40.8 : Differentiation of Common Myeloid Progenitor Cells

Common myeloid progenitors (CMPs) are oligopotent cells that can differentiate into granulocytes and macrophages. Granulocytes and macrophages are essential for protecting the body against bacterial, viral, or fungal infections. They migrate from the bone marrow into the circulating blood to reach specific tissue sites where they differentiate and help in immune surveillance. However, they survive only for a few days and must be continuously made available to the organism to maintain a robust immune system. In addition, during an injury or infection, many of these immune cells are lost in the action of immune defense. The adjoining endothelial cells of injured tissues, existing immune cells, and fibroblasts sense this crisis and release colony-stimulating factors or CSFs.

1. CSFs have short half-lives of only a few hours; however, once bound to the progenitors, they determine their lineage-commitment choices, influencing them to differentiate into granulocytes or macrophages. CSFs also help the progenitors perform specific functions. There are four types of CSFs involved in CMP differentiation. They include: Granulocyte-macrophage colony-stimulating factor or GM-CSF,
2. Granulocyte colony-stimulating factor or G-CSF,
3. Macrophage colony-stimulating factor or M-CSF, and
4. Interleukin-3 or IL-3, a multipotential colony-stimulating factor.

The GM-CSF and IL-3 trigger eosinophil production and help fight parasitic or allergic reactions. The G-CSF helps progenitors differentiate into granulocytes, while the M-CSF initiates macrophage production. Neutrophils and macrophages are phagocytic cells that attack the microbes and digest them through phagocytosis.

Recombinant G-CSF and GM-CSF injections are often administered as adjunct therapy to the cancer patient. They are subcutaneously injected to help replenish the lost immune cells and overcome side effects such as neutropenia (low level of neutrophils in the blood) and low white blood cell count, which are standard post chemotherapy or radiation therapy.