Accumulation Of Tumor Infiltrating Myeloid-Derived Suppressor Cells Associates With Changes In The Immune Landscape Of Clear Cell Renal Cell Carcinoma.

655Background: Myeloid-derived suppressor cells (MDSC) are capable of inducing profound immune suppression of anti-tumor T cell responses. Here we examined the ability of intratumoral MDSC accumulation to alter the immune landscape of RCC and to identify the factors involved. Methods: Using flow cytometry, 41 clear cell RCC nephrectomy samples were assessed for their total MDSC infiltrate and the percentage of granulocytic (PMN-MDSC) or monocytic (M-MDSC) subsets. RNA isolated from these tumor samples and 4 non-tumor samples was also evaluated for expression levels of immune-related genes using a Nanostring PanCancer immune panel. A multiple linear regression model was used to identify which immune-related genes might be significantly associated with PMN-MDSC intratumoral accumulation. Log-Rank test was used for comparison of survival curves. Results: Genes encoding cytokines, cancer-testis antigens, interleukins, and T cell function were differentially expressed by clear cell RCC and the non-tumor sample...