Title: Development of Novel Anti-DC-STAMP Monoclonal Antibody Targeting Osteolytic Periodontal Lesion
Description: Background: Dendritic cell-specific transmembrane protein (DC-STAMP) plays a key role in the induction of osteoclast (OC) cell fusion. This conclusion is supported by evidence showing that osteoclast cell fusion is diminished, while systemic bone mineral density is significantly elevated, in DC-STAMP-KO mice, when compared to their wild-type mice. Clinically available anti-bone loss drugs, such as denosumab (anti-RANKL mAb) and bisphosphonates, cause severe side effects of MRONJ or medication related osteonecrosis of the jaw, presumably by targeting the complete suppression of osteoclastogenesis, which interferes with normal osteoclast-osteoblast coupling, or by interrupting antibacterial immune responses. Therefore, this study aimed to examine the effects of locally administered anti-DC-STAMP-mAb on bone and immunological responses in the context of periodontitis using a mouse model.

Methods: A silk ligature was placed around the second maxillary molar of C57BL/6J mice (male, 6- to 7-week-old, n=6-7/group) to induce alveolar bone resorption. Immediately after ligature placement, local injection of anti-DC-STAMP-mAb or control mAb (10μg/site) on the palatal tissue was performed. Alveolar bone loss, localization of OC, and IgG antibody response to the mouse periodontal opportunistic pathogen Pasteurella pneumotropica (Pp) were measured at Day-7 and Day-14 using μCT, TRAP staining and ELISA. T-cells isolated from cervical lymph nodes were stimulated in vitro with mouse dendritic cells and Pp-antigen in the presence or absence of anti-DC-STAMP-mAb or control mAb, followed by measurement of T-cell proliferation by 3H-thymidine incorporation assay.

Results: Immunofluorescence staining demonstrated higher expression of DC-STAMP on osteoclast-like cells on the alveolar bone surface in the ligature-induced periodontitis lesion compared to the healthy non-ligatured site. However, local injection of anti-DC-STAMP-mAb significantly suppressed the ligature-triggered alveolar bone resorption compared to control mAb at Day-7 (1.18 vs. 1.68 mm, p<0.05) and Day-14 (1.58 vs. 2.28 mm, p<0.01). According to histological analyses, anti-DC-STAMP-mAb decreased the number and size of multinucleated TRAP+ cells in the alveolar bone in comparison to those found in control. Neither in vivo anti-Pp IgG antibody nor in vitro anti-Pp T-cell response was affected by anti-DC-STAMP-mAb. These results suggested the robust efficacy of anti-DC-STAMP-mAb in suppressing alveolar bone loss by downregulating osteoclast cell fusion, but without affecting antibacterial immune responses.

Conclusions: Our study demonstrated, for the first time, that anti-DC-STAMP-mAb suppressed ligature-induced periodontal bone loss without affecting adaptive immune response to bacteria or total number of osteoclast precursors. Anti-DC-STAMP-mAb-mediated suppression of periodontal bone loss could be attributed to the inhibition of cell-cell fusion between osteoclast precursors. In sum, this anti-DC-STAMP-mAb could be developed as a lead candidate targeting osteoclast-mediated periodontal bone loss, resulting in normal homeostatic bone remodeling through rescue of OB-OC coupling, while, at the same time, avoiding the side effects associated with the currently applied therapies, as noted above.