Transcervical recovery of fetal cells from the lower uterine pole: reliability of recovery and histological/immunocytochemical analysis of recovered cell populations

Trophoblast retrieval from the cervical canal to predict abnormal pregnancy early in gestation: a pilot study

BACKGROUND

The current detection of fetal chromosomal abnormalities by non-invasive prenatal testing (NIPT) mainly relies on the cell free DNA(cfDNA) in the maternal blood. However, a gestational age of less than 12 weeks or a high maternal BMI affects cfDNA fetal fraction and further the detection by NIPT negatively. In this study, we aim to retrieve the trophoblast cells from the maternal cervix to develop a new sampling method for NIPT enabling an earlier use of NIPT.

METHODS

We enrolled three patients who wanted to undergo induced abortion at Beijing Hospital between January 2022 and March 2022. Peripheral blood, cervix specimen, and the abortion tissue were collected and processed for each patient. Allele frequencies of the mutated gene loci of the maternal blood and the cervix sample were compared and the Sex Determining Region Y (SRY) gene was tested.

RESULTS

The allele frequencies of the mutated gene loci showed no significant difference between the maternal blood and the cervix sample. But we successfully detected signal of the SRY gene in the cervix sample of the only patient carrying a male fetus.

CONCLUSIONS

The detection of the SRY gene in a cervix sample indicated a successful retrieval of trophoblast cells from the cervix canal. Further study needs to be conducted to verify our finding before its application to the clinical settings.

Rarity of fetal cells in exocervical samples for noninvasive prenatal diagnosis

OBJECTIVES

The possibility to isolate fetal cells from pregnant women cervical samples has been discussed for five decades but is not currently applied in clinical practice. This study aimed at offering prenatal genetic diagnosis from fetal cells obtained through noninvasive exocervical sampling and immuno-sorted based on expression of HLA-G.

METHODS

We first developed and validated robust protocols for cell detection and isolation on control cell lines expressing (JEG-3) or not (JAR) the HLA-G antigen, a specific marker for extravillous trophoblasts. We then applied these protocols to noninvasive exocervical samples collected from pregnant women between 6 and 14 weeks of gestational age. Sampling was performed through insertion and rotation of a brush at the ectocervix close to the external os of the endocervical canal. Finally, we attempted to detect and quantify trophoblasts in exocervical samples from pregnant women by ddPCR targeting the male SRY locus.

RESULTS

For immunohistochemistry, a strong specific signal for HLA-G was observed in the positive control cell line and for rare cells in exocervical samples, but only in non-fixative conditions. HLA-G positive cells diluted in HLA-G negative cells were isolated by flow cytometry or magnetic cell sorting. However, no HLA-G positive cells could be recovered from exocervical samples. SRY gene was detected by ddPCR in exocervical samples from male (50%) but also female (27%) pregnancies.

CONCLUSIONS

Our data suggest that trophoblasts are too rarely and inconstantly present in noninvasive exocervical samples to be reliably retrieved by standard immunoisolation techniques and therefore cannot replace the current practice for prenatal screening and diagnosis.

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.

Is cervical swab an efficient method for developing a new noninvasive prenatal diagnostic test for numerical and structural chromosome anomalies?

Background/aim

Prenatal diagnosis is vital to obtain healthy generation for risky pregnancies. There have been several approaches, some of which are routinely applied in clinics to evaluate the possible prenatal deficiencies and/or diseases. In the present study, we aimed to isolate the fetal cells from endocervical samples and try to identify possible anomalies which were proved by Amniocentesis (AS) and chorionic villus sampling (CVS) methods.

Materials and methods

Endoservical specimens were collected from 100 pregnant women. Cells were separated in parallel by fluorescence-activated cell sorting (FACS) and magnetic-activated cell sorting (MACS) using human leukocyte antigen (HLA) G233 and placental alkaline phosphatase (PLAP) antibodies. CMA (comprehensive meta-analysis) were carried out and male fetuses were confirmed with Sex determining region Y (SRY) amplification.

Results

The percent of HLA G233 and placental and placental alkaline phosphatase (PLAP) positive cells were 4.55% and 84.59%, respectively. The percent of cells positive for both markers was 14.75%. CMA analyses were not informative. (SRY) was amplified in 67% of the samples.

Conclusion

However, the success rate of the both cell sorting and scanning of DNA anomalies by aCGH and/or RT-PCR was limited, preventing the applicability of this proposal in the clinics. Still, the success of the proposed method depends on the development of the novel fetal cell-specific antibodies and the improvements in the sorting systems.

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.

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.

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.

Prenatal diagnosis of trisomy 21 through detection of trophoblasts in cervical smears

BACKGROUND

Fetal cells exfoliate in the uterine cavity during early pregnancy and are a potential source of material for NIPD.

AIMS

This study was designed to test the hypothesis that fetal cells obtained from the uterine cervix during the first trimester of pregnancy could be utilized for prenatal diagnosis of chromosomal aneuploidy.

STUDY DESIGN

Fetal cells retrieved from the distal endocervical canal during the first trimester of pregnancy were hybridized with chromosome 21 specific FISH probes and analyzed with an automated fluorescence microscope.

SUBJECTS AND OUTCOME MEASURES

Cells with 3 copies of chromosome 21 were detected in 5 out of 5 trisomy 21 pregnancies.

RESULTS

The number of trisomic cells detected ranged from 1 to 27 with a median value of 5.

CONCLUSIONS

FISH-based scanning can identify trisomy 21 pregnancies by analysis of routine cervical brushings. The approach offers the potential for non-invasive prenatal diagnosis as early as 5 weeks gestation.

Retrieval of trophoblast cells from the cervical canal for prediction of abnormal pregnancy: a pilot study

BACKGROUND

Fetal cells are shed from the regressing chorionic villi and it is possible to retrieve extravillous cytotrophoblast cells by transcervical sampling. The abundance of trophoblast cells in transcervical samples suggests that this non-invasive approach could distinguish between normal and abnormal pregnancies, such as an ectopic pregnancy (EP) and blighted ovum (BO). We aim to identify and quantify fetal trophoblast cells in the cervical canal during the first trimester to assess their usefulness to predict an abnormal pregnancy.

METHODS

Patients, age 18-45, presenting with a normal intrauterine pregnancy (IUP; n = 37), diagnosis of EP (n = 10) or BO (n = 5) were enrolled for collection of transcervical specimens using a cytobrush and fixative rinse. Non-pregnant, nulliparous women (n = 7) were included as negative controls. Cells were cleared of mucus by acidification, prepared on microscope slides and labeled with a monoclonal antibody recognizing the trophoblast marker, human leukocyte antigen (HLA)-G. HLA-G positive and negative cells were counted to calculate the ratio of trophoblast cells to total cervical cells.

RESULTS

Trophoblast cells were observed in 35/37 normal IUP, 6/10 EP and 4/5 BO specimens. The average frequency of HLA-G positive cells in the normal IUP cervical samples was approximately 1 in 2000, which was 4-fold higher than samples from patients with EP or BO (P < 0.001). Receiver operating characteristic analysis showed that EP and BO pregnancies were distinguishable from normal pregnancies with 93% sensitivity, 95% specificity, 97% positive predictive value and 87% negative predictive value.

CONCLUSIONS

This pilot study presents evidence that trophoblast cells can be reliably obtained and identified among cervical cells in the first trimester by immunohistochemical staining for HLA-G, and suggests for the first time that abnormal pregnancies may be predictable based on the abundance of trophoblast cells in the cervical canal.

Endocervical fetal trophoblast for prenatal genetic diagnosis

PURPOSE OF REVIEW

For over a decade, methods of first-trimester, noninvasive prenatal genetic diagnosis have been actively pursued by many investigators. Isolation of fetal trophoblast from endocervical specimens remains an attractive approach, given the greater numbers of fetal cells than in maternal blood and the better potential for fetal-cell identification based on markers specific for a single cell type (trophoblasts).

RECENT FINDINGS

Current studies demonstrate feasibility in identification and molecular analysis of fetal trophoblast cells for prenatal genetic testing. Sampling methods involving lavage, cytobrush, or aspiration of cervical specimens, however, have limitations in the recovery of trophoblasts.

SUMMARY

Clinical applications await further systematic studies to determine safety and accuracy in recovery.

Detection of fetal cells from transcervical mucus plug before first-trimester termination of pregnancy by cytokeratin-7 immunohistochemistry

AIM

The presence of fetal cells in the endocervical mucus of pregnant women was first reported in 1971. The uterine cavity is patent during the first trimester prior to fusion of amnion and chorion. Fetal cells from degenerating chorion frondosum are theoretically shed into the uterine cavity between seven and 13 weeks' gestation and are trapped in the transcervical mucus; they can be identified by immunohistochemistry.

METHOD

Ninety-nine transcervical mucosal plugs from pregnant women of between 7 and 13 weeks before abortion were collected, fixed, embedded, sectioned and stained with monoclonal antibody of cytokeratin-7 (CK-7) by immunohistochemistry.

RESULT

The identification of trophoblasts on each slide was defined according to positive staining and histologically chorionic villous similarity under microscopic examination, using the following five categories: none (1), less than five single positive-stained cells per-section (2), more than five single positive-stained cells per-section (3), clumps of positive-stained cells (4), and histological-like intact or fragmented chorionic villi (5). From amongst 71 samples that qualified for analysis, individual slides were evaluated and categorized into three groups, with the following results: 32 (45.1%) fell into group 1 (category 1) denoting a negative result, 10 (14.1%) fell into group 2 (category 2) indicating a possible positive result and 29 (40.8%) fell into group 3 (any combination of categories 3-5) representing a positive result.

CONCLUSIONS

Fetal cells, identified by CK-7, can be found in more than 59.2% of the transcervical mucus in early pregnancy by use of a minimally invasive sampling method. Prenatal diagnosis of single-gene or chromosome disorders may be possible in the pregnant transcervical mucus by use of modern molecular methods and they deserve further study.

DNA identification of fetal cells isolated from cervical mucus: potential for early non-invasive prenatal diagnosis

OBJECTIVES

To develop a reliable method to isolate fetal cells for genetic diagnosis.

DESIGN

Aspiration of cervical mucus from pregnant women in the first trimester.

SETTING

Pregnant women were recruited before an elective termination of pregnancy.

POPULATION

Sixty pregnant women (7-10 weeks of gestation).

METHODS

Fetal cells were isolated from aspirated cervical mucus of pregnant women using a combination of enzymatic digestion, fluorescent immunohistochemistry, micromanipulation and single-cell DNA allelic profiling.

MAIN OUTCOME MEASURES

The isolation and identification of fetal cells.

RESULTS

The transformation of the tenacious cervical mucus into a single-cell suspension enabled the isolation and identification of fetal cells by fluorescent immunohistochemistry. Confirmation of fetal origin was accomplished by single-cell DNA allelic profiling alongside known maternal cells.

CONCLUSIONS

This novel non-invasive method is rapid and efficient with results attainable within 24 hours as early as seven weeks of gestation. The technique would offer earlier reassurance and the option of first trimester therapeutic abortions to both high and low risk pregnant women.

Enrichment and identification of fetal trophoblast cells from first trimester maternal cervical lavage and uterine blood specimens

First trimester prenatal diagnosis of fetal aneuploidies is an active area of research despite years of disappointing data employing maternal peripheral blood samples. To remedy this situation we have investigated other first trimester maternal specimens attempting to find a consistent fetal cell source. Using our previously established positive enrichment procedure along with a commercially available depletion method, fetal trophoblast cells were identified employing immunocytochemistry using an antibody cocktail or by using mRNA in-situ hybridization employing a cocktail of trophoblast specific probes. Fetal origin of positively identified cells was verified using interphase fluorescent in-situ hybridization (FISH) for X and Y-chromosomes. Artificial model systems were established that indicated yields of trophoblast cells and allowed the enrichment procedure to be optimized for minimal losses from maternal specimens. We demonstrate herein that blood drawn from maternal vessels near the placental implantation site to be the most consistent source of fetal cells from any first trimester maternal specimen described to date. In addition, a high yield of multinucleated syncytiotrophoblast cells was obtained using a cell depletion strategy to enrich the target cells. The safety of the procedure or even the clinical utility of blood drawn from maternal vessels near the placental implantation site is yet to be demonstrated.