Tumor-specific CD4+ T cells coordinate the adaptive immune response against cancer. Dendritic cells (DCs) are professional antigen presenting cells that are believed to be important for the initial activation of naïve tumor-specific CD4+ T cells. The role of DCs in cancer prevention mediated by CD4+ T cells was investigated using mice transgenic for a high-affinity simian diphtheria toxin receptor (DTR) under the control of the DC-specific CD11c promoter. Injection of diphtheria toxin (DT) into such mice resulted in specific depletion of CD11c-positive DCs, but it had no effect on the activation of naïve tumor-specific CD4+ T cells, as investigated in myeloma-specific T-cell receptor-transgenic mice. However, although several protocols of DT injection were tested, only partial DC elimination was obtained. Such incomplete depletion precludes any firm conclusion on the role of DCs for activation of tumor-specific CD4+ T cells. These results illustrate unexpected limitations of the CD11c-DTR BALB/c mouse model.
Previous work revealed that successful cancer immunosurveillance mediated by tumor-specific CD4+ T cells was consistently associated with elevated levels of both interleukin (IL)-1α and IL-1β at the incipient tumor site. The mechanisms of IL-1α/β secretion remain poorly understood. We aimed at setting up an experimental system for imaging of IL-1 secretion from live macrophages and DCs using confocal microscopy. Plasmids containing pro- or mature IL-1α and IL-1β labeled with enhanced green fluorescent protein (EGFP) were engineered and quality tested. An immortalized macrophage cell line was successfully transfected with the different IL-1-EGFP constructs. In resting macrophages, pro-IL-1α-EGFP was found to localize to the nucleus, while mature IL-1α-EGFP and pro- and mature IL-1β-EGFP were homogenously distributed throughout the cytoplasm and the nucleus. Preliminary findings indicate that Rab11a-positive endosomes were not important for IL-1α/β trafficking. Collectively, the results indicate that we successfully managed to establish a method for visualizing the secretion pathways of IL-1α/β in live macrophages.