Pregnancy-associated progenitor cells: an under-recognized potential source of stem cells in maternal lung

Fetal cell microchimerism and susceptibiltiy to COVID-19 disease in women

PURPOSE

The clinical outcome of COVID-19 disease is worse in males, and the reasons of this gender disparity are currently unclear, though evidences point to a combination of biological and gender-specific factors. A phenomenon unique to the female gender is the fetal cell microchimerism (FCM), defined as the presence of fetal microchimeric cells in maternal organs and in the circulation for years after delivery and usually evaluated by assessing the presence of male cells or DNA in a woman. In the present case-control study, we aimed to evaluate the possible effect of pregnancy and related FCM on the susceptibility to SARS-CoV-2 infection and on the clinical course and outcome of COVID-19.

METHODS

One hundred twenty-three women with a previous male pregnancy, comprising 63 COVID-19 cases and 60 healthy controls were enrolled. The presence of blood male DNA was assessed by the amplification of the Y-chromosome specific gene SRY.

RESULTS

The prevalence of male DNA of presumed fetal origin was significantly higher in healthy controls than in COVID-19 cases (70 vs 44.4%, P = 0.0044; OR 0.3429, 95% CI 0.1631-0.7207, P = 0.0047). Among women affected with COVID-19, the presence of male FCM did not significantly influence the severity of the disease, though the 8 deceased women studied were all FCM negative.

CONCLUSION

This is the first case-control study reporting the prevalence of FCM in COVID-19 and healthy women. Overall, our data seem to suggest a role for FCM in the protection towards the SARS-CoV-2 infection with a possible positive impact on clinical outcome.

Fetomaternal microchimerism and genetic diagnosis: On the origins of fetal cells and cell-free fetal DNA in the pregnant woman

During pregnancy several types of fetal cells and fetal stem cells, including pregnancy-associated progenitor cells (PAPCs), traffic into the maternal circulation. Whereas they also migrate to various maternal organs and adopt the phenotype of the target tissues to contribute to regenerative processes, fetal cells also play a role in the pathogenesis of maternal diseases. In addition, cell-free fetal DNA (cffDNA) is detectable in the plasma of pregnant women. Together they constitute the well-known phenomenon of fetomaternal microchimerism, which inspired the concept of non-invasive prenatal testing (NIPT) using maternal blood. An in-depth knowledge concerning the origins of these fetal cells and cffDNA allows a more comprehensive understanding of the biological relevance of fetomaternal microchimerism and has implications for the ongoing expansion of resultant clinical applications.

Forever Connected: The Lifelong Biological Consequences of Fetomaternal and Maternofetal Microchimerism

BACKGROUND

Originally studied as a mechanism to understand eclampsia-related deaths during pregnancy, fetal cells in maternal blood have more recently garnered attention as a noninvasive source of fetal material for prenatal testing. In the 21st century, however, intact fetal cells have been largely supplanted by circulating cell-free placental DNA for aneuploidy screening. Instead, interest has pivoted to the ways in which fetal cells influence maternal biology. In parallel, an increasing appreciation of the consequences of maternal cells in the developing fetus has occurred.

CONTENT

In this review, we highlight the potential clinical applications and functional consequences of the bidirectional trafficking of intact cells between a pregnant woman and her fetus. Fetal cells play a potential role in the pathogenesis of maternal disease and tissue repair. Maternal cells play an essential role in educating the fetal immune system and as a factor in transplant acceptance. Naturally occurring maternal microchimerism is also being explored as a source of hematopoietic stem cells for transplant in fetal hematopoietic disorders.

SUMMARY

Future investigations in humans need to include complete pregnancy histories to understand maternal health and transplant success or failure. Animal models are useful to understand the mechanisms underlying fetal wound healing and/or repair associated with maternal injury and inflammation. The lifelong consequences of the exchange of cells between a mother and her child are profound and have many applications in development, health, and disease. This intricate exchange of genetically foreign cells creates a permanent connection that contributes to the survival of both individuals.

Chimerism as the basis for organ repair

Organ and tissue repair are complex processes involving signaling molecules, growth factors, and cell cycle regulators that act in concert to promote cell division and differentiation at sites of injury. In embryonic development, progenitor fetal cells are actively involved in reparative mechanisms and display a biphasic interaction with the mother; and there is constant trafficking of fetal cells into maternal circulation and vice versa. This phenomenon of fetal microchimerism may have significant impact considering the primitive, multilineage nature of these cells. In published work, we have reported that fetal-derived placental cells expressing the homeodomain protein CDX2 retain all "stem" functional proteins of embryonic stem cells yet are endowed with additional functions in areas of growth, survival, homing, and immune modulation. These cells exhibit multipotency in vitro and in vivo, giving rise to spontaneously beating cardiomyocytes and vascular cells. In mouse models, CDX2 cells from female placentas can be administered intravenously to male mice subjected to myocardial infarction with subsequent homing of the CDX2 cells to infarcted areas and evidence of cellular regeneration with enhanced cardiac function. Elucidating the role of microchimeric fetal-derived placental cells may have broader scientific potential, as one can envision allogeneic cell therapy strategies targeted at tissue regeneration for a variety of organ systems.

The role of fetal-maternal microchimerism as a natural-born healer in integrity improvement of maternal damaged kidney

PURPOSE

To identify the fetal stem cell (FSC) response to maternal renal injury with emphasis on renal integrity improvement and Y chromosome detection in damaged maternal kidney.

MATERIALS AND METHODS

Eight non-green fluorescent protein (GFP) transgenic Sprague- Dawley rats were mated with GFP-positive transgenic male rats. Renal damage was induced on the right kidney at gestational day 11. The same procedure was performed in eight non-pregnant rats as control group. Three months after delivery, right nephrectomy was performed in order to evaluate the injured kidney. The fresh perfused kidneys were stained with anti-GFP antibody. Polymerase chain reaction (PCR) assay was also performed for the Y chromosome detection. Cell culture was performed to detect the GFP-positive cells. Technetium-99m-DMSA renal scan and single-photon emission computed tomography (SPECT) were performed after renal damage induction and 3 months later to evaluate the improvement of renal integrity.

RESULTS

The presence of FSCs was confirmed by immune histochemical staining as well as immunofluorescent imaging of the damaged part. Gradient PCR of female rat purified DNA demonstrated the presence of Y-chromosome in the damaged maternal kidney. Moreover, the culture of kidney cells showed GPF- positive cells by immunofluorescence microscopy. The acute renal scar was repaired and the integrity of damaged kidney reached to near normal levels in experimental group as shown in DMSA scan. However, no significant improvement was observed in control group.

CONCLUSION

FSC seems to be the main mechanism in repairing of the maternal renal injury during pregnancy as indicated by Y chromosome and GFP-positive cells in the sub-cultured medium.

Stem/progenitor cells in endogenous repairing responses: new toolbox for the treatment of acute lung injury

The repair of organs and tissues has stepped into a prospective era of regenerative medicine. However, basic research and clinical practice in the lung regeneration remains crawling. Owing to the complicated three dimensional structures and above 40 types of pulmonary cells, the regeneration of lung tissues becomes a great challenge. Compelling evidence has showed that distinct populations of intrapulmonary and extrapulmonary stem/progenitor cells can regenerate epithelia as well as endothelia in various parts of the respiratory tract. Recently, the discovery of human lung stem cells and their relevant studies has opened the door of hope again, which might put us on the path to repair our injured body parts, lungs on demand. Herein, we emphasized the role of endogenous and exogenous stem/progenitor cells in lungs as well as artificial tissue repair for the injured lungs, which constitute a marvelous toolbox for the treatment of acute lung injury. Finally, we further discussed the potential problems in the pulmonary remodeling and regeneration.

Novel insights into the link between fetal cell microchimerism and maternal cancers

INTRODUCTION

Fetal cell microchimerism (FCM) is defined as the persistence of fetal cells in the mother for decades after pregnancy without any apparent rejection. Fetal microchimeric cells (fmcs) engraft the maternal bone marrow and are able to migrate through the circulation and to reach tissues. In malignancies, the possible role of fmcs is still controversial, several studies advising a protective and repairing function, and other postulating a beneficial role in the progression of the disease. At the peripheral blood level, FCM is less frequently observed in women with several solid and hematological neoplasia with respect to healthy controls, suggesting a beneficial role in cancer surveillance. At the tissue level, fmcs were documented in neoplastic lesions of thyroid, breast, cervix, lung and melanoma, displaying epithelial, hematopoietic, mesenchymal and endothelial lineage differentiation. Fmcs expressing hematopoietic markers were hypothesized to have a role in the attack to neoplastic cells, whereas those expressing epithelial or mesenchymal antigens could be involved in repair and replacement of damaged cells. On the other hand, fetal cells showing an endothelial phenotype could have a role in tumor evolution and progression. The positive effect of FCM is supported by findings in animal models.

CONCLUSIONS

This review provides an extensive overview of the link between fetal cell microchimerism and maternal cancers. Moreover, biological mechanisms by which fetal cell microchimerism is believed to modulate the protection against cancer development or tumor progression will be discussed, together with findings in animal models.

Fetal microchimerism and maternal health: a review and evolutionary analysis of cooperation and conflict beyond the womb

The presence of fetal cells has been associated with both positive and negative effects on maternal health. These paradoxical effects may be due to the fact that maternal and offspring fitness interests are aligned in certain domains and conflicting in others, which may have led to the evolution of fetal microchimeric phenotypes that can manipulate maternal tissues. We use cooperation and conflict theory to generate testable predictions about domains in which fetal microchimerism may enhance maternal health and those in which it may be detrimental. This framework suggests that fetal cells may function both to contribute to maternal somatic maintenance (e.g. wound healing) and to manipulate maternal physiology to enhance resource transmission to offspring (e.g. enhancing milk production). In this review, we use an evolutionary framework to make testable predictions about the role of fetal microchimerism in lactation, thyroid function, autoimmune disease, cancer and maternal emotional, and psychological health.

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Fetal cell microchimerism: a protective role in autoimmune thyroid diseases

OBJECTIVE

The physiological persistence of fetal cells in the circulation and tissue of a previously pregnant woman is called fetal cell microchimerism (FCM). It has been hypothesized to play a role in systemic autoimmune disease; however, only limited data are available regarding its role in autoimmune thyroid disease (AITD).

DESIGN

Circulating FCM was analyzed in a large series of previously pregnant women with Graves' disease (GD), Hashimoto's thyroiditis (HT), or no disease (healthy controls (HCs)). To exclude the possible bias related to placental factors, the polymorphic pattern of human leukocyte antigen-G (HLA-G) gene, which is known to be involved in the tolerance of fetal cells by the maternal immune system, was investigated.

METHODS

FCM was evaluated by PCR in the peripheral blood, and the Y chromosome was identified by fluorescence in situ hybridization in some GD tissues. HLA-G polymorphism typing was assessed by real-time PCR.

RESULTS

FCM was significantly more frequent in HC (63.6%) than in GD (33.3%) or HT (27.8%) women (P=0.0004 and P=0.001 respectively). A quantitative analysis confirmed that circulating male DNA was more abundant in HC than it was in GD or HT. Microchimeric cells were documented in vessels and in thyroid follicles. In neither GD/HT patients nor HC women was the HLA-G typing different between FCM-positive and FCM-negative cases.

CONCLUSION

The higher prevalence of FCM in HC as compared to GD and HT patients suggests that it plays a possible protective role in autoimmune thyroid disorders. Placental factors have been excluded as determinants of the differences found. The vascular and tissue localization of microchimeric cells further highlights the ability of those cells to migrate to damaged tissues.

Stem cells, cell therapies, and bioengineering in lung biology and diseases. Comprehensive review of the recent literature 2010-2012

A conference, "Stem Cells and Cell Therapies in Lung Biology and Lung Diseases," was held July 25 to 28, 2011 at the University of Vermont to review the current understanding of the role of stem and progenitor cells in lung repair after injury and to review the current status of cell therapy and ex vivo bioengineering approaches for lung diseases. These are rapidly expanding areas of study that provide further insight into and challenge traditional views of mechanisms of lung repair after injury and pathogenesis of several lung diseases. The goals of the conference were to summarize the current state of the field, to discuss and debate current controversies, and to identify future research directions and opportunities for basic and translational research in cell-based therapies for lung diseases. The goal of this article, which accompanies the formal conference report, is to provide a comprehensive review of the published literature in lung regenerative medicine from the last conference report through December 2012.

Comprehensive analysis of genes expressed by rare microchimeric fetal cells in the maternal mouse lung

During pregnancy, cells from each fetus travel into the maternal circulation and organs, resulting in the development of microchimerism. Identification of the cell types in this microchimeric population would permit better understanding of possible mechanisms by which they affect maternal health. However, comprehensive analysis of fetal cells has been hampered by their rarity. In this study, we sought to overcome this obstacle by combining flow cytometry with multidimensional gene expression microarray analysis of fetal cells isolated from the murine maternal lung during late pregnancy. Fetal cells were collected from the lungs of pregnant female mice. cDNA was amplified and hybridized to gene expression microarrays. The resulting fetal cell core transcriptome was interrogated using multiple methods including Ingenuity Pathway Analysis, the BioGPS gene expression database, principal component analysis, the Eurexpress gene expression atlas, and primary literature. Here we report that small numbers of fetal cells can be flow sorted from the maternal lung, facilitating discovery-driven gene expression analysis. We additionally show that gene expression data can provide functional information about fetal cells. Our results suggest that fetal cells in the murine maternal lung are a mixed population, consisting of trophoblasts, mesenchymal stem cells, and cells of the immune system. Detection of trophoblasts and immune cells in the maternal lung may facilitate future mechanistic studies related to the development of immune tolerance and pregnancy-related complications, such as pre-eclampsia. Furthermore, the presence and persistence of mesenchymal stem cells in maternal organs may have implications for long-term postpartum maternal health.

The natural history of fetal cells in postpartum murine maternal lung and bone marrow: a two-stage phenomenon

During pregnancy, fetal cells cross into the maternal organs where they reside postpartum. Evidence from multiple laboratories suggests that these microchimeric fetal cells contribute to maternal tissue repair after injury. In mouse models, most injury experiments are performed during pregnancy; however, in a clinical setting most injuries or diseases occur postpartum. Therefore, experiments using animal models should be designed to address questions in the time period following delivery. In order to provide a baseline for such experiments, we analyzed the natural history of fetal cells in the postpartum maternal organs. Female C57BL/6J mice were mated to males homozygous for the enhanced green fluorescent protein gene. Fetal cells in the maternal lungs and bone marrow were identified by their green fluorescence using in a high-speed flow cytometer and their counts were compared between the lung and bone marrow. Spearman correlation analysis was used to identify relationships between the duration of time postpartum and the cell counts and ratio of live and dead cells. Our results show that fetal cells persist in these organs until at least three months postpartum in healthy female mice. We show a two-stage decline, with an initial two and a half-week rapid clearance followed by a trend of gradual decrease. Additionally, an increase in the ratio of live to dead cells within the lung over time suggests that these cells may replicate in vivo. The results presented here will inform the design of future experiments and may have implications for women's health.

Fetal cells in the murine maternal lung have well-defined characteristics and are preferentially located in alveolar septum

The transfer of fetal cells to maternal organs occurs in mouse and human pregnancy. Techniques such as polymerase chain reaction and flow cytometry do not permit study of fetal cell morphology or anatomic location. Using a green fluorescent protein (GFP) transgenic mouse model, our objective was to determine whether GFP+ signal emanates from intact or degraded fetal cells, and whether they have a characteristic appearance and location within maternal lung. Four wild-type female mice were mated to males homozygous for the Gfp transgene and studied at days e16-18. Controls were 2 females mated to wild-type males. Morphologic appearance and anatomic position of each GFP+ object within maternal lung was recorded. GFP signals were sufficiently bright to be visualized without anti-GFP antibody and were confirmed by confocal microscopy to be separate from fluorescent artifact. Of 438 GFP+ objects detected, 375 (85.6%) were from intact cells, and 63 (14.4%) were acellular. Four distinct categories of intact cells were observed. Of these, 23.2% had mononuclear morphology with a relatively large nucleus and GFP+ cytoplasm (Group A). An additional group of cells (10.1%) had mononuclear morphology and podocyte extensions (Group B). The remainder of cells had fragmented nuclei or cytoplasm. Both intact cells and acellular fragments were predominantly localized to the maternal alveolar septum (P<0.0001). This study demonstrates that fetal GFP+ cells are predominantly located in the alveolar septum and have characteristic morphologies, although it remains unclear whether these represent distinct categories of cells or degrading cells. Nevertheless, this naturally acquired population of fetal cells in maternal lung should be considered in studies of lung biology and repair.