Transcervical retrieval of fetal cells in the practice of modern medicine: a review of the current literature and future direction

Cell-based Noninvasive Prenatal Testing (cbNIPT)-A Review on the Current Developments and Future Prospects

Considering the diagnostic limitations of cfDNA-based noninvasive prenatal testing (NIPT), scientists have long been interested in isolating and analyzing rare intact fetal and trophoblast cells from maternal blood or endocervical samples to diagnose fetal genetic conditions. These cells may be scarce and difficult to isolate, but they are a direct source of pure fetal genetic material. In this review, we summarize the history of cell-based NIPT, present an updated review on its current developments, evaluate its genetic diagnostic potential, and discuss its future prospects for clinical use.

A Novel Paradigm for Non-Invasive Prenatal Genetic Screening: Trophoblast Retrieval and Isolation from the Cervix (TRIC)

As the prevalence of pregnancies with advanced maternal age increases, the risk of fetal chromosomal abnormalities is on the rise. Therefore, prenatal genetic screening and diagnosis have become essential elements in contemporary obstetrical care. Trophoblast retrieval and isolation from the cervix (TRIC) is a non-invasive procedure that can be utilized for prenatal genetic diagnosis. The method involves the isolation of fetal cells (extravillous trophoblasts) by transcervical sampling; along with its non-invasiveness, TRIC exhibits many other advantages such as its usefulness in early pregnancy at 5 weeks of gestation, and no interference by various fetal and maternal factors. Moreover, the trophoblast yields from TRIC can provide valuable information about obstetrical complications related to abnormal placentation even before clinical symptoms arise. The standardization of this clinical tool is still under investigation, and the upcoming advancements in TRIC are expected to meet the increasing need for a safe and accurate option for prenatal diagnosis.

Genetics in prenatal diagnosis

The options for prenatal genetic testing have evolved rapidly in the past decade, and advances in sequencing technology now allow genetic diagnoses to be made down to the single-base-pair level, even before the birth of the child. This offers women the opportunity to obtain information regarding the foetus, thereby empowering them to make informed decisions about their pregnancy. As genetic testing becomes increasingly available to women, clinician knowledge and awareness of the options available to women is of great importance. Additionally, comprehensive pretest and posttest genetic counselling about the advantages, pitfalls and limitations of genetic testing should be provided to all women. This review article aims to cover the range of genetic tests currently available in prenatal screening and diagnosis, their current applications and limitations in clinical practice as well as what the future holds for prenatal genetics.

Noninvasive isolation of transcervical trophoblast cells for fetal identification

OBJECTIVE

To identify trophoblastic cells retrieved from the cervix at a gestational age (GA) of 5-9 weeks by a noninvasive modality in fetuses.

METHOD

Transcervical cells (TCCs) were noninvasively extracted by a cytobrush using the Papanicolaou sampling method. TCCs were immunostained with antihuman leukocyte antigen (HLA)-G and anticytokeratin (CK)-7 antibodies to identify trophoblastic cells. Maternal finger blood, gestational sacs, and 20 trophoblastic cells collected by a laser-guided microscopic single-cell capture system were examined and compared by short tandem repeat (STR) genotyping.

RESULTS

Forty-nine pregnant women with GA of 5-9 weeks and six nonpregnant healthy women were included in the study. Trophoblastic cells were identified in 37 (75.5%) TCC samples, among which 34 (69.4%) were eligible for STR genotyping analysis. No trophoblastic cells were identified in nonpregnant healthy women. The STR genotyping analyses revealed 24 female and 10 male fetuses. TCC trophoblastic cells exhibited the same STR profiles as gestational sac and maternal blood in all samples, which indicated that the TCC trophoblastic cells originated from fetuses.

CONCLUSION

This primary study validated that trophoblastic cells from TCCs at GA 5-9 weeks originated from the fetus. Further studies are needed to verify whether this method can be used for early noninvasive prenatal diagnosis and paternity testing.

Isolation of HLA-G+ cells using MEM-G/9 antibody-conjugated magnetic nanoparticles for prenatal screening: a reliable, fast and efficient method

The development of an effective and noninvasive early method for obtaining fetal cells is crucial to prenatal screening. Despite proving the presence of fetal cells in the reproductive tract, their use is limited due to their inability to properly isolate them from maternal cells. Magnetic-activated cell sorting (MACS) is a simple technique to separate cells. The present study aimed to develop a MACS-based platform for the isolation of the HLA-G expressing trophoblast cells. For this purpose, first, the triazine functionalized MNPs were synthesized and characterized. Then, MNPs were directly and indirectly conjugated by the MEM-G/9 antibodies targeting HLA-G+ cells. The antibody amount on the surface of the nanoparticles was determined with the Bradford assay. The cell capture efficiency was also investigated. Various characterization methods confirmed the successful nanoparticle synthesis and antibody conjugation. The optimal initial antibody amount for the immobilization was about 20 μg and the optimal time was 3 h. The antibody-nanoparticles by the indirect method had better targeting and capture efficiency than the direct method. The MNPs indirectly conjugated with antibodies are an efficient tool for cell isolation and present considerable potential to be applied in biomedical fields.

Appropriate fixative for MEM-G/9 staining of cultured human HLA-G-positive JEG-3 trophoblast tumor cells

Human leukocyte antigen (HLA-G) participates in immunosuppression and is useful for prenatal diagnostics. Isolation of fetal cells positive for HLA-G by HLA-G antibody conjugated nanoparticles from the cervix of pregnant women is the basis for non-invasive prenatal testing. Endocervical specimens are fixed in transport medium before isolation using antibody conjugated nanoparticles. Staining of HLA-G using MEM-G/9 antibody, however, is restricted to unfixed cells. We investigated the effect of several fixatives on the interaction of HLA-G with MEM-G/9 in the HLA-G-positive cell line, JEG-3. We investigated absolute methanol, 1:1 acetate buffer:methanol, Pap solution and paraformaldehyde. The effects of these fixatives were evaluated using immunofluorescence. We found no MEM-G/9 surface staining of methanol fixed cells. Approximately 40% of JEG-3 cells fixed with paraformaldehyde failed to stain. Nearly all cells were stained with MEM-G/9 following fixation with acetate buffer:methanol or Pap solution. Our findings indicate the importance of using an appropriate fixative for preserving HLA-G cell surface antigen for studies using the MEM-G/9 antibody.

Enrichment of Placental Trophoblast Cells from Clinical Cervical Samples Using Differences in Surface Adhesion on an Inclined Plane

Placental trophoblast cells present in cervical samples have great potential towards non-invasive prenatal testing. However, cervical samples are highly heterogeneous, largely comprised of maternal cervical cells with only a small quantity of trophoblast cells. In order to use these rare cells for diagnostic applications, there is a need to enrich and isolate them from the heterogeneous maternal sample. Our goal was to investigate the use of gravitational flow on an inclined surface and optimize parameters including angle of incline, surface material, incubation time on the surface, solution volume, and device channel width in order to identify a design allowing label-free enrichment of trophoblast cells. In this work we detail the development of a new method and device for controlling cell adhesion to a surface vs. rolling into a collection area. The enrichment device design was developed for ease of use by non-specialized personal and on a slide surface for the ability to be directly integrated onto an automatic cell picker instrument, which can be used for downstream single cell isolation. JEG-3 trophoblast cells were used with clinical cervical samples to present the effect of the different optimization parameters on enrichment. We further provide an assessment of the impact shear stress and thickness of the liquid layer has on cell enrichment. We found that this method provides a maximum JEG-3 enrichment using polystyrene surfaces at a 50° incline with a 5 min incubation period prior to inclined flow. This resulted in a 396 ± 52% increase in purity of the trophoblast cells from the clinical cervical samples as confirmed using human leukocyte antigen G (HLA-G) antibody staining with fluorescence imaging to identify JEG-3 cells. Ultimately, this method is inexpensive, quick, and has the potential for direct integration into fetal cell isolation platforms.

Optimization Protocol of Fixation Method for Trophoblast Retrieval from the Cervix (TRIC): A Preliminary Study

Extravillous trophoblast cells (EVTs) secreted by the uterine cavity may help overcome limitations associated with prenatal testing currently in use. EVTs are isolated using a routine safe liquid-based Pap test (called ThinPrep); however, the ThinPrep solution contains alcohol that hinders the isolation of intact EVTs. We compared the trophoblastic cell isolation efficiency of two different methods of fixation: Thinprep (pre-fixation method) and formalin (post-fixation method). We analyzed EVTs from 20 pregnant women (5-20 weeks of gestation) who underwent invasive prenatal testing. The percentages of placental β-human chorionic gonadotropin (β-hCG)-expressing cells were calculated. The presence of XY chromosomes were used to confirm pure trophoblast cells by fluorescence in situ hybridization. The β-hCG-positive cells obtained from pre- and post-fixation were 66.4 ± 13.3% and 83.2 ± 8.1% (p = 0.003), respectively, and fluorescence-positive cells were 11.1 ± 2.1% and 23.8 ± 4.8%, respectively (p = 0.001). Post-fixation was found to be more efficient in isolating non-trophoblast cells than pre-fixation. For the successful clinical application of trophoblast retrieval and isolation from the cervix in prenatal genetic testing, each step should be optimized for consistent and reliable results.

Endocervical trophoblast for interrogating the fetal genome and assessing pregnancy health at five weeks

Prenatal testing for fetal genetic traits and risk of obstetrical complications is essential for maternal-fetal healthcare. The migration of extravillous trophoblast (EVT) cells from the placenta into the reproductive tract and accumulation in the cervix offers an exciting avenue for prenatal testing and monitoring placental function. These cells are obtained with a cervical cytobrush, a routine relatively safe clinical procedure during pregnancy, according to published studies and our own observations. Trophoblast retrieval and isolation from the cervix (TRIC) obtains hundreds of fetal cells with >90% purity as early as five weeks of gestation. TRIC can provide DNA for fetal genotyping by targeted next-generation sequencing with single-nucleotide resolution. Previously, we found that known protein biomarkers are dysregulated in EVT cells obtained by TRIC in the first trimester from women who miscarry or later develop intrauterine growth restriction or preeclampsia. We have now optimized methods to stabilize RNA during TRIC for subsequent isolation and analysis of trophoblast gene expression. Here, we report transcriptomics analysis demonstrating that the expression profile of TRIC-isolated trophoblast cells was distinct from that of maternal cervical cells and included genes associated with the EVT phenotype and invasion. Because EVT cells are responsible for remodeling the maternal arteries and their failure is associated with pregnancy disorders, their molecular profiles could reflect maternal risk, as well as mechanisms underlying these disorders. The use of TRIC to analyze EVT genomes, transcriptomes and proteomes during ongoing pregnancies could provide new tools for anticipating and managing both fetal genetic and maternal obstetric disorders.

Noninvasive Prenatal Diagnostics: Recent Developments Using Circulating Fetal Nucleated Cells

PURPOSE OF REVIEW

The purpose of this review is to highlight recent research advances in noninvasive prenatal diagnostic methods.

RECENT FINDINGS

Recent studies developing noninvasive prenatal diagnostic (NIPD) methods have been focused on either fetal nucleated red blood cells (fNRBCs) or circulating trophoblasts (cTBs). Enriched cTBs were successfully utilized for whole genome profiling and short tandem repeat (STR) identification to confirm feto-maternal relationship. However, further analysis of isolated fNRBCs remains confined to examining fetal cytogenetics.

SUMMARY

Invasive prenatal diagnostic procedures, amniocentesis and chorionic villus sampling, are the gold standard for the diagnosis of fetal chromosomal abnormalities and genetic disorders. Meanwhile, noninvasive techniques of analyzing circulating cell-free fetal DNA (cffDNA) have been limited to screening tools and are highly fragmented and confounded by maternal DNA. By detecting circulating fetal nucleated cells (CFNCs) we are able to noninvasively confirm fetal chromosomal abnormalities, truly realizing the concept of "noninvasive prenatal diagnostics". The primary technical challenge is the enrichment of the low abundance of CFNCs in maternal peripheral blood. For any cell-based NIPD method, both fetal whole genome profiling and confirmation of the feto-parental relationship are essential. This has been successfully performed using enriched and isolated cTBs, making cTB a better candidate for NIPD. cTB enumeration also correlates with abnormal fetal or placental development. On the other hand, downstream analysis of fNRBCs remains limited to examining fetal sex and aneuploidies. Furthermore, trophoblast-based NIPD via an endocervical sample is also promising because of reduced dilution from hematologic cells.

Trophoblast retrieval and isolation from the cervix: origins of cervical trophoblasts and their potential value for risk assessment of ongoing pregnancies

BACKGROUND

Early during human development, the trophoblast lineage differentiates to commence placentation. Where the placenta contacts the uterine decidua, extravillous trophoblast (EVT) cells differentiate and invade maternal tissues. EVT cells, identified by expression of HLA-G, invade into uterine blood vessels (endovascular EVT), as well as glands (endoglandular EVT), and open such luminal structures towards the intervillous space of the placenta. Endoglandular invasion diverts the contents of uterine glands to the intervillous space, while glands near the margin of the placenta that also contain endoglandular EVT cells open into the reproductive tract. Cells of the trophoblast lineage have thus been recovered from the uterine cavity and endocervical canal. An emerging non-invasive technology [trophoblast retrieval and isolation from the cervix (TRIC)] isolates and examines EVT cells residing in the cervix to explore their origin, biology and relationship to pregnancy and fetal status.

OBJECTIVE AND RATIONALE

This review explores the origins and possible uses of trophoblast cells obtained during ongoing pregnancies (weeks 5-20) by TRIC. We hypothesize that endoglandular EVT cells at the margins of the expanding placenta enter the uterine cavity and are carried together with uterine secretion products to the cervix where they can be retrieved from a Papanicolaou (Pap) smear. The advantages of TRIC for investigation of human placentation and prenatal testing will be considered. Evidence from the literature, and from archived in utero placental histological sections, is presented to support these hypotheses.

SEARCH METHODS

We used 52 out of 80 publications that appeared between 1966 and 2017 and were found by searching the PubMed and Google Scholar databases. The studies described trophoblast invasion of uterine vessels and glands, as well as trophoblast cells residing in the reproductive tract. This was supplemented with literature on human placental health and disease.

OUTCOMES

The literature describes a variety of invasive routes taken by EVT cells at the fetal-maternal interface that could displace them into the reproductive tract. Since the 1970s, investigators have attempted to recover trophoblast cells from the uterus or cervix for prenatal diagnostics. Trophoblast cells from Pap smears obtained at 5-20 weeks of gestation have been purified (>95% β-hCG positive) by immunomagnetic isolation with nanoparticles linked to anti-HLA-G (TRIC). The isolated cells contain the fetal genome, and have an EVT-like expression profile. Similar EVT-like cells appear in the lumen of uterine glands and can be observed entering the uterine cavity along the margins of the placenta, suggesting that they are the primary source of cervical trophoblast cells. Cells isolated by TRIC can be used to accurately genotype the embryo/fetus by targeted next-generation sequencing. Biomarker protein expression quantified in cervical trophoblast cells after TRIC correlates with subsequent pregnancy loss, pre-eclampsia and fetal growth restriction. A key remaining question is the degree to which EVT cells in the cervix might differ from those in the basal plate and placental bed.

WIDER IMPLICATIONS

TRIC could one day provide a method of risk assessment for maternal and fetal disease, and reveal molecular pathways disrupted during the first trimester in EVT cells associated with placental maldevelopment. As perinatal interventions emerge for pregnancy disorders and inherited congenital disorders, TRIC could provide a key diagnostic tool for personalized precision medicine in obstetrics.

Fetal genome profiling at 5 weeks of gestation after noninvasive isolation of trophoblast cells from the endocervical canal

Single-gene mutations account for more than 6000 diseases, 10% of all pediatric hospital admissions, and 20% of infant deaths. Down syndrome and other aneuploidies occur in more than 0.2% of births worldwide and are on the rise because of advanced reproductive age. Birth defects of genetic origin can be diagnosed in utero after invasive extraction of fetal tissues. Noninvasive testing with circulating cell-free fetal DNA is limited by a low fetal DNA fraction. Both modalities are unavailable until the end of the first trimester. We have isolated intact trophoblast cells from Papanicolaou smears collected noninvasively at 5 to 19 weeks of gestation for next-generation sequencing of fetal DNA. Consecutive matched maternal, placental, and fetal samples (n = 20) were profiled by multiplex targeted DNA sequencing of 59 short tandem repeat and 94 single-nucleotide variant sites across all 24 chromosomes. The data revealed fetal DNA fractions of 85 to 99.9%, with 100% correct fetal haplotyping. This noninvasive platform has the potential to provide comprehensive fetal genomic profiling as early as 5 weeks of gestation.

Quo vadis, trophoblast? Exploring the new ways of an old cell lineage

Trophoblast cells are the first embryonic lineage to differentiate during human development, and are needed to sustain fetal life through their role in constructing a placenta. As the fetus grows, the trophoblast rapidly expands and further differentiates to produce an extravillous subtype that invades the maternal tissues. Some of the extravillous trophoblast cells find their way into the reproductive tract, and can be safely captured by noninvasive collection from the endocervical canal, similarly to a Pap smear. We are developing a new technology for investigating trophoblast cells residing in the cervix to better understand their development, and to glean information from them about pregnancy status. Trophoblast retrieval and isolation from the cervix (TRIC) efficiently isolates hundreds of trophoblast cells without limitations due to early gestational age, maternal obesity, or uteroplacental insufficiency disorders. Cells that appear to be extravillous trophoblast, based on their molecular phenotype, can be purified from Pap smears obtained between 5 and 20 weeks of gestation, using magnetic nanoparticles coupled to an antibody recognizing HLA-G that they specifically produce. Information about fetal genotype and adverse pregnancy outcomes has been obtained using TRIC, and could one day provide assessment of maternal and fetal risk of disease. As perinatal interventions for placental disorders and inherited congenital disorders emerge, TRIC could provide a key diagnostic tool for personalize precision pregnancy management.

Altered Biomarkers in Trophoblast Cells Obtained Noninvasively Prior to Clinical Manifestation of Perinatal Disease

A contributing factor to poor placental perfusion, leading to intrauterine growth restriction and preeclampsia, is the failure of invading extravillous trophoblast (EVT) cells to remodel the maternal uterine arteries during the first and second trimesters of pregnancy. Noninvasive assessment of EVT cells in ongoing pregnancies is possible beginning three weeks after conception, using trophoblast retrieval and isolation from the cervix (TRIC). Seven proteins were semi-quantified by immunofluorescence microscopy in EVT cells obtained between gestational weeks 6 and 20 from pregnancies with normal outcomes (N = 29) and those with intrauterine growth restriction or preeclampsia (N = 12). Significant differences were measured in expression of PAPPA, FLT1, ENG, AFP, PGF, and LGALS14, but not LGALS13 or the lineage marker KRT7. These findings provide for the first time direct evidence of pathology-associated protein dysregulation in EVT cells during early placentation. The TRIC platform provides a novel approach to acquire molecular signatures of EVT cells that can be correlated with pregnancy outcome.

Trophoblast Retrieval and Isolation From the Cervix for Noninvasive, First Trimester, Fetal Gender Determination in a Carrier of Congenital Adrenal Hyperplasia

Congenital adrenal hyperplasia (CAH) is an autosomal recessive defect in cortisol biosynthesis that elevates fetal androgen levels to cause genital ambiguity and external genital masculinization in newborn females. Introducing dexamethasone in utero by 7 weeks gestation precludes virilization of affected females. However, identification of a male fetus prior to week 7 could avert the necessity of steroid treatment in half of pregnancies at risk of CAH. We recently introduced trophoblast retrieval and isolation from the cervix (TRIC), an approach that noninvasively isolate homogeneous trophoblast cells from pregnant women as early as 5 weeks gestation, using a Papanicolaou test. Here, we have used TRIC to correctly identify male fetal DNA when both parents were carriers of the mutation that produces CAH and previously produced an affected child. Trophoblast cells (1400) obtained by TRIC were assessed using immunocytochemistry with an antibody against the trophoblast-specific β subunit of human chorionic gonadotropin, which labeled 100% (17 of 17) of isolated cells, while none of the excluded maternal cervical cells were labeled. The isolated cells were examined by fluorescent in situ hybridization for chromosomes 18, X, and Y at a clinical cytogenetics laboratory, demonstrating 100% (18 of 18) of cells to be diploid 18/XY. Aliquots of DNA obtained from the isolated cells assayed for SRY and RNASEH genes by TaqMan assays confirmed a male fetus. This case study demonstrates the utility of TRIC to accurately identify fetal gender as a means of reducing the need for prophylactic administration of exogenous steroids in pregnancies at risk of CAH.

Trophoblast retrieval and isolation from the cervix (TRIC) is unaffected by early gestational age or maternal obesity

OBJECTIVE

The objective of this study is to evaluate whether trophoblast yield obtained by trophoblast retrieval and isolation from the cervix (TRIC) is affected by pregnancy outcome, gestational age (GA) at retrieval, maternal body mass index (BMI), parity, or maternal age.

METHODS

TRIC was performed on 224 ongoing pregnancies between 5 and 20 weeks of GA. Trophoblast cells were isolated from cervical cells using anti-human leukocyte antigen-G antibody coupled to magnetic nanoparticles. Purity was assessed by the percentage of isolated cells that express β-hCG. Patient records were monitored until delivery, and pregnancy outcomes were determined. Trophoblast yield was compared with GA at time of collection, maternal BMI, parity, maternal age, and outcome of pregnancy, using linear regression.

RESULTS

There was no effect of GA, maternal BMI, parity, and maternal age on trophoblast yield. Trophoblast yield decreased significantly with early pregnancy loss compared with uncomplicated pregnancies that delivered at term. Trophoblast yield with preeclampsia or intrauterine growth restriction was decreased compared with healthy term outcomes; however, they did not reach statistical significance.

CONCLUSIONS

If TRIC becomes available as a method for non-invasive prenatal testing, our data demonstrate that it is unaffected by BMI and is useful as early as 5 weeks of GA.

Noninvasive detection of trophoblast protein signatures linked to early pregnancy loss using trophoblast retrieval and isolation from the cervix (TRIC)

OBJECTIVE

To examine the expression pattern of biomarker proteins in extravillous trophoblast (EVT) cells obtained noninvasively by trophoblast retrieval and isolation from the cervix (TRIC) in patients with early pregnancy loss compared with control patients with uncomplicated term delivery.

DESIGN

Case-control study.

SETTING

Academic medical center.

PATIENT(S)

Women with either early pregnancy loss (EPL, n = 10) or an uncomplicated term delivery (N = 10).

INTERVENTION(S)

Endocervical specimens obtained from ongoing pregnancies at gestational ages of 5-10 weeks to generate an archive of EVT cells isolated by TRIC, with medical records examined to select specimens matched for gestational age at the time of endocervical sampling.

MAIN OUTCOME MEASURE(S)

Known serum biomarkers for adverse pregnancy outcome that are expressed by EVT cells were evaluated by semiquantitative immunocytochemistry, using antibodies against endoglin (ENG), FMS-like tyrosine kinase-1 (FLT-1), α-fetoprotein (AFP), pregnancy-associated plasma protein-A (PAPP-A), galectin-13 (LGALS13), galectin-14 (LGALS14), and placental growth factor (PGF).

RESULT(S)

The EVT purity was over 95% in all specimens, based on chorionic gonadotropin expression; however, the number of EVT cells obtained was significantly lower in women with EPL than the control group. There was a statistically significant elevation of AFP, ENG, and FLT-1, and statistically significant reduction of PAPP-A, LGALS14, and PGF in the EPL group compared with controls.

CONCLUSION(S)

In this pilot study, EVT cells isolated by TRIC early in gestation exhibited altered protein expression patterns before an EPL compared with uncomplicated term pregnancies.

Fetal Cell Based Prenatal Diagnosis: Perspectives on the Present and Future

The ability to capture and analyze fetal cells from maternal circulation or other sources during pregnancy has been a goal of prenatal diagnostics for over thirty years. The vision of replacing invasive prenatal diagnostic procedures with the prospect of having the entire fetal genome in hand non-invasively for chromosomal and molecular studies for both clinical and research use has brought many investigators and innovations into the effort. While the object of this desire, however, has remained elusive, the aspiration for this approach to non-invasive prenatal diagnosis remains and the inquiry has continued. With the advent of screening by cell-free DNA analysis, the standards for fetal cell based prenatal diagnostics have been sharpened. Relevant aspects of the history and the current status of investigations to meet the goal of having an accessible and reliable strategy for capturing and analyzing fetal cells during pregnancy are reviewed.

Trophoblast retrieval and isolation from the cervix (TRIC) for noninvasive prenatal screening at 5 to 20 weeks of gestation

OBJECTIVE

To use trophoblast cells accumulating in the endocervical canal at the beginning of pregnancy for noninvasive prenatal testing.

DESIGN

Prospective, double-blinded test for fetal gender.

SETTING

Academic medical center.

PATIENT(S)

Fifty-six women with singleton pregnancies at gestational age 5-20 weeks.

INTERVENTION(S)

Isolation of fetal cells from resident maternal cells in endocervical specimens using anti-human leukocyte antigen G coupled to magnetic nanoparticles; cell phenotyping immunofluorescently with a panel of trophoblast subtype-specific proteins; DNA integrity assessment with terminal dUTP nick-end labeling (TUNEL); and polymerase chain reaction (PCR) and fluorescent in situ hybridization (FISH) to detect sex chromosomes in individual cells.

MAIN OUTCOME MEASURE(S)

Trophoblast phenotype, TUNEL index, and percentage male cells.

RESULT(S)

The women were given a routine Papanicolaou test; fetal genders were verified from medical records. Recovery after immunomagnetic isolation averaged 746±59 cells across gestational age, with 99% expressing chorionic gonadotropin, whereas the depleted cell fraction expressed none. The isolated cells had an extravillous trophoblast phenotype and intact nuclear DNA (>95%). Fetal gender was determined in 20 specimens without error by PCR. The FISH analysis of isolated cells from male specimens validated their fetal origin.

CONCLUSION(S)

Noninvasive prenatal testing is feasible beginning at a gestational age of 5 weeks.

Endoreduplication in cervical trophoblast cells from normal pregnancies

OBJECTIVE

Fetal cells represented by extravillous trophoblasts (EVT) obtained from the cervix by a minimally invasive procedure are important for prenatal diagnosis in early pregnancies. Endoreduplication is a duplication of chromosomes without mitosis, leading to polyploidy that might represent increased cellular metabolic activity. In this study, we estimated the normal prevalence of polyploid trophoblasts exfoliated to the cervix between 5 and 13 weeks of gestation.

METHODS

Cervical samples were obtained by cytobrush, between 5 and 13 weeks of gestation from 36 randomly selected, singleton pregnancies. FISH was done with X, Y and two 21 probes.

RESULTS

We diagnosed 21 pregnancies with female and 15 pregnancies with male fetal karyotypes. A mean of 15.2 (0.02%) tetraploid cells were found in pregnancies with a female fetus and a mean of 2.0 (0.003%) tetraploid cells were found in pregnancies with a male fetus. The tetraploid cells (endoreduplicated trophoblasts) were two to three times larger than the normal cells usually seen in the cervix.

CONCLUSIONS

Extravillus trophoblasts tend to form endoreduplication to the ploidy level of 4c-8c of DNA. Those cells may represent a typical phenomenon in the growing placenta. Extravillus trophoblasts from female fetuses tend to form higher rates of endoreduplication.

Detection of ≥1Mb microdeletions and microduplications in a single cell using custom oligonucleotide arrays

OBJECTIVE

High resolution detection of genomic copy number abnormalities in a single cell is relevant to preimplantation genetic diagnosis and potentially to noninvasive prenatal diagnosis. Our objective is to develop a reliable array comparative genomic hybridization (CGH) platform to detect genomic imbalances as small as ~1Mb ina single cell.

METHODS

We empirically optimized the conditions for oligonucleotide-based array CGH using single cells from multiple lymphoblastoid cell lines with known copy number abnormalities. To improve resolution, we designed custom arrays with high density probes covering clinically relevant genomic regions.

RESULTS

The detection of megabase-sized copy number variations (CNVs) in a single cell was influenced by the number of probes clustered in the interrogated region. Using our custom array, we reproducibly detected multiple chromosome abnormalities including trisomy 21, a 1.2Mb Williams syndrome deletion, and a 1.3Mb CMT1A duplication. Replicate analyses yielded consistent results.

CONCLUSION

Aneuploidy and genomic imbalances with CNVs as small as 1.2Mb in a single cell are detectable by array CGH using arrays with high-density coverage in the targeted regions. This approach has the potential to be applied for preimplantation genetic diagnosis to detect aneuploidy and common microdeletion/duplication syndromes and for noninvasive prenatal diagnosis if single fetal cells can be isolated.