Immunomodulation of Multiple Myeloma Bone Disease

Th17 and Treg cells in bone related diseases

Bone-related diseases share the process of immune response that targets bone tissue and bone marrow and then induce adverse effects on structure and function. In recent years, reciprocal relationship between immune cells and bone systems has been uncovered gradually. Regulatory T (Treg) and T helper 17 (Th17) cells are newly identified subsets of CD4+ T cells, and the balance between them is particularly essential for maintaining immune homeostasis. Accumulated data have demonstrated quantitative or functional imbalance between Th17 and Treg in bone related diseases, suggesting that Th17 and Treg cells are involved in these bone diseases. Understanding the molecular mechanisms regulating Th17 and Treg cells will create opportunities for the development of therapeutic approaches. This review will present the role of Th17 and Treg cells in the inflammatory bone diseases and bone marrow malignancies and find the potential therapeutic target for immunotherapy.

Cellular mechanisms of multiple myeloma bone disease

Multiple myeloma (MM) is a hematologic malignancy of differentiated plasma cells that accumulates and proliferates in the bone marrow. MM patients often develop bone disease that results in severe bone pain, osteolytic lesions, and pathologic fractures. These skeletal complications have not only a negative impact on quality of life but also a possible effect in overall survival. MM osteolytic bone lesions arise from the altered bone remodeling due to both increased osteoclast activation and decreased osteoblast differentiation. A dysregulated production of numerous cytokines that can contribute to the uncoupling of bone cell activity is well documented in the bone marrow microenvironment of MM patients. These molecules are produced not only by malignant plasma cells, that directly contribute to MM bone disease, but also by bone, immune, and stromal cells interacting with each other in the bone microenvironment. This review focuses on the current knowledge of MM bone disease biology, with particular regard on the role of bone and immune cells in producing cytokines critical for malignant plasma cell proliferation as well as in osteolysis development. Therefore, the understanding of MM pathogenesis could be useful to the discovery of novel agents that will be able to both restore bone remodelling and reduce tumor burden.