Research
Neonates and infants generate vast T-cell responses against the fungus Candida albicans
Fungi are continually being encountered by each of us and are even present in the normal flora of healthy individuals. Rarely, an invasive pathology is initiated, but the figure is on the rise. Besides immune suppressed individuals, neonates especially are susceptible to fungus pathology. Even though, a great deal of information is available concerning the fungal pathogenesis, not much is known about its cellular and molecular origin - even less about age-dependency. Therfore, we characterize the molecular bases of T-cell responses in neonates and infants. So far, we show that antifungal CD4 T-cell responses are initiated from birth on to monocyte-derived antigen presenting cells (APC) pulsed with Candida albicans or Aspergillus fumigatus lysates and fungal peptide pools, respectively. Neonatal responding T-cell pool constitute 20 out of 24 different TCR-Vβ families whereas infant and adult pools display dramatically less TCR-Vβ variability. In comparison to adults, naïve T cells from neonates and infants proliferated at a 4-5 times higher frequency in response to C. albicans, which was also corroborated by an immediate co-expression of multiple cytokines. Although we demonstrate no bias for anti-fungal IL-4 expression early in life, there was a strong bias for anti-fungal IL-17 production. Frequencies of IL-17 producers were about 3 times higher among neonates compared to adults. In addition, only T cells from neonates and infants could co-express transcription factors T-bet and RORγt and eventually co-express their target genes IL-17 and IFNγ, implicating a high plasticity of T cell responses in early life.
This work highlights the gap between specific T-cell responses of neonates, infants, and adults in terms of quality and quantity. We could clearly demonstrate that T-cells of neonates and infants are predetermined to respond quickly with high plasticity to fungal pathogens, which might give an excellent opportunity for therapeutical interventions.
Sci Rep 8: 16904. link: https://www.ncbi.nlm.nih.gov/pubmed/30442915
CTLA-4 blockade in infants might be an option for tumor therapy
Blockade of CTLA-4 has been proven to be effective in tumor therapy. Its main effect is to enhance the anti-tumor immune response which eventually leads to tumor is rejected. As the immune response of neonates and infants are different to the adult one, we investigate whether immune-checkpoint therapy is indeed an option for early childhood tumor entities. So far, we find that CTLA-4 is expressed on neonatal and infant T-cells - especially high on neonatal ones. Blockade of CTLA-4 in Staphylococcus aureus-pulsed PBMCs to generate antigen-specific responses show, that T-cell responses can indeed be enhanced at that age. However, enhancement under CTLA-4 blockade shows age-specific characteristics. These differences have to be taken into account when considering using it for therapeutical intervention.
CTLA-4-induced signaling pathways in regulating differentiation and plasticity of Tc17 cells
Blockade of CTLA-4 (the first target with reported effectiveness in immune checkpoint therapy) on CD8+ T-cells is demonstrated to be of particular importance in enhancing effector functions of Tc1 cells, by secretion of granzymeB and cytokines IFNγ and TNFα. Nevertheless, the role of CTLA-4 in regulating Tc17 cells, which are generally less cytotoxic in nature but are shown to exhibit strong anti-tumor activity, due to their highly plastic nature to acquire Tc1 characteristics with increased persistence, is not completely understood. This project aims to determine the molecular mechanism by which CTLA-4 regulates Tc17 differentiation and their plasticity. In recent work, we were increasingly focusing to investigate the effects of CTLA-4 on Tc17 differentiation, and the impact of CTLA-4 signaling in Tc17 cell mediated control of Listeria monocytogenes infection and tumor growth in vivo in mouse models. Additionally, we have also focused on CTLA-4-mediated phosphorylation of targets and their capacity to influence differentiation and plasticity of Tc17 cells. In this work, we were able to demonstrate that CTLA-4 critically shapes the characteristics of Tc17 cells by regulating relative amounts of pSTAT1/3, providing new perspectives to enhance cytotoxicity of Tc17 cells. In addition, the results from this work also shows that CTLA-4 regulates the third signal for T cell differentiation, namely, cytokine receptor signaling (by regulating relative STAT activation), which is an important feature in the decision making process that determines the type of T cell differentiation. This relationship between CTLA-4 and STATs would likely impact other T cell lineages along with Tc17 cells and is likely to influence various immune settings, making this pathway acutely relevant in the context of immune checkpoint therapy and cytokine-based drug design.
Mechanisms to prevent allergy
Chronic immune disorders such as allergies are a growing medical problem and caused by inappropriate immunological responses to harmless- or self-antigens driven by a T-helper cell (Th2)-mediated immune response. The specific causes of the disease are mostly unknown and probably also different from patient to patient. Even the disease-specific immune cells that initiate or protect against pathological reactions are poorly characterized. For the patient, this means: Because detailed knowledge is lacking, the therapy affects the entire immune system. This leads to corresponding side effects and fights symptoms instead of eliminating the cause of the disease.
T cells orchestrate a defense against pathogens, but they also actively maintain tolerance to innocuous exogenous- or self-antigens, thereby suppressing unwanted inflammation. So called regulatory T cells (Tregs) also control Th2-mediated inflammation. Tregs and activated CD4+ T cells express the primary negative regulator of T cell activation the cytotoxic T-lymphocyte-associated protein 4 (CTLA-4, CD152). However, the mechanisms of CTLA-4 in the regulation of Th2-driven immune responses remain elusive. To evaluate this mechanism, we investigate the consequences of CTLA-4 in Th2 cells and Treg-mediated signals individually and combined on differentiation of mouse and human effector and memory Th2 subpopulations. Using CTLA-4 manipulation in Treg-free environement in vivo and in vitro, we find a dramatic regulation of T-effector and T-memory responses by CTLA-4.
Our findings demonstrate a hierarchical regulation to restrain Th2-responses in which Tregs are the dominant players. However, while Treg counts are low as it occurs in allergic patients, agonistic CTLA-4-signals on Th2-cells are detrimental and could be an option for therapeutic interventions in Th2-driven diseases.
PD1- and CTLA-4-induced translation inhibition: Implications for tumor therapy
Using phospho-proteomics of CD8+ T-cells, we identified signalling pathways that are induced by CTLA-4 to shut down IFN production. among identified target molecules, the translation inhibitor PDCD4 was identified to be central for CTLA-4-mediated effects. Our tumor models show indeed, that PDCD4 ko T-cells mediate enhanced rejection of established tumors.
Blockade of inhibitory co-receptors on T cells in immune-checkpoint-therapy has revolutionized cancer treatment in the recent years. Among those receptors, CTLA-4 and PD-1 are the most prominent and investigated molecules in this field. Despite the promising results of this therapeutic approach the versatile effects of these receptors on different T cell subsets, however, still remain incompletely understood. In this project we identify and investigate CTLA-4- and PD-1-induced mechanisms in CD8+ cytotoxic T lymphocytes as they are the executing effectors that eliminate tumor cells. So far, we determined signal components that were under the control of CTLA-4 by accurate mass spectrometry analysis. We revealed that CTLA-4 mediated central changes in the phosphorylation of proteins involved in T cell differentiation. Beside other molecules, we found the translational inhibitor PDCD4 as a major target by which CTLA-4 was able to inhibit anti-tumor CD8+ T cell responses via post-transcriptional regulation. Our tumor models show indeed, that PDCD4 ko T-cells mediate enhanced rejection of established tumors.In a further step we sought to analyze PD-1 induced targets, accordingly. As a result, we will help to clarify how inhibitory signals are intertwined to dampen CD8+ T cell activation. Furthermore, we will identify novel and possibly redundant inhibitory mechanisms that could be targeted to improve anti-tumor immune-checkpoint-therapy.
PDF: CTLA-4 (CD152) impairs cytotoxic T-lymphocyte responses via PDCD4 induction
Expression of the cold shock protein YB-1 in T-cells is obligatory for maintenance of T-cell homeostases
The cold shock protein YB-1 is highly expressed in tumours, such as breast cancer, and associated with hyper proliferation and resistance against apoptosis. Enhanced YB-1 expression at the transcription and nuclear protein levels have been shown to correlate with poor prognosis and resistance to chemotherapy for tumour patients. Now, we showed that deregulated YB-1 in human CD4+ T cells leads to defects in proliferation. Indeed, all leukemic T-cells analysed showed deregulated YB-1 expression (Gieseler-Halbach et al., 2017).
To address YB-1 functioning in autoimmune processes, we are currently analysing its impact on T-cell homeostases in patients suffering from Lupus Erythematodes. T-cells of those patients show dramatic instability of T-cell responses. Indeed, we know already, that they are not able to properly upregulate YB-1 expression in T-cells.
CD28 unabhängige Signaltransduktion von CTLA-4 in CD28null T-Zellen
Die eng verwandten kostimulatorischen Moleküle CTLA-4 und CD28 haben auf T-Zellen unterschiedliche Auswirkungen. Während CD28 auf T-Zellen aktivierend wirkt, ist CTLA-4 in der Lage T-Zellantworten abzuschalten. Ein möglicher Mechanismus der negativen Regulation von T-Zellen durch CTLA-4 entsteht durch Kompetition mit CD28 um die gemeinsamen Liganden CD80 und CD86. Eine von der Kompetition unabhängige, eigenständige Signaltransduktion von CTLA-4 wurde bisher nicht ausreichend untersucht. Um die direkte Signaltransduktion von CTLA-4 zu analysieren, haben wir CD28null T-Zellen verwendet. Dabei handelt es sich um eine Subpopulation von T-Zellen, die kein CD28 ausprägen. In diesen Zellen konnten wir zeigen, dass von CTLA-4 vermittelte Signaltransduktion die anti-apoptotisch wirkende Kinase Akt aktiviert, was verminderte Apoptose in T-Zellen zur Folge hat.
