High frequency of fetal cells within a primitive stem cell population in maternal blood

Fetal microchimerism cells suppress arthritis progression by inducing CD14+ IL-10+ cells in pregnant experimental mice

BACKGROUND

Fetal microchimerism occurs in the mother after a pregnancy. To investigate the role of fetal microchimerism cells (FMCs) in rheumatoid arthritis, we analyzed the population of fetal cells in pregnant experimental arthritis mice.

METHODS

We used EGFP+ fetuses, which were mated with either healthy female mice or CIA mice, and male C57BL/6J-Tg (Pgk1-EGFP)03Narl mice, to detect the population of FMCs in maternal circulation. The disease progression was determined by measuring the clinical score and histological stains during pregnancy. The fetal cells have been analyzed if expressing EGFP, CD45, and Scal by flow cytometry. We also detected the expression of CD14+ IL-10+ cells in vivo and in vitro.

RESULTS

Our data showed that the pregnancy ameliorated the arthritis progression of CIA mice. The IHC stains showed the CD45 -Sca-1+ EGFP+ FMCs were expressed in the bone marrow and peripheral blood mononuclear cells (PBMC) at 14 gestation days. However, Treg and Tc cell populations showed no significant change in the bone marrow. The data showed the H2Kb + fetal cells induced CD14+ IL10+ cell populations increased in the bone marrow in vitro and in vivo.

CONCLUSION

Our investigations demonstrated that the FMCs protected the CIA mice from cartilage damage and triggered an immunosuppressive response in them by increasing the number of CD14+ IL10+ cells. In conclusion, the FMCs could potentially exhibit protective properties within the context of inflammatory arthritis that arises during pregnancy.

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.

Pregnancy-induced physiological hypertrophic preconditioning attenuates pathological myocardial hypertrophy by activation of FoxO3a

Previous studies show a woman's pregnancy is correlated with post-reproductive longevity, and nulliparity is associated with higher risk of incident heart failure, suggesting pregnancy likely exerts a cardioprotection. We previously reported a cardioprotective phenomenon termed myocardial hypertrophic preconditioning, but it is unknown whether pregnancy-induced physiological hypertrophic preconditioning (PHP) can also protect the heart against subsequent pathological hypertrophic stress. We aimed to clarify the phenomenon of PHP and its mechanisms. The pluripara mice whose pregnancy-induced physiological hypertrophy regressed and the nulliparous mice underwent angiotensin II (Ang II) infusion or transverse aortic constriction (TAC). Echocardiography, invasive left ventricular hemodynamic measurement and histological analysis were used to evaluate cardiac remodeling and function. Silencing or overexpression of Foxo3 by adeno-associated virus was used to investigate the role of FoxO3a involved in the antihypertrophic effect. Compared with nulliparous mice, pathological cardiac hypertrophy induced by Ang II infusion, or TAC was significantly attenuated and heart failure induced by TAC was markedly improved in mice with PHP. Activation of FoxO3a was significantly enhanced in the hearts of postpartum mice. FoxO3a inhibited myocardial hypertrophy by suppressing signaling pathway of phosphorylated glycogen synthase kinase-3β (p-GSK3β)/β-catenin/Cyclin D1. Silencing or overexpression of Foxo3 attenuated or enhanced the anti-hypertrophic effect of PHP in mice with pathological stimulation. Our findings demonstrate that PHP confers resistance to subsequent hypertrophic stress and slows progression to heart failure through activation of FoxO3a/GSK3β pathway.

Contribution of fetal microchimeric cells to maternal wound healing in sickle cell ulcers

Leg ulcers are a major complication of sickle cell disease (SCD). They are particularly challenging to treat and innovative therapies are needed. We previously showed that the healing of SCD ulcers is delayed because of decreased angiogenesis. During pregnancy, fetal microchimeric cells (FMC) transferred to the mother are recruited to maternal wounds and improve angiogenesis. After delivery, FMC persist in maternal bone marrow for decades. Here, we investigated whether fetal cells could also improve SCD ulcers in the post-partum setting. We found that skin healing was similarly improved in post-partum mice and in pregnant mice, through increased proliferation and angiogenesis. In a SCD mouse model that recapitulates refractory SCD ulcers, we showed that the ulcers of post-partum SCD mice healed more quickly than those of virgin mice. This was associated with the recruitment of fetal cells in maternal wounds where they harbored markers of leukocytes and endothelial cells. In a retrospective cohort of SCD patients, using several parameters we found that SCD women who had ever had a baby had less of a burden related to leg ulcers compared to nulliparous women. Taken together, these results indicate that healing capacities of FMC are maintained long after delivery and may be exploited to promote wound healing in post-partum SCD patients.

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.

Recanalization-Like Neovascularization of Placental Intervillous Hematoma: First Two Reports

Placental intervillous hematomas have not previously been reported to undergo any sort of change, maturation, or healing. In this article, we present the first 2 case reports of recanalization-like neovascularization within placental hematomas: a 0.15 cm focus in an intervillous fibrin thrombus and a 0.2 cm focus in a subchorionic hematoma. Increased recognition and further studies are needed to gain a better understanding of this seemingly rare phenomenon and the factors that govern the lack of typical organization in placental hematomas. This might lead to a deeper knowledge of the repair process in general and shed light on how to control it in diseases caused by excessive repair.

Isolation and Characterization of a Fetal-Maternal Microchimeric Stem Cell Population in Maternal Hair Follicles Long after Parturition

Fetal-maternal microchimerism describes the acquisition of fetal stem cells (FSC) by the mother during pregnancy and their long-term persistence after parturition. FSC may engraft in a variety of maternal tissues especially if there is organ/tissue injury, but their role and mechanism of persistence still remains elusive. Clinical applications due to their pluripotency, immunomodulatory effects and accessibility make them good candidates for ex-vivo manipulation and autologous therapies. The hair follicles contain a distinctive niche for pluripotent stem cells (PSC). To date, there is no published evidence of fetal microchimerism in the hair follicle. In our study, follicular unit extraction (FUE) technique allowed easy stem cell cultures to be obtained while simple hair follicle removal by pull-out technique failed to generate stem cells in culture. We identified microchimeric fetal stem cells within the primitive population of maternal stem cells isolated from the hair follicles with typical mesenchymal phenotype, expression of PSC genes and differentiation potential towards osteocytes, adypocites and chondrocytes. This is the first study to isolate fetal microchimeric stem cells in adult human hair long after parturition. We presume a sanctuary partition mechanism with PSC of the mother deposited during early embryogenesis could explain their long-term persistence.

Incognito: Are Microchimeric Fetal Stem Cells that Cross Placental Barrier Real Emissaries of Peace?

Chimerism occurs naturaly throughout gestation and can also occur as a consequence of transfusion and transplantation therapy. It consists of the acquisition and long-term persistence of a genetically distinct population of allogenic cells inside another organism. Previous reports have suggested that feto-maternal microchimerism could exert a beneficial effect on the treatment of hematological and solid tumors in patients treated by PBSCT. In this review we report the mechanism of transplacental fetal stem cell trafficking during pregnancy and the effect of their long-term persistence on autoimmunity, GVHD, PBSCT, cancer and stem cell treatment.

Unravelling the biological secrets of microchimerism by single-cell analysis

The presence of microchimeric cells is known for >100 years and well documented since decades. Earlier, microchimeric cells were mainly used for cell-based non-invasive prenatal diagnostics during early pregnancy. Microchimeric cells are also present beyond delivery and are associated to various autoimmune diseases, tissue repair, cancer and immune tolerance. All these findings were based on low complexity studies and occasionally accompanied by artefacts not allowing the biological functions of microchimerism to be determined. However, with the recent developments in single-cell analysis, new means to identify and characterize microchimeric cells are available. Cell labelling techniques in combination with single-cell analysis provide a new toolbox to decipher the biology of microchimeric cells at molecular and cellular level. In this review, we discuss how recent developments in single-cell analysis can be applied to determine the role and function of microchimeric cells.

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.

Fetal endothelial and mesenchymal progenitors from the human term placenta: potency and clinical potential

Since the isolation of fetal stem cell populations from perinatal tissues, such as umbilical cord blood and placenta, interest has been growing in understanding their greater plasticity compared with adult stem cells and exploring their potential in regenerative medicine. The phenomenon of fetal microchimerism (FMC) naturally occurring during pregnancy through the transfer of fetal stem/progenitor cells to maternal blood and tissues has been integral in developing this dogma. Specifically, microchimeric mesenchymal stem cells and endothelial progenitors of fetal origin have now demonstrated a capacity for tissue repair in the maternal host. However, the use of similar fetal stem cells in therapy has been significantly hampered by the availability of clinically relevant cell numbers and/or contamination with cells of maternal origin, particularly when using the chorionic and decidual placenta. In the present prospective review, we highlight the importance of FMC to the field of fetal stem cell biology and issues of maternal contamination from perinatal tissues and discuss specific isolation strategies to overcome these translational obstacles.

Adverse pregnancy outcomes and risk of subsequent rheumatoid arthritis

OBJECTIVE

Pregnancy and reproductive outcomes have been associated with altered risk of some autoimmune diseases, including rheumatoid arthritis (RA). We sought to determine whether prior pregnancy resulting in a low birth weight (LBW) infant or preterm birth is associated with a risk of subsequent RA in the mother.

METHODS

We conducted an analysis of RA risk in parous women from a population-based prospective study of newly diagnosed cases of RA and age-matched healthy controls. The primary outcome measure was disease status (RA versus control), with exposures of prior preterm birth and prior delivery of an infant with LBW (≤2,500 gm), very low birth weight (VLBW; ≤1,500 gm), or extremely low birth weight (ELBW; ≤1,000 gm). A preplanned analysis including only rheumatoid factor (RF)-positive RA cases was also conducted.

RESULTS

A total of 202 RA cases and 1,102 controls were analyzed. Prior delivery of an infant with ELBW was associated with RA in the mother (relative risk [RR] 3.7 [95% confidence interval (95% CI) 1.0-13.2]). Prior VLBW (RR 4.0 [95% CI 1.3-11.4]) and ELBW (RR 5.5 [95% CI 1.4-22.5]) infants were associated with RF-positive RA. Prior LBW deliveries and preterm births were more common among RA cases than controls, but the differences were not statistically significant.

CONCLUSION

Compared to those with uncomplicated pregnancies, women with a prior VLBW or ELBW delivery had a higher risk of RA, particularly RF-positive RA. This association may reflect common risk factors for pregnancy complications and RA. Alternatively, complicated pregnancy itself may confer risk of subsequent RA.

The proper criteria for identification and sorting of very small embryonic-like stem cells, and some nomenclature issues

Evidence has accumulated that both murine and human adult tissues contain early-development stem cells with a broader differentiation potential than other adult monopotent stem cells. These cells, being pluripotent or multipotent, exist at different levels of specification and most likely represent overlapping populations of cells that, depending on the isolation strategy, ex vivo expansion protocol, and markers employed for their identification, have been given different names. In this review, we will discuss a population of very small embryonic-like stem cells (VSELs) in the context of other stem cells that express pluripotent/multipotent markers isolated from adult tissues as well as review the most current, validated working criteria on how to properly identify and isolate these very rare cells. VSELs have been successfully purified in several laboratories; however, a few have failed to isolate them, which has raised some unnecessary controversy in the field. Therefore, in this short review, we will address the most important reasons that some investigators have experienced problems in isolating these very rare cells and discuss some still unresolved challenges which should be overcome before these cells can be widely employed in the clinic.

Very small embryonic-like stem-cell optimization of isolation protocols: an update of molecular signatures and a review of current in vivo applications

As the theory of stem cell plasticity was first proposed, we have explored an alternative hypothesis for this phenomenon: namely that adult bone marrow (BM) and umbilical cord blood (UCB) contain more developmentally primitive cells than hematopoietic stem cells (HSCs). In support of this notion, using multiparameter sorting we were able to isolate small Sca1(+)Lin(-)CD45(-) cells and CD133(+)Lin(-)CD45(-) cells from murine BM and human UCB, respectively, which were further enriched for the detection of various early developmental markers such as the SSEA antigen on the surface and the Oct4 and Nanog transcription factors in the nucleus. Similar populations of cells have been found in various organs by our team and others, including the heart, brain and gonads. Owing to their primitive cellular features, such as the high nuclear/cytoplasm ratio and the presence of euchromatin, they are called very small embryonic-like stem cells (VSELs). In the appropriate in vivo models, VSELs differentiate into long-term repopulating HSCs, mesenchymal stem cells (MSCs), lung epithelial cells, cardiomyocytes and gametes. In this review, we discuss the most recent data from our laboratory and other groups regarding the optimal isolation procedures and describe the updated molecular characteristics of VSELs.

Very small embryonic-like stem cells (VSELs) represent a real challenge in stem cell biology: recent pros and cons in the midst of a lively debate

The concept that adult tissue, including bone marrow (BM), contains early-development cells with broader differentiation potential has again been recently challenged. In response, we would like to review the accumulated evidence from several independent laboratories that adult tissues, including BM, harbor a population of very rare stem cells that may cross germ layers in their differentiation potential. Thus, the BM stem cell compartment hierarchy needs to be revisited. These dormant, early-development cells that our group described as very small embryonic-like stem cells (VSELs) most likely overlap with similar populations of stem cells that have been identified in adult tissues by other investigators as the result of various experimental strategies and have been given various names. As reported, murine VSELs have some pluripotent stem cell characteristics. Moreover, they display several epiblast/germline markers that suggest their embryonic origin and developmental deposition in adult BM. Moreover, at the molecular level, changes in expression of parentally imprinted genes (for example, Igf2–H19) and resistance to insulin/insulin-like growth factor signaling (IIS) regulates their quiescent state in adult tissues. In several emergency situations related to organ damage, VSELs can be activated and mobilized into peripheral blood, and in appropriate animal models they contribute to tissue organ/regeneration. Interestingly, their number correlates with lifespan in mice, and they may also be involved in some malignancies. VSELs have been successfully isolated in several laboratories; however, some investigators experience problems with their isolation.

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.

Quo Vadis medycyno regeneracyjna?: Quo Vadis Regenerative Medicine?

There are presented the most important sources of pluripotent stem cells for potential application in the regenerative medicine. This review summarizes also advantages and disadvantages for potential application of these cells in clinical medicine.

Raising antibodies against circulating foetal cells from maternal peripheral blood

OBJECTIVE

Cells of foetal origin circulating in the maternal peripheral bloodstream present a unique source for non-invasive prenatal diagnostics. The aims of this study were to raise antibodies against identified circulating foetal cells from the maternal blood, test the properties of these antibodies and to determine the foetal cell type recognised by the antibodies.

METHOD

Cells from a male foetus were identified in a maternal blood sample by FISH analysis of the X- and Y- chromosomes. The identified cells were subjected to phage display selection using a novel single cell selection strategy. Selected antibodies were tested by immunocytochemistry on foetal and adult tissue arrays, an endothelial cell line, and peripheral blood mononuclear cells.

RESULTS

Three identified foetal cells subjected to antibody selection, yielded a total of 12 antibodies. Three antibodies gave distinct staining patterns on tissue arrays, and endothelial cells. One antibody, SF1.3, shows specific staining of a subpopulation of peripheral blood mononuclear cells, including a fraction of CD34 positive cells.

CONCLUSION

These findings indicate that the identified foetal cells could have been progenitor cells of haematopoietic origin. The antibody SF1.3 could be a potential tool toward non-invasive prenatal diagnostics.

CD133 Expression Strongly Correlates with the Phenotype of Very Small Embryonic-/Epiblast-Like Stem Cells

CD133 antigen (prominin-1) is a useful cell surface marker of very small embryonic-like stem cells (VSELs). Antibodies against it, conjugated to paramagnetic beads or fluorochromes, are thus powerful biological tools for their isolation from human umbilical cord blood, mobilized peripheral blood, and bone marrow. VSELs are described with the following characteristics: (1) are slightly smaller than red blood cells; (2) display a distinct morphology, typified by a high nuclear/cytoplasmic ratio and an unorganized euchromatin; (3) become mobilized during stress situations into peripheral blood; (4) are enriched in the CD133(+)Lin(-)CD45(-) cell fraction in humans; and (5) express markers of pluripotent stem cells (e.g., Oct-4, Nanog, and stage-specific embryonic antigen-4). The most recent in vivo data from our and other laboratories demonstrated that human VSELs exhibit some characteristics of long-term repopulating hematopoietic stem cells and are at the top of the hierarchy in the mesenchymal lineage. However, still more labor is needed to characterize better at a molecular level these rare cells.

Very small embryonic/epiblast-like stem cells (VSELs) and their potential role in aging and organ rejuvenation--an update and comparison to other primitive small stem cells isolated from adult tissues

Very small embryonic-like stem cells (VSELs) are a population of developmentally early stem cells residing in adult tissues. These rare cells, which are slightly smaller than red blood cells, i) become mobilized during stress situations into peripheral blood, ii) are enriched in the Sca1⁺Lin⁻CD45⁻ cell fraction in mice and the CD133⁺ Lin⁻CD45⁻ cell fraction in humans, iii) express markers of pluripotent stem cells (e.g., Oct4, Nanog, and SSEA), and iv) display a distinct morphology characterized by a high nuclear/cytoplasmic ratio and undifferentiated chromatin. Recent evidence indicates that murine VSELs are kept quiescent in adult tissues and protected from teratoma formation by epigenetic modification of imprinted genes that regulate insulin/insulin like growth factor signaling (IIS). The successful reversal of these epigenetic changes in VSELs that render them quiescent will be crucial for efficient expansion of these cells. The most recent data in vivo from our and other laboratories demonstrated that both murine and human VSELs exhibit some characteristics of long-term repopulating hematopoietic stem cells (LT-HSCs), are at the top of the hierarchy in the mesenchymal lineage, and may differentiate into organ-specific cells (e.g., cardiomyocytes). Moreover, as recently demonstrated the number of these cells positively correlates in several murine models with longevity. Finally, while murine BM-derived VSELs have been extensively characterized more work is needed to better characterize these small cells at the molecular level in humans.

Fetal microchimeric cells in a fetus-treats-its-mother paradigm do not contribute to dystrophin production in serially parous mdx females

Throughout every pregnancy, genetically distinct fetal microchimeric stem/progenitor cells (FMCs) engraft in the mother, persist long after delivery, and may home to damaged maternal tissues. Phenotypically normal fetal lymphoid progenitors have been described to develop in immunodeficient mothers in a fetus-treats-its-mother paradigm. Since stem cells contribute to muscle repair, we assessed this paradigm in the mdx mouse model of Duchenne muscular dystrophy. mdx females were bred serially to either ROSAeGFP males or mdx males to obtain postpartum microchimeras that received either wild-type FMCs or dystrophin-deficient FMCs through serial gestations. To enhance regeneration, notexin was injected into the tibialis anterior of postpartum mice. FMCs were detected by qPCR at a higher frequency in injected compared to noninjected side muscle (P=0.02). However, the number of dystrophin-positive fibers was similar in mothers delivering wild-type compared to mdx pups. In addition, there was no correlation between FMC detection and percentage dystrophin, and no GFP+ve FMCs were identified that expressed dystrophin. In 10/11 animals, GFP+ve FMCs were detected by immunohistochemistry, of which 60% expressed CD45 with 96% outside the basal lamina defining myofiber contours. Finally we confirmed lack of FMC contribution to statellite cells in postpartum mdx females mated with Myf5-LacZ males. We conclude that the FMC contribution to regenerating muscles is insufficient to have a functional impact.

The promise of fetal cells in maternal blood

Delaying childbirth increases the proportion of advanced maternal age pregnancies. This increases the number of pregnancies requiring invasive prenatal testing. Prenatal diagnosis of chromosomal aneuploidies and monogenic disorders requires fetal cells obtained through invasive procedures (i.e. chorionic villus sampling and amniocentesis). These procedures carry a risk of fetal loss, which causes anxiety to at-risk couples. Intact fetal cells entering maternal circulation have raised the possibility of non-invasive prenatal diagnosis. Rarity of fetal cells, however, has made it challenging. Fetal nucleated red blood cells are ideal candidate target cells because they have limited lifespan, contain true representation of fetal genotype, contain specific fetal cell identifiers (embryonic and fetal globins), and allow interrogation with chromosomal fluorescence in-situ hybridisation and possibly with array comparative genomic hybridisation. The utility of fetal nucleated red blood cells in non-invasive prenatal diagnosis has not reached clinical application because of the inconsistencies in enrichment strategies and rarity of cells.

Fetal cells traffic to injured maternal myocardium and undergo cardiac differentiation

RATIONALE

Fetal cells enter the maternal circulation during pregnancy and may persist in maternal tissue for decades as microchimeras.

OBJECTIVE

Based on clinical observations of peripartum cardiomyopathy patients and the high rate of recovery they experience from heart failure, our objective was to determine whether fetal cells can migrate to the maternal heart and differentiate to cardiac cells.

METHODS AND RESULTS

We report that fetal cells selectively home to injured maternal hearts and undergo differentiation into diverse cardiac lineages. Using enhanced green fluorescent protein (eGFP)-tagged fetuses, we demonstrate engraftment of multipotent fetal cells in injury zones of maternal hearts. In vivo, eGFP+ fetal cells form endothelial cells, smooth muscle cells, and cardiomyocytes. In vitro, fetal cells isolated from maternal hearts recapitulate these differentiation pathways, additionally forming vascular tubes and beating cardiomyocytes in a fusion-independent manner; ≈40% of fetal cells in the maternal heart express Caudal-related homeobox2 (Cdx2), previously associated with trophoblast stem cells, thought to solely form placenta.

CONCLUSIONS

Fetal maternal stem cell transfer appears to be a critical mechanism in the maternal response to cardiac injury. Furthermore, we have identified Cdx2 cells as a novel cell type for potential use in cardiovascular regenerative therapy.

[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.

Transplacental traffic after in utero mesenchymal stem cell transplantation

Transplacental traffic of fetal progenitor and differentiated cells is a well-known phenomenon in pregnancies. We hypothesize that intrauterine stem cell transplantation leads to microchimerism in the dams and that this is gestational age-dependent. EGFP+ fetal liver-derived mesenchymal stem cell (MSC) (10(5) per fetus) were injected intraperitoneally into congeneic and allogeneic recipient fetuses at E12 versus E13.5 of murine pregnancy (56 dams). Engraftment in maternal organs was evaluated using TaqMan quantitative polymerase chain reaction (PCR) and fluorescence microscopy during pregnancy (1, 3, and 7 days after in utero transplantation [IUT]) and after delivery (1 and 4 weeks after delivery). One day after IUT donor cells were mainly found in the placenta (E12: 9/10 dams vs. E13.5: 4/8 dams) and laparotomy site (E12: 5/10 dams vs. E13.5: 4/8 dams). Three days after IUT these probabilities decreased significantly in the placenta to 3/8 and 1/3, respectively, whereas it was increased within the surgical wound to 8/8 and 2/4. One week after IUT donor cells could be detected in other single maternal organs, such as bone marrow or spleen. The surgical wound was chimeric in all dams. One week after delivery the surgical wound was still a major site of engraftment in both groups. E12 IUT resulted in detectable donor cell microchimerism in the maternal bone marrow (3/4), liver (2/4), lungs (1/4), spleen (1/4), and thymus (1/4), whereas engraftment probabilities were lower following E13.5 IUT (BM: 1/4, liver: 2/4, lungs: 1/4, spleen: 1/4, thymus: 0/4). At 4 weeks after delivery persistent microchimerism was found only after E12 IUT in various maternal organs (BM: 1/4, spleen: 1/4, lungs: 1/4) and within newly created surgical wounds (3/4), but completely not in the E13.5 group. Allogeneic IUT did also not result in any detectable long-term fetal microchimerism. An earlier IUT might lead to a higher transplacental traffic of donor MSC and persistent microchimerism within maternal tissues. Even 4 weeks after delivery, these cells are present in surgical wounds.

[Fetal microchimerism and autoimmune disease]

Microchimerism is defined by the presence of circulating cells, bi-directionally transferred from one genetically distinct individual to another. The acquisition and persistence of fetal cell microchimerism, small numbers of genetically disparate cells from the fetus in the mother, is now a well-recognized consequence of normal pregnancy. Some of the autoimmune diseases that show a predilection for women in their child-bearing years and beyond are linked to fetal microchimerism from previous pregnancies. Microchimerism has been investigated in different autoimmune disorders, such as systemic sclerosis, systemic lupus erythematosus, autoimmune thyroid diseases, and primary biliary cirrhosis. Recent data have demonstrated the promising role of microchimeric cells in the maternal response to tissue injuries by differentiating into many lineages. Therefore, further understanding of fetal-maternal microchimerism may help in anticipating its implications in disease as well as in more general women's health issues.

An adult uterine hemangioblast: evidence for extramedullary self-renewal and clonal bilineage potential

Stem cells exhibit long-term self-renewal by asymmetric division and multipotent differentiation. During embryonic development, cell fate is determined with predictable orientation, differentiation, and partitioning to form the organism. This includes the formation of a hemangioblast from which 2 derivative cell clusters commit to either a hematopoietic or an endothelial lineage. Frequently, it is not clear whether tissue resident stem cells in the adult originate from the bone marrow. Here, we show that blast colony-forming cells exhibiting bilineage (hematopoietic and vascular) potential and long-term self-renewal originate from the uterus in the mouse. This is the first in vitro and in vivo evidence of an adult hemangioblast retained from development in the uterus. Our findings offer new understanding of uterine cell renewal and turnover and may provide insights and opportunities for the study of stem cell maintenance.

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.

Thyroid stem cells and cancer

BACKGROUND

Thyroid gland development and function are essential for life, and recent findings indicate the presence of stem/progenitor cells within the thyroid gland as a potential source of tissue regeneration and cancer formation.

SUMMARY

This review summarizes the current knowledge on early differentiation of thyroid cells from embryonic stem cells and highlights exciting concepts and recent novel findings on adult thyroid stem/progenitor cells in the normal thyroid gland and in thyroid cancer. Other potential sources and markers of stem/progenitor cells in the thyroid include bone marrow, microchimerism, and embryological remnant-derived multifocal solid cell nests. Finally, we discuss new therapeutic strategies that target thyroid cancer stem cells.

CONCLUSIONS

Thyroid stem/progenitor cell populations are present in the normal and diseased thyroid gland. Advances in normal and cancer thyroid stem cell biology will be essential for future targeted therapies.

Fetal-maternal exchange of multipotent stem/progenitor cells: microchimerism in diagnosis and disease

The biological concept of microchimerism, the bidirectional trafficking and stable long-term persistence of small numbers of allogeneic (fetal and maternal) cells in a genetically different organ, has gained considerable attention. Microchimerism is a common phenomenon in many species, including humans, and microchimeric cells can modify immunological recognition or tolerance, affect the course and outcome of various diseases and demonstrate stem cell-like or regenerative potential. Here, we review current knowledge of the biology of microchimerism and show how long-term allogeneic co-existence within an organism can impact on existing paradigms in chronic disease, cancer biology, regenerative medicine and fetal-maternal immunology. We discuss diagnostic challenges, clinical applications and future research directions in this exciting and rapidly emerging field of allogeneic fetal-maternal cell exchange.

CD34+ cells in maternal placental blood are mainly fetal in origin and express endothelial markers

Fetal CD34+ cells enter the maternal circulation during pregnancy and may persist for decades. These cells are usually depicted as hematopoietic stem/progenitor cells. Our objective was to further determine the phenotype of fetal chimeric CD34+ cells in placental maternal blood from the intervillous space (IVS). Human healthy term placentas were analyzed (n=9). All fetuses were male. CD34+ cells were identified in the IVS and further characterized as fetal or maternal using X and Y chromosome fluorescence in situ hybridization. The phenotype of fetal cells was further analyzed using anti-CD117 (c-kit), anti-CD133, anti-CD31, anti-von Willebrand factor (vWF), anti-vimentin, anti-CD45 and anti-cytokeratin (CK) antibodies. We used preeclamptic placentas of male (n=3) and healthy placentas of female fetuses (n=3) as controls. As expected fetal cells were easily identified in the IVS and significantly increased in cases of preeclampsia. Most CD34+ cells in the IVS were of fetal origin (90%) and were not surrounded by CK staining further showing that they were not in fetal trophoblastic villi. Similarly, about 40% of CD31+ and 6% of vimentin+ cells in the IVS were fetal in origin. No CD117+ or CD133+ fetal cells were found in the IVS of examined placentas. Besides, all the CD34+ cells identified in the IVS were co-labeled with vWF or CD31, suggesting their endothelial origin. These results suggest that most CD34+ cells in maternal placental blood at term are fetal in origin from endothelial and not hematopoietic lineages.

Fetal cells in the pregnant mouse are diverse and express a variety of progenitor and differentiated cell markers

To better understand fetomaternal cell trafficking during pregnancy, we used a mouse model to determine the cell surface markers expressed on fetal cells, based on the hypothesis that fetal progenitor cells have the capacity to repair maternal organs, whereas more differentiated cells might initiate graft versus host disease. Wild-type females were mated to either homozygous or hemizygous transgenic males and euthanized in the peripartum period. Using dual color flow cytometry, we analyzed fetal transgene positive cells for the presence of nine markers (ITGAM, ITGB1, PECAM, CD34, CD44, PTPRC, ENG, SLAMF1, and CXCR4) to begin to identify the phenotype and degree of differentiation of fetal cells in nine maternal organs (lung, liver, spleen, blood, bone marrow, kidney, heart, thymus, and brain). Fetal cells were found in all maternal organs following either type of mating, albeit always at a higher frequency following mating with homozygous males. Some organs (e.g., lung and liver) had a wide variety of fetal cell markers present, while other organs (e.g., bone marrow and spleen) had a skewed distribution of fetal cell markers. Fetal cells in the murine pregnant female are diverse. Our results suggest that the fetal cells comprise a mixed population of progenitor and differentiated cells, with different relative proportions in different maternal organs. Future studies will address whether fetal cells cross the placental barrier in a differentiated state or as a homogenous population and subsequently differentiate in target maternal organs.