Extrathymic Development Research Articles

Fibrotic liver microenvironment promotes Dll4 and SDF-1-dependent T-cell lineage development

The reconstitution of the T-cell repertoire and quantity is a major challenge in the clinical management of HIV infection/AIDS, cancer, and aging-associated diseases. We previously showed that autologous bone marrow transfusion (BMT) via the hepatic portal vein could effectively restore CD4+ T-cell count in AIDS patients also suffering from decompensated liver cirrhosis. In the current study, we characterized T-cell reconstitution in a mouse model of liver fibrosis induced by CCl4 and found that T-cell reconstitution after BMT via hepatic portal vein was also greatly enhanced. The expression of Dll4 (Delta-like 4), which plays an important role in T-cell progenitor expansion, was elevated in hepatocytes of fibrotic livers when compared to normal livers. This upregulation of Dll4 expression was found to be induced by TNFα in an NFκB-dependent manner. Liver fibroblasts transfected with Dll4 (LF-Dll4) also gained the capacity to promote T-cell lineage development from hematopoietic stem cells (HSCs), resulting in the generation of DN2 (CD4 and CD8 DN 2) and DN3 T-cell progenitors in vitro, which underwent a normal maturation program when adoptively transferred into Rag-2 deficient hosts. We also demonstrated a pivotal role of SDF-1 produced by primary liver fibroblasts (primary LF) in T-lineage differentiation from HSCs. These results suggest that Dll4 and SDF-1 in fibrotic liver microenvironment could promote extrathymic T-cell lineage development. These results expand our knowledge of T-cell development and reconstitution under pathological conditions.

Isolation and Ex Vivo Culture of Vδ1+CD4+γδ T Cells, an Extrathymic αβT-cell Progenitor.

The thymus, the primary organ for the generation of αβ T cells and backbone of the adaptive immune system in vertebrates, has long been considered as the only source of αβT cells. Yet, thymic involution begins early in life leading to a drastically reduced output of naïve αβT cells into the periphery. Nevertheless, even centenarians can build immunity against newly acquired pathogens. Recent research suggests extrathymic αβT cell development, however our understanding of pathways that may compensate for thymic loss of function are still rudimental. γδ T cells are innate lymphocytes that constitute the main T-cell subset in the tissues. We recently ascribed a so far unappreciated outstanding function to a γδ T cell subset by showing that the scarce entity of CD4(+) Vδ1(+)γδ T cells can transdifferentiate into αβT cells in inflammatory conditions. Here, we provide the protocol for the isolation of this progenitor from peripheral blood and its subsequent cultivation. Vδ1 cells are positively enriched from PBMCs of healthy human donors using magnetic beads, followed by a second step wherein we target the scarce fraction of CD4(+) cells with a further magnetic labeling technique. The magnetic force of the second labeling exceeds the one of the first magnetic label, and thus allows the efficient, quantitative and specific positive isolation of the population of interest. We then introduce the technique and culture condition required for cloning and efficiently expanding the cells and for identification of the generated clones by FACS analysis. Thus, we provide a detailed protocol for the purification, culture and ex vivo expansion of CD4(+) Vδ1(+)γδ T cells. This knowledge is prerequisite for studies that relate to this αβT cell progenitor`s biology and for those who aim to identify the molecular triggers that are involved in its transdifferentiation.

Extrathymic αβT cells differentiation

Extrathymic differentiation is an alternative pathway of αsT lymphocyte development. In the normal state, it is expressed slightly and limited mainly by the liver and intestinal mucosa, but it significantly increases with age, as well as under certain physiological and pathological conditions, and acquires more widespread distribution. In the review, phenotypic and functional properties of T lymphocytes of extrathymic origin are examined in detail depending on their localization and activation conditions. Mechanisms of induction of such differentiation are analyzed. Particular attention is paid to the biological significance of extrathymic αsT cell development.

CD5 Instructs Extrathymic Regulatory T Cell Development in Response to Self and Tolerizing Antigens

Self-reactive T cells can escape thymic deletion and therefore some of these potentially autoaggressive T cells need to convert into regulatory T (Treg) cells to help control responses against self. However, it remains unknown how peripheral self-reactive T cells are specifically instructed to become Treg cells. We report that CD5, whose expression is upregulated in T cells by self and tolerizing antigens in the thymus and periphery, governed extrathymic Treg cell development. CD5 modified effector cell-differentiating signals that inhibit Treg cell induction. Treg cell conversion of Cd5(-/-) and CD5(lo) T cells was inhibited by even small amounts of interleukin-4 (IL-4), IL-6, and interferon-γ (IFN-γ) produced by bystander lymphocytes, while CD5(hi) T cells resisted this inhibition of Treg cell induction. Our findings further revealed that CD5 promoted Treg cell induction by blocking mechanistic target of rapamycin (mTOR) activation. Therefore CD5 instructs extrathymic Treg cell development in response to self and tolerizing antigens.

γδ T cells restrain extrathymic development of Foxp3+-inducible regulatory T cells via IFN-γ.

Inducible Treg (iTreg) cells generated from Ag-stimulated naïve CD4(+) T cells in the periphery play an important role in regulating immune responses. TGF-β is a key cytokine that promotes this conversion process; however, how this process is regulated in vivo remains unclear. Here, we report that γδ T cells play a crucial role in controlling iTreg generation and suppressor function. Ag-induced iTreg generation was significantly enhanced in C57BL/6 mice in the absence of γδ T cells. Inhibition of iTreg conversion was mediated by IFN-γ produced by activated γδ T cells but not by activated CD4(+) T cells. BM chimera experiments further confirmed γδ-derived IFN-γ-dependent mechanism in regulating iTreg generation in vivo. Lastly, human peripheral blood γδ T cells also interfere with iTreg conversion via IFN-γ. Our results suggest a novel function of γδ T cells in limiting the generation of iTreg cells, potentially balancing immunity and tolerance.

Delta-Like Notch Ligands Expressed By Host Non-Hematopoietic Radioresistant Cells Regulate Graft-Versus-Host Disease and Extrathymic T Cell Development After Bone Marrow Transplantation

Allogeneic bone marrow transplantation (allo-BMT) is limited by graft-versus-host disease (GVHD). We previously reported an essential role for Notch signaling in alloreactive T cells mediating GVHD after allo-BMT, demonstrating a profound decrease in GVHD incidence and severity with genetic Notch inhibition in donor T cells or systemic antibody-mediated blockade of Delta-like1 (Dll1) and Delta-like4 (Dll4) Notch ligands (Zhang et al., Blood 117(1), 2011; Sandy et al., J Immunol 190(11), 2013; Tran et al., JCI123(4), 2013). However, the cellular source of these critical Notch ligands remains unknown. While host hematopoietic antigen-presenting cells (APCs) seem a likely source, recent evidence indicates that these cells are not solely responsible for donor T cell activation in GVHD. We considered three alternative sources of Notch ligands: donor-derived hematopoietic cells, host hematopoietic APCs surviving lethal irradiation, and host non-hematopoietic radioresistant cells.To test these possibilities, we used complementary genetic and biochemical approaches to inactivate Dll1/Dll4 in specific compartments, or to provide ubiquitous systemic blockade of these ligands. Bone marrow (BM) chimeras were created by transplanting BM from poly(I:C)-induced Mx-Cre+ x Dll1f/fDll4f/f B6-CD45.2 mice into lethally irradiated B6-CD45.1 mice, generating chimeric mice without Dll1 and Dll4 only in the host hematopoietic compartment. After 14 weeks of reconstitution, CD45.2 → CD45.1 turnover was near complete in hematopoietic progenitors and professional APCs. Dll1/Dll4 excision was >99% by qPCR. WT (wild-type) BM chimeras subjected to MHC-mismatched allo-BMT (BALB/c → [Mx-Cre- x Dll1f/fDll4f/f (B6-CD45.2) → B6-SJL CD45.1]) had evidence of severe aGVHD and poor survival, as expected. Interestingly, BM chimera mice lacking Dll1 and Dll4 expression in the host hematopoietic compartment had equally severe GVHD and impaired survival following allo-BMT (BALB/c → [Mx-Cre+ x Dll1f/fDll4f/f (B6-CD45.2) → B6-SJL CD45.1]). In contrast, both WT and Dll1/Dll4-deficient BM chimeras treated with anti-Dll1/Dll4 antibodies (i.p. x4 over days 0-10 of transplant) had markedly decreased GVHD and improved survival (log rank Χ2=30.6, p<0.0001). Anti-Dll1/Dll4 antibodies blocked cytokine production by alloreactive T cells even after transplantation of purified T cells into irradiated recipients, ruling out dominant presentation of Notch ligands by donor-derived professional APCs. We are now backcrossing our Mx-Cre+ x Dll1f/fDll4f/f mice onto a BALB/c background to allow for simultaneous elimination of both donor and host hematopoietic Dll1 and Dll4 expression during allo-BMT. In addition to Notch-dependent regulation of GVHD, we studied immature pre-T cells that arise at extrathymic sites after BMT. We and others have observed Notch-dependent T cell development in lymphoid organs during early T cell reconstitution after transplantation (Lancrin et al., J Exp Med 195(7), 2002; Maillard et al., Blood 107(9), 2006; Holland et al., JCI122(12), 2013). Thus, this phenomenon is an alternative readout for exposure to Notch ligands in the post-BMT environment. Systemic blockade of Dll1 but not Dll4 with neutralizing antibodies completely blocked the development of these cells, indicating strict Dll1-dependence. In contrast, Dll1 elimination in host, donor or both host/donor hematopoietic compartments did not abrogate extrathymic pre-T cell development, consistent with a source of Notch ligands in host radioresistant cells.Altogether, these findings suggest that Notch ligands expressed by radio-resistant non-hematopoietic host tissues have important immunobiological functions during GVHD and T cell reconstitution. Identifying the cellular source of Delta-like ligands is critical to understand the effects of Notch signaling after bone marrow transplantation. Disclosures:Yan:Genentech, Inc: Employment. Siebel:Genentech, Inc: Employment.

Making T cells functional: a new solution for the athymic BMT recipients

Thymus has long been known to be the site of T cell development and is required for the generation of a T cell repertoire1. However, the adult bone marrow transplant (BMT) or the elderly patients suffer from a loss of thymic function resulting in low T cell production, susceptibility to infection and tumour, and a poor survival for a diversity of diseases2. Increasing thymic function and/or extrathymic T-cell development can thus play an important role in patients with limited thymic function. The development and maturation of T cells involve a complex variety of interactions with nonlymphoid cell products and receptors. Generally, T cell progenitors originate in the bone marrow and, through a series of defined and coordinated developmental stages, enter the thymus, differentiate, undergo selection, and eventually mature into functional T cells (Figure 1A). Numbers of studies have indicated that T cells can develop outside the thymus3,4. However, it is controversial in disparate model systems and unclear if these cells are fully functional. The potential for extrathymic development to restore T cell immunity after BMT is poorly defined.

Extrathymic development of murine T cells after bone marrow transplantation

Restoring T cell competence is a significant clinical challenge in patients whose thymic function is severely compromised due to age or cytoreductive conditioning. Here, we demonstrate in mice that mesenteric LNs (MLNs) support extrathymic T cell development in euthymic and athymic recipients of bone marrow transplantation (BMT). Furthermore, in aged murine BMT recipients, the contribution of the MLNs to the generation of T cells was maintained, while the contribution of the thymus was significantly impaired. Thymic impairment resulted in a proportional increase in extrathymic-derived T cell progenitors. Extrathymic development in athymic recipients generated conventional naive TCRαβ T cells with a broad Vβ repertoire and intact functional and proliferative potential. Moreover, in the absence of a functional thymus, immunity against known pathogens could be augmented using engineered precursor T cells with viral specificity. These findings demonstrate the potential of extrathymic T cell development for T cell reconstitution in patients with limited thymic function.

The case for extrathymic development of vaginal T lymphocytes

The vaginal tract mucosa is populated by a small, yet phenotypically diverse and functionally significant, subset of T cells that plays a major role in local cell-mediated immunity. Although phenotypic and functional characteristics of vaginal T cells have received some attention in recent years, little is known about the development of this cell population. In this mini review, the developmental origins of vaginal T cells are traced from published work related to vaginal T cells, the vaginal mucosa environment and vaginal tract infection animal models. A CD3 +TCR +CD2 +CD5 +B220 − (CD3 +B220 −) subpopulation, which is mostly CD4 +, makes up 30–40% of vaginal T lymphocytes. This population consists of a TCRαβ + subset and TCRγδ + subset. While CD3 +B220 −TCRαβ + vaginal T cells exhibit phenotypic and functional properties consistent with that of peripheral T cells, CD3 +B220 −TCRγδ + vaginal T cells exhibit unique phenotypic and functional features that set them apart from other TCRγδ + T cell subsets populating the periphery or other mucosal areas. The vaginal mucosa is populated also by CD3 +TCRαβ +CD4 −/8 −B220 +CD2 −CD5 − T cells (CD3 +B220 +) whose relative predominance increases significantly in systemic T cell deficiency. This subset is generally unresponsive to TCR-mediated stimuli and expresses high levels of CD25, perhaps indicative of a regulatory role. Current data suggest that, while CD3 +B220 − vaginal T cells are mostly thymic in origin, CD3 +TCRαβ +B220 + cells are exclusively extrathymic.

Curriculum vitae of intestinal intraepithelial T cells: their developmental and behavioral characteristics

The alimentary tract has an epithelial layer, consisting mainly of intestinal epithelial cells (IECs), that is exposed to the exterior world through the intestinal lumen. The IEC layer contains many intestinal intraepithelial T cells (IELs), and the total number of IELs constitutes the largest population in the peripheral T-cell pool. Virtually all gammadelta-IELs and many alphabeta-IELs in the mouse small intestine are known to express CD8 alpha alpha homodimers. A wide range of evidence that supports extrathymic development of these CD8 alpha alpha(+) IELs has been collected. In addition, while several studies identified cells with precursor T-cell phenotypes within the gut epithelium, how these precursors, which are dispersed along the length of the intestine, develop into gammadelta-IELs and/or alphabeta-IELs has not been clarified. The identification of lymphoid cell aggregations named 'cryptopatches' (CPs) in the intestinal crypt lamina propria of mice as sites rich in T-cell precursors in 1996 by our research group, however, provided evidence for a central site, whereby precursor IELs could give rise to T-cell receptor-bearing IELs. In this review, we discuss the development of IELs in the intestinal mucosa and examine the possibility that CPs serve as a production site of extrathymic IELs.

Thrombospondin/CD47 Interaction: A Pathway to Generate Regulatory T Cells from Human CD4+CD25− T Cells in Response to Inflammation

Thymus-derived CD4+ CD25+ T regulatory cells (Tregs) are essential for the maintenance of self-tolerance. What critical factors and conditions are required for the extra-thymic development of Tregs remains an important question. In this study, we show that the anti-inflammatory extracellular matrix protein, thrombospondin-1, promoted the generation of human peripheral regulatory T cells through the ligation of one of its receptor, CD47. CD47 stimulation by mAb or a thrombospondin-1 peptide induced naive or memory CD4+ CD25- T cells to become suppressive. The latter expressed increased amounts of CTLA-4, OX40, GITR, and Foxp3 and inhibited autologous Th0, Th1, and Th2 cells. Their regulatory activity was contact dependent, TGF-beta independent, and partially circumvented by IL-2. This previously unknown mechanism to induce human peripheral Tregs in response to inflammation may participate to the limitation of collateral damage induced by exacerbated responses to self or foreign Ags and thus be relevant for therapeutic intervention in autoimmune diseases and transplantation.

Organizing a mucosal defense

Gastrointestinal associated lymphoid tissue can be divided into loosely organized effector sites, which include the lamina propria and intraepithelial lymphocytes, and more organized structures, such as mesenteric lymph nodes (LNs), Peyer's patches (PPs), isolated lymphoid follicles, and cryptopatches (CPs). These organized structures in the gastrointestinal tract have been hypothesized to play the role of primary lymphoid organ, supporting the extrathymic development of T lymphocytes (CPs), secondary lymphoid organs involved in the induction of the mucosal immune response (PPs), and tertiary lymphoid structures whose function is still under debate (isolated lymphoid follicles). The most widely studied lymphoid structure found in the small intestine is the PP. PPs are secondary lymphoid structures, and their development and function have been extensively investigated. However, single lymphoid aggregates resembling PPs have been also described in humans and in the murine small intestines. These isolated lymphoid follicles have both germinal centers and an overlying follicle-associated epithelium, suggesting that they also can function as inductive sites for the mucosal immune response. This review compares and contrasts the development and function of the four main organized gastrointestinal lymphoid tissues: CPs, isolated lymphoid follicles, PPs, and mesenteric LNs.

Interleukin-7 Receptor is Indispensable for Proliferation and Survival in Thymic γδT Cell Development

Interleukin-7 receptor (IL-7R) α-deficient mice have small numbers of B cells and αβT cells in periphery, they totally lack γδT cells. In addition, the V-J recombination and transcription of TCR γ genes is also severely impaired in IL-7R α-deficient mice. Stat5, a signaling molecule of the IL-7R, induces germline transcription in the TCR γ locus, and promotes V-J recombination and γδT cell development. However, the roles for IL-7R signaling pathway in thymic or extrathymic γδT cell development are largely unknown. Methods: To clarify the role of the IL-7 receptor in proliferation and survival of γδT cells, we introduced the TCR γδ transgene, V γ2 /Vδ 5 , into IL-7R α-deficient mice, and investigated the development of γδT cells. Results: We found that V γ2 /Vδ 5 transgene restored γδT cells in the epithelium of the small intestine (IEL) but not in the thymus and the spleen. Further addition of a bcl-2 transgene resulted in partial recovery of γδT cells in the thymus and the spleen of these mice. Conclusion: Taken together, this study revealed that the IL-7R α is indispensable for proliferation and survival mainly in thymic γδT cell development.

Lymphoid precursors in intestinal cryptopatches express CCR6 and undergo dysregulated development in the absence of CCR6.

Small intestinal cryptopatches (CP) are the major anatomic site for extrathymic differentiation by precursors destined to become intestinal intraepithelial T lymphocytes (IEL). We found that mice deficient in CCR6 exhibited a 2.7-fold increase in the number of alphabeta TCR IEL, but little or no expansion of gammadelta TCR IEL. Among the alphabeta TCR IEL subsets, the CD4- CD8alphaalpha+ and CD4+ CD8alphaalpha+ subsets were preferentially expanded in CCR6 null mice. Because some CD8alphaalpha+ IEL can arise through extrathymic differentiation in CP, we investigated CCR6 expression by T lymphocyte precursors undergoing extrathymic differentiation in intestinal CP. In sections of CP, 50-60% of c-kit+ precursors were CCR6+. CD11c(+) cells concentrated at the periphery of CP did not express CCR6. A subset of c-kit+, Lin- cells in lamina propria suspensions was CCR6+, but CCR6 was absent from c-kit+ precursors in bone marrow. CCR6 was absent from the vast majority of mature IEL. CCR6 is present on lymphocyte precursors in cryptopatches, expressed transiently during extrathymic IEL development, and is required for homeostatic regulation of intestinal IEL.

Extrathymic T-lymphocyte development.

Chronic exposure to oncostatin M (OM) induces massive thymus-independent extrathymic T-cell development, which takes place solely in the lymph nodes (LN), probably because of the high density of OM receptor on LN postcapillary venules. In contrast to what is observed in other models of extrathymic T-cell development, the proportions of double-negative (DN), double-positive (DP), and single-positive (SP) T cells in the OM+ LN reproduce those found in a thymus, and the T-cell receptor (TCR) repertoire of the SP cells is diversified. Analyses of T-cell development in hematopoietic chimeras expressing MHC class I only on hematopoietic or non-hematopoietic cells showed that MHC class I on hematopoietic cells was sufficient for positive selection of a diversified repertoire of CD8 T cells. However, studies of TCR-transgenic mice revealed that the hierarchy of TCR clonotype selection is not the same as in the thymus. Even though there is no cortico-medullary segregation in the OM+ LN, negative selection of T cells bearing the 2C and the anti-H-Y TCR was very effective. The progeny of the thymic-independent differentiation pathway regulated by OM is polyclonal in terms of Vβ usage, exhibits an activated-memory phenotype, and displays a rapid turnover rate. Following TCR ligation, extrathymic T cells begin to proliferate earlier than thymus-derived T cells, but their expansion is limited by a high apoptosis rate. This model provides a unique opportunity to elucidate critical interactions between T cell progenitors and stromal cells, that is, the essence of a primary T lymphoid organ.“We shall come to regard the presence of lymphocytes in the thymus as an evolutionary accident of no very great significance [1].”—P.B. Medawar (Nobel Prize in Medicine, 1960)

Reciprocal expression of CCR6 and CXCR3 chemokine receptors during intestinal extrathymic IEL development

Reciprocal expression of CCR6 and CXCR3 chemokine receptors during intestinal extrathymic IEL development

Intrathymic and extrathymic development of human plasmacytoid dendritic cell precursors in vivo

AbstractThe development of plasmacytoid dendritic cells (pDC2) from human CD34+ stem cells in vivo was studied in RAG-2−/− interleukin (IL)-2Rγ−/− mice that lack functional T and B cells and natural killer cells. CD34+ cells isolated from fetal liver or thymus were labeled with 5- and 6-carboxyfluorescein diacetate succinimidyl ester (CFSE) and were injected into a human thymus grafted subcutaneously in the RAG-2−/− IL-2Rγ−/− mice. One to 4 weeks later the CFSE label was found not only in T cells but also in CD123+/high CD4+CD45RA+ pDC2, indicating that the CD34+ cells can develop into pDC2 within a thymus. In addition to pDC2, CFSE-labeled dendritic cells with a mature phenotype, determined by the cell surface markers CD11c, CD83, and CD80, were found in the injected human thymus graft. pDC2 was not found in the periphery of mice carrying a human thymic graft, indicating that the intrathymic pDC2 failed to emigrate from the thymus. We also demonstrate that pDC2 can develop outside the thymus because relatively high percentages of pDC2 were found in the periphery after the intravenous injection of CD34+CD38−fetal liver cells in RAG-2−/− IL-2Rγ−/−mice without a human thymus graft. These data indicate that the thymus and the peripheral pDC2 develop independently of each other.

Evidence for the extrathymic origin of intestinal TCRgammadelta(+) T cells in normal rats and for an impairment of this differentiation pathway in BB rats.

The BB rat lyp mutation, one of its diabetes susceptibility genes, is responsible for a 5-fold decrease in the number of peripheral TCRalphabeta(+) T cells. In this study we show that TCRgammadelta(+) T cells are virtually undetectable among splenic T cells and intestinal intraepithelial T lymphocytes (IEL) of BB rats, while they account for 3 and 30% of these two T cell populations, respectively, in normal animals. It has been shown that murine IEL expressing TCRgammadelta develop extrathymically. We determined whether this is the case in rats. Athymic radiation chimeras reconstituted with normal hemopoietic precursors were devoid of donor-derived TCRalphabeta(+) T cells and TCRgammadelta(+) splenocytes but contained a normal number of TCRgammadelta(+) IEL, suggesting that in unmanipulated rats some of the TCRgammadelta(+) IEL may have an extrathymic origin. This was further supported by the observation that RAG1 transcripts are present in IEL of unmanipulated animals. No T cells developed in chimeras reconstituted with BB hemopoietic precursors, demonstrating that the BB rat lyp mutation inhibits both intrathymic and extrathymic development of TCRgammadelta(+) T cells.

Evidence of the extrathymic development of tyrosinase‐related protein‐2‐recognizing CD8+ T cells with low avidity

The majority of the human tumour-associated antigens characterized to date are derived from non-mutated self-proteins. However, nothing is known about the development of autoreactive and tumour-associated antigen-recognizing T cells. Tyrosinase-related protein (TRP)-2 is a non-mutated melanocyte differentiation antigen and TRP-2-recognizing CD8+ T cells are known to show responses to melanoma both in humans and mice. In addition, TRP-2-reactive T cells with low avidity have been suggested to be readily induced from the spleen cells of naïve mice. On the other hand, recent reports suggest that self antigen-reactive CD8+ T cells can be positively selected in the periphery. In this study, we tested the possibility that TRP-2-reactive CD8+ T cells in naïve mice could develop via the extrathymic pathway. As a consequence, TRP-2-reactive CD8+ T cell precursors in naïve C57BL/6 mice were suggested to express both interleukin-2 (IL-2) receptor beta chain (IL-2Rbeta) and CD44 molecules, in a manner similar to that of extrathymically developed T cells. Furthermore, IL-2Rbeta+ CD44+ CD8+ T cells were detected in the adult thymectomized and bone marrow-reconstituted mice, and functional TRP-2-reactive T cells were generated from their spleen cells. Overall, these results suggest that low avidity CD8+ T cells recognizing TRP-2 can be developed extrathymically.

Extrathymic development of V alpha 11 T cells in placenta during pregnancy and their possible physiological role.

The molecular and cellular mechanisms of the feto-maternal immune responses in the placenta in connection with natural abortion remain unclear. In this report we provide evidence that V(alpha11) T cells developed in the placenta may be responsible for the induction of natural abortion. The majority of V(alpha11) TCRs detected during pregnancy showed a consensus motif in the CDR3 region, similar to that of anti-GM3 TCR clones, and were of maternal origin. V(alpha11) TCRs were found in the middle to late stages of gestation due to de novo generation in the placenta, not to migration from the maternal side, as evidenced by the significant increases in the out-of-frame V(alpha11) TCR mRNA and the copy number of circular DNA generated by V(alpha11) gene rearrangements. Furthermore, administration of anti-V(alpha11) Ab to pregnant mice resulted in a significant decrease in the incidence of fetal demise, suggesting that V(alpha11) T cells detected in the placenta develop extrathymically and are involved in natural abortion.