Fetal cells in maternal blood: current and future perspectives

Feto-maternal microchimerism: Memories from pregnancy

There is a bidirectional transplacental cell trafficking between mother and fetus during pregnancy in placental mammals. The presence and persistence of fetal cells in maternal tissues are known as fetal microchimerism (FMc). FMc has high multilineage potential with a great ability to differentiate and functionally integrate into maternal tissue. FMc has been found in various maternal tissues in animal models and humans. Its permanence in the maternal body up to decades after delivery suggests it might play an essential role in maternal pathophysiology. Studying the presence, localization, and characteristics of FMc in maternal tissues is key to understanding its impact on the woman's body. Here we comprehensively review the existence of FMc in different species and organs and tissues, aiming to better characterize their possible role in human health and disease. We also highlight several methodological considerations that would optimize the detection, quantification, and functional determination of FMc.

Diagnostic Value of Non-Invasive Prenatal Screening of β-thalassemia by Cell Free Fetal DNA and Fetal NRBC

BACKGROUND

Beta thalassemia is a common disorder with autosomal recessive inheritance. The most prenatal diagnostic methods are the invasive techniques that have the risk of miscarriage. Now the non-invasive methods will be gradually alternative for these invasive techniques.

OBJECTIVE

The aim of this study is to evaluate and compare the diagnostic value of two non-invasive diagnostic methods for fetal thalassemia using cell free fetal DNA (cff-DNA) and nucleated RBC (NRBC) in one sampling community.

METHODS

10 ml of blood was taken in two k3EDTA tube from 32 pregnant women (mean of gestational age = 11 weeks), who themselves and their husbands had minor thalassemia. One tube was used to enrich NRBC and other was used for cff-DNA extraction. NRBCs were isolated by MACS method and immunohistochemistry; the genome of stained cells was amplified by multiple displacement amplification (MDA) procedure. These products were used as template in b-globin segments PCR. cff-DNA was extracted by THP method and 300 bp areas were recovered from the agarose gel as fetus DNA. These DNA were used as template in touch down PCR to amplify b-globin gen. The amplified b-globin segments were sequenced and the results compared with CVS resul.

RESULTS

The data showed that sensitivity and specificity of thalassemia diagnosis by NRBC were 100% and 92% respectively and sensitivity and specificity of thalassemia diagnosis by cff-DNA were 100% and 84% respectively.

CONCLUSION

These methods with high sensitivity can be used as screening test but due to their lower specificity than CVS, they cannot be used as diagnostic test.

Feto-Maternal Microchimerism: The Pre-eclampsia Conundrum

Feto-maternal microchimerism (FMM) involves bidirectional cross-placental trafficking during pregnancy, leading to a micro-chimeric state that can persist for decades. In this manner a pregnant woman will harbor cells from her mother, as well as, cells from her child. Historically, eclampsia, a severe disorder of pregnancy provided the basis for FMM following the detection of trophoblast cells in the lungs of deceased women. Bi-directional cell trafficking between mother and fetus is also altered in pre-eclampsia and has been suggested to contribute to the underlying etiology. FMM has been implicated in tolerance promotion, remission of auto-inflammatory disorders during pregnancy, or the development of autoimmune conditions post-partum. The underlying mechanism whereby the host immune system is modulated is unclear but appears to involve HLA class II molecules, in that incompatibility between mother and fetus promotes remission of rheumatoid arthritis, whereas feto-maternal HLA compatibility may assist in the post-partum initiation of scleroderma. Couples having a high degree of HLA class II compatibility have an increased risk for pre-eclampsia, while the occurrence of scleroderma and rheumatoid arthritis is greater in pre-eclamptic cases than in women with normal pregnancies, suggesting a long term autoimmune predisposition. Since pregnant women with pre-eclampsia exhibit significantly lower levels of maternally-derived micro-chimerism, the question arises whether pre-eclampsia and post-partum development of autoimmune conditions occur due to the failure of the grandmothers cells to adequately regulate an inappropriate micro-chimeric constellation.

Noninvasive prenatal screening by next-generation sequencing

Noninvasive prenatal screening (NIPS) has emerged as a highly accurate method of screening for fetal Down syndrome, with a detection rate and specificity approaching 100%. Challenging the widespread use of this technology are cost and the paradigm shift in counseling that accompanies any emerging technology. The expense of the test is expected to decrease with increased utilization, and well beyond the current NIPS technology, its components (fetal genome measurements, sequencing technology, and bioinformatics) will be utilized alone or in combinations to interrogate the fetal genome. The end goal is simple: to offer patients information early in pregnancy about fetal genomes without incurring procedural risks. This will allow patients an opportunity to make informed reproductive and pregnancy management decisions based on precise fetal genomic information.

Lab-on-a-chip technology: impacting non-invasive prenatal diagnostics (NIPD) through miniaturisation

This paper aims to provide a concise review of non-invasive prenatal diagnostics (NIPD) to the lab-on-a-chip and microfluidics community. Having a market of over one billion dollars to explore and a plethora of applications, NIPD requires greater attention from microfluidics researchers. In this review, a complete overview of conventional diagnostic procedures including invasive as well as non-invasive (fetal cells and cell-free fetal DNA) types are discussed. Special focus is given to reviewing the recent and past microfluidic approaches to NIPD, as well as various commercial entities in NIPD. This review concludes with future challenges and ethical considerations of the field.

Microfluidic sample preparation for diagnostic cytopathology

The cellular components of body fluids are routinely analyzed to identify disease and treatment approaches. While significant focus has been placed on developing cell analysis technologies, tools to automate the preparation of cellular specimens have been more limited, especially for body fluids beyond blood. Preparation steps include separating, concentrating, and exposing cells to reagents. Sample preparation continues to be routinely performed off-chip by technicians, preventing cell-based point-of-care diagnostics, increasing the cost of tests, and reducing the consistency of the final analysis following multiple manually-performed steps. Here, we review the assortment of biofluids for which suspended cells are analyzed, along with their characteristics and diagnostic value. We present an overview of the conventional sample preparation processes for cytological diagnosis. We finally discuss the challenges and opportunities in developing microfluidic devices for the purpose of automating or miniaturizing these processes, with particular emphases on preparing large or small volume samples, working with samples of high cellularity, automating multi-step processes, and obtaining high purity subpopulations of cells. We hope to convey the importance of and help identify new research directions addressing the vast biological and clinical applications in preparing and analyzing the array of available biological fluids. Successfully addressing the challenges described in this review can lead to inexpensive systems to improve diagnostic accuracy while simultaneously reducing overall systemic healthcare costs.

Prenatal diagnosis of fetal aneuploidies: post-genomic developments

Prenatal diagnosis of fetal aneuploidies and chromosomal anomalies is likely to undergo a profound change in the near future. On the one hand this is mediated by new technical developments, such as chromosomal microarrays, which allow a much more precise delineation of minute sub-microscopic chromosomal aberrancies than the classical G-band karyotype. This will be of particular interest when investigating pregnancies at risk of unexplained development delay, intellectual disability or certain forms of autism. On the other hand, great strides have been made in the non-invasive determination of fetal genetic traits, largely through the analysis of cell-free fetal nucleic acids. It is hoped that, with the assistance of cutting-edge tools such as digital PCR or next generation sequencing, the long elusive goal of non-invasive prenatal diagnosis for fetal aneuploidies can finally be attained.

Noninvasive prenatal diagnosis of fetal aneuploidies and Mendelian disorders: new innovative strategies

The application of recent technical developments, such as digital PCR or shot-gun sequencing, for the analysis of cell-free fetal DNA, have indicated that the long-sought goal of the noninvasive detection of Down syndrome may finally be attained. Although these methods are still cumbersome and not high throughput, they provide a paradigm shift in prenatal diagnosis, as they could effectively pronounce the end of invasive procedures, such as amniocentesis or chorionic villous sampling for the detection of such fetal anomalies. However, it remains to be determined how suitable these approaches are for the detection of more subtle fetal genetic alterations, such as those involved in hereditary Mendelian disorders (e.g., thalassemia and cystic fibrosis). New technical developments, such as microfluidics and reliable automated scanning microscopes, have indicated that it may be possible to efficiently retrieve and examine circulating fetal cells. As these contain the entire genomic complement of the fetus, future developments may include the noninvasive determination of the fetal karyotype.

Recent progress in non-invasive prenatal diagnosis

Although the first finding that fetal cells can enter the maternal circulation was made more than a century ago, it is still unclear if this finding will be translated into a clinically useful diagnostic tool in the foreseeable future. However, significant progress has been made via the analysis of cell-free fetal DNA in maternal plasma/serum and clinical services are now already being offered for the determination of fetal rhesus D status and sex. Currently, however, this technology is really only suited for the analysis of fetal genetic loci completely absent from the maternal genome. The detection of more subtle fetal genetic traits, such as point mutations involved in Mendelian disorders (thalassaemia, cystic fibrosis), is considerably more complex. Preliminary reports indicate that the detection of fetal aneuploidies might be possible using epigenetically modified genes, e.g. maspin on chromosome 18. Additionally, an exiting recent development is that it might be feasible to detect Down syndrome via the quantitative assessment of placentally derived cell-free mRNA of chromosome-21-specific genes such as PLAC4.

A high yield of fetal nucleated red blood cells isolated using optimal osmolality and a double-density gradient system

OBJECTIVES

To increase the yield of fetal nucleated red blood cells (NRBCs) from maternal blood using a discontinuous Percoll gradient and to determine the effects of osmolality on NRBC yield.

METHODS

Fetal NRBCs were isolated from combined umbilical cord blood and adult female blood, or from maternal blood using single or double Percoll gradients with different osmolalities. Magnetic activated cell sorting was used to enrich isolated NRBCs, and morphological differentiation was performed with Kleihauer-Betke stain. We also isolated fetal NRBCs from 25 10 mL samples of maternal blood and determined fetal sex by fluorescence in situ hybridization (FISH), using X-Y probes.

RESULTS

For single-density Percoll columns, the greatest number of NRBCs was isolated using 280 mOsm/kg H(2)O with 1.077 g/mL Percoll and 520 mOsm/kg H(2)O with 1.119 g/mL Percoll. Significantly more fetal NRBCs were isolated with double Percoll density gradients than with double-Histopaque gradients (p = 0.043). FISH analysis on NRBC in 25 cases correctly identified 15 male and 9 female euploid fetuses and one Trisomy 21 fetus.

CONCLUSION

The NRBC enrichment method we present requires less maternal blood and yields more NRBCs compared to previous methods.

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.

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.

Replicate real-time PCR testing of DNA in maternal plasma increases the sensitivity of non-invasive fetal sex determination

BACKGROUND

We determined fetal sex in pregnancies referred for invasive prenatal diagnosis procedures by analysis of DNA in maternal plasma.

METHODS

Twelve pregnancies at risk of X-linked haemophilia and 32 pregnancies at risk of chromosomal aneuploidies at a gestational age ranging from 10 to 18 weeks recruited before chorionic villus sampling or amniocentesis were involved in the study. Male fetal DNA in maternal plasma was detected by using real-time polymerase chain reaction with the SRY gene as a marker.

RESULTS

The specificity of the system reached 100% (no Y signal was detected in 17 women pregnant with a female fetus) and the sensitivity reached 100% (SRY amplification in 27 examined samples).

CONCLUSIONS

Amplification of free fetal DNA in maternal plasma is a valid and rapid technique for predicting fetal sex in first- and second-trimester pregnancies and could allow the restriction of invasive sampling procedures to male fetuses at risk of X-linked disorders.

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.

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.

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.

Maternal or fetal origin of rhesus monkey (Macaca mulatta) amniotic fluid leukocytes can be identified by polymerase chain reaction using the zinc finger Y gene

Leukocytes can be found in substantial numbers within the intrauterine tissues and amniotic fluid of women, and play a central role in the pathophysiology of infection-related preterm labor by their production of proinflammatory mediators. It remains unclear whether these leukocytes represent a fetal immune response, a maternal response, or a combination of the two. The objective of this study was to develop a test in the rhesus monkey (Macaca mulatta) suitable for determining the percentage of male fetal cells present in a population of leukocytes recovered from blood or amniotic fluid. We found inadequate specificity for rhesus monkey cells using commercial human Y-chromosome paint kits (fluorescence in situ hybridization (FISH)). Human-specific primers for the repetitive Y chromosome DYZ-1 locus employed in the polymerase chain reaction (PCR) produced an unacceptable percentage of false positives. However, we successfully developed a PCR-based test using rhesus-specific primers for the zinc finger Y (ZFY) locus. Densitometry of PCR products from known ratios of male and female adult peripheral leukocytes generated a linear standard curve which provided quantitative results and required only 400 cells per sample. The rhesus beta globin (RBG) gene served as an internal control. The PCR test correctly discriminated the sex of peripheral leukocytes in 20 adult males, 20 adult females, two male fetuses, and one female fetus. Serial samples of amniotic fluid from four chronically catheterized rhesus monkeys bearing male fetuses were used to confirm the utility of this assay for quantifying fetal cells in amniotic fluid. In conclusion, we have developed a PCR test which is suitable for distinguishing male from female cells in adult and fetal blood and in amniotic fluid, which lends itself to a variety of diagnostic and biologic applications in the rhesus monkey and potentially in other nonhuman primates.

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.

Prenatal diagnosis using fetal cells and free fetal DNA in maternal blood

The presence of fetal cells and free fetal DNA in maternal blood offers an exciting opportunity for the development of safe noninvasive forms of prenatal diagnosis. Research in this field has, however, also indicated that their levels in the maternal circulation are increased in certain pregnancy-related disorders, such as preeclampsia. Their closer examination may shed new light on the underlying etiology of this enigmatic disorder.

Fetal leukocyte trafficking as a stimulus for the production of maternal antibodies in the goat

The production of antibodies during pregnancy or after parturition is a natural occurrence in many mammalian species. Fetal cells have been detected in the peripheral blood of women and mice and are thought to be the immune stimulus for antibody production. The aim of this study was to investigate if the production of maternal anti-fetal antibodies during ruminant pregnancy is the result of fetal leukocyte trafficking across the placenta. Maternal pregnancy serum was collected from 94 does whose fetuses received sheep hematopoietic stem cells via in utero transplantation at 49 to 62 d of gestation. Serum samples were collected before surgery and at weekly intervals throughout gestation. A lymphocyte microcytotoxicity assay was used to screen the serum samples from does that carried chimeric fetuses to term (n = 75). Of these 75 does, 28 parous does had presurgery serum that contained alloreactive antibodies. Nine of the 75 does had nonreactive presurgery serum, but they produced alloreactive antibody titers during gestation. Xenoreactive antibodies were detected in the pregnancy sera from 2 of the 75 does tested. Hemolytic assays confirmed the species-specificity of the xenoreactive serum from these 2 does. In view of the fact that hematopoietic cells were the only source of anti-sheep antibody stimulation in this model, we propose that fetal leukocyte trafficking does take place across the caprine placenta.

Elevation of both maternal and fetal extracellular circulating deoxyribonucleic acid concentrations in the plasma of pregnant women with preeclampsia

OBJECTIVE

Elevated amounts of circulating fetal deoxyribonucleic acid in maternal plasma have recently been detected in pregnancies complicated by preeclampsia. We attempted to confirm this finding and simultaneously examined the quantity of maternal circulating deoxyribonucleic acid.

STUDY DESIGN

Circulating deoxyribonucleic acid was measured by realtime quantitative polymerase chain reaction in plasma samples obtained from 44 women with preeclampsia and a matched cohort of 53 normotensive pregnant women.

RESULTS

We confirmed that circulating fetal deoxyribonucleic acid levels were significantly elevated in pregnancies complicated by preeclampsia (3194.6 vs 332.8 copies/mL; P < .001). We also showed for the first time that circulating maternal deoxyribonucleic acid levels are also elevated (219,023.9 vs 20,235.8 copies/mL; P < .001). The increases in these deoxyribonucleic acid levels corresponded to the severity of the disorder, and values were correlated with each other in pregnancies complicated by preeclampsia (r = 0.556; P < .001) but not normotensive pregnancies (r = 0.046; P = .747).

CONCLUSION

The releases of both free fetal and maternal deoxyribonucleic acid were found to be affected in preeclampsia.

Assessing the chromosome copy number in metaphase II oocytes by sequential fluorescence in situ hybridization

PURPOSE

Aneuploidy in oocytes is the main cause of failed embryo implantation and of miscarriage. At present, only limited data on the prevalence of aneuploidy in freshly collected human oocytes are available and all studies have been performed with conventional methods for karyotyping. In this feasibility study, multiple-hybridization fluorescence in situ hybridization (FISH) was evaluated as an alternative method to determine the number of chromosomes in oocytes.

METHODS

Fifty-two spare oocytes were collected from 23 patients treated with gonadotropins for intrauterine insemination or intracytoplasmic sperm injection. A conventional dual color FISH approach using mixtures of chromosome-specific standard alpha-satellite probes was applied consecutively to the chromosomes of the same metaphase II oocyte. Mixtures of three to six probes were designed in order to allow chromosome identification based on signal color and centromeric index.

RESULTS

One hybridization cycle was possible in 52 uninseminated metaphase II oocytes, two hybridizations in 43 oocytes (82.7%), three hybridizations in 30 oocytes (57.6%), four hybridizations in 27 oocytes (51.9%), and five hybridizations in 15 oocytes (28.8%). Altogether, 591 chromosomes could be marked (47.4% of the entire chromosome complement, 11.4 chromosomes per oocyte). The most important single factor contributing to technical failure was loss of the oocyte from the slide.

CONCLUSION

This feasibility study demonstrates that multiple-hybridization FISH can be used for the assessment of a larger proportion of the chromosome complement in oocyte as compared to previous studies based on FISH.

Fetal DNA in maternal plasma is elevated in pregnancies with aneuploid fetuses

Current non-invasive screening methods for the prenatal diagnosis of fetal aneuploidies are hampered by low sensitivities and high false positive rates. Attempts to redress this situation include the enrichment of fetal cells from maternal blood, or the use of fetal DNA in the plasma of pregnant women. By the use of real-time quantitative polymerase chain reaction (PCR) it has recently been shown that circulatory male fetal DNA in maternal plasma is elevated in pregnancies with trisomy 21 fetuses. In this independent study we confirm and extend upon these results by showing that the levels of fetal DNA are also elevated in pregnancies with other chromosomal aneuploidies (mean=185.8 genome equivalents/ml; range=62.2-471.7) when compared to pregnancies with normal male fetuses (mean=81.9 genome equivalents/ml; range=28.8-328.9), p=0.005. This elevation was greatest for fetuses with trisomy 21, whereas it was not significant for fetuses with trisomy 18, p=0.356. These data suggest that a quantitative analysis of such fetal DNA levels may serve as an additional marker for certain fetal chromosomal abnormalities, in particular for trisomy 21.

High levels of fetal erythroblasts and fetal extracellular DNA in the peripheral blood of a pregnant woman with idiopathic polyhydramnios: case report

Abnormal amniotic fluid volume can be associated with increased maternal risk as well as perinatal morbidity and mortality. Polyhydramnios is often indicative of fetal, placental or maternal problems. In a large proportion of patients the aetiology of the disorder is unclear. Here we report on a case in which numerous fetal erythroblasts and large quantities of extracellular fetal DNA were found in the peripheral blood of a pregnant woman with idiopathic polyhydramnios bearing a male fetus. Following enrichment of erythroblasts by magnetic separation (MACS) and anti-CD71 antibodies, approximately 45-fold more erythroblasts were determined per ml peripheral maternal blood than in matched controls (231 versus 5). Single cell multiplex polymerase chain reaction (PCR) of individually micromanipulated erythroblasts showed that approximately 122 of these were of fetal origin. The concentration of extracellular fetal circulatory DNA in maternal plasma was determined by real-time quantitative PCR and shown to be almost double that of the control group (749.2 versus 404 fetal genome equivalents per ml maternal plasma). It can be speculated that the increased intrauterine pressure in polyhydramnios leads to an enhanced influx of fetal cells and free extracellular fetal DNA into the maternal circulation. This hypothesis will have to be tested with further cases.

Fetal cells in cervical mucus and maternal blood

Research in developing effective and accurate methods for non-invasive prenatal diagnosis has focused on two main techniques: the retrieval of trophoblast cells from the cervix and the enrichment of fetal erythroblasts from the blood of pregnant women. The isolation of fetal cells by both approaches has permitted the identification of fetal aneuploidies by the use of fluorescence in-situ hybridization (FISH) with appropriate probes, as well as fetal single gene disorders by polymerase chain reaction (PCR). In the latter instance, it has been shown that in order to attain the high degree of specificity required for prenatal diagnosis, it is necessary to analyse single fetal cells isolated by micromanipulation. This practice has permitted the successful characterization of fetal rhesus status, haemoglobinopathies, Duchenné's muscular dystrophy and spinal muscular atrophy, amongst others.Further developments include investigations into whether the diagnostic potential of fetal cells retrieved by either method can be expanded by the possible culturing of such cells, as well as the possibility of performing successive rounds of FISH and PCR by the recycling of isolated fetal cells.A novel observation that our group has made is that the traffic of fetal cells is enhanced in pregnancies affected by the pregnancy related disorder, pre-eclampsia. Our subsequent investigations have shown that this elevation in fetal cell traffic may serve as an early marker for those pregnancies at risk for this disorder.A very recent exciting discovery has been that free extracellular fetal DNA can be detected in the plasma and serum of pregnant women, which may permit the rapid and accurate detection of uniquely fetal loci, such as the fetal rhesus D gene in rhesus D negative pregnant women.

Detection of fetal trisomy 18 by short-term culture of maternal peripheral blood

OBJECTIVE

We report the prenatal detection by fluorescence in situ hybridization analysis of a male fetus with trisomy 18.

STUDY DESIGN

Total nucleated cells recovered from 7 mL of maternal peripheral blood by means of double-density gradient centrifugation were cultured for 3 days in a devised medium.

RESULTS

Fetal cells with X- and Y-specific signals were detected in all the established cultures, but the yield and purity were higher in the culture from the 1077 Ficoll layer. Cumulatively, 84 fetal cells were recorded by analysis of 5640 cells. The hematopoietic lineages involved in the production of the fetal cells in culture were not assessed. For the cultures established with the 1119 Ficoll layer, the involvement of progenitors or precursors of the erythroid lineage was assumed because postculture sorting was directed toward cells expressing the erythropoietin receptor.

CONCLUSION

We conclude that culturing total nucleated cells from maternal blood is a new procedure that could prove valuable in the detection of the main fetal aneuploidies affecting pregnant populations.

Detection of fetal Rhesus D and sex using fetal DNA from maternal plasma by multiplex polymerase chain reaction

OBJECTIVE

To test the sensitivity, specificity and reproducibility using fetal DNA obtained from plasma of pregnant women by polymerase chain reaction for the simultaneous detection of both fetal sex and Rhesus D genotype.

METHOD

Blood samples were obtained from 22 Rhesus D negative pregnant women about to undergo an invasive procedure. DNA was extracted from the plasma fraction and analysed by a multiplex nested polymerase chain reaction using Y chromosome-and Rhesus D-specific primers. The results of this experimental procedure were compared with those obtained from the analysis performed on material gained by the invasive procedure.

RESULTS

The sensitivity of the plasma polymerase chain reaction-based method was surprisingly high, with both fetal genotypes being correctly determined in almost 100% of the cases examined. In only one instance was a false positive result for the detection of Rhesus D recorded, which on subsequent analysis was negative.

CONCLUSIONS

The ease and rapidity with which the plasma polymerase chain reaction-based method can be performed makes it a promising method for the analysis of multiple fetal loci, such as Rhesus D and sex.

Multiplex and real-time quantitative PCR on fetal DNA in maternal plasma. A comparison with fetal cells isolated from maternal blood

Fetal DNA has recently been detected in maternal plasma by PCR and has shown promise for the prenatal determination of fetal sex or rhesus D. In order to obtain the maximum amount of information from this fetal genetic material, we have devised a sensitive multiplex PCR method to permit simultaneous analysis for both the SRY locus and the rhesus D gene. Our studies show that this technique is very sensitive and specific. In the 22 cases from rhesus D negative women examined, we were able to determine both fetal genotypes correctly. In the parallel enrichment for fetal cells, fetal erythroblasts were only detected in 14 of the 19 cases. Our data also indicate that fetal DNA from rhesus D positive fetuses is present in maternal plasma even after prophylactic anti-D treatment. Furthermore, since fetal cells have been reported to be elevated in pregnancies with aneuploid fetuses, we have quantified the amount of fetal DNA present in the maternal plasma of 10 such affected pregnancies by real-time PCR. Our results indicate that fetal DNA is elevated under such circumstances when compared to gestationally matched normal pregnancies (mean of 7% in aneuploid samples versus 3.5% in normal pregnancies). These results indicate that the quantification of fetal DNA in maternal plasma may be an additional screening tool for pregnancies at risk of bearing an aneuploid fetus.

Fetomaternal cell trafficking: a new cause of disease?

Isolation of fetal cells from maternal blood is under active investigation as a noninvasive method of prenatal diagnosis. In the context of studying cell surface antigens expressed on fetal cells we discovered that fetal cells from a prior pregnancy also could be detected. This led to the appreciation of the persistence of fetal cells in maternal blood for as long as 27 years postpartum, and the realization that following pregnancy, a woman becomes a chimera. Quantitative polymerase chain reaction analyses have shown that a term pregnancy is not required for the subsequent development of fetal cell microchimerism. As many as 500,000 fetal nucleated cells are transfused following an elective first trimester termination of pregnancy. The relationship between fetal cell microchimerism and maternal disease is currently being explored. During pregnancy, fetal cells in the maternal skin are related to polymorphic eruptions of pregnancy and increased fetomaternal trafficking is detectable in cases of preeclampsia. After delivery, more male DNA of presumed fetal origin is present in the blood and skin of women with scleroderma as compared with healthy controls. Scleroderma is of particular interest because it shows a strong female predilection and it is an autoimmune disease with clinical similarities to graft-versus-host disease. Fetomaternal cell trafficking provides a potential explanation for the increased prevalence of autoimmune disorders in adult women following their childbearing years.

Allele drop-out can occur in alleles differing by a single nucleotide and is not alleviated by preamplification or minor template increments

The ability to analyze the genetic material of single cells by the PCR opens up new prospects for diagnostics. Because only two copies of the genetic template are available for amplification, a problem that frequently arises when examining heterozygous loci in single cells is allele drop-out (ADO). ADO results from the preferential amplification of one of a pair of heterozygous alleles, in which the other allele is totally under-represented. In examining single cells from carriers heterozygous for beta-thalassemia mutations, we have found ADO to occur in alleles differing by a single nucleotide, where either the normal or the mutant genotype was absent. We have found that ADO is not overcome by either increasing the amount of DNA template to 20 pg or by primer extension preamplification (PEP), but rather that the best diagnostic accuracy is obtained by examining multiple single cells and basing a diagnosis on the combined results of such an examination.

Fetal cells in maternal blood. An update from Basel

OBJECTIVE

The efficiency of two protocols for the enrichment of fetal cells from the blood of pregnant women was compared: a triple density gradient followed by twin magnetic separations (method A) versus a single density gradient and single magnetic separation (method B).

STUDY DESIGN

Blood samples were obtained from women prior to undergoing an invasive procedure. The processed samples, 87 by method A and 332 by method B, were examined for the presence of male cells by fluorescence in situ hybridisation.

RESULTS

The simpler protocol was found to be superior. The most critical component, however, is the ability of the reader to correctly evaluate the sample, where we observed large variations, with reader B attaining a sensitivity of 82.61% with a corresponding specificity of 86.96%.

CONCLUSION

A simpler enrichment protocol can be used from smaller blood samples to attain detection efficiencies which are similar to or superior to current noninvasive methods.

Enrichment, identification and analysis of fetal cells from maternal blood: evaluation of a prenatal diagnosis system

In this study we evaluated the performance of a system for the enrichment, identification and analysis of fetal cells in maternal peripheral blood. Blood samples were collected from women after chorionic villus sampling and enriched for the presence of nucleated erythrocytes using a three-step procedure, namely: (a) centrifugation to separate nucleated red blood cells (NRBCs) from the majority of red blood cells (RBCs) and white blood cells (WBCs); (b) selective lysis of the remaining maternal RBCs; (c) separating the NRBCs from the remaining WBCs in a three-layer density gradient. Fetal cells were identified by using a monoclonal antibody against the gamma-chain of fetal haemoglobin (anti-HbF) and a nuclear stain (DAPI). Additionally, to further increase the specificity of the identification, and to eliminate some of the undesired staining by maternal leukocytes, a fluorescent antibody (CD45) was added. The sex chromosome complement of the cells was determined by fluorescence in situ hybridization (FISH) with X and Y-specific probes and the results were compared with the karyotypes obtained after analysis of chorionic villi. Using the described method, in all cases where the woman was carrying a male fetus (n=18) at least one XY cell was found, while no male cells were found in women carrying a female fetus. However, in the majority of cases with a male fetus (n=11) female HbF positive cells were found indicating the presence of maternal nucleated erythrocytes. The study demonstrates that the combination of anti-HbF and CD45 is a useful, but not fully specific, marker for fetal NRBCs and that additional markers are needed.