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

Overview and recent developments in cell-based noninvasive prenatal testing

Investigators have long been interested in the natural phenomenon of fetal and placental cell trafficking into the maternal circulation. The scarcity of these circulating cells makes their detection and isolation technically challenging. However, as a DNA source of fetal origin not mixed with maternal DNA, they have the potential of considerable benefit over circulating cell-free DNA-based noninvasive prenatal genetic testing (NIPT). Endocervical trophoblasts, which are less rare but more challenging to recover are also being investigated as an approach for cell-based NIPT. We review published studies from around the world describing both forms of cell-based NIPT and highlight the different approaches' advantages and drawbacks. We also offer guidance for developing a sound cell-based NIPT protocol.

Diagnostic Value of Non-Invasive Prenatal Screening of β-thalassemia by Cell Free Fetal DNA and Fetal NRBC

BACKGROUND

Beta thalassemia is a common disorder with autosomal recessive inheritance. The most prenatal diagnostic methods are the invasive techniques that have the risk of miscarriage. Now the non-invasive methods will be gradually alternative for these invasive techniques.

OBJECTIVE

The aim of this study is to evaluate and compare the diagnostic value of two non-invasive diagnostic methods for fetal thalassemia using cell free fetal DNA (cff-DNA) and nucleated RBC (NRBC) in one sampling community.

METHODS

10 ml of blood was taken in two k3EDTA tube from 32 pregnant women (mean of gestational age = 11 weeks), who themselves and their husbands had minor thalassemia. One tube was used to enrich NRBC and other was used for cff-DNA extraction. NRBCs were isolated by MACS method and immunohistochemistry; the genome of stained cells was amplified by multiple displacement amplification (MDA) procedure. These products were used as template in b-globin segments PCR. cff-DNA was extracted by THP method and 300 bp areas were recovered from the agarose gel as fetus DNA. These DNA were used as template in touch down PCR to amplify b-globin gen. The amplified b-globin segments were sequenced and the results compared with CVS resul.

RESULTS

The data showed that sensitivity and specificity of thalassemia diagnosis by NRBC were 100% and 92% respectively and sensitivity and specificity of thalassemia diagnosis by cff-DNA were 100% and 84% respectively.

CONCLUSION

These methods with high sensitivity can be used as screening test but due to their lower specificity than CVS, they cannot be used as diagnostic test.

The promise of fetal cells in maternal blood

Delaying childbirth increases the proportion of advanced maternal age pregnancies. This increases the number of pregnancies requiring invasive prenatal testing. Prenatal diagnosis of chromosomal aneuploidies and monogenic disorders requires fetal cells obtained through invasive procedures (i.e. chorionic villus sampling and amniocentesis). These procedures carry a risk of fetal loss, which causes anxiety to at-risk couples. Intact fetal cells entering maternal circulation have raised the possibility of non-invasive prenatal diagnosis. Rarity of fetal cells, however, has made it challenging. Fetal nucleated red blood cells are ideal candidate target cells because they have limited lifespan, contain true representation of fetal genotype, contain specific fetal cell identifiers (embryonic and fetal globins), and allow interrogation with chromosomal fluorescence in-situ hybridisation and possibly with array comparative genomic hybridisation. The utility of fetal nucleated red blood cells in non-invasive prenatal diagnosis has not reached clinical application because of the inconsistencies in enrichment strategies and rarity of cells.

Non-invasive prenatal diagnosis of aneuploidies: new technologies and clinical applications

Non-invasive prenatal diagnosis (NIPD) has substantial medical importance as it targets the development of safer and more effective methods to avoid the risk of fetal loss associated with currently used invasive methods. Several approaches have been demonstrated as being proof-of concept for NIPD of chromosomal aneuploidies. These approaches include cell-based and cell-free detection methods, involving the investigation of fetal cells in the maternal circulation, formaldehyde treatment of maternal plasma, DNA methylation studies using sodium bisulfite or restriction enzymes, protein-based studies, identification of fetal-specific mRNAs and digital polymerase chain reaction (PCR) approaches, and recently next-generation sequencing and methylated DNA immunoprecipitation real-time quantitative PCR-based approaches. Although all these NIPD methods have both advantages and limitations, some are moving closer to clinical implementation. Biotechnology companies dedicated to the development of NIPD tests such as the sequencing- or methylation-based approaches are finalizing large clinical trials. It is expected that these new technologies will facilitate safer, more sensitive and accurate prenatal diagnostic tests in the near future. In this review, we highlight the most recent advances in methods for NIPD of aneuploidies, and we discuss their future implications in clinical practice.

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.

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.

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.

The use of non-physiological conditions to isolate fetal cells from maternal blood

Fetal cells are always present in maternal blood starting in the first trimester of pregnancy, however a rapid, simple, and consistent procedure for their isolation for prenatal non-invasive genetic investigation is still lacking. Sensitivity and recovery of fetal cells is jeopardized by the minute amount of circulating fetal cells and their loss during the enrichment procedure. We report here a single-step approach to isolate fetal cells from maternal blood which relies on the use of non-physiological conditions to modify cell densities before their separation in a density gradient and in a newly developed cell separation device. Isolated fetal cells have been investigated using cytochemistry, Soret band absorption microscopy, monoclonal antibodies for epsilon- and gamma-chain-Hb, monoclonal antibody for i-antigen, and by fluorescence in situ hybridization (FISH). Fetal cells were always detected in all 105 maternal blood samples investigated and fetal aneuploidies were correctly diagnosed by FISH, in a pilot study of pathological pregnancies, in fetal cells isolated from maternal blood obtained either before or after invasive procedure.

Human skin mast cells express H2 and H4, but not H3 receptors

Mast cells generate and release histamine during anaphylactic reactions, and there is pharmacological evidence that histamine regulates this process via specific receptors. Therefore, we examined human leukemic (HMC-1) and normal skin mast cells for the expression of all four currently known histamine receptors. Both cell types expressed H2 and H4 receptors at mRNA and protein levels, whereas H3 receptor specific mRNA and receptor protein was undetectable. Similarly, immunohistochemistry of cutaneous tissue showed an absence of H3 receptor in these cells. Despite transcription of mRNA, H1 receptor protein was only moderately expressed in HMC-1 cells and was virtually absent in skin mast cells. Furthermore, only H1, H2, and H4 receptors were detectable by Western blot analysis of HMC-1 cells. Radiolabeled histamine binding was strongly inhibited only by H2 (ranitidine)- and H3/H4 (FUB 108)-specific antagonists. Histamine-induced increase of cAMP was inhibited by the H2 receptor antagonist famotidine, whereas induction of IP3 was not observed, making signaling via the H1 receptor unlikely. These data show that human mast cells constitutively express primarily H2 and H4 receptors and that H2 receptors are functionally linked to cellular processes. They provide new insights into the mechanisms that govern auto- and paracrine histamine-induced mast cell functions.

Isolation of fetal nucleated red blood cells from maternal blood in normal and aneuploid pregnancies

Fetal nucleated red blood cells (NRBC) have been widely reported in maternal blood during pregnancy. However, there is no consensus with regard to their presence in all pregnancies. Therefore, the usefulness of developing a fetal NRBC-based noninvasive method suitable for clinical prenatal diagnosis remains uncertain. Fluorescence in situ hybridization (FISH) method was used to evaluate the ability of one of our own monoclonal antibodies (mAb), 2B7.4, to isolate fetal NRBC from maternal blood by magnetic activated cell sorting (MACS). Our mAb was able to isolate from 25 to 822 NRBC from all of the 45 maternal blood samples included in this study. A correct diagnosis was achieved in 21 out of 24 pregnancies carrying trisomic fetuses (87.5%), with a fetal/maternal NRBC frequency of 8.4%. In contrast, a significantly lower percentage of fetal NRBC (0.2%) was observed in 22% of pregnancies carrying a chromosomally normal male fetus, that were correctly predicted. In conclusion, using 2B7.4 mAb we succeeded in isolating NRBC from the maternal blood samples, but most of the isolated cells were maternal in origin. Nevertheless, a higher number of fetal NRBC was found in the peripheral blood of pregnant women carrying aneuploid fetuses, which could allow development of a screening method for prenatal diagnosis of fetal aneuploidies.

Fetal cells and DNA in maternal blood

Although fetal cells have been known to escape to the maternal circulation for a number of years, research attempts to use them for prenatal diagnosis have not had any consistent success. This review attempts to trace the history of such attempts and to document their progress and reasons for success or failure. The opinions of recent conferences including that of the US National Institute of Child Health and Human Development, a sponsor of major US research in the field, are reported and discussed. It is concluded that although basic work has demonstrated the biologic availability of both fetal cells and their free DNA representatives in the maternal circulation at gestational ages relevant to prenatal diagnosis, much work remains to develop practical technology for their consistent recovery and assay.

Prenatal evaluation for fetal surgery

The selection of fetuses that may benefit with in utero surgery is being developed. Noninvasive and invasive prenatal diagnosis techniques are utilized to try and gain as much knowledge about the fetus so that the appropriate counseling of parents can be undertaken. The most common invasive techniques are amniocentesis and chorionic villus sampling for fetal karyotyping and genetic diagnosis. Noninvasive techniques include ultrasound (2D and 3D), fetal echocardiography and magnetic resonance imaging. Additional techniques such as specific Doppler evaluation of vascular components, new techniques to look at fetal electrocardiograms and the use of computer tomography are also considered. The most common conditions for which in utero fetal surgery is also being considered are twin to twin transfusion syndrome, myelomeningocele, sacrococcygeal teratoma, cystic adenomatoid malformation of the lung with fetal hydrops and other monochorionic twin abnormalities (severe discordant birth defects or twin reversal arterial perfusion sequences). Ongoing evaluation of the sensitivity, specificity, positive and negative predicted values of these evaluation tools is required so that appropriate selection of fetuses for the surgery can be made.

Developments in laboratory techniques for prenatal diagnosis

Ongoing trends in prenatal diagnosis aim at early, rapid, and ideally noninvasive diagnosis as well as at the improvement of risk-screening for aneuploidy. Interphase-fluorescence in situ hybridization and quantitative fluorescence polymerase chain reaction are efficient tools for the rapid exclusion of selected aneuploidies in addition to the established direct preparation of chromosomes from chorionic villi. Interphase fluorescence in situ hybridization has also made possible the diagnosis of selected chromosome abnormalities in single cells (e.g. in preimplantation genetic diagnosis) or noninvasive diagnosis. More complex multicolor fluorescence in situ hybridization approaches are currently being evaluated. Single cell polymerase chain reaction is the key technique for the molecular diagnosis of a growing number of monogenic conditions before implantation or, still more experimental, in fetal cells retrieved from the maternal circulation. New sources for noninvasive diagnosis came into play such as fetal DNA or cell nuclei in maternal plasma. The combination of biochemical parameters in the maternal serum, namely free beta-human chorionic gonadotropin with pregnancy associated plasma protein A and sonographic markers, has already dramatically increased the sensitivity of risk screening in the first trimester of pregnancy.

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.