Frequency of Fetal Cells in Sorted Subpopulations of Nucleated Erythroid and CD34+ Hematopoietic Progenitor Cells From Maternal Peripheral Blood

Isolation and Enrichment of Circulating Fetal Cells for NIPD: An Overview

Prenatal diagnosis plays a crucial role in clinical genetics. Non-invasive prenatal diagnosis using fetal cells circulating in maternal peripheral blood has become the goal of prenatal diagnosis, to obtain complete fetal genetic information and avoid risks to mother and fetus. The development of high-efficiency separation technologies is necessary to obtain the scarce fetal cells from the maternal circulation. Over the years, multiple approaches have been applied, including choice of the ideal cell targets, different cell recovering technologies, and refined cell isolation yield procedures. In order to provide a useful tool and to give insights about limitations and advantages of the technologies available today, we review the genetic research on the creation and validation of non-invasive prenatal diagnostic testing protocols based on the rare and labile circulating fetal cells during pregnancy.

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.

Trophoblasts Isolated from the Maternal Circulation: In Vitro Expansion and Potential Application in Non-invasive Prenatal Diagnosis

Prenatal diagnosis based on rare fetal cells in maternal blood is currently not a feasible option. An effort was made to improve cell yields by targeting trophoblast cells. After sorting, the HLA-G-positive cell fraction was analyzed directly or after culture. In situ hybridization technology was applied to prove fetal cell source in samples from women carrying a male fetus and to predict gender in samples without previous knowledge of fetal sex. In vitro culture led to a significant increase in fetal cells and accurate gender prediction in 93% of these samples. This approach might be useful for non-invasive prenatal diagnosis.

Polyomavirus JC in the context of immunosuppression: a series of adaptive, DNA replication-driven recombination events in the development of progressive multifocal leukoencephalopathy

Polyomavirus JC (JCV) is the etiological agent of progressive multifocal leukoencephalopathy (PML), a demyelinating infection of oligodendrocytes in the brain. PML, a frequently fatal opportunistic infection in AIDS, has also emerged as a consequence of treatment with several new immunosuppressive therapeutic agents. Although nearly 80% of adults are seropositive, JCV attains an ability to infect glial cells in only a minority of people. Data suggest that JCV undergoes sequence alterations that accompany this ability, and these changes can be derived from an archetype strain by mutation, deletion, and duplication. While the introductory source and primary tissue reservoir of JCV remain unknown, lymphoid cells have been identified as potential intermediaries in progression of JCV to the brain. This review is focused on sequence changes in the noncoding control region (NCCR) of the virus. We propose an adaptive mechanism that involves a sequential series of DNA replication-driven NCCR recombination events involving stalled DNA replication forks at NCCR palindromic secondary structures. We shall describe how the NCCR sequence changes point to a model in which viral DNA replication drives NCCR recombination, allowing JCV adaptation to different cell types in its progression to neurovirulence.

Raising antibodies against circulating foetal cells from maternal peripheral blood

OBJECTIVE

Cells of foetal origin circulating in the maternal peripheral bloodstream present a unique source for non-invasive prenatal diagnostics. The aims of this study were to raise antibodies against identified circulating foetal cells from the maternal blood, test the properties of these antibodies and to determine the foetal cell type recognised by the antibodies.

METHOD

Cells from a male foetus were identified in a maternal blood sample by FISH analysis of the X- and Y- chromosomes. The identified cells were subjected to phage display selection using a novel single cell selection strategy. Selected antibodies were tested by immunocytochemistry on foetal and adult tissue arrays, an endothelial cell line, and peripheral blood mononuclear cells.

RESULTS

Three identified foetal cells subjected to antibody selection, yielded a total of 12 antibodies. Three antibodies gave distinct staining patterns on tissue arrays, and endothelial cells. One antibody, SF1.3, shows specific staining of a subpopulation of peripheral blood mononuclear cells, including a fraction of CD34 positive cells.

CONCLUSION

These findings indicate that the identified foetal cells could have been progenitor cells of haematopoietic origin. The antibody SF1.3 could be a potential tool toward non-invasive prenatal diagnostics.

Comparative transcriptome analysis reveals a fetal origin for mesenchymal stem cells and novel fetal surface antigens for noninvasive prenatal diagnosis

OBJECTIVE

Mesenchymal stem cells (MSCs) are an attractive source for providing the cells necessary for regenerating damaged tissues. Fetal MSCs (fMSCs) are known to proliferate fast and have an excellent osteogenic capacity, yet the underlying mechanisms need to be explored. A better understanding of MSCs from different anatomic origins and ages will eventually benefit cell-based therapies, as well as subsequent mechanistic studies in the field of stem cell biology.

MATERIALS AND METHODS

We identified the molecular signatures of fetal and adult MSCs via a meta-analytic strategy and compared the enriched canonical pathways and genetic networks within each signature.

RESULTS

Fetal MSCs were found to express more cell cycle genes, which is consistent with the results of wetlab functional assays. In addition, the genes involved in vasculogenesis, neurogenesis, Wnt, MAPKKK pathways, and RNA splicing were found to be enriched in fMSCs. Correlating with the overexpression of multilineage differentiation genes, fMSCs share more genes with embryonic stem cells (ESCs) and are, therefore, more primitive. Further exploration into the transcriptome similarities revealed that MSCs from umbilical cord blood (UCB) express dominant fMSC genes, but not adult genes, suggesting a fetal origin for UCB MSCs. Novel surface proteins that were dominantly expressed in fetal and UCB MSCs, but not in adult MSCs or maternal PBMCs, were also identified.

CONCLUSION

Our results systematically revealed the underlying genes and regulatory networks of two MSCs from unique origins, the resulting phenotypes, as well as the origin of UCB MSCs. The novel membrane proteins on the fetal MSC surface are promising candidate biomarkers for positively isolating fetal MSCs from maternal blood for noninvasive prenatal diagnosis.

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.

Heredity--venturing beyond genetics

Our knowledge of heredity has recently undergone major upheaval. Heredity transmits considerably more than just genetic elements. First, the oocyte is full of maternal cytoplasmic components that subsequently are present in each new cell. Second, maternal cells can pass to the progeny, where they remain active into adult life (microchimerism). Here, we examine the notion that the transmission of characters involves at least two processes in addition to that of mendelian heredity, long considered to be the only hereditary mechanism. These processes all involve epigenetic processes, including the transmission of macromolecules, subcellular organelles, and living cells solely from the mother to her offspring, whether female or male, during pregnancy and lactation. We postulate that cytoplasmic heredity and maternal transmission of cells leading to a long-term state of microchimerism in progeny are two good examples of matrilineal, nonmendelian heredity. A mother's important contribution to the development and health of her progeny seems to possess many uncharted depths.

High frequency of fetal cells within a primitive stem cell population in maternal blood

BACKGROUND

During pregnancy, fetal cells enter the maternal bloodstream resulting in fetal cell microchimerism. The fetal cells persist in the mother for decades and colonize a variety of maternal organs. They are associated with maternal autoimmune diseases and may also participate in tissue repair. The identity of the microchimeric cells is not certain but they must be able to persist long-term and have potential for multitissue differentiation.

METHODS AND RESULTS

Here we tested the hypothesis that the fetal microchimeric cells are primitive stem cells, represented by CD34+ adherent cells, which have a wide potential for differentiation. We isolated these stem cells from the blood of pregnant females (n = 25) and detected fetal cells of the correct gender, using fluorescence in situ hybridization, in a high proportion (71% male fetuses and 90% female fetuses; false positive rate 11%, false negative rate 29%) of cases. By RT-PCR, we demonstrated that the cells express Oct-4, Nanog and Rex-1. No fetal cells were detected in the mononuclear or total CD34+ cell populations but high frequencies (mean 11.8%) of fetal cells were detected in the adherent CD34+ cell population.

CONCLUSIONS

These results identify adherent CD34+ stem cells as candidate fetal microchimeric cells, which are capable of sustaining the fetal cell population in the long term and have the ability to colonize multiple tissues and organs.

Fetal stem cells

Fetal stem cells can be isolated from fetal blood and bone marrow as well as from other fetal tissues, including liver and kidney. Fetal blood is a rich source of haemopoietic stem cells (HSC), which proliferate more rapidly than those in cord blood or adult bone marrow. First trimester fetal blood also contains a population of non-haemopoietic mesenchymal stem cells (MSC), which support haemopoiesis and can differentiate along multiple lineages. In terms of eventual downstream application, both fetal HSC and MSC have advantages over their adult counterparts, including better intrinsic homing and engraftment, greater multipotentiality and lower immunogenicity. Fetal stem cells are less ethically contentious than embryonic stem cells and their differentiation potential appears greater than adult stem cells. Fetal stem cells represent powerful tools for exploring many aspects of cell biology and hold considerable promise as therapeutic tools for cell transplantation and ex vivo gene therapy.

Fetal CD34+ Cells in the Maternal Circulation and Long-Term Microchimerism in Rhesus Monkeys (Macaca mulatta)

BACKGROUND

Studies in humans have shown that during pregnancy fetal cells can enter the maternal circulation and persist for many years. While we have previously reported the presence of cell-free fetal DNA during pregnancy in rhesus monkeys, it is unknown whether cells circulate and persist long term in maternal tissues. In this study, we asked whether fetal CD34 cells can be found in the maternal circulation and if male fetal cells persist in maternal tissues postdelivery.

METHODS

The presence of the Y chromosome in maternal blood and tissues was assessed using real-time PCR assays for the sex determining region Y (SRY) and testes specific protein Y (TSPY) genes. Analysis was done on CD34 and CD34 cells isolated from maternal blood collected at select time points during gestation from gravid animals with male or female fetuses, and tissues were analyzed from nongravid animals that had previously delivered male offspring.

RESULTS

All animals with male fetuses tested positive for the Y chromosome in CD34 cells (0-30 cells/50,000 genome equivalents). Y sequences were also found in one or more maternal tissues collected up to 3-years postdelivery (thyroid, heart, spleen, liver, pituitary, adrenals, skin, inguinal lymph nodes).

CONCLUSION

These studies suggest transfer of fetal CD34 cells during pregnancy and persistent fetal microchimerism in the rhesus model. Thus, rhesus monkeys can be used to further our understanding of fetal:maternal microchimerism and the role of fetal cells in maternal health and disease.

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.

Affinity-dependent alterations of mouse B cell development by noninherited maternal antigen

We have examined the passage of maternal cells into the fetus during the gestation and postpartum in mice. Using enhanced green fluorescent protein (EGFP)-transgenic females, we showed that maternal cells frequently gain access to the fetus, mostly in syngeneic pregnancies, but also in allogeneic and outbred crosses. EGFP-transgenic cells, including B, T, and natural killer cells, can persist until adulthood, primarily in bone marrow and thymus. We then asked whether maternal cells, bearing antigens not inherited by the fetus, influence the development of fetal and neonatal B lymphocytes. We have used the B cell receptor 3-83 mu/delta transgenic mouse model, whose B cells recognize the major histocompatibility complex class I molecules H-2Kk and H-2Kb, with a high or moderate affinity, respectively. The fate of transgenic B cells in animals exposed to noninherited H-2Kk or H-2Kb maternal antigens (NIMA) during gestation and lactation was compared with those of nonexposed controls. In H-2Kk-exposed fetuses, NIMA-specific transgenic B cells are partially deleted during late gestation. Nondeleted cells have downmodulated their B cell receptor. In contrast, in NIMA H-2Kb-exposed neonates, transgenic B cells present an activated phenotype, including proliferation, upregulation of surface CD69, and preferential localization in the T cell zone of splenic follicles. This state of activation is still clearly detectable up to 3 wk of age. Thus, we show that fetal and neonatal B cell development is affected by maternal cells bearing antigens noninherited by the fetus and that this phenomenon is highly dependent on the affinity of the B cell receptor for the NIMA.

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.

Conditioning with fludarabine and targeted busulfan for transplantation of allogeneic hematopoietic stem cells

A regimen of busulfan and cyclophosphamide is standard therapy before transplantation of allogeneic hematopoietic stem cells in patients with chronic myelogenous leukemia (CML) or myelodysplastic syndrome (MDS). The clinical trial reported here was undertaken to test the hypothesis that fludarabine can replace cyclophosphamide in this regimen and facilitate donor engraftment with reduced toxicity. The conditioning regimen consisted of 30 mg/m2 intravenous fludarabine daily from day -9 to day -6, and oral busulfan given at 1 mg/kg 4 times a day every 6 hours from day -5 to day -2, with doses adjusted to target plasma levels of 900 +/- 100 ng/mL at steady state. Cyclosporine and methotrexate were used for prophylaxis for graft-versus-host disease. Enrolled were 42 patients with high-risk CML (n = 4) or MDS (n = 38). The median patient age was 52 years (range, 12-65 years). Mobilized blood stem cells were obtained from HLA-compatible siblings (n = 16) or unrelated donors (n = 26). Engraftment was achieved in all patients, and the day-100 regimen-related mortality was 7%. With a median follow-up of 18 months (range, 13-27 months), the probabilities of overall survival, disease-free survival, and nonrelapse mortality were 42.4%, 34.9%, and 24%, respectively. These data indicate that the combination of fludarabine and targeted busulfan is sufficiently immunosuppressive to facilitate engraftment of blood stem cells from HLA-matched siblings and unrelated donors. Based on these encouraging results, further studies of fludarabine and targeted busulfan are warranted in standard-risk patients.

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

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

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.

Hematopoietic progenitor cells as targets for non-invasive prenatal diagnosis: detection of fetal CD34+ cells and assessment of post-delivery persistence in the maternal circulation

Culture expansion of fetal cells from the maternal circulation will provide an increased number of cells for non-invasive prenatal diagnosis. Hematopoietic CD34+ cells are potential candidates for this application. More information is needed regarding the frequency of these cells and the phenomenon of post-delivery persistence in the maternal circulation. In this study we assessed the number of fetal CD34+ cells in the maternal circulation, the effect of culture expansion on the number of fetal cells and the persistence of fetal CD34+ cells from previous pregnancies. Fetal cells were identified by the presence of Y-chromosome sequences detected by FISH and nested PCR. Fetal CD34+ cells were detected in all samples from women carrying a male fetus. A low number of residual fetal cells from previous pregnancies was detected (1-3 XY cells in 20 ml blood) in less than 1/3 of the samples from both non-pregnant women and those pregnant with a female fetus. Culturing of CD34+ cells resulted in a significant increase in fetal cell numbers. However, the number of fetal cells persisting from previous pregnancies also increased after culture. It is proposed that information derived from CD34+ cells could potentially support data derived from other cell types for more accurate non-invasive prenatal diagnosis.

Prediction of fetal D status from maternal plasma: introduction of a new noninvasive fetal RHD genotyping service

BACKGROUND

Invasive procedures to obtain fetal DNA for prenatal blood grouping present a risk to the fetus. During pregnancy, cell-free fetal DNA is present in maternal blood. The detection of RHD sequences in maternal plasma has been used to predict fetal D status, based on the assumption that RHD is absent in D- genomes.

STUDY DESIGN AND METHODS

Real-time PCR assays were designed to distinguish RHD from RHDpsi (possessed by the majority of D- black Africans). Plasma-derived DNA from 137 D- women was subjected to real-time PCR to detect fetal RHD and Y chromosome-associated SRY sequences. The accuracy of RHD genotyping from maternal plasma was investigated by comparing results with those obtained by conventional RHD genotyping from fetal tissue or serologic tests on the infant's RBCs. The quantity of fetal DNA in maternal plasma was investigated in 94 pregnancies.

RESULTS

Fetal D status was predicted with 100-percent accuracy from maternal plasma. The number of copies of fetal DNA in maternal plasma was found to increase with gestation.

CONCLUSION

Combination of the sensitivity of real-time PCR with an improved RHD typing assay to distinguish RHD from RHDpsi enables highly accurate prediction of fetal D status from maternal plasma. This has resulted in the implementation of a clinical noninvasive fetal RHD genotyping service.

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.

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.

Comparison of methods for erythroblast selection: application to selecting fetal erythroblasts from maternal blood

BACKGROUND

Many methods have been employed to obtain fetal cells from maternal blood for prenatal diagnostics, but there has been little work done that compares the efficacy of different methods. This study presents a comparison of two commonly used methods for selecting erythroblasts with selection directly from whole blood.

METHODS

Erythroblasts were isolated from maternal blood by either differential lysis or density separation, followed by selection with an antibody to the transferrin receptor. These methods were compared with antibody selection directly from whole blood. The total yield of erythroblasts was determined for each method.

RESULTS

Red cell lysis is not recommended because the lysis step cannot be well controlled. Density separation followed by antibody selection works well. However, a faster and simpler method, antibody selection directly from whole blood using Immunicon Ferrofluid and magnetic separators, works as well and has the potential to yield even more cells.

CONCLUSIONS

Considering the need for a simple and quick method for selecting fetal cells from maternal blood, we suggest selection directly from whole blood.

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

BACKGROUND

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

STUDY DESIGN AND METHODS

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

RESULTS

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

CONCLUSION

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

An immune hypothesis of sexual orientation

Sexual orientation is encoded within immune-cell subsets (ICS) of mucosal and epithelial tissues. Gender orientation may be encoded within other ICS. Many immune cells: recognize and react to H-Y and H-X antigens; and enact these perceptions and reactions in accord with the perceiver's and the perceived's MHC haplotype, XX or XY status, and immune-self recognition. Non-heterosexual orientations derive from excessive cross-priming, accompanied by clonal deletions, clonal expansions, anergy and tolerance. For at least some tissues, cross-priming sufficient to induce altered orientations may occur during critical periods of immunological development and can occur during fetal and infant development via maternal-fetal transfusion, placental pathology, and impaired maternal nutrient-status or via excessive peripheral apoptosis during postnatal illness. Mast cell interactions with neurons illustrate how mucosal perceptions can be transduced into neuronal signals that modulate CNS events. This hypothesis is testable by mixed-lymphocyte reactions in appropriate cell subsets. Dendritic-cell immunizations are a potential therapy.

Successful Diagnosis of Fetal Gender Using Conventional PCR Analysis of Maternal Serum

Background: Fetal DNA has been found in maternal plasma and serum. Diagnosis of fetal gender using maternal plasma and serum has been attempted in an effort to develop a new noninvasive method of prenatal diagnosis.

Methods: Peripheral blood samples were obtained from 61 pregnant women at 10–17 weeks of gestation before amniocentesis. DNA was extracted from 800 μL of each plasma or serum sample. To detect the Y-chromosome-specific sequences DYS14 and DYZ3 in the maternal plasma and serum, 40 cycles of PCR were carried out for each DNA extract. The PCR products were analyzed by 2.5% agarose gel electrophoresis and ethidium bromide staining, and the results were compared with the results of the cytogenetic analyses of amniocentesis.

Results: Cytogenetic analysis of amniocentesis revealed that 31 pregnant women had a male fetus and the remaining 30 pregnant women had a female fetus. Both DYS14 and DYZ3 were detected in 27 of the 31 plasma samples obtained from pregnant women carrying a male fetus and in all of 31 serum samples obtained from the same women. Neither DYS14 nor DYZ3 was detected in either the plasma or serum samples obtained from any of the 30 pregnant women carrying a female fetus.

Conclusion: PCR analysis of maternal serum can be used to diagnose fetal gender.

Optimization of the fluorescence in situ hybridization (FISH) technique for high detection efficiency of very small proportions of target interphase nuclei

Using commercially available fluorochrome-labeled probes specific for chromosomes X, Y, 13, 18, and 21, we optimized the technical protocols for fluorescence in situ hybridization (FISH) so that the highest sensitivity and specificity were achieved. Also, we compared the optical properties of different types of fluorescent labels in an effort to develop the most efficient FISH protocol, including the determination of which types of labels are the easiest to count accurately. The lymphocytes were purified from blood of normal male and female newborns, normal male and female adults, and a trisomy 21 male adult. Male and female lymphocytes were mixed in five different combinations. For each combination, the male lymphocytes either from newborns or from adults were diluted with female lymphocytes in seven different proportions. For each of these 35 different cell mixtures, 100,000 nuclei were analyzed and scored in a blind fashion. Among the different fluorochrome-labeled probes, the highest sensitivity and specificity were achieved when SpectrumAqua CEP-Y/SpectrumOrange CEP X probe mixture, SpectrumAqua CEP-18, SpectrumOrange LSI-13, and SpectrumOrange LSI-21 were hybridized. The hybridization sensitivity and specificity were higher than 99% for the identification of chromosomes X, Y, 13, and 18, and higher than 98% for the detection of trisomy 21. The proportion of false-positive signals was under 0.005% for XY detection and lower than 0.14% for autosome detection. With these high hybridization sensitivities and specificities, the optimized FISH protocol developed in our laboratory has the potential to detect very rare events, e.g., when the proportion of cells being sought is lower than 0.01%. In other words, our protocol allows the specific detection of one male cell sunken among 10,000 female cells.

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.

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.

Development, Characterization, and Use of Monoclonal Antibodies Made to Antigens Expressed on the Surface of Fetal Nucleated Red Blood Cells

Background: Current methods for obtaining fetal cells for prenatal diagnosis are invasive and carry a small (0.5–1.0%) but definite risk of miscarriage. An attractive alternative would be isolation of fetal cells from peripheral maternal blood using antibodies with high specificity and avidity.

Methods: To generate antibodies, we purified nucleated red blood cells (NRBCs) from fetal livers and used them as the immunogen to generate monoclonal antibodies (mAbs) directed against surface antigens.

Results: The four antibodies recognized at least two conformationally sensitive epitopes of the transferrin receptor. Isolation of NRBCs from 252 maternal blood samples using these antibodies in magnetic activated cell sorting after an initial density gradient centrifugation yielded 0–419 NRBCs per 25 mL of maternal blood. One antibody, 2B7.4, not only isolated the highest number of NRBCs (&gt;10 in 90% of the samples) but also isolated these NRBCs in 78 consecutive maternal samples.

Conclusion: Antibody 2B7.4 shows promise for the isolation of NRBCs from maternal blood and should allow studies concerning the source of these cells, fetal vs maternal, and the factors controlling their prevalence.

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.

Telomerase Activity in Candidate Stem Cells From Fetal Liver and Adult Bone Marrow

Telomerase is a ribonucleoprotein polymerase that synthesizes telomeric repeats onto the 3′ ends of eukaryotic chromosomes. Activation of telomerase may prevent telomeric shortening and correlates with cell immortality in the germline and certain tumor cells. Candidate hematopoietic stem cells (HSC) from adult bone marrow express low levels of telomerase, which is upregulated with proliferation and/or differentiation. To address this issue, we stimulated purified candidate HSC from human adult bone marrow with stem cell factor (SCF), interleukin-3 (IL-3), and Flt3-ligand (FL). After 5 days in culture, activity was detected in total cell extracts from IL-3–, SCF + FL–, SCF + IL-3–, FL + IL-3–, and SCF + IL-3 + FL–stimulated cultures, but not from cells cultured in SCF or FL alone. Within the CD34+fraction of the cultured cells, significant activity was found in the CD34+CD71+ fraction. In addition, PKH26 staining confirmed that detectable telomerase activity was present in dividing PKH26lo cells, whereas nondividing PKH26hi cells were telomerase negative. Because in these experiments no distinction could be made between cycling “candidate” stem cells that had retained or had lost self-renewal properties, fetal liver cells with a CD34+CD38− phenotype, highly enriched for cycling stem cells, were also examined and found to express readily detectable levels of telomerase activity. Given the replication-dependent loss of telomeric DNA in hematopoietic cells, these observations suggest that the observed telomerase activity in candidate stem cells is either expressed in a minor subset of stem cells or, more likely, is not sufficient to prevent telomere shortening.

Telomerase Activity in Candidate Stem Cells From Fetal Liver and Adult Bone Marrow

Telomerase is a ribonucleoprotein polymerase that synthesizes telomeric repeats onto the 3′ ends of eukaryotic chromosomes. Activation of telomerase may prevent telomeric shortening and correlates with cell immortality in the germline and certain tumor cells. Candidate hematopoietic stem cells (HSC) from adult bone marrow express low levels of telomerase, which is upregulated with proliferation and/or differentiation. To address this issue, we stimulated purified candidate HSC from human adult bone marrow with stem cell factor (SCF), interleukin-3 (IL-3), and Flt3-ligand (FL). After 5 days in culture, activity was detected in total cell extracts from IL-3–, SCF + FL–, SCF + IL-3–, FL + IL-3–, and SCF + IL-3 + FL–stimulated cultures, but not from cells cultured in SCF or FL alone. Within the CD34+fraction of the cultured cells, significant activity was found in the CD34+CD71+ fraction. In addition, PKH26 staining confirmed that detectable telomerase activity was present in dividing PKH26lo cells, whereas nondividing PKH26hi cells were telomerase negative. Because in these experiments no distinction could be made between cycling “candidate” stem cells that had retained or had lost self-renewal properties, fetal liver cells with a CD34+CD38− phenotype, highly enriched for cycling stem cells, were also examined and found to express readily detectable levels of telomerase activity. Given the replication-dependent loss of telomeric DNA in hematopoietic cells, these observations suggest that the observed telomerase activity in candidate stem cells is either expressed in a minor subset of stem cells or, more likely, is not sufficient to prevent telomere shortening.