Identification Of Fetal Cells Research Articles

Detection of circulating fetal cells utilizing automated microscopy: potential for noninvasive prenatal diagnosis of chromosomal aneuploidies

As fetal cells can be indisputably identified through detection of Y FISH signals, we utilized an automated microscopy system developed to identify and enumerate cells bearing X and Y FISH signals. We further investigated the potential of fetal hemoglobin expression as a gender independent marker for automated identification of fetal cells. For FISH-based scanning, verified fetal cells were identified based on the presence of a single X-signal and individual signals for each of the two Y FISH probes. For cell identification based on fetal hemoglobin expression, putative fetal cells were verified based on the presence of signals for anti-gamma or anti-epsilon globin antibody, and FISH signals for the X- and Y- chromosomes. Fetal cells were identified, by FISH-based scanning, in 28 of the 29 maternal samples from pregnancies with male fetuses. Simple density gradient centrifugation achieved a 3- to 5-fold increase in the number of fetal cells detected. Automated microscopy identified fetal cells in both first and second trimester maternal blood samples. Although we were unable to detect fetal erythroblasts in numbers sufficient for clinical diagnosis, the ability to reliably detect fetal cells by FISH-based scanning opens the possibility for prenatal detection of chromosomal aberrations utilizing circulating fetal cells.

Noninvasive prenatal diagnosis of fetal sex and common sex aneuploidy with short tandem repeats

目的 探索X染色体短串联重复序列(STR)在无创性产前诊断中用于胎儿细胞鉴定、性别判断及遗传病诊断的可行性.方法33名孕妇外周血,以血红蛋白γ链染色结合显微操作分离获取胎儿有核红细胞,经引物延伸预扩增技术扩增细胞基因组后,对2个X-STR位点DXS101、DXS6797及AMXY基因进行扩增.胎儿及其双亲的基因型对比分析.结果各孕妇外周血中均分选出胎儿细胞.联用DXS101、DXS6797及AMXY基因对胎儿细胞鉴定及性别判断的准确率达100%,并成功诊断了一例Turner's综合征胎儿.结论采用多个X-STR位点及AMXY基因扩增作为母血中胎源细胞鉴定系统,不局限于男胎,可准确判断胎儿性别及常见性染色体异常。

Fetal Microchimerism in the Maternal Mouse Brain: A Novel Population of Fetal Progenitor or Stem Cells Able to Cross the Blood–Brain Barrier?

We investigated whether fetal cells can enter the maternal brain during pregnancy. Female wild-type C57BL/6 mice were crossed with transgenic Green Mice ubiquitously expressing enhanced green fluorescent protein (EGFP). Green Mouse fetal cells were found in the maternal brain. Quantitative real-time polymerase chain reaction (PCR) of genomic DNA for the EGFP gene showed that more fetal cells were present in the maternal brain 4 weeks postpartum than on the day of parturition. After an excitotoxic lesion to the brain, more fetal cells were detected in the injured region. The presence of fetal cells in the maternal brain was also confirmed by quantitative real-time PCR for the sex-determining region of the Y chromosome. Four weeks postpartum, EGFP-positive Green Mouse fetal cells in the maternal brain were found to adopt locations, morphologies, and expression of immunocytochemical markers indicative of perivascular macrophage-, neuron-, astrocyte-, and oligodendrocyte-like cell types. Expression of morphological and immunocytochemical characteristics of neuron- and astrocyte-like cell types was confirmed on identification of fetal cells in maternal brain by Y chromosome fluorescence in situ hybridization. Although further studies are required to determine whether such engraftment of the maternal brain has any physiological or pathophysiological functional significance, fetomaternal microchimerism provides a novel model for the experimental investigation of the properties of fetal progenitor or stem cells in the brain without prior in vitro manipulation. Characterization of the properties of these cells that allow them to cross both the placental and blood-brain barriers and to target injured brain may improve selection procedures for isolation of progenitor or stem cells for brain repair by intravenous infusion.

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

To develop a reliable method to isolate fetal cells for genetic diagnosis. Aspiration of cervical mucus from pregnant women in the first trimester. Pregnant women were recruited before an elective termination of pregnancy. Sixty pregnant women (7-10 weeks of gestation). 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. The isolation and identification of fetal cells. 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. 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.

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.

ROC analysis of an erythroblast morphologic scoring system to improve identification of fetal cells in maternal blood.

Nucleated red blood cells are used in research settings as a target cell type for investigations of noninvasive prenatal diagnosis, and these cells have a characteristic nuclear morphology and hemoglobin staining pattern that makes them distinguishable from maternal cells. Recently, we developed an erythroblast scoring system based on these characteristics. Here, we employ statistical analyses to further characterize the utility of this scoring system. A total of 170 nucleated red blood cells isolated from peripheral blood of four women undergoing elective termination of a trisomy 21 male fetus were analyzed. Each of the four scoring system parameters, whose values range from 0 to 3 points, served as an independent variable to determine its significance for the correct identification of a cell as fetal or maternal. A logistic regression was used as a multivariable statistical tool. Forty-four patterns of the four parameters were found in the overall series. Some patterns were exclusively associated with maternal cells (e.g. 1-1-1-1 and 1-1-2-2), and others were exclusively associated with fetal cells (e.g. 3-2-2-2 and 3-2-3-2). A detection rate of 73.9% at a false-positive rate of 5% resulted from a random simulation model performed with a 1:5 case:control matched set. The variables most predictive of a cell being fetal were gamma hemoglobin staining intensity of cytoplasm and nuclear roundness. The modified scoring system presented here improves upon the previously reported, unmodified erythroblast scoring system. These statistical analyses suggest that the scoring system is a promising method that aids in distinguishing fetal and maternal NRBCs for prenatal diagnostic applications and that it may be amenable to automated microscopy by applying the discrete morphological parameters as computational classifiers.

Sensitivity and Specificity of the Identification of Fetal Cells in Maternal Blood by Combined Staining with Antibodies against Beta-, Gamma- and Epsilon-Globin Chains

Objectives: Antibodies against fetal and embryonic hemoglobins may identify fetal cells in maternal blood. Both γ- and Ε-globins are used as fetal cell markers. γ-Globin is not fetus specific. So far Ε-globin has been claimed to be fetus specific. In this communication, we compare the specificity of anti-Ε- and anti-γ-globin staining when combined with staining for β-globin. Methods: We applied single and double color immunofluorescent staining techniques in combination with XY chromosome hybridization. The blood sample was taken after chorion villus biopsy at 11 weeks of gestation from a woman carrying a male fetus. Results: By γ-globin staining alone, 21 fetal and 2 maternal nucleated red blood cells (NRBCs) were identified. Only 1 of the 2 maternally derived NRBCs expressed β-globin. By Ε-globin staining, 92 additional fetal NRBCs were identified. Conclusions: Ε-Globin antibody and combined Ε- and γ-globin antibody staining of a blood sample from a pregnant woman at 11 gestational weeks showed higher sensitivity but lower specificity for the fetal origin of erythroblasts with combined compared with separate staining. The final decision of the origin of cells was made by gender determination by FISH. Out of 2 γ-positive maternal cells 1 was β-globin antibody positive, 1 was β-globin negative, indicating that 100% specificity for fetal origin could not be obtained by combining all 3 hemoglobin types. Although only 1 blood sample was tested and only 2 γ-positive maternal NRBCs were identified, the result indicates that β-hemoglobin does not discriminate completely between γ-positive NRBCs of fetal and maternal origin.

Clinical Review 160: Postpartum autoimmune thyroid disease: the potential role of fetal microchimerism.

Fetal microchimerism is defined as the presence of fetal cells in maternal tissues established during pregnancy. Immune suppression of maternal immunity during pregnancy by the placenta may play an important role in allowing the establishment of such fetal microchimerism. However, peripheral blood fetal microchimerism that persists in the postpartum period is considered a natural event and implies the induction of tolerance during pregnancy. Identification of fetal cells that persist preferentially in maternal tissues subject to autoimmunity, such as skin and thyroid, has also suggested the possible immune modulation of the autoimmune response at the target tissue by fetal cells. Accumulating evidence suggests that fetal immune cells may be reactive to maternal antigens and, therefore, have the capacity to trigger graft vs. host reactions. This would provide a mechanism for the initiation and/or exacerbation of autoimmune disease. The course and severity of autoimmune thyroid disease have long been known to be profoundly influenced by pregnancy, with disease suppression prepartum and exacerbation postpartum. However, the precise mechanisms involved have not been fully understood. Here we have reviewed recent information on the possible role of fetal microchimerism in autoimmune thyroid disease, focusing on the immunological consequences of intrathyroidal fetal cells and their contribution to postpartum exacerbations.

Rhesus disease and non-immune hydrops

Hippocrates first documented the condition of ‘fetal hydrops’ in 400 BC. There was recognition of jaundice of the newborn in the 17th century, but it was not until 1909 that Buchan established a link between some cases of newborn jaundice and anaemia, and 1932 before Diamond described the condition of erythroblastosis fetalis. Between 1938 and 1941, the identification of maternal red cell antibodies, the Rhesus antigen and blood group inheritance were established. In 1947, Diamond first described post-natal treatment utilizing transfusion, with exchange transfusion being described by Mollison in 1952. Intra-uterine therapy was not established until 1963 when Liley first published the use of intraperitoneal transfusion. The last 40 years have seen rapid advances in the understanding, assessment and therapy of Rhesus disease and non-immune hydrops. We have seen exploration of: amniotic fluid bilirubin levels, to determine whether a fetus is at risk of haemolytic disease of the newborn (Freda and Liley); plasmapheresis (Powell), aiming to reduce the maternal circulating antibody levels; fetal blood sampling, to establish a diagnosis; and intraperitoneal or intravascular transfusion, as methods of direct therapy, the latter initially using fetoscopy and then using an ultrasound-guided approach to fetal vessels. Stem-cell therapy has been explored and, more recently, non-invasive methods to assess fetal anaemia have been introduced using the mean range on a computerized cardiotocograph (CTG) and middle cerebral artery maximum flow velocity. In cases where the partner is heterozygous for a particular red cell antigen, the potential for determining fetal group by identification of fetal cells in the maternal circulation for testing has also become a possibility. Approximately 20% of cases of non-immune hydrops remain ‘idiopathic’, the remainder either being a result of a cardiac structural anomaly, arrhythmia or a metabolic disorder. Twinning accounts for approximately 6% of cases of non-immune hydrops. This article aims to give an overview of what is happening today and a glimpse of what might be possible in the future.

Current state of screening for Down's syndrome.

Down's syndrome has an incidence of about 1.3 per 1000 births. Antenatal testing for this disorder on the basis of maternal age has been common practice (increasing age is associated with increasing risk of having an affected pregnancy). Since the late 1980s it has been possible to calculate a pregnancy-specific risk using maternal age and serum marker levels, but the absence of a national screening policy in the UK has resulted in a diversity of screening practice. Screening may take place in the first or second trimester of pregnancy, using maternal age in combination with up to six serum markers, with or without ultrasound markers. Additionally, some units offer the screen only to women in specific age groups. Risk and marker levels are affected by a number of factors for which adjustments in the calculation may be made. Laboratories offering screening must also establish robust monitoring and quality management systems to ensure continued confidence in the reported result. Current diagnostic techniques require the use of invasive procedures which pose a risk to the fetus and the mother. Future screening may combine new technologies with the identification of fetal cells in maternal blood to reduce or abolish the need for these procedures.

Enrichment, Immunomorphological, and Genetic Characterization of Fetal Cells Circulating in Maternal Blood

Fetal cells circulating in the peripheral blood of pregnant women are a potential target for noninvasive genetic analyses. They include epithelial (trophoblastic) cells, which are larger than peripheral blood leukocytes. We enriched circulating trophoblastic cells using the isolation by size of epithelial tumor cells (ISET) method. Peripheral blood was obtained at 11 to 12 weeks of pregnancy. Cells isolated by ISET were stained by hematoxylin and eosin or by immunohistochemistry. Large epithelial cells were microdissected and fetal cell identification was obtained by polymerase chain reaction with short tandem repeats and/or Y-specific primers. By analyzing only 2 ml of blood, we found a variable number (n = 1 to 7) of Y-positive cells (overall 15 of 23) in all of the six mothers carrying a male fetus. In contrast, none of the 26 cells isolated from seven mothers carrying a female fetus scored positive. Eleven cells were analyzed by using short tandem repeat-specific markers: six of them showed a fetal profile and five showed a maternal profile consistently with Y-specific results. Only one-fifth of the single cell DNA was used for fetal cell assessment, leaving enough material for further genetic tests. We also show that the ISET approach allows the performance of fluorescence in situ hybridization analyses and the detection of DNA point mutations in single microdissected cells. We conclude that this is a powerful approach to enrich circulating fetal cells and prove their fetal origin, and that it may have implications for noninvasive prenatal diagnosis of genetic disorders.

Novel feto‐specific mRNA species suitable for identification of fetal cells from the maternal circulation

Feto-specific markers are necessary for genetic diagnostics on fetal cells isolated from maternal blood. Differential display reverse transcription-polymerase chain reaction (DDRT-PCR) was used to identify mRNA species preferentially expressed in trophoblast-enriched primary cell cultures compared to female peripheral mononuclear blood cells (FPMBCs). We obtained 15 different cDNA clones expressed predominantly in placenta cells using a commercial kit with oligo-(dT) anchor primers and arbitrary upstream primers for differential display analysis of total RNA. Reverse Northern dot-blot analysis and semi-quantitative RT-PCR confirmed the different expression levels. Seven mRNA species were exclusively expressed in the placenta: the mRNAs of epsilon-globin, a renowned marker of fetal erythroblasts, early placenta insulin-like peptide (EPIL), Yes-associated protein (YAP65) and osteopontin were expressed at high levels, whereas the mRNAs of PP14, JM27 protein, and an unidentified expressed sequence tag (EST) were moderately expressed. A further eight mRNAs with low expression in FPMBCs and higher expression in first trimester placenta were identified. Some mRNAs were expressed in a trophoblast cell line, e.g. YAP65, whereas others were not, e.g. EPIL. The new mRNA markers may be used to construct DNA/RNA probes to identify fetal cells in maternal circulation by hybridization techniques, or to identify proteins selectively expressed in fetal cells and amenable to immunocytochemical detection.

Novel feto‐specific mRNA species suitable for identification of fetal cells from the maternal circulation

Novel feto‐specific mRNA species suitable for identification of fetal cells from the maternal circulation

Simultaneous fetal cell identification and diagnosis by epsilon-globin chain immunophenotyping and chromosomal fluorescence in situ hybridization

AbstractIsolating fetal erythroblasts from maternal blood offers a promising noninvasive alternative for prenatal diagnosis. The current immunoenzymatic methods of identifying fetal cells from background maternal cells postenrichment by labeling γ-globin are problematic. They are nonspecific because maternal cells may produce γ-globin, give poor hybridization efficiencies with chromosomal fluorescence in situ hybridization (FISH), and do not permit simultaneous visualization of the fetal cell identifier and the FISH signal. We describe a novel technique that allows simultaneous visualization of fetal erythroblast morphology, chromosomal FISH, and ε-globin labeled with AMCA (7-amino-4-methylcoumarin-3-acetic acid). AMCA was chosen as the fluorescent label to circumvent the problem of heme autofluorescence because the mean difference in relative fluorescence intensity between fetal erythroblasts stained positive for antiglobin antibody and autofluorescence of unstained cells was greater with AMCA (mean 43.2; 95% confidence interval [CI], 34.6-51.9; SD = 14.0) as the reporting label compared with fluorescein isothiocyanate (mean 24.2; 95% CI, 16.4-31.9; SD = 12.4) or phycoerythrin (mean 9.8; 95% CI, 4.8-14.8; SD = 8.0). Median FISH hybridization efficiency was 97%, comparable to the 98% (n = 5 paired samples) using Carnoy fixative. One ε-positive fetal erythroblast was identified among 105 maternal nucleated cells in 6 paired mixture experiments of fetal erythroblasts in maternal blood (P < .001). Male ε-positive fetal erythroblasts were clearly distinguishable from adult female ε-negative erythroblasts, with no false positives (n = 1000). The frequency of fetal erythroblasts expressing ε-globin declines linearly from 7 to 14 weeks' gestation (y = −15.8 × + 230.8;R2 = 0.8; P < .001). We describe a rapid and accurate method to detect simultaneously fetal erythroblast morphology, intracytoplasmic ε-globin, and nuclear FISH.

Fetal cells in transcervical samples at an early stage of gestation.

Several investigations are in progress with the aim of performing prenatal diagnosis of inherited disorders by noninvasive or minimally invasive techniques. The most important approaches are based on the detection of fetal nucleated cells in maternal blood, the analysis of fetal DNA present in maternal plasma, and the identification and isolation of fetal trophoblastic cellular elements shed into the uterine cavity and the endocervical canal. In this review, we discuss the methods that have been employed for the collection of the transcervical samples at an early stage of gestation and the techniques used for the identification of fetal cells. We also report the results of using endocervical cells for the detection of fetal chromosomal disorders by fluorescent in-situ hybridization and for performing prenatal diagnosis of fetal Rh(D) phenotypes. Recent investigations have also shown that--after the isolation of trophoblastic cells from maternal contaminants by micromanipulation--transcervical samples can be employed for the prenatal diagnosis of single gene defects, such as those causing thalassemia and sickle cell anemia. Although the present results are promising, further investigations are required to demonstrate the feasibility of performing accurate diagnosis of fetal diseases by this minimally invasive approach in all transcervical samples retrieved at an early stage of gestation.

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

The aim of this work was to isolate, enumerate and attempt the identification of fetal cells recovered from the lower uterine pole. Immediately before elective termination of pregnancy at 7-17 weeks gestation, samples were recovered by transcervical flushing of the lower uterine pole (n = 108) or transcervical aspiration of mucus from just above the internal os (n = 187), and their contents examined using histological, immunohistochemical and molecular techniques. Syncytiotrophoblasts were identified morphologically in 28 out of 89 (31%) and 50 out of 180 (28%) flushings and aspirates respectively (mean 29%). Immunocytochemistry with monoclonal antibodies (mAbs) recognizing trophoblast or epithelial cell antigens on a smaller number of samples (n = 69) identified putative placental cells in 13 out of 19 (68%) and 25 out of 50 (50%) flushings and aspirates respectively (mean 55%). These included groups of distinctive cells with a small, round, hyperchromatic nucleus, strongly reactive with mAbs PLAP, NDOG1 and FT1.41.1. Smaller groups of larger, amorphous cells, usually containing multiple large, pale staining nuclei, reactive with mAb 340 and to a lesser degree with mAb NDOG5 were also observed. Taking cellular morphology and immunophenotype into consideration, the smaller uninucleate cells were likely to be villous mesenchymal cells, while the larger cells were possibly degrading villous syncytiotrophoblast. There was no significant difference in the frequency of fetal cells obtained by the two recovery methods. Squamous or columnar epithelial cells, labelled strongly with antibodies to cytokeratins or human milk fat globule protein, were observed in 97% (29 out of 30) of aspirates. The use of cervagem in a small number of patients prior to termination of pregnancy did not appear to influence the subsequent recovery of placental cells. Y-specific DNA was detected by polymerase chain reaction (PCR) in 13 out of 26 (50%) flushings and (99 out of 154) 64% aspirates analysed (mean 62%). In-situ hybridization (ISH) revealed Y-specific targets in 40 out of 69 (60%) of aspirates analysed. A comparison of PCR data obtained from transcervical recovered samples and placental tissues showed a concordance of 80% (76 out of 95), with 10 false positives. Comparing the PCR data from tissues with data derived by ISH from 41 aspirates gave a concordance of 90% with two false positives. Although syncytiotrophoblasts were much more likely to be present in samples containing immunoreactive placental cells, the detection rates of fetal-derived DNA were similar regardless of the morphological and/or immunological presence of placental cells. We conclude that the transcervical recovery of fetal cells, while promising, requires considerable additional effort being expended in further research and development, particular in the sampling procedure.

Prenatal diagnosis using fetal cells isolated from maternal peripheral blood: a review.

Many questions remain about the feasibility of using fetal cells from maternal blood for prenatal diagnosis. Although recently there has been more focus on clinically relevant methods, many studies have been performed using blood drawn after invasive procedures, and over a wide range of gestational ages. For methods to be applicable to clinical use, more work is needed on isolating cells early in pregnancy, when termination is still an option for parents who are found to have an affected pregnancy. It is generally agreed that fetal nucleated erythrocytes are the most efficacious cell type for prenatal diagnosis, but it has not yet been shown definitively whether there is an ideal gestational age for sampling, whether ABO incompatibility might limit availability of fetal cells, or whether the number of cells present might be different in normal versus abnormal pregnancies. PCR has been shown to be a powerful tool in allowing amplification and identification of very small amounts of fetal DNA. However, this is limited to cases in which a specific and unique gene from the father is sought. This means that there is the potential to diagnose many paternally inherited autosomal dominant diseases and some autosomal recessive diseases, in which the parents have different and identifiable mutations. However, when parents are both carriers of the same autosomal recessive mutations, or when the disease is X linked, PCR will not aid in prenatal diagnosis. Cytogenetic analysis of fetal cells by FISH after cell sorting is another potentially useful method of prenatal diagnosis, but requires relatively pure samples of fetal cells or an independent marker that allows easy microscopic identification. The latter might be accomplished by identifying fetal cells through their expression of embryonic hemoglobins or because they contain HLA-G mRNA. In addition, current techniques of cell sorting must be improved so that a higher percentage of fetal cells can be isolated. Currently, the best cell sorting techniques usually produce a maximum purity of 10% fetal cells. Commonly, in normal pregnancies, fewer than 0.1% of the cells isolated after sorting are fetal in origin. Improving the concentration and quantity of fetal cells will improve the accuracy of FISH. Methods such as immunophenotyping that allow the selective identification of fetal cells by microscopy, and can be used in conjunction with FISH, may be extremely valuable because they may allow the genetic analysis of only the few fetal cells within a background preponderance of maternal cells. Although the retrieval of fetal cells from maternal blood is an attractive concept, it must be clearly stated that presently it is only in the investigational phase because of the low sensitivity and specificity. There is no current application for these methods in clinical practice. It remains to be determined whether testing maternal blood for fetal cells or DNA will be used as a screening tool, similar to the maternal serum screening currently in use, or whether the accuracy can be improved to a level such that the techniques can be used diagnostically. Although there are many questions that remain unanswered at this time, the outlook for noninvasive prenatal genetic testing in the future is optimistic.

GREATLY INCREASED EFFICIENCY of ANALYSIS of FETAL CELLS FROM MATERNAL BLOOD: IDENTIFICATION of FETAL CELLS based on CD71 EXPRESSION, LACK of BETA GLOBIN EXPRESSION and use of GAMMA GLOBIN mRNA to DISTINGUISH FETAL (XX) from MATERNAL (XX) CELLS

GREATLY INCREASED EFFICIENCY of ANALYSIS of FETAL CELLS FROM MATERNAL BLOOD: IDENTIFICATION of FETAL CELLS based on CD71 EXPRESSION, LACK of BETA GLOBIN EXPRESSION and use of GAMMA GLOBIN mRNA to DISTINGUISH FETAL (XX) from MATERNAL (XX) CELLS

Detection of fetal HLA‐DQα sequences in maternal blood: A gender‐independent technique of fetal cell identification

The objective of this study was to detect fetal HLA-DQa gene sequences in maternal blood. HLA-DQa genotypes of 70 pregnant women and their partners were determined for type A1. We specifically sought couples where the father, but not the mother, had genotype A1. In 12 women, maternal blood samples were flow-sorted. Candidate fetal cells were isolated and amplified by using PCR primers specific for a paternal HLA-DQa A1 allele. Fetal HLA-DQa A1 genotype was predicted from sorted cells; amniocytes or cheek swabs were used for confirmation. Six of twelve sorted samples had amplification products indicating the presence of the HLA-DQa A1 allele; 6/12 did not. Prediction of the fetal genotype was 100 per cent correct, as determined by subsequent amplification of amniocytes or cheek swabs. We conclude that paternally inherited uniquely fetal HLA-DQa gene sequences can be identified in maternal blood. This system permits the identification of fetal cells independent of fetal gender, and has the potential for non-invasive prenatal diagnosis of paternally inherited conditions.

Presence of cells of fetal origin in maternal circulation of pregnant women.

Fetal cells can be identified by using the polymerase chain reaction to test for the presence of human Y-chromosome-specific ZFY and SRY gene DNA sequences in maternal peripheral blood of women who bear a male fetus. Thirty-one pregnant women were studied in the first trimester to determine when fetal cells become detectable in the maternal circulation. Among the 19 women whose peripheral blood samples were positive for Y-chromosome-specific DNA sequences, the presence of fetal cells was quite case-variable from the 6th to 12th gestational weeks. Twenty-eight women who had given birth to their first male babies were studied postpartum to determine when fetal cells disappear from the maternal circulation. Fetal cells can still be detected in maternal blood 10 months postpartum in some cases. These results suggest that identification of fetal cells in the maternal circulation is possible. Nevertheless, interpretation of fetal cells in maternal circulation should be handled very carefully with respect to when these fetal cells first became detectable and potential interference from previous pregnancies.