W157 - Expression of the Co-receptors TIGIT and CD226 on Tregs and Their Role in Autoimmunity

Abstract Text: TIGIT is an important co-inhibitory receptor on Tregs, which are crucial for maintaining tolerance and preventing autoimmunity. Sharing the same ligands (CD155/CD112), the effect of co-stimulatory CD226 on Tregs is less well defined, with CD226+ Tregs linked to worsened disease activity in various inflammatory conditions. Here, we investigated the co-expression of TIGIT and CD226 on Tregs in T cell activation and autoimmunity.

Through spectral flow cytometry analysis, we observed increased frequency of TIGIT+CD226+ Tregs in the inflamed joint (synovial fluid, SF) than blood (PB) Tregs from individuals with Juvenile Idiopathic Arthritis. This suggests co-expression of these co-receptors could represent altered Treg response to certain inflammatory stimuli. Indeed, TIGIT+CD226+ Tregs from both SF and PB displayed a memory phenotype with a heightened activation state, through increased expression of CD71, 4-1BB, PD-1 and CD39.

In vitro expression kinetic assessment of TIGIT/CD226 post-activation revealed higher co-expression on Tregs than Tconv, with maintenance of TIGIT+CD226+ Treg co-expression upon further stimulation. TIGIT+CD226hi Tregs had decreased Ki67 expression after seven-day expansion, suggesting a terminal differentiated state with altered proliferative ability. Cell sorting on TIGIT-CD226- suggested that Treg phenotype is dependent on which co-receptor is upregulated first, with TIGIT-CD226hi populations predominantly expressing ICOS with altered cytokine production.

We therefore propose TIGIT+CD226+ co-expression represents a highly activated but terminally differentiated Treg state in response to continuous inflammatory stimuli, such as in the inflamed joint. This state could represent altered functional stability of Tregs and present as a possible target in monitoring or restoring tolerance in autoimmunity.