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

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.

Reliable detection of subchromosomal deletions and duplications using cell-based noninvasive prenatal testing

Objective

To gather additional data on the ability to detect subchromosomal abnormalities of various sizes in single fetal cells isolated from maternal blood, using low‐coverage shotgun next‐generation sequencing for cell‐based noninvasive prenatal testing (NIPT).

Method

Fetal trophoblasts were recovered from approximately 30 mL of maternal blood using maternal white blood cell depletion, density‐based cell separation, immunofluorescence staining, and high‐resolution scanning. These trophoblastic cells were picked as single cells and underwent whole genome amplification for subsequent genome‐wide copy number analysis and genotyping to confirm the fetal origin of the cells.

Results

Applying our fetal cell isolation method to a series of 125 maternal blood samples, we detected on average 4.17 putative fetal cells/sample. The series included 15 cases with clinically diagnosed fetal aneuploidies and five cases with subchromosomal abnormalities. This method was capable of detecting findings that were 1 to 2 Mb in size, and all were concordant with the microarray or karyotype data obtained on a fetal sample. A minority of fetal cells showed evidence of genome degradation likely related to apoptosis.

Conclusion

We demonstrate that this cell‐based NIPT method has the capacity to reliably diagnose fetal chromosomal abnormalities down to 1 to 2 Mb in size.

What is already known about this topic?

Fetal trophoblastic cells can be isolated from maternal blood and be used for the detection of fetal aneuploidies and copy number variants. The data on the detection of subchromosomal deletions and duplications is currently limited.

What does this study add?

Cell‐based NIPT can be used for the detection of copy number abnormalities of greater than or equal to 1 Mb in the fetus by low‐coverage next‐generation sequencing after single cell whole genome amplification. Data are provided here for five cases in which different subchromosomal deletions and duplications ranging from 1.2 to 18.9 Mb were detected in single cells.

Biology of human primitive erythroblasts for application in noninvasive prenatal diagnosis

OBJECTIVE

Human primitive erythroblasts produced during early embryogenesis have been found in maternal circulation at early gestation and are considered good target cells for noninvasive prenatal diagnosis. We aimed to gain a better understanding of the biology of primitive erythroblasts and maximize their potential utility for noninvasive prenatal diagnosis.

METHODS

Cells were obtained from first trimester human placental tissues. Biological properties including surface antigen composition, differentiation, proliferation, enucleation, and degeneration were studied as gestation progressed. A microdroplet culture system was developed to observe the behavior of these cells in vitro.

RESULTS

Histology showed that primitive erythroblasts undergo maturation from polychromatic to orthochromatic erythroblasts and can differentiate spontaneously in vitro. Cell surface markers and nuclear gene expression suggest that the cells do not possess stemness properties, despite being primitive in nature. They have limited proliferative activity and highly deacetylated chromatin, but a microdroplet culture system can prolong their viability under normoxic conditions. No apoptosis was seen by 11 weeks' gestation, and there was no enucleation in vitro.

CONCLUSION

These properties confirm that viable cells with intact nuclei can be obtained at very early gestation for genetic analysis.

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.

The Fetal Erythroblast Is Not the Optimal Target for Non-invasive Prenatal Diagnosis: Preliminary Results

Fetal cells, present in the blood of pregnant women, are potential targets for non-invasive prenatal diagnosis. The fetal erythroblast has been the favorite target cell type. We investigated four methods of enrichment for fetal erythroblasts, identifying only three fetal erythroblasts in 573 ml of maternal blood. This is much less than the expected two to six fetal cells per ml of maternal blood. Hamada and Krabchi used a cell type-independent marker, i.e., the Y chromosome in maternal blood from male pregnancies after Carnoy fixation, leaving the nuclei for hybridization with X-and Y-chromosome-specific probes. We found with a similar technique 28 fetal cells in 15 ml of maternal blood. The fetal origin of cells was confirmed by hybridizing the nuclei with X- and Y-chromosome-specific probes, using two consecutive hybridizations with the two probes in opposite colors (reverse FISH). Candidate fetal cells were inspected after each hybridization. Only cells that were found to change the color of both probe signals from first to second hybridization were diagnosed as fetal. To reduce the labor-intensive slide screening load, we used semi-automated scanning microscopy to search for candidate cells. We conclude that erythroblasts form only a small fraction of fetal cells present in maternal blood.

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 Number of Endovascular Trophoblasts in Maternal Blood Increases Overnight and after Physical Activity: An Experimental Study

INTRODUCTION

Fetal cells in maternal blood may be used for noninvasive prenatal diagnostics, although their low number is a challenge. This study's objectives were to evaluate whether physical activity, transabdominal and transvaginal ultrasound scans of the uterus, as well as overnight or day-to-day variation affect the number of isolated fetal cells, more specifically the presumed endovascular trophoblast (pEVT).

MATERIAL AND METHODS

In each of 3 different experiments, 10 normal singleton pregnant women (gestational age 10+4-14+4 weeks) participated. The number of pEVTs was assessed in 30-36 ml blood using specific markers for enrichment and identification.

RESULTS

The number of pEVTs increased overnight (p = 0.001) from a median of 1.5 to 3.5 and even further to a median of 6.0 after 30 min of physical activity (p = 0.04) but was not affected by transabdominal and transvaginal ultrasound scans. Repeated sampling showed that the interindividual variation of pEVTs was higher than the intraindividual variation (p < 0.001). However, even in pregnant women with a consistently low number of pEVTs, isolation of the pEVTs for prenatal diagnoses was possible in all cases by doing 2 separate blood samplings a few days apart.

DISCUSSION

The number of pEVTs identified in maternal blood can be increased by presampling conditions or repeated sampling.

Fetal gender and several cytokines are associated with the number of fetal cells in maternal blood--an observational study

Objective

To identify factors influencing the number of fetal cells in maternal blood.

Methods

A total of 57 pregnant women at a gestational age of weeks 11–14 were included. The number of fetal cells in maternal blood was assessed in 30 ml of blood using specific markers for both enrichment and subsequent identification.

Results

Participants carrying male fetuses had a higher median number of fetal cells in maternal blood than those carrying female fetuses (5 vs. 3, p = 0.04). Certain cytokines (RANTES, IL-2 and IL-5) were significantly associated with the number of fetal cells in maternal blood.

Conclusion

The number of fetal cells in maternal blood is associated with certain cytokines and fetal gender.

Membrane proteins of human fetal primitive nucleated red blood cells

In humans, primitive fetal nucleated red blood cells (FNRBCs) are thought to be as vital for embryonic life as their counterpart, adult red blood cells (adult RBCs) are in later-gestation fetuses and adults. Unlike adult RBCs, the identity and functions of FNRBC proteins are poorly understood owing to a scarcity of FNRBCs for proteomic investigations. The study aimed to investigate membrane proteins of this unique cell type. We present here, the first report on the membrane proteome of human primitive FNRBCs investigated by two-dimensional liquid chromatography coupled with mass-spectrometry (2D-LCMS/MS) and bioinformatics analysis. A total of 273 proteins were identified, of which 133 (48.7%) were membrane proteins. We compared our data with membrane proteins of adult RBCs to identify common, and unique, surface membrane proteins. Twelve plasma membrane proteins with transmembrane domains and eight proteins with transmembrane domains but without known sub-cellular location were identified as unique-to-FNRBCs. Except for the transferrin receptor, all other 19 unique-to-FNRBC membrane proteins have never been described in RBCs. Reverse-transcriptase PCR (RT-PCR) and immunocytochemistry validated the 2D-LCMS/MS data. Our findings provide potential surface antigens for separation of primitive FNRBCs from maternal blood for noninvasive prenatal diagnosis, and to understand the biology of these rare cells.

Identification of circulating fetal cell markers by microarray analysis

OBJECTIVE

Different fetal cell types have been found in the maternal blood during pregnancy in the past, but fetal cells are scarce, and the proportions of the different cell types are unclear. The objective of the present study was to identify specific fetal cell markers from fetal cells found in the maternal blood circulation at the end of the first trimester.

METHOD

Twenty-three fetal cells were isolated from maternal blood by removing the red blood cells by lysis or combining this with removal of large proportions of maternal white blood cells by magnetic-activated cell sorting. Fetal cells identified by XY fluorescence in situ hybridization and confirmed by reverse-color fluorescence in situ hybridization were shot off microscope slides by laser capture microdissection. The expression pattern of a subset of expressed genes was compared between fetal cells and maternal blood cells using stem cell microarray analysis.

RESULTS

Twenty-eight genes were identified as fetal cell marker candidates.

CONCLUSION

Of the 28 fetal marker candidate genes, five coded for proteins, which are located on the outer surface of the cell membrane and not expressed in blood. The protein product of these five genes, MMP14, MCAM, KCNQ4, CLDN6, and F3, may be used as markers for fetal cell enrichment.

Selection of antibodies against a single rare cell present in a heterogeneous population using phage display

Here we describe a new method applying phage-displayed antibody libraries to the selection of antibodies against a single identified cell on a glass slide. This is the only described method that has successfully achieved selection of antibodies against a single rare cell in a heterogeneous population of cells. The phage library is incubated with the slide containing the identified rare cell of interest; incubation is followed by UV irradiation while protecting the target cell with a minute disc. The UV light inactivates all phages outside the shielded area by cross-linking the DNA constituting their genomes. The expected yield is between one and ten phage particles from a single cell selection. The encoded antibodies are subsequently produced monoclonally and tested for specificity. This method can be applied within a week to carry out ten or more individual cell selections. Including subsequent testing of antibody specificity, a specific antibody can be identified within 2 months.

Epsilon haemoglobin specific antibodies with applications in noninvasive prenatal diagnosis

Invasive procedures for prenatal diagnosis are associated with increased risk of abortion; thus, development of noninvasive procedures would be beneficial. Based on the observation that embryonic nucleated red blood cell (NRBC) crosses the placenta and enters the circulation of pregnant women, the ability to identify such cell would allow development of such procedures. Identification of NRBCs in blood samples would be possible provided that specific antibodies are available. Here we have isolated recombinant antibodies using phage display. From the panel of antibody fragments specifically recognising epsilon-Hb, one was chosen for further characterization, DAb1. DAb1 binds to epsilon-Hb both in Western blots and immunocytochemistry. Several epsilon-Hb positive cells were detected in a blood sample taken as postchorionic villus sampling (CVS). To evaluate the sensitivity of the method, K562 cells (which express epsilon-Hb) were spiked in a blood sample followed by staining in solution and FACS analysis.

The placenta theory and the origin of infantile hemangioma

The pathogenesis of infantile hemangioma is unknown. In recent years, much of the focus has been placed at identifying the cell type(s) responsible for tumor initiation. New discoveries in infantile hemangioma suggest an involvement of progenitor cells in the pathogenesis of this vascular tumor. Both embryonic and extra-embryonic tissues have been postulated as potential sources for these progenitor cells. This review focuses on the placental theory, which proposes that a fetal placental progenitor is the cell type of origin for infantile hemangioma. Special emphasis will be placed on placental vasculogenesis and the presence and transit of placental progenitor cells during gestation.