Preclinical Evaluation of Treg Recruiting Microparticles for the Treatment of Periodontitis

Periodontal disease (gum disease) affects an estimated 78 million Americans, and is the leading cause of tooth loss according to the American Dental Association^[1].  Current treatments for periodontal diseases focus on the removal of invasive bacterial species through non-surgical scaling and root planing procedures (sometimes accompanied by antibiotics)^[2].  Although bacteria initiate the disease, tissue destruction in the periodontium (ligament and tooth supporting bone) is perpetuated by the inflammatory immune response.  Recently, a subset of lymphocytes known as regulatory T cells (Tregs) has been shown to play a critical role in the regulation of harmful inflammatory immune responses^[3].  Furthermore, the presence or absence of Tregs has been correlated with the presence or absence of aggressive periodontitis^[4].  Therefore, we hypothesized that resolution of inflammatory conditions through the recruitment of Tregs may alleviate periodontal disease symptoms and prevent alveolar bone loss.

In support of this hypothesis, here we show Treg recruitment to poly(lactic-co-glycolic) acid microparticles encapsulating CCL22 placed in the subgingival pocket, lead to the resolution of periodontal disease symptoms in both a murine and canine model.  Specifically, upon injection of CCL22 loaded microparticles in the mouse model, we observed an increase in the expression of FOXP3 (Treg transcription factor), and anti-inflammatory cytokines IL-10 and TGFβ.  Indeed, we also observed a corresponding decrease in the expression of inflammatory cytokines IL-1, TNF, and IFNγ, without affecting the protective host response (we observed comparable bacterial loads, Fig. 1A).  Furthermore, in the most widely accepted preclinical model for periodontitis (dog model), we observed decreased clinical scores for inflammation, probing depth (Fig. 1B), and bleeding on probing.  In addition, we observed a marked decrease in alveolar bone loss in the CCL22 treated animals (observed and quantified using microCT, Fig. 1C).

[1]       P. I. Eke, R. J. Genco, Journal of Periodontology 2007, 78, 1366.

[2]       R. C. Williams, D. W. Paquette, S. Offenbacher, D. F. Adams, G. C. Armitage, K. Bray, J. Caton, D. L. Cochran, C. H. Drisko, J. P. Fiorellini, W. V. Giannobile, S. Grossi, D. M. Guerrero, G. K. Johnson, I. B. Lamster, I. Magnusson, R. J. Oringer, G. R. Persson, T. E. Van Dyke, L. F. Wolff, E. A. Santucci, B. E. Rodda, J. Lessem, Journal of Periodontology 2001, 72, 1535.

[3]       Q. Tang, J. A. Bluestone, Nature Immunology 2008, 9, 239.

[4]       G. P. Garlet, C. R. Cardoso, F. S. Mariano, M. Claudino, G. F. de Assis, A. P. Campanelli, M. J. Avila-Campos, J. S. Silva, Journal of Clinical Periodontology 2010, 37, 591.