No bones about it: regulatory T cells promote fracture healing

Regulatory T cells (Tregs) are increasingly being recognized for their role in promoting tissue repair. In this issue of the JCI, Chen et al. found that Tregs at the site of bone injury contribute to bone repair. The CCL1/CCR8 chemokine system promoted the accumulation of Tregs at the site of bone injury, where Tregs supported skeletal stem cell (SSC) accumulation and osteogenic differentiation. CCL1 increased the transcription factor basic leucine zipper ATF-like transcription factor (BATF) in CCR8+ Tregs, which induced the secretion of progranulin that promoted SSC osteogenic function and new bone formation. This study highlights the ever-expanding role of Tregs in tissue repair by demonstrating their ability to expand stem cells at a site of injury.