The Role of GM-CSF on Monocyte Polarization in Controlling the Regression of Malignant Melanoma
Introduction. Melanoma develops as a malignant neoplasm of melanocytes, a type of cell that produces a pigment called melanin which gives color to the skin. Melanoma commonly develops in areas of the body with increased exposure to the sun, such as the extremities, back, and face4. DNA damage from developing melanocytes causes impaired local host immunity by reducing the amount of functional T-lymphocytes and dendritic cells. This impairs the ability of the dendritic cells to present antigens to T-cells to activate the immune response, contributing to tumorigenesis of the skin2. Studies have shown possible benefit in utilizing Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF), a glycoprotein secreted by immune cells, to aid in melanoma regression2,3. Utilization of GM-CSF has been tested to stimulate the host immune system by increasing proliferation and maturation of monocytes into macrophages and dendritic cells. Methods. Human PBMCs (peripheral blood mononuclear cells) were isolated from buffy coats from normal human donors. In the control of specific environment, GM-CSF was cultured with the PBMCs and compared to cultures of PBMC’s with M-CSF, IL-34, or IL-34 plus GM-CSF. These are additional factors which may assist in monocyte differentiation. The immunoregulatory effects on monocyte polarization in the cultures were analyzed. Results. GM-CSF-polarized macrophages expressed increased amounts of CCR2 receptors when compared to M-CSF-polarized macrophages. Upon stimulation, these GM-CSF-polarized macrophages released large amounts of pro-inflammatory immune cells such as IL-6 and TNF-alpha6. The stimulation of these pro-inflammatory cells may assist in the regression of melanoma by inducing apoptotic cell death and antagonism of T-regulatory cells3,6. IL-34-induced macrophages expressed potent immunosuppressive properties, while macrophages produced with both IL-34 plus GM-CSF retained high pro-inflammatory levels of IL-12 and low levels of IL-101. In a final comparison, GM-CSF-polarized macrophages and GM-polarized-dendritic cells were analyzed. GM-CSF-polarized macrophages showed high phagocytic abilities and produced more IL-10 upon LPS stimulation, while GM-polarized-dendritic cells were more efficient at inducing T-cell proliferation and producing TNFa, IL-1B, IL-6, and IL-12p705. Conclusions. Studies have shown that the effect of GM-CSF on monocyte differentiation into macrophages has been found to increase expression of CCR2 and pro-inflammatory markers, as well as antagonize anti-inflammatory and immunosuppressive effects. Knowledge of the heterogeneicity of GM-CSF derived cell populations and the important immunoregulatory effects of GM-CSF may play an important therapeutic role in controlling the regression of malignant melanoma.
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