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A hostile tumor microenvironment interferes with the development and function of the adaptive immune response. Here we report the mechanisms by which large numbers of tumor-infiltrating macrophages and dendritic cells (DC) can be redirected to become potent effectors and activators of the innate and adaptive immunity, respectively. We use adenoviral delivery of the CCL16 chemokine to promote accumulation of macrophages and DC at the site of preestablished tumor nodules, combined with the Toll-like receptor 9 ligand CpG and with anti-interleukin-10 receptor antibody. CpG plus anti-interleukin-10 receptor antibody promptly switched infiltrating macrophages infiltrate from M2 to M1 and triggered innate response debulking large tumors within 16 hours. Tumor-infiltrating DC matured and migrated in parallel with the onset of the innate response, allowing the triggering of adaptive immunity before the diffuse hemorrhagic necrosis halted the communication between tumor and draining lymph nodes. Treatment of B6>CXB6 chimeras implanted with BALB/c tumors with the above combination induced an efficient innate response but not CTL-mediated tumor lysis. In these mice, tumor rejection did not exceed 25%, similarly to that observed in CCR7-null mice that have DC unable to prime an adaptive response. The requirement of CD4 help was shown in CD40-KO, as well as in mice depleted of CD4 T cells, during the priming rather than the effector phase. Our data describe the critical requirements for the immunologic rejection of large tumors: a hemorrhagic necrosis initiated by activated M1 macrophages and a concomitant DC migration to draining lymph nodes for subsequent CTL priming and clearing of any tumor remnants.
Guiducci et al. (Fri,) studied this question.