antibody had a ubiquitous staining pattern, which was not specific for trophoblast cells. Neither the placenta growth factor nor the neuroD2 antibodies were able to identify any trophoblast cells. Following fluorescent in situ hybridization, no male cells were detected on any of the slides.

CONCLUSION

The antibodies used in this study were unable to improve detection of trophoblast cells in the maternal circulation.

Genotyping fetal paternally inherited SNPs by MALDI-TOF MS using cell-free fetal DNA in maternal plasma: Influence of size fractionation

The determination of fetal point mutations from fetal cell-free DNA (cf-DNA) in maternal plasma is technically challenging due to the preponderance of maternal sequences. It has recently been shown that fetal cf-DNA sequences are smaller than maternal ones and that the selection of small cf-DNA fragments by size fractionation by agarose gel electrophoresis leads to the enrichment of fetal cf-DNA sequences, thereby permitting the detection of otherwise masked fetal point mutations. In a separate development, the use of MALDI-TOF MS has also been shown to facilitate the detection of fetal point mutations from cf-DNA in maternal plasma. In this study, a combination of these approaches was examined. cf-DNA was extracted from 18 maternal plasma samples, 10 taken at term and 8 obtained early in the second trimester. A total of 41 SNP loci were examined in size-fractionated and total cf-DNA using either a conventional homogeneous MassEXTEND (hME) assay or a nucleotide-specific single allele base extension reaction (SABER) assay. The analysis of total cf-DNA indicated that size fractionation considerably enhanced the sensitivity of the standard hME assay, especially for samples taken early in pregnancy. Size fractionation also rendered the signals obtained by the SABER assay more precise.

Non-invasive antenatal RHD typing

The existence of cell free fetal DNA, derived from apoptotic syncytiotrophoblast, in the maternal circulation has opened new possibilities of non-invasive prenatal diagnosis. Although still some technical problems exists, especially the lack of a generic positive control on the presence of fetal DNA and the aspecific amplification of background maternal DNA, non-invasive prenatal RHD typing has been successfully introduced in several laboratories, especially in Europe. The diagnostic accuracy reaches>99%. In the Netherlands PCR guided administration of antenatal anti-D prophylaxis is cost-effective and nearby. In this review the main characteristics and applications of cell free fetal DNA are discussed, with an emphasis on prenatal RHD genotyping.

Genetic characterisation of circulating fetal cells allows non-invasive prenatal diagnosis of cystic fibrosis

OBJECTIVES

Cystic fibrosis (CF) is an autosomal recessive disease due to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The purpose of this study was to develop a molecular method to characterise both paternal and maternal CFTR alleles in DNA from circulating fetal cells (CFCs) isolated by ISET (isolation by size of epithelial tumour/trophoblastic cells).

METHODS

The molecular protocol was defined by developing the F508del mutation analysis and addressing it both to single trophoblastic cells, isolated by ISET and identified by short tandem repeats (STR) genotyping, and to pooled trophoblastic genomes, thus avoiding the risk of allele drop out (ADO). This protocol was validated in 100 leucocytes from F508del carriers and subsequently blindly applied to the blood (5 mL) of 12 pregnant women, at 11 to 13 weeks of gestation, whose offspring had a 1/4 risk of CF. Ten couples were carriers of F508del mutation, while two were carriers of unknown CFTR mutations.

RESULTS

Results showed that one fetus was affected, seven were heterozygous carriers of a CFTR mutation, and four were healthy homozygotes. These findings were consistent with those obtained by chorionic villus sampling (CVS).

CONCLUSION

Our data show that the ISET-CF approach affords reliable prenatal diagnosis (PND) of cystic fibrosis and is potentially applicable to pregnant women at risk of having an affected child, thus avoiding the risk of iatrogenic miscarriage.

Separation of normoblasts from whole blood by ultracentrifugation on arabino-galactan discontinuous gradients: A tool for prenatal diagnosis

Normoblasts can be separated at high resolution from whole blood by ultracentrifugation on discontinuous gradients of arabino-galactane after the red blood cells are removed by sedimentation. With this method, isolation of fetal normoblasts from maternal blood could provide a tool for rapid prenatal diagnosis. The availability of this noninvasive technique could avoid the cost and the risks of miscarriage that are associated with the current invasive procedures.

Diagnostic developments involving cell-free (circulating) nucleic acids

BACKGROUND

The detection of circulating nucleic acids has long been explored for the non-invasive diagnosis of a variety of clinical conditions. In earlier studies, detection of circulating DNA has been investigated for the detection of various forms of cancer. Metastasis and recurrence in certain cancer types have been associated with the presence of high levels of tumor-derived DNA in the circulation. In the case of pregnancies, detection of fetal DNA in maternal plasma is a useful tool for detecting and monitoring certain fetal diseases and pregnancy-associated complications. Similarly, levels of circulating DNA have been reported to be elevated in acute medical emergencies, including trauma and stroke, and have been explored as indicators of clinical severity. Apart from circulating DNA, much attention and effort have been put into the study of circulating RNA over the last few years. This area started from the detection of tumor-derived RNA in the plasma of cancer patients. Soon after that, detection of circulating fetal RNA in maternal plasma was described. Plasma RNA detection appears to be a promising approach for the development of gender- and polymorphism-independent fetal markers for prenatal diagnosis and monitoring. This development also opens up the possibility of non-invasive prenatal gene expression profiling by maternal blood analysis. Besides circulating DNA and RNA in plasma and serum, cell-free DNA in other body fluids, such as urine, has been detected in patients with different clinical conditions. Regardless of the sources of cell-free DNA for clinical use, the amount is frequently scarce.

METHODS

Technical advancements in detecting free DNA have been made over the years.

CONCLUSIONS

It is likely that further developments in the field of circulating nucleic acids will provide us with new diagnostic and monitoring possibilities over the next few years.

Noninvasive Prenatal Diagnosis for Hemoglobin Bart's Hydrops Fetalis

Hemoglobin (Hb) Bart's hydrops fetalis, the most severe thalassemic disease, occurs from homozygosity of alpha-thalassemia 1. Deletion of all 4 alpha-globin genes (- -/- -) in this condition results in the absence of alpha-globin chains, and the physiologic dysfunction of Hb Bart's (gamma4) leads to lethality, either in utero or soon after birth. The best strategy for prevention and control of the disease is prenatal diagnosis in the mothers at risk. However, conventional prenatal diagnosis involves invasive procedures that may result in infection or abortion. In this study, a simple technique was developed to identify the presence or absence of alpha-globin chains in fetal nucleated red blood cells (NRBCs) enriched from maternal blood. Mononuclear cells including fetal NRBCs were isolated from maternal blood at 10 to 26 weeks of pregnancy by density-gradient centrifugation. Immunomagnetic separation with anti-CD71 antibody was employed to enrich fetal NRBCs, whose numbers increase with increasing gestational age. For the unaffected fetus, fetal NRBCs were detected by immunofluorescence microscopy after staining with rabbit antihuman alpha-globin antibody. In contrast, fetal red blood cells homozygous for alpha-thalassemia 1, which were identified from their size and morphology, did not stain for alpha-globin antibody. In this study, 3 affected fetuses were detected from 10 pregnancies at risk of Hb Bart's hydrops fetalis, and the results were confirmed by DNA analysis. In the remaining cases, all fetal NRBCs were positive for immunofluorescence staining. DNA analysis revealed that 2 cases were normal, 1 was heterozygous for alpha-thalassemia 2, and the other 4 cases were heterozygous for alpha-thalassemia 1.

A monoclonal antibody with potential for aiding non-invasive prenatal diagnosis: utility in screening of pregnant women at risk of preeclampsia

The development of a non-invasive method of prenatal diagnosis in maternal blood has been the goal of our investigations during the last years. We have developed several anti-CD71 monoclonal antibodies and optimized a protocol for the isolation of nucleated red blood cells (NRBC) from peripheral maternal blood. The enhanced traffic of fetal erythroblasts into the maternal circulation in preeclampsia has been investigated by several groups. In this study, we compared one of our antibodies, 2F6.3, with a commercial anti-CD71 antibody in blood samples from pregnant women suffering pregnancy-induced hypertension (PIH) and in a control group of pregnant women without clinical features suggestive of an increased risk of developing preeclampsia. The mAb 2F6.3, developed by our group, has succeeded in isolating a significantly higher number of erythroblasts with less maternal cell contamination than the commercial antibody in both women with PIH and in the control group (p<0.01; Wilcoxon Signed Ranks Test). Fluorescence in situ hybridization analysis also demonstrated that 2F6.3 is a better antibody for the isolation of fetal NRBC in maternal blood than the commercial anti-CD71 antibody.

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.

Culture of Cells from Maternal Circulation, in Conditions Favoring Fetal Endothelial Cell Expansion, Does Not Facilitate the Preferential Expansion of Circulating Fetal Cells

OBJECTIVES

To establish optimal culture conditions for fetal endothelial cells, and determine whether these can be used for preferential expansion of fetal cells from maternal blood.

METHODS

Human adult microvascular and umbilical vein endothelial cells were cultured in the presence of colony-stimulating factor-1 (CSF-1), placental growth factor (PlGF), and transforming growth factor-beta1 (TGF-beta1). The effect of each cytokine was assessed. We expanded peripheral blood mononuclear cells (PBMCs) from 18 pregnant women using the conditions most favorable to fetal cells; in specimens from women carrying male fetuses (n = 9), cell origin was determined by PCR (SRY locus).

RESULTS

The optimal concentrations of CSF-1, PlGF and TGF-beta1 were 10, 100, and 5 ng/ml, respectively. PBMCs from maternal blood expanded in the presence or absence of the cytokines; PCR analysis showed no Y sequences in cultured maternal samples.

CONCLUSION

Optimal concentrations of CSF-1, PlGF and TGF-beta1 for preferential expansion of fetal endothelial cells were determined in model cultures. However, when these conditions were applied to maternal blood samples, no fetal cells could be detected based on PCR for SRY in women carrying male fetuses.

Fetal blood group genotyping from DNA from maternal plasma: an important advance in the management and prevention of haemolytic disease of the fetus and newborn

The cloning of blood group genes and subsequent identification of the molecular bases of blood group polymorphisms has made it possible to predict blood group phenotypes from DNA with a reasonable degree of accuracy. The major application of this technology, which has now become the standard of care, is the determination of a fetal RHD genotype in women with anti-D, to assess whether the fetus is at risk of haemolytic disease of the fetus and newborn (HDFN). Initially, the procurement of fetal DNA required the invasive procedures of amniocentesis or chorionic villus sampling. Since the discovery of fetal DNA in maternal plasma in 1997, the technology of detecting an RHD gene in this very small quantity of fetal DNA has developed rapidly, so that non-invasive fetal D typing can now be provided as a diagnostic service for D-negative pregnant women with anti-D. Within a few years, it is probable that fetuses of all D-negative pregnant women will be tested for RHD, to establish whether the mother requires antenatal anti-D immunoglobulin prophylaxis.

PAP: detection of ultra rare mutations depends on P* oligonucleotides: "sleeping beauties" awakened by the kiss of pyrophosphorolysis

Pyrophosphorolysis-activated polymerization (PAP) was initially developed to enhance the specificity of allele-specific PCR for detection of known mutations in the presence of a great excess of wild-type allele. The high specificity of PAP derives from the serial coupling of activation of a 3' blocked pyrophosphorolysis-activable oligonucleotide (P(*)) with extension of the unblocked, activated P(*). In theory, PAP can detect a copy of a single base mutation present in 3x10(11) copies of the wild-type allele. In practice, the selectivity of detection is limited by polymerase extension errors, a bypass reaction, from the unblocked oligonucleotide annealed to the opposing strand. Bi-directional PAP allele-specific amplification (Bi-PAP-A) is a derivative of PAP that uses two opposing pyrophosphorolysis activable oligonucleotides (P(*)) with one nucleotide overlap at their 3' termini. This eliminates the problematic bypass reaction. The selectivity of Bi-PAP-A was examined using lambda phage DNA as a model system. Bi-PAP-A selectively detected two copies of a rare mutated allele in the presence of at least 2x10(9) copies of the wild-type lambda phage DNA. We then applied Bi-PAP-A to direct detection of spontaneous somatic mutations in the lacI transgene in BigBlue transgenic mice at a frequency as low as 3x10(-9). A 370-fold variation in the frequency of a specific somatic mutation among different mouse samples was found, implying hyper-Poisson variance and clonal expansion of mutation occurring during early development. Bi-PAP-A is a simple, rapid, and general method capable of automation and particularly suited to detection of ultra rare mutations. We also show that P(*) oligonucleotides have the novel and unexpected property of high specificity to mismatches with the template throughout lengths of the P(*). Thus, PAP also can form the basis of microarray-based scanning or resequencing methods to detect virtually all mutations.

Detection of extremely rare alleles by bidirectional pyrophosphorolysis-activated polymerization allele-specific amplification (Bi-PAP-A): measurement of mutation load in mammalian tissues

Pyrophosphorolysis-activated polymerization (PAP) was developed to detect extremely rare mutations in complex genomes. In theory, PAP can detect a copy of a single base mutation present in 3 x 10(11) copies of the wild-type allele. In practice, the selectivity of detection is limited by a bypass reaction involving a polymerase extension error from the unblocked oligonucleotide annealed to the opposing strand. Bidirectional PAP allele-specific amplification (Bi-PAP-A) is a novel method that uses two opposing 3'-terminal blocked pyrophosphorolysis-activatable oligonucleotides (P*s) with one nucleotide overlap at their 3' termini. This eliminates the problematic bypass reaction. The selectivity of Bi-PAP-A was examined using lambda phage DNA as a model system. Bi-PAP-A selectively detected two copies of a rare mutated allele in the presence of at least 2 x 10(9) copies of the wild-type lambda phage DNA. Bi-PAP-A was then applied to direct detection of spontaneous somatic mutations in the mouse genome at a frequency as low as 3 x 10(-9). A 370-fold variation in the frequency of a specific somatic mutation among different mouse samples was found, suggesting clonal expansion of mutation occurring during early development and a hyper-Poisson variance. Bi-PAP-A is a rapid, general, and automatable method for the detection of rare mutations.

Circulating nucleic acids and proteomics of plasma/serum: clinical utility

Circulating tumor-specific nucleic acids have been identified in plasma, serum, and other body fluids from cancer patients with tumors originating in almost any organ site. Polymerase chain reaction provides a highly sensitive and specific technique for the detection of these genetic changes in a limited amount of tissue/fluid. The presence of elevated levels of free DNA/RNA in many medical conditions, malignancy, and infectious processes is being investigated for screening, diagnosis, prognosis, surveillance for occult disease progression, identifying potential therapeutic targets, and monitoring treatment response. Additionally, elevated fetal DNA/RNA in maternal blood is being used to determine gender identity, assess chromosomal abnormalities, and monitor pregnancy-associated complications. Questions remain on the etiology, characteristics, stability, and potential pathologic consequences of cell-free DNA/RNA in the circulation. Nevertheless, nucleic acid-based assays that monitor plasma, serum, and body fluids provide a noninvasive, facile, and practical method for assessing patients. Proteomic profiling may prove complementary to a total functionality approach in providing a comprehensive evaluation of the patient's disease.

Increased fetal DNA in the maternal circulation in early pregnancy is associated with an increased risk of preeclampsia

OBJECTIVE

The aim of our study was to determine if fetal DNA is present in the maternal circulation in early pregnancy before the clinical manifestation of preeclampsia, and if this could be predictive of the development of preeclampsia.

STUDY DESIGN

Blood were obtained from patients attending for a first antenatal visit. Cases were asymptomatic women who subsequently developed preeclampsia matched to control women for parity and gestational age. Real-time polymerase chain reaction (PCR) using TaqMan primers and probes directed against SRY gene sequences quantified fetal DNA in the maternal circulation.

RESULTS

There were 88 cases of women with preeclampsia and 176 control women, both sampled at a mean gestation (+/-SD) of 15.7 +/- 3.6 weeks. The presence of fetal DNA in the maternal circulation in early pregnancy is associated with an 8-fold increased risk of developing preeclampsia.

CONCLUSION

Increased fetal DNA is present in the maternal circulation in early pregnancy in women who subsequently develop pre-eclampsia and there appears to be a graded response between the quantity of fetal DNA and the risk of developing pre-eclampsia.

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.

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.

Advances in molecular labeling, high throughput imaging and machine intelligence portend powerful functional cellular biochemistry tools

Cellular behavior is complex. Successfully understanding systems at ever-increasing complexity is fundamental to advances in modern science and unraveling the functional details of cellular behavior is no exception. We present a collection of prospectives to provide a glimpse of the techniques that will aid in collecting, managing and utilizing information on complex cellular processes via molecular imaging tools. These include: 1) visualizing intracellular protein activity with fluorescent markers, 2) high throughput (and automated) imaging of multilabeled cells in statistically significant numbers, and 3) machine intelligence to analyze subcellular image localization and pattern. Although not addressed here, the importance of combining cell-image-based information with detailed molecular structure and ligand-receptor binding models cannot be overlooked. Advanced molecular imaging techniques have the potential to impact cellular diagnostics for cancer screening, clinical correlations of tissue molecular patterns for cancer biology, and cellular molecular interactions for accelerating drug discovery. The goal of finally understanding all cellular components and behaviors will be achieved by advances in both instrumentation engineering (software and hardware) and molecular biochemistry.

Detection of fetal Rhesus D gene in whole blood of women booking for routine antenatal care

OBJECTIVE

To determine if the RhD status of the fetus can be detected in an unselected group of RhD-negative women with ongoing pregnancies booking for routine antenatal care.

MATERIAL AND METHODS

We obtained 2.5 ml of whole blood from 202 unselected women with a normal ongoing pregnancy who booked for antenatal care before 20 weeks' gestation. DNA was extracted and real time quantitative PCR performed. Primers and a specific probe were targeted at the Rhesus D gene.

RESULTS

Of 194 women, 31 were RhD-negative with no evidence of prior isoimmunisation. They delivered 17 RhD-positive and 14 RhD-negative babies. Of the 17 RhD-negative women carrying a RhD-positive fetus, the RhD gene was detected in the maternal blood in 14 (82%). There were no false positives. The quantity of RhD gene detected in the maternal blood of RhD-negative mothers ranged from 2 x 10(2) to 4 x 10(6) copies/ml of whole blood.

CONCLUSION

Using real time quantitative PCR assays to amplify free fetal DNA in the maternal circulation, identification of RhD-positive fetuses in RhD-negative mothers is feasible when they book for antenatal care. Before such RhD genotyping can be introduced into clinical practice, however, further studies are required to show that false negative results can be eliminated and to show that this diagnostic test is reliable outside a research setting.

Down's syndrome

The sequencing of chromosome 21 and the use of models of Down's syndrome in mice have allowed us to relate genes and sets of genes to the neuropathogenesis of this syndrome, and to better understand its phenotype. Research in prenatal screening and diagnosis aims to find methods to identify fetuses with Down's syndrome, and reduce or eliminate the need for amniocentesis. Other areas of active research and clinical interest include the association of Down's syndrome with coeliac disease and Alzheimer's disease, and improved median age of death. Medical management of the syndrome requires an organised approach of assessment, monitoring, prevention, and vigilance. Improvements in quality of life of individuals with Down's syndrome have resulted from improvements in medical care, identification and treatment of psychiatric disorders (such as depression, disruptive behaviour disorders, and autism), and early educational interventions with support in typical educational settings. Approaches and outcomes differ throughout the world.

Prenatal diagnosis for chromosome abnormalities: past, present and future

Prenatal diagnosis for chromosome abnormalities has been available for over 30 years. The most common referral indication is a raised risk of Down's syndrome, and diagnosis has, until recently, been carried out by culture of cells from invasive prenatal sampling, followed by full karyotype analysis, with a waiting time of around 2 weeks for results. More recent developments in fluorescence in situ hybridisation (FISH) and quantitative fluorescence-PCR techniques have led to rapid 1-2 d reporting for Down's syndrome, opening the way to the possibility of targeted testing based on referral indication, thus reducing the incidence of difficult counselling issues and potentially unnecessary pregnancy terminations following the unexpected discovery of anomalies such as balanced chromosome rearrangements. The future of prenatal diagnosis must lie in the non-invasive diagnosis of Down's syndrome using fetal cells from maternal circulation.

Prenatal diagnosis of spinal muscular atrophy by genetic analysis of circulating fetal cells

Spinal muscular atrophy (SMA) has a prevalence of one in 6000 births and a one in 40 heterozygote frequency. We aimed to develop a routine test for non-invasive prenatal diagnosis. We tested blood with ISET (isolation by size of epithelial tumour or trophoblastic cells) in 12 pregnant women whose babies were at risk of SMA. Using genetic analysis of fetal cells, we identified SMA in all nine isolated from the three mothers carrying an affected child. There was no mutation in any of the 26 fetal cells isolated from the nine women with an unaffected child. Our results show that non-invasive detection of genetic diseases by the analysis of maternal blood is feasible.

Non-invasive prenatal diagnosis: on the horizon?

The launch of the genomics and postgenomics era has greatly expanded our understanding of the genetic basis of many diseases. In conjunction with the sociocultural trend to delay childbirth and to maintain smaller family units, extra demand may be placed on the existing prenatal diagnostic services. The inherent risk of fetal loss associated with current prenatal diagnostic procedures, such as amniocentesis and chorionic villus sampling, has spurred research into non-invasive prenatal diagnosis. Much research has been conducted on the exploitation of fetal genetic material present in the maternal circulation. The initial focus was on the isolation of intact fetal cells and subsequently, the existence of extracellular fetal DNA in maternal plasma was realized. Exciting developments have been achieved in recent years. A large-scale trial to evaluate the clinical utility of fetal cell isolation from maternal blood for fetal aneuploidy diagnosis was launched and data were recently published. Much has taken place in the research of fetal DNA analysis in maternal plasma and in one example, namely prenatal RhD determination, this type of analysis has been used in the clinical setting. This paper reviews the technological developments in non-invasive prenatal diagnosis.

Evaluation of the clinical usefulness of isolation of fetal DNA from the maternal circulation

OBJECTIVE

To assess the reliability of isolating free fetal DNA from maternal usefulness.

DESIGN

Fetal DNA was isolated from plasma or serum that was either collected prospectively or from archived samples collected for the purposes of second trimester screening.

METHODS

Prospective samples were collected from patients undergoing prenatal diagnostic procedures (n = 24). A second group of samples from Rhesus negative women (n = 28) were assayed in which blood had originally been collected for maternal triple serum screening. DNA was extracted from all samples and assayed for the presence of the beta-globin gene, sex-determing region Y (SRY) gene and Rh gene. All DNA sample handling and extraction was carried out by a single operator, and polymerase chain reaction (PCR) was carried out using previously published PCR primers and appropriate controls. The accuracy of results was assessed relative to the karyotype in the case of the SRY gene or cord blood phenotype in the case of the Rh gene.

RESULTS

The SRY PCR results were compared to fetal cell karyotypes obtained from invasive diagnostic testing, 21 out of the 24 samples were correctly 'sexed'. The RhD PCR results were compared to fetal cord blood samples at the time of delivery, and showed both false positive and false negative results. Two RhD negative babies were genotyped as RhD positive, despite repeat analysis.

CONCLUSION

It is possible to isolate fetal DNA from maternal serum. It is a potentially clinically useful technique in our laboratory and can be used to detect male fetuses, and Rh negative fetuses. To be useful in clinical practice, it is necessary to safeguard against contamination at the time of sample handling, and to use the optimal range of primers available to cover the polymorphisms present within the RhD gene. Although not robust enough yet to be used with diagnostic certainty in our hands, immense improvements in technique, probes and real-time PCR equipment make this type of diagnosis a reality in the near future.

Hematopoietic progenitor cells as targets for non-invasive prenatal diagnosis: detection of fetal CD34+ cells and assessment of post-delivery persistence in the maternal circulation

Culture expansion of fetal cells from the maternal circulation will provide an increased number of cells for non-invasive prenatal diagnosis. Hematopoietic CD34+ cells are potential candidates for this application. More information is needed regarding the frequency of these cells and the phenomenon of post-delivery persistence in the maternal circulation. In this study we assessed the number of fetal CD34+ cells in the maternal circulation, the effect of culture expansion on the number of fetal cells and the persistence of fetal CD34+ cells from previous pregnancies. Fetal cells were identified by the presence of Y-chromosome sequences detected by FISH and nested PCR. Fetal CD34+ cells were detected in all samples from women carrying a male fetus. A low number of residual fetal cells from previous pregnancies was detected (1-3 XY cells in 20 ml blood) in less than 1/3 of the samples from both non-pregnant women and those pregnant with a female fetus. Culturing of CD34+ cells resulted in a significant increase in fetal cell numbers. However, the number of fetal cells persisting from previous pregnancies also increased after culture. It is proposed that information derived from CD34+ cells could potentially support data derived from other cell types for more accurate non-invasive prenatal diagnosis.

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.

Non-invasive first trimester fetal gender assignment in pregnancies at risk for X-linked recessive diseases

OBJECTIVES

Prenatal diagnosis in families affected by X-linked recessive disorders should ideally be limited to the subjects at increased risk, i.e. male fetuses, in order to avoid the risk of fetal loss due to the invasive procedure in healthy female fetuses. The aim of the study was to assess the fetal sex within the first trimester of gestation by two non-invasive approaches, using ultrasonography and a molecular analysis of fetal DNA extracted from whole maternal blood with specific markers, in order to avoid invasive sampling in female fetuses.

METHODS

A total number of 18 fetuses at risk for an X-linked recessive disease were included in the present investigation. Maternal peripheral blood was analysed between 7 and 12 weeks of gestation by nested PCR for the detection of fetal DNA and the prediction of fetal gender. In addition, when the biparietal diameter (BPD) was between 21 and 23 mm, an ultrasonographic examination was carried out to assess the fetal gender. CVS was then performed in male fetuses only.

RESULTS

Fetal gender was correctly assigned by ultrasonography between 21 and 23 mm of BPD in all the cases studied, whereas DNA extracted from whole maternal blood accurately predicted the gender in all the female cases (10), but failed in 4 out of 8 male fetuses, erroneously assigned as females.

CONCLUSION

The present study shows that sonography is able to accurately predict the fetal gender within the first trimester of pregnancy, whereas the molecular analysis of DNA extracted from whole maternal blood is biased by false-Y-negative results in 50% of the cases.

Fetal gender and aneuploidy detection using fetal cells in maternal blood: analysis of NIFTY I data. National Institute of Child Health and Development Fetal Cell Isolation Study

OBJECTIVES

The National Institute of Child Health and Human Development Fetal Cell Isolation Study (NIFTY) is a prospective, multicenter clinical project to develop non-invasive methods of prenatal diagnosis. The initial objective was to assess the utility of fetal cells in the peripheral blood of pregnant women to diagnose or screen for fetal chromosome abnormalities.

METHODS

Results of fluorescence in situ hybridization (FISH) analysis on interphase nuclei of fetal cells recovered from maternal blood were compared to metaphase karyotypes of fetal cells obtained by amniocentesis or chorionic villus sampling (CVS). After the first 5 years of the study we performed a planned analysis of the data. We report here the data from 2744 fully processed pre-procedural blood samples; 1292 samples were from women carrying singleton male fetuses.

RESULTS

Target cell recovery and fetal cell detection were better using magnetic-based separation systems (MACS) than with flow-sorting (FACS). Blinded FISH assessment of samples from women carrying singleton male fetuses found at least one cell with an X and Y signal in 41.4% of cases (95% CI: 37.4%, 45.5%). The false-positive rate of gender detection was 11.1% (95% CI: 6.1,16.1%). This was higher than expected due to the use of indirectly labeled FISH probes in one center. The detection rate of finding at least one aneuploid cell in cases of fetal aneuploidy was 74.4% (95% CI: 76.0%, 99.0%), with a false-positive rate estimated to be between 0.6% and 4.1%.

CONCLUSIONS

The sensitivity of aneuploidy detection using fetal cell analysis from maternal blood is comparable to single marker prenatal serum screening, but technological advances are needed before fetal cell analysis has clinical application as part of a multiple marker method for non-invasive prenatal screening. The limitations of the present study, i.e. multiple processing protocols, are being addressed in the ongoing study.

Expandability of haemopoietic progenitors in first trimester fetal and maternal blood: implications for non-invasive prenatal diagnosis

OBJECTIVES

Selective amplification of rare fetal cells in maternal blood is a potential strategy for non-invasive prenatal diagnosis. We assessed the proliferative potential of first trimester fetal progenitors compared to maternal ones.

METHODS

Fetal and maternal haemopoietic progenitors were cultured separately and in two model mixtures: (i) co-cultures of male fetal nucleated cells mixed with maternal nucleated cells and (ii) co-cultures of malefetal CD34+ cells with maternal CD34+ cells. Cell origin was detected by X-Y fluorescence in situ hybridisation (FISH) RESULTS: The frequency of haemopoietic progenitors in first trimester fetal blood (predominantly CFU-GEMM) differed from those in peripheral blood from pregnant women (predominantly BFU-e). First trimester haemopoietic progenitors formed larger colonies (p=0.0001) and their haemoglobinisation was accelerated compared to those of maternal origin (p<0.001). CD34+ fetal haemopoietic progenitor cells could be expanded four times more than their maternal counterparts (median 235.8-fold, range 174.0-968.0 vs 71.9-fold, range 41.1-192.0; p=0.003). While selective expansion of fetal cells was not observed in the mononuclear cell model, the CD34+ cell rare event mixtures produced a 463.2-fold (range 128.0-2915.0) expansion of fetal cells.

CONCLUSION

Selective expansion of first trimester fetal haemopoietic progenitors may be useful for amplifying fetal cells from maternal blood.

New technique using galactose-specific lectin for isolation of fetal cells from maternal blood

To isolate fetal cells from maternal blood, we developed a new method based on galactose-bearing conjugation. Nucleated red blood cells (NRBCs), which highly express galactose on their surface, were selectively attached to a substrate coated with a galactose-containing polymer via soybean agglutinin (SBA), a galactose-specific lectin. Cord blood samples were used to evaluate enrichment efficacy of NRBCs by this method. Blood samples were obtained from 131 pregnant women between 6 and 27 gestational weeks. After preliminary condensation of fetal cells by Ficoll gradient centrifugation, NRBCs were enriched using galactose-positive selection by adjusting SBA concentration. We isolated one to several hundred NRBCs (mean+/-SD, 7.8+/-8.5) in 2.3 ml of peripheral blood samples from 96% of pregnant women. The isolated NRBCs were analyzed by a Y-chromosome FISH probe in eight cases carrying male fetuses. Y-signals were detected in all eight cases and more than half of the NRBCs were off fetal origin. The study demonstrates that our new method using galactose-specific lectin provides effective enrichment of fetal NRBCs allowing non-invasive prenatal diagnosis.

Enrichment, immunomorphological, and genetic characterization of fetal cells circulating in maternal blood

Fetal cells circulating in the peripheral blood of pregnant women are a potential target for noninvasive genetic analyses. They include epithelial (trophoblastic) cells, which are larger than peripheral blood leukocytes. We enriched circulating trophoblastic cells using the isolation by size of epithelial tumor cells (ISET) method. Peripheral blood was obtained at 11 to 12 weeks of pregnancy. Cells isolated by ISET were stained by hematoxylin and eosin or by immunohistochemistry. Large epithelial cells were microdissected and fetal cell identification was obtained by polymerase chain reaction with short tandem repeats and/or Y-specific primers. By analyzing only 2 ml of blood, we found a variable number (n = 1 to 7) of Y-positive cells (overall 15 of 23) in all of the six mothers carrying a male fetus. In contrast, none of the 26 cells isolated from seven mothers carrying a female fetus scored positive. Eleven cells were analyzed by using short tandem repeat-specific markers: six of them showed a fetal profile and five showed a maternal profile consistently with Y-specific results. Only one-fifth of the single cell DNA was used for fetal cell assessment, leaving enough material for further genetic tests. We also show that the ISET approach allows the performance of fluorescence in situ hybridization analyses and the detection of DNA point mutations in single microdissected cells. We conclude that this is a powerful approach to enrich circulating fetal cells and prove their fetal origin, and that it may have implications for noninvasive prenatal diagnosis of genetic disorders.

Circulating fetal DNA in maternal plasma

BACKGROUND

The existence of high concentrations of circulating fetal DNA in maternal plasma may enable non-invasive prenatal diagnosis. There are many applications of fetal DNA in maternal plasma for clinical diagnosis.

CONCLUSIONS

We expect fetal DNA in material plasma will be incorporated into past of the prenatal investigation of pregnant women in the near future.

Fetal and maternal progenitor cells in co-culture respond equally to erythropoietin

To explore potentially selective growth conditions for fetal cells in cultures from the blood of pregnant women, we investigated if fetal and adult erythroid progenitors with different hemoglobin expression programs are differentially responsive to erythropoietin (EPO). Co-cultures of clonogenic cells from 12-week fetal and adult peripheral blood were established, and the development of erythropoietic cells was monitored using flow cytometric profiles of correlated cellular contents of fetal and adult hemoglobin (HbF and HbA, respectively). Adult nucleated red cells were classified as F+A-, F+A+ or F-A+. All fetal cells were F+A-. The population of F+A- cells was flow-sorted and fetal cells were identified by fluorescence in situ hybridization (FISH) using chromosome-specific probes. Delayed EPO addition revealed that all types of erythroid cells entered the EPO-dependent phase with similar kinetics, beginning at about Day 4. The data suggest that fetal and adult erythroid stem/progenitor cells have the same initial maturation kinetics in culture independent of their hemoglobin chain expression program. Fetal and adult cells with different hemoglobin profiles also showed similar EPO dose-response curves, determined for different intervals during the first 2 weeks of culture. Thus, the kinetics of entry into the phase of EPO dependence, as well as the sensitivity to EPO at various stages of development, are essentially the same for erythropoietic progenitor cells derived from adult and early fetal blood, which rules out the possibility of using the timing or concentration of EPO for the selective growth of fetal cells from the blood of pregnant women.

Inconsistency of fetal trophoblast cells in first trimester maternal peripheral blood prevents non-invasive fetal testing using this cell target

We have investigated whether maternal peripheral blood from the first trimester of pregnancy is a reliable source of identifiable trophoblast cells. The cells were enriched from 30 ml of venous blood, with multiple antibodies shown previously to enrich trophoblasts and a new cocktail based on known trophoblast surface features. Three different magnetic solid phases were tested to enrich trophoblasts, and both positive and negative cell enrichment strategies were examined. The cells were identified as trophoblast by morphology coupled with immunocytochemistry to co-localize cytokeratin with one of three IGF-II, PAI-1 or hPLH proteins or by in-situ hybridization with a mixture of 50 oligos directed to eight different expressed genes, alpha-HCG, IGF-II, PAI-1, HASH2, hPLH, p57(KIP2), PP5, H-19. While these tools worked beautifully in chorionic villi cell/sprout preparations and tissue sections, we could not detect and identify any trophoblasts in maternal peripheral blood even if the maternal peripheral blood was drawn 5-20 min following termination of pregnancy or from individuals maintaining the pregnancy. Based on our own experience and that of some reports in the literature, trophoblasts do not appear to be a viable candidate for fetal screening using maternal peripheral blood as the source. It is important to note that while trophoblast deportation is a biological phenomenon that has been described repeatable, they do not provide a means to perform prenatal genetic diagnosis.

Simultaneous fetal cell identification and diagnosis by epsilon-globin chain immunophenotyping and chromosomal fluorescence in situ hybridization

Isolating fetal erythroblasts from maternal blood offers a promising noninvasive alternative for prenatal diagnosis. The current immunoenzymatic methods of identifying fetal cells from background maternal cells postenrichment by labeling gamma-globin are problematic. They are nonspecific because maternal cells may produce gamma-globin, give poor hybridization efficiencies with chromosomal fluorescence in situ hybridization (FISH), and do not permit simultaneous visualization of the fetal cell identifier and the FISH signal. We describe a novel technique that allows simultaneous visualization of fetal erythroblast morphology, chromosomal FISH, and epsilon-globin labeled with AMCA (7-amino-4-methylcoumarin-3-acetic acid). AMCA was chosen as the fluorescent label to circumvent the problem of heme autofluorescence because the mean difference in relative fluorescence intensity between fetal erythroblasts stained positive for antiglobin antibody and autofluorescence of unstained cells was greater with AMCA (mean 43.2; 95% confidence interval [CI], 34.6-51.9; SD = 14.0) as the reporting label compared with fluorescein isothiocyanate (mean 24.2; 95% CI, 16.4-31.9; SD = 12.4) or phycoerythrin (mean 9.8; 95% CI, 4.8-14.8; SD = 8.0). Median FISH hybridization efficiency was 97%, comparable to the 98% (n = 5 paired samples) using Carnoy fixative. One epsilon-positive fetal erythroblast was identified among 10(5) maternal nucleated cells in 6 paired mixture experiments of fetal erythroblasts in maternal blood (P <.001). Male epsilon-positive fetal erythroblasts were clearly distinguishable from adult female epsilon-negative erythroblasts, with no false positives (n = 1000). The frequency of fetal erythroblasts expressing epsilon-globin declines linearly from 7 to 14 weeks' gestation (y = -15.8 x + 230.8; R(2) = 0.8; P <.001). We describe a rapid and accurate method to detect simultaneously fetal erythroblast morphology, intracytoplasmic epsilon-globin, and nuclear FISH. (Blood. 2001;98:554-557)

Microsatellite analysis provides efficient confirmation of fetal trophoblast isolation from maternal circulation

Fetal trophoblasts can be found in maternal circulation from an early stage of pregnancy and thus provide a potential source of DNA for non-invasive prenatal diagnosis. We have developed a two-step method for trophoblast isolation between the 8th and 12th week of pregnancy. Blood was sampled from 14 women undergoing termination of pregnancy or spontaneous abortion. Immunomagnetic beads precoated with HLA class I and II, and with anti-cytokeratin-18 monoclonal antibodies, were used to remove CD8+ and other maternal cells, and to select for fetal trophoblasts, respectively. Microsatellite analysis was performed on DNA extracted from the isolated, maternal, paternal and placental cells after PCR amplification. Recovery of the trophoblasts was confirmed in 13/14 cases (93%) by the identification of an identical microsatellite pattern for fetal and placental cells. Further evidence was the presence of heterozygous alleles of both maternal and paternal origin. The correct prediction of gender in all five male fetuses was an additional confirmation of trophoblast recovery. We conclude that trophoblasts can be effectively isolated from maternal blood in the first trimester, and by using polymorphic microsatellite markers to confirm sample purity, this method has potential future application in prenatal diagnosis.

Noninvasive prenatal diagnosis of chromosomal aneuploidies by isolation and analysis of fetal cells from maternal blood

The isolation and analysis of nucleated fetal cells (NFCs) from maternal blood may represent a new approach to noninvasive prenatal diagnosis. Although promising, these techniques require highly accurate separation of NFCs from nucleated cells of maternal origin; the two major problems limiting these techniques are the relative rarity of fetal cells in maternal blood and the need to establish their fetal origin. We now report a novel procedure that has allowed accurate separation of NFCs from maternal cells. The technique reported involves direct micromanipulator isolation of histochemically identified hemoglobin F-positive nucleated cells to obtain fetal nucleated red blood cells (FNRBCs) of high yield and purity. Using this technique, followed by cell-by-cell multicolor fluorescence in situ hybridization (FISH) analysis of purified FNRBCs, we were able to detect some of the most common human aneuploidies (including Down syndrome, Klinefelter syndrome, and trisomy 13) in 33 pregnant women referred for amniocentesis. The procedure used, which can be completed in <72 hrs, produced complete concordance with the results of amniocentesis. We also confirm findings of prior studies suggesting that the number of FNRBCs in maternal circulation is remarkably higher in abnormal pregnancies than in normal pregnancies, especially in women carrying a fetus with trisomy 21.

Down syndrome: progress in research

This review discusses the research published in the last five years on the behavioral, genetic, medical, and neuroscience aspects of Down syndrome. The subject areas that have experienced the most active research include Alzheimer disease, language development, leukemia, and pregnancy screening and diagnosis. These and other areas are reviewed.