Forschung
Neonates and infants generate vast T-cell responses against the fungus Candida albicans
Fungi are constantly encountered by all of us and are even present in the normal flora of healthy individuals. Invasive pathology is rare, but increasing. In addition to immunocompromised individuals, neonates are particularly susceptible to fungal pathology. Although much information is available on fungal pathogenesis, little is known about its cellular and molecular origin, and even less about its age-dependency. Therefore, we are characterising the molecular basis of T-cell responses in neonates and infants. So far, we show that antifungal CD4 T-cell responses are initiated from birth against monocyte-derived antigen presenting cells (APC) pulsed with Candida albicans or Aspergillus fumigatus lysates or fungal peptide pools. The neonatal pool of responding T cells comprises 20 out of 24 different TCR-Vβ families, whereas the infant and adult pools show dramatically less TCR-Vβ variability. Compared to adults, neonatal and infant naïve T cells proliferated 4-5 times more frequently in response to C. albicans, as evidenced by immediate co-expression of multiple cytokines. Although we show no bias for anti-fungal IL-4 expression early in life, there was a strong bias for anti-fungal IL-17 production. The frequency of IL-17 producers was about 3 times higher in neonates compared to adults. In addition, only neonatal and infant T cells were able to co-express the transcription factors T-bet and RORγt and eventually their target genes IL-17 and IFNγ, suggesting a high plasticity of T cell responses in early life.
This work highlights the gap between the specific T cell responses of neonates, infants and adults in terms of quality and quantity. We have clearly demonstrated that neonatal and infant T cells are predisposed to respond rapidly and with high plasticity to fungal pathogens, which may provide an excellent opportunity for therapeutic intervention.
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 shown to be effective in tumour therapy. Its main effect is to enhance the anti-tumour immune response, which ultimately leads to tumour rejection. As the immune response of neonates and infants is different from that of adults, we are investigating whether immune checkpoint therapy is indeed an option for early childhood tumours. So far, we have found that CTLA-4 is expressed on neonatal and infant T-cells - particularly on neonatal T-cells. Blockade of CTLA-4 in Staphylococcus aureus-pulsed PBMCs to induce antigen-specific responses shows that T-cell responses can indeed be enhanced at this age. However, the enhancement by CTLA-4 blockade shows age-specific characteristics. These differences need to be taken into account when considering their use for therapeutic intervention.
Oncoimmunology. 2021 Jun 14;10(1):1938475. doi: 10.1080/2162402X.2021.1938475
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 cold shock protein YB-1 in T cells is obligatory for maintenance of T cell homeostasis
The cold shock protein YB-1 is highly expressed in tumours such as breast cancer and is associated with hyperproliferation and resistance to apoptosis. Increased YB-1 expression at the transcriptional and nuclear protein levels has been shown to correlate with poor prognosis and resistance to chemotherapy in tumour patients. We have now shown that deregulated YB-1 in human CD4+ T cells leads to proliferation defects. Indeed, all leukaemic T cells analysed showed deregulated YB-1 expression.
To address the function of YB-1 in autoimmune processes, we are currently analysing its impact on T-cell homeostasis in patients suffering from lupus erythematodes. T-cells from these patients show dramatic instability of T-cell responses. Indeed, we already know that they are unable to properly upregulate YB-1 expression in T cells.
Arthritis Rheumatol. 2020 Oct;72(10):1721-1733. doi: 10.1002/art.41382
Cell Death Differ. 2017 Feb;24(2):371-383. doi: 10.1038/cdd.2016.141
CD28-independent signalling of CTLA-4 in CD28-null T cells
The closely related costimulatory molecules CTLA-4 and CD28 have different effects on T cells. While CD28 has an activating effect on T cells, CTLA-4 is able to switch off T cell responses. One possible mechanism of negative regulation of T cells by CTLA-4 is competition with CD28 for the common ligands CD80 and CD86. Independent signalling by CTLA-4 that is not dependent on competition has not been adequately investigated. To investigate the direct signalling of CTLA-4, we used CD28-null T cells. These are a subpopulation of T cells that do not express CD28. In these cells, we were able to show that CTLA-4-mediated signalling activates the anti-apoptotic kinase Akt, leading to reduced apoptosis in T cells.
Understanding the signaling pathways and mechanisms involved in the regulation of T cell responses by molecules like CTLA-4 is valuable for gaining insights into immune system regulation and potential therapeutic targets. It provides knowledge that could be applied in various contexts, such as developing treatments for autoimmune diseases, modulating immune responses in transplantation or cancer immunotherapy, or furthering our understanding of T cell biology in general.
Nat Commun. 2022 Oct 29;13(1):6459. doi: 10.1038/s41467-022-34156-1
Arthritis Rheum. 2013 Jan;65(1):81-7. doi: 10.1002/art.37714
