What are Myeloid Cells?
Myeloid cells are a diverse group of cells that originate from the bone marrow and play a crucial role in the body's immune response. These cells include
granulocytes (neutrophils, eosinophils, and basophils), monocytes,
macrophages, and dendritic cells. They are essential for
innate immunity and are involved in various functions such as phagocytosis, antigen presentation, and cytokine production.
How Do Myeloid Cells Relate to Cancer?
In the context of cancer, myeloid cells have a dual role. On one hand, they can contribute to anti-tumor immunity by recognizing and destroying cancer cells. On the other hand, certain subsets of myeloid cells, such as myeloid-derived suppressor cells (
MDSCs), can promote tumor growth by suppressing the immune response and enhancing
angiogenesis and metastasis. This dual nature makes them a critical focus in cancer immunology.
What are Myeloid-Derived Suppressor Cells (MDSCs)?
MDSCs are a heterogeneous population of cells that expand during cancer and other pathological conditions. They are known for their potent immunosuppressive activities. MDSCs inhibit the function of T cells and natural killer (NK) cells, thereby allowing tumor cells to escape immune surveillance. Targeting MDSCs is considered a promising strategy in
cancer immunotherapy.
What Role Do Tumor-Associated Macrophages (TAMs) Play?
Tumor-associated macrophages (TAMs) are another critical subset of myeloid cells in the tumor microenvironment. TAMs can exhibit either pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes. M1 macrophages generally have anti-tumor properties, while M2 macrophages promote tumor growth and metastasis by supporting tissue remodeling, angiogenesis, and immune suppression. Hence, TAMs are often associated with poor prognosis in cancer patients.
How Do Myeloid Cells Contribute to Tumor Angiogenesis?
Myeloid cells, particularly MDSCs and TAMs, produce various growth factors such as vascular endothelial growth factor (VEGF) that promote angiogenesis, the formation of new blood vessels. This process is crucial for tumor growth as it provides the necessary oxygen and nutrients to rapidly proliferating cancer cells. Inhibiting the angiogenic function of myeloid cells is a key area of research in developing anti-cancer therapies.
Can Myeloid Cells Be Targeted for Cancer Therapy?
Yes, targeting myeloid cells has shown promise in cancer therapy. Strategies include depleting MDSCs, reprogramming TAMs from a pro-tumor (M2) to an anti-tumor (M1) phenotype, and blocking the recruitment of myeloid cells to the tumor site. These approaches aim to reduce the immunosuppressive environment and enhance the efficacy of existing
immunotherapies such as checkpoint inhibitors.
What Are Some Clinical Applications and Trials?
Several clinical trials are investigating agents that target myeloid cells. These include inhibitors of colony-stimulating factor 1 receptor (CSF1R), which is crucial for the survival and function of TAMs, and drugs that block the signaling pathways involved in MDSC recruitment and activation. Early-phase studies have shown encouraging results, but more research is needed to fully understand the therapeutic potential of these strategies.
Conclusion
Myeloid cells play a complex role in cancer, acting as both defenders and promoters of tumor growth. Understanding the intricate balance of their functions is crucial for developing effective cancer therapies. Ongoing research and clinical trials targeting myeloid cells offer hope for improved cancer treatments in the future.
