Breakthrough in AdnaGen's prenatal diagnostics project

AdnaGen had its antibodies externally assessed and has received a confirmation that they are specific for fetal erythroid cells. The assessment was performed by Prof. Dr. med. Dr. h. c. R. Parwaresch in Kiel, Germany. These antibodies can be used to distinguish fetal and maternal cells in blood of pregnant women and thus are the key component for a new dimension in prenatal diagnosis.

AdnaGen's tool for prenatal diagnostics

Scientific Background
Social developments have resulted in an increased number of prenatal tests. Currently, in Germany, one in ten pregnancies is being subjected to an amniotic fluid test. For pregnant women aged 35 or older the rate of amniocentesis is estimated to reach at least 60% (Hennen et al. 1996) - and on an average the women's age at birth raises. Approx. 20% of the mothers are at least 35 years old at birth.
At the age of 35 a pregnant woman has to balance an average risk of 0.5% to induce an abort by amniocentesis against an age related probability for trisomy 21 of less than 0.3% (Bartels et al. 2002).

The presence of fetal cells within the blood of pregnant women offers the chance to develop a prenatal diagnostic that replaces amniocentesis and thereby eliminates the risk of today's invasive diagnosis.

Literature indicates that one fetal cell is present amongst 10⁵ to 10⁷ of the mother's cells (Price et al. 1991). Subsequent investigations have revealed that the ratio of fetal cells in the blood of the mother is higher in the presence of chromosomal anomalies (Bianchi et al. 1997). This improves the chance to detect an aneuploid fetus by non-invasive diagnosis of fetal cells.

The presence of three different types of fetal cells in the maternal blood has been reported: lymphocytes, trophoblasts and nucleated red blood cells (summarized in Bianchi 1998). Lymphocytes in maternal blood have been detected as long as one to five years after delivery. This long persistence interferes with diagnosis in subsequent pregnancies. Trophoblasts are attractive target cells since they can be definitively identified because of their unique morphology. Nevertheless, diagnosis based on the analysis of trophoblasts poses a problem: Trophoblasts are part of the placenta and not of the fetus. In 99% of the analyses abnormalities seen in the trophoblasts are the same as in the fetus, but a test with 1% false results has obvious disadvantages.

Therefore, nucleated fetal red blood cells are the favored target cell type. These are abundant already in first trimester fetal blood and they have the entire gene set.

Nucleated fetal red blood cells can be characterized with a suitable combination of molecular markers. Unfortunately, these markers do not occur exclusively on fetal cells. The number of fetal cells is small in comparison to immature nucleated red cells in maternal blood, which exhibit similar characteristics. That is the reason why these markers can be used for the enrichment of fetal cells only but not for their unquestionable identification.

A marker that specifically identifies a fetal nucleated red blood cell is still missing. The discovery of a fetal specific marker is a prerequisite for an accurate diagnosis.

Diverse enrichment methods and combinations thereof have been published. The favored procedure combines the isolation of mononuclear cells by a Ficoll density gradient followed by an antigen specific depletion and enrichment by cell sorting (FACS or MACS). Depletion markers are for example the leukocyte marker CD45 or the monocyte marker CD14.

Identification of the enriched fetal cells is straight forward in the case of a male fetus. The Y-chromosome can be detected by FISH or by PCR. Cells of a female fetus are more difficult to identify. One possibility is to make a genetic fingerprint. This procedure requires the analysis of purified cells because any contamination with maternal cells impedes the analysis.

The National Institute of Child Health and Human Development organized a fetal cell isolation study (NIFTY). The participating clinical centers applied the isolation methods as described above. For the evaluation of the cell enrichment procedure the fetal gender was determined by chromosomes X and Y specific FISH probes. After a five year study the researchers see the necessity for further technological advances (Bianchi et al. 2002). AdnaGen believes that this advance can be achieved with its proprietary monoclonal antibodies, which are specific for a fetal nucleated red blood cell epitope.

Conclusion: There is no method available yet that shows the potential to be used as a routine tool in prenatal diagnosis in maternal blood. This is mainly due to the fact that so far fetal cells could not be distinguished properly from maternal cells. Antibodies with the specificity needed for that purpose were not available until now. AdnaGen's proprietary monoclonal antibodies will help to overcome these shortcomings.

The Technological Advances of AdnaGen's Prenatal Diagnostics
A fetal specific anibody is a key component, that enables prenatal diagnosis with maternal blood.
Since several years of research and development work in this field AdnaGen finally identified monoclonal antibodies for the labeling of fetal cells with the required specificity to distinguish them from maternal cells. A patent application has been filed