A model in which CY sensitizes tumor cells for TRAIL-mediated death may help explain the chemotherapy paradox, since such a magic size emphasizes tumor cell susceptibility rather than growth of anti-tumor CD8 T cells. == Results == The objective of this study was to investigate the potential discrepancy between lymphodepleting anti-tumor chemotherapy and the anti-tumor immune responses that are linked to successful chemotherapy[11],[25]. for curative reactions. The important effector molecules used by the anti-tumor immune response included IFN- and TRAIL. The importance of TRAIL was supported by experiments in nude mice where the lack of practical T cells could be compensated by agonistic anti-TRAIL-receptor (DR5) antibodies. == Summary == The data support a model in which chemotherapy sensitizes tumor cells PHA-665752 for T cell-, and possibly PHA-665752 NK cell-, mediated apoptosis. A key part of tumor cell sensitization to immune attack is supported by the part of TRAIL in tumor resolution and clarifies the paradox of successful CD8 T cell-dependent anti-tumor reactions in the absence of CD8 T cell growth. == MLL3 Intro == Tumor antigens are cross-presented to the immune system[1],[2],[3]. However, the ensuing anti-tumor CD8 T cell response is usually not effective and fails to control tumor growth. Indeed, the immunological end result of antigen cross-presentation is determined by the context in which tumor antigens are offered. Altering that context is an important goal for anti-cancer immunotherapy[4],[5],[6]. Cytotoxic chemotherapy can play a role in this process since apoptotic tumor cell death can be an immunostimulatory event (immunogenic cell death)[7],[8],[9], potentially adding an immunostimulatory transmission to cross-presented antigens. An immune priming effect has now been PHA-665752 demonstrated for a number of chemotherapeutic medicines, including gemcitabine[4],[10]and doxorubicin[7]. As a result, chemo- and immunotherapy are no longer considered to bea prioriantagonistic[11]and the concept of combined chemo-immuno therapy is receiving more attention[11],[12],[13]. However, the notion that chemotherapy and anti-tumor T cell reactions can be synergistic must be reconciled with the fact that many chemotherapeutic medicines deplete lymphocytes[14]. In fact, lymphodepletion after chemotherapy was the main reason why chemo- and immunotherapy were seen as antagonistic. The growing insight that PHA-665752 chemotherapy can be immunostimulatory presents a paradox: how are effective anti-tumor T cell reactions generated under lymphodepleting conditions? The present study is designed to address the paradoxical relationship between immunogenicity and lymphodepletion. To study this, we have used a mouse model of malignant mesothelioma (Abdominal1-HA), which is definitely sensitive to both chemotherapy and immunotherapy[4],[15],[16], in combination with the chemotherapeutic drug cyclophosphamide (CY), since CY treatment is definitely associated with innate and adaptive immune activation[17],[18],[19],[20],[21]. The Abdominal1-HA tumor cell collection was generated by transfection of the asbestos-induced Abdominal1 tumor cell collection[16]with the influenza computer virus HA gene[15]. The tumor-expressed HA protein allows us to monitor the anti-tumor T cell response[5],[15],[22], but it does not impact on tumor immunogenicity, as evidenced by the fact that Abdominal1-HA cured mice will also be safeguarded against re-challenge with the parental Abdominal1 collection[23]. The immuno-stimulatory properties of CY (Cytoxan) have been known for decades. In the 1980s, it was demonstrated that CY depleted cycling suppressor T cells, right now known as regulatory T cells, and therefore triggered anti-tumor CD8 T cells[24]. However, we have recently shown the anti-tumor PHA-665752 effectiveness of CY in the Abdominal1-HA model cannot be explained by regulatory T cell depletion only[18]. Here, we display that CY kills tumor cells by apoptosis and that it has a CD8 T cell- and NK cell-dependent anti-tumor effect in the Abdominal1-HA tumor model. At the same time, CY has a strong negative effect on T cell proliferation, limiting the potential growth of anti-tumor CD8 T cells, raising the query how a CD8 T cell-dependent anti-tumor response functions without T cell growth. We found that the anti-tumor immune response depended on different effector molecules to remove the tumor: IFN- and TRAIL. The part of TRAIL was supported by data showing that agonistic anti-TRAIL-receptor (DR5) antibodies enhanced the effects of CY in athymic nude mice. Therefore, a DR5-agonist compensates for the lack of practical T cell in nude mice. The part of TRAIL suggests that the efficacy.