Cellular Subsets of Maternal Microchimerism in Umbilical Cord Blood

Deciphering the Role of Maternal Microchimerism in Offspring Autoimmunity: A Narrative Review

Feto-maternal microchimerism is the bidirectional transfer of cells through the placenta during pregnancy that can affect the health of both the mother and the offspring, even in childhood or adulthood. However, microchimerism seems to have different consequences in the mother, who already has a developed immune system, than in the fetus, which is vulnerable with immature defense mechanisms. Studies have shown that the presence of fetal microchimeric cells in the mother can be associated with reduced fetal growth, pre-eclampsia, miscarriage, premature birth, and the risk of autoimmune disease development in the future. However, some studies report that they may also play a positive role in the healing of maternal tissue, in cancer and cardiovascular disease. There are few studies in the literature regarding the role of maternal microchimeric cells in fetal autoimmunity. Even fewer have examined their association with the potential triggering of autoimmune diseases later in the offspring's life. The objectives of this review were to elucidate the mechanisms underlying the potential association between maternal cells and autoimmune conditions in offspring. Based on our findings, several hypotheses have been proposed regarding possible mechanisms by which maternal cells may trigger autoimmunity. In Type 1 diabetes, maternal cells have been implicated in either attacking the offspring's pancreatic β-cells, producing insulin, differentiating into endocrine and exocrine cells, or serving as markers of tissue damage. Additionally, several potential mechanisms have been suggested for the onset of neonatal lupus erythematosus. In this context, maternal cells may induce a graft-versus-host or host-versus-graft reaction in the offspring, function as effectors within tissues, or contribute to tissue healing. These cells have also been found to participate in inflammation and fibrosis processes, as well as differentiate into myocardial cells, potentially triggering an immune response. Moreover, the involvement of maternal microchimeric cells has been supported in conditions such as juvenile idiopathic inflammatory myopathies, Sjögren's syndrome, systemic sclerosis, biliary atresia, and rheumatoid arthritis. Conversely, no association has been found between maternal cells and celiac disease in offspring. These findings suggest that the role of maternal cells in autoimmunity remains a controversial topic that warrants further investigation.

Maternal-Fetal Microchimerism: Impacts on Offspring's Immune Development and Transgenerational Immune Memory Transfer

Maternal-fetal microchimerism is a fascinating phenomenon in which maternal cells migrate to the tissues of the offspring during both pregnancy and breastfeeding. These cells primarily consist of leukocytes and stem cells. Remarkably, these maternal cells possess functional potential in the offspring and play a significant role in shaping their immune system development. T lymphocytes, a cell population mainly found in various tissues of the offspring, have been identified as the major cell type derived from maternal microchimerism. These T lymphocytes not only exert effector functions but also influence the development of the offspring's T lymphocytes in the thymus and the maturation of B lymphocytes in the lymph nodes. Furthermore, the migration of maternal leukocytes also facilitates the transfer of immune memory across generations. Maternal microchimerism has also been observed to address immunodeficiencies in the offspring. This review article focuses on investigating the impact of maternal cells transported within maternal microchimerism on the immune system development of the offspring, as well as elucidating the effector functions of maternal cells that migrate through the placenta and breast milk to reach the offspring.

Transplacental migration of maternal natural killer and T cells assessed by ex vivo human placenta perfusion

INTRODUCTION

The transplacental passage of cells between a mother and her fetus, known as microchimerism, is a less studied process during pregnancy. The frequency of maternal microchimeric cells in fetal tissues in physiological pregnancies and mechanisms responsible for transplacental cell trafficking are poorly understood. This study aimed to evaluate the placental trafficking of maternal peripheral blood mononuclear cells (PBMC) using human ex vivo placenta perfusion.

METHODS

Ten placentas and maternal PBMC were obtained after healthy pregnancies. Flow cytometry was used to characterize PBMC subtypes. They showed a higher percentage of CD3+ T cells compared to CD56+ NK cells. The isolated PBMC were stained with a fluorescent dye and perfused through the maternal circuit of the placenta in an ex vivo perfusion system. Subsequent immunofluorescence staining for CD3+ T cells and CD56+ NK cells was performed on placental tissue sections, and the number of detectable PBMC in different tissue areas was counted using fluorescence microscopy.

RESULTS

The applied method allowed discrimination of perfused autologous maternal cells from cells resident in the placenta before perfusion. Further, it allows additional immunohistochemical labelling and distinction of immune cell subsets. Perfused PBMC were detected in all analyzed placentas, mostly in contact to the syncytiotrophoblast. CD3+ T cells were identified more frequently than CD56+ NK cells and some CD3+ T cells were found inside fetoplacental tissues and vasculature. The results indicate that also other PBMCs than T or NK cells adhere to or enter villous tissue, but they have not been specified in this analysis.

DISCUSSION

Previous studies have detected maternal cells in the fetal circulation which we could mimick in our ex vivo placenta perfusion experiments with fluorescence labelled autologous maternal PBMC. The applied experimental settings did not allow comparison of transmigration abilities of PBMC subsets, but slight modifications of the model will permit further studies of cell transfer processes and microchimerism in pregnancy.

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.

Cross-decoration of dendritic cells by non-inherited maternal antigen-containing extracellular vesicles: Potential mechanism for PD-L1-based tolerance in cord blood and organ transplantation

Exposure to non-inherited maternal antigens (NIMA) during the fetal period induces lifelong split tolerance to grafts expressing these allo-antigens. In adult mice, the production of extracellular vesicles (EVs) from maternal microchimeric cells causes cross-decoration (XD) of offspring dendritic cells (DC) with NIMA and upregulation of PD-L1, contributing to NIMA tolerance. To see how this may apply to humans, we tested NIMA acquisition by fetal DCS in human cord blood. The average percentage of NIMA-XD among total DCs was 2.6% for myeloid and 4.5% for Plasmacytoid DC. These cells showed higher PD-L1 expression than their non-XD counterparts (mDC: p = .0016; pDC: p = .024). We detected CD9+ EVs bearing NIMA and PD-L1 in cord blood. To determine if this immune regulatory mechanism persists beyond the pregnancy, we analyzed NIMA-expressing kidney and liver transplant recipients. We found donor antigen XD DCs in peripheral blood and graft-infiltrating DCs. As in cord blood, the pattern of donor antigen expression was punctate, and PD-L1 expression was upregulated, likely due to both protein and miRNA acquired from EV. Our findings support a mechanism for split tolerance to NIMAs that develops during pregnancy and is recapitulated in adult transplant recipients.

Grandmaternal cells in cord blood

BACKGROUND

During pregnancy a feto-maternal exchange of cells through the placenta conducts to maternal microchimerism (Mc) in the child and fetal Mc in the mother. Because of this bidirectional traffic of cells, pregnant women have also acquired maternal cells in utero from their mother and could transfer grandmaternal (GdM) cells to their child through the maternal bloodstream during pregnancy. Thus, cord blood (CB) samples could theoretically carry GdMMc. Nevertheless this has never been demonstrated.

METHODS

Using Human Leukocyte Antigen (HLA)-specific quantitative PCR assays on three-generation families, we were able to test 28 CB samples from healthy primigravid women for GdMMc in whole blood (WB) and isolated cells (PBMC, T, B, granulocytes, stem cells).

FINDINGS

Five CB samples (18%) had GdMMc which could not be confounded with maternal source, with quantities 100 fold lower than maternal Mc in WB and PBMC. Risk of aneuploidies and/or related invasive prenatal procedures significantly correlated with the presence of GdMMc in CB (p=0.024). Significantly decreased HLA compatibility was observed in three-generation families from CB samples carrying GdMMc (p=0.019).

INTERPRETATION

Transgenerational transfer of cells could have implications in immunology and evolution. Further analyses will be necessary to evaluate whether GdMMc in CB is a passive or immunologically active transfer and whether invasive prenatal procedures could trigger GdMMc.

FUNDING

Provence-Alpes-Côte d'Azur APEX grant # 2012_06549E, 2012_11786F and 2014_03978) and the Foundation for Medical Research (FRM Grant #ING20140129045).

Factors Predicting the Presence of Maternal Cells in Cord Blood and Associated Changes in Immune Cell Composition

Background

Cord blood (CB) samples are increasingly used as a source of hematopoietic stem cells in transplantation settings. Maternal cells have been detected in CB samples and their presence is associated with a better graft outcome. However, we still do not know what influences the presence of maternal microchimerism (MMc) in CB samples and whether their presence influences CB hematopoietic cell composition.

Patients and Methods

Here we test whether genetic, biological, anthropometric and/or obstetrical parameters influence the frequency and/or quantity of maternal Mc in CB samples from 55 healthy primigravid women. Mc was evaluated by targeting non-shared, non-inherited Human Leukocyte Antigen (HLA)-specific real-time quantitative PCR in whole blood and four cell subsets (T, B lymphocytes, granulocytes and/or hematopoietic progenitor cells). Furthermore CB samples were analyzed for their cell composition by flow cytometry and categorized according to their microchimeric status.

Results

MMc was present in 55% of CB samples in at least one cell subset or whole blood, with levels reaching up to 0.3% of hematopoietic progenitor cells. Two factors were predictive of the presence of MMc in CB samples: high concentrations of maternal serological Pregnancy-Associated-Protein-A at first trimester of pregnancy (p=0.018) and feto-maternal HLA-A and/or –DR compatibility (p=0.009 and p=0.01 respectively). Finally, CB samples positive for MMc were significantly enriched in CD56+ cells compared to CB negative for MMc.

Conclusions

We have identified two factors, measurable at early pregnancy, predicting the presence of maternal cells in CB samples at delivery. We have shown that MMc in CB samples could have an influence on the hematopoietic composition of fetal cells. CD56 is the phenotypic marker of natural killer cells (NK) and NK cells are known to be the main effector for graft versus leukemia reactions early after hematopoietic stem cell transplantation. These results emphasize the importance of MMc investigation for CB banking strategies.