Trafficking of Multipotent Mesenchymal Stromal Cells from Maternal Circulation Through the Placenta Involves Vascular Endothelial Growth Factor Receptor-1 and Integrins

Bidirectional Feto-Maternal Traffic of Donor Mesenchymal Stem Cells Following Transamniotic Stem Cell Therapy (TRASCET)

PURPOSE

Transamniotic stem cell therapy (TRASCET) with mesenchymal stem cells (MSCs) has emerged experimentally as a potential treatment for different congenital diseases and maternal diseases of pregnancy. The broad applicability of TRASCET is predicated on hematogenous routing of donor MSCs via the placenta. We investigated whether donor MSC kinetics includes bidirectional traffic between the fetus and mother.

METHODS

Eight time-dated dams had their fetuses (n = 96) divided in 4 groups on gestational day 17 (E17, term = E21). Groups populating one uterine horn received intra-amniotic injections (50 μL) of either donor amniotic fluid-derived MSCs (2×106 cells/mL) labelled with a firefly luciferase reporter gene (MSC-injected, n = 32), or of acellular luciferase (luciferase-injected, n = 26). Contra-lateral (CL) horn fetuses received no injection (MSC-CL, n = 20 and luciferase-CL, n = 18). At term, samples from 11 fetal anatomical sites from CL fetuses, along with placentas from all fetuses and maternal blood were screened for luciferase activity via microplate luminometry.

RESULTS

Overall survival was 95 % (91/96). When controlled by the acellular injection, positive luciferase activity was observed in the placentas of all MSC-injected fetuses, confirming viability of the donor cells at term. When controlled by the acellular injection group, MSC-CL fetuses showed positive luciferase activity in the bone marrow, peripheral blood, brain and skin (p = <0.001-0.048). No luciferase activity was detected in any maternal blood sample.

CONCLUSION

Amniotic fluid-derived MSCs can traffic between the fetus and mother in both directions after simple intra-amniotic injection, in a healthy rat model. This phenomenon must be considered in TRASCET performed in twin/multiple pregnancies.

LEVEL OF EVIDENCE

N/A (animal and laboratory study).

Establishment of the fetal-maternal interface: developmental events in human implantation and placentation

Early pregnancy is a complex and well-orchestrated differentiation process that involves all the cellular elements of the fetal-maternal interface. Aberrant trophoblast-decidual interactions can lead to miscarriage and disorders that occur later in pregnancy, including preeclampsia, intrauterine fetal growth restriction, and preterm labor. A great deal of research on the regulation of implantation and placentation has been performed in a wide range of species. However, there is significant species variation regarding trophoblast differentiation as well as decidual-specific gene expression and regulation. Most of the relevant information has been obtained from studies using mouse models. A comprehensive understanding of the physiology and pathology of human implantation and placentation has only recently been obtained because of emerging advanced technologies. With the derivation of human trophoblast stem cells, 3D-organoid cultures, and single-cell analyses of differentiated cells, cell type-specific transcript profiles and functions were generated, and each exhibited a unique signature. Additionally, through integrative transcriptomic information, researchers can uncover the cellular dysfunction of embryonic and placental cells in peri-implantation embryos and the early pathological placenta. In fact, the clinical utility of fetal-maternal cellular trafficking has been applied for the noninvasive prenatal diagnosis of aneuploidies and the prediction of pregnancy complications. Furthermore, recent studies have proposed a viable path toward the development of therapeutic strategies targeting placenta-enriched molecules for placental dysfunction and diseases.

Umbilical Cord Maternal Microchimerism in Normal and Preeclampsia Pregnancies

Bidirectional exchange of cells between mother and fetus establishes microchimerism (Mc). Mc can persist for decades and is associated with later-life health and disease. Greater fetal Mc is detected in the maternal compartment in preeclampsia (PE), but whether maternal Mc (MMC) in umbilical cord blood (CB) is altered in PE is unknown. We evaluated MMc in CB from normal and PE pregnancies. DNA from CB mononuclear cells following placental delivery (n = 36 PE, n = 37 controls) and maternal blood was extracted and genotyped. MMc, quantified by qPCR assays targeting maternal-specific nonshared polymorphisms in CB, was compared using logistic and negative binomial regression models. Clinically and statistically relevant confounders were included, and included the total number of cell equivalents tested, gravidity, mode of delivery, birthweight, and fetal sex. PE participants delivered at earlier gestational ages, with higher Cesarean rates, and lower infant birthweights. CB MMc detection was similar between PE and controls (52.8% vs. 51.3%, respectively, p = 0.90) and unchanged after adjustment for confounders. MMc concentration was not different between groups (mean 73.7 gEq/105 gEq in PE vs. mean 22.8 gEq/105 in controls, p = 0.56), including after controlling for confounders (p = 0.64). There was no difference in CB MMc detection or concentration between PE and normal pregnancies, despite previously noted greater fetal Mc in the maternal compartment. This suggests possible differential transfer of cells at the maternal fetal interface in PE. Phenotypic evaluation of Mc cells may uncover underlying mechanisms for differential cellular exchange between mother and fetus in PE.

Effect of human follicle-stimulating hormone on immunomodulatory function of decidual mesenchymal stem cells by reducing interleukin-6 levels

Objective

Women with an elevated basal FSH indicate diminished ovarian reserve and reduced oocyte and embryo numbers. DMSCs are likely to be involved in immune tolerance of pregnancy maintenance. We investigate the effect of follicle-stimulating hormones on the immunomodulatory functions of DMSCs.

Methods

DMSCs were primary cultured from decidual tissue. Pretreated DMSCs with mitomycin C, combined with CD4⁺ T lymphocytes, DMSCs + CD4⁺T co-culture system was established. Different physiological dose FSH (3 ng/ml,10 ng/ml,30 ng/ml,100 ng/ml) were used to co-culture system. Cytokines (IFN-γ, IL-2, IL-4, IL-6, IL-10, TNF-α) and other proteins (FSHR, MyD88) were measured.

Results

Compared with the control group (FSH (0 ng/mL) + CD4⁺T + DMSCs), the FSH concentration was 10, 30, and 100 ng/ml, IL-6 levels were significantly reduced (P < 0.05). IL-6, MyD88 protein expression was remarkably decreased (P < 0.05).

Conclusion

FSH/FSHR could negatively regulate the immunosuppressive function of DMSCs by reducing secretion of IL-6 levels through MyD88 pathways, but upstream and downstream signalling pathways require further validation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13048-022-00993-3.

Addressing microchimerism in pregnancy by ex vivo human placenta perfusion

The physical connection of mother and offspring during pregnancy allows the bi-directional exchange of a small number of cells through the placenta. These cells, which can persist long-term in the recipient individual are genetically foreign to it and therefore fulfill the principle of microchimerism. Over the last years, pioneer research on microchimeric cells revealed their role in immune adaptation during pregnancy and priming of tolerogenic responses in the progeny. However, the mechanisms involved in cell transfer across the placenta barrier remain poorly investigated. In this review, we summarize the evidence of fetomaternal microchimerism, propose a mechanism for cell trafficking through the placenta and discuss the different models and techniques available for its analysis. Likewise, we aim to generate interest in the use of ex vivo placenta perfusion to investigate microchimerism in physiological and pathological settings.

Predictors of maternal-origin microchimerism in young women in the Philippines

OBJECTIVES

Microchimerism is the presence of a small quantity of cells or DNA from a genetically distinct individual. This phenomenon occurs with bidirectional maternal-fetal exchange during pregnancy. Microchimerism can persist for decades after delivery and have long-term health implications. However, little is known about why microchimerism is detectable at varying levels in different individuals. We examine the variability and the following potential determinants of maternal-origin microchimerism (MMc) in young women in the Philippines: gestational duration (in utero exposure to MMc), history of being breastfed (postpartum exposure to MMc), maternal telomere length (maternal cells' ability to replicate and persist), and participant's pregnancies in young adulthood (effect of adding fetal-origin microchimerism to preexisting MMc).

MATERIALS AND METHODS

Data are from the Cebu Longitudinal Health and Nutrition Survey, a population-based study of infant feeding practices and long-term health outcomes. We quantified MMc using quantitative PCR (qPCR) in 89 female participants, ages 20-22, and analyzed these data using negative binomial regression.

RESULTS

In a multivariate model including all predictors, being breastfed substantially predicted decreased MMc (detection rate ratio = 0.15, p = 0.007), and there was a trend of decreasing MMc in participants who had experienced more pregnancies (detection rate ratio = 0.55, p = 0.057).

DISCUSSION

These results might be explained by breastfeeding having lasting impact on immune regulatory networks, thus reducing MMc persistence. MMc may also decrease in response to the introduction of fetal-origin microchimerism with pregnancies experienced in adulthood.

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.

Hematogenous Donor Cell Routing Pathway After Transamniotic Stem Cell Therapy

Donor mesenchymal stem cells (MSCs) have been documented in fetal and maternal circulations after plain intra-amniotic injection, with diverse therapeutic effects. We sought to determine the pathway of this unique cell kinetic route. Rat fetuses (n = 226) were divided into two groups based on the content of intra-amniotic injections performed on gestational day 17 (E17): either a concentrated suspension of luciferase-labeled syngeneic amniotic fluid-derived MSCs (afMSCs; n = 111), or acellular luciferase (n = 115). Samples from placenta, chorion, amnion, amniotic fluid, stomach fluid, peripheral blood, and umbilical cord were procured at five daily time points thereafter until term (E18-22) for luminometry. In addition, 53 sets of fresh gestational membranes (chorion/amnion combined) from nonmanipulated term fetuses were secured to transwell inserts for in vitro analysis of MSC migration using luciferase-labeled afMSCs. Statistical analyses included the Mann-Whitney U-test, Wald test, nonlinear regression modeling, and Fisher's exact test. In vivo, luciferase activity was observed in the amnion, chorion, and placenta of fetuses receiving cells, but not in those receiving acellular luciferase (P < 0.001). There was a consistent nonlinear age-dependent relationship of luciferase activity between the amnion, chorion, and placenta following a parabolic bimodal pattern characterized by significantly higher early preterm (E18) and late-term (E22) activities (P < 0.001), with no differences between E21 and E22 (P = 0.12). In vitro, the presence of cells was documented by luminometry in 21/53 (39.6%) of the assays, in suspension and/or attached to the plastic substrate, and within all screened gestational membrane sets, irrespective of stimuli with collagen coating or fetal bovine serum. We conclude that, after intra-amniotic injection, donor MSCs undergo controlled cell routing, as opposed to passive clearance. Transgestational membrane transport appears to constitute the path for donor cells to reach the placenta, a known gateway to the fetal circulation, significantly expanding the potential applications of transamniotic stem cell therapy.

Maternal micro-chimeric cells in the multiple sclerosis brain

Maternal microchimeric cells (MMC) pass across the placenta from a mother to her baby during pregnancy. MMC have been identified in healthy adults, but have been reported to be more frequent and at a higher concentration in individuals with autoimmune diseases. MMC in brain tissue from individuals with autoimmune neurological disease has never previously been explored. The present study aims to identify and quantify MMC in adult human brain from control and multiple sclerosis (MS) affected individuals using fluorescent in situ hybridization (FISH) with a probe for the X and Y chromosomes. Post mortem brain tissue from 6 male MS cases and 6 male control cases were examined. Female cells presumed to be MMC were identified in 5/6 MS cases and 6/6 control cases. Cell specific labeling identified female cells of neuronal and immune phenotype in both control and active MS lesion tissue. This study shows that female cells presumed to be MMC are a common phenomenon in adult human brain where they appear to have embedded into brain tissue with the ability to express tissue specific markers.

Targeting senescence improves angiogenic potential of adipose-derived mesenchymal stem cells in patients with preeclampsia

BACKGROUND

Preeclampsia is a pregnancy-specific hypertensive disorder characterized by impaired angiogenesis. We postulate that senescence of mesenchymal stem cells (MSC), multipotent cells with pro-angiogenic activities, is one of the mechanisms by which systemic inflammation exerts inhibitory effects on angiogenesis in preeclampsia.

METHODS

MSC were isolated from abdominal fat tissue explants removed during medically indicated C-sections from women with preeclampsia (PE-MSC, n = 10) and those with normotensive pregnancies (NP-MSC, n = 12). Sections of the frozen subcutaneous adipose tissue were assessed for inflammation by staining for tumor necrosis factor (TNF)-alpha and monocyte chemoattractant protein (MCP)-1. Viability, proliferation, and migration were compared between PE-MSC vs. NP-MSC. Apoptosis and angiogenesis were assayed before and after treatment with a senolytic agent (1 μM dasatinib) using the IncuCyte S3 Live-Cell Analysis System. Similarly, staining for senescence-associated beta galactosidase (SABG) and qPCR for gene expression of senescence markers, p16 and p21, as well as senescence-associated secretory phenotype (SASP) components, IL-6, IL-8, MCP-1, and PAI-1, were studied before and after treatment with dasatinib and compared between PE and NP.

RESULTS

After in vitro exposure to TNF-alpha, MSC demonstrated upregulation of SASP components, including interleukins-6 and -8 and MCP-1. Staining of the subcutaneous adipose tissue sections revealed a greater inflammatory response in preeclampsia, based on the higher levels of both TNF-alpha and MCP-1 compared to normotensive pregnancies (p < 0.001 and 0.024, respectively). MSC isolated from PE demonstrated a lower percentage of live MSC cells (p = 0.012), lower proliferation (p = 0.005), and higher migration (p = 0.023). At baseline, PE-MSC demonstrated a senescent phenotype, reflected by more abundant staining for SABG (p < 0.001), upregulation of senescence markers and SASP components, as well as lower angiogenic potential (p < 0.001), compared to NP-MSC. Treatment with dasatinib increased significantly the number of apoptotic PE-MSC compared to NP-MSC (0.011 vs. 0.093) and decreased the gene expression of p16 and six SASP components. The mechanistic link between senescence and impaired angiogenesis in PE was confirmed by improved angiogenic potential of PE-MSC (p < 0.001) after dasatinib treatment.

CONCLUSIONS

Our data suggest that MSC senescence exerts inhibitory effects on angiogenesis in preeclampsia. Senolytic agents may offer the opportunity for mechanism-based therapies.

Wharton's Jelly Mesenchymal Stromal Cells Support the Expansion of Cord Blood-derived CD34+ Cells Mimicking a Hematopoietic Niche in a Direct Cell-cell Contact Culture System

Wharton’s jelly mesenchymal stromal cells (WJ-MSCs) have been recently exploited as a feeder layer in coculture systems to expand umbilical cord blood–hematopoietic stem/progenitor cells (UCB-HSPCs). Here, we investigated the role of WJ-MSCs in supporting ex vivo UCB-HSPC expansion either when cultured in direct contact (DC) with WJ-MSCs or separated by a transwell system or in the presence of WJ-MSC–conditioned medium. We found, in short-term culture, a greater degree of expansion of UCB-CD34⁺ cells in a DC system (15.7 ± 4.1-fold increase) with respect to the other conditions. Moreover, in DC, we evidenced two different CD34⁺ cell populations (one floating and one adherent to WJ-MSCs) with different phenotypic and functional characteristics. Both multipotent CD34⁺/CD38⁻ and lineage-committed CD34⁺/CD38⁺ hematopoietic progenitors were expanded in a DC system. The former were significantly more represented in the adherent cell fraction than in the floating one (18.7 ± 11.2% vs. 9.7 ± 7.9% over the total CD34⁺ cells). Short-term colony forming unit (CFU) assays showed that HSPCs adherent to the stromal layer were able to generate a higher frequency of immature colonies (CFU-granulocyte/macrophage and burst-forming unit erythroid/large colonies) with respect to the floating cells. In the attempt to identify molecules that may play a role in supporting the observed ex vivo HSPC growth, we performed secretome analyses. We found a number of proteins involved in the HSPC homing, self-renewal, and differentiation in all tested conditions. It is important to note that a set of sixteen proteins, which are only in part reported to be expressed in any hematopoietic niche, were exclusively found in the DC system secretome. In conclusion, WJ-MSCs allowed a significant ex vivo expansion of multipotent as well as committed HSPCs. This may be relevant for future clinical applications.

Malaria in pregnancy shapes the development of foetal and infant immunity

Malaria, particularly Plasmodium falciparum, continues to disproportionately affect pregnant women. In addition to the profoundly deleterious impact of maternal malaria on the health of the mother and foetus, malaria infection in pregnancy has been shown to affect the development of the foetal and infant immune system and may alter the risk of malaria and nonmalarial outcomes during infancy. This review summarizes our current understanding of how malaria infection in pregnancy shapes the protective components of the maternal immune system transferred to the foetus and how foetal exposure to parasite antigens impacts the development of foetal and infant immunity. It also reviews existing evidence linking malaria infection in pregnancy to malaria and nonmalarial outcomes in infancy and how preventing malaria in pregnancy may alter these outcomes. A better understanding of the consequences of malaria infection in pregnancy on the development of foetal and infant immunity will inform control strategies, including intermittent preventive treatment in pregnancy and vaccine development.

Placental exosomes profile in maternal and fetal circulation in intrauterine growth restriction - Liquid biopsies to monitoring fetal growth

INTRODUCTION

Placenta-derived exosomes may represent an additional pathway by which the placenta communicates with the maternal system to induce maternal vascular adaptations to pregnancy and it may be affected during Fetal growth restriction (FGR). The objective of this study was to quantify the concentration of total and placenta-derived exosomes in maternal and fetal circulation in small fetuses classified as FGR or small for gestational age (SGA).

METHODS

Prospective cohort study in singleton term gestations including 10 normally grown fetuses and 20 small fetuses, sub-classified into SGA and FGR accordingly to birth weight (BW) percentile and fetoplacental Doppler. Exosomes were isolated from maternal and fetal plasma and characterized by morphology, enrichment of exosomal proteins, and size distribution by electron microscopy, western blot, and nanoparticle tracking analysis, respectively. Total and specific placenta-derived exosomes were determined using quantum dots coupled with CD63^+ve and placental-type alkaline phosphatase (PLAP)^+ve antibodies, respectively.

RESULTS

Maternal concentrations of CD63^+ve and PLAP^+ve exosomes were similar between the groups (all p > 0.05). However, there was a significant positive correlation between the ratio of placental-derived to total exosomes (PLAP^+ve ratio) and BW percentile, [rho = 0.77 (95% CI: 0.57 to 0.89); p = 0.0001]. The contribution of placental exosomes to the total exosome concentration in maternal and fetal circulation showed a significant decrease among cases, with lower PLAP^+ve ratios in FGR compared to controls and SGA cases.

DISCUSSION

Quantification of placental exosomes in maternal plasma reflects fetal growth and it may be a useful indicator of placental function.

Fetal bone marrow homing of donor mesenchymal stem cells after transamniotic stem cell therapy (TRASCET)

PURPOSE

Donor cell engraftment patterns following transamniotic stem cell therapy (TRASCET) with amniotic fluid mesenchymal stem cells (afMSCs) are incompatible with solely direct amniotic seeding. We sought to determine whether fetal bone marrow is a component of such engraftment and to examine the chronology of afMSC placental trafficking.

METHODS

Two groups of Sprague-Dawley rat fetuses received volume-matched intraamniotic injections on gestational day 17 (E17; term E22): either afMSCs labeled with a luciferase reporter gene or luciferase protein alone. Placental samples were procured at daily time points thereafter until term. Fetal bone marrow was obtained at term only owing to size constraints. Specimens were screened for luminescence via microplate luminometry.

RESULTS

Donor afMSCs were identified in the bone marrow and placenta of fetuses receiving labeled afMSCs, but not in those receiving luciferase alone (P<0.001). Luminescence was significantly higher in placentas at E18 compared to E19 (P<0.001), E20 (P=0.007), and E21 (P=0.004), with no difference with E22/term (P=0.97).

CONCLUSIONS

Donor mesenchymal stem cells home to the fetal bone marrow after intraamniotic injection. The chronology of placental trafficking is suggestive of controlled cell routing rather than plain cell clearance. Fetal bone marrow engraftment of donor cells significantly expands potential applications of transamniotic stem cell therapy.

Microchimerism: Defining and redefining the prepregnancy context - A review

Bidirectional transplacental exchange characterizes human pregnancy. Cells exchanged between mother and fetus can durably persist as microchimerism and may have both short- and long-term consequences for the recipient. The amount, type, and persistence of microchimerism are influenced by obstetric characteristics, pregnancy complications, exposures to infection, and other factors. A reproductive-aged woman enters pregnancy harboring previously acquired microchimeric "grafts," which may influence her preconception health and her subsequent pregnancy outcomes. Many questions remain to be answered about microchimerism with broad-ranging implications. This review will summarize key aspects of this field of research and propose important questions to be addressed moving forward.

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.

Why are levels of maternal microchimerism higher in type 1 diabetes pancreas?

Maternal microchimerism (MMc) results from transfer of maternal cells to the fetus in pregnancy. These cells have been shown to persist into adulthood in healthy individuals and an increased frequency of MMc has been associated with autoimmune disease. Female (presumed maternal) islet beta cells have recently been identified at higher levels in pancreas from a child with T1D compared to three controls. There was, however, no evidence that these cells were the targets of autoimmune attack. The aim of this study was to analyze well-characterized T1D pancreases encompassing a spectrum in age at diagnosis, and duration of diabetes, for the presence of maternal microchimerism compared to control pancreases.Pancreas samples were available from six males with T1D and four male controls. Fluorescent-labeled probes were used to detect X and Y chromosomes. At least 1,000 cells, usually 4,000-8,000 cells underwent confocal imaging for each pancreas. The frequency of MMc was higher in T1D pancreases (range 0.31-0.80%, mean 0.58%) than in controls (0.24-0.50%, mean 0.38%) (p = 0.05). Intriguingly, clusters of 2-3 MMc were occasionally found in the pancreases, particularly T1D pancreases, suggesting replication of these cells. Concomitant FISH and immunofluorescence staining for insulin or CD45 was performed to phenotype cells of maternal origin. Insulin positive and insulin negative MMc were identified indicating that MMc contribute to the exocrine and endocrine compartments. No CD45 positive MMc were observed. These data confirm the presence of maternal cells in human pancreas and support previous observations that levels of MMc are higher in T1D pancreas compared to controls. MMc do not appear to be immune effector cells and those that stain positive for insulin within intact islets in T1D tissue appear healthy with no evidence that they are the focus of immune attack. This study adds support to the hypothesis that maternal stem cells have the capacity to cross the placental barrier and differentiate into both endocrine and exocrine cells but more detailed characterization of MMc in the pancreas is required.

Stem cell microchimerism and tolerance to non-inherited maternal antigens

Exposure to non-inherited maternal antigens (NIMA) in fetal and neonatal life of an F(1) backcross (BDF(1) female × B6 male) mouse can result in lifelong tolerance to allografts expressing the NIMA (H2(d)). We have recently shown that the NIMA-specific regulatory T cells were directly correlated with level of maternal microchimerism (MMc) in adult mice, indicating a causative link between the two, and that both Tregs and multi-lineage MMc were dependent on ingestion of milk from a NIMA(+) mother during nursing. Yet how maternal cells obtained in fetal and neonatal life are maintained in adult life remains unclear. Since stem cells are deficient in MHC class I & II expression, we hypothesized that maternally derived stem cells that replenish MMc remain throughout life without eliciting immunity, but differentiated maternal cells can either be deleted by alloreactive T and B effector cells or persist, inducing NIMA-specific tolerance. Consistent with this hypothesis, we found maternally-derived lineage(neg) c-kit(+) cells in the bone marrow of most of adult offspring by quantitative PCR; however, only 50% had detectable MMc in lineage(+) bone marrow cells. Mesenchymal stem cells (lineage(neg) and plate-adherent cells) propagated from the bone marrow also contained maternally-derived cells, albeit in 10-fold lower frequency compared with MMc in myeloid lineage (CD11b(+) and CD11c(+)) cells. Maternally-derived cardiac stem cells were also detected in lineage(neg) c-kit(+) cells purified from heart tissue of NIMA-exposed mice, indicating a local pool of stem cells sustaining MMc in a non-lymphoid tissue. Cardiac stem cell MMc correlated with the presence of maternally derived cardiomyocytes. Lastly, liver MMc increased after nursing suggesting a seeding of maternal cells into the liver via breast milk. Whether orally-derived liver MMc also included maternal stem cells, was not determined. Maternal stem cells in bone marrow and tissues of NIMA-exposed mice are likely responsible for sustaining MMc in adult mice, but their presence alone does not guarantee multi-lineage MMc and tolerance.

Fetal microchimerism persists at high levels in c-kit stem cells in sensitized mothers

We previously showed that fetal and maternal exposure to non-inherited maternal antigens (NIMA) during gestation and nursing resulted in lifelong tolerance to NIMA in some offspring. This NIMA-specific tolerance was mediated by regulatory T cells (Tregs) and was correlated with the level of multi-lineage maternal microchimerism (Mc) indicating a causative link between Mc and Treg development. To determine if transfer of fetal cells into mothers resulted in a similar tolerance to fetal cells, we used qPCR to detect rare fetal derived cells and a delayed type hypersensitivity (DTH) assay to detect fetal alloantigen-specific effector and regulatory T cells in mothers. We found that 5/8 B6 mothers of H2(b/d) offspring were sensitized to the alloantigens H2(d) and HY, indicating a dominance of alloantigen-specific effector T cells. Though these sensitized mothers did not have detectable fetal Mc (FMc) in any of the organs tested, they had very high levels of fetus-derived c-kit(+) stem cells in their bone marrow. The remaining 3/8 B6 mothers that were not sensitized to the fetal antigens had detectable FMc found mostly in heart, lungs and liver, and in 2/3, we could detect alloantigen-specific regulatory T cells. This data indicates that, as in NIMA-specific tolerance, tolerance in multiparous females to inherited paternal antigens (IPA) expressed by the fetus is associated with the presence of fetal Mc in differentiated cell subsets. Surprisingly, robust lin(-)c-kit(+) bone marrow cell fetal Mc can occur in sensitized mothers. This suggests a continuous source of allospecific priming, coupled with active elimination of mature IPA-expressing lin(+) cells by effector T cells of the maternal host.

Maternal Microchimerism Predicts Increased Infection but Decreased Disease due to Plasmodium falciparum During Early Childhood

Background

A mother's infection with placental malaria (PM) can affect her child's susceptibility to malaria, although the mechanism remains unclear. The fetus acquires a small amount of maternal cells and DNA known as maternal microchimerism (MMc), and we hypothesized that PM increases MMc and that MMc alters risk of Plasmodium falciparum malaria during infancy.

Methods

In a nested cohort from Muheza, Tanzania, we evaluated the presence and level of cord blood MMc in offspring of women with and without PM. A maternal-specific polymorphism was identified for each maternal-infant pair, and MMc was assayed by quantitative polymerase chain reaction. The ability of MMc to predict malaria outcomes during early childhood was evaluated in longitudinal models.

Results

Inflammatory PM increased the detection rate of MMc among offspring of primigravidae and secundigravidae, and both noninflammatory and inflammatory PM increased the level of MMc. Detectable MMc predicted increased risk of positive blood smear but, interestingly, decreased risk of symptomatic malaria and malaria hospitalization.

Conclusions

The acquisition of MMc may result in increased malaria infection but protection from malaria disease. Future studies should be directed at the cellular component of MMc, with attention to its ability to directly or indirectly coordinate anti-malarial immune responses in the offspring.

Maternal microchimerism is prevalent in cord blood in memory T cells and other cell subsets, and persists post-transplant

Among reported advantages of umbilical cord blood (CB) in transplantation is lower leukemia relapse probability. Underlying cellular mechanisms of graft-vs.-leukemia (GVL) are thought to include a prominent role for T cells. Cells of the CB's mother, maternal microchimerism (MMc), were recently strongly, but indirectly, implicated in this GVL benefit. We assayed MMc directly and hypothesized benefit accrues from CB maternal T cells. MMc was quantified in 51 CBs and, within memory T, naïve T, B, NK cells, and monocytes in 27 CBs. Polymorphism-specific quantitative-PCR assays targeted maternal genotypes non-shared with CBs. Overall MMc was common and often at substantial levels. It was present in 52.9% of CB and in 33.3-55.6% of tested subsets. Remarkably, MMc quantities were greater in memory T cells than other subsets (p < 0.001). Expressed as genome equivalents (gEq) per 10⁵ total gEq tested (gEq/10⁵), memory T cell MMc averaged 850.2 gEq/10⁵, while other subset mean quantities were 13.8-30.1 gEq/10⁵. After adjustment for proportionality in CB, MMc remained 6-17 times greater in memory T, and 3-9 times greater in naïve T, vs. non-T-cell subsets. Further, CB-origin MMc was detected in vivo in a patient up to 6 mo post-transplantation, including among T cells. Overall, results revealed levels and phenotypes of CB MMc with potential relevance to CB transplantation and, more broadly, to offspring health.

Chorion Mesenchymal Stem Cells Show Superior Differentiation, Immunosuppressive, and Angiogenic Potentials in Comparison With Haploidentical Maternal Placental Cells

Mesenchymal stem cells (MSCs) of placental origin have become increasingly translational owing to their abundance and accessibility. MSCs of different origin share several features but also present biological differences that might point to distinct clinical properties. Hence, mixing fetal and maternal cells from the same placenta can lead to contradicting results. We analyzed the biological characteristics of haploidentical MSCs isolated from fetal sources, including the umbilical cord (UC-MSCs) and chorion (Ch-MSCs), compared with maternal decidua MSCs (Dc-MSCs). All MSCs were analyzed for general stem cell properties. In addition, immunosuppressive capacity was assessed by the inhibition of T-cell proliferation, and angiogenic potential was evaluated in a Matrigel transplantation assay. The comparison between haploidentical MSCs displayed several distinct features, including (a) marked differences in the expression of CD56, (b) a higher proliferative capacity for Dc-MSCs and UC-MSCs than for Ch-MSCs, (c) a diversity of mesodermal differentiation potential in favor of fetal MSCs, (d) a higher capacity for Ch-MSCs to inhibit T-cell proliferation, and (e) superior angiogenic potential of Ch-MSCs evidenced by a higher capability to form tubular vessel-like structures and an enhanced release of hepatocyte growth factor and vascular endothelial growth factor under hypoxic conditions. Our results suggest that assessing the prevalence of fetomaternal contamination within placental MSCs is necessary to increase robustness and limit side effects in their clinical use. Finally, our work presents evidence positioning fetoplacental cells and notably Ch-MSCs in the forefront of the quest for cell types that are superior for applications in regenerative medicine.

SIGNIFICANCE

This study analyzed the biological characteristics of mesenchymal stem cells (MSCs) isolated from fetal and maternal placental origins. The findings can be summarized as follows: (a) important differences were found in the expression of CD56, (b) a different mesodermal differentiation potential was found in favor of fetal MSCs, (c) a higher immunosuppressive capacity for chorion MSCs was noted, and (d) superior angiogenic potential of Ch-MSCs was observed. These results suggest that assessing the prevalence of fetomaternal contamination within placental MSCs is necessary to increase robustness and limit side effects in their clinical use. The evidence should allow clinicians to view fetoplacental cells, notably Ch-MSCs, favorably as candidates for use in regenerative medicine.

VEGF-A promotes cardiac stem cell engraftment and myocardial repair in the infarcted heart

BACKGROUND

The objective of this study was to determine whether vascular endothelial growth factor (VEGF)-A subtypes improve cardiac stem cell (CSC) engraftment and promote CSC-mediated myocardial repair in the infarcted heart.

METHODS

CSCs were treated with VEGF receptor (VEGFR) inhibitors, VCAM-1 antibody (VCAM-1-Ab), or PKC-α inhibitor followed by the treatment with VEGF-A. CSC adhesion assays were performed in vitro. In vivo, the PKH26-labeled and VCAM-1-Ab or PKC-α inhibitor pre-treated CSCs were treated with VEGF-A followed by implantation into infarcted rat hearts. The hearts were then collected for measuring CSC engraftment and evaluating cardiac fibrosis and function 3 or 28days after the CSC transplantation.

RESULTS

All three VEGF-A subtypes promoted CSC adhesion to extracellular matrix and endothelial cells. VEGF-A-mediated CSC adhesion required VEGFR and PKCα signaling. Importantly, VEGF-A induced VCAM-1, but not ICAM-1 expression in CSCs through PKCα signaling. In vivo, VEGF-A promoted the engraftment of CSCs in infarcted hearts, which was attenuated by PKCα inhibitor or VCAM-1-Ab. Moreover, VEGF-A-mediated CSC engraftment resulted in a reduction in infarct size and fibrosis. Functional studies showed that the transplantation of the VEGF-A-treated CSCs stimulated extensive angiomyogenesis in infarcted hearts as indicated by the expression of cardiac troponin T and von Willebrand factor, leading to an improved performance of left ventricle. Blockade of PKCα signaling or VCAM-1 significantly diminished the beneficial effects of CSCs treated with VEGF-A.

CONCLUSION

VEGF-A promotes myocardial repair through, at least in part, enhancing the engraftment of CSCs mediated by PKCα/VCAM-1 pathway.

Therapeutic potential of mesenchymal stem cell transplantation in a nitrofen-induced congenital diaphragmatic hernia rat model

PURPOSE

The aim of this study was to evaluate the efficacy of mesenchymal stem cells (MSCs) in a nitrofen-induced congenital diaphragmatic hernia (CDH) rat model.

METHODS

Pregnant rats were exposed to nitrofen on embryonic day 9.5 (E9.5). MSCs were isolated from the enhanced green fluorescent protein (eGFP) transgenic rat lungs. The MSCs were transplanted into the nitrofen-induced E12.5 rats via the uterine vein, and the E21 lung explants were harvested. The study animals were divided into three: the control group, the nitrofen-induced left CDH (CDH group), and the MSC-treated nitrofen-induced left CDH (MSC-treated CDH group). The specimens were morphologically analyzed using HE and immunohistochemical staining with proliferating cell nuclear antigen (PCNA), surfactant protein-C (SP-C), and α-smooth muscle actin.

RESULTS

The alveolar and medial walls of the pulmonary arteries were significantly thinner in the MSC-treated CDH group than in the CDH group. The alveolar air space areas were larger, while PCNA and the SP-C positive cells were significantly higher in the MSC-treated CDH group, than in the CDH group. MSC engraftment was identified on immunohistochemical staining of the GFP in the MSC-treated CDH group.

CONCLUSIONS

MSC transplantation potentially promotes alveolar and pulmonary artery development, thereby reducing the severity of pulmonary hypoplasia.

High incidence of contaminating maternal cell overgrowth in human placental mesenchymal stem/stromal cell cultures: a systematic review

Placenta is a readily accessible translationally advantageous source of mesenchymal stem/stromal cells (MSCs) currently used in cryobanking and clinical trials. MSCs cultured from human chorion have been widely assumed to be fetal in origin, despite evidence that placental MSCs may be contaminated with maternal cells, resulting in entirely maternally derived MSC cultures. To document the frequency and determinants of maternal cell contamination in chorionic MSCs, we undertook a PRISMA-compliant systematic review of publications in the PubMed, Medline, and Embase databases (January 2000 to July 2013) on placental and/or chorionic MSCs from uncomplicated pregnancies. Of 147 studies, only 26 (18%) investigated fetal and/or maternal cell origin. After excluding studies that did not satisfy minimal MSC criteria, 7 of 15 informative studies documented MSC cultures as entirely fetal, a further 7 studies reported cultured human chorionic MSC populations to be either maternal (n=6) or mixed (n=1), whereas 1 study separately cultured pure fetal and pure maternal MSC from the same placenta. Maternal cell contamination was associated with term and chorionic membrane samples and greater passage number but was still present in 30% of studies of chorionic villous MSCs. Although most studies assume fetal origin for MSCs sourced from chorion, this systematic review documents a high incidence of maternal-origin MSC populations in placental MSC cultures. Given that fetal MSCs have more primitive properties than adult MSCs, our findings have implications for clinical trials in which knowledge of donor and tissue source is pivotal. We recommend sensitive methods to quantitate the source and purity of placental MSCs.

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.

In vivo implanted bone marrow-derived mesenchymal stem cells trigger a cascade of cellular events leading to the formation of an ectopic bone regenerative niche

We recently reported that mouse bone marrow stromal cells, also known as bone marrow (BM)-derived mesenchymal stem cells (MSCs), seeded onto a scaffold and implanted in vivo, led to an ectopic bone deposition by host cells. This MSCs capacity was critically dependent on their commitment level, being present only in MSCs cultured in presence of fibroblast growth factor-2. Taking advantage of a chimeric mouse model, in this study we show that seeded MSCs trigger a cascade of events resulting in the mobilization of macrophages, the induction of their functional switch from a proinflammatory to a proresolving phenotype, and the subsequent formation of a bone regenerative niche through the recruitment, within the first 2 weeks of implantation, of endothelial progenitors and of cells with an osteogenic potential (CD146+CD105+), both of them derived from the BM. Moreover, we demonstrated that, in an inflammatory environment, MSCs secrete a large amount of prostaglandin E2 playing a key role in the macrophage phenotype switch.

Human mesenchymal stem cells: a bank perspective on the isolation, characterization and potential of alternative sources for the regeneration of musculoskeletal tissues

The continuous discovery of human mesenchymal stem cells (hMSCs) in different tissues is stirring up a tremendous interest as a cell source for regenerative medicine therapies. Historically, hMSCs have been always considered a sub-population of mononuclear cells present in the bone marrow (BM). Although BM-hMSCs are still nowadays considered as the most promising mesenchymal stem cell population to reach the clinics due to their capacity to differentiate into multiple tissues, hMSCs derived from other adult and fetal tissues have also demonstrated to possess similar differentiation capacities. Furthermore, different reports have highlighted a higher recurrence of hMSCs in some of these tissues as compared to BM. This offer a fascinating panorama for cell banking, since the creation of a stem cell factory could be envisioned where hMSCs are stocked and used for ad hoc clinical applications. In this review, we summarize the main findings and state of the art in hMSCs isolation, characterization, and differentiation from alternative tissue sources and we attempt to compare their potency for musculoskeletal regeneration.

Orchestrated leukocyte recruitment to immune-privileged sites: absolute barriers versus educational gates

Complex barriers separate immune-privileged tissues from the circulation. Here, we propose that cell entry to immune-privileged sites through barriers composed of tight junction-interconnected endothelium is associated with destructive inflammation, whereas border structures comprised of fenestrated vasculature enveloped by tightly regulated epithelium serve as active and selective immune-skewing gates in the steady state. Based on emerging knowledge of the central nervous system and information from other immune-privileged sites, we propose that these sites are endowed either with absolute endothelial-based barriers and epithelial gates that enable selective and educative transfer of trafficking leukocytes or with selective epithelial gates only.

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.

Differential mesengenic potential and expression of stem cell-fate modulators in mesenchymal stromal cells from human-term placenta and bone marrow

Placenta has attracted increasing attention over the past decade as a stem cell source for regenerative medicine. In particular, the amniochorionic membrane has been shown to harbor populations of mesenchymal stromal cells (MSCs). In this study, we have characterized ex vivo expanded MSCs from the human amniotic (hAMSCs) and chorionic (hCMSCs) membranes of human full-term placentas and adult bone marrow (hBMSCs). Our results show that hAMSCs, hCMSCs, and hBMSCs express typical mesenchymal (CD73, CD90, CD105, CD44, CD146, CD166) and pluripotent (Oct-4, Sox2, Nanog, Lin28, and Klf4) markers but not hematopoietic markers (CD45, CD34). Ex vivo expanded hAMSCs were found to be of fetal origin, while hCMSCs cultures contained only maternal cells. Cell proliferation was significantly higher in hCMSCs, compared to hAMSCs and hBMSCs. Integrin profiling revealed marked differences in the expression of α subunits between the three cell sources. Cadherin receptors were consistently expressed on a subset of progenitors (ranging from 1% to 60%), while N-CAM (CD56) was only expressed in hAMSCs and hCMSCs but not in hBMSCs. When induced to differentiate, hAMSCs and hCMSCs displayed strong chondrogenic and osteogenic differentiation potential but very limited capacity for adipogenic conversion. In contrast, hBMSCs showed strong differentiation potential along the three lineages. These results illustrate how MSCs from different ontological sources display differential expression of cell-fate mediators and mesodermal differentiation capacity.

Microchimerism: tolerance vs. sensitization

PURPOSE OF REVIEW

The bidirectional exchange of cells, both mature and progenitor types, at the maternal-fetal interface is a common feature of mammalian reproduction. The presence of semiallogeneic cells in a host can have significant immunological effects on transplantation tolerance and rejection. Here, we review recent advances in this area.

RECENT FINDINGS

Maternal microchimerism (MMc) in blood and various organs was found to be directly correlated with noninherited maternal antigen (NIMA)-specific CD4(+) regulatory T cells (Tregs), in F(1) backcross mice. In humans, MMc induced NIMA-specific FoxP3(+) CD4 Tregs in lymph nodes and spleen of fetuses. Tolerance to NIMA(+) allografts could be predicted in mice by measuring levels of the NIMA-specific Tregs in offspring before transplantation. On the contrary, fetal microchimerism (FMc) in multiparous female mice was largely confined to CD34(+) hematopoietic stem cells (HSCs) and was associated with sensitization rather than Treg induction. The recent discovery of a 'layered' T-cell development in humans whereby fetal HSCs are more likely to produce Tregs than adult HSCs, which may explain why MMc often induces tolerance, whereas FMc tends to induce sensitization.

SUMMARY

Microchimerism may cause tolerance resulting in acceptance of an allograft bearing antigens shared by the microchimeric cells. However, microchimerism may also cause sensitization resulting in rejection. Distinguishing these effects prior to the transplant may revolutionize the field of living-related renal transplantation wherein MMc and FMc can exert a powerful influence on graft outcome.

MicroRNA expression during osteogenic differentiation of human multipotent mesenchymal stromal cells from bone marrow

MicroRNAs comprise a group of non-coding small RNAs (17-25 nt) involved in post-transcriptional regulation that have been identified in various plants and animals. Studies have demonstrated that miRNAs are associated with stem cell self-renewal and differentiation and play a key role in controlling stem cell activities. However, the identification of specific miRNAs and their regulatory roles in the differentiation of multipotent mesenchymal stromal cells (MSCs) have so far been poorly defined. We isolated and cultured human MSCs and osteo-differentiated MSCs from four individual donors. miRNA expression in MSCs and osteo-differentiated MSCs was investigated using miRNA microarrays. miRNAs that were commonly expressed in all three MSC preparations and miRNAs that were differentially expressed between MSCs and osteo-differentiated MSCs were identified. Four underexpressed (hsa-miR-31, hsa-miR-106a, hsa-miR-148a, and hsa-miR-424) and three novel overexpressed miRNAs (hsa-miR-30c, hsa-miR-15b, and hsa-miR-130b) in osteo-differentiated MSCs were selected and their expression were verified in samples from the fourth individual donors. The putative targets of the miRNAs were predicted using bioinformatic analysis. The four miRNAs that were underexpressed in osteo-differentiated MSCs were predicted to target RUNX2, CBFB, and BMPs, which are involved in bone formation; while putative targets for miRNAs overexpressed in osteo-differentiated MSCs were MSC maker (e.g., CD44, ITGB1, and FLT1), stemness-maintaining factor (e.g., FGF2 and CXCL12), and genes related to cell differentiation (e.g., BMPER, CAMTA1, and GDF6). Finally, hsa-miR-31 was selected for target verification and function analysis. The results of this study provide an experimental basis for further research on miRNA functions during osteogenic differentiation of human MSCs.

Thymidine kinase gene modified bone marrow mesenchymal stem cells as vehicles for antitumor therapy

Bone marrow mesenchymal stem cells (BMSCs) represent an important source of cells for tissue repair. The tropism of these cells to the sites of injury and tumors has been well established. Their tumor-homing properties make BMSCs good candidates as antitumor agent delivery vehicles. In this study, we showed that BMSCs have the ability to migrate toward various cancer cells, including prostate cancer cells in vitro and in vivo and incorporating into the tumor mass. When infected with herpes simplex virus thymidine kinase (TK) gene by lentiviral transduction, TK-BMSCs maintained their tumor tropism capabilities and significantly inhibited the growth of subcutaneous PC3 prostate cancer xenografts in nude mice, in the presence of prodrug ganciclovir (GCV). Xenogenic TK-BMSCs also survived and exerted a significant antitumor effect in an animal model bearing metastastic RIF-1 (fibrosarcoma) tumor in the presence of prodrug GCV. The present study demonstrated that overexpression of TK in BMSCs did not affect their multidifferentiation potentials and their specific homing capacities toward the tumor mass, and the TK-BMSCs alone did not cause any harmful side effects in vivo. The use of TK-BMSCs as tumor-specific delivery vehicles together with controlled prodrug treatment may be a safe and novel anticancer therapy approach.

Unravelling the mystery of stem/progenitor cells in human breast milk

BACKGROUND

Mammary stem cells have been extensively studied as a system to delineate the pathogenesis and treatment of breast cancer. However, research on mammary stem cells requires tissue biopsies which limit the quantity of samples available. We have previously identified putative mammary stem cells in human breast milk, and here, we further characterised the cellular component of human breast milk.

METHODOLOGY/PRINCIPAL FINDINGS

We identified markers associated with haemopoietic, mesenchymal and neuro-epithelial lineages in the cellular component of human breast milk. We found 2.6 ± 0.8% (mean ± SEM) and 0.7 ± 0.2% of the whole cell population (WCP) were found to be CD133+ and CD34+ respectively, 27.8 ± 9.1% of the WCP to be positive for Stro-1 through flow-cytometry. Expressions of neuro-ectodermal stem cell markers such as nestin and cytokeratin 5 were found through reverse-transcription polymerase chain reaction (RT-PCR), and in 4.17 ± 0.2% and 0.9 ± 0.2% of the WCP on flow-cytometry. We also established the presence of a side-population (SP) (1.8 ± 0.4% of WCP) as well as CD133+ cells (1.7 ± 0.5% of the WCP). Characterisation of the sorted SP and non-SP, CD133+ and CD133- cells carried out showed enrichment of CD326 (EPCAM) in the SP cells (50.6 ± 8.6 vs 18.1 ± 6.0, P-value  = 0.02). However, culture in a wide range of in vitro conditions revealed the atypical behaviour of stem/progenitor cells in human breast milk; in that if they are present, they do not respond to established culture protocols of stem/progenitor cells.

CONCLUSIONS/SIGNIFICANCE

The identification of primitive cell types within human breast milk may provide a non-invasive source of relevant mammary cells for a wide-range of applications; even the possibility of banking one's own stem cell for every breastfeeding woman.

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.

Glycosyltransferase-programmed stereosubstitution (GPS) to create HCELL: engineering a roadmap for cell migration

During evolution of the vertebrate cardiovascular system, the vast endothelial surface area associated with branching vascular networks mandated the development of molecular processes to efficiently and specifically recruit circulating sentinel host defense cells and tissue repair cells at localized sites of inflammation/tissue injury. The forces engendered by high-velocity blood flow commensurately required the evolution of specialized cell surface molecules capable of mediating shear-resistant endothelial adhesive interactions, thus literally capturing relevant cells from the blood stream onto the target endothelial surface and permitting subsequent extravasation. The principal effectors of these shear-resistant binding interactions comprise a family of C-type lectins known as 'selectins' that bind discrete sialofucosylated glycans on their respective ligands. This review explains the 'intelligent design' of requisite reagents to convert native CD44 into the sialofucosylated glycoform known as hematopoietic cell E-/L-selectin ligand (HCELL), the most potent E-selectin counter-receptor expressed on human cells, and will describe how ex vivo glycan engineering of HCELL expression may open the 'avenues' for the efficient vascular delivery of cells for a variety of cell therapies.

In vivo osteogenic differentiation of human adipose-derived stem cells in an injectable in situ-forming gel scaffold

The sol-to-gel transition occurring at around body temperature makes the MPEG-PCL diblock copolymer an ideal candidate material for use as an injectable in situ-forming gel containing human adipose tissue-derived stem cells (hADSCs). The sol can be prepared at room temperature, and the gel forms at body temperature. Solutions of the copolymer containing hADSCs and osteogenic factors injected into rats formed gel scaffolds at the injection sites. The gels thus formed showed the interconnective pore structure required to support growth, proliferation, and differentiation of hADSCs. Bromodeoxyuridine-labeled hADSCs were confirmed to be present in gels formed in vivo. Bone formation was observed only in gel implants containing both hADSCs and osteogenic factors. Subcutaneous implantation of the in situ-forming gel scaffold demonstrated that hADSCs embedded in the gel stimulated much lower host tissue responses than did the gel alone, probably because of the unique immunomodulatory properties of hADSCs. In conclusion, our data on hADSCs embedded in an in situ gel scaffold suggest that this formulation may provide numerous benefits as a noninvasive alternative for tissue-engineered bone formation.

Novel sources of fetal stem cells: where do they fit on the developmental continuum?

The recent isolation of fetal stem cells from several sources either at the early stages of development or during the later trimesters of gestation, sharing similar growth kinetics and expressing pluripotency markers, provides strong support to the notion that these cells may be biologically closer to embryonic stem cells, actually representing intermediates between embryonic stem cells and adult mesenchymal stem cells, regarding proliferation rates and plasticity features, and thus able to confer an advantage over postnatal mesenchymal stem cells derived from conventional adult sources such as bone marrow. This conclusion has been strengthened by the different pattern of growth potential between the two stage-specific types of sources, as assessed by transcriptomic and proteomic analysis. A series of recent studies regarding the numerous novel features of fetal stem cells has reignited our interest in the field of stem-cell biology and in the possibilities for the eventual repair of damaged organs and the generation of in vitro tissues on biomimetic scaffolds for transplantation. These studies, employing elegant approaches and novel technologies, have provided new insights regarding the nature and the potential of fetal stem cells derived from placenta, amniotic fluid, amnion or umbilical cord. In this update, we highlight the major progression that has occurred in fetal stem-cell biology and discuss the most important areas for future investigation in the field of regenerative medicine.

Tolerance to noninherited maternal antigens in mice and humans

PURPOSE OF REVIEW

Exposure to noninherited maternal antigens (NIMAs) in fetal and neonatal life has life-long immunological consequences. Although there is a plethora of evidence of effects of mother on the immune responses of her offspring, there is very little knowledge available on how exposure to NIMA can result in either tolerance or sensitization. Understanding the mechanism of NIMA effects will impact different fields of immunology including transplantation, autoimmunity, and tumor immunotherapy.

RECENT FINDINGS

Following the discoveries of beneficial effects of NIMA exposure on clinical outcomes in solid organ and bone marrow transplantation, it has now been shown that the exposure to NIMA induces various types of T regulatory (T(R)) cells in fetus and adult, which may partially account for tolerance to allografts bearing the NIMA. Although all offspring are exposed to the maternal antigens, they exhibit a great variability in the NIMA effects, which can be explained by the variability in the extent of maternal microchimerism (MMc).

SUMMARY

Exposure to NIMA can have tolerogenic or sensitizing effects on the offspring, resulting in acceptance or rejection of allografts expressing the NIMA. This variability may be partly explained by the level and distribution of maternal cells persisting in the offspring.

Microchimerism in endocrine pathology

Chimerism in an individual refers to the coexistence of cells arising from two distinct organisms. It can arise iatrogenically via transplant or blood transfusion, and physiologically via twin to twin transfer, or from trafficking between mother and fetus during pregnancy. Many of the diseases associated with microchimerism affect the endocrine system (e.g., autoimmune thyroid disease and diabetes mellitus type 1). Microchimerism is relevant to endocrine pathology because (a) it is associated with pregnancy, a condition of complex endocrine physiology; (b) materno-fetal and feto-maternal cellular migration must involve the placenta, itself an endocrine organ; and (c) in some species, chimerism results in states of intersexuality, a condition intimately involved with endocrine physiology. Studies of feto-maternal microchimerism in the thyroid have documented the presence of fetal cells in association with Hashimoto thyroiditis, Graves' disease, thyroid adenoma, and papillary thyroid carcinoma. Studies of materno-fetal microchimerism have documented the presence of maternal cells in juvenile diabetes and other pediatric conditions. Microchimerism plays a potential role in the repair of diseased thyroid and pancreatic tissues.

Thyroid hormone-induced angiogenesis

A series of reports in the past decade have ascribed pro-angiogenic activity to several thyroid hormone analogues, including L-thyroxine (T(4)), 3,5,3-triiodo-L-thyronine (T(3)) and diiodothyropropionic acid (DITPA). Model systems of angiogenesis have demonstrated that thyroid hormone-induced neovascularization is initiated at a cell surface receptor for the hormone on an integrin. The hormone signal is transduced within the cell by extracellular regulated kinase 1/2 (ERK1/2) into secretion of basic fibroblast growth factor (bFGF) and other vascular growth factors and consequent angiogenesis. Intact animal studies have shown that endogenous thyroid hormone supports blood vessel density in heart and brain and that thyroid hormone administration can induce angiogenesis in ischemic limbs.