Characterization of Fetomaternal Microchimerism in a Murine Model

Abstract

Fetal cells have been shown to transmigrate into the mother through the placental interface during pregnancy and these cells can persist in various maternal organs for as long as decades. In animal studies, it has been suggested that fetal cells also termed pregnancy associated progenitor cells (PAPCs) might possess multipotential differentiation capabilities. Therefore, fetal cells might have a regenerative function that is potentially useful for cell-based therapies. However, much needs to be learned about the basic biology of these fetal cells such as their long-term homing, survival, integration and differentiation in maternal organs and the origin and identity of these fetal cells.

The persistence of fetal cells in the maternal body led us to hypothesize that these multipotential fetal cells that transmigrate into the maternal body originate from the embryo proper. To test the hypothesis, a mouse model, which allows tagging of fetal cells by the reporter, green fluorescent protein (GFP) for in-depth characterization of fetal cells in healthy mothers was used. Using various methods such as flow cytometry, qPCR and immunohistochemistry (IHC), a temporal profile of fetal cells trafficking into maternal organs and blood at various pre- and post-natal time points was established. Our data demonstrated that fetal cells were able to persist into late adulthood suggesting long-term survival capabilities. The organ-specific differentiation capability of fetal cells in two maternal organs was also studied. This work showed that fetal cells could differentiate to neurons in the brain and to epithelial and endothelial cell types in the lung.

Next, genetic lineage tagging using the Cre-LoxP recombination technique was done in order to elucidate the developmental origin of fetal cells from the fetus. Meox2-cre and Nestin-cre mice were used to lineage tagged embryo proper and neuroectodermal derivatives, respectively. The presence of embryo proper-tagged fetal cells suggests an embryo proper origin rather than a trophectodermal origin. Neuroectodermally-tagged fetal cells were found in the maternal blood and solid organs such as lung and liver. Furthermore, neuroectodermally-tagged fetal cells found in the maternal blood expressed the pan-haemopoietic marker CD45, suggesting that these cells adopted a hematopoietic cell fate. These data provided insight into fetal cells originating from the embryo proper and also potentially from the neuroectodermal lineage. Lastly, using single cell gene expression analysis, it was found that fetal cells could be grouped according to their gene signatures, which suggests a diverse and mixed population of cell types transfer into mothers during pregnancy with fetal cells with a neuroectodermal signature predominating. In addition, changes in the temporal expression profile of some candidate genes such as Oct4 and Runx1 were also observed.

In conclusion, this study suggests that fetal cells are able to integrate and survive in maternal body long-term and acquire organ-specific cell fates in the lung, blood and brain. Fetal cells possibly originate from the embryo proper and in particular from the neuroectodermal lineage. Further work should focus on identifying the differentiation capability and origin of fetal cells, which may provide further knowledge, which could allow the translation of these intriguing cells into cell-therapy, based clinical applications.