Assessment of TRAT1 expression and function in CD4+ T-cells

The human immune system is regulated by a multitude of modulatory processes which ensure that reactions against pathogens such as bacteria, viruses, fungi and cancer cells can be mounted, while body tissues are not affected. In this context, so-called regulatory T-cells (Treg) are important mediators. These cells constitute a subset of CD4+ T helper cells, which are central modulators of virtually all immune responses. Indeed, deficiencies in Treg function can be observed in several diseases, which are caused by aberrant reactions of the immune system (e.g. allergies and autoimmune diseases such as rheumatoid arthritis and type I diabetes). Treg differ from other immune cells by their specific gene expression profile, which governs their unique functions. To the date, this genetic signature has not been fully explored. In the project Assessment of expression and function of TRAT1 in CD4+ T-cells, supervised by Klaus Schmetterer, MD, PhD (Department of Laboratory Medicine, Medical University of Vienna), the role of the signaling molecule TRAT1 will be further assessed. Preliminary experiments have indicated that Treg, in contrast to conventional CD4+ T-cells (Tconv) lack TRAT1 expression, which indicates selective function of this molecule. In the course of the project, TRAT1 will be specifically activated or deactivated by genetic methods (e.g. Crispr/Cas9 knockout) and the effects of this manipulation on Treg and Tconv function will be evaluated. Novel insights about the function of TRAT1 in CD4+ T-cells will be gained from these experiments. This could lead to the development of new approaches for the manipulation of Treg in the therapy of allergies and autoimmune diseases. Furthermore, these studies could also provide information whether TRAT1 can be used as diagnostic markers for these diseases.

In this project, researchers at the Medical University of Vienna investigated a previously poorly understood component of the immune system. The protein molecule TRAT1 (T Cell Receptor-Associated Transmembrane Adaptor 1) plays a central role in how so-called T helper cells (a specialized subgroup of immune cells) distinguish between immune attack and self-regulation. This mechanism is essential for limiting inflammation and preventing autoimmune diseases. T helper cells act as the "conductors" of the immune response by controlling the function and specialization of other immune cells, thereby tailoring immune reactions to specific pathogens. There are effector T helper cells, which actively combat invading pathogens, and regulatory T cells (Tregs), which prevent excessive immune responses. Until now, the mechanisms governing the balance between these two cell types have only been partially understood. In this FWF-funded study, a research team at the Medical University of Vienna led by the groups of Ralf Schmidt and Klaus Schmetterer (Clinical Institute of Laboratory Medicine) demonstrated that TRAT1 functions as a molecular switch in these processes. In "attack" cells (effector T cells), TRAT1 ensures controlled activation. When TRAT1 is knocked out using CRISPR/Cas9 gene editing, these cells become more active but lose the ability to produce certain inflammatory signaling molecules, such as interleukin-17. In contrast, in "protective" cells (Tregs), TRAT1 supports their suppressive function, albeit in a complex manner. It enhances the suppression of other immune cells, but not uniformly across all cell types. These findings show that TRAT1 acts as a dual regulator of the immune system: on the one hand, it dampens excessive immune activity, while on the other hand, it strengthens targeted immune suppression mediated by regulatory T cells. Although these results were obtained in cell culture, they also have high clinical relevance. Altered TRAT1 expression patterns were identified in immune cell datasets from patients with graft-versus-host disease (GvHD) and systemic lupus erythematosus. This suggests that signal filtering in T helper cells is impaired in these diseases. In the long term, these insights could contribute to the development of new cell-based immunotherapies, such as customized CAR-Treg cells designed to selectively prevent harmful immune reactions. This concept has already been demonstrated in a novel three-dimensional cell culture model of transplant rejection. The results were recently published in the scientific journal Cell Communication and Signaling.