Accumulation of tumor infiltrating myeloid-derived suppressor cells associates with changes in the immune landscape of clear cell renal cell carcinoma.

Abstract

655 Background: 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 samples. The transcription of 55 immune-related genes was significantly associated (FDR adjusted p < 0.05) with PMN-MDSC infiltration, including mediators of MDSC recruitment such as CXCL1, CXCL3, CXCL5, CXCR2, IL8, LIF, S100A8, CSF3R, and CCR3, and molecules governing MDSC expansion and function such as IL10, C/EBPB, CD44, COX2, and NFATC3. When a statistically significant 10 gene signature was analyzed in the context of patient survival using the TCGA database of clear cell RCC patients (n = 945), a strong association between the expression of these genes and reduced survival was observed. Moreover, this association seemed to be additive, with expression of 7-10 of these genes correlating with poorer survival when compared to patients expressing 3 or less (p < 0.0001). Conclusions: Consistent with previous studies defining the immunoregulatory role of MDSCs, these results suggest that MDSC accumulation can alter the inflammatory state of the tumor, and indicate that mediators associated with the function of PMN-MDSCs can have a negative impact on outcome. Mechanistic studies aimed at identifying the functionally relevant mediators are ongoing.