Functional modulation of regulatory T cells and analyses of the underlying mechanisms

• Applicant: Professor Dr. Alexander Steinkasserer
• Subject Area: Immunology
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 445886458

The overall aim of this project is the identification of new pathways to specifically modulate Treg differentiation and stability in the context of autoimmunity. We have shown that the specific loss of CD83 expression by Tregs, surprisingly leads to the downregulation of Treg-specific differentiation markers and the induction of an inflammatory profile. In addition, these Treg-specific conditional knockout mice showed aggravated autoimmunity and an impaired resolution of inflammation. Within this proposal we will focus on the following major aims:Aim #1: Are Treg specific TLR pathways modified by CD83 expression? Previously we showed that soluble CD83 modulates the TLR4 pathway by binding to MD2 and TLR4. Noteworthy, TLRs are expressed at much higher levels on Tregs when compared to e.g. with effector T cells. It was also shown that LPS binding to TLR2 induces Treg proliferation with a temporal loss of the suppressive function. It is still obscure how these effects are mechanistically regulated. Thus, using our CD83 cKO Treg mice we will investigate if CD83 expression modulates Treg function and stability via the MD2-TLR pathways by destabilizing factors such as IRAK1. Aim #2: Decipher new signaling pathways involved in CD83-dependent Treg modulation. With the help of gene arrays we identified several pathways potentially involved in CD83 dependent modulation of Treg cells. However, for a detailed mechanistic analyses signaling events must be investigated also on protein levels, including phosphorylation events. Thus, within aim 2 we will compare unstimulated and stimulated Treg cells derived from CD83 cKO mice by phospho-proteomics. This approach will enable us not only to confirm data derived from aim 1 but also to identify new pathways and involved networks. Aim #3: Identify and characterize newly elucidated CD83 modulated pathways in human Tregs. Two different approaches will be used: first, CD83 expression will be knocked down in human Tregs using siRNAs, and re-stimulated cells will be investigated regarding specific target genes which have been identified within aim 1 and 2, on RNA and protein levels. In addition we will knockdown CD83 in naïve human T cells, differentiate them into iTregs and analyze them again, in comparison to murine Tregs, on RNA and protein levels.Aim #4: Characterize CD83 impact on the establishment of different tissue resident Tregs. Very recently, it has been shown that non-lymphoid tissue (NLT) Tregs show different expression profiles and tissue adaptations. Thus, within this aim we will examine if CD83 is differentially expressed in different NLT Tregs compared to lymphoid Tregs. Interestingly, a recent study reported a higher CD83 expression in colonic Tregs when compared to skin Tregs. With the main focus on colonic Tregs and IBD we will investigate how NLT Tregs, derived from CD83 cKO mice, are influenced by the loss of CD83 expression.

• DFG Programme: Research Grants