Alum (aluminum hydroxide) is the most widely used adjuvant in human vaccines, but the mechanism of its adjuvanticity remains unknown. In vitro studies showed no stimulatory effects on dendritic cells (DCs). In the absence of adjuvant, Ag was taken up by lymph node (LN)–resident DCs that acquired soluble Ag via afferent lymphatics, whereas after injection of alum, Ag was taken up, processed, and presented by inflammatory monocytes that migrated from the peritoneum, thus becoming inflammatory DCs that induced a persistent Th2 response. The enhancing effects of alum on both cellular and humoral immunity were completely abolished when CD11c+ monocytes and DCs were conditionally depleted during immunization. Mechanistically, DC-driven responses were abolished in MyD88-deficient mice and after uricase treatment, implying the induction of uric acid. These findings suggest that alum adjuvant is immunogenic by exploiting “nature's adjuvant,” the inflammatory DC through induction of the endogenous danger signal uric acid.

Tolerance is the usual outcome of inhalation of harmless antigen, yet T helper (Th) type 2 cell sensitization to inhaled allergens induced by dendritic cells (DCs) is common in atopic asthma. Here, we show that both myeloid (m) and plasmacytoid (p) DCs take up inhaled antigen in the lung and present it in an immunogenic or tolerogenic form to draining node T cells. Strikingly, depletion of pDCs during inhalation of normally inert antigen led to immunoglobulin E sensitization, airway eosinophilia, goblet cell hyperplasia, and Th2 cell cytokine production, cardinal features of asthma. Furthermore, adoptive transfer of pDCs before sensitization prevented disease in a mouse asthma model. On a functional level, pDCs did not induce T cell division but suppressed the generation of effector T cells induced by mDCs. These studies show that pDCs provide intrinsic protection against inflammatory responses to harmless antigen. Therapies exploiting pDC function might be clinically effective in preventing the development of asthma.

Defective homologous recombination (HR) DNA repair imposed by BRCA1 or BRCA2 deficiency sensitizes cells to poly (ADP-ribose) polymerase (PARP)-1 inhibition and is currently exploited in clinical treatment of HR-deficient tumors. Here we show that mild hyperthermia (41-42.5°C) induces degradation of BRCA2 and inhibits HR. We demonstrate that hyperthermia can be used to sensitize innately HR-proficient tumor cells to PARP-1 inhibitors and that this effect can be enhanced by heat shock protein inhibition. Our results, obtained from cell lines and in vivo tumor models, enable the design of unique therapeutic strategies involving localized ondemand induction of HR deficiency, an approach that we term induced synthetic lethality.anti-cancer treatment | RAD51 | double-strand break M any anti-cancer therapies are based on cytotoxicity of DNA double strand breaks (DSBs) induced by ionizing radiation or, indirectly, by chemical agents. However, efficient DSB repair mechanisms protect cells from the genotoxic effects of DSBs, thereby reducing the effectiveness of the therapies. Two major pathways are involved in DSB repair in mammalian cells: homologous recombination (HR) and nonhomologous end joining (NHEJ). HR uses intact homologous DNA sequences, usually the sister chromatid in postreplicative chromatin, to faithfully restore DNA breaks (1), whereas NHEJ operates throughout the entire cell cycle and does not require a DNA template (2). Agents inhibiting DNA repair processes potentiate the cytotoxicity of DSBs in cancer therapy (3). Elevated temperature is one such agent that, via unclear mechanisms, interferes with multiple pathways of DNA repair (4-6) and is clinically applied (7). ResultsTo investigate if HR, among other processes and DSB repair pathways, is influenced by elevated temperature, we used an isogenic set of mouse embryonic stem (ES) cells that are either HR proficient (wild-type) or HR deficient (Rad54 −/− ) due to the disruption of the Rad54 gene, which is important for HR activity (1). We compared radiosensitization of these cells by incubating them at 37°C or 41°C before irradiation. For this and subsequent experiments we chose temperatures below 43°C, because they are relevant in clinical practice (8). Interestingly, we observed that wild-type but not Rad54 −/− cells were radiosensitized by preincubation at 41°C compared with cells incubated at 37°C (Fig. 1A). Similarly, HeLa cells, in which the important HR factors XRCC3 or BRCA2 were down-regulated using siRNA, were refractory to further temperature-mediated radiosensitization (Fig. 1B and Fig. S1). These results suggest that elevated temperature inactivates HR. To directly measure the effect of temperature on HR, we quantitated HR-mediated gene targeting in ES cells (9) and found that the efficiency of gene targeting was significantly reduced by preincubation at 41°C compared with 37°C (Fig. 1C). Similarly, preincubation at 41°C reduced the frequency of spontaneous and mitomycin C-induced sister chromatid exchanges in SW-1573 cells (Fig. S2A), w...

Airway DCs play a crucial role in the pathogenesis of allergic asthma, and interfering with their function could constitute a novel form of therapy. The sphingosine 1-phosphate receptor agonist FTY720 is an oral immunosuppressant that retains lymphocytes in lymph nodes and spleen, thus preventing lymphocyte migration to inflammatory sites. The accompanying lymphopenia could be a serious side effect that would preclude the use of FTY720 as an antiasthmatic drug. Here we show in a murine asthma model that local application of FTY720 via inhalation prior to or during ongoing allergen challenge suppresses Th2-dependent eosinophilic airway inflammation and bronchial hyperresponsiveness without causing lymphopenia and T cell retention in the lymph nodes. Effectiveness of local treatment was achieved by inhibition of the migration of lung DCs to the mediastinal lymph nodes, which in turn inhibited the formation of allergen-specific Th2 cells in lymph nodes. Also, FTY720-treated DCs were intrinsically less potent in activating naive and effector Th2 cells due to a reduced capacity to form stable interactions with T cells and thus to form an immunological synapse. These data support the concept that targeting the function of airway DCs with locally acting drugs is a powerful new strategy in the treatment of asthma.

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