uPA and uPA-Receptor Are Involved in Cancer-associated Myeloid-derived Suppressor Cell Accumulation

Myeloid-derived suppressor cells (MDSC) have been shown to play a critical role in tumor-induced immunosuppression, in many mouse and human cancers. The aim of this study was to show that MDSC accumulation is tumor burden-dependent, and to investigate the role of the tumor-derived urokinase plasminogen activator (uPA) and its receptor (uPAR) on MDSC recruitment. Levels of MDSC were assessed in tumor-bearers, and the ability to recruit MDSC by uPA was investigated in normal, tumor-bearers, uPAR(-/-), and CD11b(-/-) mice. uPAR expression in MDSC was also explored. MDSC accumulate to dramatic levels in tumor-bearers, and tumor-derived factors such as uPA also increase to great levels in circulation. MDSC can be recruited by uPA, and uPAR but not CD11b are required for such recruitment. MDSC accumulation is tumor burden-dependent, and tumor-derived factors such as uPA and its receptor uPAR play a role in their recruitment.