Radiation-induced CXCL16 release by breast cancer cells attracts effector T cells.

Recruitment of effector T cells to inflamed peripheral tissues is regulated by chemokines and their receptors, but the factors regulating recruitment to tumors remain largely undefined. Ionizing radiation (IR) therapy is a common treatment modality for breast and other cancers. Used as a cytocidal agent for proliferating cancer cells, IR in combination with immunotherapy has been shown to promote immune-mediated tumor destruction in preclinical studies. In this study we demonstrate that IR markedly enhanced the secretion by mouse and human breast cancer cells of CXCL16, a chemokine that binds to CXCR6 on Th1 and activated CD8 effector T cells, and plays an important role in their recruitment to sites of inflammation. Using a poorly immunogenic mouse model of breast cancer, we found that irradiation increased the migration of CD8(+)CXCR6(+) activated T cells to tumors in vitro and in vivo. CXCR6-deficient mice showed reduced infiltration of tumors by activated CD8 T cells and impaired tumor regression following treatment with local IR to the tumor and Abs blocking the negative regulator of T cell activation, CTLA-4. These results provide the first evidence that IR can induce the secretion by cancer cells of proinflammatory chemotactic factors that recruit antitumor effector T cells. The ability of IR to convert tumors into "inflamed" peripheral tissues could be exploited to overcome obstacles at the effector phase of the antitumor immune response and improve the therapeutic efficacy of immunotherapy.

Cutting edge: a critical role of nitric [corrected] oxide in preventing inflammation upon apoptotic cell clearance.

Apoptotic cells are removed by phagocytes without causing inflammation. It remains largely unresolved whether anti-inflammatory mediators prevent neutrophil infiltration upon apoptotic cell clearance in vivo. In this study, we showed that, upon induction of apoptosis in the thymus by x-ray, inducible NO synthase knockout (KO) mice exhibited higher levels of neutrophil infiltration and production of MIP-2 and keratinocyte-derived chemokine (KC) in the thymus than wild-type (WT) mice. Furthermore, administration of NG-nitro-L-arginine methyl ester, an inhibitor of NO synthase, to x-irradiated WT mice increased the level of neutrophil infiltration to that of KO mice by the augmentation of MIP-2 and KC production. Additionally, thymic macrophages isolated from x-irradiated KO mice produced more MIP-2 and KC than those from WT mice. Thus, although apoptosis is believed to be noninflammatory, this is actually achieved by the production of immunosuppressive signals such as NO that counteract proinflammatory chemokines such as MIP-2 and KC.