Lisa Föhse

CCR6 and NK1.1 distinguish between IL‐17A and IFN‐γ‐producing γδ effector T cells

γδ T cells are a potent source of innate IL‐17A and IFN‐γ, and they acquire the capacity to produce these cytokines within the thymus. However, the precise stages and required signals that guide this differentiation are unclear. Here we show that the CD24low CD44high effector γδ T cells of the adult thymus are segregated into two lineages by the mutually exclusive expression of CCR6 and NK1.1. Only CCR6+ γδ T cells produced IL‐17A, while NK1.1+ γδ T cells were efficient producers of IFN‐γ but not of IL‐17A. Their effector phenotype correlated with loss of CCR9 expression, particularly among the NK1.1+ γδ T cells. Accordingly, both γδ T‐cell subsets were rare in gut‐associated lymphoid tissues, but abundant in peripheral lymphoid tissues. There, they provided IL‐17A and IFN‐γ in response to TCR‐specific and TCR‐independent stimuli. IL‐12 and IL‐18 induced IFN‐γ and IL‐23 induced IL‐17A production by NK1.1+ or CCR6+ γδ T cells, respectively. Importantly, we show that CCR6+ γδ T cells are more responsive to TCR stimulation than their NK1.1+ counterparts. In conclusion, our findings support the hypothesis that CCR6+ IL‐17A‐producing γδ T cells derive from less TCR‐dependent selection events than IFN‐γ‐producing NK1.1+ γδ T cells.

Age, microbiota, and T cells shape diverse individual IgA repertoires in the intestine

High-throughput sequencing reveals stability of the intestinal IgA repertoire after plasma cell depletion and changes in repertoire diversity with age and microbial colonization.

CCR6 and NK1.1 distinguish between IL-17A and IFN-gamma-producing gammadelta effector T cells.

γδ T cells are a potent source of innate IL‐17A and IFN‐γ, and they acquire the capacity to produce these cytokines within the thymus. However, the precise stages and required signals that guide this differentiation are unclear. Here we show that the CD24low CD44high effector γδ T cells of the adult thymus are segregated into two lineages by the mutually exclusive expression of CCR6 and NK1.1. Only CCR6+ γδ T cells produced IL‐17A, while NK1.1+ γδ T cells were efficient producers of IFN‐γ but not of IL‐17A. Their effector phenotype correlated with loss of CCR9 expression, particularly among the NK1.1+ γδ T cells. Accordingly, both γδ T‐cell subsets were rare in gut‐associated lymphoid tissues, but abundant in peripheral lymphoid tissues. There, they provided IL‐17A and IFN‐γ in response to TCR‐specific and TCR‐independent stimuli. IL‐12 and IL‐18 induced IFN‐γ and IL‐23 induced IL‐17A production by NK1.1+ or CCR6+ γδ T cells, respectively. Importantly, we show that CCR6+ γδ T cells are more responsive to TCR stimulation than their NK1.1+ counterparts. In conclusion, our findings support the hypothesis that CCR6+ IL‐17A‐producing γδ T cells derive from less TCR‐dependent selection events than IFN‐γ‐producing NK1.1+ γδ T cells.

High TCR diversity ensures optimal function andhomeostasis of Foxp3+ regulatory Tcells

Dominant tolerance to self‐antigen requires the presence of sufficient numbers of CD4+Foxp3+ Treg cells with matching antigen specificity. However, the size and role of TCR repertoire diversity for antigen‐specific immuno‐regulation through Treg cells is not clear. Here, we developed and applied a novel high‐throughput (HT) TCR sequencing approach to analyze the TCR repertoire of Treg cells and revealed the importance of high diversity for Treg‐cell homeostasis and function. We found that highly polyclonal Treg cells from WT mice vigorously expanded after adoptive transfer into non‐lymphopenic TCR‐transgenic recipients with low Treg‐cell diversity. In that system, we identified specific Treg‐cell TCR preferences in distinct anatomic locations such as the mesenteric LN indicating that Treg cells continuously compete for MHC class‐II‐presented self‐, food‐, or flora‐antigen. Functionally, we showed that high TCR diversity was required for optimal suppressive function of Treg cells in experimental acute graft versus host disease (GvHD). In conclusion, we suggest that efficient immuno‐regulation by Treg cells requires high TCR diversity. Thereby, continuous competition of peripheral Treg cells for limited self‐antigen shapes an organ‐optimized, yet highly diverse, local TCR repertoire.

IFN-γ Production by Allogeneic Foxp3+ Regulatory T Cells Is Essential for Preventing Experimental Graft-versus-Host Disease

It is emerging that CD4+Foxp3+ regulatory T (Treg) cells can produce the proinflammatory cytokine IFN-γ when stimulated in a Th1 cytokine environment. In this study, we report that Foxp3+ Treg cells readily produced IFN-γ in vivo in a highly inflammatory model of graft-versus-host disease (GVHD) and during a Th1-dominated immune response to intracellular bacteria. Moreover, stimulation in vitro via TCR in the presence of IL-12 alone was sufficient to induce IFN-γ production by Treg cells in a dose-dependent manner. Transfer of donor Treg cells can prevent lethal GVHD; therefore, we used this model as a robust readout for in vivo Treg function. Interestingly, >50% of allogeneic donor, but not residual recipient Foxp3+ Treg cells produced IFN-γ after transplantation, suggesting that this cytokine production was alloantigen specific. These IFN-γ producers were stable Foxp3+ Treg cells because methylation analysis of the Foxp3 gene locus of transferred and reisolated Treg cells during GVHD showed a fully demethylated Treg-specific–demethylated region. Next, we addressed whether IFN-γ production was supporting or rather impairing the immunosuppressive function of Treg cells during GVHD. Blocking of IFN-γ with specific mAb completely abolished the beneficial effect of donor Treg cells. We could further show that only wild-type Treg cells, but not Treg cells from IFN-γ–deficient donor mice, prevented GVHD. This indicated that Treg cell-intrinsic IFN-γ production was required for their protective function. In conclusion, our data show that IFN-γ produced by Foxp3+ Treg cells has essential immune-regulatory functions that are required for prevention of experimental GVHD.

Foxp3 + T cells expressing RORγt represent a stable regulatory T-cell effector lineage with enhanced suppressive capacity during intestinal inflammation

Foxp3 (forkhead box P3 transcription factor)-expressing regulatory T cells (Tregs) are essential for immunological tolerance, best illustrated by uncontrolled effector T-cell responses and autoimmunity upon loss of Foxp3 expression. Tregs can adopt specific effector phenotypes upon activation, reflecting the diversity of functional demands in the different tissues of the body. Here, we report that Foxp3+CD4+ T cells coexpressing retinoic acid-related orphan receptor-γt (RORγt), the master transcription factor for T helper type 17 (Th17) cells, represent a stable effector Treg lineage. Transcriptomic and epigenetic profiling revealed that Foxp3+RORγt+ T cells display signatures of both Tregs and Th17 cells, although the degree of similarity was higher to Foxp3+RORγt− Tregs than to Foxp3−RORγt+ T cells. Importantly, Foxp3+RORγt+ T cells were significantly demethylated at Treg-specific epigenetic signature genes such as Foxp3, Ctla-4, Gitr, Eos, and Helios, suggesting that these cells have a stable regulatory rather than inflammatory function. Indeed, adoptive transfer of Foxp3+RORγt+ T cells in the T-cell transfer colitis model confirmed their Treg function and lineage stability in vivo, and revealed an enhanced suppressive capacity as compared with Foxp3+RORγt− Tregs. Thus, our data suggest that RORγt expression in Tregs contributes to an optimal suppressive capacity during gut-specific immune responses, rendering Foxp3+RORγt+ T cells as an important effector Treg subset in the intestinal system.

Induced and thymus‐derived Foxp3+ regulatory T cells share a common niche

Foxp3+ regulatory T (Treg) cells, which play a central role for the maintenance of immune homeostasis and self‐tolerance, are known to be both generated in the thymus (thymus‐derived, tTreg cells) and in the periphery, where they are converted from conventional CD4+ T cells (induced Treg (iTreg) cells). Recent data suggest a division of labor between these two Treg‐cell subsets since their combined action was shown to be essential for protection in inflammatory disease models. Here, using the transfer colitis model, we examined whether tTreg cells and iTreg cells fill different niches within the CD4+ T‐cell compartment. When naive T cells were co‐transferred with either pure tTreg cells or with a mixture of tTreg cells and iTreg cells, induction of Foxp3+ Treg cells from naive T cells was not hampered by preoccupation of the Treg‐cell niche. Using neuropilin‐1 (Nrp1) as a surface marker to separate tTreg cells and iTreg cells, we demonstrate that tTreg cells and iTreg cells alone can completely fill the Treg‐cell niche and display comparable TCR repertoires. However, when transferred together Nrp1+ tTreg cells outcompeted Nrp1− iTreg cells and dominated the Treg‐cell compartment. Taken together, our data suggest that tTreg cells and iTreg cells share a common peripheral niche.

A clonotypic Vγ4Jγ1/Vδ5Dδ2Jδ1 innate γδ T-cell population restricted to the CCR6+CD27− subset

Here we investigate the TCR repertoire of mouse Vγ4(+) γδ T cells in correlation with their developmental origin and homeostasis. By deep sequencing we identify a high frequency of straight Vδ5Dδ2Jδ1 germline rearrangements without P- and N-nucleotides within the otherwise highly diverse Trd repertoire of Vγ4(+) cells. This sequence is infrequent in CCR6(-)CD27(+) cells, but abundant among CCR6(+)CD27(-) γδ T cells. Using an inducible Rag1 knock-in mouse model, we show that γδ T cells generated in the adult thymus rarely contain this germline-rearranged Vδ5Dδ2Jδ1 sequence, confirming its fetal origin. Single-cell analysis and deep sequencing of the Trg locus reveal a dominant CDR3 junctional motif that completes the TCR repertoire of invariant Vγ4(+)Vδ5(+) cells. In conclusion, this study identifies an innate subset of fetal thymus-derived γδ T cells with an invariant Vγ4(+)Vδ5(+) TCR that is restricted to the CCR6(+)CD27(-) subset of γδ T cells.

Differential Postselection Proliferation Dynamics of αβ T Cells, Foxp3+ Regulatory T Cells, and Invariant NKT Cells Monitored by Genetic Pulse Labeling

The thymus generates two divergent types of lymphocytes, innate and adaptive T cells. Innate T cells such as invariant NKT cells provide immediate immune defense, whereas adaptive T cells require a phase of expansion and functional differentiation outside the thymus. Naive adaptive T lymphocytes should not proliferate much after positive selection in the thymus to ensure a highly diverse TCR repertoire. In contrast, oligoclonal innate lymphocyte populations are efficiently expanded through intrathymic proliferation. For CD4+Foxp3+ regulatory T cells (Tregs), which are thought to be generated by agonist recognition, it is not clear whether they proliferate upon thymic selection. In this study, we investigated thymic and peripheral T cell proliferation by genetic pulse labeling. To this end, we used a mouse model in which all developing αβ thymocytes were marked by expression of a histone 2B–enhanced GFP (H2BeGFP) fusion-protein located within the Tcrd locus (TcrdH2BeGFP). This reporter gene was excised during TCR α-chain VJ-recombination, and the retained H2BeGFP signal was thus diluted upon cell proliferation. We found that innate T cells such as CD1d-restricted invariant NKT cells all underwent a phase of intense intrathymic proliferation, whereas adaptive CD4+ and CD8+ single-positive thymocytes including thymic Tregs cycled, on average, only once after final selection. After thymic exit, retention or loss of very stable H2BeGFP signal indicated the proliferative history of peripheral αβ T cells. There, peripheral Tregs showed lower levels of H2BeGFP compared with CD4+Foxp3− T cells. This further supports the hypothesis that the Treg repertoire is shaped by self-Ag recognition in the steady-state.

Limited niche availability suppresses murine intrathymic dendritic-cell development from noncommitted progenitors

The origins of dendritic cells (DCs) and other myeloid cells in the thymus have remained controversial. In this study, we assessed developmental relationships between thymic dendritic cells and thymocytes, employing retrovirus-based cellular barcoding and reporter mice, as well as intrathymic transfers coupled with DC depletion. We demonstrated that a subset of early T-lineage progenitors expressed CX3CR1, a bona fide marker for DC progenitors. However, intrathymic transfers into nonmanipulated mice, as well as retroviral barcoding, indicated that thymic dendritic cells and thymocytes were largely of distinct developmental origin. In contrast, intrathymic transfers after in vivo depletion of DCs resulted in intrathymic development of non-T-lineage cells. In conclusion, our data support a model in which the adoption of T-lineage fate by noncommitted progenitors at steady state is enforced by signals from the thymic microenvironment unless niches promoting alternative lineage fates become available.