Gene amplification to detect fetal nucleated cells in pregnant women

DNA enrichment by allele-specific hybridization (DEASH): a novel method for haplotyping and for detecting low-frequency base substitutional variants and recombinant DNA molecules

Detecting rare sequence variants in genomic DNA is central to the analysis of de novo mutation and recombination events and the detection of rare pathological mutations in mixed cell populations. Current PCR techniques suffer from noise that limits detection to variants present at a frequency of at least 10(-4)-10(-5) per cell. We now describe an alternative approach that recovers genomic DNA molecules containing a known single-nucleotide variant by hybridization selection using a biotinylated allele-specific oligonucleotide, followed by hybrid capture on streptavidin-coated paramagnetic beads and subsequent analysis by PCR. This technique of DNA enrichment by allele-specific hybridization (DEASH) is fast, effective for all tested single-nucleotide polymorphisms (SNPs), and can recover large (>10 kb) single-stranded molecules. A single round of DEASH is effective in separating haplotypes from genomic DNA and can not only readily detect and validate DNA molecules containing a single base change at a frequency of 10(-5) per cell, but can also place these changes within the context of an extended haplotype. This technique offers a new approach to the analysis of mutation and recombination, and has the potential to detect very rare de novo base substitutions.

Long-term feto-maternal microchimerism: nature's hidden clue for alternative donor hematopoietic cell transplantation?

During pregnancy, fetal hematopoietic cells carrying paternal human leukocyte antigens (HLA) migrate into maternal circulation, and, vice versa, maternal nucleated cells can be detected in fetal organs and umbilical cord blood, indicating the presence of bidirectional cell traffic between mother and fetus. By taking advantage of fluorescence in-situ hybridization or polymerase chain reaction-based techniques, researchers recently found that postpartum persistence of such reciprocal chimerism was common among healthy individuals and may sometimes cause tissue chimerism. Although the biological significance of long-lasting feto-maternal microchimerism is unknown, a number of investigations have suggested its association with the development of "autoimmune" diseases such as systemic sclerosis. However, the very common presence of feto-maternal microchimerism among subjects without any autoimmune attack may allow us the more appealing hypothesis that it is an indicator for the acquired immunological hyporesponsiveness to noninherited maternal or fetal HLA antigens. An offspring's tolerance to noninherited maternal antigens has been clinically suggested by the retrospective analysis of renal transplantations or haploidentical hematopoietic stem cell transplantations, and whether postpartum mothers can tolerate paternally derived fetal antigens is an intriguing question. Although an exact linkage between microchimerism and transplantation tolerance is yet to be elucidated, long-term acceptance of a recipient's cell in the donor may have a favorable effect on preventing the development of severe graft-versus-host disease, and the donor cell microchimerism in the recipient might facilitate the graft acceptance. If this concept holds true, HLA-mismatched hematopoietic stem cell transplantation would be more feasible among haploidentical family members mutually linked with feto-maternal microchimerism. Further studies are warranted to investigate the potential role of feto-maternal microchimerism in human transplantation medicine.

Prenatal diagnosis using fetal cells isolated from maternal peripheral blood: a review

Many questions remain about the feasibility of using fetal cells from maternal blood for prenatal diagnosis. Although recently there has been more focus on clinically relevant methods, many studies have been performed using blood drawn after invasive procedures, and over a wide range of gestational ages. For methods to be applicable to clinical use, more work is needed on isolating cells early in pregnancy, when termination is still an option for parents who are found to have an affected pregnancy. It is generally agreed that fetal nucleated erythrocytes are the most efficacious cell type for prenatal diagnosis, but it has not yet been shown definitively whether there is an ideal gestational age for sampling, whether ABO incompatibility might limit availability of fetal cells, or whether the number of cells present might be different in normal versus abnormal pregnancies. PCR has been shown to be a powerful tool in allowing amplification and identification of very small amounts of fetal DNA. However, this is limited to cases in which a specific and unique gene from the father is sought. This means that there is the potential to diagnose many paternally inherited autosomal dominant diseases and some autosomal recessive diseases, in which the parents have different and identifiable mutations. However, when parents are both carriers of the same autosomal recessive mutations, or when the disease is X linked, PCR will not aid in prenatal diagnosis. Cytogenetic analysis of fetal cells by FISH after cell sorting is another potentially useful method of prenatal diagnosis, but requires relatively pure samples of fetal cells or an independent marker that allows easy microscopic identification. The latter might be accomplished by identifying fetal cells through their expression of embryonic hemoglobins or because they contain HLA-G mRNA. In addition, current techniques of cell sorting must be improved so that a higher percentage of fetal cells can be isolated. Currently, the best cell sorting techniques usually produce a maximum purity of 10% fetal cells. Commonly, in normal pregnancies, fewer than 0.1% of the cells isolated after sorting are fetal in origin. Improving the concentration and quantity of fetal cells will improve the accuracy of FISH. Methods such as immunophenotyping that allow the selective identification of fetal cells by microscopy, and can be used in conjunction with FISH, may be extremely valuable because they may allow the genetic analysis of only the few fetal cells within a background preponderance of maternal cells. Although the retrieval of fetal cells from maternal blood is an attractive concept, it must be clearly stated that presently it is only in the investigational phase because of the low sensitivity and specificity. There is no current application for these methods in clinical practice. It remains to be determined whether testing maternal blood for fetal cells or DNA will be used as a screening tool, similar to the maternal serum screening currently in use, or whether the accuracy can be improved to a level such that the techniques can be used diagnostically. Although there are many questions that remain unanswered at this time, the outlook for noninvasive prenatal genetic testing in the future is optimistic.

A rapid combined immunocytochemical and fluorescence in situ hybridisation method for the identification of human fetal nucleated red blood cells

Fetal nucleated red blood cells are found in the maternal circulation during pregnancy. If a simple routine method of detection of these cells was developed, it could be used as the basis of non-invasive prenatal diagnosis of fetal genetic disorders. Fetal male and adult female blood were mixed to mimic maternal blood in pregnancy and used to establish a simple technique to unequivocally detect fetal nucleated red blood cells. These were identified by combined immunocytochemistry using a human fetal haemoglobin antibody and a rapid and simple-to-use fluorescence in situ hybridisation method using X and Y chromosome probes. Initial studies using the alkaline phosphatase anti-alkaline phosphatase technique as the first procedure showed that the stain was unstable and unsuitable for in situ hybridisation. An immunoperoxidase technique was found to produce a stable stain resistant to harsh fixation steps required in subsequent in situ hybridisation. This enabled the simultaneous visualisation of immunopositivity and in situ hybridisation signals on the same cell with neither procedure affecting the other's signal quality. We are currently using this procedure to detect a range of endoplasmic reticulum proteins in fetal nucleated red blood cells from maternal blood in an attempt to diagnose disorders of liver protein expression in early pregnancy.

The time of appearance and disappearance of fetal DNA from the maternal circulation

A single copy Y-chromosome DNA sequence was amplified using the polymerase chain reaction (PCR) from the peripheral blood of 30 women who had achieved a pregnancy through an in vitro fertilization (IVF) programme. The time of conception was known precisely and was confirmed by serial ultrasound scans. Conceptions were dated as the number of weeks after fertilization plus 2, to give a time equivalent to the obstetric menstrual dating of the pregnancy (LMP). Y-chromosome-specific DNA was detected in all pregnancies with a male fetus (18/30). The earliest detection was at 4 weeks and 5 days, and the latest at 7 weeks and 1 day. Y-chromosome-specific sequences were no longer detected in any of the male pregnancies 8 weeks after delivery. No Y-chromosome sequences were detected in any of the pregnancies where only female babies were delivered. This demonstrates that fetal DNA appears in the maternal circulation early in the first trimester, that it can be identified in all pregnancies tested by 7 weeks, that it continues to be present throughout pregnancy, and that it has been cleared from the maternal circulation 2 months after parturition. Early non-invasive prenatal diagnosis for aneuploidies and inherited disorders will be possible in all pregnancies if fetal cells can be isolated free from maternal contamination (or identified accurately in the presence of maternal cells) without problems of contamination from previous pregnancies.

Fetal granulocytes in maternal venous blood detected by in situ hybridization

Fetal male cells from maternal venous blood were detected by a non-radioactive in situ hybridization method using the biotinylated Y-specific DNA probe pY431. The hybridizations were performed on Ficoll-Paque-isolated nucleated blood cells obtained from 11 pregnant women in the seventh to 31st week of gestation. A Y-specific signal was detected in both granulocytes and lymphocyte-like cells in seven of the 11 women studied. These women gave birth to boys. In one of the four remaining cases, a Y-specific signal was detected in the lymphocyte-like cells but not in the granulocytes. This woman gave birth to a girl. The other three women had no cells with a Y-specific signal and all three gave birth to girls. Altogether, 83,500 nucleated cells were analysed. One hundred and three cells showed a Y-specific signal. Of these Y-specific cells, 62 per cent were granulocytes and 38 per cent lymphocyte-like cells. Our results suggest that fetomaternal transfer of granulocytes is common and that it occurs as early as in the seventh week of gestation. None of the ten non-pregnant female control samples showed positive cells with the Y-chromosome-specific probe; approximately 97 per cent of the cells from the five adult male controls showed a Y-specific signal. Our results indicate that in situ hybridization using a Y-specific DNA probe performed on granulocytes in maternal blood can be used for fetal male sex determination.

Analysis of peripheral blood of pregnant women for the presence of fetal Y chromosome-specific ZFY gene deoxyribonucleic acid sequences

Deoxyribonucleic acid sequences of human ZFY (zinc-finger-Y) gene, a Y-chromosome-specific gene and candidate for the testis-determining factor, has been identified by an in vitro enzymatic deoxyribonucleic acid amplification method in peripheral blood specimens of women pregnant with male fetuses. This technique permits detection of ZFY gene deoxyribonucleic acid sequences in as few as a single male cell among 1,000,000 female cells. Maternal blood results were confirmed by amplification of ZFY gene deoxyribonucleic acid sequences in chorionic villus cells and by karyotyping in 33 of 36 pregnant women. There was no false-positive male result, and two of the three blood specimens with false-negative results were obtained from pregnant women at a very early gestational age. With properly designed guidelines, this deoxyribonucleic acid amplification method may be an alternative to determine the fetal sex for those pregnancies at risk for X-linked genetic disorders.

Molecular genetic approaches to the analysis and diagnosis of human inherited disease: an overview

The advent of recombinant DNA technology has contributed enormously to our understanding of human genome pathology. In this review, current approaches to the analysis and diagnosis of human genetic disease are presented and their contribution to diagnostic medicine assessed. At the level of the gene, the nonrandom nature of human gene mutation is described and the role of the local DNA sequence environment explored.

Trophoblast-like cells sorted from peripheral maternal blood using flow cytometry: a multiparametric study involving transmission electron microscopy and fetal DNA amplification

Three monoclonal antibodies (MAbs) against trophoblast (GB17, GB21, and GB25) and flow cytometry were used to sort trophoblast-like cells (TLCs) from peripheral blood of pregnant women. Sorted TLCs were processed for electron microscopy and fetal DNA amplification of the Y-specific sequences from mothers carrying male fetuses. At the ultra-structural level, most of the nucleated cells had the morphology of leucocytes, suggesting maternal contaminants, and we did not find the characteristic features of the free intervillous trophoblast cells. Nevertheless, polymerase chain reaction (PCR) analysis showed an amplification of Y-specific sequences in two out of three samples of sorted TLCs. These results suggest that besides the maternal leucocytes, sufficient trophoblast nucleated fetal cells can be obtained using cell enrichment by sorting. This sensitive method holds promise for non-invasive prenatal diagnosis of fetal sex and if sufficient Y(positive) nuclei are found, for the diagnosis of selected numerical chromosome abnormalities.

Absence of fetal cells in maternal circulation at a level of 1 in 25,000

A dual polymerase chain reaction (PCR) technique is developed which enables the detection of one part male DNA in 25,000 parts female DNA. The technique amplifies a part of the X-Y homologous amelogenin gene in which the Y counterpart has a 189 bp deletion within one of the introns. This deletion has made it possible to identify individual X and Y counterparts based on the difference in size between them. None of the 18 pregnant women studied showed a positive Y-signal although eight of them bear male fetuses excluding the presence of fetal cells at one in 25,000 maternal cells. The results presented here show that a sensitivity of greater than one in 25,000 is required for detection of fetal genetic disease using maternal peripheral blood.

Detection of fetal cells in maternal blood

We report the detection of fetal cells in the maternal circulation by enzymatic amplification of a single copy gene sequence that was fetal-specific. Fetal HLA-A2-positive cells were sorted from maternal HLA-A2-negative cells by flow cytometry and confirmed by demonstration of a fetal-specific HLA-DR4 sequence. However, this sequence could not be detected in unenriched maternal DNA prepared at 28 and 32 weeks' gestation. The sensitivity of detection was 1 HLA-DR4-positive cell in 10(5) HLA-DR4-negative cells. We conclude that prenatal diagnosis of paternally inherited autosomal-dominant genetic defects may be possible by selective gene amplification of maternal peripheral blood. However, preliminary enrichment for fetal cells may be necessary.

Isolation of fetal trophoblast cells from peripheral blood of pregnant women

Fetal trophoblast cells were isolated from maternal peripheral blood by means of murine monoclonal antibodies of high specificity and affinity for human syncytiotrophoblast and nonvillous cytotrophoblast cells. The cells were isolated in sufficient numbers to allow polymerase chain reaction (PCR) amplification of the Y-chromosome-specific DNA sequence from the peripheral blood of thirteen pregnant women. The fetal sex predicted by PCR analysis of the isolated trophoblast cells accorded with that ascertained by karyotyping of chorionic villus samples in eleven of twelve women studied in early pregnancy and with the sex of the baby on delivery in one woman studied at 34 weeks' gestation. Isolation of these fetal cells could allow noninvasive diagnosis of a wide range of inherited disorders.

Prenatal sex determination by DNA amplification from maternal peripheral blood

The polymerase chain reaction was used to amplify a Y-specific repeat sequence in peripheral blood DNA samples from 19 pregnant women who had a gestational age of 9 to 41 weeks. Y-specific sequences were amplified from all 12 women who bore a male fetus but in none of 7 women who bore a female fetus. With stringent precautions against contamination, this technique may assist prenatal diagnosis of sex-linked genetic disorders.