Comprehensive Mutation and Copy Number Profiling in Archived Circulating Breast Cancer Tumor Cells Documents Heterogeneous Resistance Mechanisms.

Addressing drug resistance is a core challenge in cancer research, but the degree of heterogeneity in resistance mechanisms in cancer is unclear. In this study, we conducted next-generation sequencing (NGS) of circulating tumor cells (CTC) from patients with advanced cancer to assess mechanisms of resistance to targeted therapy and reveal opportunities for precision medicine. Comparison of the genomic landscapes of CTCs and tissue metastases is complicated by challenges in comprehensive CTC genomic profiling and paired tissue acquisition, particularly in patients who progress after targeted therapy. Thus, we assessed by NGS somatic mutations and copy number alterations (CNA) in archived CTCs isolated from patients with metastatic breast cancer who were enrolled in concurrent clinical trials that collected and analyzed CTCs and metastatic tissues. In 76 individual and pooled informative CTCs from 12 patients, we observed 85% concordance in at least one or more prioritized somatic mutations and CNA between paired CTCs and tissue metastases. Potentially actionable genomic alterations were identified in tissue but not CTCs, and vice versa. CTC profiling identified diverse intra- and interpatient molecular mechanisms of endocrine therapy resistance, including loss of heterozygosity in individual CTCs. For example, in one patient, we observed CTCs that were either wild type for ESR1 (n = 5/32), harbored the known activating ESR1 p.Y537S mutation (n = 26/32), or harbored a novel ESR1 p.A569S (n = 1/32). ESR1 p.A569S was modestly activating in vitro, consistent with its presence as a minority circulating subclone. Our results demonstrate the feasibility and potential clinical utility of comprehensive profiling of archived fixed CTCs. Tissue and CTC genomic assessment are complementary, and precise combination therapies will likely be required for effective targeting in advanced breast cancer patients.Significance: These findings demonstrate the complementary nature of genomic profiling from paired tissue metastasis and circulating tumor cells from patients with metastatic breast cancer. Cancer Res; 78(4); 1110-22. ©2017 AACR.

Hematogenous metastasis of ovarian cancer: rethinking mode of spread.

Ovarian cancer has a clear predilection for metastasis to the omentum, but the underlying mechanisms involved in ovarian cancer spread are not well understood. Here, we used a parabiosis model that demonstrates preferential hematogenous metastasis of ovarian cancer to the omentum. Our studies revealed that the ErbB3-neuregulin 1 (NRG1) axis is a dominant pathway responsible for hematogenous omental metastasis. Elevated levels of ErbB3 in ovarian cancer cells and NRG1 in the omentum allowed for tumor cell localization and growth in the omentum. Depletion of ErbB3 in ovarian cancer impaired omental metastasis. Our results highlight hematogenous metastasis as an important mode of ovarian cancer metastasis. These findings have implications for designing alternative strategies aimed at preventing and treating ovarian cancer metastasis.

FISH-based determination of HER2 status in circulating tumor cells isolated with the microfluidic CEE™ platform.

Determination of HER2 status in breast cancer patients is considered standard practice for therapy selection. However, tumor biopsy in patients with recurrent and/or metastatic disease is not always feasible. Thus, circulating tumor cells (CTCs) are an alternative source of tumor cells for analysis of HER2. An antibody cocktail for recovery of variable, high- and low-, EpCAM-expressing tumor cells was developed based on FACS evaluation and then verified by CTC enumeration (based on CK and CD45 staining) with comparison to EpCAM-only and with CellSearch® (n=19). HER2 fluorescence in situ hybridization (FISH) on all (CK+ and CK-) captured cells was compared to HER2 status on the primary tumors (n=54) of patients with late stage metastatic/recurrent breast cancer. Capture of low EpCAM-expressing tumor cells increased from 27% to 76% when using the cocktail versus EpCAM alone, respectively. Overall, CTC detection with the OncoCEE™ platform was better compared to CellSearch® (68% vs. 89%, respectively), and a 93% concordance in HER2 status was observed. HER2 FISH analysis of CK+ and CK- CTCs is feasible using the CEE™ platform. Although larger clinical studies are warranted, the results demonstrate adequate sensitivity and specificity as needed for incorporation into laboratory testing.

A novel platform for detection of CK+ and CK- CTCs.

UNLABELLED: Metastasis is a complex, multistep process that begins with the epithelial-mesenchymal transition (EMT). Circulating tumor cells (CTC) are believed to have undergone EMT and thus lack or express low levels of epithelial markers commonly used for enrichment and/or detection of such cells. However, most current CTC detection methods target only EpCAM and/or cytokeratin (CK) to enrich epithelial CTCs, resulting in failure to recognize other, perhaps more important, CTC phenotypes that lack expression of these markers. Here, we describe a population of complex aneuploid CTCs that do not express CK or CD45 antigen in patients with breast, ovarian, or colorectal cancer. These cells were not observed in healthy subjects. We show that the primary epithelial tumors were characterized by similar complex aneuploidy, indicating conversion to an EMT phenotype in the captured cells. Collectively, our study provides a new method for highly efficient capture of previously unrecognized populations of CTCs. SIGNIFICANCE: Current assays for CTC capture likely miss populations of cells that have undergone EMT. Capture and study of CTCs that have undergone EMT would allow a better understanding of the mechanisms driving metastasis.

Detection of EpCAM-Negative and Cytokeratin-Negative Circulating Tumor Cells in Peripheral Blood.

Enrichment of rare circulating tumor cells (CTCs) in blood is typically achieved using antibodies to epithelial cell adhesion molecule (EpCAM), with detection using cytokeratin (CK) antibodies. However, EpCAM and CK are not expressed in some tumors and can be downregulated during epithelial-to-mesenchymal transition. A micro-fluidic system, not limited to EpCAM or CK, was developed to use multiple antibodies for capture followed by detection using CEE-Enhanced (CE), a novel in situ staining method that fluorescently labels the capture antibodies bound to CTCs. Higher recovery of CTCs was demonstrated using antibody mixtures compared to anti-EpCAM. In addition, CK-positive breast cancer cells were found in 15 of 24 samples (63%; range 1-60 CTCs), while all samples contained additional CE-positive cells (range 1-41; median = 11; P = .02). Thus, antibody mixtures against a range of cell surface antigens enables capture of more CTCs than anti-EpCAM alone and CE staining enables the detection of CK-negative CTCs.

Efficient capture of circulating tumor cells with a novel immunocytochemical microfluidic device.

Ability to perform cytogenetic interrogations on circulating tumor cells (CTCs) from the blood of cancer patients is vital for progressing toward targeted, individualized treatments. CTCs are rare compared to normal (bystander) blood cells, found in ratios as low as 1:10(9). The most successful isolation techniques have been immunocytochemical technologies that label CTCs for separation based on unique surface antigens that distinguish them from normal bystander cells. The method discussed here utilizes biotin-tagged antibodies that bind selectively to CTCs. The antibodies are introduced into a suspension of blood cells intending that only CTCs will display surface biotin molecules. Next, the cell suspension is passed through a microfluidic channel that contains about 9000 transverse, streptavidin coated posts. A CTC making contact with a post has the opportunity to engage in a biotin-streptavidin reaction that immobilizes the cell. Bystander blood cells remain in suspension and pass through the channel. The goal of the present study is to establish the technical performance of these channels as a function of antigen density and operating conditions, especially flow rate. At 18 µL/min, over 70% of cells are captured at antigen densities greater than 30 000 sites/cell while 50% of cells are captured at antigen densities greater than 10 000. It is found that lower flow rates lead to decreasing cell capture probabilities, indicating that some streamlines develop which are never close enough to a post to allow cell-post contact. Future modeling and streamline studies using computational fluid dynamics software could aid in optimization of channel performance for capture of rare cells.

Plasma cell-free DNA in ovarian cancer: an independent prognostic biomarker.

BACKGROUND: Cell-free DNA reflects both normal and tumor-derived DNA released into the circulation through cellular necrosis and apoptosis. The authors sought to determine the role of preoperative total plasma cell-free DNA levels in predicting clinical outcome in patients with ovarian cancer. METHODS: After institutional review board consent, DNA was extracted from plasma of 164 women with invasive epithelial ovarian carcinoma (EOC), 49 with benign ovarian neoplasms, and 75 age-matched controls. The samples were randomly divided into training (n = 144) and validation (n = 144) sets. Quantification of cell-free DNA was performed using real-time polymerase chain reaction for beta-globin, and the number of genome equivalents (GE) per milliliter of plasma was determined. Cell-free DNA was correlated with clinicopathologic parameters. RESULTS: The training and validation sets were similar in terms of demographic features. In the training set, EOC patients had a median preoperative cell-free DNA level of 10,113 GE/mL, compared with patients with benign ovarian neoplasms (median, 2365 GE/mL; P < .0001) and controls (median, 1912 GE/mL, P < .0001). Cell-free DNA >22,000 GE/mL was significantly associated with decreased patient survival (P < .001). After adjusting for other clinical variables, preoperative cell-free DNA >22,000 GE/mL was an independent predictor (P = .02) for disease-specific survival. Analysis of the validation set confirmed significantly higher cell-free DNA levels in EOC (median, 13,672 GE/mL) and that cell-free DNA >22,000 GE/mL was associated with a 2.83-fold increased risk of death from disease (P < .001). CONCLUSIONS: Preoperative plasma total cell-free DNA levels are significantly elevated in patients with EOC. Elevated plasma cell-free DNA is an independent predictor for death from disease in ovarian cancer.

Stability of placental RNA using dried maternal blood spots.

Having demonstrated successful recovery and detection of placental transcripts from dried blood spots (DBS), various preanalytical conditions were examined to determine optimal handling of samples. The role of several factors was explored, including temperature (4 degrees C versus 25 degrees C), processing time (24 h to 8 weeks), and addition of preservatives (RNA later and formalin) that may interfere with stability and detection of placental transcripts in DBS. mRNA transcripts encoding human glyceraldehyde-3-phosphate dehydrogenase (GAPDH; internal control) and beta-human chorionic gonadotrophin (beta HCG; placental) were analysed by real-time-polymerase chain reaction using DBS from 23 pregnant women. GAPDH and beta HCG transcripts were detected in all samples 24 h after collection. Although treatment of blood with RNA later did not affect RNA recovery, formalin treatment negatively affected RNA recovery from DBS. Temperature did not have a significant effect on levels of either transcript. Storage time caused a significant decrease in GAPDH after 4 weeks (P = 0.014) and beta HCG after 1 week (P = 0.007). Decrease of beta HCG levels after 1 week followed by steady detectable levels for up to 4 weeks suggests two populations of circulating placental transcript exist, a population susceptible to degradation in blood versus a more stable form. Therefore, defining proper parameters for collection and storage of DBS further reinforces reliable analysis of target sequences for clinical testing.

Metronomic chemotherapy enhances the efficacy of antivascular therapy in ovarian cancer.

Metronomic chemotherapy is the frequent administration of low doses of chemotherapeutic agents targeting tumor-associated endothelial cells. We examined the efficacy of metronomic taxanes alone and in combination with AEE788-a dual epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor (VEGFR) inhibitor-in an orthotopic mouse model of ovarian cancer. Growth-modulating effects of metronomic and maximum tolerated dose (MTD) regimens on overall survival were tested in vivo using both chemotherapy-sensitive (HeyA8 and SKOV3ip1) and chemotherapy-resistant (HeyA8-MDR) models. Treated tumors were stained for microvessel density (CD31), proliferation index (proliferating cell nuclear antigen), and apoptosis (terminal deoxyribonucleotide transferase-mediated nick-end labeling). The cytotoxic effects of MTD and metronomic dosing were tested with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. Effects of metronomic regimens on circulating endothelial precursors (CEP) and tumor-specific cell-free DNA levels were assessed. In vivo, metronomic docetaxel resulted in significant reduction of tumor growth in the taxane-sensitive cell lines, whereas metronomic docetaxel plus AEE788 had an additive effect resulting in significant prolongation in survival. Combination therapy was effective even in the taxane-resistant model. Metronomic chemotherapy alone and combined with AEE788 resulted in a decrease in the proliferative index and microvessel density of treated tumors, whereas combination therapy increased the apoptotic index (P < 0.001). In vitro, metronomic taxanes caused endothelial cell toxicity at 10- to 100-fold lower concentrations compared with MTD dosing. Metronomic regimens inhibited mobilization of CEPs (P < 0.05) and led to a decrease in cell-free DNA levels (P < 0.05). Our results suggest that metronomic taxane chemotherapy with dual EGFR and VEGFR inhibition is highly efficacious and should be considered for future clinical trials.

Quantification of total plasma cell-free DNA in ovarian cancer using real-time PCR.

Our objective was to compare the levels of total circulating plasma cell-free DNA (CfDNA) using real-time PCR in patients with late-stage ovarian cancer with those in unaffected controls. Following IRB consent, DNA was extracted from archived frozen plasma of 19 patients with primary ovarian carcinoma and 12 age-matched controls using Qiagen DNA Isolation Kits. Quantification of total CfDNA was performed using real-time PCR with the TaqMan Assay for GAPDH, beta-actin and beta-globin and the number of genome equivalents (GE/mL) were determined from a standard curve. CfDNA levels of these loci were compared between the groups with Student's t-test, with P < 0.05 being statistically significant. The mean age of the patients was 61.6 years (+/-9.6) and of the controls was 54 years (+/-12.2). All patients had high-grade, advanced stage (III or IV) serous ovarian carcinomas. Preoperative CA-125 levels ranged from 43 to 15,626 IU/mL (mean 2487.2 +/- 3686 IU/mL). Total CfDNA in ovarian cancer was higher among patients with ovarian cancer as compared to controls at all three loci: GAPDH (P = 0.022), beta-actin (P = 0.025), and beta-globin (P = 0.0089). CfDNA is elevated in advanced stage disease compared to controls. These preliminary results suggest that total CfDNA in the plasma of patients with ovarian cancer may be useful for noninvasive screening and disease surveillance.

Recovery and amplification of placental RNA from dried maternal blood spots: utility for non-invasive prenatal diagnosis.

Methods utilizing circulating cell-free RNA in plasma have clinical applications for cancer and prenatal genetic analysis. Given these potential roles, the feasibility of detecting placental specific RNA in dried maternal blood spots after storage at room temperature for varying lengths of time was investigated. Using real-time polymerase chain reaction (PCR), positive amplification of placental-specific beta-human chorionic gonadotrophin transcripts was demonstrated in nine of 11 dried blood samples from first and second trimester pregnancies stored at room temperature for up to 4 weeks. This work demonstrates feasibility in isolation and amplification of placental mRNA using dried maternal blood spots. With the development of fetal and placental RNA markers, this approach would allow simplified collection, transport, and storage of samples for prenatal genetic diagnosis and pregnancy related complications.

Circulating cell-free DNA: a novel biomarker for response to therapy in ovarian carcinoma.

INTRODUCTION: Cell-free DNA (CFDNA) is a reflection of both normal and tumor-derived DNA released into the circulation through cellular necrosis and apoptosis. We sought to determine whether tumor-specific plasma DNA could be used as a biomarker for tumor burden and response to therapy in an orthotopic ovarian cancer model. METHODS: Female nude mice injected intraperitoneally with HeyA8 ovarian cancer cells were treated with either docetaxel alone or in combination with anti-angiogenic agents (AEE788-dual VEGFR and EGFR antagonist or EA5-monoclonal antibody against ephrin A2). Following DNA extraction from plasma, quantification of tumor-specific DNA was performed by real-time PCR using human specific beta-actin primers. The number of genome equivalents (GE/ml) were determined from a standard curve. Apoptosis was assessed by TUNEL staining of treated tumors. RESULTS: The levels of tumor-specific DNA in plasma increased progressively with increasing tumor burden (R2=0.8, p<0.01). Additionally, tumor-specific plasma DNA levels varied following treatment with chemotherapy. In mice with established tumors (19 days following tumor injection), tumor-specific plasma DNA levels increased by 63% at 24 hours following a single dose of docetaxel (15 mg/kg), and then declined to 20% below baseline at 72 hours and were 83% lower than baseline 10 days following therapy. In addition, docetaxel treatment resulted in a significant increase in the apoptotic index at 24 hours (p<0.01). Moreover, in two separate therapy experiments using a combination of cytotoxic chemotherapy with anti-angiogenic agents, tumor-specific plasma DNA levels were significantly higher in mice treated with vehicle compared to the treatment groups. The correlation between tumor weight and tumor-specific DNA in these experiments was 0.71-0.76 (p<0.01). CONCLUSIONS: Our results indicate that tumor-specific CFDNA levels correlate with increasing tumor burden and decline following therapy. Thus, tumor-specific DNA may be a useful surrogate biomarker of therapeutic response and should be evaluated in future clinical trials.

Endocervical fetal trophoblast for prenatal genetic diagnosis.

PURPOSE OF REVIEW: For over a decade, methods of first-trimester, noninvasive prenatal genetic diagnosis have been actively pursued by many investigators. Isolation of fetal trophoblast from endocervical specimens remains an attractive approach, given the greater numbers of fetal cells than in maternal blood and the better potential for fetal-cell identification based on markers specific for a single cell type (trophoblasts). RECENT FINDINGS: Current studies demonstrate feasibility in identification and molecular analysis of fetal trophoblast cells for prenatal genetic testing. Sampling methods involving lavage, cytobrush, or aspiration of cervical specimens, however, have limitations in the recovery of trophoblasts. SUMMARY: Clinical applications await further systematic studies to determine safety and accuracy in recovery.

Quantitative DNA perturbations of p53 in endometriosis: analysis of American and Icelandic cases.

OBJECTIVE: To investigate quantitative aberrations involving p53 copy numbers in eutopic endometrial and endometriotic tissue from two populations. DESIGN: Comparative analysis of normal and diseased tissue. SETTING: Tissue specimens collected in Iceland and USA. PATIENT(S): Subjects with moderate/severe endometriosis (Iceland, n = 26; USA, n = 45). Paraffin-embedded tissue from 19 matched Icelandic cases and seven unaffected controls. American cases were fresh surgical tissue from 17 matched cases and 28 unaffected controls. DNA isolation and real-time polymerase chain reaction (PCR) with TaqMan assay were performed. MAIN OUTCOME MEASURE(S): The frequency of p53 loss and/or gain based on quantitative differences for copy numbers of p53 located on chromosome (17p) and GAPDH on a control locus (chromosome 12p). RESULT(S): Among American cases, significant p53 gain (n = 13) or loss (n = 4) was observed in 17 of 21 cases. In Icelandic cases this was not seen to the same degree. Mean normalized p53 values were 3.46 and 1.16 copies per reaction, respectively. Significant differences were observed between normalized p53 in the control blood and affected tissue for the American and Icelandic cases compared to standard GAPDH control but not in normal Icelandic and American endometrium. CONCLUSION(S): The results continue to support a role for nonrandom somatic p53 locus alterations in the pathogenesis of late or severe-stage endometriosis. Differences between Icelandic and American subjects have implications for generalization of genome-wide approaches.

Cell-free fetal DNA in maternal blood: kinetics, source and structure.

The kinetics and structure of cell-free fetal DNA in maternal plasma is currently under investigation. Plasma fetal DNA seems quite stable albeit cleared rapidly following birth, suggesting continuous fetal DNA release into the maternal circulation during pregnancy. However, to understand better the kinetics of circulating DNA, studies to determine the biological (structural) form in which fetal and maternal DNA exist and the mechanisms underlying variation in plasma are warranted to ensure quantitative diagnostic reliability. It is likely that circulating fetal DNA is released from fetal and/or placental cells undergoing apoptosis. Thus, the majority of fetal DNA is proposed to circulate in membrane-bound vesicles (apoptotic bodies). This review summarizes the latest reports in this field.

Somatic DNA alterations in endometriosis: high frequency of chromosome 17 and p53 loss in late-stage endometriosis.

PROBLEM: Genetic predisposition to endometriosis is well established, but the gene(s) involved largely remain unknown. Although endometriosis is considered a benign disease, it displays several features similar to malignancy: altered morphology, disregulated growth, invasion. We hypothesize endometriosis arises as result of somatic DNA alterations occurring in a multi-step process, analogous to origin of neoplasia. Since chromosome 17 and TP53 tumor suppressor gene (TSG) alterations occur frequently in premalignant and malignant tissues, including endometrial and ovarian epithelial carcinomas, we sought to determine if similar somatic changes occur in late stage endometriosis. METHOD OF STUDY: To determine the frequencies of monosomy for chromosome 17, as well as for perturbations of p53 and other loci on 17, two different approaches were used. Fluorescent in situ hybridization (FISH) analysis was used to detect monosomy for the 17 centromere and for the p53 locus. For FISH, archival tissue (n=6) and fresh endometriotic touch preparations were prepared from women (n=8) undergoing extirpation of advanced stage endometriosis. Direct-labeled probes specific for p53 (17p13.1) and for the chromosome 17 alpha-satellite centromere region (1711.1-q11.1) were used to compare single glandular and stromal cells from endometriosis and normal tissue. DNA analysis of polymorphic DNA loci were used to detect loss of heterozygosity (LoH) for other loci on 17. We assessed matched endometriotic and normal DNA (peripheral blood) from women with severe/late stage disease (n=15), studying these dinucleotide markers: HGH (located on 17q22-24), D17S250 (17q11.2-q12) and CHRNB1 (17p13.1). RESULTS: Loss of the chromosome 17 centromere (monosomy) was shown by FISH in some cells from all 14 endometriosis specimens, although in no case did every cell show monosomy 17. In 12 of 14 specimens, significant proportions of cells not only were monosomic for the chromosome 17-centromere (8 to 42% of cells) but also showed loss of p53 locus. In the two remaining cases, p53 loss alone was observed in 8 and 14%. LoH for other alleles on chromosome 17 was observed less often, namely only 3 of 15 specimens for HGH, 1 of 15 for D17S250, and 0 of 15 for CHRNB1. CONCLUSIONS: Our study indicates that perturbations of chromosome 17 in general and the p53 locus in particular occur frequently in severe/late stage endometriosis. That not all cells show loss of whole chromosome 17 or the p53 locus suggests somatic mutation, perhaps occurring late in the pathogenesis of endometriosis. Clonal evolution of endometriosis must depend not only on somatic mutations for p53 but also on other oncogenes or TSG. Alternatively, the clone could begin with a germline or somatic mutation involving a nonneoplastic process, followed by one or more somatic mutations involving an oncogene or TSG like p53. Additional candidate genes clearly must be evaluated in order to determine the precise role chromosome 17 and p53 alterations play in endometriosis; however, additional genes seem unlikely to involve region connoted by HGH, D17S250 or CHRNB1.

Heritability and molecular genetic studies of endometriosis.

Endometriosis is well established as a condition showing heritable tendencies. Polygenic/multifactorial etiology appears far more likely to be the etiology than Mendelian inheritance. The current task is to determine the number and location of genes responsible for endometriosis. This paper shall review the basis for concluding that endometriosis is a genetic disorder of polygenic/multifactorial inheritance and outline selected strategies for identifying the number and location of causative genes. It shall also illustrate our approach to testing the hypothesis that endometriosis bears similarity to neoplasia and, hence, is a multistep phenomenon of clonal origin.

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.