Culture of fetal erythroid progenitor cells from maternal blood for non-invasive prenatal genetic diagnosis

The Blood Circulating Rare Cell Population. What is it and What is it Good For?

Blood contains a diverse cell population of low concentration hematopoietic as well as non-hematopoietic cells. The majority of such rare cells may be bone marrow-derived progenitor and stem cells. This paucity of circulating rare cells, in particular in the peripheral circulation, has led many to believe that bone marrow as well as other organ-related cell egress into the circulation is a response to pathological conditions. Little is known about this, though an increasing body of literature can be found suggesting commonness of certain rare cell types in the peripheral blood under physiological conditions. Thus, the isolation and detection of circulating rare cells appears to be merely a technological problem. Knowledge about rare cell types that may circulate the blood stream will help to advance the field of cell-based liquid biopsy by supporting inter-platform comparability, making use of biological correct cutoffs and “mining” new biomarkers and combinations thereof in clinical diagnosis and therapy. Therefore, this review intends to lay ground for a comprehensive analysis of the peripheral blood rare cell population given the necessity to target a broader range of cell types for improved biomarker performance in cell-based liquid biopsy.

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.

Persistence of male hematopoietic CD34+ cells in the circulation of women does not affect prenatal diagnostic techniques

OBJECTIVE

We aimed to verify whether fetal microchimerism, because of persisting fetal hematopoietic CD34(+) cells from previous pregnancies, could interfere with the development of genetic tests based on using these cells, isolated from maternal blood for the diagnosis of fetal aneuploidies.

STUDY DESIGN

CD34(+) cells, isolated from blood of parous women with at least 1 son and nulliparous women, were analyzed by using qualitative polymerase chain reaction (PCR), quantitative PCR, and fluorescence in situ hybridization (FISH) to establish whether these molecular techniques are concurrently capable of detecting circulating male DNA.

RESULTS

By qualitative PCR, male DNA was found both in parous and nulliparous women, whereas by quantitative PCR and FISH analyses, no male DNA or male nuclei were revealed except in 1 cultured CD34(+) sample from a nulliparous woman.

CONCLUSION

Fetal hematopoietic CD34(+) cells can be used in the noninvasive prenatal testing of fetal aneuploidies because the presence of fetal microchimerism does not affect fetal diagnosis in current pregnancies.

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.

Fetomaternal cell traffic, pregnancy-associated progenitor cells, and autoimmune disease

Fetal cells in maternal blood are a potential source of fetal genetic material that can be obtained non-invasively. Efforts to isolate these cells from maternal peripheral blood are limited by their low circulating numbers (approximately 1 per ml of maternal blood in euploid pregnancies). Expansion of these cells by culture would provide more cells for diagnosis and give an opportunity to study fetal metaphase chromosomes. Despite extensive optimization of culture conditions, many groups have failed reproducibly to grow fetal cells from pre-procedural maternal samples. An unexpected benefit of this research has been the discovery of a novel population of fetal cells, the pregnancy-associated progenitor cell (PAPC), which remains in maternal blood and tissue for decades following delivery. These cells might play a role in some autoimmune diseases, such as scleroderma. PAPCs appear to have stem cell characteristics, such as the ability to proliferate and differentiate. Recently developed animal models will help to ascertain whether these cells cause disease, respond to disease, or have therapeutic applications.

Fetal nucleated red blood cells in peripheral blood of pregnant women: detection and determination of location on a slide using laser-scanning cytometry

OBJECTIVE

The purpose of the study was to assess the feasibility of analysis of fetal nucleated red blood cells (NRBC) present in the maternal circulation by laser-scanning cytometry.

METHODS

CD71-positive cells were obtained by magnetic cell sorting of peripheral blood of pregnant women after density centrifugation. Immunofluorescence for the Hbgamma-chain was combined with fluorescent staining of DNA (TO-PRO-3) and fluorescence in situ hybridization (FISH) with a Y-chromosome specific probe. The cells were scanned on a slide using a laser-scanning cytometer (LSC). Events double positive for Hbgamma and TO-PRO-3 were relocated and their morphology and FISH reactivity were visually assessed. Determination of male fetal sex with LSC was compared with findings from amniocentesis.

RESULTS

In 8/15 pregnancies with male fetuses and in 0/9 with females (apart from one case with a male/female twin pregnancy), we detected Y-chromosome-positive NRBC. In pregnancies with female fetuses, Y-chromosome-positive cells other than NRBC were found in all women who had previously given birth to male babies, whereas women with no abortion and no male babies in their history did not present with Y-chromosome-positive non-NRBC.

CONCLUSION

On the basis of automatic relocation of once-defined cells of fetal origin from the current pregnancy, laser-scanning cytometry is likely to facilitate repeated (poly-)FISH analysis and single-cell PCR for noninvasive prenatal diagnosis.

Intact fetal cell isolation from maternal blood: improved isolation using a simple whole blood progenitor cell enrichment approach (RosetteSep)

Isolation and analysis of intact fetal cells in maternal blood is an attractive method of non-invasive prenatal diagnosis; however, detection levels are not optimal. The poor sensitivity and inconsistent recovery of fetal cells is compounded by small numbers of circulating fetal cells and loss of fetal cells during enrichment procedures. Optimizing selection criteria by utilizing less complicated methods for target cell enrichment is essential. We report here salutary results using a simple density-based depletion method that requires neither MACS (magnetic-activated cell sorting) nor flow cytometric separation for enrichment of progenitor cells. Maternal blood samples (n = 81) were obtained from women prior to invasive prenatal genetic diagnostic procedures and processed randomly within 24 h using one of two density-based enrichment methods. For progenitor cell enrichment, samples (n = 49) were labeled with a RosetteSep progenitor antibody cocktail to remove unwanted mature T-cells, B-cells, granulocytes, natural killer cells, neutrophils and myelomonocytic cells. For CD45-negative cell enrichment, samples (n = 14) were labeled with RosetteSep CD45 antibody to remove unwanted maternal white cells. The desired cellular fraction was collected and analyzed by either fluorescent in situ hybridization (FISH) or real-time PCR for the presence of intact fetal cells and to quantify Y-chromosome-specific DYS1 sequences, respectively. Overall, FISH and real-time PCR correct detection rates for the progenitor cell enrichment approach were 53% and 89% with 3% (1 out of 30 cases) and 0% false-positive detection, respectively. Fetal sequences were detected in the range from 0.067 to 1.167 genome equivalents per milliliter of blood. No fetal cells were detected using the CD45-negative enrichment method. Flow cytometric analysis of cord blood showed that a unique myeloid population of cells was recovered using RosetteSep trade mark progenitor enrichment compared with the CD45-negative enrichment method. Sensitivity of the RosetteSep progenitor enrichment approach for detection of fetal cells in this pilot study shows great promise with recovery of cells that are suitable for FISH and automated microscope scanning. This simple and rapid method may also allow expansion in culture and characterization of the fetal cell type(s) that circulate in maternal blood, hence, greatly improving reliability of non-invasive prenatal diagnosis.

Non-invasive prenatal diagnosis: on the horizon?

The launch of the genomics and postgenomics era has greatly expanded our understanding of the genetic basis of many diseases. In conjunction with the sociocultural trend to delay childbirth and to maintain smaller family units, extra demand may be placed on the existing prenatal diagnostic services. The inherent risk of fetal loss associated with current prenatal diagnostic procedures, such as amniocentesis and chorionic villus sampling, has spurred research into non-invasive prenatal diagnosis. Much research has been conducted on the exploitation of fetal genetic material present in the maternal circulation. The initial focus was on the isolation of intact fetal cells and subsequently, the existence of extracellular fetal DNA in maternal plasma was realized. Exciting developments have been achieved in recent years. A large-scale trial to evaluate the clinical utility of fetal cell isolation from maternal blood for fetal aneuploidy diagnosis was launched and data were recently published. Much has taken place in the research of fetal DNA analysis in maternal plasma and in one example, namely prenatal RhD determination, this type of analysis has been used in the clinical setting. This paper reviews the technological developments in non-invasive prenatal diagnosis.

Expandability of haemopoietic progenitors in first trimester fetal and maternal blood: implications for non-invasive prenatal diagnosis

OBJECTIVES

Selective amplification of rare fetal cells in maternal blood is a potential strategy for non-invasive prenatal diagnosis. We assessed the proliferative potential of first trimester fetal progenitors compared to maternal ones.

METHODS

Fetal and maternal haemopoietic progenitors were cultured separately and in two model mixtures: (i) co-cultures of male fetal nucleated cells mixed with maternal nucleated cells and (ii) co-cultures of malefetal CD34+ cells with maternal CD34+ cells. Cell origin was detected by X-Y fluorescence in situ hybridisation (FISH) RESULTS: The frequency of haemopoietic progenitors in first trimester fetal blood (predominantly CFU-GEMM) differed from those in peripheral blood from pregnant women (predominantly BFU-e). First trimester haemopoietic progenitors formed larger colonies (p=0.0001) and their haemoglobinisation was accelerated compared to those of maternal origin (p<0.001). CD34+ fetal haemopoietic progenitor cells could be expanded four times more than their maternal counterparts (median 235.8-fold, range 174.0-968.0 vs 71.9-fold, range 41.1-192.0; p=0.003). While selective expansion of fetal cells was not observed in the mononuclear cell model, the CD34+ cell rare event mixtures produced a 463.2-fold (range 128.0-2915.0) expansion of fetal cells.

CONCLUSION

Selective expansion of first trimester fetal haemopoietic progenitors may be useful for amplifying fetal cells from maternal blood.

Fetal cell isolation from maternal blood cultures by flow cytometric hemoglobin profiles. Results of a preliminary clinical trial

OBJECTIVE

We conducted a trial to test if the blood of pregnant women contains fetal clonogenic erythroid cells the progeny of which can be identified and isolated by a newly developed flow-sorting procedure.

METHODS

We have previously demonstrated the identification of fetal nucleated red cells in cocultures of fetal and adult blood. The procedure is based on profiles of the correlated contents of fetal and adult hemoglobin (HbF and HbA, respectively), using antibodies specific for the different hemoglobin chains. In such profiles, fetal cells contain only HbF, while the vast majority of adult cells contain either only HbA or a combination of HbA and HbF. HbF+ HbA- cells are flow sorted and fetal cells identified by fluorescence in situ hybridization, using chromosome-specific probes. This technique provides a yield that approaches 100%, meaning that fetal cells will be found even if the culture contains only a single fetal erythroid colony among thousands of maternal colonies. Peripheral blood samples were obtained from 11 women carrying chromosomally normal male fetuses, from 5 women carrying trisomy 21 fetuses, and from 2 women carrying trisomy 18 fetuses. A further six samples came from women with an unknown fetal karyotype. As positive controls, we used blood samples drawn after termination procedures that tended to induce some fetomaternal hemorrhage. In parallel to the method being tested, we employed alternative techniques of fetal cell detection: one third of the mononuclear cell preparations from each maternal blood sample was not cultured but labeled with anti-HbF antibodies for flow sorting of F+ cells. Ten percent of the total harvested cell population of each culture was subjected to quantitative polymerase chain reaction analysis targeting a Y-chromosome-specific sequence.

RESULTS

Most post-termination blood samples yielded fetal cells with high purity which demonstrates the validity of the method. However, no fetal cells were found in any of the maternal blood samples with normal or abnormal pregnancies, neither before nor after culture.

CONCLUSION

We conclude that a cell culture approach targeting clonogenic erythroid cells offers no advantage over established methods of direct isolation.

Evaluation of a culture system for enrichment of CD34+ hematopoietic progenitor cells present in maternal blood

BACKGROUND

Clonogenic expansion of fetal cells in maternal blood is one approach to overcome the very low number of target cells available for prenatal genetic analysis. However, efficient methods of enrichment, culturing conditions and subsequent analysis of fetal cells are lacking. Optimization of this technique requires more detailed evaluation of the composition and distribution of fetal cells that cross the placenta into the maternal circulation. Previous studies by others have shown that fetal blood is rich in CD34+ progenitor cells capable of expansion in cultures supplemented with hematopoeitic growth factors. Moreover, CD34+ fetal cells have been recovered from maternal blood following enrichment.

OBJECTIVE

In this study, we examine the type and frequency of hematopoietic progenitor cells detected in maternal (n = 13) and non-pregnant control (n = 4) peripheral blood specimens.

METHODS

A methylcellulose-based culture system was used to perform colony assays on CD34+-enriched or non-enriched cells. Overall, a total of 2,249 colonies were scored for colony type among the 17 samples. To determine whether fetal cells were present and expanded, all colonies present in each of the 10 confirmed male-cases (n = 1,525 colonies) were examined either by PCR or FISH.

RESULTS

With CD34+-enriched maternal samples, we observed a significantly higher number of burst-forming unit-erythroid (BFU-E) and a reduced number of colony-forming unit-granulocyte, macrophage (CFU-GM) colonies compared to the non-enriched samples. Of 1,067 colonies analyzed by PCR for the amelogenin locus on X and Y, none were found positive for the 250-bp Y-specific sequences. Of 458 colonies tested by FISH for presence of X and Y probe signals, no XY-male cells were detected.

CONCLUSION

We conclude that hematopoiesis is enhanced during pregnancy, but the number of fetal progenitor cells is either very low or fail to expand using the enrichment techniques and culturing conditions described in this study. Further development of methods is warranted before considering this approach for prenatal diagnosis.

Inability to clonally expand fetal progenitors from maternal blood

OBJECTIVES

To confirm the recent report of the culture of single clones of fetal progenitor cells from maternal blood.

METHODS

Hemopoietic progenitor cells were cultured from 16 blood samples obtained from women pregnant with a male singleton fetus. Single colonies were isolated by micro-manipulation and examined by multiplex real-time PCR.

RESULTS

Of a total of 1,674 colonies examined, 1,648 were identified as being maternal. No colonies were detected of fetal origin.

CONCLUSIONS

The clonal expansion of single fetal colonies from the maternal circulation is not feasible by current methods.

Prenatal diagnosis of genetic abnormalities using fetal CD34+ stem cells in maternal circulation and evidence they do not affect diagnosis in later pregnancies

In the present study, we report a new method for enrichment and analysis of fetal CD34+ stem cells after culture in order to determine whether it is feasible for noninvasive prenatal diagnosis. We also determined whether fetal CD34+ stem cells persist in maternal blood after delivery and assessed whether they have an impact on noninvasive prenatal diagnosis of genetic abnormalities. Peripheral blood samples were obtained from 35 pregnant women, 13 non-pregnant women who had given birth to male offsprings, 12 women who had never been pregnant, and eight pregnant women with male fetuses. CD34+ stem cells were enriched and either cultured for prenatal diagnosis or analyzed with fluorescence in situ hybridization (FISH)/polymerase chain reaction (PCR) to determine peristance in maternal blood. Fetal/maternal cells can be isolated and grown "in vitro" to provide enough cells for a more accurate fetal sex or aneuploid prediction than is provided by unenriched and uncultured CD34+ stem cells. The presence of fetal cells in maternal blood samples from mothers who had given birth to male offspring was found in 3 of 13 blood samples. PCR was positive for Y chromosome in one woman who had never been pregnant. Analysis of cultured CD34+ stem cells from mothers with Y PCR positivity did not detect any male cells in any samples. Even if PCR positivity is due to persistence of fetal stem cells from previous pregnancies, it does not seem to affect this new system of enrichment, culture, and FISH analysis of CD34+ fetal stem cells.

Isolation of fetal cells from the maternal circulation: prospects for the non-invasive prenatal diagnosis

The research into non-invasive and invasive prenatal diagnostic techniques developed almost in parallel. On the one hand the need was arising to ensure the birth of normal progeny in all cases, while on the other, it was not possible to eliminate the abortion risks connected with the invasiveness of amniocentesis (risk of abortion 1/200), chorion villi sampling, (risk of abortion 2%) and funicolocentesis (risk of abortion 3-4%). One of the first researchers in the non-invasive field was Adinolfi who published the earliest data in 1974 on the possibility of detecting three types of fetal cells in the maternal circulation using flow cytometry. Adinolfi suggested the possibility of using fetal cells present in the maternal circulation for prenatal diagnosis of chromosome or biochemical anomalies. Our review takes into consideration the latest methodological and technical progress in relation to the study of fetal cells in maternal circulation, without considering cells present in the endocervical canal where from the 8th week of pregnancy it is only possible to obtain trophoblast cells. This technique has since been abandoned due to the scarcity of cellular material available, the greater risk of contamination by cells of maternal origin, and also because the recovery of the cells is unpredictable, despite their potential use for the early non-invasive diagnosis of sex. The following issues are addressed in this review: the characterization of the fetal cell types present in the maternal circulation, the methods of their separation and enrichment, and the methods of genetic diagnostics applied.

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.

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.

Clonal culture of fetal cells from maternal blood

Successful isolation and genetic testing of fetal cells obtained from maternal blood could eliminate the risks associated with invasive prenatal testing. We used clonal in-vitro expansion of fetal haemopoietic cells and micromanipulation and fluorescent PCR of single colonies to obtain pure fetal colonies from peripheral blood of 12 healthy pregnant women. Of 2966 randomly selected colonies, 42 contained fetal and other cells and, for four women, two to four colonies each contained purely fetal cells. Detection of fetal cells has been hampered by rarity in maternal blood, but with our approach many cells are available for analysis.

Fetal cells from maternal blood: purpose, biological questions, technical challenges

The maternal peripheral blood circulation can serve as a source of fetal cells for the prenatal diagnosis of genetic abnormalities, eliminating the need for fetal cell sampling by invasive techniques. However, the extreme scarcity of these cells leads to a variety of biological questions and technical hurdles on the way to a clinical test. On the biological side, we need to know the numbers of fetal cells, their distinguishing properties, and the variables that affect these properties. On the technical side, we need to identify fetal cells and maximize both yield and purity of the isolation procedure. Here we review the questions and challenges as they present themselves in our specific approach to the fetal cell isolation project. We also briefly discuss the question of whether these cells could help to diagnose fetal infections.

Fetal cells in cervical mucus and maternal blood

Research in developing effective and accurate methods for non-invasive prenatal diagnosis has focused on two main techniques: the retrieval of trophoblast cells from the cervix and the enrichment of fetal erythroblasts from the blood of pregnant women. The isolation of fetal cells by both approaches has permitted the identification of fetal aneuploidies by the use of fluorescence in-situ hybridization (FISH) with appropriate probes, as well as fetal single gene disorders by polymerase chain reaction (PCR). In the latter instance, it has been shown that in order to attain the high degree of specificity required for prenatal diagnosis, it is necessary to analyse single fetal cells isolated by micromanipulation. This practice has permitted the successful characterization of fetal rhesus status, haemoglobinopathies, Duchenné's muscular dystrophy and spinal muscular atrophy, amongst others.Further developments include investigations into whether the diagnostic potential of fetal cells retrieved by either method can be expanded by the possible culturing of such cells, as well as the possibility of performing successive rounds of FISH and PCR by the recycling of isolated fetal cells.A novel observation that our group has made is that the traffic of fetal cells is enhanced in pregnancies affected by the pregnancy related disorder, pre-eclampsia. Our subsequent investigations have shown that this elevation in fetal cell traffic may serve as an early marker for those pregnancies at risk for this disorder.A very recent exciting discovery has been that free extracellular fetal DNA can be detected in the plasma and serum of pregnant women, which may permit the rapid and accurate detection of uniquely fetal loci, such as the fetal rhesus D gene in rhesus D negative pregnant women.

A new methodology of fetal stem cell isolation, purification, and expansion: preliminary results for noninvasive prenatal diagnosis

We developed a combined methodological approach to enrich and to proliferate in vitro fetal CD34+ stem progenitor cells. Using a magnetic cell-sorting technique, CD34+ cells from pregnant women at the early-second trimester were isolated and enriched and compared to those isolated from blood of nonpregnant women. The number and frequency of CD34+ cells were significantly higher (p < 0.001) in the pregnant women. Unenriched peripheral blood mononuclear cells (PBMC) and enriched CD34+ cells were cultured in a methylcellulose system to evaluate the cloning potential of progenitor cells. After culture, the numbers of burst-forming units erythroid/colony-forming units erythroid (BFU-E/CFU-E) and colony-forming units granulocyte-macrophage (CFU-GM) colonies were increased by 33 and 16 times, respectively. Finally, to distinguish between fetal and maternal cells, four cases of cultured cells were hybridized with specific probes for X and Y chromosomes and two cases with a specific probe for chromosome 21. In normal pregnancies, we identified a high number of male fetal cells and an elevated fetal/maternal ratio. When we analyzed blood samples from pregnancies with trisomic fetuses, we scored a high ratio of trisomic cells respect to maternal cells that was significantly different from the ratio of pregnancies with normal fetuses. Our results demonstrate fetal progenitor cells may be cultured and detected successfully with an appropriate combined methodological approach, which may significantly increase the feasibility of noninvasive prenatal diagnosis.

Detection of fetal trisomy 18 by short-term culture of maternal peripheral blood

OBJECTIVE

We report the prenatal detection by fluorescence in situ hybridization analysis of a male fetus with trisomy 18.

STUDY DESIGN

Total nucleated cells recovered from 7 mL of maternal peripheral blood by means of double-density gradient centrifugation were cultured for 3 days in a devised medium.

RESULTS

Fetal cells with X- and Y-specific signals were detected in all the established cultures, but the yield and purity were higher in the culture from the 1077 Ficoll layer. Cumulatively, 84 fetal cells were recorded by analysis of 5640 cells. The hematopoietic lineages involved in the production of the fetal cells in culture were not assessed. For the cultures established with the 1119 Ficoll layer, the involvement of progenitors or precursors of the erythroid lineage was assumed because postculture sorting was directed toward cells expressing the erythropoietin receptor.

CONCLUSION

We conclude that culturing total nucleated cells from maternal blood is a new procedure that could prove valuable in the detection of the main fetal aneuploidies affecting pregnant populations.

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.

Circulating hematopoietic progenitor cells in first trimester fetal blood

The yolk sac and aorto-gonad-mesonephros region are well recognized as the principal sites of hematopoiesis in the developing embryo, and the liver is the principal site of hematopoiesis in the fetus. However, little is known about circulating hematopoietic stem and progenitor cells in early fetal life. We investigated the number and characteristics of circulating progenitors in first trimester blood of 64 human fetuses (median gestational age, 10+4 weeks; range, 7+6-13+6 weeks). CD34+ cells accounted for 5.1 ± 1.0% of CD45+ cells in first trimester blood, which is significantly more than in term cord blood (0.4 ± 0.03%;P = .0015). However, the concentration of CD34+ cells (6.6 ± 2.4 × 104/mL) was similar to that in term cord blood (5.6 ± 3.9 × 104/mL). The total number of progenitors cultured from unsorted mononuclear cells (MNCs) in first trimester blood was 19.2 ± 2.1 × 103/mL, which is similar to that in term cord blood (26.4 ± 5.6 × 103/mL). All lineages were seen: colony-forming unit–GEMM (CFU-GEMM), CFU-GM, BFU-e, BFU-MK, and CFU-MK. Clonogenic assays of CD34+ cells purified from first trimester samples produced mainly two lineages: BFU-e (39.0 ± 9.6 × 103/mL CD34+ cells) and CFU-GEMM (22.6 ± 4.7 × 103/mL CD34+ cells). Short-term liquid culture of first trimester blood MNCs in SCF + IL-3 + Flt-3 (stem cell factor + interleukin-3 + Flt-3) increased, by 7-fold, the numbers of CFU-GEMM and induced a dramatic increase in BFU-e (65.6 ± 12.1–fold). These data show that significant numbers of committed and multipotent progenitors with capacity for expansion circulate in first trimester fetal blood and can be CD34 selected. These cells should be suitable targets for gene transfer and stem cell transplantation and, because fetal hematopoietic progenitors have been demonstrated in the maternal circulation from early gestation, may also be manipulated for noninvasive prenatal diagnosis of major genetic disorders.

First trimester prenatal diagnosis: fetal cells in the maternal circulation

The recovery of fetal cells from the maternal circulation represents a promising approach to noninvasive prenatal diagnosis. Advances in techniques of sensitive molecular genetic analysis have enabled the conclusive demonstration of the presence of fetal cells in maternal blood. In most pregnancies, there are few fetal cells detectable. In some abnormal pregnancies, there appears to be increased fetomaternal transfusion, which facilitates recognition of aneuploid fetal cells. This review article describes general strategies of fetal cell isolation, current technical challenges, and clinical applications that are envisioned for the future. The increased appreciation of fetal cell microchimerism, and its association with complications of pregnancy and the postpartum development of autoimmune disease, is also discussed.

Fetal RhD genotyping from maternal plasma

The prenatal diagnosis of fetal rhesus D (RhD) status is useful for the management of RhD-negative women with partners heterozygous for the RHD gene. Conventional methods for prenatal fetal RhD status determination involve invasive procedures such as fetal blood sampling and amniocentesis. The recent demonstration of the existence of cell-free fetal DNA in maternal plasma and serum opens up the possibility of determining fetal RhD status by analysis of maternal plasma or serum DNA. This possibility has recently been realized by three independent groups of investigators. This development represents an important step towards the routine application of noninvasive fetal blood group diagnosis in sensitized pregnancies and may become a model for developing safer noninvasive prenatal tests for other single-gene disorders.

The application of individualised fetal growth curves

Individually adjusted or 'customised' growth charts aim to optimise the assessment of fetal growth by taking individual variation into account, and by projecting an optimal curve which delineates the potential weight gain in each pregnancy. This results in an increased detection rate of true growth restriction and a reduction in false positive diagnoses for IUGR. An adjustable standard can apply across geographical boundaries, as individual variation exceeds that between different maternity populations.

Antenatal screening for Down's syndrome

BACKGROUND

In 1968 the first antenatal diagnosis of Down's syndrome was made and screening on the basis of selecting women of advanced maternal age for amniocentesis was gradually introduced into medical practice. In 1983 it was shown that low maternal serum alpha fetoprotein (AFP) was associated with Down's syndrome. Later, raised maternal serum human chorionic gonadotrophin (hCG), and low unconjugated oestriol (uE3) were found to be markers of Down's syndrome. In 1988 the three biochemical markers were used together with maternal age as a method of screening, and this has been widely adopted. PRINCIPLES OF ANTENATAL SCREENING FOR DOWN'S SYNDROME: Methods of screening need to be fully evaluated before being introduced into routine clinical practice. This included choosing markers for which there is sufficient scientific evidence of efficacy, quantifying performance in terms of detection and false positive rates, and establishing methods of monitoring performance. Screening needs to be provided as an integrated service, coordinating and managing the separate aspects of the screening process. SERUM MARKERS AT 15-22 WEEKS OF PREGNANCY: A large number of serum markers have been found to be associated with Down's syndrome between 15 and 22 weeks of pregnancy. The principal markers are AFP, hCG or its individual subunits (free alpha- and free beta-hCG), uE3, and inhibin A. Screening performance varies according to the choice of markers used and whether ultrasound is used to estimate gestational age (table 1). When an ultrasound scan is used to estimate gestational age the detection rate for a 5% false positive rate is estimated to be 59% using the double test (AFP and hCG), 69% using the triple test (AFP, hCG, uE3), and 76% using the quadruple test (AFP, hCG, uE3, inhibin A), all in combination with maternal age. Other factors that can usefully be taken into account in screening are maternal weight, the presence of insulin dependent diabetes mellitus, multiple pregnancy, ethnic origin, previous Down's syndrome pregnancy, and whether the test is the first one in a pregnancy or a repeat. Factors such as parity and smoking are associated with one or more of the serum markers, but the effect is too small to justify adjusting for these factors in interpreting a screening test.

URINARY MARKERS AND FETAL CELLS IN MATERNAL BLOOD

Urinary beta-core hCG has been investigated in a number of studies and shown to be raised in pregnancies with Down's syndrome. This area is currently the subject of active research and the use of urine in future screening programmes may be a practical possibility. Other urinary markers, such as total oestriol and free beta-hCG may also be of value. Fetal cells can be identified in the maternal circulation and techniques such as fluorescent in situ hybridisation can be used to identify aneuploidies, including Down's syndrome and trisomy 18. This approach may, in the future, be of value in screening or diagnosis. Currently, the techniques available do not have the performance, simplicity, or economy needed to replace existing methods.

DEMONSTRATION PROJECTS

Demonstration projects are valuable in determining the feasibility of screening and in refining the practical application of screening. They are of less value in determining the performance of different screening methods. Several demonstration projects have been conducted using the triple and double tests. In general, the uptake of screening was about 80%. The screen positive rates were about 5-6%. About 80% of women with positive screening results had an invasive diagnostic test, and of those found to have a pregnancy with Down's syndrome, about 90% chose to have a termination of pregnancy. ULTRASOUND MARKERS AT 15-22 WEEKS OF PREGNANCY: There are a number of ultrasound markers of Down's syndrome at 15-22 weeks, including nuchal fold thickness, cardiac abnormalities, duodenal atresia, femur length, humerus length, pyelectasis, and hyperechogenic bowel. (ABSTRA

Characterization of fetal haematopoietic progenitors circulating in maternal blood of seven aneuploid pregnancies

A retrospective study was carried out in order to investigate the phenotype of fetal haematopoietic progenitors circulating in the maternal blood of seven aneuploid pregnancies. Five of the blood samples were taken during pregnancies affected by various fetal aneuploidies, while the other two were collected after therapeutic abortion due to prenatal cytogenetic diagnosis of trisomies 21 and 18. Haematopoietic progenitor cells, isolated by labelling the erythropoietin receptors with the biotinylated ligand before magnetic sorting and/or fibronectin cell adhesion assay, were cultured in a suitable semisolid medium. Single- or dual-colour fluorescence in situ hybridization (FISH) was utilized to identify and enumerate fetal cells amplified in culture. Fetal trisomies were confirmed in the FISH analysis with chromosome-specific probes in all the cases analysed. The fetal purity rate ranged from 16 to 26 per cent. Haematopoietic progenitors of fetal origin were found to include CFU-E, CFU-GEMM, and possibly also M-BFU-E. Interestingly, a more immature progenitor with high self-renewal capacity (CFU-blast cell) isolated by fibronectin sorting was shown to have a relatively high frequency in one case of Down syndrome. In general, the results of this study demonstrate the feasibility of diagnosing the major fetal chromosomopathies by culturing fetal cells taken from maternal blood. Furthermore, our initial data on the sequential sorting for fibronectin and erythropoietin receptors lead us to believe that this approach may broaden the range of fetal haematopoietic progenitors retrievable from the maternal circulation.