Across a majority of cancer types tumor-associated neutrophils (TAN) are linked with poor prognosis. However, the underlying mechanisms, especially the intratumoral behavior of TAN, are largely unknown. Using intravital multiphoton imaging on a mouse model with neutrophil-specific fluorescence, we measured the migration of TAN in distinct compartments of solid tumor cell lesions in vivo . By longitudinally quantifying the infiltration and persistence of TAN into growing tumors in the same animals, we observed cells that either populated the peripheral stromal zone of the tumor (peritumoral TAN) or infiltrated into the tumor core (intratumoral TAN). Intratumoral TAN showed prolonged tumor-associated persistence and reduced motility compared to peritumoral TAN, whose velocity increased with tumor progression. Selective pharmacological blockade of CXCR2 receptors using AZD5069 profoundly inhibited recruitment of TAN into peritumoral regions, while intratumoral infiltration was only transiently attenuated and rebounded at later time points. Our findings unravel distinct spatial dynamics of TAN that are partially and differentially regulated via the CXCR2 signaling pathway.

Toll-like receptors (TLRs) are located either on the cell surface or intracellularly in endosomes and their activation normally contributes to the induction of protective immune responses. However, in cancer their activation by endogenous ligands can modulate tumour progression. It is currently unknown how endosomal TLRs regulate endogenous anti-tumour immunity. Here we show that TLR3, 7 and 9 deficiencies on host cells, after initial tumour growth, result in complete tumour regression and induction of anti-tumour immunity. Tumour regression requires the combined absence of all three receptors, is dependent on both CD4 and CD8 T cells and protects the mice from subsequent tumour challenge. While tumours in control mice are infiltrated by higher numbers of regulatory T cells, tumour regression in TLR-deficient mice is paralleled by altered vascular structure and strongly induced influx of cytotoxic and cytokine-producing effector T cells. Thus, endosomal TLRs may represent a molecular link between the inflamed tumour cell phenotype, anti-tumour immunity and the regulation of T-cell activation.

To assess the role of alveolar macrophages (AMs) during a pulmonary Aspergillus fumigatus infection AMs were depleted by intratracheal application of diphtheria toxin (DTX) to transgenic CD11c.DTR mice prior to fungal infection. Unexpectedly, all CD11c.DTR mice treated with DTX died within 4-5 days, whether being infected with A. fumigatus or not. Despite measurable impact of DTX on lung functional parameters, these constrictions could not explain the high mortality rate. Instead, DTX-treated CD11c.DTR animals developed fulminant myocarditis (FM) characterized by massive leukocyte infiltration and myocardial cell destruction, including central parts of the heart's stimulus transmission system. In fact, standard limb lead ECG recordings of diseased but not healthy mice showed a "Brugada"-like pattern with an abnormally high ST segment pointing to enhanced susceptibility for potential lethal arrhythmias. ). However, the key limitation of such systems is the absence of the cell subset under study for the entire life span, including the prenatal phase. This makes these animal models unusable for investigations where cells of interest have to be depleted at defined time points. To overcome these limitations conditional cell depletion strategies in which a defined cell population can be eliminated by chemical or physical treatment of the organism at any time point during an experimental procedure have been introduced [3][4][5].A widely used system of this type is the diphtheria toxin receptor-mediated conditional cell ablation in mice and rats [6,7]. Diphtheria toxin (DTX) is a two-subunit exotoxin secreted by Corynebacterium diphtheriae as virulence factor and binds to toxinsensitive cells via its receptor-binding domain. The host cell receptor for DTX is the heparin-binding EGF-like growth factor (HB-EGF), here termed diphtheria toxin receptor (DTR) [8]. Binding of DTX to DTR leads to rapid death of the DTR-expressing cell due to blockade of protein synthesis. DTR is expressed on many cell types and in different tissues [9,10] CD11c-LuciDTR mice and CD11c-DOG mice were both generated using the same bacterial artificial chromosome (BAC) in which the endogenous CD11c promoter is flanked by very large DNA sequences, likely to include many or all regulatory and enhancer elements. CD11c-LuciDTR mice and CD11c-DOG mice differ in the genes cloned under the CD11c promoter (DTR, Ovalbumin and eGFP for CD11c.DOG and eGFP, Cre recombinase, DTR, and luciferase for CD11c.LuciDTR). All three systems have been mainly used to characterize DC and also macrophage (M ) behavior in the context of different immunological questions. Among these models CD11c.DTR mice [7] have by far been used most extensively with >1000 studies relating to their use. We and others previously reported that CD11c.DTR mice treated systemically with DTX can develop adverse side effects and mortality and hence recommended the use of BM chimeras [16,17]. However, the reason for the morbidity that was observed 4-6 days after DTX treatment had not been elucidated...