Project Summary The recurrence of periodontal disease (PD) is a poorly immunologically defined or therapeutically targeted clinical challenge. Uncovering the homeostatic and pathogenic potential of long-term immune cells in periodontal tissues is crucial to revealing the cellular drivers of PD recurrence. This proposal focuses on an overlooked periodontal-associated cellular compartment, CD4+ T memory cells (TM), which can readily recognize microbial antigens for a quick and robust response. For this purpose, we will utilize a newly characterized murine model of recurrent PD and a method for gingival T-cell enrichment. In this model, time is a critical variable for recognizing disease initiation, resolution, and recurrence. By establishing this model, we will be able to define a “recovered” baseline instead of a “healthy” baseline state, which is more clinically accurate. Also, it allows defining how multiple relapse episodes incrementally impact the complex periodontally-associated immune network. The preliminary studies revealed that CD4+ TM developed in the gingiva soon after birth due to increasing environmental antigenic exposure. While the mice fully recovered from ligature-induced PD, the bone loss rate accelerated during PD recurrence. Most intriguingly, CD4+ TM subtypes are enriched in the gingiva during PD recurrence. Gingival CD4+ tissue-resident memory cells induced bone loss when circulating T cell infiltration was inhibited. Based on these findings, we will test the hypothesis that the PD-induced generation and persistence of CD4+ TM subtypes determine PD recurrence. Thus, targeted depletion of these cells by inhibiting metabolic checkpoints will enhance immune-regulatory responses and inhibit PD recurrence. There are three interconnected but independent Aims: 1) To identify the spatiotemporal development of CD4+ TM cells in periodontal tissues. Here, the focus will be on understanding the constitutive and pathologic generation of CD4+ TM cells to dete