Biphasic calcium phosphate recruits Tregs to promote bone regeneration.

The use of bone substitute materials is crucial for the healing of large bone defects. Immune response induced by bone substitute materials is essential in bone regeneration. Prior research has mainly concentrated on innate immune cells, such as macrophages. Existing research suggests that T lymphocytes, as adaptive immune cells, play an indispensable role in bone regeneration. However, the mechanisms governing T cell recruitment and specific subsets that are essential for bone regeneration remain unclear. This study demonstrates that CD4 T cells are indispensable for ectopic osteogenesis by biphasic calcium phosphate (BCP). Subsequently, the recruitment of CD4 T cells is closely associated with the activation of calcium channels in macrophages by BCP to release chemokines Ccl3 and Ccl17. Finally, these recruited CD4 T cells are predominantly Tregs, which play a significant role in ectopic osteogenesis by BCP. These findings not only shed light on the immune-regenerative process after bone substitute material implantation but also establish a theoretical basis for developing bone substitute materials for promoting bone tissue regeneration. STATEMENT OF SIGNIFICANCE: Bone substitute material implantation is essential in the healing of large bone defects. Existing research suggests that T lymphocytes are instrumental in bone regeneration. However, the specific mechanisms governing T cell recruitment and specific subsets that are essential for bone regeneration remain unclear. In this study, we demonstrate that activation of calcium channels in macrophages by biphasic calcium phosphate (BCP) causes them to release the chemokines Ccl3 and Ccl17 to recruit CD4 T cells, predominantly Tregs, which play a crucial role in ectopic osteogenesis by BCP. Our findings provide a theoretical foundation for developing bone substitute material for bone tissue regeneration.