The role of innate immune signaling in regulation of tumor-associated myeloid cells

Abstract

Tumor progression is frequently associated with a profound alteration in myelopoiesis, which results in expansion of tumor-associated myeloid cells represented by tumor-associated macrophages and myeloid-derived suppressor cells. These tumor-associated myeloid cells not only facilitate tumor growth, but also hamper cancer immunotherapy by immune and non-immune mechanisms. However, tumor-associated myeloid cells also have a critical role for tumor growth inhibition in immunotherapy for cancer. Recent evidence indicates that innate immune signaling elicited by Toll-like receptor ligands can induce both differentiation and ‘reeducation’ of tumor-associated myeloid cells, which positively and negatively affect tumor development and growth. Therefore, innate immune signaling could be a useful target for cancer treatment by modulating the phenotype of tumor-associated myeloid cells.