Fig. 5.1
Proven features of amniotic fluid stem cells (AFSCs) supporting a role in fetal cell microchimerism
Fetal cell microchimerism is also represented by the presence of fetal DNA in the maternal circulation [2, 3, 21, 38, 47]. Recently, it has been reported that AFSCs underlie a strictly regulated survival control. The capacity of AFSCs to maintain homeostasis via fine-tuned, apoptotic disposal of excess or defective cells was demonstrated by the observation that slight deregulation immediately triggers AFSCs to go into apoptosis [14]. Assuming that AFSCs could be candidates for PAPCs, such a stringent survival control in AFSCs could give rise to cell-free DNA in vivo (Fig. 5.1).
Taking all that into account, AFSCs perfectly fulfil the major features, which must be designated to a stem cell type to be considered as a candidate for the origin of PAPCs. Furthermore, one could also assume AFSCs to be the origin of cell-free, fetal DNA in the mother’s blood, which is already routinely used for non-invasive prenatal diagnosis. Accordingly, we have recently suggested a model in which AFSCs give rise to what we currently know as PAPCs and cell-free, fetal DNA [65].
4 Features, Which Need to be Tested to Further Support a Role of Amniotic Fluid Stem Cells in Fetal Cell Microchimerism
Migration is normally used to describe any directed cell movement within the body, whereas invasion is defined as the penetration of tissue barriers and infiltration into tissues [36]. Extravasation is used to describe the process by which a circulating cell passes through the blood vessel wall into various body areas [39]. Considering everything what is known about PAPCs today, one would assume that these fetal, microchimeric cells harbour additional potentials, such as migration, extravasation and invasion [2, 6, 15, 17, 19, 34, 44, 54] (Fig. 5.2). To our best knowledge, explicit experimental approaches to investigate in detail whether the here described c-kit-positive, monoclonal AFSCs harbour the potential for migration, extravasation or invasion, have not been reported so far.
Fig. 5.2
Features, which need to be tested to further support a role of AFSCs in fetal cell microchimerism
Last but not least, ultimate support of the hypothesis that AFSCs could function as PAPCs would be to prove that AFSCs floating in the amniotic fluid could finally end as cells in maternal tissues or as cell-free, fetal DNA in the maternal circulation during pregnancy (Fig. 5.2).
Unravelling the identity of PAPCs in support of AFSCs might give answers to two very important questions in stem cell biology: What is the origin of PAPCs? What is the biological function of AFSCs? Accordingly, we think it is absolutely warranted to design experimental settings and approaches to investigate these features in AFSCs.
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