Frequencies of fetal nucleated red blood cells in maternal blood during different stages of gestation

Noninvasive prenatal diagnosis targeting fetal nucleated red blood cells

Noninvasive prenatal diagnosis (NIPD) aims to detect fetal-related genetic disorders before birth by detecting markers in the peripheral blood of pregnant women, holding the potential in reducing the risk of fetal birth defects. Fetal-nucleated red blood cells (fNRBCs) can be used as biomarkers for NIPD, given their remarkable nature of carrying the entire genetic information of the fetus. Here, we review recent advances in NIPD technologies based on the isolation and analysis of fNRBCs. Conventional cell separation methods rely primarily on physical properties and surface antigens of fNRBCs, such as density gradient centrifugation, fluorescence-activated cell sorting, and magnetic-activated cell sorting. Due to the limitations of sensitivity and purity in Conventional methods, separation techniques based on micro-/nanomaterials have been developed as novel methods for isolating and enriching fNRBCs. We also discuss emerging methods based on microfluidic chips and nanostructured substrates for static and dynamic isolation of fNRBCs. Additionally, we introduce the identification techniques of fNRBCs and address the potential clinical diagnostic values of fNRBCs. Finally, we highlight the challenges and the future directions of fNRBCs as treatment guidelines in NIPD.

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.

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.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

Basic investigation of the lectin method for separation and recovery of nucleated red blood cells in maternal blood, and a study into the frequency of nucleated red blood cells in fetomaternal disorders

We previously reported the separation and recovery of nucleated red blood cells (NRBCs) in maternal blood using the lectin method. In the present study, we verified the lectin method and investigated the appearance of NRBCs during pregnancy. For the concentration of lectin soy bean agglutinin, 7 mL of maternal peripheral blood was collected from 20 subjects, and the relative fluorescence intensity was measured using flowcytometry; 50 mg/mL, used in previous studies, was the optimal concentration. The number of cells recovered at each step of the lectin method was also investigated by FACS using fluorescence-labeled CD11a and CD33, and the results showed the usefulness of the method. Next, 7 mL of maternal peripheral blood was collected from 292 women with a normal single pregnancy (389 specimens), and NRBCs were separated and recovered using the lectin method. NRBCs slightly increased over the course of pregnancy (y = 4.29x + 5.03, r2 = 0.11). When blood was collected multiple times in the same subjects, NRBCs increased in 63 of 77 subjects (83.1%, percent change: 2.4 +/- 19.0). No NRBCs were recovered in 17 subjects (4.7%). Regarding the relationship between fetomaternal disorders and the frequency of NRBCs, 89.4 +/- 92.6 cells appeared per 10 mL of maternal blood in the normal group, but NRBCs increased in patients with 18 trisomy, placenta previa, pre-eclampsia, intrauterine fetal death, and 21 trisomy. NRBC examination may play an assisting role not only in fetal diagnosis but also in fetomaternal diagnosis.

Studies on preliminary concentration methods for recovery of fetal nucleated red blood cells in maternal blood

Non-invasive prenatal diagnostic methods posing no danger to the embryo have been desired for many years in the field of prenatal medicine. We are in the process of improving the lectin method that we developed for recovering fetus-derived nucleated red blood cells (NRBC) in the maternal peripheral blood. We previously used Ficoll density-gradient centrifugation for preliminary concentration in the lectin method. In the present study, we developed a molecular filter method, compared it with the Ficoll method, and tested its applicability to prenatal diagnosis. We tested the usefulness of a high molecular filter method for preliminary concentration. First, in a basic study, we prepared three kinds of non-woven cloth (NWC1-3) and a multi-porous filter (MP) to determine the optimal filter. Next, we compared the recovery rates of the Ficoll and filter methods as preliminary concentration methods in 34 normal pregnant women. Then, to examine whether the recovered NRBC were derived from the fetus, we attempted prenatal diagnosis by the fluorescence in situ hybridization (FISH) technique in 12 women pregnant with a male fetus (determined later by ultrasound) at between 8 and 16 weeks of gestation. Among the four devices used in the basic study of the high molecular filter method, NWC-2 had the best recovery rate. Therefore, we compared the numbers of NRBC recovered by the lectin method after preliminary concentration with NWC-2 or by Ficoll centrifugation, and found that the mean recovery rate of NWC-2 was 4.2 +/- 5.0 times as high as that of the Ficoll method, indicating that the NWC-2 filter method is superior as a preliminary concentration method. Next, FISH analysis of the 12 pregnant women with a male fetus for the Y chromosome showed that 19.5 +/- 12.8 NRBC were recovered, in 12.7 +/- 8.1 (63.6%) of which a Y signal was confirmed, suggesting the NWC-2 filter method can be applied to prenatal diagnosis. We consider the filter-lectin method to be a superior method for isolation and recovery of NRBC in the maternal blood which can be applied to prenatal diagnosis.

Sex-determining region Y levels in maternal plasma: Evaluation in abnormal pregnancy

AIM

A number of studies for the measurement of cell-free fetal DNA in maternal blood have been reported; however, their clinical significance has remained unclear. We proposed to clarify the relationship between fetal DNA levels and obstetrical disorders.

METHODS

One hundred and eighty-five cases of normal pregnancy, ranging from 8 to 40 weeks' gestation, and 70 cases of abnormal pregnancy were included. SRY levels in maternal plasma were quantified with a real-time quantitative polymerase chain reaction.

RESULTS

Sex-determining region Y (SRY) levels and the number of patients with positive levels peaked at 33-36 weeks in normal pregnancy. The SRY levels in threatened abortion (11.6 +/- 4.8 copies/mL to 0 +/- 0, P < 0.05) and threatened preterm labor (44.6 +/- 16.1 copies/mL to 15.9 +/- 6.2, P < 0.01) were significantly higher than those of the normal group. In pre-eclamptic patients, SRY levels were markedly higher than those of the normal group (173.2 +/- 94.8 copies/mL to 22.4 +/- 8.9, P < 0.05). Patients with premature separation of the placenta (266.8 +/- 137.1 copies/mL to 4.9 +/- 3.7, P < 0.05) and placenta previa (167.7 +/- 32.4 copies/mL to 37.0 +/- 17.3, p <0.01) also showed elevated SRY levels.

CONCLUSION

Sex-determining region Y levels in maternal plasma were elevated in patients with an abnormal pregnancy, particularly those with placental injury of damage. These results suggested that increased SRY levels are consistently caused by the leak of fetal components, and thus the measurement of SRY levels in maternal plasma is useful for the evaluation of placental injuries.

Method of separation and concentration of fetal nucleated red blood cells in maternal blood and its application to fetal diagnosis

A fetal diagnostic method that is without risk to the embryo has been long awaited in the field of gene diagnosis. Establishment of non-invasive fetal diagnosis using maternal peripheral blood will greatly contribute to perinatal medical care. The lectin method that we have studied and developed selectively recovers nucleated red blood cells (NRBC) among fetal cells mixed in maternal peripheral blood. Maternal blood, 7 mL, was collected with ethylene diamine tetraacetic acid (EDTA) treatment in each week of gestation and subjected to preliminary concentration by density centrifugation (Histopaque [Histopaque-1077; Sigma Diagnostics, MO, USA], specific gravity: 1.095), and NRBC were separated and collected on slide glasses by the lectin method (soybean agglutinin [SBA]: 50 microg/mL). To investigate selective adhesion of the erythrocyte fraction, the SBA concentration was set to 50 microg/mL, and the cells were labeled with CD11a and CD33 (anti-white blood cell antibodies) and investigated by flowcytometry. Erythrocytes adhered at a high rate (87.0 +/- 9.7%) while the adhesion rates of granulocytes, monocytes, and lymphocytes were low, confirming the usefulness of the method for separation and recovery of the erythrocyte fraction. When recovery of NRBC was investigated using this method, a mean of 6.57 +/- 7.12 cells were recovered from 1 mL of maternal blood (May-Gluüwald-Giemsa stain). The number of recovered NRBC increased slowly with pregnancy, but differences were not significant. To confirm that recovered NRBC were derived from the fetus, NRBC were recovered by the lectin method in four patients suspected of 18 trisomy by echography and analyzed by fluorescence in situ hybridization. Three hybridization signals were detected in NRBC at a high frequency, showing that most cells were derived from the fetus and thus, fetal diagnosis may be possible. Since the procedure of the lectin method we have developed is simple, and high concentration efficiency can be obtained at a low cost, it may be clinically applicable.

Analysis of Fetal Blood Cells in the Maternal Circulation: Challenges, Ongoing Efforts, and Potential Solutions

The invasive procedures amniocentesis and chorionic villus sampling (CVS) are routinely applied in pregnancies at risk for fetal abnormalities and the results obtained are the gold standard for prenatal diagnosis. Because these methods of fetal cell procurement involve a 0.5-2% risk for fetal loss, they are recommended mainly in cases at high risk for fetal genetic or cytogenetic abnormalities. The development of a reproducible, reliable, noninvasive method based on retrieval of rare fetal cells from the maternal circulation will render testing feasible for the general population. Despite intensive investigation, a satisfactory, clinically acceptable method has not yet emerged. Several cell types have been targeted to this end, mostly nucleated red blood cells (NRBC), CD34+ hematopoietic progenitors, and trophoblasts. Although these cell types have been unequivocally proven to be present in the maternal circulation, each bears a significant disadvantage, rendering their application in clinical testing currently impossible: NRBC cannot be expanded in culture, thereby ruling out metaphase chromosome analysis, an essential component of prenatal diagnosis. CD34+ cells do posses the potential for in vitro proliferation, however, they have been found to persist in the maternal circulation after delivery, thereby complicating diagnosis in consecutive pregnancies. Trophoblasts are not consistently detected in the maternal circulation. Moreover, due to the lack of a definitive fetal cell marker and a reliable sorting method, foolproof fetal cell identification of any of these cell types is not possible. This report outlines the obstacles that impede development of a method for noninvasive fetal cell sampling for prenatal genetic diagnosis, along with a description of our efforts to analyze simultaneously two fetal blood cell types, NRBC and CD34+ cells in maternal blood during pregnancy, and the problems encountered. This work and that of others lead us to suggest potential future directions to help develop this important technique.

Significantly higher number of fetal cells in the maternal circulation of women with pre-eclampsia

Although the pathophysiology of pre-eclampsia is unknown, several studies have indicated that abnormal placentation early in pregnancy might play a key role. It has recently been suggested that this abnormal placentation may result in transfusion of fetal cells (feto-maternal transfusion) in women with pre-eclampsia. In the present study, fetal nucleated red blood cells were isolated from 20 women with pre-eclampsia and 20 controls using a very efficient magnetic activated cell sorting (MACS) protocol. The number of male cells was determined using two-color fluorescence in situ hybridization (FISH) for X and Y chromosomes. Significantly more XY cells could be detected in women with pre-eclampsia (0.61+/-1.2 XY cells/ml blood) compared to women with uncomplicated pregnancies (0.02+/-0.04 XY cells/ml blood) (Mann-Whitney U-test, p<0.001). These results suggest that fetal cell trafficking is enhanced in women with pre-eclampsia, and this finding may contribute to the understanding of the pathophysiology of the disease.

Kinetics of fetal cellular and cell-free DNA in the maternal circulation during and after pregnancy: implications for noninvasive prenatal diagnosis

BACKGROUND

Fetal genetic material is detectable in the maternal circulation and has been used for noninvasive prenatal diagnosis. However, few data are available concerning its quantity and natural history during gestation.

STUDY DESIGN AND METHODS

This study prospectively characterized the kinetics of cellular and cell-free fetal DNA in the circulation of 25 healthy women during and after uncomplicated pregnancy. Real-time kinetic PCR was used to quantitate human Y-chromosome sequences, and liquid oligomer hybridization with (32)P-labeled probes was used to verify the identity of amplified products.

RESULTS

In all male pregnancies, but no female pregnancies, low-level fetal Y-chromosome DNA was detected in both cellular and cell-free compartments beginning at 7 to 16 weeks but increasing steadily after 24 weeks and reaching a peak at parturition. The fetal DNA decreased rapidly after birth.

CONCLUSION

Fetal genetic material can be detected throughout pregnancy, and its quantity is a function of gestational age and of whether the plasma or cellular compartment is examined. Both the absolute quantity of fetal DNA and its ratio to total DNA (maternal + fetal) are greater in the plasma than in the cellular compartment. Fetal DNA is cleared rapidly from both compartments after parturition, which suggests that turnover is dynamic. Because they provide prospective and quantitative data concerning fetal DNA levels, these observations and kinetic PCR methods may have implications for noninvasive prenatal diagnosis. Further studies will be needed to determine the immunologic implications of fetal-maternal DNA exchange and cellular microchimerism.

Prenatal diagnosis on fetal cells from maternal blood: practical comparative evaluation of the first and second trimesters

Objectives- Several attempts have been made to determine the gestational period in which the maximum number of fetal cells can be found in maternal blood and consequently which is the best week in which to perform a reliable non-invasive prenatal diagnosis. Most studies conclude that the number of nucleated red blood cells (NRBC) increases in line with gestation, but the number of cells that are fetal in origin (FNRBC) decreases in the third trimester. The aim of the present study was to make a practical comparative evaluation of the first and second trimesters to ascertain the period in which a greater number of FNRBC can be found of the total number of NRBC identified. Methods- Double density gradient and a posterior positive selection (CD71) by magnetic activated cell sorting (MACS) were employed. In the final fraction, erythroblasts were identified using Kleihauer staining and were studied using the fluorescence in situ hybridization (FISH) interphasic technique. Results- There was a significant difference (p<0.05) between the mean number of FNRBC found in the first and second trimesters. Conclusions- The number of FNRBC increases from the first to the second trimester. It appears that the optimum week in which to perform a reliable non-invasive prenatal diagnosis is around the 15th week.

Optimization of nucleated red blood cell (NRBC) recovery from maternal blood collected using both layers of a double density gradient

The isolation of fetal nucleated red blood cells (NRBC) from maternal blood represents a promising approach to non-invasive prenatal diagnosis. However, the number of fetal NRBC in maternal circulation is quite low and therefore difficult to isolate. An enrichment procedure in which both layers from a double density 1.077/1.107 g/ml gradient are collected was optimized, followed by MACS selection using non-commercial monoclonal antibodies. The influence of the delay in processing maternal blood on the NRBC distribution in both interfaces of the gradient was also studied in cord blood and peripheral maternal blood samples. A significant increase in the number of NRBC isolated from maternal blood was achieved by collecting both layers of the double density gradient compared with the previous protocol in which only the lower layer was recovered. Cord blood samples showed significant differences in the number of NRBC recovered when processed at 24 instead of within 3 h. This effect was also observed in the number of NRBC collected only from the upper layer of peripheral maternal blood samples. Therefore, in order to minimize the target cell losses, it is advisable to process the maternal blood samples as soon as possible.

Fetal cells in maternal blood

Fetal lymphocytes, trophoblasts, and nucleated red blood cells have each been separated from maternal blood by methods such as flow cytometry, magnetic cell sorting, and charge flow separation. The frequency of fetal cells among circulating maternal mononuclear cells remains to be ascertained. Current estimates range from about 10-5 to 10-7, but the numbers may be increased in women carrying aneuploid fetuses. Fetal cells separated from maternal blood have been studied by methods such as polymerase chain reaction and fluorescence in situ hybridization. Among fetal conditions so far identified are sex; human leukocyte antigen and Rh blood types; trisomy 13, 18 and 21; triploidy; and sickle cell anemia and thalassemia. Thus, fetal cell separation might one day be used for screening of the common aneuploidies and, ultimately, for prenatal diagnosis. Individual fetal erythroid precursors have been cultured after separation in some laboratories. Culturing and karyotyping of separated fetal cells might enable diagnosis of a spectrum of chromosomal and genetic disorders. Further development will be required, however, before regular clinical application of these methodologies.

Magnetic-activated cell sorting (MACS) significantly decreases the hybridization efficiency of fluorescencein situ hybridization (FISH)

Fetal cells were enriched from maternal blood using density gradient centrifugation of Histopaque followed by magnetic-activated cell sorting (MACS) to select CD71-positive cells. For each specimen, cells partially purified by Histopaque were split into equal portions, and each portion was subjected to purification by MACS in parallel. Cells before and after MACS were subjected to dual-color fluorescence in situ hybridization (FISH) analysis with X- and Y-chromosome-specific probes. We found that the hybridization rates were decreased by approximately 10% after MACS based on duplicated analysis for each sample.

Y specific sequence gene analysis of single fetal nucleated erythroblasts from the peripheral blood of pregnant women

The single cell isolation technique was used to detect fetal nucleated erythroblasts (FNRBCs) at a single cell level from the peripheral blood of pregnant women in order to investigate the feasibility of this method for noninvasive prenatal diagnosis. Single fetal nucleated erythroblasts were isolated from the peripheral blood samples from 51 pregnant women (14 to 26 weeks of gestation) by micromanipulation techniques after density gradient centrifugation. Nested polymerase chain reaction method was used to amplify the SRY gene. It was found that the concordance rate of amplification results with real fetal sex was 82.61%. The sensitivity and specificity were 80% and 87.50% respectively. It was suggested that it is feasible and promising in non invasive prenatal diagnosis to detect fetal nucleated erythroblasts at a single cell level by using micromanipulation techniques.