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

Isolation and Enrichment of Circulating Fetal Cells for NIPD: An Overview

Prenatal diagnosis plays a crucial role in clinical genetics. Non-invasive prenatal diagnosis using fetal cells circulating in maternal peripheral blood has become the goal of prenatal diagnosis, to obtain complete fetal genetic information and avoid risks to mother and fetus. The development of high-efficiency separation technologies is necessary to obtain the scarce fetal cells from the maternal circulation. Over the years, multiple approaches have been applied, including choice of the ideal cell targets, different cell recovering technologies, and refined cell isolation yield procedures. In order to provide a useful tool and to give insights about limitations and advantages of the technologies available today, we review the genetic research on the creation and validation of non-invasive prenatal diagnostic testing protocols based on the rare and labile circulating fetal cells during pregnancy.

Overview and recent developments in cell-based noninvasive prenatal testing

Investigators have long been interested in the natural phenomenon of fetal and placental cell trafficking into the maternal circulation. The scarcity of these circulating cells makes their detection and isolation technically challenging. However, as a DNA source of fetal origin not mixed with maternal DNA, they have the potential of considerable benefit over circulating cell-free DNA-based noninvasive prenatal genetic testing (NIPT). Endocervical trophoblasts, which are less rare but more challenging to recover are also being investigated as an approach for cell-based NIPT. We review published studies from around the world describing both forms of cell-based NIPT and highlight the different approaches' advantages and drawbacks. We also offer guidance for developing a sound cell-based NIPT protocol.

Non-invasive prenatal screening: A 20-year experience in Italy

Over the past two decades, there has been a rapid evolution in prenatal screening for fetal chromosome abnormalities. Initially, testing was focused on the identification of affected pregnancies in either the first, or, the second trimester (e.g. the Combined test or the triple test). This was replaced by sequential modalities (e.g. contingent screening) that have enhanced detection while reducing the need for invasive testing. More recently, the introduction of technologies based on cell-free DNA (cfDNA) in maternal plasma and enrichment of fetal cells in maternal circulation have further refined the concept of sequential screening. In this review, we document our experience with serum and ultrasound-based contingent screening where we were able to achieve a detection rate of 96.8%, a false-positive rate of 2.8% and an odds of being affected given a positive result of 1:11. We also describe our initial experience with a novel sequential protocol that includes the analysis of fetal cells in maternal blood. Methods for enrichment for fetal cells cfDNA and cfDNA technologies offer the possibility of greater sensitivity and specificity as well as expansion in the scope of genetic disorders detectable. As costs decline, these technologies will become increasingly used as primary screening tools. In the meantime, sequential use offers a practical approach to maximizing the benefits of prenatal testing.

Genome-wide copy number analysis on DNA from fetal cells isolated from the blood of pregnant women

OBJECTIVE

Non-invasive prenatal testing (NIPT) based on fetal cells in maternal blood has the advantage over NIPT based on circulating cell-free fetal DNA in that there is no contamination with maternal DNA. This will most likely result in better detection of chromosomal aberrations including subchromosomal defects. The objective of this study was to test whether fetal cells enriched from maternal blood can be used for cell-based NIPT.

METHODS

We present a method for enriching fetal cells from maternal blood, subsequent amplification of the fetal genome and detection of chromosomal and subchromosomal variations in the genome.

RESULTS

An average of 12.8 fetal cells from 30 mL of maternal blood were recovered using our method. Subsequently, whole genome amplification on fetal cells resulted in amplified fetal DNA in amounts and quality high enough to generate array comparative genomic hybridization as well as next-generation sequencing profiles. From one to two fetal cells, we were able to demonstrate copy number differences of whole chromosomes (21, X-, and Y) as well as subchromosomal aberrations (ring X).

CONCLUSION

Intact fetal cells can be isolated from every maternal blood sample. Amplified DNA from isolated fetal cells enabled genetic analysis by array comparative genomic hybridization and next-generation sequencing. © 2016 John Wiley & Sons, Ltd.

Aneuploidy screening using circulating fetal cells in maternal blood by dual-probe FISH protocol: a prospective feasibility study on a series of 172 pregnant women

BACKGROUND

A long sought goal in medical genetics has been the replacement of invasive procedures for the detection of chromosomal aneuploidies by isolating and analyzing fetal cells or free fetal DNA from maternal blood, avoiding risk to the fetus. However, a rapid, simple, consistent, and low-cost procedure suitable for routine clinical practice has not yet been achieved. The purpose of this study was to assess the feasibility of predicting fetal aneuploidy by applying our recently established dual-probe FISH protocol to fetal cells isolated and enriched from maternal blood.

METHODS

A total of 172 pregnant women underwent prospective testing for fetal aneuploidy by FISH analysis of fetal cells isolated from maternal blood. Results were compared with the karyotype determined through invasive procedures or at birth.

RESULTS

Seven of the samples exhibited fetal aneuploidy, which was confirmed by invasive prenatal diagnosis procedures. After enrichment for fetal cells, the frequency of trisomic cells was at least double in samples from aneuploid pregnancies (range 0.38-0.90%) compared to samples from normal pregnancies (≤0.18%). One false negative result was also obtained.

CONCLUSIONS

Noninvasive prenatal aneuploidy screening using fetal cells isolated from maternal blood is feasible and could substantially reduce the need for invasive procedures.

Practicability of prenatal testing using lectin-based enrichment of fetal erythroblasts

AIM

The aim of this study was to investigate the practicability and efficiency of lectin-based isolation of fetal erythroblasts for clinical use in non-invasive prenatal testing.

METHODS

Peripheral blood samples were collected from 39 pregnant women. Leukocytes were removed with an anti-CD45 antibody after density gradient centrifugation. After blood cells were attached to slides by binding to a galactose-specific lectin and galactose-bound vinyl polymer, the slides were stained with May-Grünwald-Giemsa stain and cells were classified by automated image analysis based on their size and the nuclear area/cytoplasmic area ratio. In 14 samples from the women with male fetuses, fetal origin of the isolated erythroblasts was confirmed by detecting the Y chromosome using fluorescence in situ hybridization. In eight samples, single erythroblasts were collected by the laser capture microdissection technique for amplification of the sex-determining region Y gene to confirm fetal origin.

RESULTS

Panning with an anti-CD45 antibody achieved stable removal of leukocytes without aggregation. In all samples, erythroblasts were successfully identified by automated image analysis (18-6000/10 mL of blood). The number of slides required to examine 10 mL of blood ranged from one to six, which was reasonable for clinical use. The Y chromosome was detected in 7.5-43.6% of erythroblasts by fluorescence in situ hybridization, and the sex-determining region Y gene was amplified in seven of eight samples.

CONCLUSION

The combination of lectin-based erythroblast isolation and automated image analysis is a practical and efficient method for isolating fetal erythroblasts as a source of fetal genomes.

The promise of fetal cells in maternal blood

Delaying childbirth increases the proportion of advanced maternal age pregnancies. This increases the number of pregnancies requiring invasive prenatal testing. Prenatal diagnosis of chromosomal aneuploidies and monogenic disorders requires fetal cells obtained through invasive procedures (i.e. chorionic villus sampling and amniocentesis). These procedures carry a risk of fetal loss, which causes anxiety to at-risk couples. Intact fetal cells entering maternal circulation have raised the possibility of non-invasive prenatal diagnosis. Rarity of fetal cells, however, has made it challenging. Fetal nucleated red blood cells are ideal candidate target cells because they have limited lifespan, contain true representation of fetal genotype, contain specific fetal cell identifiers (embryonic and fetal globins), and allow interrogation with chromosomal fluorescence in-situ hybridisation and possibly with array comparative genomic hybridisation. The utility of fetal nucleated red blood cells in non-invasive prenatal diagnosis has not reached clinical application because of the inconsistencies in enrichment strategies and rarity of cells.

Efficiency of manual scanning in recovering rare cellular events identified by fluorescence in situ hybridization: simulation of the detection of fetal cells in maternal blood

Fluorescence in situ hybridization (FISH) and manual scanning is a widely used strategy for retrieving rare cellular events such as fetal cells in maternal blood. In order to determine the efficiency of these techniques in detection of rare cells, slides of XX cells with predefined numbers (1–10) of XY cells were prepared. Following FISH hybridization, the slides were scanned blindly for the presence of XY cells by different observers. The average detection efficiency was 84% (125/148). Evaluation of probe hybridization in the missed events showed that 9% (2/23) were not hybridized, 17% (4/23) were poorly hybridized, while the hybridization was adequate for the remaining 74% (17/23). In conclusion, manual scanning is a relatively efficient method to recover rare cellular events, but about 16% of the events are missed; therefore, the number of fetal cells per unit volume of maternal blood has probably been underestimated when using manual scanning.

Detection of chromosomal aneuploidies in fetal cells isolated from maternal blood using single-chromosome dual-probe FISH analysis

Detection of chromosomal aneuploidies using fetal cells isolated from maternal blood, for prenatal non-invasive genetic investigation, has been a long-sought goal of clinical genetics to replace amniocentesis and chorionic villous sampling to avoid any risk to the fetus. The purpose of this study was to develop a sensitive and specific new assay for diagnosing aneuploidy with circulating fetal cells isolated from maternal blood as previously reported using two novel approaches: (i) simultaneous immunocytochemistry (ICC) evaluation using a monoclonal antibody for i-antigen, followed by fluorescence in situ hybridization (FISH); (ii) dual-probe FISH analysis of interphase nuclei using two differently labeled probes, specific for different loci of chromosomes 21 and 18; in addition, short tandem repeats (STR) analysis on single cells isolated by micromanipulation was applied to confirm the presence of fetal cells in the cell sample enriched from maternal blood. Blood samples were obtained from women carrying trisomic fetuses, and from non-pregnant women and men as controls. Using ICC-FISH approach, a large heterogeneity in immunostaining pattern was observed, which is a source of very subjective signal interpretation. Differently, dual-probe FISH analysis provided for a correct diagnosis of all pregnancies: the mean percentage of trisomic cells was 0.5% (range, 0.36-0.76%), while the mean percentage of trisomic cells in the control group (normal pregnancies or non-pregnant women) was ≤0.20%. The application of the dual-probe FISH protocol on fetal cells isolated from maternal blood enables accurate molecular detection of fetal aneuploidy, thus providing a foundation for development of non-invasive prenatal diagnostic testing.

Fetal-maternal exchange of multipotent stem/progenitor cells: microchimerism in diagnosis and disease

The biological concept of microchimerism, the bidirectional trafficking and stable long-term persistence of small numbers of allogeneic (fetal and maternal) cells in a genetically different organ, has gained considerable attention. Microchimerism is a common phenomenon in many species, including humans, and microchimeric cells can modify immunological recognition or tolerance, affect the course and outcome of various diseases and demonstrate stem cell-like or regenerative potential. Here, we review current knowledge of the biology of microchimerism and show how long-term allogeneic co-existence within an organism can impact on existing paradigms in chronic disease, cancer biology, regenerative medicine and fetal-maternal immunology. We discuss diagnostic challenges, clinical applications and future research directions in this exciting and rapidly emerging field of allogeneic fetal-maternal cell exchange.

Assessment of the female fetal DNA concentration in the plasma of the pregnant women as preeclampsia indicator--preliminary report

OBJECTIVES

This research was designed to analyze the presence of fetal female DNA, expressed in copy number, in the plasma of the pregnant woman with preeclampsia-complicated pregnancy.

STUDY DESIGN

Twenty-four pregnant women with female fetuses identified by means of ultrasound scanning were enrolled in this pilot study. The study group consisted of 12 pregnant women with symptoms of preeclampsia, with 12 healthy women, matched for gestational age, as controls.

RESULTS

Mean DNA number of genomic equivalents per reaction in the group was 201 geq/PCR (from 44.9 to 375) and increased over time after onset of PE, which was the reason for pregnancy termination. In the group of women with preeclampsia, a notably higher DNA copy number in comparison to the control group was noted (p=0.0003 U Mann-Whitney test).

CONCLUSIONS

The pilot study presented in this work confirms that also in the case of preeclampsia-complicated pregnancy with female fetuses it is possible to implement the method of fetal DNA quantification. Use of the presented methods confirms that in severe preeclampsia-complicated pregnancies an increase of the number of DNA genomic equivalents per reaction in comparison to the control group is observed. Due to the small study group further research on the described issue is vital, but this study proves that it is also feasible among women carrying female fetuses.

Persistence of male hematopoietic CD34+ cells in the circulation of women does not affect prenatal diagnostic techniques

OBJECTIVE

We aimed to verify whether fetal microchimerism, because of persisting fetal hematopoietic CD34(+) cells from previous pregnancies, could interfere with the development of genetic tests based on using these cells, isolated from maternal blood for the diagnosis of fetal aneuploidies.

STUDY DESIGN

CD34(+) cells, isolated from blood of parous women with at least 1 son and nulliparous women, were analyzed by using qualitative polymerase chain reaction (PCR), quantitative PCR, and fluorescence in situ hybridization (FISH) to establish whether these molecular techniques are concurrently capable of detecting circulating male DNA.

RESULTS

By qualitative PCR, male DNA was found both in parous and nulliparous women, whereas by quantitative PCR and FISH analyses, no male DNA or male nuclei were revealed except in 1 cultured CD34(+) sample from a nulliparous woman.

CONCLUSION

Fetal hematopoietic CD34(+) cells can be used in the noninvasive prenatal testing of fetal aneuploidies because the presence of fetal microchimerism does not affect fetal diagnosis in current pregnancies.

A microfluidics approach for the isolation of nucleated red blood cells (NRBCs) from the peripheral blood of pregnant women

OBJECTIVE

Nucleated red blood cells (NRBCs) have been identified in maternal circulation and potentially provide a resource for the monitoring and diagnosis of maternal, fetal, and neonatal health and disease. Past strategies used to isolate and enrich for NRBCs are limited to complex approaches that result in low recovery and less than optimal cell purity. Here we report the development of a high-throughput and highly efficient microfluidic device for isolating rare NRBCs from maternal blood.

MATERIAL AND METHODS

NRBCs were isolated from the peripheral blood of 58 pregnant women using a microfluidic process that consists of a microfluidic chip for size-based cell separation and a magnetic device for hemoglobin-based cell isolation.

RESULTS

The microfluidic-magnetic combination removes nontarget red blood cells and white blood cells at a very high efficiency (approximately 99.99%). The device successfully identified NRBCs from the peripheral blood of 58/58 pre-termination samples with a mean of 37.44 NRBC/mL (range 0.37-274.36 NRBC/mL). These results were compared with those from previous studies.

CONCLUSION

The microfluidic device results in an approximate 10- to 20-fold enrichment of NRBCs over methods described previously. The reliability of isolation and the purity of the NRBC product have the potential to enable the subsequent application of molecular diagnostic assays.

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.