Fetal cells participate over time in the response to specific types of murine maternal hepatic injury

Are fetal microchimerism and circulating fetal extracellular vesicles important links between spontaneous preterm delivery and maternal cardiovascular disease risk?

Trafficking and persistence of fetal microchimeric cells (fMCs) and circulating extracellular vesicles (EVs) have been observed in animals and humans, but their consequences in the maternal body and their mechanistic contributions to maternal physiology and pathophysiology are not yet fully defined. Fetal cells and EVs may help remodel maternal organs after pregnancy-associated changes, but the cell types and EV cargos reaching the mother in preterm pregnancies after exposure to various risk factors can be distinct from term pregnancies. As preterm delivery-associated maternal complications are rising, revisiting this topic and formulating scientific questions for future research to reduce the risk of maternal morbidities are timely. Epidemiological studies report maternal cardiovascular risk as one of the major complications after preterm delivery. This paper suggests a potential link between fMCs and circulating EVs and adverse maternal cardiovascular outcomes post-pregnancies, the underlying mechanisms, consequences, and methods for and how this link might be assessed.

A history of cesarean section and future maternal long-term risk for neoplasms: a population-based cohort study

OBJECTIVE

Mode of delivery has long-term implications on the mother, including recent data regarding the level of transmission of fetal microchimeric cells (FMc) and their possible effect on cancer development. We aimed to evaluate the association between cesarean section (CS) and future risk for neoplasms.

STUDY DESIGN

A population-based cohort analysis comparing the long-term risk for neoplasms between patients that delivered only by CS to those that delivered only vaginally (VD). Neoplasms were pre-defined based on ICD-9 codes. Deliveries occurred between the years 1991-2017 in a tertiary medical center. Kaplan-Meier survival curves were used to compare the cumulative incidence of neoplasms and Cox proportional hazards models were constructed to control for confounders.

RESULTS

During the study period 105,992 patients met the inclusion criteria; 14150 (13.4%) of patients had only CS and 91842 (86.6%) had VD (comparison group). The CS group had significantly higher incidence of benign and malignant neoplasms (4.73 per 1000 patient-years versus 3.88 per 1000 patient-years, OR = 1.26, 95% CI 1.16-1.37; p = 0.001; 2.19 per 1000 patient-years of follow up versus 1.93 per 1000 patient-years, OR = 1.16, 95% CI 1.03-1.31; p = 0.013). Specifically, the CS group had higher incidence of uterine cancer (1.2 versus 0.06 per 1000 patient-years, OR = 1.97, 95% CI 1.14-3.39; p = 0.013). The cumulative incidence of benign, malignant and uterine neoplasms was significantly higher in the CS group (Log rank test p = 0.001; 0.036 and 0.014; respectively). Importantly, no significant association was found with breast and ovarian malignancies." When performing a Cox regression model controlling for confounders, the risk for malignancy-related hospitalizations remained significant (adjusted HR = 1.22, 95% CI 1.01-1.48; p = 0.031) but not for uterine cancer (adjusted HR = 1.6, 95% CI 0.9-2.8; p = 0.103).

CONCLUSION

Our findings provide support to linkage between delivery by cesarean section and future maternal malignancy.

Fetomaternal microchimerism in tissue repair and tumor development

In various placental mammals, the bidirectional exchange of cells during pregnancy can lead to the acquisition of genetically unique cells that can persist in both mother and child for decades. Over the years, it has become increasingly clear that this phenomenon, termed fetomaternal microchimerism may play key roles in a number of biological processes. In this perspective, we explore the concept of fetomaternal microchimerism and outline how fetal microchimeric cells are detected and immunologically tolerated within the maternal setting. Moreover, we discuss undertakings in the field that hint at the significant plasticity of fetal microchimeric cells and their potential roles in promoting maternal wound healing. Finally, we explore the multifaceted roles of fetal microchimeric cells in cancer development and progression. A deeper understanding of fetomaternal chimerism in healthy and diseased states will be key toward developing more efficient anti-cancer treatments and regenerative therapies.

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.

Pregnancy, postpartum and parity: Resilience and vulnerability in brain health and disease

Risk and resilience in brain health and disease can be influenced by a variety of factors. While there is a growing appreciation to consider sex as one of these factors, far less attention has been paid to sex-specific variables that may differentially impact females such as pregnancy and reproductive history. In this review, we focus on nervous system disorders which show a female bias and for which there is data from basic research and clinical studies pointing to modification in disease risk and progression during pregnancy, postpartum and/or as a result of parity: multiple sclerosis (MS), depression, stroke, and Alzheimer's disease (AD). In doing so, we join others (Shors, 2016; Galea et al., 2018a) in aiming to illustrate the importance of looking beyond sex in neuroscience research.

Medawar's Paradox and Immune Mechanisms of Fetomaternal Tolerance

Brazilian-born British biologist Dr. Peter Medawar played an integral role in developing the concepts of immunologic rejection and tolerance, which led to him receiving the Nobel Prize "for the discovery of acquired immunologic tolerance" and eventually made organ transplantation a reality. However, at the time of his early work in tolerance, a paradox to his theories was brought to his attention; how was pregnancy possible? Pregnancy resembles organ transplantation in that the fetus, possessing paternal antigens, is a semi-allogeneic graft that can survive without immunosuppression for 9 months. To answer this question, Medawar proposed three hypotheses of how a mother supports her fetus in utero, now known as "Medawar's Paradox." The mechanisms that govern fetomaternal tolerance are still incompletely understood but may provide critical insight into how to achieve immune tolerance in organ transplantation. Here, we review current understanding of the immune factors responsible for fetomaternal tolerance during pregnancy and discuss the potential implications for advances in transplantation science.

Genomic evidence of Y chromosome microchimerism in the endometrium during endometriosis and in cases of infertility

BACKGROUND

Previous studies, which were primarily based on the fluorescent in-situ hybridisation (FISH) technique, revealed conflicting evidence regarding male foetal microchimerism in endometriosis. FISH is a relatively less sensitive technique, as it is performed on a small portion of the sample. Additionally, the probes used in the previous studies specifically detected centromeric and telomeric regions of Y chromosome, which are gene-sparse heterochromatised regions. In the present study, a panel of molecular biology tools such as qPCR, expression microarray, RNA-seq and qRT-PCR were employed to examine the Y chromosome microchimerism in the endometrium using secretory phase samples from fertile and infertile patients with severe (stage IV) ovarian endometriosis (OE) and without endometriosis.

METHODS

Microarray expression analysis followed by validation using RNA-seq and qRT-PCR experiments at the RNA levels and further validation at the DNA level by qPCR of target inserts for selected targets in eutopic endometrium samples obtained from control (CON) and stage IV ovarian endometriosis (OE), either from fertile (FCON and FOE; n = 30/each) or infertile (ICON and IOE; n = 30/each) women, were performed.

RESULTS

Six coding (AMELY, PCDH11, SRY, TGIF2LY, TSPY3, and USP9Y) and 10 non-coding (TTTY2, TTTY4C, TTTY5, TTTYY6, TTTY8, TTTY10, TTTY14, TTTY21, TTTY22, and TTTY23) genes exhibited a bimodal pattern of expression characterised by low expression in samples from fertile patients and high expression in samples from infertile patients. Seven coding MSY-linked genes (BAGE, CD24, EIF1AY, NLGN4Y, PRKY, VCY and ZFY) exhibited differential regulation in microarray analysis, and this change was validated by RNA-seq or qRT-PCR. DNA inserts for 7 genes in various samples were validated by qPCR. The prevalence and concentration of PCR-positive target inserts for BAGE, PRKY, TTTY9A and ZFY displayed higher values in the fertile, control (FCON) patients compared with the fertile, endometriosis patients (FOE).

CONCLUSION

Several coding and non-coding MSY-linked genes displayed microchimerism as evidenced by the presence of their respective DNA inserts, along with their differential transcript expression, in the endometrium during endometriosis and in cases of infertility.

Pregnancy protects the kidney from acute ischemic injury

A complex analysis of acute kidney injury (AKI) in pregnant women shows that it is caused by the interaction of gestation-associated pathologies and beneficial signaling pathways activated by pregnancy. Studies report an increase in the regeneration of some organs during pregnancy. However, the kidney response to the injury during pregnancy has not been addressed. We investigated the mechanisms of the pregnancy influence on AKI. During pregnancy, the kidneys were shown to be more tolerant to AKI. Pregnant animals showed remarkable preservation of kidney functions after ischemia/reperfusion (I/R) indicated by the decrease of serum creatinine levels. The pregnant rats also demonstrated a significant decrease in kidney injury markers and an increase in protective markers. Two months after the I/R, group of pregnant animals had a decreased level of fibrosis in the kidney tissue. These effects are likely linked to increased cell proliferation after injury: using real-time cell proliferation monitoring we demonstrated that after ischemic injury, cells isolated from pregnant animal kidneys had higher proliferation potential vs. control animals; it was also supported by an increase of proliferation marker PCNA levels in kidneys of pregnant animals. We suggest that these effects are associated with hormonal changes in the maternal organism, since hormonal pseudopregnancy simulated effects of pregnancy.

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.

Migration of microchimeric fetal cells into maternal circulation before placenta formation

Fetal cell microchimerism is defined as the persistence of pluripotent fetal cells in the maternal body long after delivery. The exact process by which fetal cells cross the placental barrier and enter maternal circulation is still being investigated. We reported that fetal cells persist only in the maternal bone marrow and may give rise to subpopulations with the ability to differentiate into the tissue-specific mature cells within injured maternal organs. Moreover, most of the fetal cells enter the maternal circulation during the early stages of pregnancy. These results indicate that the fetal cells with a multilineage potential, which were detected in a variety of maternal organs during pregnancy did not pass through the placental barrier; rather, they were derived from the fetal cells that entered maternal circulation early after implantation, and sustained their population long after delivery.

Chimeric maternal cells in offspring do not respond to renal injury, inflammatory or repair signals

Maternal microchimerism (MMc) can persist for years in a child, and has been implicated in the pathogenesis of chronic inflammatory autoimmune diseases. Chimeric cells may either contribute to disease by acting as immune targets or expand in response to signals of injury, inflammation or repair. We investigated the role of maternal cells in tissue injury in the absence of autoimmunity by quantifying MMc by quantitative PCR in acute and chronic models of renal injury: (1) reversible acute renal injury, inflammation and regeneration induced by rhabdomyolysis and (2) chronic injury leading to fibrosis after unilateral ureteral obstruction. We found that MMc is common in the mouse kidney. In mice congenic with their mothers neither acute nor chronic renal injury with fibrosis influenced the levels or prevalence of MMc. Maternal cells expressing MHC antigens not shared by offspring (H2(b/d)) were detected at lower levels in all groups of homozygous H2(b/b) or H2(d/d) offspring, with or without renal injury, suggesting that partial tolerance to low levels of alloantigens may regulate the homeostatic levels of maternal cells within tissues. Maternal cells homozygous for H2(b) were lost in H2(b/d) offspring only after acute renal failure, suggesting that an inflammatory stimulus led to loss of tolerance to homozygous maternal cells. The study suggests that elevated MMc previously found in association with human autoimmune diseases may not be a response to non-specific injury or inflammatory signals, but rather a primary event integral to the pathogenesis of autoimmunity.

Fetomaternal microchimerism: Some answers and many new questions

The transfer of fetal cells into mothers during pregnancy and their organ specific integration is a well recognized phenomenon in placental vertebrates. Recently, it has been reported that some fetal cells found in the mothers have progenitor cell-like features such as multilineage differentiation potential and as a consequence they were termed pregnancy associated progenitor cells (PAPC). The multilineage differentiation potential suggested some level of cellular plasticity, which these cells share with other stem or progenitor cells. In this context, we have shown that PAPCs indeed express neural stem cell and markers for developing neurons in the brain and that PAPCs morphologically mature into neurons over time. The stem/progenitor properties of PAPCs raises the hope that they might be valuable for studying the functional integration of foreign cells into preexisting tissues and organs, for example in cellular therapies. The functional integration of transplanted cells and their connectivity to the host circuitry is still a major bottleneck in cellular therapies particularly for the brain. The animal models of fetomaternal microchimerism might provide valuable insights into the mechanism how cells survive, migrate, integrate and differentiate in a foreign environment of a host. This review discusses some of the recent findings in the field of fetomaternal microchimerism. It also tries to identify some major gaps of knowledge and raises some questions resulting from the recent advances. Studying fetomaternal microchimerism and the properties of PAPCs in greater detail might pave the way to advance cell based regenerative medicine as well as transplantation medicine.

Ccl2/Ccr2 signalling recruits a distinct fetal microchimeric population that rescues delayed maternal wound healing

Foetal microchimeric cells (FMCs) traffic into maternal circulation during pregnancy and persist for decades after delivery. Upon maternal injury, FMCs migrate to affected sites where they participate in tissue healing. However, the specific signals regulating the trafficking of FMCs to injury sites had to be identified. Here we report that, in mice, a subset of FMCs implicated in tissue repair displays CD11b⁺ CD34⁺ CD31⁺ phenotype and highly express C-C chemokine receptor 2 (Ccr2). The Ccr2 ligand chemokine ligand 2 (Ccl2) enhances the recruitment of FMCs to maternal wounds where these cells transdifferentiate into endothelial cells and stimulate angiogenesis through Cxcl1 secretion. Ccl2 administration improves delayed maternal wound healing in pregnant and postpartum mice but never in virgin ones. This role of Ccl2/Ccr2 signalling opens new strategies for tissue repair through natural stem cell therapy, a concept that can be later applied to other types of maternal diseases.

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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Need for gender-specific pre-analytical testing: the dark side of the moon in laboratory testing

Many international organisations encourage studies in a sex-gender perspective. However, research with a gender perspective presents a high degree of complexity, and the inclusion of sex-gender variable in experiments presents many methodological questions, the majority of which are still neglected. Overcoming these issues is fundamental to avoid erroneous results. Here, pre-analytical aspects of the research, such as study design, choice of utilised specimens, sample collection and processing, animal models of diseases, and the observer's role, are discussed. Artefacts in this stage of research could affect the predictive value of all analyses. Furthermore, the standardisation of research subjects according to their lifestyles and, if female, to their life phase and menses or oestrous cycle, is urgent to harmonise research worldwide. A sex-gender-specific attention to pre-analytical aspects could produce a decrease in the time for translation from the bench to bedside. Furthermore, sex-gender-specific pre-clinical pharmacological testing will enable adequate assessment of pharmacokinetic and pharmacodynamic actions of drugs and will enable, where appropriate, an adequate gender-specific clinical development plan. Therefore, sex-gender-specific pre-clinical research will increase the gender equity of care and will produce more evidence-based medicine.

Blood kidney injury molecule-1 is a biomarker of acute and chronic kidney injury and predicts progression to ESRD in type I diabetes

Currently, no blood biomarker that specifically indicates injury to the proximal tubule of the kidney has been identified. Kidney injury molecule-1 (KIM-1) is highly upregulated in proximal tubular cells following kidney injury. The ectodomain of KIM-1 is shed into the lumen, and serves as a urinary biomarker of kidney injury. We report that shed KIM-1 also serves as a blood biomarker of kidney injury. Sensitive assays to measure plasma and serum KIM-1 in mice, rats, and humans were developed and validated in the current study. Plasma KIM-1 levels increased with increasing periods of ischemia (10, 20, or 30 minutes) in mice, as early as 3 hours after reperfusion; after unilateral ureteral obstruction (day 7) in mice; and after gentamicin treatment (50 or 200 mg/kg for 10 days) in rats. In humans, plasma KIM-1 levels were higher in patients with AKI than in healthy controls or post-cardiac surgery patients without AKI (area under the curve, 0.96). In patients undergoing cardiopulmonary bypass, plasma KIM-1 levels increased within 2 days after surgery only in patients who developed AKI (P<0.01). Blood KIM-1 levels were also elevated in patients with CKD of varous etiologies. In a cohort of patients with type 1 diabetes and proteinuria, serum KIM-1 level at baseline strongly predicted rate of eGFR loss and risk of ESRD during 5-15 years of follow-up, after adjustment for baseline urinary albumin-to-creatinine ratio, eGFR, and Hb1Ac. These results identify KIM-1 as a blood biomarker that specifically reflects acute and chronic kidney injury.

Maternal-fetal cellular trafficking: clinical implications and consequences

PURPOSE OF REVIEW

Maternal-fetal cellular trafficking (MFCT) is the bidirectional passage of cells between mother and fetus during pregnancy. This results in the presence of fetal cells in the maternal circulation, known as fetal microchimerism, and maternal cells in the fetal circulation, known as maternal microchimerism. The biologic role of this transplacental cellular trafficking during pregnancy is not known, although it has been implicated in development of the fetal immune system, tolerance mechanisms during pregnancy, tissue repair in autoimmune disease and cancer, and immune surveillance.

RECENT FINDINGS

Clinical utility of MFCT has been identified in prenatal testing for aneuploidies and prediction of pregnancy complications. Additionally, this transplacental passage of cells has been implicated in the delicate balance between immunologic priming and tolerance, which can influence the occurrence of autoimmune disease and transplantation outcomes. Ongoing studies are evaluating the utility of microchimerism in predicting the risk of graft rejection in transplantation.

SUMMARY

In this review, we will discuss the clinical implications of MFCT in pregnancy, fetal surgery, autoimmune disease, transplantation, and cancer.

Cigarette smoke exposure during pregnancy alters fetomaternal cell trafficking leading to retention of microchimeric cells in the maternal lung

Cigarette smoke exposure causes chronic oxidative lung damage. During pregnancy, fetal microchimeric cells traffic to the mother. Their numbers are increased at the site of acute injury. We hypothesized that milder chronic diffuse smoke injury would attract fetal cells to maternal lungs. We used a green-fluorescent-protein (GFP) mouse model to study the effects of cigarette smoke exposure on fetomaternal cell trafficking. Wild-type female mice were exposed to cigarette smoke for about 4 weeks and bred with homozygote GFP males. Cigarette smoke exposure continued until lungs were harvested and analyzed. Exposure to cigarette smoke led to macrophage accumulation in the maternal lung and significantly lower fetal weights. Cigarette smoke exposure influenced fetomaternal cell trafficking. It was associated with retention of GFP-positive fetal cells in the maternal lung and a significant reduction of fetal cells in maternal livers at gestational day 18, when fetomaternal cell trafficking peaks in the mouse model. Cells quickly clear postpartum, leaving only a few, difficult to detect, persisting microchimeric cells behind. In our study, we confirmed the postpartum clearance of cells in the maternal lungs, with no significant difference in both groups. We conclude that in the mouse model, cigarette smoke exposure during pregnancy leads to a retention of fetal microchimeric cells in the maternal lung, the site of injury. Further studies will be needed to elucidate the effect of cigarette smoke exposure on the phenotypic characteristics and function of these fetal microchimeric cells, and confirm its course in cigarette smoke exposure in humans.

Fetal cell microchimerism in the maternal mouse spinal cord

Fetal cell microchimerism refers to the persistence of fetal cells in the maternal tissues following pregnancy. It has been detected in peripheral organs and the brain, but its existence in the spinal cord has not been reported. Our aim was to detect fetal cell microchimerism in the spinal cord of maternal mice. C57BL/6 female mice were crossed with GFP transgenic male mice and sacrificed after their first or third delivery. GFP-positive cells, which were presumably from fetuses whose fathers were GFP transgenic, were detected in the spinal cord by fluorescence microscopy and immunohistochemistry. PCR was also performed to detect GFP DNA, which must come from GFP hemizygous fetuses. We found GFP-positive cells and detectable GFP DNA in most of the maternal spinal cords. Twenty percent (1/5) of the mice that were only pregnant once had detectable fetal cells, while 80% (4/5) of those that were pregnant three times had detectable fetal cells. Some fetal cells, which not only emitted green fluorescence but also expressed NeuN, were detected in the spinal cords from maternal mice. These results indicate that fetal cells migrate into the spinal cord of a maternal mouse during and/or after the gestational period, and the fetal cells may differentiate into neurons in the spinal cord.

The health effects of fetal microchimerism can be modeled in companion dogs

Fetal microchimerism (FMC) has been described to have a range of effects on health and disease. Y-chromosomal DNA has been detected in Golden Retrievers suggesting persistent FMC. In that report, nine dogs had evidence of microchimerism without prior pregnancy. To further understand this finding, a dam with prior male live births giving birth to her fourth litter of puppies, all females, was evaluated for FMC along with two of her daughters. All three female dogs had evidence of Y-chromosomal DNA in their blood. This suggests that male cells carried by the dam from previous pregnancy trafficked to her daughters to establish microchimerism in younger siblings. Companion dogs share many of the same cancers as humans, have out-bred genetics, and share the human environment, making them optimal models of human disease. Understanding the impact of FMC on health and disease of dogs could elucidate mechanisms useful for clinical interventions in humans.

Pregnancy-acquired fetal progenitor cells

The transfer and persistence of fetal progenitor cells into the mother throughout pregnancy has sparked considerable interest as a trafficking stem cell and immunological phenomenon. Indeed, the intriguing longevity of semi-allogeneic fetal microchimeric cells (FMC) in parous women raises questions over their potential clinical implications. FMC have been associated with both immune-modulatory roles and participation in maternal tissue repair. Although their influence on maternal health is as yet unresolved, FMC selectively home to damaged maternal tissues and often integrate, adopting site-appropriate phenotypes. FMC features, such as plasticity and persistence in their maternal host, suggest that they likely include pluripotent, or various multipotent and committed stem and progenitor cells. Recent efforts to determine what cell types are involved have established that FMC include cells of ectodermal, endodermal, mesodermal, and perhaps trophectodermal lineages. This review details FMC phenotypes and discusses how FMC themselves may be considered a naturally occurring stem cell therapy.

HLA-targeted cell sorting of microchimeric cells opens the way to phenotypical and functional characterization

Microchimerism refers to the presence of less than 1% of non-host cells in a person. Our group developed a reliable method for separating viable microchimeric cells from the host environment. Optimal separation of microchimeric cells at proportions as low as 0.01% could be established with two monoclonal antibodies directed against different HLA antigens, one targeting the microchimeric cells and the other the host cells. Purity of separated cell populations was validated by HLA-allele-specific and Y-chromosome directed real-time qPCR assays. The methodology was used successfully to separate microchimeric maternal cells from child umbilical cord mononuclear cells after pregnancy. Cell sorting with HLA monoclonal antibodies targeting allelic differences enables reliable microchimeric cell detection and separation in blood specimens. With this approach, maximal enrichment of potentially viable microchimeric cells from a background cell population is reached, which opens the way to phenotypical and functional characterization of microchimeric cells.

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 genetic basis of graves' disease

The presented comprehensive review of current knowledge about genetic factors predisposing to Graves’ disease (GD) put emphasis on functional significance of observed associations. In particular, we discuss recent efforts aimed at refining diseases associations found within the HLA complex and implicating HLA class I as well as HLA-DPB1 loci. We summarize data regarding non-HLA genes such as PTPN22, CTLA4, CD40, TSHR and TG which have been extensively studied in respect to their role in GD. We review recent findings implicating variants of FCRL3 (gene for FC receptor-like-3 protein), SCGB3A2 (gene for secretory uteroglobin-related protein 1- UGRP1) as well as other unverified possible candidate genes for GD selected through their documented association with type 1 diabetes mellitus: Tenr–IL2–IL21, CAPSL (encoding calcyphosine-like protein), IFIH1(gene for interferon-induced helicase C domain 1), AFF3, CD226 and PTPN2. We also review reports on association of skewed X chromosome inactivation and fetal microchimerism with GD. Finally we discuss issues of genotype-phenotype correlations in GD.

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.

The otherness of self: microchimerism in health and disease

Microchimerism (Mc) refers to the harboring of a small number of cells (or DNA) that originated in a different individual. Naturally acquired Mc derives primarily from maternal cells in her progeny, or cells of fetal origin in women. Both maternal and fetal Mc are detected in hematopoietic cells including T and B cells, monocyte/macrophages, natural killer (NK) cells and granulocytes. Mc appears also to generate cells such as myocytes, hepatocytes, islet β cells and neurons. Here, the detrimental and beneficial potential of Mc is examined. The prevalence, diversity and durability of naturally acquired Mc, including in healthy individuals, indicates that a shift is needed from the conventional paradigm of 'self versus other' to a view of the normal 'self' as constitutively chimeric.

Fetal microchimerism in skin wound healing

Skin wound healing is a complex regenerative process involving various cell types. We recently investigated whether fetal microchimeric cells (FMCs) acquired during gestation contribute to maternal wound healing and used fetal microchimerism to investigate the recruitment of distant endothelial progenitor cells in skin wounds. Our study showed that fetal progenitor cells are recruited into maternal wounds and participate in inflammation and angiogenesis. These fetal cells might have beneficial effects in situations of maternal defective healing, and might also modify the adult maternal wound environment toward a scarless fetal-like wound healing.

Fetal progenitor cells naturally transferred through pregnancy participate in inflammation and angiogenesis during wound healing

The phenotype and fate of fetal microchimeric cells transfered into the maternal circulation during pregnancy are not well described. Since progenitors from distal sites mobilize during wound healing, we analyzed the recruitment and plasticity of fetal progenitors into maternal wounds. Wounds were generated on normal and bleomycin-induced fibrotic skin of parous or pregnant wild-type females with fluorescent GFP(+) fetuses. Analyses were performed on skin and blood specimens through PCR, immunohistochemistry, and flow cytometry. Controls consisted of parous and pregnant females without wounds and virgin females with wounds. Fetal cells were detected in all skin specimens of parous mice as long as healing was not achieved. During early stages of wound healing, fetal cells expressed mainly leukocyte markers, while in later phases endothelial markers prevailed. Fetally derived vessels connected to maternal circulation were also found, demonstrating the transfer of fetal endothelial progenitor cells. Wounding mobilized fetal CD34(+)ckit(-) cells into the blood during pregnancy. Most of this population was CD11b(-)VEGFR2(-). Another part was CD11b(+) with a fraction expressing VEGFR2. VEGFa-spiked Matrigel plugs partially mimicked this fetal progenitor recruitment and mobilization into the blood. In summary, fetal cells that mobilize in response to wounding are mainly progenitor cells and participate in angiogenesis and inflammation.

Fetal microchimerism: benevolence or malevolence for the mother?

For a long time, the conventional view was that the fetus and maternal vascular system are kept separate. In fact there is a two way traffic of cells through the placenta and the transplacental passage of cells is in fact the norm. The fetal cells can persist in a wide range of woman's tissues following a pregnancy or an abortion and she becomes a chimera. Fetal cells have been found in the maternal circulation and they were shown to persist for the entire life in humans, thus demonstrating long-term engraftment and survival capabilities. Microchimerism is a subject of much interest for a number of reasons. Studies of fetal microchimerism during pregnancy may offer explanations for complications of pregnancy, such as preeclampsia, as well as insights into the pathogenesis of autoimmune diseases which usually ameliorate during pregnancy. The impact of the persistence of allogenic cells of fetal origin and of the maternal immunological response to them on the mother's health is still not clear. On the beneficial side, it has been proposed that genetically disparate fetal microchimerism provides protection against some cancers, that fetal microchimerism can afford the mother new mechanisms of protection to some diseases, that fetal microchimerism can enlarge the immunological repertoire of the mother improving her defense against aggressor. Fetal cells are often present at sites of maternal injury and may have an active role in the repair of maternal tissues.

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

Novel therapies are needed for the treatment of acute and chronic lung diseases, many of which are incurable. The use of exogenous stem cells has shown promise in both animal models and clinical trials. However, to date, the stem cell literature has under-recognized naturally acquired pregnancy-associated progenitor cells (PAPCs). These cells are found at sites of injury or disease in female tissues. They persist for decades after parturition in maternal blood and organs, with the largest number being found in the maternal lungs. Their presence there may be one explanation for the sex differences observed in the prevalence and prognosis of some lung diseases. Although the clinical significance of these cells is as yet unknown, the literature suggests that some of the PAPCs are stem cells or have stem cell-like properties. PAPCs harvested from the blood or organs of parous women could potentially be used as an alternate source of cells with regenerative properties for the woman herself or her children. Because PAPCs preferentially traffic to the maternal lung they may play a significant role in recovery or protection from lung disease. In this review article, we discuss ongoing research investigating the administration of both adult and placenta-derived stem cells to treat lung disease, and how PAPCs may also play an important future therapeutic role.

In utero cell transfer between porcine littermates

Trafficking of cells between mother and fetus during the course of normal pregnancy is well documented. Similarly, cells are known to travel between twins that share either a placenta (i.e. monozygotic) or associated chorion (i.e. monochorionic). Transferred cells are thought to be channelled via the vessels of the placenta or vascular connections established via the chorion and the long-term presence of these cells (i.e. microchimerism) can have important consequences for immune system function and reparative capacity of the host. Whether cells can be transferred between twins with separate placentas and separate chorions (i.e. no vascular connections between placentas) has not been investigated nor have the biological consequences of such a transfer. In the present study, we tested the possibility of this type of cell transfer by injecting human cord blood-derived cells into a portion of the littermates of swine and probing for human cells in the blood and tissues of unmanipulated littermates. Human cells were detected in the blood of 78% of unmanipulated littermates. Human cells were also detected in various tissues of the unmanipulated littermates, including kidney (56%), spleen (33%), thymus (11%) and heart (22%). Human cells were maintained in the blood until the piglets were sacrificed (8 months after birth), suggesting the establishment of long-term microchimerism. Our findings show that the transfer of cells between fetuses with separate placentas and separate chorions is significant and thus such twins may be subject to the same consequences of microchimerism as monozygotic or monochorionic counterparts.

[Fetal microchimerism: self and non-self, finally who are we?]

For a long time, the conventional view was that the fetus and maternal vascular system are kept separate. In fact there is a two-way traffic of immune cells through the placenta and the transplacental passage of cells is in fact the norm. The fetal cells can persist in a wide range of woman's tissue following a pregnancy or an abortion and she becomes a chimera. Fetal cells have been found in the maternal circulation and they were shown to persist for almost three decades in humans, thus demonstrating long-term engraftment and survival capabilities. Microchimerism is a subject of much interest for a number of reasons. Studies of fetal microchimerism during pregnancy may offer explanations for complications of pregnancy, such as preeclampsia, as well as insights into the pathogenesis of autoimmune disease which usually ameliorates during pregnancy. The impact that the persistence of allogenic cells of fetal origin and the maternal immunological response to them has on the mother's health and whether it is detrimental or beneficial to the mother is still not clear. Although microchimerism has been implicated in some autoimmune diseases, fetal microchimerism is common in healthy individuals. On the beneficial side, it has been proposed that genetically disparate fetal microchimerism provides protection against some cancers, that fetal microchimerism can afford the mother new alleles of protection to some diseases she has not, that fetal microchimerism can enlarge the immunological repertoire of the mother improving her defense against aggressor. Fetal cells are often present at sites of maternal injury and may have an active role in the repair of maternal tissues.

[The role of pregnancy associated progenitor cells in the regeneration of injured maternal organs]

Microchimeric fetal cells are present in the maternal body over a long period and thought to have the ability to colonize multiple tissues and organs. They are found in a wide range of maternal tissues affected with variety of diseases, thus, there is a possibility that they may contribute tissue repair and regeneration. To assess their possibility of use in regenerative medicine, we investigated whether fetal cells regenerate infracted maternal organs. We crossbred wild female mice with male transgenic mice, expressing enhanced green fluorescent protein (EGFP), and total hysterectomies were performed at the day 6 of pregnancies. On day 60 after the operations, the mice were injected with streptozotocin (STZ) to induce multiple organs injuries. We also created the ischemic organ injury model ; myocardial infarction model and cerebral infarction model. Detection and quantification of fetal cells were then attempted in a variety of maternal organs via a fluorescent microscope and quantitative PCR amplification of the gfp transgene. Fetal cells were detected only in maternal bone marrow before maternal organs injuries were induced, however, they were detected not only in bone marrow but also in the maternal injured organs. Histological analysis showed that differentiated fetal cells were observed and their morphological appearance was indistinguishable from their maternal counterparts. These results indicate that fetal cells sustained their population in the maternal bone marrow, may have contributed to the maternal tissue regeneration.

Pregnancy-associated progenitor cells differentiate and mature into neurons in the maternal brain

Bidirectional cell trafficking between fetus and mother during pregnancy is a well-established phenomenon observed in placental vertebrates including humans. Although studies have shown that transmigratory fetal cells, also termed pregnancy-associated progenitor cells (PAPCs), can integrate into multiple maternal organs, the integration, long-term survival, and differentiation of PAPCs in the brain has not been extensively studied. Using a murine model of fetomaternal microchimerism, we show that PAPCs integrated and persisted in several areas of the maternal brain for up to 7 months postpartum. Besides expressing neural stem cell or immature neuronal markers, PAPCs were observed to express mature neuronal markers, indicating that PAPCs adopted a neuronal fate. Further, PAPCs also displayed morphologically neuronal maturation by an increasing axonal/dendritic complexity over time. Therefore, PAPCs seem to undergo a molecular and morphological maturation program similar to that observed during adult neurogenesis. We provide evidence that neuronal gene expression of PAPCs was not a consequence of cell fusion with maternal neurons. In addition, in mothers with experimentally induced Parkinson's disease (PD), the frequency of PAPCs within the hippocampus initially increased whereas long-term presence of PAPCs was compromised. Also, the spatial distribution of PAPCs within the hippocampus was altered in mothers with PD. Thus, the disease context influenced the initial attraction, long-term survival, and spatial distribution of PAPCs, which may have wider implications on cell replacement strategies in human neurodegenerative diseases such as PD.

Naturally acquired microchimerism

Bi-directional transplacental trafficking occurs routinely during the course of normal pregnancy, from fetus to mother and from mother to fetus. In addition to a variety of cell-free substances, it is now well recognized that some cells are also exchanged. Microchimerism refers to a small number of cells (or DNA) harbored by one individual that originated in a genetically different individual. While microchimerism can be the result of iatrogenic interventions such as transplantation or transfusion, by far the most common source is naturally acquired microchimerism from maternal-fetal trafficking during pregnancy. Microchimerism is a subject of much current interest for a number of reasons. During pregnancy, fetal microchimerism can be sought from the mothers blood for the purpose of prenatal diagnosis. Moreover, studies of fetal microchimerism during pregnancy may offer insight into complications of pregnancy, such as preeclampsia, as well as insights into the pathogenesis of autoimmune diseases such as rheumatoid arthritis which usually ameliorates during pregnancy. Furthermore, it is now known that microchimerism persists decades later, both fetal microchimerism in women who have been pregnant and maternal microchimerism in her progeny. Investigation of the long-term consequences of fetal and maternal microchimerism is another exciting frontier of active study, with initial results pointing both to adverse and beneficial effects. This review will provide an overview of microchimerism during pregnancy and of current knowledge regarding long-term effects of naturally acquired fetal and maternal microchimerism.

Some severe maternal diseases might be caused by fetal-versus-maternal disease (FVMD)

Pregnancy-related disease is a common challenging clinical problem. From our review and clinical experience, we hypothesize that many severe pregnancy-related complications might be caused by a fetal-versus-maternal disease (FVMD), based on the fact that maternal disease is related to immunity and that fetal cells are present in maternal blood. Fetus is a semi-antigen and can be considered as a tumor or graft. The pathophysiology of FVMD must be complex. We speculate it to be a three-step process: impaired maternal immunological function, fetal T-cell activation and injury of target organs. More experiments and research will be needed to prove our hypothesis.

Fetal cell microchimerism in cancer: a meaningful event?

The influence of pregnancy on the occurrence and evolution of maternal tumors has been long debated. Breast carcinomas or melanomas have been suspected to be more severe during gestation. Recently, many investigators have described the transfer and persistence of fetal cells in maternal circulation and tissues during and after pregnancy. These fetal microchimeric cells have been described in a variety of maternal injured tissues where they displayed the host-tissue phenotype. Given the wide variety of injury and tissue types described, cancer has appeared as a potential situation that could be influenced by fetal microchimeric cells. This new unexplored effect of gestation on tumor course has been hypothesized as either protective against cancer, via the activity of allogenic fetal cells, or as promoting cancer, via a supportive role of fetal microchimeric cells in the tumor stroma. In this review, we will detail recent data supporting these hypotheses.