Siegfried Kohler

Depletion of autoreactive immunologic memory followed by autologous hematopoietic stem cell transplantation in patients with refractory SLE induces long-term remission through de novo generation of a juvenile and tolerant immune system

Clinical trials have indicated that immunoablation followed by autologous hematopoietic stem cell transplantation (ASCT) has the potential to induce clinical remission in patients with refractory systemic lupus erythematosus (SLE), but the mechanisms have remained unclear. We now report the results of a single-center prospective study of long-term immune reconstitution after ASCT in 7 patients with SLE. The clinical remissions observed in these patients are accompanied by the depletion of autoreactive immunologic memory, reflected by the disappearance of pathogenic anti-double-stranded DNA (dsDNA) antibodies and protective antibodies in serum and a fundamental resetting of the adaptive immune system. The latter comprises recurrence of CD31(+)CD45RA(+)CD4(+) T cells (recent thymic emigrants) with a doubling in absolute numbers compared with age-matched healthy controls at the 3-year follow-up (P = .016), the regeneration of thymic-derived FoxP3(+) regulatory T cells, and normalization of peripheral T-cell receptor (TCR) repertoire usage. Likewise, responders exhibited normalization of the previously disturbed B-cell homeostasis with numeric recovery of the naive B-cell compartment within 1 year after ASCT. These data are the first to demonstrate that both depletion of the autoreactive immunologic memory and a profound resetting of the adaptive immune system are required to reestablish self-tolerance in SLE.

Life after the thymus: CD31+ and CD31- human naive CD4+ T-cell subsets.

Early in life, thymic export establishes the size and the diversity of the human naive T-cell pool. Yet, on puberty thymic activity drastically decreases. Because the overall size of the naive T-cell pool decreases only marginally during ageing, peripheral postthymic expansion of naive T cells has been postulated to account partly for the maintenance of T-cell immunity in adults. So far, the analysis of these processes had been hampered by the inability to distinguish recent thymic emigrants from proliferated, peripheral, naive T cells. However, recently, CD31 has been introduced as a marker to distinguish 2 subsets of naive CD4(+) T cells with distinct T-cell receptor excision circle (TREC) content in the peripheral blood of healthy humans. Here, we review studies that have characterized TREC(hi) CD31(+ thymic)naive CD4(+) T cells and have accordingly used the assessment of this distinct subset of naive CD4(+) T cells as a correlate of thymic activity. We will discuss further potential clinical applications and how more research on CD31(+ thymic)naive and CD31(- central)naive CD4(+) T cells may foster our knowledge of the impact of thymic involution on immune competence.

Activation of human NK cells by plasmacytoid dendritic cells and its modulation by CD4+ T helper cells and CD4+ CD25hi T regulatory cells

Plasmacytoid dendritic cells (pDC) represent a specialized cell population that produce type I interferon (IFN) in response to virus. Although type I IFN is a natural killer (NK) cell modulator, a direct role for pDC in coordinating NK cell functions has not yet been elucidated in detail, especially in humans. Here we report that human pDC, following engagement of Toll‐like receptor (TLR) 9, not only activate autologous NK cells, as indicated by the induction of CD69 expression, but also enhance their effector functions, especially cytotoxicity. Moreover, they can induce selective proliferation of CD56bright CD16– NK cells. This activity can be strongly augmented by the addition of autologous CD4+ CD25– T helper cells in an IL‐2‐dependent fashion. Strikingly, CD4+ CD25hi T regulatory (Treg) cells completely abrogate this IL‐2‐dependent proliferation of NK cells, while they are not able to influence NK cell activation or proliferation solely induced by pDC. Our data show that TLR9‐engaged pDC represent a critical stimulus for human NK cells and that CD4+ Th cells and CD4+ CD25hi Treg cells play an important role in modulating human NK cell responses.

Post-thymic in vivo proliferation of naive CD4 + T cells constrains the TCR repertoire in healthy human adults

In spite of thymic involution early in life, the numbers of naive CD4+ T cells only slowly decline in ageing humans implying peripheral post‐thymic naive CD4+ T cell expansion. This proliferation may compensate for continuous activation and death of naive CD4+ T cells but may also have negative consequences for protective immunity. Here we show that naive CD4+ T cells that have proliferated in the periphery are characterized by a highly restricted oligoclonal TCR repertoire. Additionally these cells, which constitute the majority of naive CD4+ T cells in the elderly, display signatures of recent TCR engagement. Our results demonstrate for the first time that peripheral post‐thymic proliferation of naive CD4+ T cells in healthy human individuals causes a significant contraction of the peripheral TCR repertoire. This age‐dependent deterioration of CD4+ T cell immunity could entail ageing‐associated autoimmunity, increased susceptibility to infection or cancer and decreased efficiency of vaccination.

Foxp3+ Helios+ regulatory T cells are expanded in active systemic lupus erythematosus

Objectives Recent data debate the suitability of Helios, an Ikaros family member, as a marker for thymic-derived regulatory T cells (Treg). Nevertheless, Foxp3+ Helios+ Treg may be of particular relevance in mediating immune tolerance in chronic autoimmunity, such as systemic lupus erythematosus (SLE), as they possess enhanced suppressive function, compared to Foxp3+ Helios− Treg. Methods Multicolour flow cytometry was performed to analyse Foxp3 and Helios expression in peripheral blood CD4 T cells from SLE patients, compared to healthy controls (HC) and systemic sclerosis (SSc) and rheumatoid arthritis (RA) patients. Cytokine production, chemokine receptor expression for CXCR3 and CCR4, basal signal transducer and activator of transcription 5 (STAT5)a phosphorylation levels and T-cell receptor (TCR) Vβ repertoire were analysed by flow cytometry, and the methylation status of the Foxp3 locus (Treg-specific demethylated region, TSDR) by real-time PCR. Results Frequencies of Foxp3+ Helios+ Treg, unlike Foxp3+ Helios− T cells, were significantly increased in SLE patients and positively correlated with disease activity, whereas they were unaltered in SSc and RA patients. Compared to HC, Foxp3+ Helios+ Treg in SLE predominantly displayed a CD45RA−/CD31−/FoxP3low memory phenotype with increased Ki-67 expression, enhanced basal pSTAT5a levels and a restricted TCR repertoire. Nonetheless, similar to HC, Foxp3+ Helios+ Treg in SLE lacked effector cytokine production, possessed a highly demethylated TSDR and expressed comparable levels of CXCR3 and CCR4. Conclusions Our data suggest that Helios-expressing Foxp3+ Treg with functional suppressive capacity and migratory potential into inflamed tissues are expanded in active SLE, presumably through γ-chain signalling cytokines and TCR stimulation, to compensate for autoreactive effector responses.

A Converse 4-1BB and CD40 Ligand Expression Pattern Delineates Activated Regulatory T Cells (Treg) and Conventional T Cells Enabling Direct Isolation of Alloantigen-Reactive Natural Foxp3+ Treg

Natural regulatory T cells (nTreg) play a central role in the induction and maintenance of immunological tolerance. Experimental transplant models and recent clinical trials demonstrate that nTreg can control alloreactivity. To upgrade Treg-based cell therapies to a selective suppression of undesired immune reactions, only the transfer of Ag-specific nTreg represents the appropriate therapeutic option. However, Ag-specific nTreg are present at extremely low frequencies in the periphery, and so far appropriate surface markers for their precise identification are missing. In this study, we demonstrate that activated nTreg and activated conventional T cells differ in their 4-1BB and CD40 ligand (CD40L) expression signatures, allowing a clear dissection from each other. Based on the expression of 4-1BB and absence of CD40L expression, human alloantigen-reactive Foxp3+ nTreg can be directly isolated from MLR cultures with high purity. Alloantigen-reactive 4-1BB+CD40L− nTreg were characterized by a completely demethylated Treg-specific demethylated region and showed alloantigen-specific suppressive properties superior to polyclonal Treg. Importantly, isolated 4-1BB+CD40L− nTreg maintain the nTreg phenotype and alloantigen-reactivity after in vitro expansion. Our results offer the possibility to simultaneously analyze Ag-specific nTreg and conventional T cells, and to establish cellular therapies with Ag-specific nTreg aiming at a specific inhibition of unwanted immunity.

Cytokine-induced human IFN-γ–secreting effector-memory Th cells in chronic autoimmune inflammation

T-helper (Th) cells activated by cytokines in the absence of T-cell receptor ligation are suspected to participate in inflammatory processes by production of interferon-gamma (IFN-gamma). Still, the relevance of such a mechanism has not been addressed in humans. Here we demonstrate that a subset of human effector-memory Th cells expressing functional interleukin-12R (IL-12R), IL-18Ralpha, and CCR5 ex vivo can be induced to secrete IFN-gamma by cytokines signaling via the IL-2R common gamma-chain in combination with IL-12 and IL-18. Cytokine-driven IFN-gamma production depends on JAK3- and p38 mitogen-activated kinase signals and is sensitive to suppression by CD25(++) regulatory T cells. Contrary to IFN-gamma(+) Th cells induced upon antigen-specific stimulation, their cytokine-activated counterparts characteristically lack expression of costimulator 4-1BB (CD137). Strikingly, the majority of Th cells infiltrating inflamed joints of rheumatoid arthritis patients is equipped with receptors prerequisite for cytokine-induced IFN-gamma secretion. Among these cells, we detected a substantial fraction that secretes IFN-gamma directly ex vivo but lacks 4-1BB expression, indicating that cytokine-induced IFN-gamma(+) Th cells operate in autoimmune inflammation. Our data provide a rationale for how human effector-memory Thcells can participate in perpetuating inflammatory processes in autoimmunity even in the absence of T-cell receptor ligation.

Treatment of spondyloarthropathies with antibodies against tumour necrosis factor α: first clinical and laboratory experiences

Drug treatment of patients with spondyloarthropathies (SpA), especially ankylosing spondylitis (AS) has limited capacity.1 Pain but not disease activity can be reduced by non-steroidal anti-inflammatory drugs (NSAIDs), in severe cases very high doses are needed.2 By examination of sacroiliac biopsy specimens we have shown that, in correlation to disease activity assessed by magnetic resonance imaging (MRI), T cells and macrophages3 and tumour necrosis factor α (TNFα) mRNA4 and protein (fig 1) but no bacterial DNA5 is present in these joints that are pathognomonically involved in AS.6 Furthermore, anti-TNFα monoclonal antibodies (mAb) have recently been shown to be efficacious in Crohns disease7—a disease that is strongly linked to AS because more than 60% of AS patients have clinically often silent gut lesions resembling Crohns colitis.8 Furthermore, in another chronic inflammatory rheumatic disease, rheumatoid arthritis (RA), anti-TNF treatment has proved efficacious and even seems to prevent joint damage.9 Figure 1 Immunohistological examination of a sacroiliac biopsy specimen obtained by computed tomography guided biopsy of a 23 year old patient with ankylosing spondylitis, four years disease duration, with inflammatory back pain grade 6 on a visual analogue scale (0–10). The red staining indicates a mononuclear cell positive for TNFα (APAAP staining technique). TNFα is a cytokine that is mainly produced by monocytes and macrophages and to a lesser degree by T cells. There are two specific receptors, a 55 kDa and a 75 kDa present on many cell types. TNFα mediates inflammatory and immunoregulatory activities. Effects on cells such as lymphocyte activation and fibroblast proliferation, on mediators such as other cytokines like interleukin 1(IL1), IL6 and IL8, chemokines, prostaglandins, metalloproteinases, on the vasculature by promoting angiogenesis and on upregulation of adhesion molecules and transendothelial migration of leucocytes are well described. In in vitro and in …

IL-17-producing CD4(+) T cells contribute to the loss of B-cell tolerance in experimental autoimmune myasthenia gravis

The role of Th17 cells in the pathogenesis of autoantibody‐mediated diseases is unclear. Here, we assessed the contribution of Th17 cells to the pathogenesis of experimental autoimmune myasthenia gravis (EAMG), which is induced by repetitive immunizations with Torpedo californica acetylcholine receptor (tAChR). We show that a significant fraction of tAChR‐specific CD4+ T cells is producing IL‐17. IL‐17ko mice developed fewer or no EAMG symptoms, although the frequencies of tAChR‐specific CD4+ T cells secreting IL‐2, IFN‐γ, or IL‐21, and the percentage of FoxP3+ Treg cells were similar to WT mice. Even though the total anti‐tAChR antibody levels were equal, the complement fixating IgG2b subtype was reduced in IL‐17ko as compared to WT mice. Most importantly, pathogenic anti‐murine AChR antibodies were significantly lower in IL‐17ko mice. Furthermore, we confirmed the role of Th17 cells in EAMG pathogenesis by the reconstitution of TCR β/δko mice with WT or IL‐17ko CD4+ T cells. In conclusion, we show that the level of IgG2b and the loss of B‐cell tolerance, which results in pathogenic anti‐murine AChR‐specific antibodies, are dependent on IL‐17 production by CD4+ T cells. Thus, we describe here for the first time how Th17 cells are involved in the induction of classical antibody‐mediated autoimmunity.

Direct assessment of thymic reactivation after autologous stem cell transplantation.

Methods to quantify Th cell reconstitution after immunosuppressive therapies such as hematopoietic stem cell transplantation are becoming a key issue since persistent Th cell deficiencies may result in severe complications and adverse events. We employed here cytometric monitoring of CD31+ thymus-naive Th cells for the direct assessment of human thymic function in 10 patients undergoing autologous stem cell transplantation for severe autoimmune diseases. High frequencies of posttransplant recurring naive Th cells coexpressed CD31 and stable long-term reconstitution with elevated absolute counts of CD31+ thymus-naive Th cells that were enriched with T cell receptor excision circles was demonstrated. Cytometric monitoring of CD31+ thymus-naive Th cells enables to directly evaluate human thymic function ex vivo.