Differential immune landscapes in appendicular versus axial skeleton

Area of Science:

• Oncology
• Immunology
• Skeletal Biology

Background:

• Bone metastases affect ~400,000 people in the U.S., primarily in the spine, leading to fractures, pain, and paralysis.
• Cancer's predilection for the axial skeleton (spine) over the appendicular skeleton is not fully understood.
• Immune cells in the bone marrow microenvironment significantly influence tumor growth and progression.

Purpose of the Study:

• To investigate differences in immune cell landscapes between axial and appendicular bones in a non-cancerous state.
• To understand the normal immune microenvironment of the spine versus long bones.
• To identify potential factors contributing to the spine's susceptibility to bone metastases.

Main Methods:

• Utilized mass cytometry by time-of-flight (CyTOF) to analyze immune cell populations.
• Compared immune cell landscapes in bone marrow from human clinical samples and C57BL/6J mice.
• Analyzed cytokine concentrations in vertebral and long bone marrow.

Main Results:

• Significant differences in immune cell populations were observed between axial and appendicular bones in both mice and humans.
• A predominance of myeloid progenitor cells was found in the spine.
• Cytokine analysis indicated a more myeloid-enriched environment in vertebral bone marrow.

Conclusions:

• The immune microenvironment of the spine differs significantly from that of long bones.
• These immune differences may contribute to the spine's susceptibility to cancer metastasis.
• Understanding these distinct immune landscapes could inform future therapeutic strategies for bone metastases.