Transcriptional profiling of tumor associated macrophages in human renal cell carcinoma reveals significant heterogeneity and opportunity for immunomodulation

Among the more notable immunotherapies are checkpoint inhibitors, which prevent suppressive signaling on T cells, thereby (re)activating them to kill tumor cells. Despite remarkable treatment responses to immune checkpoint blockade, with a subset of patients achieving complete responses, a large population have little-to-no response, dictating the necessity of further research in this field. Myeloid derived cells heavily infiltrate the tumor microenvironment (TME) of many cancers and are believed to have a number of potent anti-inflammatory effects. Here we use primary non-metastatic renal cell carcinoma to interrogate the gene expression profiles of M2-tumor associated macrophages (M2-TAMs). We performed Fluorescent Activated Cell (FACS) sorting on monocytes from the peripheral blood and tumors of fresh clear cell renal cell carcinoma (ccRCC) samples obtained after patients underwent a partial (7 patients-87.5%) or radical (1 patient-12.5%) nephrectomy. We then utilized NanoString gene expression profiling to show that TAMs express a heterogeneous transcriptional profile that does not cleanly fit into the traditional M1-M2 TAM paradigm. We identified expression of M1 associated costimulatory molecules, a multitude of diverse chemokines, canonical M2 associated molecules, as well as factors involved in the Complement system and checkpoint receptors. Our data are in agreement with other published literature investigating TAMs in various non-ccRCC TMEs, and support the growing literature concerning expression of Complement factors and checkpoint receptors on TAMs.