While the immune system is well known to be a key player during fracture repair, it is essential to understand how the immune system modulates fracture repair, especially the key role of regulatory T-cells (Tregs). Bone remodelling is a complex physiological process initiated by early regulation of inflammatory immunity and entails multiple events, including angiogenesis and osteogenesis. The innate and adaptive immune response was reported to play a crucial role in the remobilization and differentiation of several cell types during the fracture repair process, such as mesenchymal stem cells (MSCs).

Osteoblastic differentiation is vital during bone remodelling and fracture healing and is regulated by an array of biological factors. MSCs are capable of being stimulated towards osteoblasts and are the main prohealing cell type in fracture healing. MSCs are a type of precursor cell with a series of therapeutic molecules. They can respond to the surrounding microenvironment. MSCs can regulate their own fate and behaviour by sensing the surrounding microenvironment for indicators such as inflammation, infection, or tissue damage. Meanwhile, the release of cytokines, chemokines, and extracellular vesicles (EV) from MSCs may promote an immune response. Better understanding the crosstalk between the immune system and MSCs will provide new and effective insights for bone fracture treatment.

The aim of this Special Issue is to collect original research and review articles that will improve our understanding on the immune response of MSCs in the context of bone repair. We welcome research investigating the importance of the communication between immune cells and MSCs. We particularly encourage submissions including the application of MSCs in tissue repair strategies.

Potential topics include but are not limited to the following:

• The role and mechanism of exosomes derived from immune cells in osteoblastic differentiation
• Interaction between MSCs and immune cells MSC-based treatments for bone fracture
• Effects of the immune microenvironment on MSC behaviour
• The role of cytokines, chemokines, and exosomes in MSC-based transplantation and therapeutics in bone fracture
• Immune response of MSCs in osteoblastic differentiation
• Mechanism of stem cell therapy regulated by the immune system
• Stem cell-driven models of osteoblastic differentiation
• System review of the crosstalk between the immune system and MSCs in the context of osteoblastic differentiation