Representative tumor cell lines were chosen based on the degree of change seen in MHC class II expression on BM-DCs during initial screening experiments

Representative tumor cell lines were chosen based on the degree of change seen in MHC class II expression on BM-DCs during initial screening experiments. investigated the utility of using the canine DH82 cell line for assessment of canine myeloid responses to tumor-derived soluble factors (TDSFs). Phenotypic comparisons to canine bone marrow-derived DCs (BM-DCs) and bone marrow-derived macrophages (BM-Ms) were performed and expression of myeloid cell markers CD11b, CD11c, CD80, and major histocompatibility complex (MHC) class II were evaluated by flow cytometry. Phenotypic and functional changes of DC populations were then determined following Menaquinone-7 exposure to tumor-conditioned media (TCM) from canine osteosarcoma, melanoma and mammary carcinoma cell lines. == Results == We found that the canine BM-DCs and the Menaquinone-7 DH82 cell line shared similar CD11b, CD11c and MHC II expression and morphologic characteristics that were distinct from canine BM-Ms. Myeloid cells exposed to TDSFs showed decreased expression of MHC class II and CD80, had reduced phagocytic activity and suppressed the proliferation of responder immune cells. == Conclusion == These results show that soluble factors secreted from canine tumor cells suppress the activation and function of canine myeloid cells. Our results suggest that, similar to humans, dysregulated myeloid cells may contribute to immunosuppression in dogs with cancer. Keywords:Canine, Myeloid, Dendritic cells, Macrophages, DH82, Cancer, Immunology == 1. Introduction == Cancer is an important disease affecting all species. Within veterinary medicine, the National Cancer Institute estimates that nearly 6 million new cases are diagnosed in dogs each year (Shilling, 2010). Cancer has profound effects on immunity, resulting in tumor-related immunosuppression that Menaquinone-7 contributes to tumor escape, metastases and resistance to therapy (Zou, 2005). In particular, immunosuppression limits the efficacy of cancer immunotherapy, a therapy designed to enhance anti-tumor immune responses (Zou, 2005). Numerous changes in both innate and adaptive immune responses occur in humans and mice with cancer. Alterations of T cell, B cell, NK cell and myeloid cell function, increased regulatory T cell activity, tumor-associated macrophages (TAMs) and recently, myeloid-derived suppressor cells (MDSCs) have all been described (Gabrilovich and Nagaraj, 2009;Mantovani et al., 2008;Pollard, 2004;Zou, 2005). Similarly, immune alterations in canine cancer patients have been reported including elevated levels of circulating regulatory T cells (Tregs), altered cytokine profiles, natural killer (NK) cells with a reduced proliferative and killing capacity and altered CD8+ (cytolytic) T cell to Treg ratios (Biller et al., 2010;Funk et al., 2005;Itoh et al., 2009;O’Neill et al., 2009) but at present, few studies have investigated altered myeloid cell function in canine cancer. Myeloid cells are innate immune cells including monocytes, macrophages, dendritic cells (DCs) and their progenitors (Gabrilovich and Nagaraj, 2009;Papenfuss, 2010). These potent immune cells play pivotal roles in initiating and Menaquinone-7 regulating inflammation and shaping adaptive immune responses. Acting both on innate (e.g. NK cells, neutrophils and other myeloid cells) and adaptive (e.g. CD4+ T cells and CD8+ T cells) immune cells, myeloid cells play important roles in host defense and homeostasis. In cancer, dysregulated and suppressive myeloid cells are now recognized as contributing to immunosuppression, metastatic spread and therapeutic failures in humans and mice (Mantovani et al., 2010;Schmid and Varner, 2010;Yang and Carbone, 2004). Recent work in dogs suggests that peripheral blood myeloid cell populations (e.g. monocytes and neutrophils) may be a prognostic indicator in canine cancer and that canine myeloid cells may be useful for canine cancer vaccines but, at present, the effects of cancer on canine myeloid cell responses has not been studied (Bird et al., 2008;Perry et al., 2011;Sottnik et al., 2010). Tumors are able to alter myeloid cell differentiation, maturation and function to promote systemic CBL2 immunosuppression. Specifically, tumors are able to generate TAMs, dysregulated or tolerogenic DCs (Tol-DCs) and MDSCs, which can contribute to the immunosuppression seen during cancer (Chioda et al., 2011;Huang et al., 2011;Mantovani et al., 2009;Pollard, 2004). Tumor-derived soluble factors (TDSFs), such as cytokines, growth factors or tumor exosomes secreted by tumor cells can have direct effects on myeloid cells (Finn, 2008;Mantovani et al., 2008;Pollard, 2004;Zou, 2005). Human and mouse studies.