The Effect of the Elapsed Time Between Blood Draw and Processing on the Recovery of Fetal Cells From Maternal Blood

OBJECTIVE

To test the hypothesis that a delay in initial fetal cell enrichment processing of maternal blood samples (defined as the time between blood draw and the initial density gradient centrifugation step) compromises the ability to recover fetal cells, we performed a randomized comparison of immediate (within 4 hours of draw) versus delayed (between 18-24 hours of draw) processing.

METHODS

Four centers participated: two centers utilized flow cytometry (FLOW), and two centers utilized magnetic-activated cell sorting (MACS) techniques. Each center collected 34 samples. The outcome was the percentage of gamma positive (gamma(+)) cells for FLOW or the number of nucleated red blood cells (NRBCs) for MACS, found in the final enriched cell population. Both outcomes reflect cell properties that are potentially fetal in origin, thus making them representative of the ability to recover fetal cells.

RESULTS

Our results did not support our hypothesis that delay in processing compromises fetal cell recovery. Instead, in MACS processing, we observed an increase in recovered NRBCs when blood sample processing was delayed compared with immediate processing. There was no significant difference in gamma(+) cells with FLOW.

CONCLUSION

Time-related changes in the density of target cells, perhaps associated with their progress towards apoptosis during the delay period, may result in increased intact fetal cells with the study methods utilized.

Fetal Cell Based Prenatal Diagnosis: Perspectives on the Present and Future

The ability to capture and analyze fetal cells from maternal circulation or other sources during pregnancy has been a goal of prenatal diagnostics for over thirty years. The vision of replacing invasive prenatal diagnostic procedures with the prospect of having the entire fetal genome in hand non-invasively for chromosomal and molecular studies for both clinical and research use has brought many investigators and innovations into the effort. While the object of this desire, however, has remained elusive, the aspiration for this approach to non-invasive prenatal diagnosis remains and the inquiry has continued. With the advent of screening by cell-free DNA analysis, the standards for fetal cell based prenatal diagnostics have been sharpened. Relevant aspects of the history and the current status of investigations to meet the goal of having an accessible and reliable strategy for capturing and analyzing fetal cells during pregnancy are reviewed.

Tracking fetal development through molecular analysis of maternal biofluids

Current monitoring of fetal development includes fetal ultrasonography, chorionic villus sampling or amniocentesis for chromosome analysis, and maternal serum biochemical screening for analytes associated with aneuploidy and open neural tube defects. Over the last 15 years, significant advances in noninvasive prenatal diagnosis (NIPD) via cell-free fetal (cff) nucleic acids in maternal plasma have resulted in the ability to determine fetal sex, RhD genotype, and aneuploidy. Cff nucleic acids in the maternal circulation originate primarily from the placenta. This contrasts with cff nucleic acids in amniotic fluid, which derive from the fetus, and are present in significantly higher concentrations than in maternal blood. The fetal origin of cff nucleic acids in the amniotic fluid permits the acquisition of real-time information about fetal development and gene expression. This review seeks to provide a comprehensive summary of the molecular analysis of cff nucleic acids in maternal biofluids to elucidate mechanisms of fetal development, physiology, and pathology. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.

Prenatal diagnosis using cell-free nucleic acids in maternal body fluids: A decade of progress

The ability to detect cell-free fetal nucleic acids in pregnant women has greatly evolved over the past decade. Dozens of papers have explored the biology, kinetics, and clinical significance of both cell-free fetal DNA and mRNA in the maternal circulation. As a result, our overall understanding of fetal nucleic acid trafficking has expanded. To date, two applications, gender determination and fetal RhD status, have translated into clinical medicine. However, with advanced molecular techniques such as mass spectrometry, real-time quantitative polymerase chain reaction, and gene expression arrays, the ease with which fetal genes can be detected within the mother has greatly improved. Newly identified placental and fetal mRNA transcripts as well as an epigenetically modified placental DNA marker, maspin, have universal applicability. Global expression analyses of fetal mRNA in both amniotic fluid and blood provide new insights into fetal development and pathology. Prenatal diagnosis is poised to evolve from detection of aneuploidy to detection of deviation from normal development, which should provide novel opportunities for fetal treatment.

The chromatin of differentiating erythroblasts is cleaved into large size fragments independent of caspase activated DNase and apoptosis inducing factor

Erythroblast cell differentiation involves self-controlled and limited nuclear proteolysis prior nucleus loss. Early evidence suggests that apoptotic-like pathways are activated during this process. The chromatin of developing erythroblasts becomes fragmented in vivo, however, the exact mechanisms and molecules involved remain elusive. In this study, erythroblasts were differentiated in culture from CD34-enriched umbilical cord blood progenitor cells and the characteristics of DNA fragmentation were examined. This analysis shows that the chromatin of differentiating erythroblasts is cleaved into discrete fragments of 50-200 kb. This process most likely involves one or several endonucleases as we detect in vivo double strand DNA cleavage. However, major players of the apoptotic DNA degradation, caspase activated DNase and apoptosis inducing factor, are not activated in these cells. Therefore, our data suggests that erythroblast chromatin degradation may involve enzymes distinct form those active in apoptotic cells.

Fetal Cell-Free Nucleic Acids in the Maternal Circulation: New Clinical Applications

Six years after the demonstration of the presence of cell-free fetal nucleic acids in maternal plasma, perinatal clinical applications continue to expand. The focus of this article is on advances that have occurred since the CNAPS II conference held in Hong Kong in 2001. Circulating fetal DNA levels (fDNA) are elevated in pregnancies complicated by fetal trisomies 13 and 21 but not 18. Measurement of fDNA levels improves the performance of the current standard maternal serum screen, by increasing the detection of Down syndrome cases by 5% with no increase in the false-positive rate. fDNA levels are elevated in women who have developed clinical symptoms of preeclampsia, but they are also elevated by the early second trimester in women who will eventually develop preeclampsia. fDNA and mRNA gamma globin measurement may have clinical utility as markers for fetomaternal hemorrhage in the late first trimester. Cell-free fetal DNA levels are quite high in the amniotic fluid, permitting fetal genomic isolation and analysis using comparative genomic hybridization techniques. Fetal DNA crosses the blood-brain barrier and is detectable in maternal cerebrospinal fluid in a subset of pregnant women. The biological implications of this are currently unknown. Review of the literature suggests that the placenta is the predominant source of the circulating fetal nucleic acids. However, detection of gamma globin mRNA sequences in the plasma of pregnant women suggests that fetal blood cells also contribute to the pool of nucleic acids. Widespread incorporation of fetal nucleic acid measurement into routine prenatal care depends on the identification of a readily accessible gender-independent fetal marker.

Circulating Fetal DNA: Its Origin and Diagnostic Potential—A Review

OBJECTIVE

In contrast to the traditional teaching that the placenta forms an impermeable barrier, multiple studies show that both intact fetal cells and cell-free nucleic acids circulate freely in maternal blood. Complications of pregnancy, such as pre-eclampsia, or fetal cytogenetic abnormalities, such as trisomy 21, increase transfusion of both intact fetal cells and cell-free fetal nucleic acids into the maternal circulation. The objective of our research is to show that abnormal feto-maternal trafficking of nucleic acids is associated with fetal and placental pathology, and that these observations may lead to novel non-invasive diagnostic and screening tests.

METHODS

Real-time quantitative PCR amplification of DYS1 is used to measure the levels of male fetal DNA in case-control sets of serum or plasma taken from pregnant women. In our laboratory, we use DYS1, a Y-chromosome specific gene, as a uniquely fetal DNA marker for the development of gestation-specific normal values and theoretical models.

RESULTS

Women carrying fetuses with trisomies 21 or 13 (but not 18) have increased levels of fetal DNA in their fresh or archived serum and/or plasma samples. Women destined to develop pre-eclampsia have a characteristic bi-phasic elevation of cell-free fetal DNA that precedes clinical symptoms. Data obtained from a variety of clinical scenarios suggest that the placenta is the predominant source of the circulating fetal nucleic acids, although apoptotic haematopoietic cells may contribute to the pool as well.

CONCLUSIONS

Fetal cell-free DNA is elevated in a number of conditions associated with placental pathology. Widespread clinical implementation of fetal DNA as a screening tool awaits discovery of a reliable gender-independent marker, which may be DNA polymorphisms, epigenetic markers, or mRNA. Fetal cell-free nucleic acids have potential for non-invasive monitoring of placental pathology.

Detection of chromosome 21-encoded mRNA of placental origin in maternal plasma

BACKGROUND

mRNA of placental origin (i.e., human placental lactogen and beta-human chorionic gonadotropin) has been demonstrated to be easily detectable in maternal plasma. We tested whether detection of chromosome 21-encoded mRNA of placental origin is possible in maternal plasma obtained during the first trimester.

METHODS

Plasma samples were obtained from pregnant women between weeks 9-13 of pregnancy. RNA was isolated from 800 or 1600 microL of plasma by silica-based affinity isolation and, after on-column DNase treatment, was subjected to two-step, one-tube reverse transcription-PCR with gene specific primers.

RESULTS

Three chromosome 21-encoded genes located within the Down syndrome critical region with overexpression in trisomy 21 placentas were screened for expression in early placental tissue to select their potential use for RNA based plasma screening. One of the chromosome 21-encoded genes (LOC90625) showed strong expression in first trimester placenta similar to CSH1 (human placental lactogen) and was selected for plasma analysis. The RNA isolation assay was validated with CSH1 mRNA, which could be detected in the plasma of all women tested in weeks 9-13 of pregnancy. RNA from the chromosome 21-encoded, placentally expressed gene, LOC90625, was present in maternal first-trimester plasma and could be detected in 60% of maternal plasma samples when 800 microL of plasma was used and in 100% of samples when 1600 microL of plasma was used.

CONCLUSION

The detection of chromosome 21-encoded mRNA of placental origin in maternal plasma during the first trimester may allow development of plasma-RNA-based strategies for prenatal prediction of Down syndrome. LOC90625 is a candidate gene for this purpose.

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.

Developments in laboratory techniques for prenatal diagnosis

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