Successful prenatal diagnosis from maternal blood with magnetic-activated cell sorting

Unexpected activity of magnetically separable Fenton catalyst in clay slurries

Maghemite/silica nanocomposite microspheres (γ-Fe₂O₃/SiO₂ MS) have been tested as magnetically separable heterogeneous Fenton catalyst in beidellite clay slurries in the presence of methylorange (MO) as a model pollutant. Due to its strong magnetic susceptibility, the catalyst was easily recovered from the clay slurries by a selective magnetic sorting, even in highly concentrated slurries. The Fenton oxidation of MO was strongly enhanced in the clay slurries in comparison to the reaction in aqueous phase, highlighting a synergistic catalytic effect. The influence of different experimental parameters such as the presence of specific Reactive Oxygen Species (ROS) scavengers, pH, H₂O₂, catalyst and clay concentrations, on the catalytic activity was also evaluated. Contrary to what was observed in aqueous phase, generation of hydroxyl radicals via the Haber-Weiss mechanism was not the unique pathway that caused MO degradation in the beidellite slurries. We also observed that the synergistic effect is more marked at pH near neutrality and low amounts of H₂O₂ and clay. Furthermore, the unchanged activity of the catalyst during five successive cycles together with the low level of iron leaching, makes it suitable candidate for an application as a magnetic heterogeneous Fenton catalyst in wastewater treatment, especially for surface waters or sludges naturally containing fine clay particles.

Prenatal diagnosis: update on invasive versus noninvasive fetal diagnostic testing from maternal blood

The modern obstetrics care includes noninvasive prenatal diagnosis testing such as first trimester screening performed between 11 and 14 weeks' gestation and second trimester screening performed between 15 and 20 weeks. In these screening tests, biochemical markers are measured in the maternal blood with or without ultrasound for fetal nuchal translucency with reported accuracy of up to 90%. Invasive procedures, including amniocentesis or chorionic villi sampling, are used to achieve over 99% accuracy. During these procedures direct fetal material is examined and, therefore, these tests are highly accurate with the caveat of a small risk for pregnancy loss. Much research now focuses on other noninvasive highly accurate and risk-free tests that will identify fetal material in the maternal blood. Fetal cells and fetal DNA/RNA provide fetal information but are hard to find in an overwhelming background of maternal cells and in the absence of specific fetal cell markers. The most experience has been accumulated with fetal rhesus and fetal sex determination from maternal blood, with an accuracy of up to 100% by using gene sequences that are absent from maternal blood. Although not clinically applicable yet, fetal cells, fetal DNA/RNA and fetal proteomics in combination with cutting edge technology are described to prenatally diagnose aneuploidies and single-gene disorders.

An improved flow cytometric approach for isolation of fetal cells from maternal blood for non invasive prenatal diagnosis of hemoglobinopathies

Prenatal diagnosis is an option for couples at risk of having a child affected with hemoglobinopathies. Chorionic villus sampling (CVS) and cordocentesis are accurate but a finite risk of fetal loss exists. A non invasive, risk free strategy that has emerged is isolation of fetal erythroblasts from maternal blood. Enrichment of nucleated red blood cells (nRBCs) from 7.0 mL maternal blood was done using a Percoll discontinuous density gradient and isolation by flow sorting using a combination of three monoclonal antibodies: CD45 per CP, glycophorin A-phycoerythrin (PE) and Hb F-fluorescein isothiocyanate (FITC) in 43 cases between 7 and 21 weeks' gestation. The percentage of nRBCs ranged from 0.0001-2.03%. The presence of dual fluorescence (glycophorin A-PE and Hb F-FITC) was confirmed by confocal microscopy. A sufficient number of nRBCs could be isolated in the first and second trimester of pregnancy to provide a simple flow cytometric approach as a potential for non invasive diagnosis of beta-globin defects.

Clinical Potential for Noninvasive Prenatal Diagnosis Through Detection of Fetal Cells in Maternal Blood

Fetal cells circulate in maternal blood and are considered a suitable means by which to detect fetal genetic and chromosomal abnormalities. This approach has the advantage of being noninvasive. Since the early 1990s, nucleated erythrocytes (NRBCs) have been considered good target cells for a number of techniques, including fluorescence-activated cell sorting and magnetic cell sorting, using antibodies such as anti-transferrin receptor and anti-gamma-hemoglobin antibodies, followed by analysis with fluorescence in situ hybridization or polymerase chain reaction. In the late 1990s, the National Institute of Child Health and Human Development Fetal Cell Isolation Study assessed the reliability of noninvasive prenatal diagnosis of fetal aneuploidy using NRBCs isolated from maternal circulation. This study revealed the limitations of NRBC separation using antibodies specific for NRBC antigens. A more recent study has demonstrated the efficiency and success of recovery of NRBCs using a galactose-specific lectin, based on the observation that erythroid precursor cells have a large quantity of galactose molecules on their cell surface. Thus, recent advances in this field enhance the feasibility of this diagnostic method. This review article focuses on various methods of detection of fetal cells within the maternal circulation, as well as the status of previous and current studies and the prospective view for noninvasive prenatal diagnosis using fetal cells from the maternal circulation.

Quantification of all fetal nucleated cells in maternal blood in different cases of aneuploidies

We quantified all fetal nucleated cells (FNCs) per unit volume of maternal blood in different aneuploid pregnancies using molecular cytogenetic techniques. Seven cases of male trisomy 18, two triploidies (69,XXX), two 47,XXX, one 47,XXY, one 47,XYY, one male trisomy 13, and one case of 47,XY,r(22),+r(22) were analyzed. Whole blood samples were obtained from 15 women between 17 and 29 gestational weeks and harvested without using fetal cell enrichment procedures. Fluorescence in situ hybridization and primed in situ labeling were performed to identify the FNCs. All slides were manually scanned to quantify those cells. We have identified 4-20 FNCs/ml of maternal blood in the cases of trisomy 18; 10 and 25 FNCs/ml in the two cases of triploidy; 16 and 14 FNCs/ml, respectively, in the two X trisomies; 19 FNCs/ml in the 47,XXY; 26 FNCs/ml in the 47,XYY; nine FNCs/ml in the trisomy 13; and 10 FNCs/ml in the case of r(22). To detect all FNCs in all aneuploid pregnancies, we have used a very simple method that minimizes the manipulation steps to avoid losing fetal cells. The number of FNCs identified in aneuploid pregnancies was 2-5 times higher than in normal pregnancies. This higher number of FNCs will favor the design of a non-invasive pre-natal test.

A monoclonal antibody with potential for aiding non-invasive prenatal diagnosis: utility in screening of pregnant women at risk of preeclampsia

The development of a non-invasive method of prenatal diagnosis in maternal blood has been the goal of our investigations during the last years. We have developed several anti-CD71 monoclonal antibodies and optimized a protocol for the isolation of nucleated red blood cells (NRBC) from peripheral maternal blood. The enhanced traffic of fetal erythroblasts into the maternal circulation in preeclampsia has been investigated by several groups. In this study, we compared one of our antibodies, 2F6.3, with a commercial anti-CD71 antibody in blood samples from pregnant women suffering pregnancy-induced hypertension (PIH) and in a control group of pregnant women without clinical features suggestive of an increased risk of developing preeclampsia. The mAb 2F6.3, developed by our group, has succeeded in isolating a significantly higher number of erythroblasts with less maternal cell contamination than the commercial antibody in both women with PIH and in the control group (p<0.01; Wilcoxon Signed Ranks Test). Fluorescence in situ hybridization analysis also demonstrated that 2F6.3 is a better antibody for the isolation of fetal NRBC in maternal blood than the commercial anti-CD71 antibody.

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

BACKGROUND

Prenatal diagnosis of trisomy 21 is based on fetal karyotyping generally obtained using invasive methods. During pregnancy, the circulating fetal cells in maternal blood constitute a potential source for development of a noninvasive prenatal diagnosis. The objective of this study was the identification and quantification of all fetal nucleated cells per unit volume of peripheral blood of pregnant women carrying male fetuses with trisomy 21 using molecular cytogenetic techniques.

METHODS

Peripheral blood samples were obtained from 16 women carrying male fetuses with trisomy 21. We used a simple and rapid method of harvesting blood without recourse to any enrichment procedures or cell-separation techniques. To evaluate the potential of this method, 16 specimens were analyzed by molecular cytogenetic techniques such as fluorescence in situ hybridization (FISH) and primed in situ labeling (PRINS) using specific probes to chromosomes X, Y and 21.

RESULTS

The number of fetal cells varied between 6 and 32 per mL of maternal blood. This number is 3-5 times higher than that from normal pregnancies.

CONCLUSIONS

Our current results are in agreement with the results previously reported by other groups showing that the number of fetal cells in maternal blood in trisomic 21 pregnancies is higher than in normal pregnancies. This high number of fetal cells is regarded as an advantage for the development of a noninvasive prenatal diagnostic test.

Probing the fetal genome: progress in non-invasive prenatal diagnosis

Progress in our understanding of the molecular basis of heritable diseases, through identification of specific mutations, has provided a foundation for the development of DNA-based prenatal diagnosis. Genetic analysis of fetal DNA is now routinely performed from chorionic villus samples obtained as early as the tenth week of gestation or by amniocentesis from week 15 onwards. However, both of these approaches involve invasive procedures with increased risk of fetal loss. To avoid such complications, attempts have been made to develop non-invasive tests through the identification, characterization and isolation of fetal cells or free fetal DNA from the maternal circulation. Recently, progress has been made towards the development of novel strategies that are expected to provide non-invasive means for early prenatal diagnosis in pregnancy.

Enrichment of fetal cells from maternal blood by magnetic activated cell sorting (MACS) with fetal cell specific antibodies: one-step versus two-step MACS

We report here the results of fetal cell enrichment from maternal blood in 58 pregnant women by the use of magnetic activated cell sorting (MACS) with erythroblast-specific and/or maternal cell specific antibodies. Two approaches were compared; one-step MACS to enrich CD71+ (a membrane-bound marker) or GPA+ (another marker, glycophorin A) fetal cells versus two-step MACS to deplete CD14+ maternal cells and subsequently to enrich fetal (CD71+ or GPA+) cells. The existence of fetal cells was ensured by both FISH with Y-specific probes and karyotyping of respective amniotic and/or chorionic vullus cells, the results being applied for comparison of detection rate for XY fetuses between the two MACS procedures. In 24 (38.8%) of the 58 blood samples examined, Y-positive cells were observed by FISH, whereas there were 38 true XY fetuses later confirmed by karyotyping, including two cases of 47,XY,+21. On the other hand, in Y-negative cells by FISH, there were two cases of 47,XX,+18. The average number of cells sorted did not differ among one-step MACS procedures with anti-CD14, anti-CD71 and anti-GPA antibodies. With the latter, 12 (75%) of 16 Y-positive fetuses were detected, while only one (20%) of 5 Y-positive fetuses was detected by two-step MACS with anti-CD14/anti-GPA antibodies. The detection rate significantly varied (p = 0.0024) between the two procedures, although the numbers of cases examined were small. There was no statistical difference (p > 0.05) between one-step and two-step MACS with other combinations of antibodies. These findings indicate that one-step MACS using the anti-GPA antibody is more effective than two step MACS for enrichment of fetal cells from maternal blood.

Comparison of different CD71 monoclonal antibodies for enrichment of fetal cells from maternal blood

Different approaches have been proposed for the enrichment of fetal nucleated red blood cells (NRBC) from maternal blood as an alternative way to obtain fetal tissue for non-invasive prenatal diagnosis. The main purpose of this study was to compare two of our monoclonal antibodies (2E11.3 and 2B7.4 mAbs) with the most widely used commercial anti-CD71 mAb, in terms of their ability to isolate NRBC from maternal blood by magnetic activated cell sorting (MACS). Peripheral blood samples were obtained from 60 pregnant women at a mean gestational age of 16 weeks (range: 10-19 weeks). The number of NRBC isolated by our antibodies (median: 68, range: 0-2102) was significantly higher than that obtained by the commercial antibody (median: 38, range: 0-2165) in the same samples. However, in the final preparations, contamination by maternal nucleated blood cells was lower when the commercial antibody was used. Since fetal NRBC are rare in maternal blood, the improved NRBC recovery achieved by our non-commercial antibodies should facilitate the non-invasive detection of fetal aneuploidies in maternal blood.

Quantitative FISH analysis and in vitro suspension cultures of erythroid cells from maternal peripheral blood for the isolation of fetal cells

Several techniques for the enrichment of nucleated fetal red blood cells present in maternal blood have been reported. Here we describe the use of a quantitative fluorescence in situ hybridization (FISH) method and in vitro suspension cultures of erythroid cells from newborn cord blood and maternal peripheral blood. Together with a rapid high performance liquid chromatography (HPLC) method, that allows us to determine as few as 100 cells containing haemoglobin F (HbF), we have scrutinized the reported enrichment methods for fetal nucleated cells in peripheral maternal blood. One hundred FISH analyses on maternal peripheral blood were performed. The method comprises a cell lysis method for depletion of red cells with minimal losses of nucleated cells, uniform numbers of cells (750 000 cells each) on microscopic slides, and inclusion of internal controls to monitor the efficacy of hybridization. Twenty-six cultures of pure erythroid progenitor cells from maternal peripheral blood were analysed for the expansion of fetal cells. To generate these in vitro cultures, nucleated cells from 10-20 ml of peripheral blood from 26 pregnant women were grown in media containing growth factors and hormones to yield over 10(7) of immature erythroid cells within two weeks. Of those, 13 cultures were from pregnancies with confirmed male fetuses. A total of approximately 8x10(8) maternal cells were added into tissue culture medium for these 13 cultures, resulting in about 2x10(8) nearly pure erythroid cells after two weeks. Whereas fetal cells, alone or added into cultures of peripheral blood, grow rapidly and can be detected quantitatively, we could not find any fetal cells in cultures from maternal blood. Likewise, in 7.5x10(7) peripheral blood cells probed by FISH analysis (half of which were from pregnancies with male fetuses) no single Y chromosome was detected. In summary, suspension cultures of erythroid cells can be established routinely and easily. With the quantitative FISH technique used, 750 000 cells per slide can be screened reliably for cells with Y chromosomes. However, the stringent quality-criteria and most elaborate methods indicate that fetal cells in maternal peripheral blood can not be found using the current technology.

A magnetic colloid system for isolation of rare cells from blood for fish analysis

To improve cell recovery of trophoblast and nucleated red blood cells from maternal blood for diagnosis of chromosomal abnormalities, we have investigated the use of a magnetic sorting system that utilizes a ferrofluid. The main advantage of this system is that the beads used are small enough to allow visualization of chromosome-specific sequences by fluorescence in situ hybridization (FISH). The ferrofluid was validated using MAb340, a trophoblast-specific antibody, and anti-CD71, used to sort for nucleated red blood cells. Antigen-positive cells could be efficiently sorted from a 1000-fold excess of antigen-negative cells and easily stained by FISH. We are currently evaluating its use on maternal blood samples.

Development of a rapid means of estimating the haemoglobin F content of candidate fetal cells isolated from maternal blood using HPLC

Prenatal diagnosis of genetic disorders in nucleated fetal red blood cells present in maternal blood requires methods to detect and enrich for such cells. Here we describe a rapid high performance liquid chromatography (HPLC) method that allows one to determine as few as 100 cells containing haemoglobin F (HbF) in the presence of a vast excess of haemoglobin A (HbA)-producing cells. The HPLC separations of haemoglobins were performed with a weak cation exchange column-silica gel-bound asparaginic acid-and ammonium phosphate buffer as the mobile phase. Separations were carried out in 7 min. When applied to estimation of the recovery of fetal cells from maternal blood, the HPLC method indicates in a timely manner whether or not to proceed with further techniques (i.e., FISH or PCR). Several current techniques such as Ficoll gradients and fluorescence (FACS) or magnetic (MACS) activated cell sorting were thus evaluated. Unexpectedly, our method indicates high cell losses with both single gradient and triple density Ficoll pre-enrichment methods. Less than 20 per cent of the nucleated red blood cells can be recovered in the most optimal setting. Lysis of erythrocytes may be an alternative technique that leaves nucleated red blood cells of all maturation stages intact. Thus, any further improvements in the technology for fetal cell recovery may be aided by monitoring the yield with HPLC.

A rapid combined immunocytochemical and fluorescence in situ hybridisation method for the identification of human fetal nucleated red blood cells

Fetal nucleated red blood cells are found in the maternal circulation during pregnancy. If a simple routine method of detection of these cells was developed, it could be used as the basis of non-invasive prenatal diagnosis of fetal genetic disorders. Fetal male and adult female blood were mixed to mimic maternal blood in pregnancy and used to establish a simple technique to unequivocally detect fetal nucleated red blood cells. These were identified by combined immunocytochemistry using a human fetal haemoglobin antibody and a rapid and simple-to-use fluorescence in situ hybridisation method using X and Y chromosome probes. Initial studies using the alkaline phosphatase anti-alkaline phosphatase technique as the first procedure showed that the stain was unstable and unsuitable for in situ hybridisation. An immunoperoxidase technique was found to produce a stable stain resistant to harsh fixation steps required in subsequent in situ hybridisation. This enabled the simultaneous visualisation of immunopositivity and in situ hybridisation signals on the same cell with neither procedure affecting the other's signal quality. We are currently using this procedure to detect a range of endoplasmic reticulum proteins in fetal nucleated red blood cells from maternal blood in an attempt to diagnose disorders of liver protein expression in early pregnancy.

Prenatal diagnosis by analysis of fetal cells in maternal blood

The data accumulated thus far indicate that fetal NRBCs are the target cell type of choice in maternal blood for most investigators, although some groups continue to work with the trophoblast. Reports of persistent circulation of hematopoietic stem cells, lymphoid/myeloid progenitors, and lymphocytes mandate that removal of these cell types must occur before clinical diagnosis of the current pregnancy can be made. In selected cases, accurate detection of fetal aneuploidy has been made from fetal cells in maternal blood; the clinical evaluation sponsored by the National Institute of Child Health and Human Development will determine the sensitivity and specificity of cytogenetic diagnosis in a larger group of pregnant women, but this information will not be available for several years. At present, detection of uniquely fetal, paternally inherited gene polymorphisms or mutations such as the Rh(D) antigen is possible only because the mother lacks these genes; hence, maternal cell contamination does not hinder diagnosis. Currently the presence of large numbers of maternal cells in enriched samples precludes single-gene diagnosis for conditions in which the mother carries a mutant gene, because her cells are preferentially amplified and difficult to distinguish from those of the fetus. It is likely, however, that as techniques of individual fetal cell isolation are perfected, maternal cell contamination will no longer be an issue, and the entire fetal genome will become available for diagnosis and therapy. Pediatricians need to be aware of the progress of research in this field, because fetal cell isolation from maternal blood not only could change prenatal diagnosis but would change the amount of genetic information that arrives with a newborn infant at birth. The ultimate goal of this work is to diagnose noninvasively, in the first trimester, the common fetal aneuploidies and single-gene disorders, to permit in utero treatment, or to allow low-risk pregnant women carrying an abnormal fetus an opportunity for reproductive choice.