Comparison of MDSC subtypes from spleen and tumor of mice with RM-1 tumors

Myeloid derived suppressor cells (MDSC) in the tumor microenvironment suppress T-cell mediated immune surveillance that clears tumor cells. As such, MDSC promote tumor growth. There are two subtypes of tumor MDSC, CD11b+Ly6ChiLy6G- monocytic MDSC (M-MDSC) , and CD11b+Ly6ClowLy6Ghigh granulocytic MDSC (G-MDSC). Cells with these markers also exist in the spleen of tumor bearing mice or in the spleen of mice with tissue-specific inflammation. Some have argued that the tumor MDSC is an activated version of the spleen MDSC, implying that they are similar to one another. Here we isolated the MDSC subtypes from the RM-1 tumors and from the spleen of mice with prostatic inflammation (n=4 per subtype per tissue, 16 total samples). We then analyzed RNA from these cells to determine how the transcript profile was altered by tissue location and MDSC subtype. Platform: Affymetrix Mouse Gene 1.0 ST v1 Genechip To generate tumor MDSC 1 x106 RM-1 tumor cells were injected into the peritoneal cavity of C57Bl/6J mice. 7 d later, tumor-derived MDSC were harvested from ascites by serial lavage with sterile PBS and MDSC subtypes were isolated by fluorescence-activated cell sorting (n=4 pools of cells from 2-3 mice each). To generate activated peripheral MDSC from the spleen, POET-3 mice were injected with 5 x 106 activated OT-I cells to induce prostate inflammation. 6 days later the mice were killed, spleens harvested, and MDSC subsets were isolated by fluorescence-activated cell sorting (n=4 mice). RNA was isolated and used for transcript profiling using Affymetrix microarrays.