Tumor development depends on immunomodulatory signals produced by multiple cells within the microenvironment, resulting in the recruitment of suppressive cell populations which limit anti-tumor immunity. Expression markers for suppressive cells can indicate their relative contribution to tumor immunoregulation and highlight potential treatments to limit proliferation and spread. With this goal in mind, Rt-PCR analysis was carried out on murine tumor cell lines grown in vivo and in vitro, along with immunohistochemical analysis of expression markers. In vivo, murine tumors of lung, breast and colorectal origin were found to upregulate the Treg marker FoxP3, the suppressive DC marker B7-H3, and the MSC marker arginase I. IHC studies were inconclusive, but in vitro coculturing lung or breast tumor with myeloid cells induced production of arginase I by myeloid cells. Chemokines found to recruit myeloid cells were also upregulated. MSC recruitment pathways may provide a novel target for future combination therapies.