Novel approaches to manipulating foetal cells in the maternal circulation for non-invasive prenatal diagnosis of the unborn child

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.

Forever Connected: The Lifelong Biological Consequences of Fetomaternal and Maternofetal Microchimerism

BACKGROUND

Originally studied as a mechanism to understand eclampsia-related deaths during pregnancy, fetal cells in maternal blood have more recently garnered attention as a noninvasive source of fetal material for prenatal testing. In the 21st century, however, intact fetal cells have been largely supplanted by circulating cell-free placental DNA for aneuploidy screening. Instead, interest has pivoted to the ways in which fetal cells influence maternal biology. In parallel, an increasing appreciation of the consequences of maternal cells in the developing fetus has occurred.

CONTENT

In this review, we highlight the potential clinical applications and functional consequences of the bidirectional trafficking of intact cells between a pregnant woman and her fetus. Fetal cells play a potential role in the pathogenesis of maternal disease and tissue repair. Maternal cells play an essential role in educating the fetal immune system and as a factor in transplant acceptance. Naturally occurring maternal microchimerism is also being explored as a source of hematopoietic stem cells for transplant in fetal hematopoietic disorders.

SUMMARY

Future investigations in humans need to include complete pregnancy histories to understand maternal health and transplant success or failure. Animal models are useful to understand the mechanisms underlying fetal wound healing and/or repair associated with maternal injury and inflammation. The lifelong consequences of the exchange of cells between a mother and her child are profound and have many applications in development, health, and disease. This intricate exchange of genetically foreign cells creates a permanent connection that contributes to the survival of both individuals.

Comparison between paramagnetic and CD71 magnetic activated cell sorting of fetal nucleated red blood cells from the maternal blood

Background

Fetal nucleated red blood cells (NRBC) from maternal circulation are rare events but can be enriched and used to evaluate the genetics of the fetus. We compared two simplified selection methods of the fetal cells from the maternal blood.

Methods

We isolated fetal cells from maternal blood through double‐density gradient centrifugation followed either by magnetic cell selection, based on the paramagnetic proprieties of the NRBC hemoglobin, converted to methemoglobin, or by a positive magnetic‐activated cell sorting (MACS) enrichment, using anti‐CD71 monoclonal antibodies. Finally, the cells were identified through fluorescence in situ hybridization (FISH) with specific chromosome X and Y probes.

Results

We processed 10 mL of peripheral blood samples from 27 pregnant women with singleton normal male fetuses. Hemoglobin‐based enrichment isolated significantly more NRBCs: 29.7 × 10⁴ cells than anti‐CD71 MACS: 10.1 × 10⁴ cells (P < .001). The FISH analysis found at least one XY cell in 81.5% and 61.5% of cases, respectively, for paramagnetic and anti‐CD71 selection. Also, the average number of XY cells identified through paramagnetic selection was 5.09 ± 2.5, significantly higher than those observed through CD71 sorting: 3.38 ± 1.7 cells (average ± SE) (P = .03).

Conclusion

The combination of density gradient centrifugation with paramagnetic selection has the advantage of simplicity and achieves a minimal manipulation and treatment of cells. It yields an increased number of NRBCs and FISH confirmed fetal cells, compared to the anti‐CD71 sorting.

Noninvasive Approaches to Prenatal Diagnosis: Historical Perspective and Future Directions

The field of prenatal screening and diagnosis has undergone enormous progress over the past four decades. Most of this period has been characterized by gradual improvements in the technical and public health aspects of prenatal screening for Down syndrome. Compared to the direct analysis of fetal cells from amniocentesis or chorionic villus sampling, noninvasive approaches using maternal blood or ultrasound have the great advantage of posing no risk of miscarriage to the pregnancy. Recent advances in molecular genetics and DNA sequencing have revolutionized both the accuracy and the range of noninvasive testing for genetic abnormalities using cell-free DNA in maternal plasma. Many of these advances have already been incorporated into clinical care, including diagnosis of fetal blood group and aneuploidy screening. The accelerated pace of these recent developments is creating not just technical and logistical challenges, but is also magnifying the ethical and public policy issues traditionally associated with this field.

Detection of aneuploidy from single fetal nucleated red blood cells using whole genome sequencing

OBJECTIVE

The objective of the study was to detect aneuploidy in single fetal nucleated red blood cells (FNRBCs) from placental villi using whole genome amplification (WGA) and next generation sequencing.

METHODS

Three single FNRBCs per sample were manually picked from villi collected from ten women undergoing elective first-trimester termination of pregnancy, and one or two cells were picked from each of four aneuploid chorionic villus samples. Following WGA and addition of adaptor and index sequences, samples were sequenced on the Illumina MiSeq. Leading and trailing 15 bases were trimmed, and reads were aligned to the human reference genome. Z-scores were calculated to determine deviation of the mean of the test from reference samples, with a score of 3 used as the threshold for classification of a particular chromosome as trisomic.

RESULTS

We successfully made correct diagnoses from ten single cells isolated from villi from two cases of trisomy 21 (one case from a single cell and one from two cells), two cases of trisomy 18 (two cells each), and a case of trisomy 15 (three cells).

CONCLUSION

With their faithful representation of fetal genome, diagnosis using single FNRBCs provides a definitive result compared with non-invasive prenatal testing using cell-free fetal DNA, and is a safer alternative to invasive amniocentesis.

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.