Immature myeloid cell (ImC)- mediated immunosuppression in advanced renal cell cancer (RCC)

Abstract

10042 Background: RCC affects the immunsystem by inhibiting the process of differentiation of antigen-resenting cells from their myeloid precursors by secreting tumor-derived factors such as VEGF. ImC induce a profound state of immune suppression that foster tumor tolerance by inhibition of tumor specific T cells. In this study, we asked whether increased ImC frequencies can be found in peripheral blood from RCC patients and if ImC frequencies correlated positively with increased levels of tumor-derived serum markers. Methods: ImC frequencies from healthy volunteers and RCC patients were determined by FACS. ImC were isolated by magnetic bead separation techniques and their immunosuppressive activity was determined in IFN-γ ELISPOT analyses, CTL and T-cell proliferation assays. The production of reactive oxygen species by ImC was analyzed utilizing specific probes and inhibitors. Tumor-derived serum markers were quantified by ELISA, enzyme immune assays and cytometric bead arrays. Microarray analyses were performed to identify novel, highly specific ImC markers. Results: RCC patients demonstrate higher ImC frequencies (0.8 - 3.2% of total PBMC) compared to healthy donors. The increased ImC frequencies are positively correlated with serum levels of VEGF, PGE-2, IL-13 and M-CSF in RCC patients and the concentration of byproducts of oxidative burst, including iso-prostane and malondialdehyde, was significantly enhanced. Isolated ImC exhibited profound immunosuppressive effects on CTL and CD4+ T cell response in an antigen specific fashion. Immunosuppression by ImC was mediated by release of ROS, including peroxide and superoxide anions and by generation of nitric oxide radicals as evidenced in functional assays. Results from microarray analyses reveal EP-1, EphA5, and PEX-5 as novel ImC markers. Conclusions: These data suggest that RCC may induce the development of immunosuppressive ImC population through secretion of cytokines such as VEGF, IL-13, M-CSF and PGE-2. Inhibition of specific cytokine activity or the use of differentiating agents may represent strategies to decrease immunosuppressive ImC population. Results from a phase I clinical trial investigating the effects of all-trans retinoic acid (ATRA) on differentiation of ImC in RCC patients will be presented. No significant financial relationships to disclose.