T-cell-secreted TNF-alpha induces emergency myelopoiesis and myeloid-derived suppressor cell-differentiation in cancer

Hematopoiesis in cancer patients is characterized by reduced production of red blood cells and an increase in myelopoiesis, which contributes to the immune-suppressive environment in cancer. Some tumors produce growth factors that directly stimulate myelopoiesis such as G-CSF or GM-CSF. However, for a majority of tumors that do not directly secrete hematopoietic growth factors, the mechanisms involved in the activation of myelopoiesis are poorly characterized. In this study, we document in different murine tumor models activated hematopoiesis with increased proliferation of long-term and short-term hematopoietic stem cells and myeloid progenitor cells. As a consequence, the frequency of myeloid-derived suppressor cells (MDSC) and its ratio to CD8+ T cells increased in tumor-bearing mice. Activation of hematopoiesis and myeloid differentiation in tumor-bearing mice was induced by tumor necrosis factor alpha (TNF-alpha), which was mainly secreted by activated CD4+ T cells. Therefore, the activated adaptive immune system in cancer induces emergency myelopoiesis and immunosuppression.

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