K.O'Donoghue, M.Choolani, J. de la Fuente, S. Kumar, C. Campagnoli, P.R. Bennett, I.A.G. Roberts and N.M. Fisk.
Identification of fetal mesenchymal stem cells in maternal blood: implications for non-invasive prenatal diagnosis (2003) K. O'Donoghue, M. Choolani, J. Chan, J. de la Fuente, S. Kumar, C. Campagnoli, P.R. Bennett, I.A.G. Roberts and N.M. Fisk.Molecular Human Reproduction, Vol. 9, No. 8, 497-502
Summary:
My paper is based off the recent identification of mesenchymal stem cells (MSC) in first trimester fetal blood. The authors of my paper state that strategies for genetic prenatal diagnosis on fetal cells in the maternal circulation have been limited by lack of a cell type present only in fetal blood. By discovering MSC in first trimester fetal blood it offers the prospect of targeting MSC for non-invasive prenatal diagnosis. The authors of the paper developed protocols for fetal MSC enrichment from maternal blood and determined sensitivity and specificity in mixing experiments of male fetal MSC added to female blood. They also used the optimal protocol to isolate fetal MSC from maternal blood in the first trimester using blood taken after surgical termination of pregnancy as a model of increased feto-maternal haemorrhage. Their experiments showed that they could isolate fetal MSC from maternal blood, however, it is rare in post-termination blood which suggest they are unlikely to have a role in non-invasive prenatal diagnosis.
The aim of this study was to investigate fetal MSC as potential targets for non-invasive prenatal diagnosis in first trimester maternal blood. They established a protocol for fetal MSC enrichment from maternal blood and determined sensitivity and specificity in mixing experiments with adult nucleated cells. They then applied this method to the isolation of fetal MSC from maternal blood after first trimester termination of pregnancy, which is a biological model of increased feto-maternal haemorrhage.
According to the paper, invasive procedures limit the uptake of prenatal diagnosis for chromosomal and monogenic disorders, because of their associated risk of fetal loss. Throughout the last 20 years there has been much interest in the development of non-invasivie techniques. Of these, isolation of fetal cells from the maternal circulation early in preganacy could replace existing methods such as serum and nuchal screening, since it should allow exact genetic diagnosis without risk to the fetus.
In non-invasive prenatal diagnosis, fetal cells must be distinguished from maternal cells, usually by enriching them to an acceptable level of purity before identifying them as uniquely of fetal orgin. Many approaches have been designed to recover fetal cells from maternal blood, but all are problematic: enrichment procedures result in significant loss of rare fetal cells, and most known fetal cells types are also found in adult blood, rendering identification difficult. The recent identification of mesenchymal stem cells (MSC) in first trimester fetal blood offers the prospect of targeting fetal MSC for non-invasive prenatal diagnosis, since MSC are not known to circulate in healthy adults.
Since between 11-13 weeks is recognized as the optimal time for prenatal diagnosis, as most of the risk of spontaneous miscarriage has passed and late first trimester diagnosis is still possible, the researchers used this as the optimal time for taking fetal cells. Unlike other candidates for non-invasive prenatal diagnosis, fetal MSC have a characteristic morphology and immunophenotype and are readily expandable in vitro and like their counterparts in adult bone marrow they have the capacity to differentiate into a number of mesenchymal lineages.
In their study to establish optimal cell purification and culture systems for detection of fetal MSC in maternal blood, cultured male fetal MSC were mixed with 20-40 ml adult female whole blood, to achieve dilutions of 1 in 10^5 to 1 in 10^8 nucleated cells. Numbers of MSC > 100 were obtained by serial dilutions from a larger known concentration, and, for greater accuracy, cell number of MSC were counted.
Since feto-maternal haemorrhage after first trimester termination of pregnancy results in an 80-fold increase in fetal cell numbers in maternal blood, and is a useful biological model with which to evalute fetal cell enrichement and expansion strategies under development. The researchers applied their enrichment protocol to the isolation of MSC from first trimester post-termination maternal blood. Although it was possible to isolate fetal MSC in maternal blood, fetal cells were identified in only one of 20 patients tested. This suggested to the researchers that fetal MSC are likely to circulate at a very low frequency in maternal blood, since their enrichment protocol in model mixtures was sensitive enough to detect one MSC among 2.5x10^7 adult nucleated cells or one cell in 3.3 ml whole blood. The researchers came up with possible reasons for the low frequency of fetal MSC detected in maternal blood, thinking that fetal MSC may only be present in the cirulation in extremely low numbers at or below the level of sensitivity of the culture assay they used. Among others within the paper.
The authors concluded that they have isolated fetal MSC from maternal blood for the first time, but acknowledge that the rarity of fetal MSC circulating in maternal blood appears to preclude clinical application in non-invasive prenatal testing. Besides this, the discovery of a unique fetal stem cell cirulating in maternal blood with the potential to persist in tissues year after pregnancy provides information about feto-maternal trafficking in early pregnancy and emphasizes increasing awareness that cellular trafficking may have far-reaching biological consequences.
Critique:
Though I found the information within this paper extremely interesting, I found that it lacked necessary information which would of made the paper clearer. I understood that the point of the paper was to look into the identification of mesenchymal stem cells and their use in non-invasive diagnosis. However, the exact reasoning behind the enrichment protocol and how this was useful in identifying and determing fetal MSC was not clear. It was obviously important to the researchers in determining the amount of fetal MSC that was present and identifying them as fetal MSC but it was unclear why it was so important. I found the diagrams to be interesting, since they gave a visual of the cells and tissues which we are discussing, however, it would of been more helpful if the authors of the paper had included some more figures and diagrams of the different trials that they did and the results they obtained. Over all it was an extremely interesting and illuminating paper, giving me more idea of the types of study which are being done with fetal cells, however, the topic is still much discussed and studied and therefore is obviously not fully represented as it may be in the future.
Savannah Isaacs
