Detection of fetal HLA-DQa sequences in maternal blood: a gender-independent technique of fetal cell identification

The clinical utility of fetal cell sorting to determine prenatally fetal E/e or e/e Rh genotype from peripheral maternal blood

OBJECTIVE

This study was undertaken to determine the fetal E/e or e/e Rh genotype prenatally from peripheral maternal blood by examining sorted fetal cells from alloimmunized and nonalloimmunized pregnancies.

STUDY DESIGN

Eighteen maternal peripheral venous blood samples were obtained before amniocentesis from 15 pregnant women who were homozygous for the e allele. Five were not alloimmunized and 10 were alloimmunized. The mononuclear cell layer was isolated from the maternal blood and enriched for fetal nucleated red blood cells by flow cytometry with monoclonal antibodies to CD36 or CD71 and to glycophorin A. Eight samples were treated with CD45 monoclonal antibody-coated magnetic beads before they were sorted to deplete the maternal sample of leukocytes (CD45(+) cells). We defined the positive fetal cell fractions as the monoclonal antibody positive-sorted cells derived from the maternal samples. These included sorted cells that were CD36(+)/glycophorin A(+), CD71(+)/glycophorin A(+) and CD45(-) cells that were sorted to become CD45(-)/CD36(+)/glycophorin A(+) or CD45(-)/CD71(+)/glycophorin A(+). The negative fractions were the cells that were negative for either CD36/glycophorin A or CD71/glycophorin A or were the CD45(+) cells. Deoxyribonucleic acid was isolated from all fractions and amplified by polymerase chain reaction with allele-specific primers for the E or e Rh genes. Gel electrophoresis was performed to detect fetal E/e or e/e Rh genotype. The fetal E/e or e/e Rh genotype was confirmed by serologic and deoxyribonucleic acid testing. The accuracy of E/e or e/e Rh genotype determination from the positive cell fractions was compared with that of E/e or e/e Rh genotype determination from the negative fractions.

RESULTS

Fetal E/e or e/e Rh genotype was determined correctly in 17 of 18 of the fetal cell enriched positive fractions (94%). Fetal E/e or e/e Rh genotype was determined correctly in 11 of 14 of the maternal samples in the negative unselected cell fractions (79%). Fetal E/e or e/e Rh genotype was determined correctly in 15 of 16 sample fractions that underwent magnetic bead separation with CD45 and were subsequently sorted into positive and negative fractions (94%). Fetal E/e or e/e Rh genotype was determined correctly in 13 of 13 of the samples obtained from the alloimmunized pregnancies (100%).

CONCLUSIONS

The use of monoclonal antibodies for cell sorting or for magnetic separation predicted fetal E/e or e/e Rh genotype from peripheral maternal blood correctly in as many as 100% of alloimmunized pregnancies. Thus noninvasive fetal E/e or e/e Rh genotyping can be performed by polymerase chain reaction amplification of the rare fetal cells in maternal blood. The correct prediction of fetal E/e or e/e Rh genotype from the cell population not selected by the monoclonal antibodies suggests that there are fetal cell types other than fetal nucleated erythrocytes that can also be used as a source of fetal deoxyribonucleic acid for noninvasive genetic diagnosis. Improved technology may provide methods less laborious than cell sorting to accurately determine fetal Rh type from different fetal cell types that circulate in maternal blood.

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.

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.

Prenatal diagnosis of sickle cell anaemia and thalassaemia by analysis of fetal cells in maternal blood

Currently, amniocentesis, chorionic villus sampling (CVS) and fetal blood sampling are used to obtain fetal cells for genetic diagnosis. These invasive procedures pose a small but not negligible risk for the fetus. Efforts have been directed towards the enrichment of fetal cells, such as erythroblasts, from maternal blood and progress has been made in the diagnosis of some chromosomal disorders and in sex determinations. We now report the detection of point mutations in single gene disorders using this method of prenatal diagnosis by enriching fetal cells from maternal blood by magnetic cell sorting followed by isolation of pure fetal cells by microdissection. In two pregnancies at risk for sickle cell anaemia and beta-thalassaemia, we successfully identified the fetal genotypes. Thus, prenatal diagnosis of single gene disorders by recovering fetal cells from maternal circulation appears to be a feasible approach.

Rapid molecular determination of fetal rhesus E type

The successful prophylaxis of RhD disease has brought attention to other Rh antigens, such as RhE antigen, that can cause hydrops fetalis. Our purpose was to develop simple molecular techniques to permit fetal RhE genotyping. We obtained amniotic fluid, villi, and fetal blood from two RhE-sensitized pregnancies, performed the Polymerase Chain Reaction (PCR), and made a presumptive fetal genotype diagnosis. The restriction enzyme MnlI was used to determine the E/e subtypes. DNA sequencing was used to demonstrate base-pair differences between the mother and fetus in one case. Conventional serology was used to confirm the fetal blood type. Maternal, paternal, and fetal genotypes were identified using molecular techniques. The presence of the fetal E allele was correctly predicted in both cases. Sequencing of maternal and fetal PCR products in one case demonstrated one base-pair substitution associated with the E/e polymorphism. Prenatal diagnosis of the fetal RhE genotype is now possible by PCR. The use of amniocytes obtained in one procedure of amniocentesis for RhE genotyping in sensitized pregnancies is less invasive than currently accepted techniques of cordocentesis, or serial amniocenteses done for delta OD450 measurement.

Fetal RhD genotyping in fetal cells flow sorted from maternal blood

OBJECTIVE

The aim of this study was to determine the accuracy of noninvasive fetal RhD genotyping by fetal cell isolation from maternal blood.

STUDY DESIGN

Candidate fetal cells from 18 pregnant women (one twin gestation) were flow-sorted. Polymerase chain reaction amplification of a 261 bp fragment of the RhD gene was performed on sorted fetal cells. The presence of amplified product was considered predictive of the Rhd-positive genotype in the fetus.

RESULTS

Sixteen of the 19 fetal RhD genotypes were correctly predicted in fetal cells isolated from maternal blood (10 were Rh positive, 6 were Rh negative). In 3 cases no amplification products were detected in RhD-positive fetuses. The association between presence of the fragment and RhD-positive genotype was significant (p=0.003, Fisher's exact test).

CONCLUSIONS

Noninvasive prenatal diagnosis of the fetal RhD genotype is feasible. Absence of amplification products in the reaction requires confirmation that fetal material is present. Improvements in fetal cell purity and yield should increase diagnostic accuracy, although the current protocol has a positive predictive value of 100% and a negative predictive value of 67%.

Prenatal diagnosis by analysis of fetal cells in maternal blood

The data accumulated thus far indicate that fetal NRBCs are the target cell type of choice in maternal blood for most investigators, although some groups continue to work with the trophoblast. Reports of persistent circulation of hematopoietic stem cells, lymphoid/myeloid progenitors, and lymphocytes mandate that removal of these cell types must occur before clinical diagnosis of the current pregnancy can be made. In selected cases, accurate detection of fetal aneuploidy has been made from fetal cells in maternal blood; the clinical evaluation sponsored by the National Institute of Child Health and Human Development will determine the sensitivity and specificity of cytogenetic diagnosis in a larger group of pregnant women, but this information will not be available for several years. At present, detection of uniquely fetal, paternally inherited gene polymorphisms or mutations such as the Rh(D) antigen is possible only because the mother lacks these genes; hence, maternal cell contamination does not hinder diagnosis. Currently the presence of large numbers of maternal cells in enriched samples precludes single-gene diagnosis for conditions in which the mother carries a mutant gene, because her cells are preferentially amplified and difficult to distinguish from those of the fetus. It is likely, however, that as techniques of individual fetal cell isolation are perfected, maternal cell contamination will no longer be an issue, and the entire fetal genome will become available for diagnosis and therapy. Pediatricians need to be aware of the progress of research in this field, because fetal cell isolation from maternal blood not only could change prenatal diagnosis but would change the amount of genetic information that arrives with a newborn infant at birth. The ultimate goal of this work is to diagnose noninvasively, in the first trimester, the common fetal aneuploidies and single-gene disorders, to permit in utero treatment, or to allow low-risk pregnant women carrying an abnormal fetus an opportunity for reproductive choice.