Abstract 2939: Leukocyte chemoattractant chemerin as a novel immunotherapeutic agent

Cancer immunotherapy offers the potential of potent anti-tumor responses while avoiding non-specific toxicities associated with traditional cytotoxic chemotherapy. Localization of key immune cells to tumor sites has been shown to be important for anti-tumor efficacy. Chemerin is a recently described chemoattractant initially isolated from human inflammatory fluids. Chemokine-like receptor 1 (CMKLR1) constitutes the main cellular receptor for chemerin, and is expressed by macrophages, natural killer (NK) cells, and immature dendritic cells (DCs), but has not been shown on T lymphocytes. Chemerin is synthesized and circulates systemically as an inactive precursor, prochemerin, but can be rapidly converted into its active form by proteolytic cleavage of carboxy-terminal residues by multiple proteases. To evaluate chemerin as a potential immunotherapy, we performed intratumoral injections of recombinant active murine chemerin that resulted in significantly decreased tumor growth in a B16 melanoma as well as JC breast tumor models. Tumors lines showed no expression of CMKLR1 by flow cytometric (FACS) analysis, and treatment with exogenous recombinant murine chemerin had no effect on in vitro proliferation. Compared to control media, B16 tumor-conditioned serum-free media was able to attract CMKLR1-transfected L1.2 cells (L1.2/CMKLR1) after the addition of inactive, recombinant murine prochemerin, indicating the ability of tumor-derived factors to activate prochemerin. Treatment with the pan-matrix metalloproteinase (MMP) inhibitor GM6001 resulted in reduced chemotaxis, suggesting the activation of chemerin was in part mediated by MMPs. This supports the ability of tumors to activate prochemerin. B16, as well as additional mouse tumor lines (JC, CT26, EMT6), were then transfected to constitutively express chemerin. Experiments using all tumor lines showed consistent and significantly decreased growth of chemerin-expressing tumors compared with control tumors. There were greater numbers of leukocytes in both the tumors and draining lymph nodes compared to controls. CMKLR1 knockout mice we generated showed abrogated response to chemerin-expressing tumors, supporting the hypothesis that the anti-tumor effects are mediated by this receptor. CD4 and CD8 T lymphocytes from tumor-bearing mice were isolated and shown, for the first time, to have significant CMKLR1 expression compared to control lymphocytes from naive mice. Incubation of naive T cells with tumor-conditioned media recapitulated these results, suggesting CMKLR1 expression can be induced by tumor-derived factors. These data suggest not only that tumor-derived proteases can activate chemerin, but also that chemerin expression at tumor sites results in the recruitment of CMKLR1-positive cells, potentially including CMKLR1+ lymphocytes, and establishment of an effective anti-tumor immune response. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2939.