Fetus specific immune recognition and regulation by T cells at the fetal-maternal inferface in human pregnancy

During pregnancy the maternal immune system tolerates the persistence of fetal cells in maternal tissue. The fetus expresses maternal as well as paternal encoded molecules but is not rejected by the maternal immune system. The aim of this thesis was to determine whether maternal T cells contribute to fetus specific immune recognition and if mechanisms of fetus specific immune regulation exist in human pregnancy. A special emphasis is given to fetus specific immune recognition and immune regulation by maternal T cells at the fetal-maternal interface. In this thesis, we demonstrate that CD4+CD25bright regulatory T cells which are concentrated in decidual tissue have the capacity to down regulate fetus specific and 3rd party (non-specific) responses. In contrast, CD4+CD25bright T cells in maternal peripheral blood can regulate 3rd party (non-specific) responses, comparable to non-pregnant controls, while the capacity to regulate the fetus specific response is absent. These data suggest a preferential recruitment of fetus specific regulatory T cells from the peripheral blood to the fetal maternal interface. Analysis of the CD8+ T cell pool during pregnancy shows that decidual CD8+ T cells mainly consist of differentiated Effector-Memory T cells, while unprimed Na_ve cells are almost absent. Decidual Effector-Memory CD8+ T cells contain significantly reduced levels of the cytolytic molecule perforin. These data are suggestive for an alternative CD8+ T cell differentiation and regulation process that may play a crucial role in maintenance of maternal immune tolerance to the fetus. Database analysis of clinical pregnancy data, fetal-maternal HLA mismatches and decidual lymphocyte responses led to the conclusion that a fetal-maternal HLA-C mismatch is crucial for decidual CD4+ T cell activation and required for induction of functional CD4+CD25bright regulatory T cells in decidua. Hereby we provide the first evidence that decidual T cells specifically recognize a fetal HLA-C mismatch at the fetal-maternal interface, possibly using the indirect allorecognition pathway. However HLA-C recognition does not induce a destructive immune response in uncomplicated pregnancies. Besides TCR mediated allorecognition, low frequencies of decidual T cells express NK receptors that can specifically recognize HLA-C allotypes. Engagement of NK receptors on T cells can result in down regulation of TCR mediated T cell activation. Although, no experimental evidence is present so far, NK receptor expression on decidual T cells may provide an alternative way for decidual T cells to recognize allogeneic fetal cells and modulate the decidual immune response. In conclusion, this thesis shows that decidual T cells comprise a very heterogenic subset of T cells that include activated CD4+ and Effector-Memory type CD8+ T cells. However, these highly activated T cells are found together with T cell subsets that are capable to suppress the decidual lymphocyte response. Furthermore, we show that decidual T cells can specifically recognize a fetal-maternal HLA-C mismatch. Hereby we demonstrate that mechanisms of fetus specific allorecognition and T cell regulation are present at the fetal-maternal interface in uncomplicated human pregnancy. In summary our data show that the maternal T cells in the uterus recognize foreign fetal cells, however, due to the presence of immune suppressive regulatory T cells no detrimental immune reaction is induced. In future research it is important to translate our results to aberrant pregnancies where fetal growth retardation, maternal hypertension, pre-term birth or miscarriages may occur. Hereby, it is important to determine whether these immune suppressive regulatory T cells are present in the uterus, if they function properly and what factors (proteins or cells) attract or induce regulatory T cells at the fetal-maternal interface. Further unravelling of the mechanisms immune regulation during pregnancy may be crucial to understand why some pregnancies are successful whereas others are not.UBL - phd migration 201

Mixed signature of activation and dysfunction allows human decidual CD8(+) T cells to provide both tolerance and immunity

Stemcel biology/Regenerative medicine (incl. bloodtransfusion

A microRNA profile of human CD8(+) regulatory T cells and characterization of the effects of microRNAs on Treg cell-associated genes.

Recently, regulatory T (Treg) cells have gained interest in the fields of immunopathology, transplantation and oncoimmunology. Here, we investigated the microRNA expression profile of human natural CD8(+)CD25(+) Treg cells and the impact of microRNAs on molecules associated with immune regulation. We purified human natural CD8(+) Treg cells and assessed the expression of FOXP3 and CTLA-4 by flow cytometry. We have also tested the ex vivo suppressive capacity of these cells in mixed leukocyte reactions. Using TaqMan low-density arrays and microRNA qPCR for validation, we could identify a microRNA 'signature' for CD8(+)CD25(+)FOXP3(+)CTLA-4(+) natural Treg cells. We used the 'TargetScan' and 'miRBase' bioinformatics programs to identify potential target sites for these microRNAs in the 3'-UTR of important Treg cell-associated genes. The human CD8(+)CD25(+) natural Treg cell microRNA signature includes 10 differentially expressed microRNAs. We demonstrated an impact of this signature on Treg cell biology by showing specific regulation of FOXP3, CTLA-4 and GARP gene expression by microRNA using site-directed mutagenesis and a dual-luciferase reporter assay. Furthermore, we used microRNA transduction experiments to demonstrate that these microRNAs impacted their target genes in human primary Treg cells ex vivo. We are examining the biological relevance of this 'signature' by studying its impact on other important Treg cell-associated genes. These efforts could result in a better understanding of the regulation of Treg cell function and might reveal new targets for immunotherapy in immune disorders and cancer

A Signature of Maternal Anti-Fetal Rejection in Spontaneous Preterm Birth: Chronic Chorioamnionitis, Anti-Human Leukocyte Antigen Antibodies, and C4d

Chronic chorioamnionitis is found in more than one-third of spontaneous preterm births. Chronic chorioamnionitis and villitis of unknown etiology represent maternal anti-fetal cellular rejection. Antibody-mediated rejection is another type of transplantation rejection. We investigated whether there was evidence for antibody-mediated rejection against the fetus in spontaneous preterm birth.This cross-sectional study included women with (1) normal pregnancy and term delivery (n = 140) and (2) spontaneous preterm delivery (n = 140). We analyzed maternal and fetal sera for panel-reactive anti-HLA class I and class II antibodies, and determined C4d deposition on umbilical vein endothelium by immunohistochemistry. Maternal anti-HLA class I seropositivity in spontaneous preterm births was higher than in normal term births (48.6% vs. 32.1%, p = 0.005). Chronic chorioamnionitis was associated with a higher maternal anti-HLA class I seropositivity (p<0.01), significant in preterm and term birth. Villitis of unknown etiology was associated with increased maternal and fetal anti-HLA class I and II seropositivity (p<0.05, for each). Fetal anti-HLA seropositivity was closely related to maternal anti-HLA seropositivity in both groups (p<0.01, for each). C4d deposition on umbilical vein endothelium was more frequent in preterm labor than term labor (77.1% vs. 11.4%, p<0.001). Logistic regression analysis revealed that chronic chorioamnionitis (OR = 6.10, 95% CI 1.29–28.83), maternal anti-HLA class I seropositivity (OR = 5.90, 95% CI 1.60–21.83), and C4d deposition on umbilical vein endothelium (OR = 36.19, 95% CI 11.42–114.66) were associated with preterm labor and delivery.A major subset of spontaneous preterm births has a signature of maternal anti-fetal cellular and antibody-mediated rejections with links to fetal graft-versus-host disease and alloimmune reactions

Mycobacterium tuberculosis peptides presented by HLA-E molecules are targets for human CD8 T-cells with cytotoxic as well as regulatory activity

Tuberculosis (TB) is an escalating global health problem and improved vaccines against TB are urgently needed. HLA-E restricted responses may be of interest for vaccine development since HLA-E displays very limited polymorphism (only 2 coding variants exist), and is not down-regulated by HIV-infection. The peptides from Mycobacterium tuberculosis (Mtb) potentially presented by HLA-E molecules, however, are unknown. Here we describe human T-cell responses to Mtb-derived peptides containing predicted HLA-E binding motifs and binding-affinity for HLA-E. We observed CD8(+) T-cell proliferation to the majority of the 69 peptides tested in Mtb responsive adults as well as in BCG-vaccinated infants. CD8(+) T-cells were cytotoxic against target-cells transfected with HLA-E only in the presence of specific peptide. These T cells were also able to lyse M. bovis BCG infected, but not control monocytes, suggesting recognition of antigens during mycobacterial infection. In addition, peptide induced CD8(+) T-cells also displayed regulatory activity, since they inhibited T-cell proliferation. This regulatory activity was cell contact-dependent, and at least partly dependent on membrane-bound TGF-beta. Our results significantly increase our understanding of the human immune response to Mtb by identification of CD8(+) T-cell responses to novel HLA-E binding peptides of Mtb, which have cytotoxic as well as immunoregulatory activity

Major histocompatibility complex (MHC)-mediated immune regulation of decidual leukocytes at the fetal-maternal interface

Self and non-self recognition is the key mechanism by which the immune system determines whether or not to mount an immune response. During pregnancy the maternal immune system must tolerate the persistence of non-self semi-allogeneic fetal cells in the maternal tissue. Although many mechanisms have been shown to contribute to the prevention of a destructive maternal immune response to fetal cells, the immune acceptance of the allogeneic fetus in pregnancy largely remains an immunological paradox (Billingham et al., 1953). The aim of this review is to describe the expression of the polymorphic histocompatibility antigens at the fetal-maternal interface, their interaction with maternal leukocytes and their possible roles in immune regulation at the fetal-maternal interface during human pregnancy.Transplantation and autoimmunit

HLA-C mediated immune regulation at the fetal-maternal interface

Transplantation and autoimmunit

Immunoregulation during human pregnancy

Transplantation and autoimmunit

Perforin-low decidual CD8+T cells are fully functional upon stimulation

Transplantation and autoimmunit